INTEGRATED SYSTEM FOR CAPTURING CO2 AND PRODUCING SODIUM BICARBONATE (NAHCO3) FROM TRONA (NA2CO3 - 2H2O - NAHCO3)

Abstract

The present invention presents an integrated system for the production of Na.sub.2HCO.sub.3 from CO.sub.2 captured from industries or power plants by means of a dry carbonate process starting from trona as raw material (Na.sub.2CO.sub.3NaHCO.sub.3-2H.sub.2O) and converting it into sodium carbonate (Na.sub.2CO.sub.3). The optimized integration of the unit allows coupling the system with renewable energies at medium temperatures below 220 C., such as biomass or medium temperature solar thermal energy systems. The use of this invention integrated in a CO.sub.2 emitting plant results in a global system of almost zero CO.sub.2 emissions, being able to meet the heat requirements of the global integrated system, minimizing the energy consumption of the CO.sub.2 capture system and conversion to bicarbonate. This optimized integration reduces the energy and economic penalty of integrating the CO.sub.2 capture system and conversion to value-added chemical.

Claims

1. Integrated CO.sub.2 capture system and production of sodium bicarbonate (Na.sub.2HCO.sub.3) characterized by the integration of: a. CO.sub.2 capture through a dry carbonation process b. Conversion of trona (Na.sub.2CO.sub.3NaHCO.sub.3-2H.sub.2O) into sodium carbonate (Na.sub.2CO.sub.3) c. Generation of sodium bicarbonate from the Na.sub.2CO.sub.3 generated and the CO.sub.2 captured.

2. Integrated CO.sub.2 capture system and NaHCO.sub.3 generation according to claim 1 wherein it is integrated in the output current of fossil fuel thermal plants and in CO.sub.2 emitting industrial installations.

3. Integrated system of CO.sub.2 capture and generation of NaHCO.sub.3 according to claim 1 wherein the subsystem of CO.sub.2 capture uses the dry carbonation process.

4. Integrated system according to the claim 1 wherein the contribution of heat at medium temperature (140-230 C.) for the regeneration of sorbent and dissociation of the trona in the process of CO.sub.2 capture can come from renewable energy, solar thermal technology of medium temperature or biomass.

5. Integrated system of CO.sub.2 capture and generation of NaHCO.sub.3 according to claim 1 wherein it allows generating near-zero CO.sub.2 emissions systems, with an efficiency of capture above 90% in technologies based on fossil fuel, through the support of renewable energies. For coal plants the additional heat required is of the order of 10% of the total heat supplied to the global system.

6. Integrated CO.sub.2 capture system and generation of NaHCO.sub.3 according to claim 1 wherein the required CO.sub.2 for the production of NaHCO.sub.3 from Trona is supplied by the CO.sub.2 capture subsystem.

7. Integrated CO.sub.2 capture system and NaHCO.sub.3 generation according to claim 6 wherein the CO.sub.2 needed for the production of sodium bicarbonate comes from the captured CO.sub.2 and in turn the conversion to sodium bicarbonate permanently fixes the captured CO.sub.2.

8. Integrated system of CO.sub.2 capture and generation of NaHCO.sub.3 according to claim 1 wherein it internally generates the fresh sorbent (Na.sub.2CO.sub.3) that must be replaced to keep the CO.sub.2 capture process active and allows the generation of the Na.sub.2CO.sub.3 needed in the make up for the dry carbonation process from the calcination of the trona to produce bicarbonate.

9. Integrated CO.sub.2 capture system and NaHCO.sub.3 generation according to claim 1 wherein it reduces the energy requirements of the whole integrated system due to the composition and temperature of the streams in sodium carbonate regenerator in the process of CO.sub.2 capture and trona calciner (150-220 C.), and in both carbonation towers (60 C.).

