Title of Invention

"METHOD FOR REDUCING SULFUR COMPOUNDS IN THE GAS IN COKE DRY QUENCHING EQUIPMENT"

Abstract

A method for reducing sulfur compounds in gas in coke dry quenching equipment comprising a step of adding lime into the coke dry quenching equipment; wherein a gas temperature in a part or all of the space inside a pre-chamber of the coke dry quenching equipment is 1000-1100°C; wherein more than 10 wt% of the lime has a grain size of less than 10mm; wherein an amount of the lime to be added is 25-640 g per one ton of coke; and wherein the lime is added between intermittent additions of the red-hot coke or the lime is added in the pre-chamber with the red-hot coke at the same time.

Full Text

[0001] This application claims priority to Japanese Patent Application No. 2002-376817 filed in Japan on December 26, 2002, which is incorporated herein by reference in its entirety. Field of the Invention [0002] The invention relates to a technology for reducing the concentration of sulfur compounds in a gas produced in coke dry quenching (hereinafter referred to as simply CDQ) equipment by adding 1ime. Description of the Related Art [0003] A coke oven is an external heating type furnace which is large in size and has good thermal efficiency. In view of the progress made in energy recovery, modern coke ovens incorporate very advanced energy recovery technology. The energy recovery is mainly performed using CDQ equipment wherein the coke is cooled down by a large amount of circulating gas (usually nitrogen gas) and the heated circulating gas is then used to generate steam which is then used by a steam turbine to generate electricity. [0004] In the CDQ equipment, red-hot coke from a coke oven is thrown in (e.g. added to) a pre-chamber and then passes through a cooling chamber in the lower portion. Circulation gas is fed into the cooling chamber as a cooling gas to quench the coke and become heated. The heated circulation gas is fed into a heat exchanger such as boiler to generate steam. The steam is used for operating steam turbine which generates electricity. Thus CDQ equipment performs two functions: a) quenching coke; and b) recovering heat energy. The cooled down coke discharged from the cooling chamber is charged into a blast furnace to serve as a reducing fuel for heating and reducing sintered ore. [0005] Technology for introducing air into the pre-chamber has been proposed to stabilize gas components and to increase the recovered amount of heat from the burning coke. [0006] In the conventional method for manufacturing quick lime by thermal decomposition of lime (mainly made of calcium carbonate, slaked lime) where a fuel oil burner is used, carbon dioxide is generated by the combustion of the fuel oil and there is decomposition of the lime. Thus the conventional method is a carbon dioxide generating process. [0007] However, the issue of a slight amount of sulfur compounds being produced by coke-burning due to air in the pre-chamber, has not been studied. [0008] Sulfur compounds generated by coke-burning are carried with the circulation gas through the circulation apparatus of the CDQ equipment and are partially condensed into sulfuric acid (H2SO4) or sulfurous acid (H2SO3) after cooling down at lower temperature portion (exit) of the boiler (heat-exchanger) , which causes metal corrosion on the surface of metal portion of the apparatus. Therefore, periodic maintenance is required wherein the operation is shut down, and repair works such as grinding and polishing of the corroded metal surface portion are performed, and if necessary, replacement of the corroded portion if the corrosion is extensive. If such metal corrosion is avoided, the frequency of maintenance can be reduced, which can lead to a great reduction in work, time and cost. However, effective technology for the prevention of metal corrosion of the circulation apparatus of CDQ equipment, specially at the low temperature portion of the boiler, has not yet been proposed. Summary of the Invention [0009] An object of the invention is to provide a method for reducing sulfur compounds in the gas in CDQ equipment, the sulfur compound being generated by the burning of coke is in air existing in the pre-chamber. [0010] The inventors have surprisingly found that when lime is added into pre-chamber of CDQ equipment that: (1) by adding lime into the pre-chamber of the CDQ equipment, sufficient temperature and residence time for thermal decomposition of lime is obtained without the need for additional amounts of other fuels such as heavy oil; (2) since only the sensible heat of the red-hot coke is used for decomposing the lime, this heat source does not increase the carbon dioxide amounts; and (3) there is a high heat recovery efficiency expected when compared to the decomposition of lime to form quicklime separately by using oil burner and adding the formed quicklime into the CDQ equipment. [0011] The present invention can be accomplished by any of the following ten methods for reducing sulfur compounds in the gas in CDQ equipment. [0012] According to a first aspect of the present invention, the method for reducing sulfur compounds in the gas in CDQ equipment comprises a step of throwing lime in the CDQ equipment. [0013] According to a second aspect of the present invention, the lime is thrown in a pre-chamber where red-hot coke is to be subsequently thrown in. [0014] According to a third aspect of the present invention, the lime is thrown in a bucket and/or bucket truck for transporting and throwing into red-hot coke. [0015] According to a fourth aspect of the present invention, the gas temperature in part or all of the space inside the pre-chamber is 1000-1100°C. [0016] According to a fifth aspect of the present invention, the lime includes more than 10 wt% of lime of which grain size is less than 10mm. [0017] According to a sixth aspect of the present invention, the amount of lime to be thrown in is 25-64 0 g per one ton of coke. [0018] According to a seventh aspect of the present invention, the lime is thrown in the pre-chamber between intermittent throw-ins of the red-hot coke or the lime is thrown in the pre-chamber with the red-hot coke at the same time. [0019] According to a eighth aspect of the present invention, the lime is thrown in through a coke throw-in opening located on the top of CDQ equipment and/or one or more lime throw-in openings located in the pre-chamber. [0020] According to a ninth aspect of the present invention, the lime is thrown by the force of gas movement using nitrogen gas and/or circulation gas as the carrier gas. [0021] According to a tenth aspect of the present invention, the lime is thrown in the bucket and/or bucket truck before, at the same time and/or after loading of the red-hot coke onto the bucket and/or