Patent Application
20200002183
The invention falls within the technical sector of CO2 capture and storage (CCS), specifically with regard to CO2 capture in power plants and industrial processes and its subsequent use (CCU) for the production of chemicals of industrial interest. This invention integrates the processes of CO2 capture and production of sodium bicarbonate with the support of renewable energy, biomass or solar energy at medium temperature (<220° C.), resulting in a global system of almost zero emissions with a reduced energy penalty and low cost.
CO2 capture and storage has a great growth potential on a global scale due to the urgent need to reduce greenhouse gas emissions in order to mitigate global warming. The CO2 capture processes developed in recent years at research and development (R&D) level have as main objectives the reduction of their costs and their energy requirements, so as to reduce or eliminate the energy and economic penalties associated with the integration of CO2 capture systems. Currently, the only commercially available post combustion CO2 capture technology is based on the chemical absorption of CO2 by amines [1].
The process of CO2 capture by dry sodium carbonate (dry carbonation process) is based on the chemical adsorption of CO2 into sodium carbonate. By adsorption the sodium carbonate (Na2CO3) is converted to sodium bicarbonate (NaHCO3) or an intermediate salt (Na2CO3-3NaHCO3) by chemical reaction with CO2 and steam [2]. The sorbent regenerates back to its carbonate form (Na2CO3) when heated, thus releasing an almost pure CO2 flow after steam condensation. CO2 adsorption occurs at low operating temperature (T<80° C.) while sorbent regeneration takes place at higher temperatures but also at relatively low temperatures (T>100° C.). For the complete regeneration of the sorbent in a sufficiently fast way it is enough to operate with temperatures of the order of 200° C.
Different patents describe processes and improvements to optimize the carbonation of Na2CO3, which is exothermic [3,4]. The management of this heat released in the reactor is essential to effectively implement the process in a commercial system minimizing the energy penalty of the process in which it is integrated.
On the other hand, there are different production processes for sodium bicarbonate, an intermediate solvent in the dry carbonate process. SOLVAY's patent for the production of sodium bicarbonate ES2409084 (A1) [5], describes a procedure for producing sodium bicarbonate from a stream carrying sodium carbonate, part of which is generated by a crystallizer, where that stream carries sodium carbonate (A) with at least 2% by weight of sodium chloride and/or sodium sulphate. The process includes an aqueous dissolution process, generation of sodium bicarbonate crystals and their separation. Patent US2015175434 (A1) [6] describes a process for the joint production of sodium bicarbonate and other alkaline compounds in which CO2 is generated as an intermediate product that can be used to replenish the production phase of sodium bicarbonate.
Na2CO3 can be obtained from the decomposition of the natural mineral trona (Na2CO3-NaHCO3-2H2O), composed of sodium carbonate (Na2CO3) in approximately 46% and sodium bicarbonate (NaHCO3) in 35% by weight and widely available. The region of the world with the highest production of this mineral is Wyoming (United States) whose mines produced more than 17 million tons of trona. The US Geological Survey in 1997 estimated that the total trona reserve is 127 million tonnes, although only 40 million tonnes are recoverable [7]. Trona is stable up to 57° C. dry, and creates intermediate compounds such as wegschiderite (Na2CO3-3NaHCO3) and sodium monohydrate (Na2CO3— H2O) between 57° C. and 160° C. [8]. Above 160° C., trona decomposes to Na2CO3 [9].
A relevant technological challenge is the development of a method for the conversion of the Na2CO3 fraction in the trona into a commercial value-added product such as sodium bicarbonate (NaHCO3) that is profitable.
The generation of sodium bicarbonate from trona is described in different patents [10-11]. Patent US2013095011 (A1) [12] describes a process for the production of sodium carbonate and sodium bicarbonate from trona. It includes the grinding of the trona and its dissolution in a solution with sodium carbonate and an additive that generates solid particles suspended in the aqueous solution and that can be separated.
For the generation of sodium bicarbonate crystals from trona in WO2013106294 (A1) [13] a process for the production of sodium bicarbonate crystals from trona and water is described; US2011064637 (A1) [14] a process for the joint production of sodium carbonate and sodium bicarbonate crystals from sodium sesquicarbonate powder is described. The process uses a suspension of water and a gas containing CO2. In US2009238740 (A1) [15] is presented a method of preparing sodium bicarbonate from trona containing sodium fluoride as impurity by preparing a trona solution and introducing CO2 until the solution reaches a pH in the range of 7.5 to 8.75 precipitating the sodium carbonate in the trona solution. US2006182675 (A1) [16] contains a process for the production of bicarbonate obtained from trona including the stages of purification, evaporation-decarbonation, crystallization, centrifugation and drying. In US2004057892 (A1) [17] a method for producing sodium bicarbonate from trona ore is patented. The process uses the effluent water stream from the conversion of trona to sodium carbonate as a supply for the conversion of sodium carbonate to sodium bicarbonate.
