CO2 Concentration In Flue Gas Research Articles

Effects of sodium aluminate on fleeting semi-dry carbonation and properties of steel slag powders in low concentration CO2 atmosphere

Accelerated carbonation suffers from the limitation of low efficiency when CO2 supply is inadequate. This study aims at proposing a carbonation accelerator of sodium aluminate (SA) to stimulate the reaction between steel slag and CO2. Additionally, a fleeting semi-dry carbonation is proposed and mixed gas with 20 vol% CO2 was used to simulate the CO2 concentration of flue gas. According to the MGC results, with only 0.07 wt% of SA added, steel slag obtained 3.55 wt% of CO2 uptake after 10 min carbonation under 20 vol% CO2 atmosphere, which is 36.02 % higher than that of the carbonated control steel slag. As a result of elevated carbonation efficiency, f-CaO (free calcium oxide) in SA incorporated steel slag (SA-SS) is decreased more substantially than that of the control steel slag after carbonation. According to autoclaving test, cement paste cast with carbonated SA-SS showed less expansion than the one cast with carbonated control steel slag. Mortar cast with carbonated SA-SS obtained a competitive compressive strength of 40.63 MPa at 28 d. SA plays the role as a pH buffer that slows down the alkalinity decrease during the fleeting carbonation and hence enables more CO2 to dissolve in water. With enhanced carbonation efficiency, CaCO3 particles in carbonated SA-SS are big cubes which is opposed to the small, shapeless grains in carbonated control steel slag.

Simulation analysis of CO2 in-situ enrichment technology of fluidized catalytic cracking regenerator

In a typical refinery, >30% CO2 is emitted from the Fluidized Catalytic Cracking(FCC) regenerator. To realize green and low-carbon production, how to capture CO2 in flue gas with low cost and high efficiency is crucial for the development of FCC. The CO2 in-situ enrichment technology of FCC regenerator was proposed in this paper. The regenerator plays the role of CO2 enricher, and additional carbon capture equipment is no longer required. The viability of this technology was critically discussed. Computational Fluid Dynamics was used to investigate the distribution pattern of the flow hydrodynamics and the pattern of coking reaction. Two extreme cases of CO2 in-situ enrichment technology were compared with conventional regeneration. The CO2 concentration in flue gas and dry flue gas exceeds 85% and 93%, respectively. Parameters such as pressure, superficial gas velocity, and O2 concentration were examined. The optimal operating conditions for new technology were obtained.

Flue gas CO2 supply methods for microalgae utilization: A review

The potential for utilizing flue gas as a carbon source in microalgal cultivation holds great promise. Incorporating flue gas as a carbon source into microalgae culture processes can accelerate the growth rate of microalgae, consequently enhancing the overall economic viability of the integrated process. There are two key sources of flue gas to consider: flue gas from coal-fired power plants, characterized by a CO2 concentration of 12–15 w/w%, and flue gas from coal chemical processes, boasting a CO2 concentration of 90–99 w/w%. Additionally, the choice between an open or sealed microalgae culture system can also influence economic efficiency. Thus, there are four distinct microalgal cultivation routes to assess: in-situ open systems, off-situ open systems, in-situ sealed systems, and off-situ sealed systems. The incorporation of flue gas as a carbon source in microalgae cultivation demonstrates significant potential for reducing both environmental impact and costs, rendering it a highly promising and sustainable approach for economically efficient microalgae cultivation. In this review, the in-situ open route is recommended for the situation with high flue gas CO2 concentration and the target products of low-margin commodities, while the off-situ sealed route is suitable for the situation with low flue gas CO2 concentration and the target products of high value-added products.