bucket truck. Brief Description of the Drawings FIG.l is schematic diagram of typical CDQ equipment to be used in the invention. FIG.2(A) is schematic diagram of a crusher used for crushing biomass. FIG.2 (B)-(E) illustrate mesh patterns and mesh sizes of both exit screens installed at exit portions of the crusher of FIG.2(A) and classifying screens for classifying crushed lime and defining grain size of the crushed lime and percentage of specific grain size. Detailed Description of the Invention [0022] In an embodiment of the present invention, is a method for reducing sulfur compounds in a gas in a CDQ equipment, wherein lime is charged into (thrown in) the CDQ equipment to reduce the sulfur compound in the gas. [0023] During the burning of coke, sulfur contained in the coke is converted into sulfur compounds (SOx) which migrate into the gas. Lime thrown in the pre-chamber directly or indirectly via a bucket truck is thermally decomposed due to the heat of the red-hot coke according to the thermal decomposition reaction, i.e., CaCO3 → CaO + CO2 at 700-900°C. Sulfur compounds such as SO2 or H2S in the gas (circulating gas and gas in the pre-chamber) is converted into gypsum (CaSO4) through the reaction with CaO formed by thermal decomposition of lime, i.e.: (1) CaO + SO2 + l/2O2 - CaSO4; and (2) CaO + H2S - CaS + H2O, CaS + 2O2 → CaSO4. There is sufficient time for the reactions to proceed, since it takes about one hour for the lime thrown in to pass through the area in the CDQ equipment where the temperature is 800-1000°C. SO2 or H2S is deposited as gypsum (immobilized) on the surface of the coke. As a result, sulfur compounds in the gas are reduced to a large extent (for example, SOx concentration is reduced by 92%), and acid corrosion in the system is drastically reduced. Thus, the system becomes close to a maintenance free state. In the present invention, sulfur compounds in the gas are immobilized by throwing lime in and the remaining unreacted CaCO3 and CaO can be used as alternative material to lime in the sintering process, which is capable of desulfurization both in the CDQ and sintering process. [0024] In an embodiment of the present invention, the lime can be any of calcium carbonate (CaCO3) , slaked lime(calcium hydroxide, Ca(OH)2), mixture of one or more of the above and quick lime (calcium oxide, CaO) and natural limestone of which a main component is calcium carbonate are available. [0025] As for the grain size of lime, there is no special restriction. Preferably more than 10 wt% of the lime should have a grain size of less than 10mm. More precisely 10-100 wt% of the lime should have a grain size of less than 10mm, preferably 50-100 wt%, and should include 0-90 wt% having a grain size of 10-200 mm, preferably 0-50 wt%. The reason is that some large size lime particles may be difficult to be thermally decomposed and to contribute to the desulfurization process in the CDQ equipment, which may lead to a reduction of sulfur immobilization. Therefore additional lime would be required. In other words, when the size range of the lime is in the preferred size range, the lime can be thermally decomposed and contribute to the desulfurization process sufficiently while being maintained for about 1 hour in the high temperature area where the temperature is more than 700°C after being thrown in the pre-chamber. If the grain size is too large, the thermal decomposition reaction will not go beyond the surface of the grain into the center thereof (a portion of the lime is converted into CO2 gas, which embrittles the portion to become fine particles) before the lime particles exit out of the high temperature area; therefore, the thermal decomposition reaction using the recycled heat of the coke is insufficient and the contact between the lime and the circulation gas does not sufficiently promote a reaction with sulfur compound in the gas. Thus, reduction of the sulfur compounds by immobilization would be difficult. [0026] However, lime having a grain size of more than 200mm can be used in the invention. Such large size lime particles normally can be ground (with weighted friction) to the extent that the size falls into the range mentioned above while passing through the CDQ equipment. When the extra amount of lime is added, in case some portion of lime remains without being thermally decomposed, the remaining lime can be used in a sintering process. Since normally coke after passing through CDQ equipment is preferably required to be 45-55 mm in average grain size with a narrow size distribution, large sized coke is crushed by coke cutter and classified using a screen having a mesh of 25-30 mm. If the lime is crushed into fine grains, the small size allows the grains to be sent to a sintering process with powdered coke. [0027] The reason that lime should include more than 10 wt% of lime, preferably 50-100 wt%, of which grain size is less than 10mm, is because this size is convenient to handle since the size of lime used in sintering processes generally is less than 10 mm. In view of this and the fact that lime of less than 15 mm size is used in some cases, the preferred conditions are as follows. 10-100 wt% of the lime should have a grain size of less than the size of lime to be used in the sintering process, preferably 50-100 wt%, and should include 0-90 wt% of lime having a grain size greater than the size of lime to be used in sintering process but less than 200 mm, preferably 0-50 wt%. [0028] The size of the lime is defined as follows. [0029] The size of the lime is defined as mesh size in the longitudinal direction of the screen (shown by arrow in FIG. 2 (B)-(E)) used for classifying the crushed lime crushed by crusher. The definition does not depend on the shapes of mesh, some examples of which are illustrated in FIG.2 (B)-(E). [0030] The crusher breaks down the material to small size fragments using impact, friction, cutting etc. Typical machines using impact force are a hammer mill and ball mill, a typical machine using friction is a grinding mill and a typical machine using cutting is a cutter type. As the shape of most crushed lime is close to a sphere or a cubic (as is the case with coal or food), the natural particle diameter seems to be a good measure of the crushed grain size. Therefore, the concept of representative diameter or mean diameter can easily be obtained. However, in this invention, the size of the lime is defined by the mesh size of the screen the crushed lime passes through. Screens used for size classification are not the screens attached to the crusher shown in FIG.2, but another screen separately prepared only for classifying the already crushed lime. Classification is made by passing the lime particles through a screen and reducing the vibration in a direction vertical to