Huairong Zhou

The pursuit of low-energy-consumption CO₂ capture technology has promoted the renewal and iteration of absorbents for chemical absorption. In order to evaluate the regeneration energy consumption of absorbents and obtain the distribution of energy consumption, a coupling method combining rigorous energy balance and simple estimation is proposed in this study. The data regarding energy balance and material balance from process simulation are transformed into the model parameters required in the simple estimation model. Regenerative energy consumption and distribution are determined by the empirical estimation formula. Two CO₂ capture processes of an MEA aqueous solution and MEA–n-propanol aqueous solution (phase-change absorbent) were used to verify the feasibility and applicability of the coupling method. The effects of n-propanol concentration, CO₂ loading in the lean solution, and temperature on energy consumption were discussed. The results show that the energy consumption of 30 wt% MEA aqueous solution is the lowest at 3.92 GJ·t⁻¹-CO₂ when CO₂ load in the lean solution is 0.2 mol CO₂·mol⁻¹-MEA, and the reaction heat Q_rec, sensible heat Q_sen, and latent heat Q_latent were 1.97 GJ·t⁻¹-CO₂, 1.09 GJ·t⁻¹-CO₂, and 0.86 GJ·t⁻¹-CO₂, respectively. The lowest energy consumption of the phase-change absorbent with CO₂ loading of 0.35 mol CO₂·mol⁻¹-MEA in the lean solution is 2.32 GJ·t⁻¹-CO₂. Q_rec, Q_sen, and Q_latent were 1.9 GJ·t⁻¹-CO₂, 0.29 GJ·t⁻¹-CO₂, and 0.14 GJ·t⁻¹-CO₂, respectively. This study provides a simple and meaningful method for accurately assessing absorber performance and process improvement, which can accelerate the development of economically viable, absorption-based CO₂ capture processes.

The calculation of vapor-liquid equilibrium is to derive the relationship between T, p, x_i and y_i when the system is in phase equilibrium. The calculation of the bubble and dew point temperature and its composition of the solution is a typical vapor-liquid balance calculation, which is also a very important calculation step in the chemical separation process. Since the vapor-liquid equilibrium equation contains complex implicit functional relationships, it is necessary to make appropriate assumptions to simplify the calculation steps. In this paper, the equation is partially simplified to calculate the bubble and dew point of a mixed solution based on the premise that the vapor phase can be considered as an ideal gas at low pressure. Even so, the calculation process also needs to use iterative operations in order to obtain more accurate results. The iterative process is very tedious and error-prone for manual calculations, and learning to use modern computational tools to solve such problems can reduce computational time and improve computational accuracy. Therefore, in this paper, we take the methanol-water mixture system as an example and use MATLAB to perform iterative trial difference calculation, and finally obtain the solution bubble, dew point temperature and composition under the corresponding conditions.

Direct CO₂ methylation with toluene, as one of the CO₂ hydrogenation technologies, exhibits great potential for the CO₂ utilization to produce the valuable para-xylene (PX), but the tandem catalysis remains a challenge for low conversion and selectivity due to the competitive side reactions. The thermodynamic analyses and the comparation with two series of catalytic results of direct CO₂ methylation are conducted to investigate the product distribution and possible mechanism in adjusting the feasibility of higher conversion and selectivity. Based on the Gibbs energy minimization method, the optimal thermodynamic conditions for direct CO₂ methylation are 360-420 °C, 3 MPa with middle CO₂/C₇H₈ ratio (1:1 to 1:4) and high H₂ feed (CO₂/H₂ = 1:3 to 1:6). As a tandem process, the toluene feed would break the thermodynamic limit and has the higher potential of >60% CO₂ conversion than that of CO₂ hydrogenation without toluene. The direct CO₂ methylation route also has advantages over the methanol route with a good prospect for >90% PX selectivity in its isomers due to the dynamic effect of selective catalysis. These thermodynamic and mechanistic analyses would promote the optimal design of bifunctional catalysts for CO₂ conversion and product selectivity from the view of reaction pathways of the complex system.

