Title of Invention	A PROCESS FOR SEPARATION OF CARBON DIOXIDE FROM FUEL GASIFICATION AND COMBUSTION PRODUCTS AND REGENERATION BY A THERMAL PROCESS
Abstract	The present invention relates to a process for separation of carbon dioxide from fuel gas and flue gas combustion products using ammonia absorption comprising the steps of entering the fuel or flue gas (10) through a heat exchanger (1) for releasing heat and discharging from the heat exchanger (1), the fuel or flue gas enters to a gas cooling scrubber (2) for further cooling with water (30) to increase ammonia absorption efficiency and leaving from the gas cooling scrubber (2), the fuel or flue gas (10) enters to a carbon dioxide absorber (3) wherein the CO2 in the fuel or flue gas reacts with ammonia solution to form ammonium carbonate solution (20) and washing fuel or flue gas with water after step (c) in a ammonia wash scrubber (4) for washing out traces of ammonia carried over by the fuel or flue gas with water to convert to ammonia solution (40) and leaving carbon dioxide free gas (50) from the ammonia wash scrubber (4) through the stack characterised in that said ammonia dissolves with water converts into alkaline ammonium hydroxide that reacts with carbon dioxide of fuel or flue gas forming ammonium bicarbonate solution leaving carbon dioxide free gas.

Title of Invention

A PROCESS FOR SEPARATION OF CARBON DIOXIDE FROM FUEL GASIFICATION AND COMBUSTION PRODUCTS AND REGENERATION BY A THERMAL PROCESS

Abstract

The present invention relates to a process for separation of carbon dioxide from fuel gas and flue gas combustion products using ammonia absorption comprising the steps of entering the fuel or flue gas (10) through a heat exchanger (1) for releasing heat and discharging from the heat exchanger (1), the fuel or flue gas enters to a gas cooling scrubber (2) for further cooling with water (30) to increase ammonia absorption efficiency and leaving from the gas cooling scrubber (2), the fuel or flue gas (10) enters to a carbon dioxide absorber (3) wherein the CO2 in the fuel or flue gas reacts with ammonia solution to form ammonium carbonate solution (20) and washing fuel or flue gas with water after step (c) in a ammonia wash scrubber (4) for washing out traces of ammonia carried over by the fuel or flue gas with water to convert to ammonia solution (40) and leaving carbon dioxide free gas (50) from the ammonia wash scrubber (4) through the stack characterised in that said ammonia dissolves with water converts into alkaline ammonium hydroxide that reacts with carbon dioxide of fuel or flue gas forming ammonium bicarbonate solution leaving carbon dioxide free gas.