Multivariate time series prediction for CO2 concentration and flowrate of flue gas from biomass-fired power plants

Integrating CO2 capture with biomass-fired combined heat and power (bio-CHP) plants is a promising method to achieve negative emissions. However, the use of versatile biomass, including waste, and the dynamic operation of bio-CHP plants leads to large fluctuations in the flowrate and CO2 concentration of the flue gas (FG), which further affect the operation of post-combustion CO2 capture. To optimize the dynamic operation of CO2 capture, a reliable model to predict the FG flowrate and CO2 concentration in real time is essential. In this paper, a data-driven model based on the Transformer architecture is developed. The model validation shows that the root mean squared error (RMSE), mean absolute percentage error (MAPE), and Pearson correlation coefficient (PPMCC) of Transformer are 0.3553, 0.0189, and 0.8099 respectively for the prediction of FG flowrate; and 13.137, 0.0318, and 0.8336 respectively for the prediction of CO2 concentration. The potential impact of various meteorological parameters on model accuracy is also assessed by analyzing the Shapley value. It is found that temperature and direct horizontal irradiance (DHI) are the most important factors, which should be selected as input features. In addition, using the near-infrared (NIR) spectral data as input features is also found to be an effective way to improve the prediction accuracy. It can reduce RMSE and MAPE for CO2 concentration from 0.2982 to 0.2887 and 0.0158 to 0.0157 respectively, and RMSE and MAPE for FG flowrate from 4.9854 to 4.7537 and 0.0141 to 0.0121 respectively. The Transformer model is also compared to other models, including long short-term memory network (LSTM) and artificial neural network (ANN), which results show that the Transformer model is superior in predicting complex dynamic patterns and nonlinear relationships.

Grafting amine-functionalized ligand layer on catalyst for electrochemical CO2 capture and utilization

Direct electrochemical CO2 capture and utilization from flue gas offers appealing route to closing the carbon cycle and avoiding the cost for CO2 purification. Yet, the low CO2 concentration in flue gas and competing oxygen reduction reaction (ORR) pose severe challenges for this process. Herein, we report 4-aminobutylphosphonic acid ligand layer capped Ag nanoparticles (NH2BPA-Ag) for high-efficiency conversion of simulated flue gas (SFG). The amino group in NH2BPA is available for CO2 capture and activation, while phosphonic acid groups inhibit ORR by desorbing *OOH intermediate. NH2BPA-Ag achieves 82% CO Faradaic efficiency (FECO) in H-cell for SFG reduction and enhances FECO 2.6 times over pristine Ag nanoparticles. In a membrane electrode assembly electrolyzer, NH2BPA-Ag shows 79.6% FECO and 38.1% full-cell energy efficiency at 48 mA cm-2 for SFG conversion. This study highlights the strategy of tailoring catalytic microenvironments at molecular level for realizing a highly selective performance.

Reducing the Energy Penalty of Retrofit Decarbonization in Combined Cycle Power Plants

Abstract This study is a continuation of previous work aimed at elucidating the effect of hydrogen-cofiring and exhaust gas recirculation (EGR) on combined cycle (CC) performance. The thermodynamic analysis was expanded to include postcombustion capture (PCC) by means of mono-ethanolamine (MEA). Attention was paid to net power output and thermal efficiency. Part-load operation of the CC without carbon capture was taken as a reference. Decarbonization solutions, in ascending order of complexity, included the following: (1) adding a PCC unit; (2) combining EGR with PCC, so as to exploit the increase in the flue gas CO2 concentration while reducing the exhaust gas flow delivered to the absorber; (3) including hydrogen cofiring at the largest capability dictated by the gas turbine (GT) combustion system, with the opportunity to explore a wider range of EGR rates, while still relying on PCC of the residual CO2 in flue gas, before discharge into the environment. Scenarios were first discussed under the same GT load for consistency with the published literature, thus enabling the validation of the modeling procedure. Then, CC net power production was assumed as the basis of comparison. The third solution was found to be the most promising thus minimizing both the energy penalty due to carbon capture and CO2 emission intensity (EI).

Enhanced single-loop control of a moving bed temperature swing adsorption CO2 capture process

Using a model in gPROMS, we study a Zeolite 13X-based moving bed temperature swing adsorption (MBTSA) process designed to capture CO2 from a coal-fired power plant. Two enhanced single-loop control strategies were compared to a proportional-integral configuration for variations in power plant load, control variable setpoints, flue gas CO2 concentration and external heat source temperature. Measurement delays were also investigated. Adaptive adjustment of controller parameters with system load gave smoother and narrower manipulated variable profiles and efficient CO2 recovery setpoint tracking. The controller gain is the most important parameter for adaptive tuning. A combined feedback and feedforward scheme showed improved control of the regenerated sorbent temperature, possibly due to better decoupling of the higher-level control loops. When delays were considered, the investigated strategies significantly outperformed the reference case for CO2 recovery control. The results demonstrate that the MBTSA process can be efficiently controlled for several disturbances and changes in operation.

