Title of Invention	"A METHOD OF STORING ENERGY IN ELECTRIC POWER GRID HAVING A FUSSIL FUEL AND APPARATUS THEREOF"
Abstract	Method for managing electric power generated during periods of low demand, in an electric power market where consumption of electric power exhibits periods of different demands. The method includes upgrading solid fossil fuel by electromagnetic radiation (EMR) drying during the periods of low demand, storing and utilization of the upgraded fuel. Fuel utilization may include burning for electric power generation during periods of high demand, burning in another heat-consuming industrial process, or trading the fuel with another business entity. The EMR drying used in the method includes reducing the inherent moisture content in the upgraded fossil fuel at least in half.

Title of Invention

"A METHOD OF STORING ENERGY IN ELECTRIC POWER GRID HAVING A FUSSIL FUEL AND APPARATUS THEREOF"

Abstract

Method for managing electric power generated during periods of low demand, in an electric power market where consumption of electric power exhibits periods of different demands. The method includes upgrading solid fossil fuel by electromagnetic radiation (EMR) drying during the periods of low demand, storing and utilization of the upgraded fuel. Fuel utilization may include burning for electric power generation during periods of high demand, burning in another heat-consuming industrial process, or trading the fuel with another business entity. The EMR drying used in the method includes reducing the inherent moisture content in the upgraded fossil fuel at least in half.