10. A process for using the integrated CO.sub.2 capture system and production of sodium bicarbonate (Na.sub.2HCO.sub.3) according to claim 1 comprising integrating the following: a. capturing CO.sub.2 through a dry carbonation process; b. Converting trona (Na.sub.2CO.sub.3NaHCO.sub.3-2H.sub.2O) into sodium carbonate (Na.sub.2CO.sub.3); and c. Generating sodium bicarbonate from the Na.sub.2CO.sub.3 generated and the CO.sub.2 captured.

11. The process according to claim 10, wherein the process is integrated in the output current of fossil fuel thermal plants and in CO.sub.2 emitting industrial installations.

12. The process according to claim 10, wherein the subsystem of CO.sub.2 capture uses the dry carbonation process.

13. The process according to claim 10, wherein the contribution of heat at medium temperature (140-230 C.) for the regeneration of sorbent and dissociation of the trona in the process of CO.sub.2 capture can come from renewable energy, solar thermal technology of medium temperature or biomass.

14. The process according to claim 10, wherein the process allows generating near-zero CO.sub.2 emissions systems, with an efficiency of capture above 90% in technologies based on fossil fuel, through the support of renewable energies. For coal plants the additional heat required is of the order of 10% of the total heat supplied to the global system.

15. The process according to claim 10, wherein the required CO.sub.2 for the production of NaHCO.sub.3 from Trona is supplied by the CO.sub.2 capture subsystem.

16. The process according to claim 10, wherein the CO.sub.2 needed for the production of sodium bicarbonate comes from the captured CO.sub.2 and in turn the conversion to sodium bicarbonate permanently fixes the captured CO.sub.2.

17. The process according to claim 10, wherein the process internally generates the fresh sorbent (Na.sub.2CO.sub.3) that must be replaced to keep the CO.sub.2 capture process active and allows the generation of the Na.sub.2CO.sub.3 needed in the make up for the dry carbonation process from the calcination of the trona to produce bicarbonate.

18. The process according to claim 10, wherein the process reduces the energy requirements of the whole integrated system due to the composition and temperature of the streams in sodium carbonate regenerator in the process of CO.sub.2 capture and trona calciner (150-220 C.), and in both carbonation towers (60 C.).

Description

DESCRIPTION OF THE FIGURES

[0042] FIG. 1. Schematic representation of the invention with representation of the different solid and gas streams and interaction between the CO.sub.2 capture and NaHCO.sub.3 generation subsystems.

[0043] FIG. 2. Schematic representation of the CO.sub.2 capture and storage subsystem using the dry carbonation process. The figure illustrates a possible configuration for the CO.sub.2 capture subsystem. The different reaction processes units, heat exchange and product separation are shown.

TABLE-US-00001 Meaning Components 1. Power plant 2. Water-Flue gases heat exchanger 3. CO.sub.2 capture reactor 4. Solid-gas separator 5. Heat exchanger NaHCO.sub.3Na.sub.2CO.sub.3 6. Sorbent Regenerator 7. Solid-gas separator 8. CO.sub.2 cooler (20 C.) 9. CO.sub.2 compressor (1-10 bar) 10. CO.sub.2 cooler (20 C.) 11. CO.sub.2 compressor (10-25 bar) 12. CO.sub.2 cooler (20 C.) 13. CO.sub.2 compressor (25-75 bar) 14. CO.sub.2 cooler (20 C.) Flows F1. Flue gases at the power plant exhaust F2. Water for the CO.sub.2 capture reactor F3. Make-up of the sorbent needed in each cycle F4. Product at the exit of the carbonator F5. Flue gases at the exit of the carbonator F6. Solids at the carbonator outlet (60 C.) F7. Solids at regenerator input (140 C.) F8. CO.sub.2 recovered from the system F9. Regenerated Na.sub.2CO.sub.3 (80 C.) F10. Regenerated Na.sub.2CO.sub.3 (200 C.) F11. CO.sub.2 to the storage system (20 C., 75 bar)

[0044] FIG. 3. Schematic representation of the sodium bicarbonate production subsystem. The figure illustrates a possible configuration for the production of NaHCO.sub.3. Use of natural Trona mineral and CO.sub.2 from the capture subsystem (CO2 EN). Excess Na2CO3 is sent to the capture subsystem for sorbent make-up. The different reaction processes units, heat exchange and product separation are shown.