the screen as much as possible. If the inclination angle of the screen is zero, the vibration is made in horizontal direction. [0031] Small size lime is obtained as follows, for example. As shown in FIG.2, lime material 3 01 is charged into the crusher 302 (hammer type) along the thick arrow line. A rotor 3 03 rotates the charged lime along the fine arrow line in the rotational direction 305. The rotated lime is crushed to become smaller by collision with the hammer 3 04 mounted in the crusher or passing through gap between the hammer 304 and the rotor 303. Size-reduced lime can fly out due to centrifugal force through a screen fixed to the outer wall of the rotating path. If the screen 307 has specific shape 308 and mesh size (examples are shown in FIG.2(B)-(E)), only the reduced size lime 306 which can pass through the mesh can fly out of the screen 307. [0032] Examples of screening are described below. [0033] Crushed lime is made by a Hammer-type crusher (crushing amount is l00kg/h, rotation speed is 200rpm, hammer width is 10 mm, the number of hammers are 12, exit screen mesh size is50 mm(square mesh)). The crushed lime is screened using a vibration screen (mesh size 10 mm (square mesh), inclined by 5°, vibration amplitude 10 mm in the direction horizontal and vertical to the inclination direction, and frequency is 30/min). If the lime which has not yet passed through the mesh is 10, 9, 10 wt% respectively, for each of the three trial runs, the crushed lime is defined as including 10 wt% of lime having a grain size of less than 10mm (wt% values of three trial runs are averaged and rounded off) . In like manner, if the lime which has not yet passed through the mesh is 20, 20, 20 wt% respectively, wherein the exit screen mesh size is 3 0 mm and the vibration screen mesh size is 10 mm, then the crushed lime sample is defined as one including 20 wt% of lime having a grain size of less than 10mm. Also, if the lime which has not yet passed through the mesh is 80, 79, 79 wt% respectively, the exit screen mesh size is 10 mm and vibration screen mesh is 10 mm, the crushed lime is defined as including 80 wt% of lime having a grain size of less than 10mm. [0034] By using another more compact crusher (crushing amount is 50kg/h, 200rpm, hammer width is 10 mm, the number of hammers is 12), data reliability can be raised. [0035] As mentioned above, the percentage of the lime having a size of less than 10 mm is defined as wt% of lime of which has not yet passed through the mesh screen. In order to change the wt%, the mesh size of the screen attached to the crusher is changed. The grain size can be changed by changing: a) the shape of the hammer; b) width of the hammer; c) the rotational speed; d) the screen position; e) type of crusher, i.e., grind mill cutter or cutter mill; and f) the mesh size of the crusher screen described above. In any event, grain size is defined by screening. Screening itself can be changed by changing vibration type or condition (for example, impulse by cam, circular/elliptical motion of screen, frequency) and shape of screen mesh (rectangular, circular, or elliptical). However, as long as the vibration screening described above is used, grain size is defined as a common numeric value. [0036] There is no specific limit on the amount of lime to be added. Sulfur compounds in the gas can be reduced in proportion to the amount added. Preferably 25-64 0g of lime per one ton of coke should be added. If the amount of lime added is less than 25g per one ton of coke, sulfur compounds may not be able to eliminated completely. On the contrary, if the amount of lime added is more than 640g per one ton of coke, sulfur compounds can be eliminated completely but some amount of lime remains unreacted. However as long as the amount of remaining lime is within some amount which can be used completely for the abovementioned sintering process, it would be harmless. [0037] The reason the preferred amount of lime ranges widely is because the amount of sulfur compounds generated by coke burning depends on existing amounts of air per one ton of coke. Some air is naturally introduced at the opening where coke is thrown in, and some air may be intentionally introduced for some purpose. [0038] For example, when air of 5-20 m3 (as measured under ambient conditions) is fed into a pre-chamber, coke of 1.13-4.5 Kg burns, which converts sulfur of 4.5-20.3g contained in the coke into 3.2-14.2 liter of SOx. This corresponds to a SOx concentration of 13-52 ppm in the discharged gas according to experimental data by an actual production system. [0039] Assuming that the lime and the thermal decomposition product CaO around the coke is fluidized by the circulation gas as in the fluidized bed, Ca/S ≥ 2, i.e., the amount of the Ca component in the added lime is more than 2 times the sulfur component (S) in the circulation gas. Under this condition, it is possible to desulfurize effectively. Consequently, an appropriate amount of lime per one ton coke should be 25-130 g in terms of CaCO3. [0040] Assuming that the lime and the thermal decomposition product CaO around the coke is packed as in a packed bed, the ratio Ca/S ≥ 10 is a condition to make it possible to desulfurize effectively, since contact with the gas is reduced. Consequently, an appropriate amount of lime per one ton coke should be 14 0-640 g in terms of CaCO3 for packed beds. [0041] Coke in CDQ equipment behaves like in a moving bed. In other words, the degree of gas contact is in between that of a fluidized bed and a packed bed. In view of this, appropriate amounts of lime per one ton coke can be 25-640 g in terms of CaCO3. However, it is preferable that the pilot experimental test is performed using a production system to determine the appropriate amount of lime to be added under the moving bed conditions with respect to any change in the air amount. [0042] A technique of using a biomass other than coke to be thrown in the pre-chamber has been proposed by the Applicant. In the case where the alternative fuel, such as biomass is used, the amount of lime to be added can be determined by estimating the generated amounts of sulfur compounds in the gas while taking into account any difference in the air amounts and added amounts of biomass or the like. However, it is preferable that the verifying test is performed using production equipment to determine the appropriate amount of lime to be added with respect to the air and biomass amounts. [0043] It is not necessary for the lime to be thrown in the pre-chamber. The gist of the invention is to immobilize sulfur compounds in the CDQ gas by reacting the sulfur compounds with calcium oxide (CaO) which is produced by thermally decomposing the lime, especially lime stone, calcium carbonate and slaked lime. (Even calcium