Full Text	ENERGY MANAGEMENT IN A POWER GENERATION PLANT FIELD OF THE INVENTION This invention relates to energy management methods in utilities burning solid fossil fuel. BACKGROUND OF THE INVENTION Power-producing utilities struggle with uneven demand for electricity during each daily cycle. During one-day period, demand changes on an hourly basis, with peak demand periods typically in the morning and evening and low demand during the night. The gap between the high demand and low demand levels can reach over 30% of the high demand level. Since electricity is a commodity that cannot be stored in its raw form, a great deal of a utility's generation capacity is not efficiently utilized. In addition, frequent large fluctuations in generation levels are costly in terms of operating costs and mechanical wear, particularly in power plants burning solid fossil fuel such as coal. Electric power utilities burning fossil fuel are operating a process that converts heat contained in the fuel to steam, which then drives a turbine that generates electricity. A coal-fired utility process contains coal handling and coal preparation units, boilers with burners, ash and emission treatment units, turbine and generation related facilities, water treatment units and auxiliaries. The coal handling and preparation systems include off-loading facilities for trains, barges or other transportation means, coal stockyard which typically stores coal for 1.5-2 months production, materials handling facilities to drive coal from the stockyard to the plant, coal feeders, pulverization plant and feeding facilities to the boilers' burners. Coal-fired power generation plants are expensive and complex to operate with very slow process dynamics. A coal-fired power plant requires many hours of preparation before generation of electricity can commence, making it uneconomical to switch off during low demand periods. At the same time, power generation units must be tightly synchronized with their load for plant integrity and operation safety considerations. If the demand is reduced to a level below a critical value, coal fuel alone cannot sufficiently maintain the necessary thermal conditions of the boiler, and other fuels such as diesel must be used together with coal to keep the boiler at the appropriate conditions. This is an undesired condition that increases operating expense. To reduce the gap in load between high demand and low demand periods in order to even out demands, utilities implement an aggressive time-of-use pricing strategy to encourage customers to reduce consumption during high demand periods and to increase consumption during low demand periods. Although the price for electricity in highdemand periods may be several times the price for electricity in a low-demand period, this strategy alone is not always sufficient to bridge the demand gap. Many different solutions have been proposed to store excess electricity generated during low-demand periods for use during high-demand periods. Among the solutions that have been proposed is pumping water to high elevations during low demand and the use of this water in reverse to power hydroelectric units during high-demand periods. This method is known as "pumped storage" and is used in a few locations around the world including the USA. Pumped storage requires large capital costs and has a large impact on the environment. US 3,631,673 suggests accumulating energy in off-peak hours by storing compressed air. In peak hours, the compressed air drives a gas turbine. US 5,491,969 suggests that the compressed air is used for combusting fuel in a gas turbine (regular compressors are then switched off). US 3,849,662 discloses a power plant burning coal gas obtained by coal gasification, in a steam turbine. Coal gas produced during off-peak hours is stored in a pressurized holder and is burnt in a gas turbine during peak hours. Over 30% of electric power in the US is generated from coal. Coal production in the US is 1.1 billion short tons per year. More than 90% of this coal is used for generating electricity. America has coal reserves which will last for 250 years at the current consumption levels. The quality of coal can be assessed in terms of various attributes such as heat value, moisture content, volatile matter content, ash content, and sulfur content. Each attribute, to a greater or lesser extent, affects the manner in which the coal is used, its burning characteristics and hence its economic value. These attributes vary from coal deposit to coal deposit and moreover, within a given deposit, the characteristics of the coal can vary substantially. Deposits, such as those encountered in the Powder River Basin (PRB) in the states of Wyoming and Montana, as well as in other similar deposits throughout the world, contain coal which is commonly known as "low rank" coal. Low rank coal includes sub-bituminous and lignite coals and is also known as brown coal. The water content of these coals is considerable, and reaches levels of well over 30%. In connection with moisture content of coal, the following definitions and standard methods set forth by the American Society for Testing and Materials (ASTM) will be relied on in the present application. Total moisture means the measure of weight loss in an air atmosphere under rigidly controlled conditions of temperature, time and air flow, as determined according to either § 870.19(a) or § 870.20(a), incorporated herein by reference; Inherent moisture means moisture that exists as an integral part of the coal seam in its natural state, including water in pores, but excluding that present in macroscopically visible fractures, as determined; Excess moisture means the difference between total moisture and inherent moisture, calculated according to § 870.19 for high-rank coals or according to § 870.20 for low-rank coals, both incorporated herein by reference. "Excessive moisture" will be referred to in the present application as "surface moisture"; Low-rank coals means sub-bituminous C and lignite coals; High-rank coals means anthracite, bituminous, and sub-bituminous A and B coals. Laboratory procedure for estimation of inherent moisture is outlined in ASTM D1412-93 incorporated herein by reference. Collection of coal samples for the estimation is also determined in ASTM documents. In brief, the laboratory procedure is as follows. The coal is ground to fine powder, and exposed to the open air for a certain period of time so that the surface moisture of the coal is mostly dried, and the residual surface moisture of the coal equals the ambient moisture. The assumption is that the residual moisture in the coal is inherent moisture. Coal is then heated in an oven and the inherent moisture content is calculated from the loss in mass. There are two distinct types of moisture in coal: surface moisture and inherent moisture. Surface moisture is the water contained in a coal particle that may be the result of wetting the coal by physically pouring water on it under normal conditions, such as in the case of rain or spraying systems. Exposing the coal particle to a source of heat such as the sun or a flow of hot gases or physical drying mechanisms such as centrifugals, can drive this moisture off. Inherent moisture is the water that is locked inside the coal particle, mostly since its formation, or which penetrated the coal particle in a process that takes a long period of time and high pressure. Inherent moisture is typically locked in the coal particle in capillaries or is chemically bounded to the coal and is impossible to drive out by processes which are used for drying Surface moisture, unless more extreme forces are used in the form of high temperature and/or high pressure. Traditional coal dewatering or drying processes for inherent moisture are complex and are conducted in extreme conditions. Most of these processes are based on a technique in which coal particles are heated by conventional heating and pressure is introduced or built in the system. The combined force in the process expels the inherent moisture from the coal particles. The final moisture content of coal treated in this type of process is mostly dependent on the ambient conditions prevailing inside the process. The end result is that drying inherent moisture in coal to low levels requires a great deal of energy and a long residence time of the coal in the drying process. Existing dewatering techniques make use of conventional heat transfer processes to evaporate the water off the coal particles. A disadvantage of these processes is the fact that the coal particles are heated from the outside inwards in order to evaporate the water. Coal is known to be a heat insulator, with a very high resistance for heat transfer that leads to inefficiency, as much heat is wasted on heating each coal particle and its environment, while the temperature gradient must be big enough to overcome the high resistance of the coal particle to heat transfer. Such heating is risky and requires special care, as exposing coal to high temperature can ignite it. The dewatering process for upgrading of low-rank high inherent moisture coals has historically been faced with two major drawbacks, which limited the deployment of industrial dewatering systems on a large scale. Low-rank upgraded coal produced to date has exhibited low auto-ignition points and spontaneous combustion that occurs faster than in other coals, including low-rank raw coal. It was found in tests that when a pile of dewatered coal is exposed to airflow for a number of hours (typically less than 72 hours), the coal reaches temperatures at which spontaneous combustion or auto-ignition occurs. Spontaneous heating and spontaneous combustion of coal particles have been common problems of high inherent moisture content raw coals, but such events usually occur after longer open-air exposure periods of days and weeks. This phenomenon is aggravated by the dewatering process which substantially increases the surface-area-to-volume ratio, hence making the coal particles more active in absorbing air moisture, further reducing the upgraded coal shelf life. Another problem observed in dewatering coal is the production of large quantities of coal fines. Each transfer of dried coal after it leaves the process degrades the coal particle size further and produces more coal dust, as dried coal is more brittle. Dried coal does not have the inherent ability to trap small particles on its surfaces like moist coal. This causes dust-size particles to be released and become lost in transportation, and has a high risk of causing fires or explosions. An article in The Australian Coal Review, October 1999, p.27, treats dry cleaning of coal, i.e. separation of coal from rejects (rocks) without water floatation. In the dry cleaning process, the moisture content of feed coal should not reach a level where the particles stick together, which is a function of the surface moisture. Thus, a low-rank coal can have quite a high inherent moisture level and still be superficially dry and suitable for dry cleaning. The article suggests that thermal drying can be employed to reduce the surface moisture to a sufficiently low level and recommends conveying the coal on a belt through a microwave dryer. In this type of dryers, water readily absorbs the heat energy and is vaporized while coal is not heated. US 4280033 discloses MW drying apparatus and process for high-grade ground coal for coking or gasification. The apparatus comprises an endless conveyor belt passing through a closed treatment zone, electrode plates at opposite sides of the coal belt, and air blowing system for passing hot air over the belt to remove humidity. US 4259560 discloses MW heating/drying method for conductive powder materials, especially coal before coking. Pulverizing is used to avoid arcing, moisture content can be regulated in real time by IR detector measurements. The removal of various contaminants from coal using Electro Magnetic Radiation (EMR) is also known. In this regard, reference is made to 'Mossbauer analysis of the microwave desulferization process of raw coal1 by S. Weng (1993); 'Effect of microwave heating on magnetic separation of pyrite' by Uslu et all (2003); and 'Microwave embrittlement and desulpherisation of coal' by Marland et all (1998). SUMMARY OF THE INVENTION This invention relates to a novel energy management system and a process for upgrading solid fossil fuel such as coal, for use therein. More particularly it is concerned with a process for storing inexpensive electricity generated during low-demand periods in the form of upgraded coal, for use during high-demand periods when the cost of electricity is a great deal higher. The invention combines business methods whereby electricity is generated and stored during low-demand periods and used for generating electricity at high prices during high-demand periods, with physical methods allowing such storage. In the method of the present invention, low cost electricity is consumed during low-demand hours, e.g. in the night, to upgrade low-cost, low-heat value fossil fuel for use as a substitute for high-cost, high-heat value fuel. The upgraded fuel is stored and is used in power generation units throughout the day, particularly during high-demand periods, to generate electricity that is salable in the retail energy market at a considerably higher price. According to a first aspect of the present invention, there is provided a method for managing electric power generated during periods of low demand, in an electric power market where consumption of electric power exhibits periods of different demands. The method includes upgrading solid fossil fuel by electromagnetic radiation (EMR) drying during the periods of low demand and utilization of the upgraded fuel. The utilization preferably includes burning the upgraded fossil fuel for electric power generation at least during periods of high demand. However, it may include also burning the fuel in another heat-consuming industrial process or trading the fuel with another business entity. The management method is particularly useful for application in a powergeneration plant, where the upgrading is performed by means of electric power generated by the same plant. Preferably, the upgraded fossil fuel is stored and burnt also at the same plant, for electric power generation at least during periods of high demand. Preferably, the quantity of the upgraded and stored fossil fuel produced during low-demand periods covers all fuel consumption for power generation at the same plant during periods of high demand. More preferably, average daily quantity of the upgraded and stored fossil fuel covers at least average daily fuel consumption for power generation at the same plant. Preferably, the EMR drying used in the method includes reducing the inherent moisture content