Biomass production of Chlorella pyrenoidosa by filled sphere carrier reactor: Performance and mechanism

Microalgae-based Carbon Capture, Utilization and Storage is vital for mitigating global climate change. A filled sphere carrier reactor was developed to achieve high biomass production and carbon sequestration rate of Chlorella pyrenoidosa. By introducing air (0.04% CO2) into the reactor, the dry biomass production achieved 8.26 g/L with the optimized parameters of polyester carrier, 80% packing density, 5-fold concentrated nutrient combining 0.2 mol/L phosphate buffer. At simulated flue gas CO2 concentration of 7%, the dry biomass yield and carbon sequestration rate reached up to 9.98 g/L and 18.32 g/L/d in one day, which were as high as 249.5 and 79.65 times comparing with those of suspension culture at day 1, respectively. The mechanism was mainly attributed to the obvious intensification of electron transfer rate and remarkable increase of RuBisCO enzyme activity in the photosynthetic chloroplast matrix. This work provided a novel approach for potential microalgae-based carbon capture and storage.

Hybrid membrane-cryogenic CO2 capture technologies: A mini-review

The use of membranes to capture CO2 is a proven carbon capture technique. Gas separation membranes enhance the mole fraction of CO2 in the feed gas. The membrane separation technique is low-cost because of its compact size, excellent energy efficiency, minimum environmental effect, simplicity of scale-up, fewer moving parts, moderate energy consumption, and ease of handling. Hybrid membrane cryogenic (HMC) and low-temperature membrane cryogenic (LTMC) are hybrid capture systems that combine the advantages of membrane and cryogenic techniques. In the HMC process, the flue gas is first pre-treated by the membrane process for CO2 enrichment and the cryogenic process to capture the CO2. In the LTMC process, low-temperature membrane units increase flue gas CO2 concentration to 50%–75%, and a cryogenic process liquefies the rich CO2 stream. Permeability and selectivity are the crucial parameters of the membrane which determine the CO2 purity and recovery of capture. Most polymeric membranes have a trade-off of CO2/N2 selectivity (αCO2/N2) and CO2 permeability (PCO2). The operating temperatures also impact membrane performance. An anti-trade-off effect was observed upon cooling down by increasing PCO2 and αCO2/N2. With increased PCO2 and αCO2/N2, sub-ambient temperature-based membrane cryogenic CO2 capture techniques will lower power consumption and energy cost for CO2 capture (CC). This review analyses the costs and energy requirements of various HMC and LTMC configurations for CO2 capture. The study also examines the features of the different membranes used and the effect of operating and membrane parameters on the process performance.

Modification of a 240 kWth grate incineration system for oxyfuel combustion of wood chips

The objective of this work is the application of the oxyfuel combustion technology for grate incineration systems to increase the CO2 concentration in the flue gas for higher efficiency when processing the gas for storage or utilization. Therefore, an experimental 240 kWth moving grate combustion facility has been modified to allow the investigation of the combustion behavior under various oxyfuel conditions. Subsequent to the modification, combustion experiments with dried wood chips under air and several oxyfuel atmospheres have been performed. During oxyfuel operation, the oxygen concentration in the gas supply streams towards the furnace has been set to 30 vol.-% dry with recycled flue gas being the rest of the gas composition. The oxygen distribution between primary and secondary zone has been varied (30%/70%, 40%/60%). Additionally, one case with increased oxygen concentration in the primary zone (40 vol.-% dry) has been investigated. The results show that oxyfuel grate incineration of the given fuel in this setup is feasible. However, the combustion behavior differs significantly between air and oxyfuel conditions in the investigated cases. The CO2 concentration in the dry flue gas could be increased to around 73 vol.-% with 5.7 vol.-% excess O2. Compared to the reference air cases the emission rates of CO were also increased during oxyfuel operation. However, it seems manageable given enough excess oxygen (∼7 vol.-% dry). Although the temperature at the end of the furnace is comparable among the cases, oxyfuel combustion leads to lower maximum temperatures along the combustion chamber. Differences between 150 °C and 200 °C have been measured among corresponding air and oxyfuel cases. Also, the temperatures of the grate and inside the fuel bed are reduced during oxyfuel operation even in the case with increased O2 concentration leading to the impression that the thermal strain on the grate is lower compared to air operation with the same fuel throughput.