Full Text	FIELD OF INVENTION The present invention relates to a process of separation of carbon dioxide from fuel gas and combustion products using ammonia absorption and subsequent regeneration by a thermal process to prevent the harmful emission of carbon dioxide green house gas adaptable to power plants, steel plants, fertilizer plants, refineries, waste disposal plants and other industries. BACKGROUND OF THE INVENTION AND PRIOR ARTS The greenhouse gas carbon dioxide in the atmosphere has reached an alarming level to cause a global warming and climate damage. Burning of the fossil fuels like coal, oil and the natural gas for transportation, an electric power generation, the production of steel, cement, fertilizer and the chemicals emit carbon dioxide to the atmosphere which acts like a blanket warming up the earth and referred as a global warming. This can lead to a major environmental catastrophe on the earth in the coming decades. Hence, there is a necessity to invent new technology to mitigate carbon dioxide emissions into atmosphere. The fossil fuel fired in electric power generation is one of the major sources of carbon dioxide emissions from thermal power plants. In these power plants the chemical pollutants like SOx, NOx, in ppm levels are removed by the pollution control devices and the stack gases emitted to the atmosphere are nitrogen, water vapour and harmful carbon dioxide. The present global warming crisis calls for a separation of carbon dioxide from nitrogen in the flue gas by a suitable method as described in the present art, so that carbon dioxide captured can be transported and sequestrated in empty oil and gas wells under earth or in the ocean, instead of direct emission to the atmosphere. Presently these options are being studied, as nature is already using the natural reservoirs as the main carbon dioxide sink. The separation of carbon dioxide from other gases like nitrogen is an important step in the carbon capture for sequestration. Amine absorption process is a well known method used in fertilizer and refinery industries for separation of the carbon dioxide from other gases in the production of hydrogen but is too costly and a high energy process to adopt for capturing a large amount of carbon dioxide emitted from the thermal power plants at an uneconomical decrease in efficiency of 11-13%. Further the amines are costly and it degrades with limited life. The technologies are being developed to use oxygen directly for combustion or the gasification with fossil fuels instead of air, which emit only carbon dioxide without nitrogen and can be directly captured and sequestrated. But oxygen separation from air, using liquefaction technologies is a capital intensive and costing about 15 to 20% of capital cost of power plant and further this method would be applicable to new green field contents only and cannot be retrofitted in existing power plants which use air for combustion. Development of membranes for carbon dioxide separation is at an infant stage and is not providing an immediate solution. Recently the proposed methods are based on the absorption reaction of carbon dioxide with oxides and hydroxides of sodium, potassium, lithium, magnesium , calcium to form carbonates and subsequently decompose at high temperature for evolving pure carbon dioxide for sequestration. USP 2007217981 and USP 2005180910 describe an art of capturing carbon dioxide from flue gas effluent of a power plant to form magnesium carbonate from the base solution and the carbonate is subsequently heated for CO2 recovery. USP 2007261947 describes a process of sequestration of carbon dioxide by mineral carbonation using magnesium or calcium silicate hydroxide minerals to form the corresponding carbonates. Though the mineral silicate hydroxides are cheaper, the corresponding carbonates have to be decomposed at a high temperature above 900 deg.C consuming high energy for the regeneration of carbon dioxide, decreasing the overall efficiency of power generation and these methods are not presently economical. USP 7132090 describes a method for conversion of carbon dioxide to mineral carbonates and store the same in the ground without regeneration. Such a method is not applicable for large scale power plants emitting large quantity of carbon dioxide requiring a huge land areas for storing the mineral carbonates. An USP 6667022 describes a method and apparatus for removing C02 using two fluidized beds for producing hydrogen from one bed and C02 from another bed by capturing C02 with calcium oxide forming CaC03. Since CaC03 decomposes at 970 deg.C the reaction heat has to be supplied from combustion bringing down the overall efficiency. The aim of present invention is to use ammonia for absorption of carbon dioxide and the regeneration of carbon dioxide at low temperature using waste heat, as a simple and economically cheap process to separate carbon dioxide present in fuel syn gas or flue gas, from other gases like nitrogen. The process of this invention has been tested in bench scale. Such a method can be quickly adopted in the existing and newer thermal power plants at an affordable cost. Such a method can also be adopted in steel plants, fertilizer plants, refineries, waste disposal plants and other industries which emit carbon dioxide. OBJECTS OF THE INVENTION It is therefore an object of the present invention to propose a process of separation of carbon dioxide from fuel gas and combustion product using ammonia absorption and subsequent regeneration by a thermal process which eliminates the disadvantages of the existing state of art. Another object of the present invention is to propose a process of separation of carbon dioxide from fuel gas and combustion product using ammonia absorption and subsequent regeneration by a thermal process which ensures the complete removal of CO2by ammonia absorption and subsequent regeneration by a thermal process. A further object of the present invention is to propose a process of separation of carbon dioxide from fuel gas and combustion product using ammonia absorption and subsequent regeneration by a thermal process which ensures removal of other acid gases also. A still further object of the present invention is to propose a process of separation of carbon dioxide from fuel gas and combustion product using ammonia absorption and subsequent regeneration by a thermal process which makes a pollution free atmosphere. An yet further object of the present invention is to propose a process of separation of carbon dioxide from fuel gas and combustion product using ammonia absorption and subsequent regeneration by a thermal process which prevents a global warming. SUMMARY OF THE INVENTION The present invention relates to a process of separation carbon dioxide present in a mixture of gases primarily nitrogen, present in fuel syn gas or flue gas combustion products arising out of fossil fuel conversion in thermal power plants, fertilizer plants, steel plants and other chemical plants, using absorption with ammonia solution wherein the carbon dioxide forms ammonium carbonate in solution; such a solution on heating evolves carbon dioxide at a temperature low enough to use the heat energy from the waste heat available in the above plants and the ammonia solution recirculated back for absorption of carbon dioxide; such an integrated process flow diagram is shown in the figure 1; or alternatively ammonium bicarbonate solid can be crystallized out of ammonium carbonate solution which can be used as a fertilizer; the ammonia absorption process can also remove other harmful acid gases such as compounds of sulphur and nitrogen along with carbon dioxide from fossil fuel syn gas or flue gas; the removal of carbon dioxide from air blown gasification process can contribute to increase in calorific value for better combustion in gas turbines. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING Fig.l - shows a process flow-diagram for separation of CO2from fue gas according to the invention DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION The integrated process system for carbon dioxide separation proposed in the present art is shown in Figure-1. The incoming fuel gas or flue gas having carbon dioxide is cooled in a heat exchanger (1) by exchanging the heat with ammonium carbonate solution from the absorber. The fuel gas or flue gas is further cooled in a gas cooling scrubber (2) with water to increase ammonia absorption efficiency. The gas is scrubbed with ammonia solution in the CO2 absorber (3) to form ammonium carbonate solution. The traces of ammonia carried over by the gas is washed away by scrubbing with water in ammonia wash scrubber (4) to form ammonia solution and the CO2free flue gas leaves the stack or CO2free fuel gas is used in the process further. In the regeneration cycle of the process, the ammonium carbonate solution from the absorber (3) is partially heated in the heat exchanger (1) with heat from inlet fuel gas or flue gas and then heated to regeneration temperature using steam from reboiler (5).The evaporated ammonia and CO2in vapor phase from the evaporator (6) is passed to ammonia recovery scrubber (7) where scrubbing with water dissolves ammonia alone and the separated carbon dioxide gas can be sent for sequestration or for other applications. The recovered ammonia solution from the reactors (7) and (4) are recirculated to the absorber (3) again, with the required makeup solution.The details of the process is further discussed under the following description. The carbon dioxide separation process described in this art is based on the bench scale tests conducted on absorption reaction between carbon dioxide and ammonia solution. The ammonia dissolved in water forms ammonium hydroxide solution which is alkaline in nature with a pH 13-14. When carbon dioxide gas is passed though ammonium hydroxide solution, carbon dioxide is absorbed in a mild exothermic reaction, to form concentrated ammonium carbonate solution. In the absorption process the alkalinity of ammonia solution decreases with the associated decrease of pH and this pH change is used to control the process effectively. The absorption of carbon dioxide decreases with the increase in temperature of ammonium carbonate solution and above 60°C, the ammonium carbonate solution decomposes to release carbon dioxide back. In the present invention, the absorption reaction of carbon dioxide by ammonia solution to form ammonium carbonate and regeneration of carbon dioxide on heating, is used in the carbon dioxide separation of CO2from other gases like nitrogen to obtain a steady stream of carbon dioxide which can be sequestrated. The ammonium hydroxide rich solution after removal of carbon dioxide is recirculated back for absorption. Alternatively a crystalline ammonium bicarbonate solid compound can be separated from ammonium carbonate solution at suitable pH and this can be used as a potential soil nutrient fertilizer providing both carbon and nitrogen to earth for plant growth. In this art, a gas mixture of CO2and other gases like nitrogen, CO2varying up to 15 % corresponding to the amount of CO2present in the gasification and combustion products of fossil fuels, is passed through the inlet at the bottom of the absorption reactor (3) and ammonia solution of suitable concentration is sprayed through nozzles from top of the reactor in counter current to the flow of gas. After absorption of CO2by ammonia solution, the remaining nitrogen gas exits from top of the reactor and CO2absorbed ammonium carbonate solution leaves bottom of the reactor through a separate exit port. The concentration of ammonia solution is varied up to 25 % by weight of ammonia in water solution, depending on the concentration of CO2and quantity of gas. Ammonia solution of 28 % concentration and above is classified as hazardous chemical and equipment and system design would require extra features with higher margin of safety and cost. Hence the ammonia solution used in this art is kept below 28% concentration. The gas and solution in counter current flow, promote good liquid to gas contact for absorption of carbon dioxide. The solution is sprayed through non clogging nozzles made of stainless steel having resistance to ammonia corrosion. The spray nozzle provides fine droplets to promote large surface area of liquid film for coming into contact with carbon dioxide gas for efficient absorption. In larger equipment, plurality of such spray nozzles is to be arranged in different tires within the reactor depending on the relative quantities of ammonia solution and gas. Spray nozzle absorption is preferred over packed bed absorption as the ammonium bicarbonate solid crystals formed can deposit and choke the packed bed, increase the pressure drop and hinder the process. The absorption process depends on the temperature of the reactant solution and gas and lowering the temperature promotes better absorption. It is found that carbon dioxide can be absorbed over a range of temperatures from 5 deg.C to 60 deg.C. Even at room temperature, the ammonia is partly in vapor phase and so at higher temperatures the quantity of ammonia in liquid phase decreases with a decrease In CO2absorption capacity. The evolved carbon dioxide gas carries some ammonia with it which is washed away in the following ammonia wash reactor (4) with a spray of water or lean ammonium carbonate solution, the reactor having a configuration similar to the absorption reactor(3) and the extent of washing is monitored by pH of the solution. The gas coming out of this reactor(4) Is Nitrogen, free of carbon dioxide and can be emitted safely . If the gas quantity is very large, several absorbers in parallel can be used. If carbon dioxide is not fully absorbed in one stage within the practically designed height of the reactor, more stages in series can be used to bring down carbon dioxide to the required levels. In the bench scale tests one absorber of one meter height brought down the CO2level from around 13 % at the inlet to 2 % at the outlet and two such absorbers brought down the CO2to 0.2 to 0.4 % at the outlet of the second absorber, constituting separation of more than 98 % carbon dioxide. The carbon dioxide absorbed in ammonia solution forms ammonium carbonate liquid and the pH decreases. Typically Ammonium hydroxide solution of pH 13 to 14 decreases to 8 to 9 when saturation happens with the formation of ammonium bicarbonate crystals. The ammonium bicarbonate crystals have been separated and confirmed by x-ray diffraction analysis. In large scale power plants it is possible to adopt the method described in this art to convert harmful carbon dioxide emission into a useful fertilizer product. Alternatively the ammonium carbonate solution formed after absorption is decomposed using waste heat in the plant to evolve ammonia and carbon dioxide in gas phase. The ammonia is washed away by spraying water in a scrubber reactor (7) and recirculated back to the absorption reactor for carbon dioxide absorption. The left out carbon dioxide gas can be used in sequestration or other applications. In this art the bench scale tests revealed that ammonium carbonate solution evolves ammonia and carbon dioxide in the range of 60°C to 100°C and nearly 100 % carbon dioxide is regenerated back in the most optimum temperature range of 70- 95°C at near atmospheric pressure. The heat energy for regeneration of carbon dioxide can be derived from the