in the upgraded fossil fuel by 50% or more. In accordance with a second aspect of the present invention, there is provided a method of upgrading solid fossil fuel. The method includes dewatering of the solid fossil fuel by EMR, such that the inherent moisture content in the upgraded fossil fuel is reduced at least in half. Daily quantity of upgraded fossil fuel obtained by the electrical dewatering process is commensurate to daily consumption of the power generation plant or/and another industrial process. The solid fossil fuel may be low-rank coal, oil shale, tar sand, subbituminous coal, etc., with high inherent moisture content. However, high-rank coals with initial low inherent moisture can be further dried as low as 1% inherent moisture. The method may be best performed where electric power consumption due to other consumers exhibits periods of different demands and the electric dewatering process is performed during low-demand periods of the electric power consumption. Preferably, the EMR dewatering process is carried out by using electric power produced by a power generation plant burning the fossil fuel in its upgraded state. More specifically, it is carried out where the power generation plant operates with daily peaks of electric power production and the drying process is performed predominantly during off-peak hours of the electric power production. The method includes storing of upgraded fossil fuel obtained during the off-peak hours and using the upgraded fossil fuel for electric power production during the daily peaks. Preferably, the quantity of upgraded fossil fuel obtained during the off-peak hours covers at least daily consumption of the power generation plant or the period between two subsequent low demand periods. This substantially reduces the operating costs of the dewatering process. The EMR drying may be preceded by driving off surface moisture by means of hot gases. Preferably, the EMR drying is performed by means of microwave radiation. The method of the present invention in particular provides dewatering (drying) low-grade solid fossil fuels at low temperatures and pressures by means of electromagnetic radiation. This method requires short start up and shutdown periods suitable for interruptible operation during short periods, and has a small footprint that allows the method to be deployed inside or alongside the power plant. The use of this method for upgrading low-rank coal during low demand periods to produce the next day's demand for coal can save utilities millions of Dollars a year in fuel costs. The physical dewatering process is based on exposing the solid fossil fuel to high frequency electromagnetic radiation. There are many benefits of a radiation-based dewatering process over other processes. Radiation dewatering is performed at atmospheric pressure and does not require heating the fuel particle itself. The start-up procedure of the process and its shutdown are quick, making the process suitable for non-continuous and interruptible operations constrained by the need to utilize low-cost electricity. Furthermore, radiation can be more efficient than other techniques in that the dewatering of fuel particles does not require the complete evaporation of the water, as some of the water may be driven off the fuel particles mechanically. Unlike existing inherent moisture dewatering processes involving extreme heat and pressure conditions, which require large spaces and are normally deployed near the source of the fuel, the method of the invention can be implemented with a small footprint, it is quiet, environmentally friendly and is simple to operate, making it suitable for both sides of the fuel's value chain - the source side as well as the utility's side. One fundamental premise of the process is subjecting the fuel particles to electromagnetic radiation at radio, microwave or higher frequencies. The intensity of the radiation i.e. the energy density per unit volume of fuel and the frequency of the radiation may be varied according to requirements, taking into account all relevant factors. Another important premise of the process is the use of cheap electricity during low demand periods to dewater and upgrade the fuel that is used to produce more expensive electricity throughout the day, in particular during high demand periods. This introduces to the utilities an innovative means by which electricity can be generated and stored inside the fuel during low demand periods to be used during high demand periods to produce higher revenues. When the process is deployed near a utility's power generation unit, it becomes possible to a large extent to integrate the process with the utility's existing fuel handling facilities, hence saving large capital expenses. In this case, the process of dewatering is carried out in a stage prior to a pulverizing unit which mills the fuel solids to powder before feeding the powder to the boiler's burners. In such a case, the low-grade fuel may be drawn from a stockyard by means of conventional and existing material handling facilities. The fuel may then be dried by means of conventional heat i.e. a stream of hot gases, and then passed through the radiation units. Dewatered (upgraded) fuel may be stored for later use, or may flow directly from the radiation units into the existing pulverization unit. Normal power plant operation processes can then proceed. When the upgraded fuel is stored for later use, existing or new enclosed storage facilities may be used, such as bins or silos or any other confined dry material storage unit. This fuel can be then fed directly to the pulverization unit, and re-enter the normal power plant processes. Keeping the upgraded fuel in a confined storage environment and under controlled conditions extends its shelf life and reduces the risks of undesired ignition. The accumulated fuel may be stored in silos, bins or any other means of storage. During the storage period the storage facilities may be purged with inert gases such as nitrogen or carbon dioxide, to prevent the fuel and fines from combusting. Prior to subjecting the low-grade solid fuel to radiation, it may be sized. This could be done in any appropriate way, for example by grading or milling. Further particle sizing is performed during the pulverizing step which takes place after the dewatering process and prior to the fuel being fed to the burner. Drying of low-grade fuel by EMR produces fines and the radiated fuel exhibits brittle characteristics which may prove to be beneficial in the pulverizing unit. The method of present invention allows the fossil fuel to be upgraded close to the place of its consumption, both in space and in time, so that the dried fossil fuel does not need much additional handling such as transportation. Immediately following the drying, the fuel may undergo a further size reduction process of pulverizing. Thus coal fines are not lost in transportation and the risk of causing fires and explosions is diminished. The fuel could be processed in batches but preferably is processed on a semi-continuous or continuous basis. Thus the fuel may be transported through or past one or more sources of electromagnetic radiation on appropriate transport devices. Such devices are preferably inert to electromagnetic radiation. Any appropriate material may be used for the transport devices and for example use may be made of conveyors or other transport devices which are made from materials, e.g. ceramic or stainless steel material, which are inert to radiation. This ensures that no energy is wasted unnecessarily to heat up elements of the process which do not contribute to the main objective of driving the locked moisture out of the fuel particles. The fuel may be subjected to the radiation in one or more stages. The electromagnetic radiation at the appropriate frequency excites the water molecules locked inside the fuel particles, and consequently increases the water's temperature so that the water is driven out and is released from the fuel. This, in turn, may raise the temperature of the fuel particles. Higher water temperature reduces surface tension effects so that the forces that lock the water inside the capillaries in the fuel particles are reduced and the dewatering process becomes more efficient. It is also possible to vary the physical characteristics of each stage. For example at least in one stage the fuel may be subjected to electromagnetic radiation in the presence of a suitable inert gas, such as nitrogen or carbon dioxide, which acts as an ignition suppression agent to prevent it from burning and suppresses conditions which may be developed and could lead to explosion. This gas could also heat the processed fuel to dry off its surface moisture which may be originally contained in the fuel or which is built up during the radiation process. In most cases the water vapour that is released by the radiation process is clean and could be released to the atmosphere. The fuel may be subjected to a cooling step which will also remove the water vapour, and thereafter dry fuel may be screened and recovered. It may also be required that the dewatered coal particles are kept in certain ambient conditions so as to drive off all excess surface moisture which may accumulate as a result of the radiation. According to a next aspect of the present invention, there are provided the following systems for practicing the above methods. A system for energy production by burning solid fossil fuel in a power generation plant including burners comprises an EMR drying plant for upgrading the solid fossil fuel and transportation means for moving the upgraded solid fossil to the burners. The EMR plant is adapted to reduce inherent moisture content in the upgraded solid fossil fuel by 50% or more. The system preferably comprises storage means suitable to store a quantity of the upgraded solid fossil fuel at least commensurate to daily consumption of the power generation plant. A system for producing upgraded solid fossil fuel for burning in an industrial process such as power generation, the system comprising an EMR drying plant adapted to reduce inherent moisture content in the upgraded solid fossil fuel by 50% or more, and storage means suitable to store a quantity of said upgraded solid fossil fuel at least commensurate to daily consumption of the industrial process. A system for producing upgraded solid fossil fuel, comprising an EMR drying plant adapted to reduce inherent moisture content in the upgraded solid fossil fuel by 50% or more, the EMR drying plant being adapted to process one of the following: low-rank coals, oil shale, tar sand. According to a further aspect of the present invention, there is provided upgraded solid fossil fuel obtained by EMR drying by the above described methods or in the above described systems. Our tests show that the upgraded fuel has increased heat value or reduced emissions, while at the same time its economic value increases as well. BRIEF DESCRIPTION OF THE DRAWINGS In order to understand the invention and to see how it may be carried out in practice, an embodiment will now be described, by way of non-limiting example only, with reference to the accompanying Fig. 1 which is a schematic diagram of low-rank coal drying and utilization according to the method of the present invention. DETAILED DESCRIPTION OF THE DRAWING With reference to Fig.l, the steps and the components of one example of process and system in accordance with the invention are depicted on the background of the existing process of coal-burning in a power-production utility, as described in the Background of the Invention. For illustration purposes, Fig. 1 shows the process for dewatering coal, but it is similarly suitable for any other solid fossil fuel. The described process is designed to be performed between the coal stockyard and the coal bunkers feeding the pulverization plant. A production scheme for practicing the process includes the following main components: coal stock 10, coal preparation unit 12, loading station 16, microwave drying plant 20, cooling and curing unit 34, dry coal storage units 66, pulverizing unit 68, and water treatment plant 30. The other components of the scheme will become clear further on. In this drawing, an enclosed area 8 represents the process of the present invention while the portion lying outside the enclosed area represents the existing process at the utility. Low-rank wet coal is stored in the stock 10 and is fed using appropriate techniques to the coal preparation unit 12 in which the coal can be sized. If necessary the coal could be graded or milled in any appropriate way. The coal is then passed to the loading station 16 where the coal is transferred to transport devices (e.g. conveyors) which are transparent to microwave radiation and which can withstand the process temperature without resulting mechanical damage. For example ceramics, plastic or stainless steel materials, which are not heated by microwave radiation and which do not materially attenuate such radiation, can be used in the construction of suitable conveyors (not shown). The loading station 16 uses conventional material handling systems. The design may be different for each specific application, and if a batch or continuous process strategy is deployed. In a batch operation the coal is loaded at a certain profile in the MW plant 20, and the energy required for drying is dependent on the radiation time. In a continuous operation, the coal is moved through the microwave drying plant 20 and the energy required for drying is dependent on the speed of motion. The microwave drying plant 20 comprises a housing and a number of microwave radiation sources (not shown). The housing is made of special material such as stainless steel and is shielded so that microwave radiation does not escape from the housing, thereby ensuring that the environment is electromagnetically safe, and the released water vapour and gasses are controlled. The housing is also designed to focus the electromagnetic radiation directly onto the coal, so as to maximize the yield of dried coal relatively to the energy input. MW radiation sources may be made using magnetron or other suitable technology. The radiation frequency of each source and the energy density prevailing in the housing can be varied according to requirements taking into account all relevant circumstances. Similarly, the period for which the coal is subjected to the radiation can be varied taking into account the efficiency of the dewatering process. Forced air or inert gas such as nitrogen or carbon dioxide, depending on the process conditions, is directed from a source 22 to the plant 20. The injection of forced air or inert gases is used to maintain a low humidity environment inside the housing. Humidity inside the housing is due to the water released from the coal, and