carbonate, which is the hardest among these to be decomposed, can be decomposed at a temperature above 900 °C). To keep the thermal decomposition reaction going, the heat of the red-hot coke (about 1000 °C) in the pre-chamber can be used and the heat of the red-hot coke discharged from the coke oven loaded on a bucket or bucket truck can be used. Conventionally, the heat of the red-hot coke (before being thrown in the pre-chamber) has not been taken advantage of. It has been wasted by radiating away into the atmosphere during the time from loading on the bucket or bucket truck to reaching CDQ (about 5 minutes). The inventive process includes putting the lime together with the red-hot coke on the bucket to effectively utilize the heat to preheat the lime for thermal decomposition. [0044] Details are explained according to drawings. FIG.l is schematic diagram of typical CDQ equipment to be used in the invention. [0045] Red-hot coke 151, at around 1000°C, made in a coke oven 2 01 is extruded into a bucket or bucket truck (hereinafter referred to simply as bucket truck or the like) 102 to be transported to CDQ 101 equipment. The red-hot coke is discharged into pre-chamber 105 through a top coke throw-in opening 104 by opening a top lid 103 located on the top of CDQ 101 equipment normally covering the coke throw-in opening 104. After throwing in the red-hot coke 151, the top lid 103 is closed to shut out the natural inflow of air. The empty bucket truck or the like 102 is returned to the coke oven 201 for the next loading. [0046] High-temperature coke 151 in the pre-chamber 105 is dropped down to pass through a cooling chamber 106 in the lower section to be cooled down to 200°C by circulation gas 107 and then discharged out from a discharging exit 108 at the bottom of the cooling chamber 106. In FIG.l, red-hot coke is represented by thick arrow line 151 before being thrown in the CDQ equipment, coke inside the CDQ equipment is represented by numeral 153 and the moving direction is represented by the nonenumerated thick arrow line, and coke (including lime and gypsum) discharged out from the CDQ equipment is represented by numeral 155. [0047] Heat is recovered by a heat-exchanger (boiler) 109 through the circulation gas 107 mainly consisting of nitrogen gas. Steam 111 generated by the heat works the steam turbine 113 to generate electricity. Outside air 117 is added into a ring duct 115 which is a gas exhaustion exit to burn residual volatile components and coke powder in case those volatile components or powdered coke (and powdered lime and gypsum in this invention) reach the heat exchanger to cause coking or some heat transmission trouble. A dust catcher 123 is mounted in a circulation path 121 between the ring duct 115 and the heat exchanger 109 to collect the coke powder, lime powder and gypsum powder, the collected powder is to be used in the next sintering process. The circulation gas 107 after heat exchanging with boiler 109 is returned to the cooling chamber 106 through a circulation gas entrance 127 by adjusting the gas pressure using circulation gas blower 125 in the circulation path 121. A gas releasing path 129 to release part of circulation gas 107 can be installed in the circulation path 121 between the circulation gas blower 125 and the circulation gas entrance 127 in order to keep a flow rate of the circulation gas into the CDQ 101 equipment. When appropriate, a flow control valve, flow meter and/or exhaust gas purification apparatus can be installed on the gas releasing path 129. [0048] A method for reducing sulfur compounds in the gas in the CDQ equipment of the present invention is further explained based on PIG.1. [0049] As shown in FIG.l, lime 181a can be thrown in a pre-chamber 105 of the CDQ 101 equipment where red-hot coke 151 is thrown in, referred to as throw-in type (A) or lime as 181b can be put in a bucket and/or a bucket truck 102, referred to as throw-in type(B) or lime can be put both in the pre-chamber and the bucket and/or the bucket truck, combination of type (A) and type (B). [0050] Certain embodiments of throw-in type (A) are now discussed. [0051] In throw-in type (A-l) , the red hot coke 151 is batch-charged (thrown in by a batch operation) at intervals of several minutes to several tens of minutes. The lime 181a can be added between the throw-ins of the red-hot coke 151 through appropriate lime throwing-in apparatus 183, which makes throw-in timing easy. Preferably, however, the lime should be put in immediately after the red-hot coke 151 is charged in the pre-chamber 105. Normally the temperature of the space inside the CDQ 101 equipment is 1000-1100 °C because of the heat of the red-hot coke, it is not necessary for the lime to be well mixed with the coke. Further, there is sufficient time (residence time) for the reactions, since it takes about one hour for the lime thrown in to pass through the area in the CDQ equipment where the temperature is 800-1000°C. Therefore throw-in timing has no specific restriction. However throw-in of lime immediately after throw-in of red-hot coke 151 can increase an amount of immobilized sulfur compounds before the sulfur compounds in the gas is flown into the gas circulation path, which leads to a reduction in the condensation of the sulfur components contained in the gas at the exit portion of boiler, so acid corrosion in the system can be reduced. [0052] An "interval of coke batch-charging" is the time it takes all the red-hot coke in a first bucket truck or the like 102 which has been thrown in the pre-chamber 105 to the time a bottom portion of a second bucket truck or the like 102 starts to open for throw-in of red-hot coke of the next batch. [0053] When lime is thrown in between red-hot coke throw-ins, coke layer and lime layer descend in the CDQ equipment, they are stacked alternately like sandwiches while the lime layer having a thermal decomposition reaction and a desulfurization reaction to be converted into gypsum becomes immobilized as it is deposited on the coke, then discharged outside from the bottom discharging exit 108. [0054] In throw-in type (A-2) , lime 181a can be thrown in the pre-chamber 105 by using throwing-in apparatus 183 at the same time as the red-hot coke 151 is thrown in. This simultaneous throw-in is one of the preferred embodiments. Since the lime is scattered in the red-hot coke layer, the heat of the red-hot coke surrounding the lime can be effectively utilized to promote the thermal decomposition reaction. Thermally decomposed lime can easily contact sulfur compounds in the circulation gas flowing through the gap between cokes, which leads to effective immobilization of the sulfur components. [0055] "Simultaneous throw-in" means that the throw-in of lime starts and finishes during the time from the