The resource endowment structure of being coal-rich and oil-poor makes China’s production of coal-based ammonia and urea, with a low production cost and a good market, a competitive advantage. However, the process suffers from high CO₂ emissions and low energy efficiency and carbon utilization efficiency due to the mismatch of hydrogen-to-carbon ratio between raw coal and chemicals. Based on the coal-to-urea (CTU) process and coal-based chemical looping technology for urea production processes (CTU_CLAS&H), a novel urea synthesis process from a coal and coke-oven gas-based co-feed chemical looping system (COG-CTU_CLAS&H) is proposed in this paper. By integrating chemical looping air separation and chemical looping hydrogen production technologies and the synergies between coal gasification, low-energy consumption CO₂ capture and CO₂ utilization are realized; the excess carbon emissions of the CTU process are avoided through coupling the pressure swing adsorption of COG, and the low carbon emissions of the proposed system are obtained. In this work, the novel process is studied from three aspects: key unit modeling, parameter optimization, and technical-economic evaluation. The results show that COG-CTU_CLAS&H achieves the highest system energy efficiency (77.10%), which is much higher than that of the CTU and CTU_CLAS&H processes by 40.03% and 32.80%, respectively, when the optimized ratio of COG to coal gasified gas is 1.2. The carbon utilization efficiency increases from 35.67% to 78.94%. The product cost of COG-CTU_CLAS&H is increased compared to CTU and CTU_CLAS&H, mainly because of the introduction of COG, but the technical performance advantages of COG-CTU_CLAS&H make its economic benefits obvious, and the internal rate of return of COG-CTU_CLAS&H is 26%, which is larger than the 14% and 16% of CTU and CTU_CLAS&H, respectively. This analysis will enable a newly promising direction of coal and COG-based co-feed integrated chemical looping technology for urea production.

The solid heat carrier moving bed with internals is an advanced oil shale retorting technology. However, the retorting gas produced by pyrolysis is generally used as fuel gas. The content of CO, H₂, and CH₄ in the retorting gas is high, and direct combustion leads to resource waste and environmental pollution. In addition, heteroatomic sulfur and nitrogen, as well as unsaturated hydrocarbons, reduce the quality of shale oil. To solve these problems, this paper proposed a chemical looping enhanced oil shale-to-liquid fuels (CLeSTL) process. The chemical looping hydrogen production technology is applied to convert retorting gas to hydrogen, and the hydrogen produced is used for shale oil hydrogenation to improve the oil quality. In this paper, the new process is modeled and simulated; then technoeconomic analysis is carried out. Technical analysis shows that shale oil yield is increased from 65% to 95.7% and the yield of light fraction is increased from 20% to 64%–83%. Economic analysis shows that the CLeSTL process with ligh fraction hydrogenation has the highest investment profit rate and large profit space. In addition, when the oil price is lower than 50 USD/bbl, the investment profit is 5%, which shows strong anti-risk ability.

A novel process path is proposed to produce glycolic acid (GA) from CO₂ as the feedstock, including CO₂ capture, power-to-hydrogen, CO₂ hydrogenation to methanol, methanol oxidation to formaldehyde, and formaldehyde carbonylation units. The bottlenecks are discussed from the perspectives of carbon utilization, CO₂ emissions, total site energy integration, and techno-economic analysis. The carbon utilization ratio of the process is 82.5%, and the CO₂ capture unit has the largest percentage of discharge in carbon utilization. Among the indirect emissions of each unit, the CO₂ hydrogenation to methanol has the largest proportion of indirect carbon emissions, followed by the formaldehyde carbonylation to glycolic acid and the CO₂ capture. After total site energy integration, the utility consumption is 1102.89 MW for cold utility, 409.67 MW for heat utility, and 45.98 MW for power. The CO₂ hydrogenation to methanol makes the largest contribution to utility consumption due to the multi-stage compression of raw hydrogen and the distillation of crude methanol. The unit production cost is 834.75 $/t-GA; CO₂ hydrogenation to methanol accounts for the largest proportion, at 70.8% of the total production cost. The total production cost of the unit depends on the price of hydrogen due to the currently high renewable energy cost. This study focuses on the capture and conversion of CO₂ emitted from coal-fired power plants, which provides a path to a feasible low-carbon and clean use of CO₂ resources.