due to the low temperature of the process. A substantial amount of water vapour 28 is released from the coal. This water vapour is driven off to the atmosphere by means of the air or inert gases 22 that are injected into the housing. In the case where an excessive amount of water is released from the coal, water 24 which drains from the unit can be directed to the water treatment plant 30. This process may not be required when the water which is removed from the coal can be released to the environment. The MW drying plant 20 may comprise for example a single stage. It also could be made of a plurality of stages depending on the extent of dewatering required, and the amount of coal which is being dewatered. Multiple MW plant units can be stacked in parallel and in series to each other. Parallel units serve to increase the capacity of the entire process while series units serve to increase the capacity of each line individually. Dried coal emerging from the plant 20 is directed to the coal cooling and curing unit 34. At this stage, the coal may contain surface moisture which is the result of the inherent moisture driven off by the electromagnetic radiation (see below). Upgraded coal 64 emerging from the cooling and curing unit 30 can be directed either to the dry coal enclosed storage units 66 or to the next stage in the utility's process which will be usually the pulverizing unit 68, preparing the coal for burning. The storage unit 66 is sized to hold enough upgraded coal to last during a high-load period of power production, when the MW radiation plant is not operational. Inert gases 70 may also be introduced to the enclosed storage units 66 in order to keep the coal under conditions that are not conducive to ignition or fire. As shown by the divisive broken line in Fig. 1, the enclosed storage units 66 may be part of an existing utility structure, or may be specially added to accommodate the upgraded coal produced by the drying process. A bypass connection 72 provides for direct connection between the cooling and curing unit 30 and the pulverizing unit 68. The bypass may be operational during low-demand periods of power production. The mode of operation of the process is such that the coal serves as capacity for storing energy, where cheap electric power is used to upgrade coal that is used during a high demand period. This strategy further benefits the utility in that it keeps the power plant operational at a certain load during low demand periods and hence produces more balanced and stable load characteristics throughout the day and so stabilizes electricity generation. The process also requires relatively short start up and shutdown periods. To reduce the cost of the energy required for the entire process, the MW plant units should have a process capacity which is sufficient to dry the amount of coal required for a whole day's operation in a matter of a few hours when demand for electricity is at its lowest. This requires that the process only works certain hours, and is switched on and off as demand changes throughout the day. The exemplary process of the present invention departs from the utility's normal process at the coal stockyard 10 and returns to the normal process at the input to the pulverizing unit 68. The confined storage facility 66 is designed to hold coal for high-demand periods, and has a storage capacity which will last during a high-demand period when the dewatering MW plant 20 is not operational. Although MW radiation was used as an example, other electromagnetic radiation may be used. Electromagnetic radiation heats the inherent moisture locked inside the coal particle. When this water is heated, it results in pressure increase inside the coal particle which serves as a driving force for the water vapour to escape from each coal particle. On its way to the coal particle's surface, the water vapour may mechanically carry along other water that is locked inside the particle. This process may increase the thermal yield of the radiation, as not all inherent moisture must be evaporated in order to escape from the coal particle. The result is that process conditions are kept at relatively low temperatures and not all the water released from the coal is in the vapour phase. Liquid water may be driven off the coal's surface and away from the housing by mechanical means. The injection of forced air or inert gas 22 serves as a method for the removal of the excess water, but other methods are also possible. Dewatering tests shown below conducted on low-rank coal such as Powder River Coal by means of high frequency electromagnetic radiation in moderate process conditions proved that the inherent moisture can be reduced to levels of 1-2% from levels of over 25%. Furthermore, tests showed that the process is also suitable for high-rank coals with initial low inherent moisture of 6-10% which can be reduced to as low as 1%. Also, the EMR drying of coal proved to conserve its volatile matter content, a critical attribute of coal heat value and its quick burning capability inside a boiler. The process of upgrading solid fossil fuels by EMR is rich in process variables that are easy to control such as radiation level, radiation time, particle size and others, factors which make the process easy to control and optimize. An amount of raw PRB coal was shipped to a laboratory in Haifa, Israel, for initial tests. Samples were treated in a domestic microwave oven with an output power of 900 Watt and frequency of 2,450 MHz. In addition to the treated coal, a sample of raw coal was also analyzed and the following Table 1 is a summary of the tests: (Table Removed) From the laboratory analysis it is evident that: - loss of weight observed during the physical tests is attributed to reduced inherent moisture of the coal; - treated coal shows different compositions based on the fact that the water was driven out and the sample total mass was reduced; - volatile matter was not affected by the process, which is a major departure from all other inherent moisture drying processes for PRB coal. In fact, the content of volatile matter has increased proportionally to the reduction in inherent moisture. The laboratory results as indicated in the table above have shown that the drying of inherent moisture in PRB coal is not only possible, but the process is also relatively efficient. Furthermore, if the process is conducted during low electricity demand periods it is also highly economical. The following Table 2 summarizes the process efficiency: Table 2 Initial temperature: Boiling point: Thermodynamics: Energy to heat 1.0 Ib water Energy to boil the water (latent heat) Total energy to heat and evaporate 1.0 Ib of water Test Results CaseB Amount of water evaporated Energy to evaporate Total energy to heat and evaporate 1.0 Ib of water Efficiency CaseC Amount of water evaporated (Table Removed) The electromagnetic radiation technique for drying inherent moisture in coal offers at least the following potential benefits: a relatively simple and inexpensive process at low pressure and temperature, a short residence time in the EMR unit which enables large quantity of coal to be processed on a continuous or semi-continuous basis, a clean and environmentally friendly treatment method, a process that can start up and shutdown easily, a process with a small footprint that could be deployed in a normal utility, a process that makes use of low cost energy to upgrade coal used during high demand periods to produce high cost electricity, a process that yields fuel which will be consumed within a short period of time hence eliminating the problem of spontaneous combustion, a process that is deployed in close proximity to the stage where the coal is pulverized to powder, hence eliminating the problem of coal fines and a solution that can integrate well into the entire power generation process of a utility. Although a description of a specific embodiment has been presented, it is contemplated that various changes could be made without deviating from the scope of the present invention. For example, the present method could be modified and used for upgrading other solid fossil fuels than coal. The methods of the present invention may be practiced in a separate fuel-drying utility (not producing electric power), the upgraded solid fuel may be traded to other consumers or may be used in other industrial facilities such as cement kilns, furnaces, etc. WE CLAIM: 1. A method of storing energy in an electric power grid having a fossil fuel plantfor generating electric power and users capable of consuming said electric power,wherein the consumption of electric power by said users is variable between periods ofhigh demand and periods of low demand and said fossil fuel plant is operable on low grade fossil fuel and high grade fossil fuel, said high grade fossil fuel having more energy per unit of mass than said low grade fossil fuel, said fossil fuel plant capable of variable output of energy having high output and low output and consuming variable amounts of fossil fuel in a period, said method comprising the steps of: a. defining a mid-level output of energy in between said high output and low output, during said period of time said fossil fuel plant is at or below said mid-level of output, and said consumption of electric power is low, said fossil fuel plant having excess energy output; b. using said excess energy output to power fossil fuel upgrading apparatus to process low grade fossil fuel and create a higher grade fossil fuel, and storing said higher grade fossil fuel with greater energy per unit of mass than said low grade fossil fuel during the period of time in which said fossil fuel plant has excess energy output; and c. operating said fossil fuel plant with low grade fossil fuel and high grade fossil fuel in which the ratio of high grade fossil fuel and low grade fossil fuel varies over time, said ratio of high grade fossil fuel increasing during a period of time in which said consumption of electric power is at high demand and said ratio of low grade fossil fuel increasing during a period of time in which said consumption of electric power is at low demand. 2. The method as claimed in claim 1, wherein said low grade fossil fuel is processed by electromagnetic radiation to produce a higher grade fossil fuel. 3. The method as claimed in claim 1, wherein said step of storing creates a reserve of higher grade fossil fuel in an amount to allow said fossil fuel plant to substantially continue at an efficient level of operation during said period of high demand on said higher grade fossil fuel. 4. The method as claimed in claim 1, wherein said periods of low demand and high demand are cyclical. 5. The method as claimed in claim 4, wherein said reserve is sized to at least the amount of higher grade fossil fuel selected from the group consisting of the amount anticipated to be produced during said period of excess energy output or said amount anticipated to be used during said period in which demand is greater than the said efficient level on low grade fossil fuel. 6. The method as claimed in claim 4, wherein said periods of are cyclical over a day. 7. The method as claimed in claim 1, wherein said fossil fuel is upgraded to remove at least 5% of the inherent water content. 8. The method as claimed in claim 1, wherein said low grade fossil fuel and said higher grade fossil fuel are selected from one or more of the groups consisting of low rank coal, high rank coal, and ranks in between, lignite, sub-bituminous and bituminous coals, oil shale, and tar sand. 9. The method as claimed in claim 1, wherein said processing to said higher grade fossil fuel removes one or more impurities. 10. The method as claimed in claim 9, wherein said impurities comprise at least one of the compositions of the group consisting of sulfur and ash. 11. The method as claimed in claim 2, wherein said electromagnetic radiation is microwave radiation. 12. The method as claimed in claim 3, wherein said reserve is maintained in a container to maintain the higher grade fossil fuel. 13. An apparatus for generating electrical power for a power grid having periods of low demand and periods of high demand, comprising: a. a source of lower grade fossil fuel in communication with a conveying system; b. a conveying system for receiving said lower grade fossil fuel from said source and at least one higher grade fossil fuel from a reserve and transporting said lower grade fossil fuel and higher grade fossil fuel to a burner; c. a burner in communication with said conveying system for consuming said lower grade fossil fuel and said higher grade fossil fuel, said burner powering an electric generator; d. an electric generator producing electrical power for said grid from thermal energy from said burner, said electrical generator and burner capable of operating between a low output and a high output and having an efficient operating mode in between said low output and high output, said burner and electric generator capable of operating in said efficient operating mode during low demand periods to create excess electricity; and e. fossil fuel processing facilities in communication with said conveying system to receive low grade fossil fuel during said low demand periods as said burner and electric generator are operated in an efficient operating mode and powered by excess electricity to create higher grade fossil fuel, said fossil fuel processing facilities further comprising at least one reserve for said higher grade fossil fuel sized to at least the amount of higher grade fossil fuel selected from the group consisting of the amount anticipated to be produced during said period of excess energy output or said amount anticipated to beused during said period in which demand is greater than the said efficient level on low grade fossil fuel, wherein said reserve receives said higher grade fossil fuel during periods of low demand and releases said higher grade fossil fuel to said conveying system during periods of high demand to allow the burner and electric generator to operate in said efficient mode of operation. 14. The apparatus as claimed in claim 13. wherein said reserve is a container. 15. The apparatus as claimed in claim 14, wherein said container is purged or maintained with inert gases to prevent ignition. 16. The apparatus as claimed in claim 13, wherein said fossil fuel processing facilities perform one or more of the group of upgrades consisting of size reduction, drying, and removal of impurities. 17. The apparatus as claimed in claim 13, wherein said fossil fuel processing facilities comprise electromagnetic radiation. 18. The apparatus as claimed in claim 13, wherein periods of high demand and low demand are cyclical over a period of time. 19. The apparatus as claimed in claim 18, wherein said period of time is a day.

