Grid-Energy Firming Process

Abstract

A grid-energy firming process and a grid energy firming system. The process comprises alternating between a process for generating electrical energy, and a process for generating gaseous fuels in response to the energy demands of a grid energy system. The system comprises a reactor containing a carbonaceous fuel, and a heat exchanger to extract heat from the flue gas and/or gaseous fuel.

Claims

1. A grid-energy firming process, the process comprising alternating between a process for generating electrical energy, and a process for generating gaseous fuels in response to the energy demands of a grid energy system, wherein the process comprises combusting a carbonaceous fuel in the presence of a metal oxide, wherein the ratio of oxygen carbonaceous fuel in the combustion reaction is controlled such that when the ratio of oxygen; carbonaceous fuel is increased, the combustion reaction produces CO.sub.2, H.sub.2O and heat, and when the ratio of oxygen, carbonaceous fuel is decreased, the combustion reaction produces syngas and CO.sub.2.

2. A process according to claim 1, wherein the process for generating electrical energy comprises a process for heat generation, wherein the heat generated is converted to electrical energy.

3. A process according to claim 2, wherein the process for heat generation, comprises reacting a carbonaceous fuel with oxygen in the presence of a metal oxide to provide a metal carbonate, water and heat.

4. A process according to claim 3, wherein the metal oxide is selected from calcium oxide and/or magnesium oxide, and the metal carbonate is calcium carbonate and/or magnesium carbonate.

5. A process according to claim 2, wherein the oxygen is oxygen from air.

6. A process according to claim 2, wherein the water and heat are released as a flue gas.

7. A process according to claim 2, comprising the overall reaction:
C.sub.aH.sub.bO.sub.c+aCaO+x(a+b/2−c)O.sub.2+3.29x(a+b/2−c)N.sub.2.fwdarw.3.29x(a+b/2−c)N.sub.2+(1−x)(a+b/2−c)O.sub.2+bH.sub.2O+aCaCO.sub.3 where a, b and c are the molar component of the carbonaceous fuel, and x is the excess air fraction.

8. A process according to claim 1, wherein the process for generating gaseous fuels comprises gasifying a carbonaceous fuel with vitiated air in the presence of metal oxide and water to provide a metal carbonate, a gaseous fuel and heat.

9. A process according to claim 8, comprising: a) gasification of the carbonaceous fuel to produce carbon monoxide and hydrogen: b) reaction of carbon monoxide with water to produce carbon dioxide and hydrogen, and c) recarbonation of the metal oxide by carbon dioxide to produce metal carbonate.

10. A process according to claim 8, wherein the metal oxide is selected from calcium oxide and/or magnesium oxide, and the metal carbonate is calcium carbonate and/or magnesium carbonate.

11. A process according to claim 8, wherein the gaseous fuel is combusted to provide heat energy.

12. A process according to claim 8, wherein the gaseous fuel is selected from syngas, or hydrogen.

13. A process according claim 8, wherein the gaseous fuel is a low or zero carbon fuel.

14. A process according to claim 8, comprising the overall reaction:
C.sub.aH.sub.bO.sub.c+aCaO+N.sub.2+H.sub.2O.fwdarw.N.sub.2+C.sub.xH.sub.y+(a−x)CaCO.sub.3 where a, b and c are the molar component of the carbonaceous fuel, and x may vary from 0 to 8 and y may vary from 2 to 14.

15. A process according to claim 2, wherein the heal generation process and the process for generating gaseous fuels occurs in a single reactor.

16. A process according to claim 15, wherein the reactor is a bed reactor.

17. A process according to claim 3, wherein the carbonaceous fuel comprises a solid fuel.

18. A process according to claim 17, wherein the carbonaceous fuel is selected from coal, coke, lignite, biomass, one or more hydrocarbons, or a combination thereof.

19. A grid energy firming system, for a process of claim 1, the system comprising a reactor containing a carbonaceous fuel, and a heat exchanger to extract heat from the flue gas and/or gaseous fuel.

20. A use of a process or system according to claim 1, in grid energy firming.

21. A use according to claim 20, wherein heat is converted to electrical energy for release into a grid energy system.

22. A use according to claim 20, comprising the storage and release of gaseous fuel to a grid energy system.

23. A use according to claim 22, wherein the gaseous fuel is directly released to the grid energy system.

24. A use according to claim 22, wherein the gaseous fuel is combusted to provide heat which is converted into electrical energy for release to the grid energy system.

25. A use according to claim 20, wherein electrical energy is supplied to the grid when demand exceeds supply, and a gaseous fuel is produced and stored when supply exceeds demand.