beginning of the dropping of the red-hot coke 151 from the bucket truck or the like 102 to finishing the drop. The simultaneous throw-in allows for good mixing of the coke and lime, which increases the contact probability between lime and coke (this increases heat transfer efficiency and promotes the thermal decomposition reaction) and also increases contact probability with circulation gas (this increases reaction efficiency between CaO and sulfur compound in the gas, which promotes sulfur immobilization). [0056] In the case of simultaneous throw-in, red-hot coke 151 and lime 181a of each batch are layered to form a multilayer, the multilayer descends in the CDQ equipment and the lime continues to be converted into gypsum deposited on the surface of coke through a thermal decomposition reaction and a desulfurization reaction until being finally discharged from the bottom discharging exit 108. [0057]- Throw-in type (A-3) is a combination of type (A-l) and type (A-2) . At some stage, lime is thrown in between red-hot coke throw-ins and at another stage, simultaneous throw-in is made. The required amount of lime is added to form separated layers of coke and lime or mixed layers for the purpose of utilizing advantageous features of respective throw-in types. [0058] In any throw-in types described above, the throw-in amount of lime 181a and red-hot coke 151 of each batch can be thrown in all at once, or continuously over a fixed period of time, or intermittently over a period. There is no specific restriction with the manner of throw-in. In the case of continuous or intermittent throw-in, the feeding rate can be constant or changed. [0059] In the abovementioned throw-in type(A), the lime 181a can be thrown in the pre-chamber through a top coke throw-in opening 104 on the top of the CDQ 101 equipment and/or through one or more lime throw-in opening 185 installed on the pre-chamber 105. [0060] As for the number of lime throw-in openings 185 installed on the pre-chamber 105, there is no specific restriction. However, the pre-chamber is recommended to have two or more lime throw-in openings, preferably three or more, and more preferably 4-16 lime throw-in openings equally spaced on the circumference for the purpose of scattering the lime uniformly in the pre-chamber 105 to increase contact probability with sulfur compounds in the circulation gas (this leads to increased reaction efficiency). Seventeen or more openings can be installed but the configuration and control becomes complicated and less than 17 openings are usually sufficient. A plurality of openings is preferably installed on the same circumference, i.e., at the same position of height in order to make it easy to control throw-in amounts or feed rates of lime 181a, carrier gas flow rates, throw-in flow speeds and throw-in angles at respective openings. [0061] Throw-in amounts, throw-in timings, throw-in flow speeds and others can be the same at respective openings, or can be changed respectively as long as sulfur compounds in the gas can be effectively immobilized by effectively utilizing the heat present in the coke. For example, throw-in amounts, throw-in timings, throw-in flow speeds and others can be changed at the respective openings to avoid uneven distribution of lime such as differences between the central area and peripheral area in the pre-chamber as locations lacking in lime can cause a decrease in the total reaction efficiency with sulfur compounds in the circulation gas. Further, the type of lime to be thrown in or its blend can be changed according to the throw-in timing. [0062] As shown in FIG.l, the installed position of the lime throw-in opening 185 is preferably above the ring duct 115 on the portion of pre-chamber where the cross section expands downwardly in addition to on the top lid 103 of pre-chamber. [0063] In throw-in type (A) , each factor such as throw-in amounts, throw-in flow speeds (flow rate) and throw-in angles at respective openings are to be determined according to total throw-in amount of lime, throw-in timing, throw-in position (from the top lid or from the downwardly expanding portion of the pre-chamber) and/or the number of openings to be used. The determination for optimum condition can be made by pilot experimentation or computer simulation, preferably should finally be made by verifying tests using production equipment. Specially throw-in amounts, throw-in flow speeds (flow rate) and throw-in angles are recommended to be adjusted by changing the carrier gas flow rate described later on so that the lime can be distributed uniformly in the pre-chamber. [0064] In the case where the lime is thrown in through a top coke throw-in opening 104 between the throw-ins of the red-hot coke 151 (throw-in type (A) , the opening 104 does not have to be opened completely and can be opened just enough to let the lime pass through. It is also possible to form a separate lime throw-in opening (not shown) in a part of the top lid 103. A plurality of lime throw-in openings can be installed around the top coke throw-in opening but as it may make the apparatus complicated, it would be easier and more convenient to utilize openings in the top lid 103. [0065] In the case where the lime 181a is thrown through the top coke throw-in opening 104 or through the lime throw-in opening 185 installed on the circumference of pre-chamber 105, the opening size can be enlarged or a movable mechanism or nozzle can be installed on the end edge of the opening so that the lime can easily be scattered uniformly in the pre-chamber 105. However, it is more preferable to use carrier gas (described later on) for the scattering since existing driving apparatus or mechanism, even if they are available, are required to be made of high heat resistance members, which adds to the expense. [0066] In the case of throw-in type (A-2) where the red-hot coke 151 and the lime 181a are thrown in simultaneously, it is better for the lime 181a to be thrown in together with the red-hot coke 151 through the coke throw-in opening 104 than to be thrown in through the lime throw-in opening 185 installed on the circumference of the pre-chamber 105, since it is difficult to scatter the lime uniformly due to the falling red-hot coke 151 blocking the thrown in lime toward the center area. [0067] With regard to the manner for throwing in (transporting) the coke, there are multiple methods. For example, the first method is to use an appropriate throwing-in apparatus 183 such as a delivery apparatus, e.g., a screw feeder or a table feeder which drops the lime through the opening by gravity. A second method is to use carrier gas by which the lime is transported and thrown in (blown into) . Nitrogen gas and/or a part of circulation gas are used as the carrier gas. [0068] In the second