Full Text

ENERGY MANAGEMENT IN A POWER GENERATION PLANT
FIELD OF THE INVENTION
This invention relates to energy management methods in utilities burning solid
fossil fuel.
BACKGROUND OF THE INVENTION
Power-producing utilities struggle with uneven demand for electricity during each
daily cycle. During one-day period, demand changes on an hourly basis, with peak
demand periods typically in the morning and evening and low demand during the night.
The gap between the high demand and low demand levels can reach over 30% of the
high demand level. Since electricity is a commodity that cannot be stored in its raw
form, a great deal of a utility's generation capacity is not efficiently utilized. In addition,
frequent large fluctuations in generation levels are costly in terms of operating costs and
mechanical wear, particularly in power plants burning solid fossil fuel such as coal.
Electric power utilities burning fossil fuel are operating a process that converts
heat contained in the fuel to steam, which then drives a turbine that generates electricity.
A coal-fired utility process contains coal handling and coal preparation units, boilers with
burners, ash and emission treatment units, turbine and generation related facilities, water
treatment units and auxiliaries.
The coal handling and preparation systems include off-loading facilities for trains,
barges or other transportation means, coal stockyard which typically stores coal for 1.5-2
months production, materials handling facilities to drive coal from the stockyard to the
plant, coal feeders, pulverization plant and feeding facilities to the boilers' burners.
Coal-fired power generation plants are expensive and complex to operate with
very slow process dynamics. A coal-fired power plant requires many hours of
preparation before generation of electricity can commence, making it uneconomical to
switch off during low demand periods. At the same time, power generation units must be
tightly synchronized with their load for plant integrity and operation safety
considerations. If the demand is reduced to a level below a critical value, coal fuel alone
cannot sufficiently maintain the necessary thermal conditions of the boiler, and other
fuels such as diesel must be used together with coal to keep the boiler at the appropriate
conditions. This is an undesired condition that increases operating expense.
To reduce the gap in load between high demand and low demand periods in order
to even out demands, utilities implement an aggressive time-of-use pricing strategy to
encourage customers to reduce consumption during high demand periods and to increase
consumption during low demand periods. Although the price for electricity in highdemand
periods may be several times the price for electricity in a low-demand period,
this strategy alone is not always sufficient to bridge the demand gap.
Many different solutions have been proposed to store excess electricity generated
during low-demand periods for use during high-demand periods. Among the solutions
that have been proposed is pumping water to high elevations during low demand and the
use of this water in reverse to power hydroelectric units during high-demand periods.
This method is known as "pumped storage" and is used in a few locations around the
world including the USA. Pumped storage requires large capital costs and has a large
impact on the environment.
US 3,631,673 suggests accumulating energy in off-peak hours by storing
compressed air. In peak hours, the compressed air drives a gas turbine. US 5,491,969
suggests that the compressed air is used for combusting fuel in a gas turbine (regular
compressors are then switched off). US 3,849,662 discloses a power plant burning coal
gas obtained by coal gasification, in a steam turbine. Coal gas produced during off-peak
hours is stored in a pressurized holder and is burnt in a gas turbine during peak hours.
Over 30% of electric power in the US is generated from coal. Coal production in
the US is 1.1 billion short tons per year. More than 90% of this coal is used for
generating electricity. America has coal reserves which will last for 250 years at the
current consumption levels.
The quality of coal can be assessed in terms of various attributes such as heat
value, moisture content, volatile matter content, ash content, and sulfur content. Each
attribute, to a greater or lesser extent, affects the manner in which the coal is used, its
burning characteristics and hence its economic value. These attributes vary from coal
deposit to coal deposit and moreover, within a given deposit, the characteristics of the
coal can vary substantially.
Deposits, such as those encountered in the Powder River Basin (PRB) in the
states of Wyoming and Montana, as well as in other similar deposits throughout the
world, contain coal which is commonly known as "low rank" coal. Low rank coal
includes sub-bituminous and lignite coals and is also known as brown coal. The water
content of these coals is considerable, and reaches levels of well over 30%.
In connection with moisture content of coal, the following definitions and standard
methods set forth by the American Society for Testing and Materials (ASTM) will be relied
on in the present application.
Total moisture means the measure of weight loss in an air atmosphere under
rigidly controlled conditions of temperature, time and air flow, as determined according
to either § 870.19(a) or § 870.20(a), incorporated herein by reference;
Inherent moisture means moisture that exists as an integral part of the coal seam
in its natural state, including water in pores, but excluding that present in
macroscopically visible fractures, as determined;
Excess moisture means the difference between total moisture and inherent
moisture, calculated according to § 870.19 for high-rank coals or according to § 870.20
for low-rank coals, both incorporated herein by reference. "Excessive moisture" will be
referred to in the present application as "surface moisture";
Low-rank coals means sub-bituminous C and lignite coals;
High-rank coals means anthracite, bituminous, and sub-bituminous A and B
coals.
Laboratory procedure for estimation of inherent moisture is outlined in ASTM
D1412-93 incorporated herein by reference. Collection of coal samples for the estimation
is also determined in ASTM documents.
In brief, the laboratory procedure is as follows. The coal is ground to fine powder,
and exposed to the open air for a certain period of time so that the surface moisture of the
coal is mostly dried, and the residual surface moisture of the coal equals the ambient
moisture. The assumption is that the residual moisture in the coal is inherent moisture.
Coal is then heated in an oven and the inherent moisture content is calculated from the
loss in mass.
There are two distinct types of moisture in coal: surface moisture and inherent
moisture. Surface moisture is the water contained in a coal particle that may be the result
of wetting the coal by physically pouring water on it under normal conditions, such as in
the case of rain or spraying systems. Exposing the coal particle to a source of heat such
as the sun or a flow of hot gases or physical drying mechanisms such as centrifugals, can
drive this moisture off.
Inherent moisture is the water that is locked inside the coal particle, mostly since
its formation, or which penetrated the coal particle in a process that takes a long period of
time and high pressure. Inherent moisture is typically locked in the coal particle in
capillaries or is chemically bounded to the coal and is impossible to drive out by
processes which are used for drying Surface moisture, unless more extreme forces are
used in the form of high temperature and/or high pressure.
Traditional coal dewatering or drying processes for inherent moisture are
complex and are conducted in extreme conditions. Most of these processes are based on a
technique in which coal particles are heated by conventional heating and pressure is
introduced or built in the system. The combined force in the process expels the inherent
moisture from the coal particles. The final moisture content of coal treated in this type of
process is mostly dependent on the ambient conditions prevailing inside the process. The
end result is that drying inherent moisture in coal to low levels requires a great deal of
energy and a long residence time of the coal in the drying process.
Existing dewatering techniques make use of conventional heat transfer processes
to evaporate the water off the coal particles. A disadvantage of these processes is the fact
that the coal particles are heated from the outside inwards in order to evaporate the water.
Coal is known to be a heat insulator, with a very high resistance for heat transfer that
leads to inefficiency, as much heat is wasted on heating each coal particle and its
environment, while the temperature gradient must be big enough to overcome the high
resistance of the coal particle to heat transfer. Such heating is risky and requires special
care, as exposing coal to high temperature can ignite it.
The dewatering process for upgrading of low-rank high inherent moisture coals
has historically been faced with two major drawbacks, which limited the deployment of
industrial dewatering systems on a large scale. Low-rank upgraded coal produced to date
has exhibited low auto-ignition points and spontaneous combustion that occurs faster
than in other coals, including low-rank raw coal. It was found in tests that when a pile of
dewatered coal is exposed to airflow for a number of hours (typically less than 72 hours),
the coal reaches temperatures at which spontaneous combustion or auto-ignition occurs.
Spontaneous heating and spontaneous combustion of coal particles have been common
problems of high inherent moisture content raw coals, but such events usually occur after
longer open-air exposure periods of days and weeks. This phenomenon is aggravated by
the dewatering process which substantially increases the surface-area-to-volume ratio,
hence making the coal particles more active in absorbing air moisture, further reducing
the upgraded coal shelf life.
Another problem observed in dewatering coal is the production of large quantities
of coal fines. Each transfer of dried coal after it leaves the process degrades the coal
particle size further and produces more coal dust, as dried coal is more brittle. Dried coal
does not have the inherent ability to trap small particles on its surfaces like moist coal.
This causes dust-size particles to be released and become lost in transportation, and has a
high risk of causing fires or explosions.
An article in The Australian Coal Review, October 1999, p.27, treats dry cleaning
of coal, i.e. separation of coal from rejects (rocks) without water floatation. In the dry
cleaning process, the moisture content of feed coal should not reach a level where the
particles stick together, which is a function of the surface moisture. Thus, a low-rank coal
can have quite a high inherent moisture level and still be superficially dry and suitable for
dry cleaning. The article suggests that thermal drying can be employed to reduce the
surface moisture to a sufficiently low level and recommends conveying the coal on a belt
through a microwave dryer. In this type of dryers, water readily absorbs the heat energy
and is vaporized while coal is not heated.
US 4280033 discloses MW drying apparatus and process for high-grade ground
coal for coking or gasification. The apparatus comprises an endless conveyor belt passing
through a closed treatment zone, electrode plates at opposite sides of the coal belt, and air
blowing system for passing hot air over the belt to remove humidity.
US 4259560 discloses MW heating/drying method for conductive powder
materials, especially coal before coking. Pulverizing is used to avoid arcing, moisture
content can be regulated in real time by IR detector measurements.
The removal of various contaminants from coal using Electro Magnetic
Radiation (EMR) is also known. In this regard, reference is made to 'Mossbauer
analysis of the microwave desulferization process of raw coal1 by S. Weng
(1993); 'Effect of microwave heating on magnetic separation of pyrite' by
Uslu et all (2003); and 'Microwave embrittlement and desulpherisation of
coal' by Marland et all (1998).
SUMMARY OF THE INVENTION
This invention relates to a novel energy management system and a process for
upgrading solid fossil fuel such as coal, for use therein. More particularly it is concerned
with a process for storing inexpensive electricity generated during low-demand periods in
the form of upgraded coal, for use during high-demand periods when the cost of
electricity is a great deal higher.
The invention combines business methods whereby electricity is generated and
stored during low-demand periods and used for generating electricity at high prices
during high-demand periods, with physical methods allowing such storage.
In the method of the present invention, low cost electricity is consumed during
low-demand hours, e.g. in the night, to upgrade low-cost, low-heat value fossil fuel for
use as a substitute for high-cost, high-heat value fuel. The upgraded fuel is stored and is
used in power generation units throughout the day, particularly during high-demand
periods, to generate electricity that is salable in the retail energy market at a considerably
higher price.
According to a first aspect of the present invention, there is provided a method for
managing electric power generated during periods of low demand, in an electric power
market where consumption of electric power exhibits periods of different demands. The
method includes upgrading solid fossil fuel by electromagnetic radiation (EMR) drying
during the periods of low demand and utilization of the upgraded fuel.
The utilization preferably includes burning the upgraded fossil fuel for electric
power generation at least during periods of high demand. However, it may include also
burning the fuel in another heat-consuming industrial process or trading the fuel with
another business entity.
The management method is particularly useful for application in a powergeneration
plant, where the upgrading is performed by means of electric power generated
by the same plant. Preferably, the upgraded fossil fuel is stored and burnt also at the same
plant, for electric power generation at least during periods of high demand.
Preferably, the quantity of the upgraded and stored fossil fuel
produced during low-demand periods covers all fuel consumption for power generation
at the same plant during periods of high demand. More preferably, average daily
quantity of the upgraded and stored fossil fuel covers at least average daily fuel
consumption for power generation at the same plant.
Preferably, the EMR drying used in the method includes reducing the
inherent moisture content in the upgraded fossil fuel by 50% or more.
In accordance with a second aspect of the present invention, there is
provided a method of upgrading solid fossil fuel. The method includes
dewatering of the solid fossil fuel by EMR, such that the inherent moisture
content in the upgraded fossil fuel is reduced at least in half. Daily quantity of
upgraded fossil fuel obtained by the electrical dewatering process is
commensurate to daily consumption of the power generation plant or/and another
industrial process.
The solid fossil fuel may be low-rank coal, oil shale, tar sand, subbituminous
coal, etc., with high inherent moisture content. However, high-rank
coals with initial low inherent moisture can be further dried as low as 1%
inherent moisture.
The method may be best performed where electric power consumption
due to other consumers exhibits periods of different demands and the electric
dewatering process is performed during low-demand periods of the electric
power consumption.
Preferably, the EMR dewatering process is carried out by using electric
power produced by a power generation plant burning the fossil fuel in its
upgraded state. More specifically, it is carried out where the power generation
plant operates with daily peaks of electric power production and the drying
process is performed predominantly during off-peak hours of the electric power
production.
The method includes storing of upgraded fossil fuel obtained during the
off-peak hours and using the upgraded fossil fuel for electric power production
during the daily peaks. Preferably, the quantity of upgraded fossil fuel obtained
during the off-peak hours covers at least daily consumption of the power
generation plant or the period between two subsequent low demand periods. This
substantially reduces the operating costs of the dewatering process.
The EMR drying may be preceded by driving off surface moisture by
means of hot gases.
Preferably, the EMR drying is performed by means of microwave
radiation.
The method of the present invention in particular provides dewatering
(drying) low-grade solid fossil fuels at low temperatures and pressures by means
of electromagnetic radiation. This method requires short start up and shutdown
periods suitable for interruptible operation during short periods, and has a small
footprint that allows the method to be deployed inside or alongside the power
plant. The use of this method for upgrading low-rank coal during low demand
periods to produce the next day's demand for coal can save utilities millions of
Dollars a year in fuel costs.
The physical dewatering process is based on exposing the solid fossil fuel
to high frequency electromagnetic radiation. There are many benefits of a
radiation-based dewatering process over other processes. Radiation dewatering is
performed at atmospheric pressure and does not require heating the fuel particle
itself. The start-up procedure of the process and its shutdown are quick, making
the process suitable for non-continuous and interruptible operations constrained
by the need to utilize low-cost electricity. Furthermore, radiation can be more
efficient than other techniques in that the dewatering of fuel particles does not
require the complete evaporation of the water, as some of the water may be
driven off the fuel particles mechanically.
Unlike existing inherent moisture dewatering processes involving extreme
heat and pressure conditions, which require large spaces and are normally
deployed near the source of the fuel, the method of the invention can be
implemented with a small footprint, it is quiet, environmentally friendly and is
simple to operate, making it suitable for both sides of the fuel's value chain - the
source side as well as the utility's side.
One fundamental premise of the process is subjecting the fuel particles to
electromagnetic radiation at radio, microwave or higher frequencies. The
intensity of the radiation i.e. the energy density per unit volume of fuel and the
frequency of the radiation may be varied according to requirements, taking into
account all relevant factors. Another important premise of the process is the use
of cheap electricity during low demand periods to dewater and upgrade the fuel