[0045]

TABLE-US-00002 Meaning Components 15. Heat exchanger TronaNa.sub.2CO.sub.3 16. Fluidized bed reactor 17. Solid-gas separator 18. Heat exchanger WaterWater + CO.sub.2 19. CO.sub.2 capture and production reactor NaHCO.sub.3 20. Solid-liquid separator Flows F12. Crushed trona F13. Hot trona at fluidized bed reactor inlet (125 C.) F14. Product at the outlet of the fluidized bed reactor F15. CO.sub.2 and steam (220 C.) F16. CO.sub.2 and water (95 C.) F17. Water (35 C.) F18. Superheated steam (205 C.) F19. Na.sub.2CO.sub.3 hot (220 C.) F20. Na.sub.2CO.sub.3 cooled (40 C.) F3. Make up of the sorbent needed at each cycle F21. Product inlet to the NaHCO.sub.3 production reactor F11. CO.sub.2 capture system F22. Product at the exit of the NaHCO.sub.3 production reactor. F23. Process water F24. NaHCO.sub.3 system product

DETAILED DESCRIPTION OF THE INVENTION

[0046] The present invention refers to an integrated system of production of sodium bicarbonate (Na.sub.2HCO.sub.3) from CO.sub.2 captured by a dry carbonation process from trona (Na.sub.2CO.sub.3NaHCO.sub.3-2H.sub.2O) as raw material and converting it into sodium carbonate (Na.sub.2CO.sub.3). Part of Na.sub.2CO.sub.3 is recycled as sorbent in the CO.sub.2 capture process and the rest is used together with part of the captured CO.sub.2 for the production of sodium bicarbonate as a commercially valuable chemical.

[0047] The optimized integration of the system allows the coupling of a medium-temperature heat supply system, which can be based on medium-temperature solar thermal energy or on biomass, capable of satisfying the heat needs of the integrated unit, thereby minimizing the energy consumption of the CO.sub.2 capture system and the production of bicarbonate. This optimized integration reduces the energy and, above all, the economic penalty of CO.sub.2 capture. Depending on the configuration adopted, the thermal energy to be provided for CO.sub.2 capture is of the order of 915 kWhth per ton of CO.sub.2 captured, while the thermal energy consumption for the conversion of CO.sub.2 to sodium bicarbonate would have a thermal energy consumption of the order of 250 kWhth per ton of NaHCO.sub.3 produced. To these consumptions is added the energy consumption associated with the compression of CO.sub.2 for storage, which in the case of an increase in pressure from atmospheric pressure to 75 bar is of the order of 112 kWh.sub.el per tonne of CO.sub.2.

[0048] The proposed system is composed of two subsystems, one associated with the dry carbonation process for CO.sub.2 capture, based on the use of sodium carbonate as a CO.sub.2 sorbent and another related to the production of sodium bicarbonate from trona.

[0049] The conceptual scheme of the integrated system is shown in FIG. 1 that illustrates the logical structure of streams integration between both processes of capture and generation of sodium bicarbonate with part of the captured CO.sub.2. The process also allows regeneration and control of the amount of captured CO.sub.2 and recirculated Na.sub.2CO.sub.3 to optimize the mode of operation, energy consumption and economic return of the system as a whole.

[0050] The main units of the first subsystem (CO.sub.2 capture) are shown in FIG. 2. They are a CO.sub.2 capture reactor (carbonator), a desorption reactor (regenerator), two separation units, heat exchangers for heat recovery, a water condensation unit at the end of the process and compressors for pure CO.sub.2.

[0051] The elements that make up the second subsystem, conversion from CO.sub.2 to sodium bicarbonate, (FIG. 3) use similar units: a fluid bed reactor for the conversion of trona into sodium carbonate, a carbonation tower for the production of sodium bicarbonate, two separation units and heat exchangers for heat recovery and energy optimization of the processes.