flue gas waste heat energy which is discharged at around 140°C in the stack of present power plants. In this art, it is proposed as one of the major advantages of ammonia absorption and regeneration process to use the large quantity of low temperature waste heat for regenerating carbon dioxide, as this low temperature heat cannot be recovered easily and efficiently by other methods and is usually carried by flue gas causing thermal pollution apart from CO2greenhouse pollution. In the present thermal power plants, the fuels like coal, oil, natural gas, blast furnace gas, coke oven gas or any other natural or synthetic fuel containing carbon or hydrocarbons are used for combustion with air or oxygen to form combustion products having carbon dioxide and the associated heat energy is exchanged with steam and converted to electricity in a turbo-generator . The resulting flue gas combustion products are nitrogen, water vapor and carbon dioxide with small amounts of polluting oxides of sulphur. Nitrogen, chlorine, etc originating from the fuel itself. The oxides of sulphur SOx and nitrogen NOx are acid gases. In the present thermal power plants, the acid gases are removed in separate pollution control devices like Flue gas desulphurlzation unit (FGD) for removing sulphur oxides and selective catalytic reduction unit (SCR) for removing nitrogen oxides. The left out major gases are nitrogen, water vapor which is harmless and carbon dioxide which is a harmful greenhouse gas are emitted to the atmosphere. Ammonia solution being alkaline, the present art of removal of carbon dioxide using ammonia absorption process can additionally remove other acid gases like SOx and NOx also without separate pollution control devices like FGD and SCR. It is proposed as an additional feature of the invention that adoption of ammonia absorption and regeneration process described in the present art, with thermal power plants can thus lead to removal of carbon dioxide and other acid gases together, with lower capital cost and ultra low emissions. In the advanced combined cycle power plants involving gasification of fossil fuels, the fuel syn gas formed has carbon monoxide, hydrogen, carbon dioxide, nitrogen and small amounts of corrosive acid gases like Hydrogen sulphide, HCl, HCN, originating from Sulphur, Nitrogen and Chlorine present in coal in the reducing atmosphere. The acid gases being corrosive, affect the life of turbines, fuel cells and other downstream components and their removal is necessary. Ammonia being alkaline can absorb and remove these acid gases apart from carbon dioxide in gasification process also and thereby eliminate the necessity of introducing separate impurity removal or pollution control devices for each of the acid gas components. Further air blown fluidized bed gasification process is more suitable for high ash sub bituminous coals and high moisture lignite coals. The air blown gasification of these fuels produce syn gas having carbon monoxide, hydrogen, carbon dioxide, nitrogen and acid gases with lower calorific value due to dilution effect of large quantities of nitrogen originating from air used for gasification. In this invention it was found during tests that carbon dioxide present in syn gas to the tune of 12% can be removed to less than 1% using ammonia solution absorption process. The removal of carbon dioxide can lead to improvement of calorific value facilitating better combustion in gas turbines. In producer gas also it was found during tests that removal of CO2from 6% to less than 0.4 % is possible using ammonia absorption process. Therefore the present art can be used for separation of carbon dioxide from a mixture of gases in any fuel gas like syn gas, blast furnace gas, coke oven gas etc., or flue gas combustion products of fossil fuels and send carbon dioxide for sequestration or other applications. WE CLAIM 1. A process for separation of carbon dioxide from fuel gas and flue gas combustion products using ammonia absorption comprising the steps of: a) entering the fuel or flue gas (10) through a heat exchanger (1) for releasing heat; b) discharging from the heat exchanger (1), the fuel or flue gas enters to a gas cooling scrubber (2) for further cooling with water (30) to increase ammonia absorption efficiency; c) leaving from the gas cooling scrubber (2), the fuel or flue gas (10) enters to a carbon dioxide absorber (3) wherein the CO2in the fuel or flue gas reacts with ammonia solution to form ammonium carbonate solution (20); d) washing fuel or flue gas with water after step (c) in a ammonia wash scrubber (4) for washing out traces of ammonia carried over by the fuel or flue gas with water to convert to ammonia solution (40); e) leaving carbon dioxide free gas (50) from the ammonia wash scrubber (4) through the stack; characterised in that said ammonia dissolves with water converts into alkaline ammonium hydroxide that reacts with carbon dioxide of fuel or flue gas forming ammonium bicarbonate solution leaving carbon dioxide free gas. 2. A process of regeneration of carbon dioxide by a thernnal process comprises the steps of: a) heating the ammonium carbonate solution (20) fed from the absorber (3) into a heat exchanger (1) wherein the hot inlet flue gas or fuel gas (10) exchanges heat; b) reheating the solution to a regeneration temperature using steam from reboiler (5) after discharging from the heat exchanger (1); c) passing ammonium carbonate solution through a evaporator (6) wherein ammonia is evaporated and carbon dioxide is in vapor phase; d) scrubbing vaporized ammonia and carbon dioxide gas with water in ammonia recovery scrubber (7) wherein ammonia alone dissolves with water and the separated carbon dioxide is allowed to pass for sequestration and other application. 3. The process as claimed in claim 1, wherein better absorption of carbon dioxide in ammonia solution takes place over a range of temperature from 5°C to 60°C. 4. The process as claimed in claim 1, wherein better absorption of carbon dioxide takes place where concentration of ammonia solution is 5%-28%. 5. The process as claimed in claim 1, wherein 98-99% carbon dioxide is removed. 6. The process as claimed in claim 1, wherein ammonia solution absorbs residual acidic gases like hydrogen sulphide, HCl, HCN in fuel gas or SOx and NOx in flue gas, originating from sulphur, nitrogen and chlorine in the fuel. 7. The process as claimed in claim 2, wherein ammonium carbonate solution evolves ammonia and carbon dioxide in the temperature range 70°C to 90°C at atmospheric pressure. The present invention relates to a process for separation of carbon dioxide from fuel gas and flue gas combustion products using ammonia absorption comprising the steps of entering the fuel or flue gas (10) through a heat exchanger (1) for releasing heat and discharging from the heat exchanger (1), the fuel or flue gas enters to a gas cooling scrubber (2) for further cooling with water (30) to increase ammonia absorption efficiency and leaving from the gas cooling scrubber (2), the fuel or flue gas (10) enters to a carbon dioxide absorber (3) wherein the CO2 in the fuel or flue gas reacts with ammonia solution to form ammonium carbonate solution (20) and washing fuel or flue gas with water after step (c) in a ammonia wash scrubber (4) for washing out traces of ammonia carried over by the fuel or flue gas with water to convert to ammonia solution (40) and leaving carbon dioxide free gas (50) from the ammonia wash scrubber (4) through the stack characterised in that said ammonia dissolves with water converts into alkaline ammonium hydroxide that reacts with carbon dioxide of fuel or flue gas forming ammonium bicarbonate solution leaving carbon dioxide free gas.