method of using a circulation gas, the temperature of the gas decreases. An example is where a gas after having passed through the circulation gas blower 125 is branched and fed into the throwing-in apparatus 183 of a delivery apparatus such as a table feeder via pipe 186 and the delivery apparatus and the fed gas work in combination so that the gas can be fed as a transporting gas into a lime transporting pipe 187 extending from the delivery apparatus to the lime throw-in opening 185. In the case of using nitrogen gas, the gas is supplied from a nitrogen gas supply source to the throwing-in apparatus 183 of a delivery apparatus such as table feeder via pipe 18 8 and, as is the case with using circulation gas above, the delivery apparatus and the fed nitrogen gas work in combination so that the gas can be fed as a transporting gas into a lime transporting pipe 187 extending from the delivery apparatus to the lime throw-in opening 185. Further in the case of using both nitrogen gas and the circulation gas, pipe paths for both are to be installed. By this method, nitrogen gas and circulation gas can be used concurrently or alternately by switching the pipe paths, resulting in the formation of an effective feeding of carrier gas. [0069] As gases available for a transportation gas in addition to nitrogen gas and circulation gas, the following gases can be used; i.e., inert gas such as argon gas, air (part of air introduced for some other specific purpose), a variety of gases generated in iron making process such as coke oven gas, blast furnace gas and converter gas are available as alternative oxygen sources to the purposefully introduced air. [0070] Gas flow transportation can scatter lime over wide areas by using less numbers of throw-in openings, which leads to providing more uniform thickness lime layers (in case of simultaneous throw-in, providing better dispersibility) compared to dropping lime simply by gravity. Using circulation gas 107 as a carrier gas can minimize the disadvantage of cost for using nitrogen gas. [0071] The manner using gravity to drop lime has the advantage of low running costs, since it does not use carrier gases. Throwing in of lime from the top coke throw-in opening 104 is preferable because even though the lime drops by gravity, the lime still can be scattered (dispersed) moderately because of heat convection of gas in the pre-chamber 105. [0072] In the case of throw-in type (B) , a bucket is a container for transporting red-hot coke. A bucket truck is a bucket with a truck as shown in FIG.l. Needless to say, other transporting and throwing-in equipment can be used in the invention. [0073] In the throw-in type (B) , lime 181b is put together with the red-hot coke 151 on the bucket and/or bucket truck 102 in order to utilize a sensible heat of red-hot coke discharged from coke oven loaded on a bucket and/or bucket truck before being thrown in the pre-chamber and then the loaded lime and red-hot coke are transported to the pre-chamber 105 of the CDQ 101 equipment (precisely to the position just above a coke throw-in opening 104) to. be thrown in at this part of the apparatus. The methods for throwing lime in a CDQ equipment include both throw-in type (A) and throw-in type (B). [0074] There is no special timing to be required for putting the lime in the bucket and/or bucket truck. The lime can be put in the bucket and/or bucket truck anytime such as before the red-hot coke 151 is loaded on the bucket truck or the like 102 from a coke oven 2 01, at the same time the red-hot coke is loaded or after red-hot coke is loaded since the heat of the coke is available in all cases for preheating the lime. [0075] (1) Lime 181b is loaded in the bucket truck or the like 102 before the red-hot coke 151 is loaded. For example, the lime is put in the empty bucket truck or the like 102 while it returns to coke oven after throwing a red-hot coke 151 in the CDQ 101 equipment. The lime is put in the empty bucket truck or the like 102 by a lime throwing-in apparatus (for example, a rotary feeder in addition to a screw feeder or table feeder as described above with respect to throw-in type (A)) using gravity or air transportation, then red-hot coke 151 from the coke oven is loaded in the bucket truck or the like 102 containing the lime. [0076] (2) Lime 181b is loaded in the bucket truck or the like 102 where the red-hot coke 151 is already loaded. For example, red-hot coke is discharged from the coke oven by using an extruding machine to be loaded in the bucket truck or the like 102, then the bucket truck is advanced to a position under a lime throwing-in apparatus (for example, a rotary feeder can be used in addition to a screw feeder or table feeder as described above with respect to throw-in type (A)) where the lime 181b is put in the bucket truck or the like 102 already containing the red-hot coke by gravity or air transportation. Either manner is simple and easy in operation and does not interfere with the lime throwing-in apparatus, the coke extruding machine and the CDQ equipment. [0077] In the manner of (1) above, after loading red-hot coke, the bucket truck or the like 102 can reach the CDQ 101 equipment without spending time loading the lime before reaching the CDQ equipment. In the manner of (2) above, the red-hot coke 151 in the bucket truck or the like 102 can be covered with the lime 181b, which can promote thermal decomposition of the lime while limiting the radiation of heat of the red-hot coke and also preventing the red-hot coke 151 from contacting the air, otherwise the red-hot coke burns. [0078] The abovementioned two throw-in types (A) and (B) can be combined. In a preferable embodiment, only a specific amount of lime, which is just enough to promote thermal decomposition of the lime 181b while restraining the radiation of heat of the red-hot coke 151, is added to the red-hot coke in the bucket truck or the like 102 (throw-in types (B) ) , and then the rest of amount required is thrown in by throw-in type (A) so that the lime can be uniformly mixed and dispersed with the red-hot coke. [0079] In the inside of the pre-chamber, all or at least part of the space has gas at a preferred temperature of 1000-1100°C. The higher temperature increases the reaction rate with respect to the thermal decomposition reaction of the lime and the reaction between the sulfur compounds in the gas and the thermal decomposition product CaO, which immobilizes sulfur components in the gas as gypsum CaSO4. As a result, higher desulfurization effects are realized. Immobilized sulfur as gypsum deposited on the surface of the coke is discharged out of a bottom discharging exit 108 of the CDQ equipment together with cooled down coke 155 and the remaining unreacted CaCO3 and/or CaO. Large size coke is