[0052] In the CO.sub.2 capture subsystem (FIG. 2), combustion gases from a fossil fuel power plant or an industrial application are sent to the carbonation tower. In the carbonator, CO.sub.2, H.sub.2O and Na.sub.2CO.sub.3 react exothermically to form NaHCO.sub.3. This reactor operates at low temperature (T=60 C.) and atmospheric pressure (p=1 atm), so the released heat can be used for low temperature thermal storage. The system integrates a separator that divides the bicarbonate solution stream from the residual flue gas stream. With this configuration 90% of CO.sub.2 input can be captured. The outgoing bicarbonate stream is sent to a regenerator. In it, the inverse (endothermic) reaction takes place, leading to the formation of Na.sub.2CO.sub.3, H.sub.2O and CO.sub.2 from NaHCO.sub.3. This heat can be supplied by a moderate temperature source of both fossil and renewable origin. In order not to introduce new CO.sub.2 emissions from fossil fuels, heat can be supplied either from biomass or from solar energy by means of a system based on parabolic troughs that are particularly suitable for medium temperature (200 C.) operation. In the regenerator the output streams are separated: Na.sub.2CO.sub.3 is sent back to the carbonation tower, while the CO.sub.2 not used in the generation of bicarbonate is sent to a stage of water condensation and subsequent compression for storage. Intermediate cooling is required to reduce the power required by the compression process. The system will need some sorbent to replace deactivated Na.sub.2CO.sub.3 with irreversible reactions associated with the SO.sub.2 and HCl reaction normally present in flue gases.

[0053] The second subsystem (FIG. 2) uses a fraction of the CO.sub.2 captured in the first subsystem and trona to produce NaHCO.sub.3. Ground trona ore is introduced into the fluidized bed reactor along with superheated steam at 200 C. The fluidized bed reactor operates in the range of 200-220 C. and atmospheric pressure. Under these operating conditions the trona becomes Na.sub.2CO.sub.3. An additional flow of CO.sub.2 and steam is generated during the conversion of the trona which is separated from the Na.sub.2CO.sub.3 flow. Part of the flow of Na.sub.2CO.sub.3 is sent to the capture subsystem by dry carbonate as a fresh replacement sorbent, while the rest is sent to a carbonation tower along with the CO.sub.2 and H.sub.2O stream, and additional pure CO.sub.2 from the capture subsystem (FIG. 1) in order to produce NaHCO.sub.3, a product with added value for the chemical industry and suitable for sale.

[0054] In the proposed invention CO.sub.2 from fossil fuel power plants (coal, natural gas or fuel oil), or from industrial processes (refineries, cement plants, metallurgical industry, etc.) is captured through the dry carbonate process using as raw material a mineral abundant in nature and relatively low cost (trona ore).

[0055] The optimized integration of CO.sub.2 capture and sodium bicarbonate production results in a synergistic configuration in terms of energy consumption and associated costs of CO.sub.2 capture processes and conversion to high value-added chemical (sodium bicarbonate). The integration of both presents an energy penalty of the power plant (or CO.sub.2 emitting industry to which it is applied) moderate compared to that it has with other CO.sub.2 capture systems. This energy penalty is associated with the extra energy consumed in the processes. The heat supplied both in the sorbent regenerator in the CO.sub.2 capture subsystem and in the fluidized bed reactor in the sodium bicarbonate production subsystem may originate from both fossil fuel, with the corresponding penalty in terms of additional CO.sub.2 emissions and cost of operation, or from renewable sources that allow virtually zero CO.sub.2 emissions. This can be achieved either by the use of biomass or by solar energy at medium temperature. In both cases and thanks to the optimization of subsystem integration made in this invention in terms of operating conditions and fraction of CO.sub.2 captured in the exhaust gas used for the production of a chemical product with added value (NaHCO.sub.3). In addition, the process itself generates the replacement sorbent for the capture process in the plant. Therefore there is a synergy of the integrated whole against the behaviour of the isolated systems. This translates into a clear energy, environmental and economic benefit from the integration of systems that cannot be expected from the analysis of their isolated behaviour and with a clear advantage over other capture systems (or CO.sub.2 capture and use).