The current state of the art for the production of NaHCO3 from trona can be summarized as follows. A vertical tubular reactor with a perforated bottom that separates the upper fluidization chamber from a lower stagnation chamber is fed with ground natural trona. A stream of gas is passed through the stagnation chamber in upward direction through the perforated bottom into the fluidization chamber at a speed high enough to hold a portion of the load in suspension, and to carry away decomposition gases, such as steam and CO2, that are generated during the reaction. The fluidized bed reactor acts both as a calciner for the trona and as a separator of the fine trona particles from the coarse portion of the load remaining suspended in the fluidized bed.
The thermal energy required to convert the raw material (trona) into raw sodium carbonate can be supplied by heating the fluidization gas or by placing internal heating devices or around the fluidized bed, preferably within the fluidized bed. The temperature of the fluidized bed must be in the range of 140°-220° C. [8]. The reaction that takes place in the fluidized bed reactor is:
For the production of sodium bicarbonate the intermediate Na2CO3 solution is centrifuged to separate the liquid from the crystals. The crystals are then dissolved in a carbonate solution (a solution of Na2CO3) in a rotating diluter, thus becoming a saturated solution. This solution is filtered to remove any insoluble material and then pumped through a feed tank to the top of a carbonation tower. The purified CO2 is introduced into the lower part of the carbonation tower and remains pressurized. As the saturated sodium solution evolves through the carbonator, it cools and reacts with the CO2 to form sodium bicarbonate crystals. These crystals are collected at the bottom of the reactor and transferred to another centrifuge, where the excess solution is separated by filtration. The crystals are then washed in a bicarbonate solution, forming a cake-like substance ready for drying in the filtrate. The filtrate removed from the centrifuge is recycled into the rotary dilution vessel, where it is used to saturate more intermediate Na2CO3 crystals. The washed filter cake is then dried either on a continuous belt conveyor or in a flash dryer.
In the carbonation tower, the saturated solution of Na2CO3 evolves from the top to the bottom. As it falls, the solution cools and reacts with the CO2 to form NaHCO3 crystals. After filtration, washing and drying, the crystals are sorted by particle size and packed properly. The reaction that takes place in the carbonation tower is:
The heat required in this endothermic process can be supplied by fossil fuels or renewable sources such as solar energy or biomass. Since the operating temperature is moderate (200° C.) a low cost parabolic trough (PTC) system could be used to supply the heat required for endothermic reactions. The parabolic trough concentrator (PTC) is a solar concentrator technology that converts solar radiation into thermal energy in the receiver by means of a linear focusing system. The applications of PTC parabolic trough systems can be divided into two main groups. The first and most developed is associated with concentrated solar power (CSP) plants for the generation of electricity using temperatures relatively around 300-400° C. The second group of applications is associated with the supply of thermal energy in applications that require temperatures in the range 85-250° C. The second group of applications is associated with the supply of thermal energy in applications that require temperatures in the range 85-250° C. The second group of applications is associated with the supply of thermal energy in applications that require temperatures in the range 85-250° C. These applications, which mainly use heat from industrial processes, can be cleaning, drying, evaporation, distillation, pasteurization, sterilization, among others, as well as applications with low temperature heat demand and high consumption rates (domestic hot water, heating, heated swimming pools), as well as heat-based cooling [18]. Currently the term medium temperature collectors is used to refer to collectors operating in the range of 80-250° C.
Regarding CO2 capture systems with production of sodium bicarbonate, in US20100028241A1 [20] and WO2009029292A1 [21] there is a reaction system for partial carbon capture (CO2 and CO) in coal plants and production of hydrogen and hydrogen compounds from sodium chloride NaCl, coal and water. Sodium hydroxide generated from chloride is used to produce sodium carbonate and bicarbonate. Chemical reactions between gases, hydroxide, carbon or natural gas produce solid carbonate and hydrogen, valuable substances that can be sold or used to generate electricity. WO2011075680A1 [22] describes a process by which CO2 is absorbed by an aqueous caustic mixture and then reacted with hydroxide to form carbonate/bicarbonate. This involves the use of a liquid mixture separation process and the use of an electrolysis process. In patent US20060185985A1 [23] the same process of using hydroxide and electrolysis to obtain carbonate and bicarbonate from CO2 captured by an aqueous mixture is presented. These aqueous CO2 capture solutions are described in patent US20100051859A1 [24] in which water is processed to generate an acidic solution and an alkaline solution that captures the CO2.
The invention presented in this document consists of the synergistic integration of: i) a CO2 capture system based on the use of trona as a precursor of Na2CO3 that will be used as a CO2 sorbent; ii) CO2 capture of effluent gases through a dry carbonate capture process (dry carbonation process), therefore not based on aqueous solutions such as the above-mentioned patents; iii) production process of sodium bicarbonate as a product that can be partly reused in the capture process and the rest can be in other applications.
This synergistic integration of both processes has several advantages such as: i) energy consumption allows the integration with heat sources for sorbent regeneration based on renewable energies such as biomass or medium temperature solar energy (<220° C.); ii) sorbent: the bicarbonate produced in the process allows the regeneration of the raw material used in the CO2 capture process while the excess of bicarbonate produced is a chemical product with economic value and whose sale could reduce the economic penalty of the plant; iii)) the proposed integration using as heat sources renewable energy (solar, biomass, wind) results in global systems of zero CO2 emissions with a reduced penalty of the integrated system performance and with a low energy penalty.
The present invention refers to an integrated system of production of sodium bicarbonate (Na2HCO3) from CO2 captured by a dry carbonation process from trona (Na2CO3—NaHCO3-2H2O) as raw material and converting it into sodium carbonate (Na2CO3). Part of Na2CO3 is recycled as sorbent in the CO2 capture process and the rest is used together with part of the captured CO2 for the production of sodium bicarbonate as a commercially valuable chemical.
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 CO2 capture system and the production of bicarbonate. This optimized integration reduces the energy and, above all, the economic penalty of CO2 capture. Depending on the configuration adopted, the thermal energy to be provided for CO2 capture is of the order of 915 kWhth per ton of CO2 captured, while the thermal energy consumption for the conversion of CO2 to sodium bicarbonate would have a thermal energy consumption of the order of 250 kWhth per ton of NaHCO3 produced. To these consumptions is added the energy consumption associated with the compression of CO2 for storage, which in the case of an increase in pressure from atmospheric pressure to 75 bar is of the order of 112 kWhel per tonne of CO2.
The proposed system is composed of two subsystems, one associated with the dry carbonation process for CO2 capture, based on the use of sodium carbonate as a CO2 sorbent and another related to the production of sodium bicarbonate from trona.
The conceptual scheme of the integrated system is shown in
The main units of the first subsystem (CO2 capture) are shown in
The elements that make up the second subsystem, conversion from CO2 to sodium bicarbonate, (
In the CO2 capture subsystem (
The second subsystem (
In the proposed invention CO2 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).
The optimized integration of CO2 capture and sodium bicarbonate production results in a synergistic configuration in terms of energy consumption and associated costs of CO2 capture processes and conversion to high value-added chemical (sodium bicarbonate). The integration of both presents an energy penalty of the power plant (or CO2 emitting industry to which it is applied) moderate compared to that it has with other CO2 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 CO2 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 CO2 emissions and cost of operation, or from renewable sources that allow virtually zero CO2 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 CO2 captured in the exhaust gas used for the production of a chemical product with added value (NaHCO3). 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 CO2 capture and use).
The CO2 capture and storage subsystem shown in
The synergy obtained by integrating both systems is reflected in the flow diagram in
The advantages of this technology are:
As an example of the invention, the process of producing sodium bicarbonate using CO2 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 CO2 (˜15% vol). The main data for the coal-fired power plant are shown in Table 1.
Table 2 shows the molar fluxes of the combustion gases taken to illustrate the invention.
Other parameters used in the analysis are shown in Table 3 while Table 4 shows the energy consumption associated with the different components.
CO2 storage pressure
The capture subsystem has a yield of 90%. It uses 430 tons/hr of Na2CO3 as a sorbent to remove 125 tons/hr of CO2 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 CO2 capture is 114 MWth. The energy consumption for the compression of CO2 and the transport of solids amounts to 16 MWel. 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.
In the NaHCO3 production subsystem (
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 CO2 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| P201600616 | Jul 2016 | ES | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/ES2017/000091 | 7/13/2017 | WO | 00 |