Experimental study and modified modeling on effect of SO2 on CO2 absorption using amine solution

Understanding the competitive mechanism in absorption process between SO2 and CO2 is essential for simultaneous absorption of SO2 and CO2. In this study, the effect of SO2 on CO2 absorption using amine solution was studied experimentally and theoretically. The CO2 absorption rates in MEA/MMEA/MDEA solutions were determined using wetted wall column. Results showed that the reduction of flue gas temperature was beneficial for CO2 absorption at the typical coal-fired flue gas CO2 concentration. On this basis, the effect of SO2 on CO2 absorption performance was studied. Firstly, the overall CO2 mass transfer coefficient decreased under exposure to SO2. Secondly, in the presence of SO2, pH variation of amine solution increased. In addition, the saturated CO2 capacity largely decreased when SO2 was continuously bubbled into the solution. Furthermore, the quantum chemical calculation showed that CO2 had little effect on the absorption performance of SO2 whereas SO2 greatly weakened the interaction between CO2 and amines. The overall CO2 mass transfer coefficient was modified considering the effect of SO2. The competitive absorption factor, χ, was introduced to modify the CO2 liquid phase diffusion coefficients. The average deviation of overall CO2 mass transfer coefficient narrowed to 1.76 % (0.5 mol/L MEA), 1.13 % (1.0 mol/L MEA), 1.88 % (1.0 mol/L MMEA) and 1.43 % (1.0 mol/L MDEA) respectively, which agreed well with the experimental results.

The balance of contradictory factors in the selection of biodiesel and jet biofuels on algae fixation of flue gas

The purpose would discover the impacts of the contradictory factors in application of algae in CO2 sequestration with sustainable biofuel benefit. Based on LCA approach, the quantitively AI assessment model and approach have been established coupling upstream CO2 source and downstream algal product at the uniform algae level of Nannochloropsis oceanica, which would benefit for algae biofuel deliverables choice. The AI model investigated the effects of interaction factors on the energy consumption, including transportation distances with purification modes coupling with CO2 concentration in flue gas, lipid content with specific productivity coupling the nutrient supply, refining process with final products. Computational framework of AI model is classified into three sub-models, including CO2 capture and purification model, algae cultivation and harvesting model, refining process and biofuel product model. According to uncertainty analysis by AI model, the positive energy gains have been conducted at a wide range of lipid contents despite of jet biofuel or biodiesel coupling solar energy utilization and by-product of bioactive nutrients effects. Biodieselwet and HTL-HRJ jet biofuel performed the priorities in energy consumption in three pathways of jet biofuel and three pathways of biodiesels. The allocation analysis confirmed that algae biofuel will be promising in the direction of cultivating appropriate algae for the target biofuel product requirement and enhancing by-product recovery. The results would enhance the interests in both LCA and CO2 sequestration with sustainable biofuel benefit.

Techno-economic assessment of post-combustion CO2 capture using aqueous piperazine at different flue gas compositions and flowrates via a general optimization methodology