crushed by a coke cutter and classified with a screen, where powdered coke, which is not able to pass through the mesh is collected and even-sized coke grains are collected after passing through the mesh. Gypsum CaSO4 and unreacted CaCO3 and/or CaO are sent to the following sintering process together with the powdered coke. The even-sized coke, which has passed through the mesh is fed into a blast furnace. Normally sintered ore, in particular a self-fluxing sintered ore or lime-containing sintered ore which is a sintered ore into which CaO (usually limestone powder) is burnt in advance so that the flux does not have to be added to the blast furnace, is manufactured by sintering iron ore with added powdered coke and added lime. In the present invention, CaCO3 and CaO already included in the powdered coke are available as an alternative material to lime, which leads to a reduction in lime consumption in the sintering process otherwise to be added. Thus, lime can be effectively utilized as a desulfurization agent in the iron making process. In both the CDQ and sintering process, the lime is converted into CaSO4. [008 0] If the gas temperature of the space inside the pre-chamber is less than 1000°C, the thermal decomposition reaction CaCO3 → CaO + CO2 hardly progresses (to be decomposed beyond 900°C). In addition to that, the reaction efficiency of desulfurization can hardly be high, which may cause the elimination ratio of sulfur compounds (desulfurization percentage) to be low. On the contrary, if the temperature is more than 1100°C, the cooling efficiency of the CDQ is lowered due to increased heat loss such as heat radiation, which leads to lowering total thermal efficiency. [0081] Inside the space of the pre-chamber does not have to have a uniform temperature distribution over the whole space. Even if there are pockets of temperature out of range mentioned above, it is harmless as a whole. Examples [0082] The present invention is explained below based on the following specific examples. However, it should be understood that the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. [0083] Comparative Example 1 (no lime is thrown in) - normal operation of the CDQ equipment shown in FIG.l was run assuming that 5 m3 (as measured under ambient conditions) per one ton of coke is introduced into the pre-chamber. The value of 5 m3 (as measured under ambient conditions) is the air amount naturally introduced into the pre-chamber when a top lid 103 is opened to throw in the coke, which seems to be a fairly accurate value estimated based on the operation record of CDQ production equipment. The sulfur content of the coke used in this comparison example was 0.4 wt% (dry) and the volatile matter (VM) was 3%. The gas temperature of the space inside the pre-chamber was 1000-1100°C during the operation. The gas temperature of this space was measured by a temperature sensor 191 located in the position inside the pre-chamber 105 as shown in FIG.l. Coal pieces charged into the coke oven 201 were less than 10 mm in grain size. [0084] An amount of oxygen gas (02) in the charged 5 m3 (as measured under ambient conditions) was 1.05 m3 (as measured under ambient conditions), which generated 4.5 g sulfur(S) containing gas by burning 1.13 Kg red-hot coke. As a result 3.2 1 (as measured under ambient conditions) of SOx was generated. The generated SOx was measured as a SOx concentration in the released gas which was released through the gas releasing path 129 in FIG.l. The result was that the SOx amount in the released gas was 13 ppm (averaged SOx concentration of released gas released during the CDQ operation) in the case of using no lime. [0085] Example 1 (lime is thrown in) - it is assumed that 5 m3 (as measured under ambient conditions) per one ton of coke is introduced into pre-chamber as well as in the comparison example. Lime is thrown in the pre-chamber between the intermittently performed throw-ins of the red-hot coke 151 through 4 lime throw-in openings 185 equally spaced on the circumference of the pre-chamber by using appropriate throw-in apparatus 183, a table feeder and a gas transportation system using air as the carrier gas. More precisely, equal amounts of lime are blown into the pre-chamber through each of 4 lime throw-in openings 185 at the same time by controlling the table feeder and transporting gas flow rate so that a uniform lime layer can be formed on the coke. The amount of lime thrown in is 3 00 g per one ton of red-hot coke. Other conditions are the same as that of Comparative Example 1. The sulfur content of the coke used in this Example 1 is 0.4 wt% (dry) and the volatile matter (VM) is 3%. The lime used is all calcium carbonate (CaCO3) . The coal, which is charged into coke oven 201, is less than 10 mm in grain size. The lime used in this Example 1 includes 10 wt% of lime of which grain size is less than 10mm. More precisely, as shown in FIG. 2, the lime used is made by Hammer-type crusher (crushing amount = l00kg/h, rotation speed = 20 0rpm, hammer width = 10 mm, the number of hammers = 12, exit screen mesh size = 50 mm (square mesh)). The crushed lime is screened by using vibration screen (mesh size = 10 mm (square mesh), inclined by 5°, vibration amplitude = 10 mm in the direction horizontal and vertical to the inclination direction, frequency = 3 0/min.) The lime, prior to passing through the mesh, is 10, 9, 10 wt%, respectively, for each of the three trial runs. Thus, the crushed lime is determined to include 10 wt% of lime of which grain size is less than 10mm and then is used for the run of Example 1. [0086] In this example, the CDQ equipment is operated by throwing in 300g of lime (CaCO3) per one ton of red-hot coke. The SOx concentration is measured in a released gas, which is released through a gas releasing path 129 in FIG.l. It is confirmed that the SOx amount in the released gas is lowered to 1 ppm (average SOx concentration of released gas released during the CDQ operation). In other words, the elimination or recovery ratio of sulfur compounds (desulfurization percentage) is 92%. [0087] As a result, acid corrosion caused by condensation of H2SO4 or H2SO3 on the surface of heat exchange pipe of the boiler 109 or at the exit section of the boiler 109 can be drastically reduced. [0088] Example 2 - the lime used in this example is the same as the one used in Example 1. The lime is put in the bucket truck 102 where red-hot coke is already loaded. Normally, in a CDQ operation, l00t/h red-hot coke is thrown in the pre-chamber having a gas temperature of 1000°C, and this generates 70.2t/h steam, i.e., 0.702t-steam/t-coke, and when the lime of 30g/h is added into the pre-chamber together with red-hot coke, the CDQ equipment generates 0.635t-steam/t-coke. However, the present inventors have found