that is used to produce more expensive electricity throughout the day, in
particular during high demand periods. This introduces to the utilities an
innovative means by which electricity can be generated and stored inside the fuel
during low demand periods to be used during high demand periods to produce
higher revenues.
When the process is deployed near a utility's power generation unit, it
becomes possible to a large extent to integrate the process with the utility's
existing fuel handling facilities, hence saving large capital expenses. In this case,
the process of dewatering is carried out in a stage prior to a pulverizing unit
which mills the fuel solids to powder before feeding the powder to the boiler's
burners. In such a case, the low-grade fuel may be drawn from a stockyard by
means of conventional and existing material handling facilities. The fuel may
then be dried by means of conventional heat i.e. a stream of hot gases, and then
passed through the radiation units. Dewatered (upgraded) fuel may be stored for
later use, or may flow directly from the radiation units into the existing
pulverization unit. Normal power plant operation processes can then proceed.
When the upgraded fuel is stored for later use, existing or new enclosed
storage facilities may be used, such as bins or silos or any other confined dry
material storage unit. This fuel can be then fed directly to the pulverization unit,
and re-enter the normal power plant processes. Keeping the upgraded fuel in a
confined storage environment and under controlled conditions extends its shelf
life and reduces the risks of undesired ignition. The accumulated fuel may be
stored in silos, bins or any other means of storage. During the storage period the
storage facilities may be purged with inert gases such as nitrogen or carbon
dioxide, to prevent the fuel and fines from combusting.
Prior to subjecting the low-grade solid fuel to radiation, it may be sized.
This could be done in any appropriate way, for example by grading or milling.
Further particle sizing is performed during the pulverizing step which takes place
after the dewatering process and prior to the fuel being fed to the burner. Drying
of low-grade fuel by EMR produces fines and the radiated fuel exhibits brittle
characteristics which may prove to be beneficial in the pulverizing unit.
The method of present invention allows the fossil fuel to be upgraded
close to the place of its consumption, both in space and in time, so that the dried
fossil fuel does not need much additional handling such as transportation.
Immediately following the drying, the fuel may undergo a further size reduction
process of pulverizing. Thus coal fines are not lost in transportation and the risk
of causing fires and explosions is diminished.
The fuel could be processed in batches but preferably is processed on a
semi-continuous or continuous basis. Thus the fuel may be transported through
or past one or more sources of electromagnetic radiation on appropriate transport
devices. Such devices are preferably inert to electromagnetic radiation.
Any appropriate material may be used for the transport devices and for
example use may be made of conveyors or other transport devices which are
made from materials, e.g. ceramic or stainless steel material, which are inert to
radiation. This ensures that no energy is wasted unnecessarily to heat up elements
of the process which do not contribute to the main objective of driving the locked
moisture out of the fuel particles.
The fuel may be subjected to the radiation in one or more stages. The
electromagnetic radiation at the appropriate frequency excites the water
molecules locked inside the fuel particles, and consequently increases the water's
temperature so that the water is driven out and is released from the fuel. This, in
turn, may raise the temperature of the fuel particles. Higher water temperature
reduces surface tension effects so that the forces that lock the water inside the
capillaries in the fuel particles are reduced and the dewatering process becomes
more efficient.
It is also possible to vary the physical characteristics of each stage. For
example at least in one stage the fuel may be subjected to electromagnetic
radiation in the presence of a suitable inert gas, such as nitrogen or carbon
dioxide, which acts as an ignition suppression agent to prevent it from burning
and suppresses conditions which may be developed and could lead to explosion.
This gas could also heat the processed fuel to dry off its surface moisture which
may be originally contained in the fuel or which is built up during the radiation
process.
In most cases the water vapour that is released by the radiation process is
clean and could be released to the atmosphere.
The fuel may be subjected to a cooling step which will also remove the
water vapour, and thereafter dry fuel may be screened and recovered. It may also
be required that the dewatered coal particles are kept in certain ambient
conditions so as to drive off all excess surface moisture which may accumulate as
a result of the radiation.
According to a next aspect of the present invention, there are provided the
following systems for practicing the above methods.
A system for energy production by burning solid fossil fuel in a power
generation plant including burners comprises an EMR drying plant for upgrading
the solid fossil fuel and transportation means for moving the upgraded solid
fossil to the burners. The EMR plant is adapted to reduce inherent moisture
content in the upgraded solid fossil fuel by 50% or more. The system preferably
comprises storage means suitable to store a quantity of the upgraded solid fossil
fuel at least commensurate to daily consumption of the power generation plant.
A system for producing upgraded solid fossil fuel for burning in an
industrial process such as power generation, the system comprising an EMR
drying plant adapted to reduce inherent moisture content in the upgraded solid
fossil fuel by 50% or more, and storage means suitable to store a quantity of said
upgraded solid fossil fuel at least commensurate to daily consumption of the
industrial process.
A system for producing upgraded solid fossil fuel, comprising an EMR
drying plant adapted to reduce inherent moisture content in the upgraded solid
fossil fuel by 50% or more, the EMR drying plant being adapted to process one
of the following: low-rank coals, oil shale, tar sand.
According to a further aspect of the present invention, there is provided
upgraded solid fossil fuel obtained by EMR drying by the above described
methods or in the above described systems. Our tests show that the upgraded fuel
has increased heat value or reduced emissions, while at the same time its
economic value increases as well.
BRIEF DESCRIPTION OF THE DRAWINGS
In order to understand the invention and to see how it may be carried out in
practice, an embodiment will now be described, by way of non-limiting example
only, with reference to the accompanying Fig. 1 which is a schematic diagram of
low-rank coal drying and utilization according to the method of the present
invention.
DETAILED DESCRIPTION OF THE DRAWING
With reference to Fig.l, the steps and the components of one example of
process and system in accordance with the invention are depicted on the
background of the existing process of coal-burning in a power-production utility,
as described in the Background of the Invention. For illustration purposes, Fig. 1
shows the process for dewatering coal, but it is similarly suitable for any other
solid fossil fuel. The described process is designed to be performed between the
coal stockyard and the coal bunkers feeding the pulverization plant.
A production scheme for practicing the process includes the following
main components: coal stock 10, coal preparation unit 12, loading station 16,
microwave drying plant 20, cooling and curing unit 34, dry coal storage units 66,
pulverizing unit 68, and water treatment plant 30. The other components of the
scheme will become clear further on. In this drawing, an enclosed area 8
represents the process of the present invention while the portion lying outside the
enclosed area represents the existing process at the utility.
Low-rank wet coal is stored in the stock 10 and is fed using appropriate
techniques to the coal preparation unit 12 in which the coal can be sized. If
necessary the coal could be graded or milled in any appropriate way.
The coal is then passed to the loading station 16 where the coal is
transferred to transport devices (e.g. conveyors) which are transparent to
microwave radiation and which can withstand the process temperature without
resulting mechanical damage. For example ceramics, plastic or stainless steel
materials, which are not heated by microwave radiation and which do not
materially attenuate such radiation, can be used in the construction of suitable
conveyors (not shown). The loading station 16 uses conventional material
handling systems. The design may be different for each specific application, and
if a batch or continuous process strategy is deployed. In a batch operation the
coal is loaded at a certain profile in the MW plant 20, and the energy required for
drying is dependent on the radiation time. In a continuous operation, the coal is
moved through the microwave drying plant 20 and the energy required for drying
is dependent on the speed of motion.
The microwave drying plant 20 comprises a housing and a number of
microwave radiation sources (not shown). The housing is made of special
material such as stainless steel and is shielded so that microwave radiation does
not escape from the housing, thereby ensuring that the environment is
electromagnetically safe, and the released water vapour and gasses are
controlled. The housing is also designed to focus the electromagnetic radiation
directly onto the coal, so as to maximize the yield of dried coal relatively to the
energy input.
MW radiation sources may be made using magnetron or other suitable
technology. The radiation frequency of each source and the energy density
prevailing in the housing can be varied according to requirements taking into
account all relevant circumstances. Similarly, the period for which the coal is
subjected to the radiation can be varied taking into account the efficiency of the
dewatering process.
Forced air or inert gas such as nitrogen or carbon dioxide, depending on
the process conditions, is directed from a source 22 to the plant 20. The injection
of forced air or inert gases is used to maintain a low humidity environment inside
the housing. Humidity inside the housing is due to the water released from the
coal, and due to the low temperature of the process. A substantial amount of
water vapour 28 is released from the coal. This water vapour is driven off to the
atmosphere by means of the air or inert gases 22 that are injected into the
housing.
In the case where an excessive amount of water is released from the coal,
water 24 which drains from the unit can be directed to the water treatment plant
30. This process may not be required when the water which is removed from the
coal can be released to the environment.
The MW drying plant 20 may comprise for example a single stage. It also
could be made of a plurality of stages depending on the extent of dewatering
required, and the amount of coal which is being dewatered.
Multiple MW plant units can be stacked in parallel and in series to each
other. Parallel units serve to increase the capacity of the entire process while
series units serve to increase the capacity of each line individually.
Dried coal emerging from the plant 20 is directed to the coal cooling and
curing unit 34. At this stage, the coal may contain surface moisture which is the
result of the inherent moisture driven off by the electromagnetic radiation (see
below).
Upgraded coal 64 emerging from the cooling and curing unit 30 can be
directed either to the dry coal enclosed storage units 66 or to the next stage in the
utility's process which will be usually the pulverizing unit 68, preparing the coal
for burning.
The storage unit 66 is sized to hold enough upgraded coal to last during a
high-load period of power production, when the MW radiation plant is not
operational. Inert gases 70 may also be introduced to the enclosed storage units
66 in order to keep the coal under conditions that are not conducive to ignition or
fire. As shown by the divisive broken line in Fig. 1, the enclosed storage units 66
may be part of an existing utility structure, or may be specially added to
accommodate the upgraded coal produced by the drying process.
A bypass connection 72 provides for direct connection between the
cooling and curing unit 30 and the pulverizing unit 68. The bypass may be
operational during low-demand periods of power production.
The mode of operation of the process is such that the coal serves as
capacity for storing energy, where cheap electric power is used to upgrade coal
that is used during a high demand period. This strategy further benefits the
utility in that it keeps the power plant operational at a certain load during low
demand periods and hence produces more balanced and stable load
characteristics throughout the day and so stabilizes electricity generation. The
process also requires relatively short start up and shutdown periods.
To reduce the cost of the energy required for the entire process, the MW
plant units should have a process capacity which is sufficient to dry the amount
of coal required for a whole day's operation in a matter of a few hours when
demand for electricity is at its lowest. This requires that the process only works
certain hours, and is switched on and off as demand changes throughout the day.
The exemplary process of the present invention departs from the utility's
normal process at the coal stockyard 10 and returns to the normal process at the
input to the pulverizing unit 68. The confined storage facility 66 is designed to
hold coal for high-demand periods, and has a storage capacity which will last
during a high-demand period when the dewatering MW plant 20 is not
operational.
Although MW radiation was used as an example, other electromagnetic
radiation may be used. Electromagnetic radiation heats the inherent moisture
locked inside the coal particle. When this water is heated, it results in pressure
increase inside the coal particle which serves as a driving force for the water
vapour to escape from each coal particle. On its way to the coal particle's
surface, the water vapour may mechanically carry along other water that is
locked inside the particle. This process may increase the thermal yield of the
radiation, as not all inherent moisture must be evaporated in order to escape from
the coal particle. The result is that process conditions are kept at relatively low
temperatures and not all the water released from the coal is in the vapour phase.
Liquid water may be driven off the coal's surface and away from the housing by
mechanical means. The injection of forced air or inert gas 22 serves as a method
for the removal of the excess water, but other methods are also possible.
Dewatering tests shown below conducted on low-rank coal such as
Powder River Coal by means of high frequency electromagnetic radiation in
moderate process conditions proved that the inherent moisture can be reduced to
levels of 1-2% from levels of over 25%. Furthermore, tests showed that the
process is also suitable for high-rank coals with initial low inherent moisture of
6-10% which can be reduced to as low as 1%. Also, the EMR drying of coal
proved to conserve its volatile matter content, a critical attribute of coal heat
value and its quick burning capability inside a boiler. The process of upgrading
solid fossil fuels by EMR is rich in process variables that are easy to control such
as radiation level, radiation time, particle size and others, factors which make the
process easy to control and optimize.
An amount of raw PRB coal was shipped to a laboratory in Haifa, Israel,
for initial tests. Samples were treated in a domestic microwave oven with an
output power of 900 Watt and frequency of 2,450 MHz. In addition to the treated
coal, a sample of raw coal was also analyzed and the following Table 1 is a
summary of the tests:
(Table Removed)
From the laboratory analysis it is evident that:
- loss of weight observed during the physical tests is attributed to reduced
inherent moisture of the coal;
- treated coal shows different compositions based on the fact that the water
was driven out and the sample total mass was reduced;
- volatile matter was not affected by the process, which is a major
departure from all other inherent moisture drying processes for PRB coal. In fact,
the content of volatile matter has increased proportionally to the reduction in
inherent moisture.
The laboratory results as indicated in the table above have shown that the
drying of inherent moisture in PRB coal is not only possible, but the process is
also relatively efficient. Furthermore, if the process is conducted during low
electricity demand periods it is also highly economical.
The following Table 2 summarizes the process efficiency:
Table 2
Initial temperature:
Boiling point:
Thermodynamics:
Energy to heat 1.0 Ib water
Energy to boil the water (latent heat)
Total energy to heat and evaporate
1.0 Ib of water
Test Results
CaseB
Amount of water evaporated
Energy to evaporate
Total energy to heat and evaporate
1.0 Ib of water
Efficiency
CaseC
Amount of water evaporated
(Table Removed)
The electromagnetic radiation technique for drying inherent moisture in
coal offers at least the following potential benefits: a relatively simple and
inexpensive process at low pressure and temperature, a short residence time in
the EMR unit which enables large quantity of coal to be processed on a
continuous or semi-continuous basis, a clean and environmentally friendly
treatment method, a process that can start up and shutdown easily, a process with
a small footprint that could be deployed in a normal utility, a process that makes
use of low cost energy to upgrade coal used during high demand periods to
produce high cost electricity, a process that yields fuel which will be consumed
within a short period of time hence eliminating the problem of spontaneous
combustion, a process that is deployed in close proximity to the stage where the
coal is pulverized to powder, hence eliminating the problem of coal fines and a
solution that can integrate well into the entire power generation process of a
utility.
Although a description of a specific embodiment has been presented, it is
contemplated that various changes could be made without deviating from the scope
of the present invention. For example, the present method could be modified and
used for upgrading other solid fossil fuels than coal. The methods of the present
invention may be practiced in a separate fuel-drying utility (not producing electric
power), the upgraded solid fuel may be traded to other consumers or may be used
in other industrial facilities such as cement kilns, furnaces, etc.