Full Text

FIELD OF INVENTION
The present invention relates to a process of separation of carbon dioxide from
fuel gas and combustion products using ammonia absorption and subsequent
regeneration by a thermal process to prevent the harmful emission of carbon
dioxide green house gas adaptable to power plants, steel plants, fertilizer plants,
refineries, waste disposal plants and other industries.
BACKGROUND OF THE INVENTION AND PRIOR ARTS
The greenhouse gas carbon dioxide in the atmosphere has reached an alarming
level to cause a global warming and climate damage. Burning of the fossil fuels
like coal, oil and the natural gas for transportation, an electric power generation,
the production of steel, cement, fertilizer and the chemicals emit carbon dioxide
to the atmosphere which acts like a blanket warming up the earth and referred
as a global warming. This can lead to a major environmental catastrophe on the
earth in the coming decades. Hence, there is a necessity to invent new
technology to mitigate carbon dioxide emissions into atmosphere.

The fossil fuel fired in electric power generation is one of the major sources of
carbon dioxide emissions from thermal power plants. In these power plants the
chemical pollutants like SOx, NOx, in ppm levels are removed by the pollution
control devices and the stack gases emitted to the atmosphere are nitrogen,
water vapour and harmful carbon dioxide.
The present global warming crisis calls for a separation of carbon dioxide from
nitrogen in the flue gas by a suitable method as described in the present art, so
that carbon dioxide captured can be transported and sequestrated in empty oil
and gas wells under earth or in the ocean, instead of direct emission to the
atmosphere. Presently these options are being studied, as nature is already using
the natural reservoirs as the main carbon dioxide sink.
The separation of carbon dioxide from other gases like nitrogen is an important
step in the carbon capture for sequestration. Amine absorption process is a well
known method used in fertilizer and refinery industries for separation of the
carbon dioxide from other gases in the production of hydrogen but is too costly
and a high energy process to adopt for capturing a large amount of carbon
dioxide emitted from the thermal power plants at an uneconomical decrease in
efficiency of 11-13%. Further the amines are costly and it degrades with limited
life. The technologies are being developed to use oxygen directly for combustion
or the gasification with fossil fuels instead of air, which emit only carbon dioxide

without nitrogen and can be directly captured and sequestrated. But oxygen
separation from air, using liquefaction technologies is a capital intensive and
costing about 15 to 20% of capital cost of power plant and further this method
would be applicable to new green field contents only and cannot be retrofitted in
existing power plants which use air for combustion. Development of membranes
for carbon dioxide separation is at an infant stage and is not providing an
immediate solution.
Recently the proposed methods are based on the absorption reaction of carbon
dioxide with oxides and hydroxides of sodium, potassium, lithium, magnesium ,
calcium to form carbonates and subsequently decompose at high temperature
for evolving pure carbon dioxide for sequestration. USP 2007217981 and USP
2005180910 describe an art of capturing carbon dioxide from flue gas effluent of
a power plant to form magnesium carbonate from the base solution and the
carbonate is subsequently heated for CO2 recovery. USP 2007261947 describes a
process of sequestration of carbon dioxide by mineral carbonation using
magnesium or calcium silicate hydroxide minerals to form the corresponding
carbonates. Though the mineral silicate hydroxides are cheaper, the
corresponding carbonates have to be decomposed at a high temperature above
900 deg.C consuming high energy for the regeneration of carbon dioxide,
decreasing the overall efficiency of power generation and these methods are not
presently economical. USP 7132090 describes a method for conversion of carbon

dioxide to mineral carbonates and store the same in the ground without
regeneration. Such a method is not applicable for large scale power plants
emitting large quantity of carbon dioxide requiring a huge land areas for storing
the mineral carbonates.
An USP 6667022 describes a method and apparatus for removing C02 using
two fluidized beds for producing hydrogen from one bed and C02 from another
bed by capturing C02 with calcium oxide forming CaC03. Since CaC03
decomposes at 970 deg.C the reaction heat has to be supplied from combustion
bringing down the overall efficiency.
The aim of present invention is to use ammonia for absorption of carbon dioxide
and the regeneration of carbon dioxide at low temperature using waste heat, as
a simple and economically cheap process to separate carbon dioxide present in
fuel syn gas or flue gas, from other gases like nitrogen. The process of this
invention has been tested in bench scale. Such a method can be quickly adopted
in the existing and newer thermal power plants at an affordable cost. Such a
method can also be adopted in steel plants, fertilizer plants, refineries, waste
disposal plants and other industries which emit carbon dioxide.

OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a process of
separation of carbon dioxide from fuel gas and combustion product using
ammonia absorption and subsequent regeneration by a thermal process which
eliminates the disadvantages of the existing state of art.
Another object of the present invention is to propose a process of separation of
carbon dioxide from fuel gas and combustion product using ammonia absorption
and subsequent regeneration by a thermal process which ensures the complete
removal of CO2by ammonia absorption and subsequent regeneration by a
thermal process.
A further object of the present invention is to propose a process of separation of
carbon dioxide from fuel gas and combustion product using ammonia absorption
and subsequent regeneration by a thermal process which ensures removal of
other acid gases also.
A still further object of the present invention is to propose a process of
separation of carbon dioxide from fuel gas and combustion product using
ammonia absorption and subsequent regeneration by a thermal process which
makes a pollution free atmosphere.