An overall techno-economic assessment of a post-combustion CO2 capture process using aqueous piperazine is presented. A two-step techno-economic optimization approach is developed and implemented. First, two-objective technical optimization problems are solved at different combinations of CO2 capture efficiencies and CO2 concentrations in the flue gas, which aim at minimizing the specific equivalent work while maximizing the volume-based productivity of the capture process. Increasing minimum specific reboiler duties between 2.4 and 2.9 MJthkgCO2captured−1 are obtained for decreasing flue gas CO2 concentrations between 33 and 4 vol%, on a dry basis, with absorber packing heights below 10 m. Then, costs are computed at the technical optimal conditions as a function of the CO2 capture efficiency, flue gas flowrate and CO2 concentration. As a result, maps of minimum cost of CO2 captured, of minimum cost of CO2 avoided, and of minimum cost of CO2 generated by the CO2 point source are obtained, as well as of the associated optimal operating conditions and performance indicators of the capture process, which allow to assess the economic feasibility and performance of the capture process under different cost scenarios and assumptions when applied to different flue gas compositions and flowrates typical of industrial CO2 intensive point sources.

CO2 Electrolysis System under Industrially Relevant Conditions.

ConspectusCarbon dioxide emissions from consumption of fossil fuels have caused serious climate issues. Rapid deployment of new energies makes renewable energy driven CO2 electroreduction to chemical feedstocks and carbon-neutral fuels a feasible and cost-effective pathway for achieving net-zero emission. With the urgency of the net-zero goal, we initiated our research on CO2 electrolysis with emphasis on industrial relevance.The CO2 molecules are thermodynamically stable due to high activation energy of the two C═O bonds, and efficient electrocatalysts are required to overcome the sluggish dynamics and competitive hydrogen evolution reaction. The CO2 electrocatalysts that we have explored include molecular catalysts and nanostructured catalysts. Molecular catalysts are centered on earth abundant elements such as Fe and Co for catalyzing CO2 reduction, and using Fe catalysts, we proposed an amidation strategy for reduction of CO2 to methanol, bypassing the inactive formate pathway. For nanostructured catalysts, we developed a carbon enrichment strategy using nitrogen-rich nanomaterials for selective CO2 reduction.Direct CO2 electroreduction from the flue gas stream represents the "holy grail" in the field, because typical CO2 concentration in flue gas is only 6-15%, posing a significant challenge for CO2 electrolysis. On the other hand, direct electroreduction of CO2 in the flue gas eliminates the carbon capture process and simplifies the overall carbon capture and utilization (CCU) scheme. However, direct flue gas reduction is frustrated by the reactive oxygen (5-8%), low CO2 concentration (6-15%), and potentially toxic impurities. Surface CO2 enrichment catalysts with high O2 tolerance could be viable for achieving direct CO2 electroreduction for decarbonization of flue gas.In addition to the electrocatalysts, the incorporation of catalysts into the electrolyzer and development of a suitable process was also investigated to meet industrial demands. A membrane electrode assembly (MEA) is a zero-gap configuration with cathode and anode catalysts coated on either side of an ion exchange membrane. We adopted the MEA configuration due to the structural simplicity, low ohmic resistance, and high efficiency. The electrode factors (for example, membrane type, catalyst layer porosity, and MEA fabrication method) and the electrolyzer factors (for example, flow channels, gas diffusion layer) are critical to highly efficient operation. We separately developed an anion-exchange membrane-based system for CO production and cation-exchange membrane-based system for formate production. The optimized electrolyzer configuration can generate uniform current and voltage distribution in a large-area electrolyzer and operate using an industrial CO2 stream. The optimized process was developed with the targets of long-term continuous operation and no electrolyte consumption.

Sensitivity Analysis of Post Combustion Carbon Capture Using Monoethanolamine (MEA) as a Solvent. A Simulation Study

Carbon capturing and storage (CCS) is new technology to remove CO2 from the processes that involve elimination of CO2 as its effect on the environment and incessant increase in temperature of the Earth, makes it interesting as well as most dangerous issue that should be dealt timely to reduce the greenhouse gas emissions. In the present research, the data obtained from the experimental study of CO2 capture pilot plant at the Laboratory of Engineering Thermodynamic in TU Kaiserslautern, Germany, is used for the rate based model validation for different cases using monoethenolamine (MEA) as a solvent. Process simulation sensitivity analysis performed includes a wide range of CO2 concentrations for flue gas of different sources i.e. natural gas fired power plant, exhaust gas recycle and coal based power plant. Results obtained from sensitivity analysis point out the effects of lean loading, stripper pressure, MEA concentration and CO2 concentration in flue gas on energy requirement of reboiler and degree of regeneration using MEA as a solvent for a pilot-scale study. It was found that the specific reboiler duty is least for coal-fired power plant in comparison to the natural gas �fired and exhaust gas recycled power plant, keeping the flow rate of the flue gas constant.