WE CLAIM:
1. A method of storing energy in an electric power grid having a fossil fuel plantfor
generating electric power and users capable of consuming said electric power,wherein the
consumption of electric power by said users is variable between periods ofhigh demand and
periods of low demand and said fossil fuel plant is operable on low grade fossil fuel and high
grade fossil fuel, said high grade fossil fuel having more energy per unit of mass than said
low grade fossil fuel, said fossil fuel plant capable of variable output of energy having high
output and low output and consuming variable amounts of fossil fuel in a period, said method
comprising the steps of:
a. defining a mid-level output of energy in between said high output and low output, during
said period of time said fossil fuel plant is at or below said mid-level of output, and said
consumption of electric power is low, said fossil fuel plant having excess energy
output;
b. using said excess energy output to power fossil fuel upgrading apparatus to process low
grade fossil fuel and create a higher grade fossil fuel, and storing said higher grade fossil fuel
with greater energy per unit of mass than said low grade fossil fuel during the period of time
in which said fossil fuel plant has excess energy output; and
c. operating said fossil fuel plant with low grade fossil fuel and high grade fossil fuel in
which the ratio of high grade fossil fuel and low grade fossil fuel varies over time, said
ratio of high grade fossil fuel increasing during a period of time in which said
consumption of electric power is at high demand and said ratio of low grade fossil fuel
increasing during a period of time in which said consumption of electric power is at low
demand.
2. The method as claimed in claim 1, wherein said low grade fossil fuel is processed by electromagnetic radiation to produce a higher grade fossil fuel.
3. The method as claimed in claim 1, wherein said step of storing creates a reserve of higher grade fossil fuel in an amount to allow said fossil fuel plant to substantially continue at an efficient level of operation during said period of high demand on said higher grade fossil fuel.
4. The method as claimed in claim 1, wherein said periods of low demand and high demand are cyclical.
5. The method as claimed in claim 4, wherein said reserve is sized to at least the amount of higher grade fossil fuel selected from the group consisting of the amount anticipated to be produced during said period of excess energy output or said amount anticipated to be used during said period in which demand is greater than the said efficient level on low grade fossil fuel.
6. The method as claimed in claim 4, wherein said periods of are cyclical over a day.
7. The method as claimed in claim 1, wherein said fossil fuel is upgraded to remove at least
5% of the inherent water content.
8. The method as claimed in claim 1, wherein said low grade fossil fuel and said higher grade
fossil fuel are selected from one or more of the groups consisting of low rank coal, high rank
coal, and ranks in between, lignite, sub-bituminous and bituminous coals, oil shale, and tar
sand.
9. The method as claimed in claim 1, wherein said processing to said higher grade fossil fuel
removes one or more impurities.
10. The method as claimed in claim 9, wherein said impurities comprise at least one of the compositions of the group consisting of sulfur and ash.
11. The method as claimed in claim 2, wherein said electromagnetic radiation is microwave radiation.
12. The method as claimed in claim 3, wherein said reserve is maintained in a container to maintain the higher grade fossil fuel.
13. An apparatus for generating electrical power for a power grid having periods of low
demand and periods of high demand, comprising:
a. a source of lower grade fossil fuel in communication with a conveying system;
b. a conveying system for receiving said lower grade fossil fuel from said source and at least
one higher grade fossil fuel from a reserve and transporting said lower grade fossil fuel and
higher grade fossil fuel to a burner;
c. a burner in communication with said conveying system for consuming said lower grade
fossil fuel and said higher grade fossil fuel, said burner powering an electric generator;
d. an electric generator producing electrical power for said grid from thermal energy from
said burner, said electrical generator and burner capable of operating between a low output
and a high output and having an efficient operating mode in between said low output and
high output, said burner and electric generator capable of operating in said efficient operating
mode during low demand periods to create excess electricity; and
e. fossil fuel processing facilities in communication with said conveying system to receive
low grade fossil fuel during said low demand periods as said burner and electric generator are
operated in an efficient operating mode and powered by excess electricity to create higher
grade fossil fuel, said fossil fuel processing facilities further comprising at least one reserve
for said higher grade fossil fuel sized to at least the amount of higher grade fossil fuel
selected from the group consisting of the amount anticipated to be produced during said
period of excess energy output or said amount anticipated to beused during said period in
which demand is greater than the said efficient level on low grade fossil fuel,
wherein said reserve receives said higher grade fossil fuel during periods of low demand and releases said higher grade fossil fuel to said conveying system during periods of high demand to allow the burner and electric generator to operate in said efficient mode of operation.
14. The apparatus as claimed in claim 13. wherein said reserve is a container.
15. The apparatus as claimed in claim 14, wherein said container is purged or maintained with inert gases to prevent ignition.
16. The apparatus as claimed in claim 13, wherein said fossil fuel processing facilities perform one or more of the group of upgrades consisting of size reduction, drying, and removal of impurities.
17. The apparatus as claimed in claim 13, wherein said fossil fuel processing facilities
comprise electromagnetic radiation.
18. The apparatus as claimed in claim 13, wherein periods of high demand and low demand
are cyclical over a period of time.
19. The apparatus as claimed in claim 18, wherein said period of time is a day.