Description

[0066] FIG. 1 is a schematic representation of a process and system of the invention comprising a single reactor for both the heat generation and the generation of gaseous fuel, together with subsequent combustion of the gaseous fuel to generate more heat;

[0067] FIG. 2 is a schematic representation of a process and system of the invention comprising a single reactor for each of the heat generation and the gaseous fuel processes, together with a subsequent separation step for the gaseous fuels; and

[0068] FIG. 3 is a schematic representation of a process and system of the invention comprising multiple reactors, together with a subsequent separation step for the gaseous fuels.

[0069] FIG. 1 shows one implementation of the process and system of the invention. The system comprises fluidised bed reactor 5 comprising the carbonaceous fuel (for instance wet biomass) and lime. The reactor 5 is held at a temperature of approximately 750° C. To this is added air of controlled oxygen content, either vitiated if the reactor is in gaseous fuel generation mode, or non-vitiated if heat is to be generated. The solid reaction products, primarily ash and calcium carbonate, are removed from the reactor and distributed on land to improve soil quality. The hot gaseous products pass from the reactor to a heat exchanger 10 where they are cooled. The gaseous products in this example will be hot flue gas containing, for instance, water as steam together with nitrogen and any unreacted oxygen, if operating in heat generation mode; or hot gaseous fuel, such as hydrogen, if operating in gaseous fuel generation mode. The cooled flue gas, now water and oxygen depleted air, will be released to the environment. In this example, at least some of the cooled gaseous fuel, hydrogen, is combusted in chamber 15, and the hot flue gas (water as steam) passed through heat exchanger 10. The heat in this process is converted to electricity in turbine 20.

[0070] FIG. 2 shows an alternative implementation of the process and system of the invention. The system of FIG. 2 comprises a fixed bed heat generation reactor 25 and a fixed bed gaseous fuel generation reactor 30, together with a single heat exchanger 10, passing heat into turbine 20, and a gas separator 35. In this implementation, heat generation reactor 25 comprises carbonaceous fuel (in this case lignite) and a combination of lime and magnesium oxide. When electricity is required for the grid energy system, pure oxygen is introduced to reactor 25 to combust the lignite, the carbon dioxide produced recarbonates the lime and magnesium oxide in situ to form calcium/magnesium carbonate. The solid reaction products, primarily ash and calcium/magnesium carbonate are removed from reactor 25 and distributed on land to improve soil quality. The hot flue gases, including water as steam, pass to heat exchanger 10 where they are cooled. The cooled flue gas, including liquid water, is then released to the environment and the heat is used to drive turbine 20 thereby generating electricity. When electricity demand in the grid energy system is low, the gaseous fuel generation process is operated, using gaseous fuel generation reactor 30. A carbonaceous fuel, in this example wet biomass, is added to the reactor 30, together with lime and vitiated air. The solid reaction products, namely ash and calcium carbonate are removed from reactor 30 and distributed on land. The hot gaseous fuel (in this example syngas formed of carbon monoxide and hydrogen as carbon dioxide has been sequestered during the formation of calcium carbonate) is passed to heat exchanger 10, where they are cooled. In this example, the cooled syngas is then separated in gas separator 35, to provide pure carbon monoxide and hydrogen.

[0071] FIG. 3 shows a further implementation of the process and system of the invention. The system of FIG. 3 is similar to the system of FIG. 2, and comprises a heat generation reactor 25, for instance a Combined Heat and Power (CHP) reactor, and (in this case) a fluidised bed gaseous fuel generation reactor 30, together with a single heat exchanger 10, passing heat into turbine 20, and a gas separator 35. However, in this implementation, the heat generation reactor 25 and gaseous fuel generation reactor 30 do not facilitate recarbonation. Recarbonation occurs in fluidised bed recarbonation reactor 40. As such, the hot flue gas released from heat generation reactor 25 in this example includes carbon dioxide, as does the gaseous fuel released from reactor 30. By way of specific illustration, heat generation reactor 25 comprises carbonaceous fuel, such as biogas which is burned in air. The hot flue gases comprise carbon dioxide and water and are transferred to recarbonation reactor 40, where they are passed over lime, which absorbs the carbon dioxide and forms calcium carbonate. When the gaseous fuel generation process is operating in reactor 30, the carbonaceous fuel, for instance coke, is reacted with vitiated air and water (often as moisture carried in the air). The gaseous fuel released from this reactor 30 comprises, for instance, syngas (hydrogen, carbon monoxide—and carbon dioxide). The fuel is transferred to recarbonation reactor 40, where it is passed over lime which absorbs the carbon dioxide. After recarbonation in reactor 40, all gases are passed to heat exchanger 10, and processed as described above for FIG. 2. In this example, the separate production of ash from reactors 25 and 30, and calcium carbonate from reactor 40 provides for the use of calcium carbonate as a commodity product without further purification if desired, whilst the ash may be spread on the land as before.

[0072] It would be appreciated that the process and system of the invention are capable of being implemented in a variety of ways, only a few of which have been illustrated and described above.