Optimum design of industrial post-combustion CO2 capture processes using phase-change solvents

Phase-change solvents (PCSs) is a class of chemicals that promises significant cost reductions in post-combustion CO2 capture. However, their use in the design of efficient absorption/desorption processes is challenged by their non-ideal behavior. A generic and flexible model is proposed for the design of phase-change CO2 capture process systems, that enables the effective identification of highly performing flowsheet configurations and recycle stream redistribution policies. The validation of the model using experimental data for the PCS mixture of MAPA/DEEA (3-(Methylamino)-Propylamine/2-(Diethylamino)-Ethanol) indicates only 4% and 0.5% differences in the reboiler duty and in the absorption and desorption temperatures. The novel PCS mixture of S1N/DMCA (N-Cyclohexyl-1,3-Propanediamine/N,N-Dimethylcyclohexylamine) and the PCS MCA (N-methylcyclohexylamine) are used in the optimum design of CO2 capture process units in two industrial cases; a quicklime production plant and a gas-fired power plant. The reboiler duty of S1N/DMCA reaches 2.1 GJ/ton CO2 and the solvent exhibits up to 47% lower operating costs than the conventional MEA (Monoethanolamine), with only 1.7% higher capital costs. The loading of S1N/DMCA reaches up to 1.35 mol CO2/mol of solvent at the exit stream of the phase-separator, whereas this solvent exhibits up to 181% higher CO2 release efficiency than MEA in the desorber. S1N/DMCA is an excellent option for plants with flue gas CO2 concentration as low as 3.5 mol%.

Experimental Investigation on the Performance of [APMIm][NTf2] for Capturing CO2 from Flue Gas of the Cement Kiln Tail

Facing the global warming trend, humanity has been paying more and more attention to the Carbon Capture, Utilization and Storage. Large amounts of CO2 is emitted with burning fossil fuel as well as by some special industrial processes like the decomposition of calcium carbonate in a cement plant. The cement industry contributes about 7% of the total worldwide CO2 emissions and the CO2 concentration of flue gas of the cement kiln tail even exceeds 30%. Ionic liquid is considered to be an effective and potential material to capture CO2. In order to investigate the performance of ionic liquids for capturing CO2 from flue gas of the cement kiln tail, an experiment system was established and an ionic liquid, [APMIm][NTf2] (1-aminopropyl-3-imidazolium bis(trifluoromethylsulfonyl)imine), was tested using pure CO2 and simulated gas. The results showed that both physical and chemical absorption play roles while physical absorption dominates in the absorption process. Both the absorption capacity and rate decrease with raising the operating temperature. In the experiment with pure CO2, the absorption capacity is \(0.296\,{\rm{mo}}{{\rm{l}}_{{\rm{C}}{{\rm{O}}_2}}} \cdot {\rm{mo}}{{\rm{l}}_{{\rm{IL}}}}^{ - 1}\) at 30°C and \(0.067\,{\rm{mo}}{{\rm{l}}_{{\rm{C}}{{\rm{O}}_2}}} \cdot {\rm{mo}}{{\rm{l}}_{{\rm{IL}}}}^{ - 1}\) at 70°C. Meanwhile, the ionic liquid can be regenerated for recycling without obvious changes of the absorption capacity. When the ionic liquid is used for flue gas of the cement kiln tail rather than pure CO2, a sharp decrease of the absorption capacity and rate was observed obviously. The absorption capacity at 30°C dropped even to \(0.038\,{\rm{mo}}{{\rm{l}}_{{\rm{C}}{{\rm{O}}_2}}} \cdot {\rm{mo}}{{\rm{l}}_{{\rm{IL}}}}^{ - 1}\), 12.8% of that for pure CO2. Additionally, a natural desorption of CO2 from the ionic liquid was observed and affected the experimental results of the absorption capacity and the absorption-desorption rate to some extent.