An yet further object of the present invention is to propose a process of
separation of carbon dioxide from fuel gas and combustion product using
ammonia absorption and subsequent regeneration by a thermal process which
prevents a global warming.
SUMMARY OF THE INVENTION
The present invention relates to a process of separation carbon dioxide present
in a mixture of gases primarily nitrogen, present in fuel syn gas or flue gas
combustion products arising out of fossil fuel conversion in thermal power plants,
fertilizer plants, steel plants and other chemical plants, using absorption with
ammonia solution wherein the carbon dioxide forms ammonium carbonate in
solution; such a solution on heating evolves carbon dioxide at a temperature low
enough to use the heat energy from the waste heat available in the above
plants and the ammonia solution recirculated back for absorption of carbon
dioxide; such an integrated process flow diagram is shown in the figure 1; or
alternatively ammonium bicarbonate solid can be crystallized out of ammonium
carbonate solution which can be used as a fertilizer; the ammonia absorption
process can also remove other harmful acid gases such as compounds of sulphur
and nitrogen along with carbon dioxide from fossil fuel syn gas or flue gas; the
removal of carbon dioxide from air blown gasification process can contribute to
increase in calorific value for better combustion in gas turbines.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Fig.l - shows a process flow-diagram for separation of CO2from fue gas
according to the invention
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
The integrated process system for carbon dioxide separation proposed in the
present art is shown in Figure-1. The incoming fuel gas or flue gas having carbon
dioxide is cooled in a heat exchanger (1) by exchanging the heat with
ammonium carbonate solution from the absorber. The fuel gas or flue gas is
further cooled in a gas cooling scrubber (2) with water to increase ammonia
absorption efficiency. The gas is scrubbed with ammonia solution in the CO2
absorber (3) to form ammonium carbonate solution. The traces of ammonia
carried over by the gas is washed away by scrubbing with water in ammonia
wash scrubber (4) to form ammonia solution and the CO2free flue gas leaves the
stack or CO2free fuel gas is used in the process further. In the regeneration
cycle of the process, the ammonium carbonate solution from the absorber (3) is
partially heated in the heat exchanger (1) with heat from inlet fuel gas or flue
gas and then heated to regeneration temperature using steam from reboiler
(5).The evaporated ammonia and CO2in vapor phase from the evaporator (6) is

passed to ammonia recovery scrubber (7) where scrubbing with water dissolves
ammonia alone and the separated carbon dioxide gas can be sent for
sequestration or for other applications. The recovered ammonia solution from
the reactors (7) and (4) are recirculated to the absorber (3) again, with the
required makeup solution.The details of the process is further discussed under
the following description.
The carbon dioxide separation process described in this art is based on the
bench scale tests conducted on absorption reaction between carbon dioxide and
ammonia solution. The ammonia dissolved in water forms ammonium hydroxide
solution which is alkaline in nature with a pH 13-14. When carbon dioxide gas is
passed though ammonium hydroxide solution, carbon dioxide is absorbed in a
mild exothermic reaction, to form concentrated ammonium carbonate solution.
In the absorption process the alkalinity of ammonia solution decreases with the
associated decrease of pH and this pH change is used to control the process
effectively. The absorption of carbon dioxide decreases with the increase in
temperature of ammonium carbonate solution and above 60°C, the ammonium
carbonate solution decomposes to release carbon dioxide back.
In the present invention, the absorption reaction of carbon dioxide by ammonia
solution to form ammonium carbonate and regeneration of carbon dioxide on
heating, is used in the carbon dioxide separation of CO2from other gases like

nitrogen to obtain a steady stream of carbon dioxide which can be sequestrated.
The ammonium hydroxide rich solution after removal of carbon dioxide is
recirculated back for absorption. Alternatively a crystalline ammonium
bicarbonate solid compound can be separated from ammonium carbonate
solution at suitable pH and this can be used as a potential soil nutrient fertilizer
providing both carbon and nitrogen to earth for plant growth.
In this art, a gas mixture of CO2and other gases like nitrogen, CO2varying
up to 15 % corresponding to the amount of CO2present in the gasification and
combustion products of fossil fuels, is passed through the inlet at the bottom of
the absorption reactor (3) and ammonia solution of suitable concentration is
sprayed through nozzles from top of the reactor in counter current to the flow
of gas. After absorption of CO2by ammonia solution, the remaining nitrogen gas
exits from top of the reactor and CO2absorbed ammonium carbonate solution
leaves bottom of the reactor through a separate exit port. The concentration of
ammonia solution is varied up to 25 % by weight of ammonia in water solution,
depending on the concentration of CO2and quantity of gas. Ammonia solution
of 28 % concentration and above is classified as hazardous chemical and
equipment and system design would require extra features with higher margin
of safety and cost. Hence the ammonia solution used in this art is kept below
28% concentration. The gas and solution in counter current flow, promote
good liquid to gas contact for absorption of carbon dioxide. The solution is

sprayed through non clogging nozzles made of stainless steel having resistance
to ammonia corrosion. The spray nozzle provides fine droplets to promote large
surface area of liquid film for coming into contact with carbon dioxide gas for
efficient absorption. In larger equipment, plurality of such spray nozzles is to be
arranged in different tires within the reactor depending on the relative quantities
of ammonia solution and gas. Spray nozzle absorption is preferred over packed
bed absorption as the ammonium bicarbonate solid crystals formed can deposit
and choke the packed bed, increase the pressure drop and hinder the process.
The absorption process depends on the temperature of the reactant solution and
gas and lowering the temperature promotes better absorption. It is found that
carbon dioxide can be absorbed over a range of temperatures from 5 deg.C to
60 deg.C. Even at room temperature, the ammonia is partly in vapor phase and
so at higher temperatures the quantity of ammonia in liquid phase decreases
with a decrease In CO2absorption capacity. The evolved carbon dioxide gas
carries some ammonia with it which is washed away in the following ammonia
wash reactor (4) with a spray of water or lean ammonium carbonate solution,
the reactor having a configuration similar to the absorption reactor(3) and the
extent of washing is monitored by pH of the solution. The gas coming out of this
reactor(4) Is Nitrogen, free of carbon dioxide and can be emitted safely .
If the gas quantity is very large, several absorbers in parallel can be used. If
carbon dioxide is not fully absorbed in one stage within the practically designed

