Design and control of a comprehensive Ethylenediamine (EDA) process with external/internal heat integration

Ethylenediamine (EDA), also known as Ethane-1,2-Diamine, is a valuable raw material, and the synthesis will produce several higher polyamines. This study proposes a systematic synthesis method for separating six products from the EDA plant as the fresh feed. For the separation of six components, there are forty-two possible sequences. There will be only seven promising sequences left with the constraint of azeotrope and heuristics in distillation. To minimize the total annual cost (TAC), the pressure-swing configuration and the purity of flow rate that how close to the azeotrope can be optimized. Furthermore, unlike ordinary optimization, this study provides a method that considers the heat-integrated pressure-swing distillation (PSD) system during the iterative procedure. It is proved that this method can indeed find the genuinely optimal sequence distinct from the traditional iterative result based on the objective function, the lowest TAC. Through the other energy-saving strategies, the optimal result will save TAC of 15.15% by the external and internal heat integration, known as dividing wall columns (DWC). Afterward, basic and improved control structures are explored based on the optimal results in steady-state design. With the proposed control strategies, the purities of all components can be kept within acceptable ranges when faced with the inevitable throughput and composition changes.

Intensification, optimization and economic evaluations of the CO2-capturing oxy-combustion CO2 power system integrated with the utilization of liquefied natural gas cold energy

This work focuses on the investigation of CO2-capturing oxy-combustion CO2 power system integrated with the utilization of liquefied natural gas (LNG) cold energy. Working fluid CO2 is compressed and combusted with high purity oxygen and natural gas and is then expanded by the gas turbine to atmospheric pressure for driving the electricity generator. After recuperating the residual heat in the exhaust stream, the concentration of water is reduced to the standard of less than 1 ppm, to avoid the corrosion caused by the formation of ice in the following cryogenic process. Next, CO2 is compressed to its condensation pressure and condensed by using LNG cold energy. Liquid CO2 is then pumped to high pressure for recirculation where excess CO2 is captured. Besides, reheating procedure is applied to two-stage turbine expansion to increase energy efficiency, and an additional natural gas turbine is installed to generate more electricity. On the basis of 100 kg/s for both recirculating CO2 and LNG, this LNG enhanced CO2 power system shows its superiority in the net power output of 134.61 MW, the annual profit of 52.58 MUSD, the energy efficiency of 66.94%, CO2 recovery of 98.60% and the CO2 captured purity of 99.94 mol%. Furthermore, when turbine outlet pressure is adjusted to CO2 condensation pressure, higher energy efficiency can be achieved at 69.01%, but the net power output will decrease to 53.54 MW.

Cost evaluation for a two-staged reverse osmosis and pressure retarded osmosis desalination process

This research provides an analysis of energy efficiency and cost evaluation for three types of two-staged reverse osmosis (RO) and hollow fibre pressure retarded osmosis (PRO) hybrid process; one without direct feed flow (Hybrid A), one with direct feed flow (Hybrid B) and one with direct feed flow and a turbine (Hybrid C). Firstly, models are built from first principles assuming multi-staged RO-PX (pressure exchanger) has equal stage recovery considering the effect of booster pumps and pressure drop in the RO system. Then, all simulations are implemented by MATLAB 2018b, and energy efficiencies are assessed based on the normalised specific energy consumption, NSEC. All hybrid processes are found to have higher total water prices (TWP) when the electricity price is 0.10 US$/kWh; however, they show certain advantages under different electricity prices when wastewater pretreatment and delivery of wastewater are neglected. Hybrid C is especially attractive even in countries where water prices are low, and electricity prices are high due to its insensitiveness to electricity prices. The requirement of wastewater pretreatment and wastewater pump and the further development of PRO membranes are the keys to practical operations.

Hollow fiber-based rapid temperature swing adsorption process for carbon capture from coal-fired power plants

Post-combustion carbon capture is one of the feasible methods to reduce emission of carbon dioxide (CO2) from coal-fired power plants. The biggest challenge in this technology is reduction of energy consumption. This work proposes a hollow fiber based rapid temperature swing adsorption (RTSA) method for capturing CO2 from typical coal-fired power plants. The proposed RTSA approach can shorten the operating time and using low-grade energy for regeneration of adsorption elements. In this study, the tank-in-series model is used to simulate the RTSA process including adsorption and desorption periods. A dual-column operating procedure is then used to treat the flue gas continuously from the coal-fired power plants. Main operating variables including inlet gas volume flow rate (0.1–0.2 m3/s), abandon time (0–10 s), desorption temperature (80–120 °C) on key performance factors such as discharge gas purity, capture ratio of CO2, and energy consumption per unit CO2, etc. are investigated for reducing the energy consumption. This study found that the inlet gas volume flow rate will significantly affect the capture ratio, where smaller gas volume flow rate would be beneficial to increase capture ratio. The abandon time obviously affects the purity of the captured CO2, where the longer abandon time leads to higher purity. Desorption temperature affects both the capture ratio and purity of captured CO2. The higher the desorption temperature, the greater the purity and capture ratio. For one typical basic unit with dual-column hollow fiber-based RTSA, the study found that when the inlet gas volume flow rate is 0.12 m3/s, the desorption waiting time is 7 s, and the desorption temperature is 120 °C, both the CO2 purity and capture ratio can exceed 90%. With considering the possibility of using steam in a low-pressure turbine as a source of heat required for Dual column vacuum RTSA (DC-vRTSA), the impact on the efficiency and stream data of typical coal-fired power plants are calculated. DC-vRTSA at 120 °C, 100 °C and 80 °C will reduce the efficiency of coal-fired power plants by 8.2%, 6%, and 3.4%, respectively.

Hybrid membrane process for post-combustion CO2 capture from coal-fired power plant

Post-combustion CO2 capture is a promising way to reduce CO2 emissions at the coal-fired power plants. Even though several studies have been conducted regarding a wide variety of CO2 capture techniques, gas separation membrane process has shown potential as an energy-efficient, low-cost CO2 capture option. However, most of the previous researches focused only on CO2-selective membrane, and there's limited literature about the application of N2-selective membrane. In this study, both CO2-selective and N2-selective membranes are considered and relevant issues regarding the CO2-selective membrane, such as pressure ratio, attainability, and multistage configuration, are studied and extended to the N2-selective membrane. Polaris® membrane is served as a typical CO2-selective membrane; on the other hand, membrane properties of N2-selective membrane with selectivity up to 200 are considered. Hybrid membrane process applying both CO2- and N2-selective membranes for capturing at least 90% CO2 from a typical 550 MW subcritical coal-fired power plant is designed, simulated and analyzed using Aspen Plus® simulation software. The optimization and economic analysis are also applied with the cost factor defined in this work, which is a comprehensive index to evaluate the applicability of the membrane, including permeance, membrane lifetime and membrane price. The results reveal the relationship between the optimal design variables and membrane properties. Moreover, the selectivity-limited region is identified, which leads to two different dominant strategies for the cost reduction in a different region, either by the increase in selectivity or the reduction of the cost factor.