[0056] The CO.sub.2 capture and storage subsystem shown in FIG. 2 uses a solid-solid heat exchanger (HEATEXCH) between the two reactors to reduce the total amount of heat required in the regenerator. This heat exchanger allows an increase of the temperatures in the regenerator, which improves the reaction speed, with a small additional expenditure of thermal energy. FIG. 3 shows the schematic of a possible configuration for sodium bicarbonate production. Before entering the fluidized bed reactor, the trona, under ambient conditions, passes through a solid-solid heat exchanger (HEATEXT) where it exchanges heat with the Na.sub.2CO.sub.3 stream leaving the fluidized bed reactor. Another heat exchanger (HEATEXVV) is used to heat the water entering the fluid bed from the gases coming out of it, which allows superheated steam to be supplied to the reactor.

[0057] The synergy obtained by integrating both systems is reflected in the flow diagram in FIG. 1. [0058] For the production of NaHCO.sub.3 from trona, the necessary CO.sub.2 is supplied by the CO.sub.2 capture subsystem (x*CO2 in the diagram). Therefore, part of the captured CO.sub.2 is used and the rest is stored, giving rise to a new application of CCUS (Carbon Dioxide Capture, Utilization and Storage) not identified to date. [0059] In order to capture CO.sub.2 in the dry carbonate process, a contribution of fresh Na.sub.2CO.sub.3 is required, which with the proposed integration is supplied by the Trona production subsystem (MAKEUP in FIG. 1). This makes the CO.sub.2 capture system substantially cheaper, which is novel.

[0060] The advantages of this technology are: [0061] CO.sub.2 capture technology in fossil fuel thermal plants and in industrial plants with reduced energy and economic penalties of the whole system. [0062] CO.sub.2 capture technology and conversion to chemical product with added value, sodium bicarbonate, both for thermal fossil fuel plants and for other CO.sub.2 emitting industrial plants with a significant economic return because the effect of energy penalty is supplemented by the sale of NaHCO.sub.3. It also generates the amount of fresh sorbent that needs to be replenished due to its deactivation. [0063] A fraction of the captured CO.sub.2 is integrated into the production of sodium bicarbonate, which reduces/eliminates storage requirements. This increases the sustainability of the CO.sub.2 capture process. [0064] In the case of integration of renewable energy source (biomass or solar medium temperature) a global system of almost zero CO.sub.2 emissions is obtained both for fossil fuel power plants and for other industrial plants. It includes industrial sectors such as coal, steel, cement. [0065] It allows optimizing the configuration of the integration and the fraction of recirculated Na.sub.2CO.sub.3 and stored CO.sub.2 in the form of bicarbonate according to the production requirements from the environmental point of view according to the characteristics of the integration. [0066] It can be incorporated into existing thermal and industrial plants without any relevant penalty for their performance.

Example of the Invention

[0067] As an example of the invention, the process of producing sodium bicarbonate using CO.sub.2 captured by a dry carbonation process in a coal-fired power plant (150 MWel) is shown. The combustion gases of the plant have a concentration of CO.sub.2 (15% vol). The main data for the coal-fired power plant are shown in Table 1.

TABLE-US-00003 TABLE 1 Data from the invention example. Reference thermal power station. 150 MWel coal plant Item Magnitude Units Coal consumption 61 ton/hr Air Flow 692 ton/hr Gross input power 447 MW.sub.th Net input power 397 MW.sub.th Net power produced 150 MW.sub.el Net yield 33.5 %

[0068] Table 2 shows the molar fluxes of the combustion gases taken to illustrate the invention.