height of the reactor, more stages in series can be used to bring down carbon
dioxide to the required levels. In the bench scale tests one absorber of one
meter height brought down the CO2level from around 13 % at the inlet to 2 %
at the outlet and two such absorbers brought down the CO2to 0.2 to 0.4 % at
the outlet of the second absorber, constituting separation of more than 98 %
carbon dioxide.
The carbon dioxide absorbed in ammonia solution forms ammonium carbonate
liquid and the pH decreases. Typically Ammonium hydroxide solution of pH 13 to
14 decreases to 8 to 9 when saturation happens with the formation of
ammonium bicarbonate crystals. The ammonium bicarbonate crystals have
been separated and confirmed by x-ray diffraction analysis. In large scale power
plants it is possible to adopt the method described in this art to convert harmful
carbon dioxide emission into a useful fertilizer product.
Alternatively the ammonium carbonate solution formed after absorption is
decomposed using waste heat in the plant to evolve ammonia and carbon
dioxide in gas phase. The ammonia is washed away by spraying water in a
scrubber reactor (7) and recirculated back to the absorption reactor for carbon
dioxide absorption. The left out carbon dioxide gas can be used in sequestration
or other applications. In this art the bench scale tests revealed that ammonium
carbonate solution evolves ammonia and carbon dioxide in the range of 60°C to

100°C and nearly 100 % carbon dioxide is regenerated back in the most
optimum temperature range of 70- 95°C at near atmospheric pressure. The heat
energy for regeneration of carbon dioxide can be derived from the flue gas waste
heat energy which is discharged at around 140°C in the stack of present power
plants. In this art, it is proposed as one of the major advantages of ammonia
absorption and regeneration process to use the large quantity of low
temperature waste heat for regenerating carbon dioxide, as this low temperature
heat cannot be recovered easily and efficiently by other methods and is usually
carried by flue gas causing thermal pollution apart from CO2greenhouse
pollution.
In the present thermal power plants, the fuels like coal, oil, natural gas, blast
furnace gas, coke oven gas or any other natural or synthetic fuel containing
carbon or hydrocarbons are used for combustion with air or oxygen to form
combustion products having carbon dioxide and the associated heat energy is
exchanged with steam and converted to electricity in a turbo-generator . The
resulting flue gas combustion products are nitrogen, water vapor and carbon
dioxide with small amounts of polluting oxides of sulphur. Nitrogen, chlorine,
etc originating from the fuel itself. The oxides of sulphur SOx and nitrogen NOx
are acid gases. In the present thermal power plants, the acid gases are
removed in separate pollution control devices like Flue gas desulphurlzation unit
(FGD) for removing sulphur oxides and selective catalytic reduction unit (SCR)

for removing nitrogen oxides. The left out major gases are nitrogen, water vapor
which is harmless and carbon dioxide which is a harmful greenhouse gas are
emitted to the atmosphere. Ammonia solution being alkaline, the present art of
removal of carbon dioxide using ammonia absorption process can additionally
remove other acid gases like SOx and NOx also without separate pollution
control devices like FGD and SCR. It is proposed as an additional feature of the
invention that adoption of ammonia absorption and regeneration process
described in the present art, with thermal power plants can thus lead to removal
of carbon dioxide and other acid gases together, with lower capital cost and ultra
low emissions.
In the advanced combined cycle power plants involving gasification of fossil
fuels, the fuel syn gas formed has carbon monoxide, hydrogen, carbon dioxide,
nitrogen and small amounts of corrosive acid gases like Hydrogen sulphide, HCl,
HCN, originating from Sulphur, Nitrogen and Chlorine present in coal in the
reducing atmosphere. The acid gases being corrosive, affect the life of turbines,
fuel cells and other downstream components and their removal is necessary.
Ammonia being alkaline can absorb and remove these acid gases apart from
carbon dioxide in gasification process also and thereby eliminate the necessity of
introducing separate impurity removal or pollution control devices for each of the
acid gas components.

Further air blown fluidized bed gasification process is more suitable for high ash
sub bituminous coals and high moisture lignite coals. The air blown gasification
of these fuels produce syn gas having carbon monoxide, hydrogen, carbon
dioxide, nitrogen and acid gases with lower calorific value due to dilution effect
of large quantities of nitrogen originating from air used for gasification. In this
invention it was found during tests that carbon dioxide present in syn gas to the
tune of 12% can be removed to less than 1% using ammonia solution absorption
process. The removal of carbon dioxide can lead to improvement of calorific
value facilitating better combustion in gas turbines. In producer gas also it was
found during tests that removal of CO2from 6% to less than 0.4 % is possible
using ammonia absorption process. Therefore the present art can be used for
separation of carbon dioxide from a mixture of gases in any fuel gas like syn gas,
blast furnace gas, coke oven gas etc., or flue gas combustion products of fossil
fuels and send carbon dioxide for sequestration or other applications.