Documents:

1241-DELNP-2007-Abstract-(17-02-2012).pdf

1241-delnp-2007-abstract.pdf

1241-DELNP-2007-Claims-(17-02-2012).pdf

1241-delnp-2007-claims.pdf

1241-DELNP-2007-Correspondence Others-(17-02-2012).pdf

1241-delnp-2007-Correspondence Others-(22-10-2014).pdf

1241-delnp-2007-correspondence-others-1.pdf

1241-DELNP-2007-Correspondence-Others.pdf

1241-delnp-2007-description (complete).pdf

1241-DELNP-2007-Drawings-(17-02-2012).pdf

1241-delnp-2007-drawings.pdf

1241-DELNP-2007-Form-1-(17-02-2012).pdf

1241-delnp-2007-form-1.pdf

1241-delnp-2007-form-18.pdf

1241-DELNP-2007-Form-2-(17-02-2012).pdf

1241-delnp-2007-form-2.pdf

1241-delnp-2007-form-26.pdf

1241-DELNP-2007-Form-3-(17-02-2012).pdf

1241-DELNP-2007-Form-3.pdf

1241-delnp-2007-form-5.pdf

1241-DELNP-2007-GPA-(17-02-2012).pdf

1241-delnp-2007-pct-101.pdf

1241-delnp-2007-pct-210.pdf

1241-delnp-2007-pct-237.pdf

1241-delnp-2007-pct-306.pdf

1241-delnp-2007-pct-notification.pdf

Petition 137.pdf

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Patent Number

263717

Indian Patent Application Number

1241/DELNP/2007

PG Journal Number

47/2014

Publication Date

21-Nov-2014

Grant Date

17-Nov-2014

Date of Filing

14-Feb-2007

Name of Patentee

MICROCOAL INC

Applicant Address

SUITE 214, 5301 LIMESTONE, ROAD, CITY OF WILMINGTON, NEWCASTLE, DE 19808, USA

Inventors:

#	Inventor's Name	Inventor's Address
1	LIVNEH, BEN ZION	43 ETOSHA CRESCENT, P.O.BOX 10, STRATHAVON, 2031,JOHANNESBURG,SOUTH AFRICA
2	BARNEA, ELI	14 SWEDEN STREET, 34980 HAIFA, ISRAEL
3	YANIV, ISAAC	75 YAKINTON STREET, 34972 HAIFA, ISRAEL

PCT International Classification Number

F23G 5/46

PCT International Application Number

PCT/IL2004/001077

PCT International Filing date

2004-11-24

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2004/6277	2004-08-05	South Africa