Understanding the impact of solvent properties and process design on the cost of CO2 capture for absorption systems

Carbon capture and storage (CCS) is one of the technologies that may enable large-scale fossil fuel power generations and industries to stay economically viable while reducing their CO2 emissions. Currently, the cost of CO2 capture using chemical absorption, the most promising technology for post-combustion CO2 capture, is high and improvements in absorption technology are essential to make CCS competitive. The objective of this thesis is to evaluate the impacts of solvent parameters and process configurations on performance and costs of absorption systems to identify areas for future development. This is achieved by performing a high-level assessment of two solvent classes (aqueous and phase-change) in a conventional and an encapsulated solvent system. For aqueous solvents in a conventional absorption system, cost reductions through improvements in process design are smaller than reductions through improvements in solvent properties. Among the solvent properties, solvent stability to SOx and NOx, heat of reaction, solvent concentration, and solvent working capacity have the largest influence on CO2 capture cost. For phase-change solvents in a conventional absorption system, cost reductions can be achieved when the CO2 absorption process is operated in a packed column and low-grade heat is utilised to fully supply the dissolution heat exchanger duty. Using this configuration, the capture cost for phase-change solvents can be up to 40 % lower than that of current estimates using MEA 30 %-wt. For encapsulated solvent systems, the capture cost using MEA 30 %-wt. can be up to double the cost of using the same solvent in a conventional absorption system. Among the different configurations investigated, using a fluidized-bed configuration coupled with heat recovery between the rich and lean sorbent streams resulted in lower costs than the alternate fixed-bed configuration. In order for encapsulated solvent systems to be economically competitive, improvements in heat recovery, a thinner capsule shell, and novel absorber and regenerator columns are necessary. The results of a Monte Carlo analysis show that to achieve significant cost reductions, new solvents do not necessarily require superior values for all properties and various combinations can be used. However, in general it was found that all solvents require good stability towards SOx and NOx, low heat of reaction and water vaporization, as well as being inexpensive

Selective H2S Absorption Using the Mixture of NaOH-NaHCO3-Na2CO3 Buffer Solvent Solution

Acid gas enrichment unit (AGEU) involves selective separation of H2S from acid gas mixture, for example using absorption with an NaOH solvent solution. Sodium carbonate (Na2CO3) and sodium bicarbonate (NaHCO3) buffer addition to NaOH solution suppresses CO2 absorption, thereby increasing the selectivity of H2S absorption. This study evaluated the effect of buffer addition to increase H2S absorption selectivity using an NaOH solution. It was shown that both buffer addition and L/G ratio decrease could increase H2S selectivity by limiting CO2 absorption. Based on the simulation results, in the 0.006 to 0.030 L/G ratio range and NaOH solvent concentration greater than 2%-mass, the addition of NaHCO3 with mass ratio greater than 1.5:1 to NaOH and the addition of Na2CO3 at 1.26 times NaHCO3’s mass increased H2S absorption selectivity up to 17.3%. The combination of an L/G ratio of 0.006 and solvent with a composition of 5%-mass NaOH, 15%-mass NaHCO3, and 18.9%-mass Na2CO3 produced the highest H2S selectivity of 23.1 (379.7% H2S selectivity increase)

Selective H2S Absorption Using the Mixture of NaOH-NaHCO3-Na2CO3 Buffer Solvent Solution

Acid gas enrichment unit (AGEU) involves selective separation of H2S from acid gas mixture, for example using absorption with an NaOH solvent solution. Sodium carbonate (Na2CO3) and sodium bicarbonate (NaHCO3) buffer addition to NaOH solution suppresses CO2 absorption, thereby increasing the selectivity of H2S absorption. This study evaluated the effect of buffer addition to increase H2S absorption selectivity using an NaOH solution. It was shown that both buffer addition and L/G ratio decrease could increase H2S selectivity by limiting CO2 absorption. Based on the simulation results, in the 0.006 to 0.030 L/G ratio range and NaOH solvent concentration greater than 2%-mass, the addition of NaHCO3 with mass ratio greater than 1.5:1 to NaOH and the addition of Na2CO3 at 1.26 times NaHCO3’s mass increased H2S absorption selectivity up to 17.3%. The combination of an L/G ratio of 0.006 and solvent with a composition of 5%-mass NaOH, 15%-mass NaHCO3, and 18.9%-mass Na2CO3 produced the highest H2S selectivity of 23.1 (379.7% H2S selectivity increase)

Pengaruh Tekanan Dan Tahap Kompresi Dalam Pemurnian Biogas Menjadi Biometana Dengan Absorpsi CO2 Menggunakan Air Bertekanan

Palm oil mill effluent (POME) from condensate stew, hydrocyclone water, and sludge separator contains organic carbon with a COD more than 40 g/L and a nitrogen content of about 0.2 and 0.5 g/L as ammonia nitrogen and total nitrogen. At present, the POME is converted into biogas using anaerobic ponds. Biogas produced contains 60% methane (CH4) and 40% carbon dioxide (CO2) and can be purified into biomethane through CO2 absorption using water. This study evaluates the optimum pressure and feed compression stage in biogas upgrading into biomethane. The results show the rate of circulation of water needed to separate CO2 from biogas feed decreases with increasing absorber pressure due to increased solubility of CO2 in water. Water circulation pumps and biogas compressor works increase due to the increase in pressure difference needed. The optimum pressure of the biogas biogas purification unit is within the range of 7-10 bar. At the same absorber pressure, the 1 stage feed compression unit is cheaper than that of 2 stages. However, the overall process with 1 compression stage might not be more economical than the 2-stage if consider the higher methane loss

Process simulations of post-combustion CO2 capture for coal and natural gas-fired power plants using a polyethyleneimine/silica adsorbent

The regeneration heat for a polyethyleneimine (PEI)/silica adsorbent based carbon capture system is first assessed in order to evaluate its effect on the efficiency penalty of a coal or natural gas power plant. Process simulations are then carried out on the net plant efficiencies for a specific supercritical 550 MWe pulverized coal (PC) and a 555 MWe natural gas combined cycle (NGCC) power plant integrated with a conceptually designed capture system using fluidized beds and PEI/silica adsorbent. A benchmark system applying an advanced MEA absorption technology in a NETL report (2010) is used as a reference system. Using the conservatively estimated parameters, the net plant efficiency of the PC and NGCC power plant with the proposed capture system is found to be 1.5% and 0.6% point higher than the reference PC and NGCC systems, respectively. Sensitivity analysis has revealed that the moisture adsorption, working capacity and heat recovery strategies are the most influential parameters to the power plant efficiency. Under an optimal scenario with improvements in increasing the working capacity by 2% points and decreasing moisture adsorption by 1% point, the plant efficiencies with the proposed capture system are 2.7% (PC) and 1.9% (NGCC) points higher than the reference systems

Nonlinear dynamic analysis and control design of a solvent-based post-combustion CO2 capture process

A flexible operation of the solvent-based post-combustion CO2capture (PCC) process is of great importance to make the technology widely used in the power industry. However, in case of a wide range of operation, the presence of process nonlinearity may degrade the performance of the pre-designed linear controller. This paper gives a comprehensive analysis of the dynamic behavior and nonlinearity distribution of the PCC process. Three cases are taken into account during the investigation: 1) capture rate change; 2) flue gas flowrate change; and 3) re-boiler temperature change. The investigations show that the CO2capture process does have strong nonlinearity; however, by selecting a suitable control target and operating range, a single linear controller is possible to control the capture system within this range. Based on the analysis results, a linear model predictive controller is designed for the CO2capture process. Simulations of the designed controller on an MEA based PCC plant demonstrate the effectiveness of the proposed control approach

Solvent Development for Post-Combustion CO

Chemical absorption is widely regarded as the most promising technology for post-combustion CO2 capture from large industrial emission sources with CO2 separation from natural gas using aqueous amine solvent system having been applied since the 1930s. The use of monoethanolamine (MEA) in CO2 absorption system possesses several drawbacks, such as high regeneration energy, high solvent loss, and high corrosion tendency. Various solvents have been developed for post-combustion CO2 capture application including the development of aqueous solvents and phase-change solvents. Some of these alternate solvents have been reported to have better solvent properties, which could improve the CO2 absorption system performance. This paper reviews key parameters involved in the design improvement of several chemical absorption process systems. In addition, some novel solvent systems are also discussed, for example encapsulated solvents systems. Some of the key solvent parameters that affect the capture performance, such as heat of reaction, absorption rate, solvent working capacity, solvent concentration, and solvent stability, are discussed in this paper, particularly in relation to the economic viability of the capture process. In addition, some guidelines for the future solvent development are discussed

Solvent Development for Post-Combustion CO2 Capture: Recent Development and Opportunities

Chemical absorption is widely regarded as the most promising technology for post-combustion CO2 capture from large industrial emission sources with CO2 separation from natural gas using aqueous amine solvent system having been applied since the 1930s. The use of monoethanolamine (MEA) in CO2 absorption system possesses several drawbacks, such as high regeneration energy, high solvent loss, and high corrosion tendency. Various solvents have been developed for post-combustion CO2 capture application including the development of aqueous solvents and phase-change solvents. Some of these alternate solvents have been reported to have better solvent properties, which could improve the CO2 absorption system performance. This paper reviews key parameters involved in the design improvement of several chemical absorption process systems. In addition, some novel solvent systems are also discussed, for example encapsulated solvents systems. Some of the key solvent parameters that affect the capture performance, such as heat of reaction, absorption rate, solvent working capacity, solvent concentration, and solvent stability, are discussed in this paper, particularly in relation to the economic viability of the capture process. In addition, some guidelines for the future solvent development are discussed

Solvent Development for Post-Combustion CO 2

Chemical absorption is widely regarded as the most promising technology for post-combustion CO2 capture from large industrial emission sources with CO2 separation from natural gas using aqueous amine solvent system having been applied since the 1930s. The use of monoethanolamine (MEA) in CO2 absorption system possesses several drawbacks, such as high regeneration energy, high solvent loss, and high corrosion tendency. Various solvents have been developed for post-combustion CO2 capture application including the development of aqueous solvents and phase-change solvents. Some of these alternate solvents have been reported to have better solvent properties, which could improve the CO2 absorption system performance. This paper reviews key parameters involved in the design improvement of several chemical absorption process systems. In addition, some novel solvent systems are also discussed, for example encapsulated solvents systems. Some of the key solvent parameters that affect the capture performance, such as heat of reaction, absorption rate, solvent working capacity, solvent concentration, and solvent stability, are discussed in this paper, particularly in relation to the economic viability of the capture process. In addition, some guidelines for the future solvent development are discussed