that when lime is put in the bucket truck in advance by 30g/h, then thrown in the pre-chamber together with the red-hot coke, the CDQ equipment generates 0.64t-steam/t-coke. Consequently, the percentage of lime which is decomposed on the bucket truck before being thrown in CDQ is: (0.64-0.635)/(0.702-0.635)x 100 = 7.5% In other words, the heat of the red-hot coke which has been radiated away into the atmosphere while staying in the bucket truck can be recovered as decomposing heat for 7.5% of the lime amount. [0089] As described above, the present invention can reduce sulfur compounds in the CDQ gas. In the case of inducing 5 m3 (as measured under ambient conditions) air per one ton coke into the pre-chamber, the SOx concentration can be reduced from 13 ppm to 1 ppm, i.e., by 92%. This would allow a reduction in the frequency of maintenance for acid corrosion from every 3 years to at least every 5 years, which leads to a large reduction in time for repair, work and cost. Previously, corroded metal portions had to be replaced earlier than expected, since the repair involved grinding of the corroded portion and the necessary grinding made the part thinner than expected. The present invention would also allow the apparatus, which used to be corroded quickly, to be in operation for a longer time. The reduction in the SOx amount to be discharged leads to a reduction in running costs for the gas purification apparatus. [0090] Coke cooled down by CDQ are then screened. Even-sized coke grains are collected once they pass through a mesh, and then are sent to a blast furnace and the powdered coke which has not passed through the mesh is sent to sintering process to make sintered ore. In the sintering process, iron ore is sintered with powdered coke and lime to form 10-20 mm size sintered ore. In the present invention, lime added to the CDQ equipment immobilizes the sulfur component as gypsum (CaSO4) , which is discharged from the CDQ equipment and screened to be collected with the powdered coke which has not passed through the mesh. Thus, the gypsum (CaSO4) is also fed into a sintering process, which provides a derived effect of the present invention that the lime amount to be added into the sintering process can be drastically reduced up to zero, since gypsum (CaSO4) can also work as an alternative material to lime by generating CaO through thermal decomposition in addition to unreacted CaCO3 and CaO as alternative material to lime in the sintering process. Once immobilized, sulfur as gypsum (CaSO4) is sent to a blast furnace and a sintering process where the sulfur component of the gypsum is gasified and exhausted again. However, the amount of sulfur in the gypsum was originally a part of the sulfur contained in the coke and the existing sulfur eliminating apparatus installed in the sintering process and the blast furnace has sufficient capacity to purify the sulfur component from coke in the process. Thus, the sintering process, let alone the blast furnace, does not need any-additional facilities for treating the sulfur component brought from the CDQ equipment. WE CLAIM: 1. A method for reducing sulfur compounds in gas in coke dry quenching equipment (101) comprising a step of adding lime into the coke dry quenching equipment; wherein a gas temperature in a part or all of the space inside a pre-chamber (105) of the coke dry quenching equipment (101) is 1000-1100°C; wherein more than 10 wt% of the lime has a grain size of less than 10mm; wherein an amount of the lime to be added is 25-640 g per one ton of coke; and wherein the lime is added between intermittent additions of the red-hot coke (151) or the lime is added in the pre-chamber (105) with the red-hot coke (151) at the same time. 2. The method as claimed in claim 1, wherein the lime is added into a pre-chamber (105) where red-hot coke (151) is also to be added. 3. The method as claimed in claim 1, wherein the lime is placed into a bucket and/or bucket truck (102) for transporting and adding red-hot coke into the coke dry quenching equipment (101). 4. The method as claimed in claim 2, wherein the lime is added through a coke addition opening (104) located on top of the coke dry quenching equipment (151) and/or one or more lime addition openings located on the pre-chamber (105). 5. The method as claimed in claim 1, wherein the lime is added by gas transportation using nitrogen gas and/or circulation gas as a carrier gas. 6. The method as claimed in claim 3, wherein the lime is added in the bucket and/or bucket truck (102) before, at the same time and/or after loading of red-hot coke (151) onto the bucket and/or bucket truck (102). 7. The method as claimed in claim 1, wherein the lime is added in the pre-chamber (105) between intermittent additions of the red-hot coke (151). 8. The method as claimed in claim 1, wherein the lime is added in the pre-chamber (105) with the red-hot coke (151) at the same time. 9. The method as claimed in claim 4, wherein the lime is added through a coke addition opening (104) located on top of the coke dry quenching equipment (101) and/or one or more lime addition openings located on the pre-chamber (105). 10. The method as claimed in claim 4, wherein the lime is added through one or more lime addition openings located on the pre-chamber (105). 11. The method as claimed in claim 5, wherein the lime is added by gas transportation using nitrogen gas as a carrier gas. 12. The method as claimed in claim 5, wherein the lime is added by gas transportation using circulation gas as a carrier gas. 13. The method as claimed in claim 6, wherein the lime is added in the bucket and/or bucket truck (102) before loading of red-hot coke (151) onto the bucket and/or bucket truck (102). 14. The method as claimed in claim 6, wherein the lime is added in the bucket and/or bucket truck (102) at the same time as the red-hot coke (151). 15. The method as claimed in claim 6, wherein the lime is added in the bucket and/or bucket truck (102) after loading of red-hot coke (151) onto the bucket and/or bucket truck (102).

Documents:

1474-DEL-2003-Abstract-(16-09-2011).pdf

1474-del-2003-abstract.pdf

1474-DEL-2003-Claims-(16-09-2011).pdf

1474-del-2003-claims.pdf

1474-DEL-2003-Correspondence Others-(16-09-2011).pdf

1474-del-2003-correspondence-others.pdf

1474-del-2003-correspondence-po.pdf

1474-DEL-2003-Description (Complete)-(16-09-2011).pdf

1474-del-2003-description (complete).pdf

1474-DEL-2003-Drawings-(16-09-2011).pdf

1474-del-2003-drawings.pdf

1474-del-2003-form-1.pdf

1474-del-2003-form-13.pdf

1474-del-2003-form-18.pdf

1474-del-2003-form-2.pdf

1474-DEL-2003-Form-3-(16-09-2011).pdf

1474-del-2003-form-3.pdf

1474-del-2003-form-5.pdf

1474-DEL-2003-GPA-(16-09-2011).pdf

1474-del-2003-gpa.pdf

1474-DEL-2003-Petition-137-(16-09-2011).pdf