TABLE-US-00004 TABLE 2 Composition of the exhaust gases in the reference coal-fired power plant Compound at the output Mole flow Mass expenditure stream (kmol/hr) (tons/hr) N2 17154.21 529.71 CO.sub.2 3085.62 135.96 H2O 1471.86 29.4 O2 781.8 27.57 CO 140.7 3.93 NO 135.36 4.47 SO 37.53 2.64

[0069] Other parameters used in the analysis are shown in Table 3 while Table 4 shows the energy consumption associated with the different components.

TABLE-US-00005 TABLE 3 Reference parameters for the invention example Regenerator temperature 200 C. Fluidized Bed Reactor Temperature 220 C. Carbonation Temperature and 60 C. Na.sub.2CO.sub.3 Activity 0.75 Minimal temperature difference in heat exchangers 15 C. Transport consumption of solids 5.5 kwh.sub.el/tn Reference solar hours 12 Isentropic performance of compressors 0.9 .sub.CO2 storage pressure 75 bar

TABLE-US-00006 TABLE 4 Energy consumption in the reference plant of the invention example with the CO.sub.2 capture system and production of NaHCO.sub.3. Generated power Power consumption CFFP 150 MW.sub.el 447 MW.sub.th Regenerating Heat 114 MW.sub.th CO.sub.2 compression power 13.3 MW.sub.el Power for transport of solids 2.47 MW.sub.el Net power 134.23 MW.sub.el Fluidized Bed Reactors 51 MW.sub.th Total heat required 612 MW.sub.th

[0070] The capture subsystem has a yield of 90%. It uses 430 tons/hr of Na.sub.2CO.sub.3 as a sorbent to remove 125 tons/hr of CO.sub.2 in a continuous cycle. The replacement sorbent flow is close to 3 ton/hr. As shown in Table 4, the heat required for sorbent regeneration after CO.sub.2 capture is 114 MW.sub.th. The energy consumption for the compression of CO.sub.2 and the transport of solids amounts to 16 MW.sub.el. The total efficiency of the integrated plant (coal combustion plant+capture) considering the required heat input the power consumed is reduced from 33.5% to 24%. Considering only the effect of the power required for compression and transport, for this example the reduction in the available electrical energy is 10% which has an effect on the overall efficiency of 3%. Considering that the temperatures in the reactors allow the integration of solar energy input, the whole system could operate with a penalty on the economic performance (available energy/purchased energy) lower than 3% achieving almost zero emissions.

[0071] In the NaHCO.sub.3 production subsystem (FIG. 3), the heat required in the fluidized bed reactor to decompose 192 ton/hr (53.3 kg/sec) of trona is 51 MWth at T=220 C. to produce 135.5 ton/hr of Na.sub.2CO.sub.3 (plus 18.5 ton/hr of CO.sub.2 and 40 ton/hr of water). As a replacement sorbent for the CO.sub.2 capture process 3 to/h of Na.sub.2CO.sub.3 are used. The rest, (132.5 ton/hr) is sent to the carbonation tower where it reacts with 37.5 ton/hr of CO.sub.2 from the CO.sub.2 capture system (in addition to CO.sub.2 effluent from the fluidized bed) to produce NaHCO.sub.3. From the reaction Na.sub.2CO.sub.3+H.sub.2O+CO.sub.2.fwdarw.2NaHCO.sub.3 it results that 207.5 ton/hr of NaHCO.sub.3 are produced with a total flow of approximately 95 m.sup.3/hr. In this way, a chemical product of high economic value (NaHCO.sub.3) is obtained from a relatively low-cost and abundant raw material such as trona and from part of the captured CO.sub.2 (from thermal power stations or industrial processes). This integrated process of capture and conversion to NaHCO.sub.3 reduces (and eliminates depending on the mode of operation chosen) the need for total storage of CO.sub.2, with the requirements of compression system and energy penalty that entails.

[0072] The overall performance of the system, and the available/required electrical power is reduced by the integration of the production of sodium bicarbonate, which in turn captures CO.sub.2 that does not need to be compressed. The economic income associated with the new product compensates for the penalty associated with this process. The total heat requirements are increased by taking into account the 51 MW thermal required in the fluidized bed reactor.