Techno-economic assessment and comparison of absorption and membrane CO2 capture processes for iron and steel industry

An economic assessment of the post-combustion CO2 capture process for the iron and steel industry is presented herein. Absorption- and membrane-based CO2 capture processes were modeled and simulated using Unisim® and MATLAB®, and an economic assessment based on the multiparameter scaling methodology was used to evaluate the economics of the CO2 capture processes. Flue gases with CO2 concentrations in the range of 4.8–27.3 mol% were selected from a typical steel plant, and their techno-economic impact on process design and CO2 capture cost was systematically analyzed. As the flue gas CO2 concentration increased from 4.8 to 27.3 mol%, the CO2 capture cost of the absorption-based process without CO2 compression decreased from 73.5 USD2019/tCO2 to 55.3 USD2019/tCO2, and that of the membrane-based process decreased from 271.7 USD2019/tCO2 to 41.7 USD2019/tCO2. The economics of the CO2 compression process integrated case were also evaluated. This dramatic change in the capture cost for membrane systems is related to the high partial pressure of CO2 being favored for membranes, compared to absorption-based processes. The case study confirms that the membrane-based CO2 capture process becomes more cost-effective and energy-efficient than the absorption-based process as the CO2 concentration of flue gas increases.

Energy and exergy analysis of MSW-based IGCC power/polygeneration systems

Since municipal solid waste (MSW) is a negatively priced, abundant, and essentially renewable feedstock, energy recovered from MSW is a useful technology to reduce the consumption of fossil fuels, and also reduces the expenses needed to dispose of MSW. Three configurations of MSW-based IGCC power system (Design 1), MSW-based IGCC polygeneration system (Design 2), and CaO-based IGCC polygeneration system (Design 3) are proposed. Design 1 uses a combination of an identified MSW gasifier, an integrated intermittent chemical-loop air separation (IICLAS), and Rankine and Brayton cycles to generate electricity and achieve the high concentration of CO2 emissions around 93.3%~94.7%. The process for co-production of DME and MeOH in Design 2, which replaces the Rankine cycle in Design 1, could increase the net energy efficiency of Design 1 by 71.6%, but the total CO2 emissions from Design 2 are merely 7.97% of Design 1. The calcium looping gasification (CaLG) process in Design 3, which replaces the MSW gasifier in Design 2, could increase the production rate of DME of Design 2 by 12.5%. The CO2 concentration from the calcinator in Design 3 is higher than CO2 concentration in flue gas from Designs 1 and 2 by 2.0%~3.5%. Through exergy analysis, the overall exergy efficiency of Design 3 is lower than Designs 1 and 2 by 3.2%~10.1% due to the exergy destruction rate and ratio in the gasification zone of Design 3 higher than other designs. The GaLG process could increase the DME yield as well as the outlet CO2 concentration, but this approach design induces a higher exergy loss.

Flue gas carbonation of cement-based building products

Flue gas carbonation of three commonly used cement-based building products, concrete masonry blocks, cement-bond fiberboards and cement-bond bead boards, was studied to investigate the feasibility of using as-captured cement kiln flue gas to accelerate hydration and store carbon dioxide for emission reduction. Compared to pure gas carbonation, the use of flue gas does not require chemical separation which is energy-intensive. However, the reaction efficiency was low because of low CO2 concentration in flue gas. It could take up to two weeks to achieve required strength. This paper presents an innovative process in which flue gas carbonation was carried out in 5 h with 7 cycles of injection and release. Cement-based building products could achieve 5-6% CO2 uptake independent from types of products. Compared to pure gas carbonation, degree of carbonation was low in flue gas but strength gain was in the same order of magnitude. Reaction product was typical calcium silicate carbo-hydrates, a carbonate modified hydrate. The size of carbonate crystal was much smaller by flue gas carbonation. However, their contribution to strength gain was comparable to larger crystals in pure gas carbonation. The successful capture and utilization of cement kiln flue gas made it feasible to establish a network to link cement plants (CO2 sources) to concrete plants (CO2 sinks) for emission reduction through utilization.