WE CLAIM
1. A process for separation of carbon dioxide from fuel gas and flue gas
combustion products using ammonia absorption comprising the steps of:
a) entering the fuel or flue gas (10) through a heat exchanger (1) for
releasing heat;
b) discharging from the heat exchanger (1), the fuel or flue gas enters to a
gas cooling scrubber (2) for further cooling with water (30) to increase
ammonia absorption efficiency;
c) leaving from the gas cooling scrubber (2), the fuel or flue gas (10) enters
to a carbon dioxide absorber (3) wherein the CO2in the fuel or flue gas
reacts with ammonia solution to form ammonium carbonate solution (20);
d) washing fuel or flue gas with water after step (c) in a ammonia wash
scrubber (4) for washing out traces of ammonia carried over by the fuel or
flue gas with water to convert to ammonia solution (40);
e) leaving carbon dioxide free gas (50) from the ammonia wash scrubber (4)
through the stack;
characterised in that said ammonia dissolves with water converts into
alkaline ammonium hydroxide that reacts with carbon dioxide of fuel or
flue gas forming ammonium bicarbonate solution leaving carbon dioxide
free gas.

2. A process of regeneration of carbon dioxide by a thernnal process
comprises the steps of:
a) heating the ammonium carbonate solution (20) fed from the absorber (3)
into a heat exchanger (1) wherein the hot inlet flue gas or fuel gas (10)
exchanges heat;
b) reheating the solution to a regeneration temperature using steam from
reboiler (5) after discharging from the heat exchanger (1);
c) passing ammonium carbonate solution through a evaporator (6) wherein
ammonia is evaporated and carbon dioxide is in vapor phase;
d) scrubbing vaporized ammonia and carbon dioxide gas with water in
ammonia recovery scrubber (7) wherein ammonia alone dissolves with
water and the separated carbon dioxide is allowed to pass for
sequestration and other application.

3. The process as claimed in claim 1, wherein better absorption of carbon
dioxide in ammonia solution takes place over a range of temperature from
5°C to 60°C.
4. The process as claimed in claim 1, wherein better absorption of carbon
dioxide takes place where concentration of ammonia solution is 5%-28%.

5. The process as claimed in claim 1, wherein 98-99% carbon dioxide is
removed.
6. The process as claimed in claim 1, wherein ammonia solution absorbs
residual acidic gases like hydrogen sulphide, HCl, HCN in fuel gas or SOx
and NOx in flue gas, originating from sulphur, nitrogen and chlorine in the
fuel.
7. The process as claimed in claim 2, wherein ammonium carbonate solution
evolves ammonia and carbon dioxide in the temperature range 70°C to
90°C at atmospheric pressure.

The present invention relates to a process for separation of carbon dioxide from fuel gas and flue gas combustion products using ammonia absorption comprising the steps of entering the fuel or flue gas (10) through a heat exchanger (1) for releasing heat and discharging from the heat exchanger (1), the fuel or flue gas enters to a gas cooling scrubber (2) for further cooling with water (30) to increase ammonia absorption efficiency and leaving from the gas
cooling scrubber (2), the fuel or flue gas (10) enters to a carbon dioxide absorber (3) wherein the CO2 in the fuel or flue gas reacts with ammonia solution to form ammonium carbonate solution (20) and washing fuel or flue gas
with water after step (c) in a ammonia wash scrubber (4) for washing out traces of ammonia carried over by the fuel or flue gas with water to convert to ammonia solution (40) and leaving carbon dioxide free gas (50) from the ammonia wash scrubber (4) through the stack characterised in that said ammonia dissolves with water converts into alkaline ammonium hydroxide that reacts with carbon dioxide of fuel or flue gas forming ammonium bicarbonate
solution leaving carbon dioxide free gas.

Documents:

730-KOL-2009-(28-08-2013)-ABSTRACT.pdf

730-KOL-2009-(28-08-2013)-CLAIMS.pdf

730-KOL-2009-(28-08-2013)-CORRESPONDENCE.pdf

730-KOL-2009-(28-08-2013)-FORM-1.pdf

730-KOL-2009-(28-08-2013)-FORM-2.pdf

730-kol-2009-abstract.pdf

730-kol-2009-claims.pdf

730-kol-2009-correspondence.pdf

730-kol-2009-description (complete).pdf

730-kol-2009-drawings.pdf

730-kol-2009-form 1.pdf

730-kol-2009-form 18.pdf

730-kol-2009-form 2.pdf

730-kol-2009-form 3.pdf

730-kol-2009-gpa.pdf

730-kol-2009-specification.pdf

« Previous Patent

Next Patent »

Patent Number

260556

Indian Patent Application Number

730/KOL/2009

PG Journal Number

19/2014

Publication Date

09-May-2014

Grant Date

07-May-2014

Date of Filing

12-May-2009

Name of Patentee

BHARAT HEAVY ELECTRICALS LIMITED

Applicant Address

REGIONAL OPERATIONS DIVISION (ROD), PLOT NO: 9/1, DJ BLOCK 3RD FLOOR, KARUNAMOYEE, SALT LAKE CITY, KOLKATA-700091, HAVING ITS REGISTERED OFFICE AT BHEL HOUSE, SIRI FORT, NEW DELHI - 110049

Inventors:

#	Inventor's Name	Inventor's Address
1	NARAYANAN RAM MOHAN	BHEL, TRICHY 14
2	RAMAMURTHY BALACHANDRAN	BHEL, TRICHY 14

PCT International Classification Number

C10J3/02

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA