Ammonia-based CO2 Capture Process Research Articles

Integration of rich and lean vapor recompression configurations for aqueous ammonia-based CO2 capture process

Post-combustion carbon capture (PCC) using a chemical solvent is the most mature and well-proven technology to mitigate carbon dioxide (CO2) emission. However, substantial energy consumption for solvent regeneration is still a critical challenge for widespread deployment of this PCC. In this study, a novel low-energy, combined rich and lean vapor recompression (RLVR) process for the CO2 capture process using dilute aqueous ammonia (NH3) solvent was developed and optimized by integrating of rich vapor recompression (RVR) and lean vapor recompression (LVR) approaches. A parametric study showed that the minimum total equivalent work can be obtained when CO2 loading and NH3 concentration of lean solution are 0.275 mol CO2/mol NH3 and 5.0 wt%, respectively and the pressures of stripper, rich and lean solvent flash drums are maintained at 10.5 bar, 4.62 bar and 6.93 bar, respectively. Under such operation conditions, the total equivalent work required for a CO2 capture plant was remarkably reduced to 0.123 kW h/kg of CO2 captured, which is equivalent to about 10% energy penalty. This amounts to 26–54% reduction from recent literature reports. Furthermore, this combined RLVR process can completely eliminate the need of reboiler, leads to improving the flexibility of the capture plant since it can be separated from power plant steam systems.

Analysis of a rich vapor compression method for an ammonia-based CO2 capture process and freshwater production using membrane distillation technology

Post-combustion capturing of CO2 through chemical solvent absorption is a promising technique for reducing the CO2 emissions from fossil fuel power plants. However, the energy penalty associated with the absorbent regeneration continues to be a critical challenge in the chemical solvent absorption process. In this study, the operating parameters of ammonia-based CO2 capture were optimized to reduce the energy penalty. This optimized process was considered a base process to which process modifications were added, with the goal of further reducing the energy consumption. These process modifications included absorber inter-cooling and rich vapor compression (RVC) combined with cold solvent split (CSS) processes. The combined RVC and CSS process was compared with the base process and advanced NH3-based CO2 capture processes, such as the rich split process and the inter-heating process. Compared to the base process, the combined process reduced the energy requirements by 20.2%, which was higher than the 11.6% and 8.26% energy reductions obtained via the rich split and inter-heating processes, respectively. The combined process was also compared with MEA-based process modifications. The energy savings from the combined process were higher than those of the MEA-based process modifications. To estimate the trade-offs between the energy savings resulting from the combined process vs. the capital cost of the additional equipment required, the Aspen Capital Cost Estimator (ACCE) was used. The results showed that the combined process saved $0.707 million per year. Furthermore, a membrane distillation (MD) technology was integrated with the CO2 capture unit to produce freshwater. This additional process produced freshwater at a rate of 719.240 m3/day at a feed stream temperature to the MD unit of 35.66 ℃.

Thermodynamic properties in ternary system of NH4HCO3–H2O–ethanol based on antisolvent method to strengthen crystallization of carbonized ammonia

One of the main challenges of the ammonia-based CO2 capture process is how to further reduce the regeneration energy consumption. An antisolvent crystallization method was proposed to strengthen the crystallization process of carbonized ammonia, and heating the crystal products instead of rich solution can greatly reduce renewable energy consumption. The main component of the crystal product was NH4HCO3 analyzed by X-ray diffraction. Therefore, it is very important to study the thermodynamic properties of ammonium bicarbonate in the ternary system of NH3–H2O–ethanol. In this paper, the solubility curves under different temperature and solvent compositions were determined by static method and the mathematical model of solubility was established. The effects of the addition of ammonium carbamate which was produced in the initial stage of the CO2 absorption process and the addition of ammonia on the solubility in ternary system of NH4HCO3–H2O–ethanol were studied. The dissolution heat was also calculated in the end. The research of this article has a guiding significance for the antisolvent method to strengthen the crystallization of carbonized ammonia of ammonia-based carbon capture technology. It is helpful to further strengthen the crystallization process of low carbonized ammonia and improve the crystallization yield.

A novel ammonia-based CO2 capture process hybrid ammonia absorption refrigeration

This paper proposed a novel ammonia-based CO2 capture process hybrid ammonia absorption refrigeration to recovery escaped ammonia in the desorption process. The evaporated ammonia was separated with CO2 via gas-liquid phase, and throttled to produce cooling load. The phase envelope of the CO2 and NH3 mixture was investigated to guide the design of the parameters. A preliminary thermodynamic performance was presented to evaluated the performance. The results showed that the regenerator can regenerate CO2 with a ratio of 90% and this process can produce a cooling load of 113.3 MW. The parameter study indicated that it is competitive with the chilled ammonia process.

Investigation of metal ion additives on the suppression of ammonia loss and CO2 absorption kinetics of aqueous ammonia-based CO2 capture

Aqueous ammonia is an attractive absorbent for the capture of CO2 from industrial flue gases. However evaporative ammonia loss limits the application of the ammonia-based CO2 capture process. The use of metal ion additives (where M(II)=Cu(II), Zn(II) and Ni(II)), has been reported previously for the effective suppression of ammonia loss in the post combustion capture of CO2. In this study, we have investigated the absorption of CO2 into various M(II)/NH3 solutions, the resulting loss of ammonia to evaporation, and have attempted to rationalise the observed effects using an extended chemical model that includes all chemical reactions in solution. The theoretical and experimental investigations suggest that complexation of ammonia by metal ions effectively reduces the concentration of free ammonia, resulting in reduced evaporative loss but also reduced reactivity towards CO2. Simple reduction of the total NH3 concentration to the same concentration of free NH3 concentration as that obtained by the addition of M(II) showed a similar reduction in the ammonia loss as well as the CO2 absorption rate. The effects on CO2 absorption capacity at 25 and 80°C, cyclic capacity and regeneration energy are also simulated and discussed.

Modeling analysis of energy requirement in aqueous ammonia based CO2 capture process

Aqueous ammonia is a promising alternative absorbent for CO2 capture from the flue gas of coal-fired power plants. The efficiency penalty of aqueous ammonia based CO2 capture process, however, is considerably heavy, resulting from the energy requirement for CO2 regeneration and NH3 abatement cycle. The paper focused on the whole process including CO2 absorption, CO2 regeneration, CO2 compression, NH3 abatement and NH3 recovery process, and analyzed the effects of operating parameters on the energy requirement of this process with a validated and reliable model. The sensible heat, stripping heat and desorption heat were calculated to gain insights into the regeneration process. The orthogonal analysis method was then adopted to find out the achievable minimum energy requirement for CO2 capture. The minimum energy requirement was identified as 2.89MJ/kg CO2 for CO2 regeneration process and 4.07MJ/kg CO2 for the whole process.

Development of a novel process for aqueous ammonia based CO2 capture

Aqueous ammonia based CO2 capture process has been receiving increasing attention. However, the high volatility of ammonia brings with the extra energy requirement associated with the recovery of ammonia and operation disturbance resulting from the solid precipitation during CO2 regeneration process. Here, a novel process for ammonia based CO2 capture technology was proposed. With the integration of CO2 absorption, CO2 regeneration, product purification, SO2 absorption, NH3 abatement and NH3 recovery, the total energy requirement for CO2 capture was significantly reduced. It has shown that this process can achieve the ammonia abatement and recovery in an energy-saving way as well as the elimination of solid problem in CO2 stripper with no need of extra heat input. The energy requirement for CO2 regeneration and NH3 recovery can be decreased by about 32% compared to conventional ammonia based CO2 capture process, which will certainly contribute to the advancement of ammonia based CO2 capture technology.

Modelling analysis of solid precipitation in an ammonia-based CO2 capture process

Aqueous ammonia is a promising absorbent for CO2 capture. However, the high volatility of ammonia raises operating problems in aqueous ammonia-based post-combustion CO2 capture process. In pilot-plant trials at Australia's Munmorah Power Station, solids precipitated in the overhead condenser and the reflux lines of the stripper, shutting down the entire pilot plant. In this study, we adopted a rigorous rate-based model developed in our previous work to investigate how operating conditions, such as ammonia concentration in the solvent, stripper pressure and condenser temperature, affect precipitation of the solid. We then applied a rich split configuration to the solvent regeneration process, optimising both the split ratio and feeding position, with the aim of eliminating the precipitation. Based on this study, applying a rich split configuration to the conventional regeneration process will significantly reduce both solid accumulation rate and the energy requirement for CO2 regeneration.

Rate-based modelling of CO2 regeneration in ammonia based CO2 capture process

A rigorous, rate-based model was developed to simulate the regeneration of CO2 in aqueous ammonia-based CO2 capture process. The model was based on the Aspen RateSep module, which adopts the kinetic, thermodynamic and transport properties of the NH3–CO2–H2O system available in Aspen Plus V7.3. We compared the modelling results with those obtained from pilot-plant trials at the Munmorah Power Station, New South Wales, Australia. The results agreed reasonably well for all 30 cases considered, including the energy requirement for regeneration, stripping temperature, and ammonia concentration in the product. Using the validated model, we then further analysed the pilot plant results to gain insights into the CO2 regeneration process.

Process modeling of an advanced NH₃ abatement and recycling technology in the ammonia-based CO₂ capture process.

An advanced NH3 abatement and recycling process that makes great use of the waste heat in flue gas was proposed to solve the problems of ammonia slip, NH3 makeup, and flue gas cooling in the ammonia-based CO2 capture process. The rigorous rate-based model, RateFrac in Aspen Plus, was thermodynamically and kinetically validated by experimental data from open literature and CSIRO pilot trials at Munmorah Power Station, Australia, respectively. After a thorough sensitivity analysis and process improvement, the NH3 recycling efficiency reached as high as 99.87%, and the NH3 exhaust concentration was only 15.4 ppmv. Most importantly, the energy consumption of the NH3 abatement and recycling system was only 59.34 kJ/kg CO2 of electricity. The evaluation of mass balance and temperature steady shows that this NH3 recovery process was technically effective and feasible. This process therefore is a promising prospect toward industrial application.

Theoretical and experimental study of NH3 suppression by addition of Me(II) ions (Ni, Cu and Zn) in an ammonia-based CO2 capture process

Aqueous ammonia is a promising solvent for CO2 capture, but its application is limited by the high volatility of ammonia. In the present study, we theoretically and experimentally investigate the potential of three metal ions – Ni(II), Cu(II) and Zn(II) – as additives to reduce ammonia volatilisation in ammonia-based CO2 capture technology. A thermodynamic equilibrium model of the Me(II)–NH3–CO2–H2O system was established to provide theoretical guidance for the study and analysis of experimental results. The effect of factors such as ammonia concentration, absorption time, CO2 loading, regeneration on ammonia loss and/or CO2 absorption rate was investigated experimentally. The experimental results were in good agreement with the theoretical simulation. Ni(II), Cu(II) and Zn(II) were highly soluble in ammonia solution at a pH range of 9–11, due to the complexation of metal ions with free ammonia. Among the three metal species, Cu(II) had the best adaptability to the variation of pH and CO2 loading, and Ni(II) suppressed ammonia volatilisation most effectively. Our theoretical and experimental results showed that the order of ammonia suppression efficiency was Ni(II)>Cu(II)>Zn(II). The addition of Me(II) ions (Ni, Cu and Zn) significantly reduced ammonia loss in absorption and regeneration processes, and only slightly decreased the rate of CO2 absorption. The regeneration result showed that metal additives can accelerate the CO2 desorption rate. This study provided a novel approach to effective NH3 suppression in an aqueous ammonia-based CO2 capture process, which holds the potential of an industrial application.

Ammonia based CO2 capture process using hollow fiber membrane contactors

Due to its low regeneration energy demands relative to MEA, ammonia is one of the most attractive solvents for post-combustion CO2 capture processes. Nevertheless, additionally to a lower kinetic constant, a high ammonia slip takes place when the absorption process is performed in a packed column. In this study, the feasibility of an ammonia based CO2 capture process using hollow fiber membrane contactors is investigated. CO2 absorption experiments in ammonia have been performed with porous polypropylene membranes (Oxyphan) and with two different dense skin composite hollow fibers: tailor made (Teflon AF2400) and commercial (TPX). It is shown that microporous membranes do not offer stable performances, due to salt precipitation and pore blocking. Contrarily however, dense skin membranes show stable and attracting performances, whatever the operating conditions: reduced ammonia slip and intensified CO2 mass transfer are obtained compared to packed column. The potentialities of dense skin membrane contactors, particularly based on fluorinated polymers, are discussed with regard to both increased CO2 mass transfer performances and mitigation of ammonia volatilization compared to conventional gas/liquid contactors.

Modelling and Experimental Study of SO2 Removal and NH3 Recycling in an Ammonia Based CO2 Capture Process

The high NH3 loss to the gas stream (NH3 slip) is one of the major issues in the ammonia based CO2 capture technology. Meanwhile, the removal of sulphur dioxide pollutant (SO2) from flue gas is a prerequisite for many CO2 capture processes. Flue gas desulphurization (FGD) is not installed in Australian power plants and significant capital/investment costs are required to install FGD. In this study, we proposed an advanced process configuration to combine SO2 removal and NH3 recycling in one process development and solve these two problems together. A rate-based model for the system of NH3-CO2-SO2-H2O was established and employed to simulate the process flow sheet. The temperature, pH and N/S ratio profile, SO2 removal and NH3 recycling efficiency along the column were analysed. Experimental work using a bubble column was carried out to provide an initial test on the technical feasibility of the SO2 and NH3 absorption process. Both the modelling and experimental results suggest that the proposed process results in excellent removal and recovery of SO2 and NH3.

Experimental Studies of Additives for Suppression of Ammonia Vaporization in the Ammonia based CO2 Capture Process

Ammonia-based CO2 capture process is a one of the promising technologies for CO2 mitigation in the industrial and power sector. Even though the process has many advantages compared with amine based CO2 capture processes, such as low reaction heat, low corrosiveness, and low chemical cost, it has received lesser attention than the amine processes. One of the important reasons is ammonia slip caused by the intrinsic nature of its high volatility. Many studies have been conducted to reduce ammonia slip, but few studies have been considered property changes such as heat of reaction, overall mass transfer coefficient and transfer capacity, comprehensively. To reduce ammonia slip, in this study, three additives have been tested. The property changes with additives were examined regarding ammonia vaporization, heat of reaction, overall mass transfer coefficient, and transfer capacity. According to the results, additives were effect in reducing the ammonia vaporization without any significant change on CO2 adsorption properties. Under laboratory conditions the most effective additive was additive A based on higher CO2 loading capacity, and less influence on reaction heat and mass transfer coefficient. For more practical evaluation, comprehensive studies including physic-chemical property changes in field conditions should be regarded.

Process analysis for ammonia-based CO2 capture in ironmaking industry

Abstract In this work, low concentrated ammonia solution (up to ∼10 wt.%) was used to capture from blast furnace gas (BFG), compared to exhausted gas from power plant have a high CO2 concentration(up to ∼23 vol.%). Pilot plant with processing capacity of 50 Nm3-BFG/hr was built at POSCO in late 2008. Changing the operating conditions in pilot test with the absorption and regeneration temperature, circulating flow-rate of ammonia solution between absorber and stripper, the side stream ratio of columns for removing the slipped ammonia, and then collect the data such as gas flow rates, concentration of gas. Based on the collected data, we analyze the results such as CO2 removal efficiency, purity of recovered CO2 and consumed utilities (steam, cooling water, …). Through the analysis of results, we will find the main factors affecting the operation of ammonia-based CO2 capture process and design CO2 capture plant with the capacity of 1000 Nm3-BFG/hr.

CO2 capture by aqueous amines and aqueous ammonia–A Comparison

This paper presents the results of ASPEN simulations of a carbon-dioxide (CO2) removal and recovery plant that captures CO2 from a 500 MWe (net) conventional coal-fired power plant flue gas stream. At a constant CO2 recovery rate of 86.5% by weight, the performance of aqueous ammonia solution as an alternative to various aqueous amino solvents (MEA, AMP and MDEA) is compared in terms of the process scenarios, solvent loadings and overall energy consumption. The overall mass transfer co-efficient and CO2 loading data generated for aqueous ammonia solutions using a laboratory scale wetted wall gas-liquid contactor are also presented. The ASPEN simulation results in conjunction with the laboratory data show, that capturing CO2 from coal-fired power plant flue gas, using aqueous ammonia solvent, will require ammonia concentration no more than 5% by weight and absorber temperature 10 ∘C or lower, if the vapor phase ammonia losses are to be contained and the precipitation of ammonium bi-carbonate in the absorber is to be avoided. Under such an operating scenario, the aqueous ammonia based CO2 capture process has overall energy requirement comparable to the conventional 30% by weight aqueous MEA based process. The ASPEN results further show that 30% by weight AMP based process has the lowest overall energy requirement among the solvents considered in this paper.