Shuiping Yan

Innovative Use of Membrane Contactor as Condenser for Heat Recovery in Carbon Capture

The gas-liquid membrane contactor generally used as a nonselective gas absorption enhancement device is innovatively proposed as a condenser for heat recovery in liquid-absorbent-based carbon capture. The membrane condenser is used as a heat exchanger to recover the latent heat of the exiting vapor from the desorber, and it can help achieve significant energy savings when proper membranes with high heat-transfer coefficients are used. Theoretical thermodynamic analysis of mass and heat transfer in the membrane condensation system shows that heat recovery increases dramatically as inlet gas temperature rises and outlet gas temperature falls. The optimal split mass flow rate is determined by the inlet gas temperature and the overall heat-transfer coefficient in the condensation system. The required membrane area is also strongly dependent on the overall heat-transfer coefficient, particularly at higher inlet gas temperatures. Mass transfer across the membrane has an insignificant effect on heat transfer and heat recovery, suggesting that membrane wetting may not be an issue when a membrane condenser is used for heat recovery. Our analysis provides important insights into the energy recovery performance of the membrane condensation system as well as selection of operational parameters, such as split mass flow rate and membrane area, thickness, and thermal conductivity.

Enhancing ethanol production from thermophilic and mesophilic solid digestate using ozone combined with aqueous ammonia pretreatment

Pretreatment with ozone combined with aqueous ammonia was used to recover residual organic carbon from recalcitrant solid digestate for ethanol production after anaerobic digestion (AD) of rice straw. Methane yield of AD at mesophilic and thermophilic conditions, and ethanol production of solid digestate were investigated. The results showed that the methane yield at thermophilic temperature was 72.2% higher than that at mesophilic temperature under the same conditions of 24days and 17% solid concentration. And also the ethanol production efficiency of solid digestate after thermophilic process was 24.3% higher than that of solid digestate after mesophilic process. In this study, the optimal conditions for integrated methane and ethanol processes were determined as 55°C, 17% solid concentration and 24days. 58.6% of glucose conversion, 142.8g/kg of methane yield and 65.2g/kg of ethanol yield were achieved, and the highest net energy balance was calculated as 6416kJ/kg.

An alternative parameter to characterize biogas materials: Available carbon-nitrogen ratio

Available carbon-nitrogen ratio (AC/N) was proposed as an alternative parameter for evaluating the potential of biogas materials in this paper. In the calculation of AC/N ratio, only the carbon that could be effectively utilized in anaerobic digestion (AD) process is included. Compared with total C/N, AC/N is particularly more suitable for the characterization of biogas materials rich in recalcitrant components. Nine common biogas materials were selected and a series of semi-continuous tests for up to 110days were carried out to investigate the source of available carbon and the relationship between AC/N and the stability of AD process. The results showed that only the carbon existing in proteins, sugars, fat and hemicelluose should be considered as available carbon for anaerobic microbes. Besides, the optimal AC/N for semi-continuous AD process was preliminarily determined to be 11-15. Taken together, our results demonstrate that AC/N is more effective than total C/N in the evaluation of the potential performance of AD process.

Removal of methylene blue from aqueous solution by cattle manure-derived low temperature biochar

Biochar is a low cost and renewable adsorbent which can be used to remove dye from wastewater. Cattle manure-derived low temperature biochar (CMB) was studied to remove methylene blue (MB) from aqueous solution in this paper. The effect of factors including initial concentration of MB, dosage, contact time, and pH on the adsorption properties of MB onto biochar were studied. Characterization of the CMB and MB adsorbed on CMB was performed using techniques including BET, FTIR and SEM. The adsorption isotherm, kinetics, thermodynamics and mechanism were also studied. The results showed the equilibrium data were well fitted to the Langmuir isotherm model, and the saturation adsorption capacity of CMB200 was 241.99 mg g−1. Pseudo-second order kinetics was the most suitable model for describing the adsorption of MB onto biochar. The adsorption thermodynamics of MB on biochar showed that the adsorption was a spontaneous and endothermic process. Through zeta potential measurement, Boehm titration, cation exchange, deashing and esterification experiments, the importance of ash to adsorption was verified, as well as the adsorption mechanism. The adsorption mechanism of MB on CMB200 involved cation exchange, electrostatic interaction, hydrogen bonding, physical effects and others. This work shows that CMB200 holds promise to act as an effective adsorbent to remove MB in wastewater.

Closing CO2 Loop in Biogas Production: Recycling Ammonia As Fertilizer

We propose and demonstrate a novel system for simultaneous ammonia recovery, carbon capture, biogas upgrading, and fertilizer production in biogas production. Biogas slurry pretreatment (adjusting the solution pH, turbidity, and chemical oxygen demand) plays an important role in the system as it significantly affects the performance of ammonia recovery. Vacuum membrane distillation is used to recover ammonia from biogas slurry at various conditions. The ammonia removal efficiency in vacuum membrane distillation is around 75% regardless of the ammonia concentration of the biogas slurry. The recovered ammonia is used for CO2 absorption to realize simultaneous biogas upgrading and fertilizer generation. CO2 absorption performance of the recovered ammonia (absorption capacity and rate) is compared with a conventional model absorbent. Theoretical results on biogas upgrading are also provided. After ammonia recovery, the treated biogas slurry has significantly reduced phytotoxicity, improving the applicability for agricultural irrigation. The novel concept demonstrated in this study shows great potential in closing the CO2 loop in biogas production by recycling ammonia as an absorbent for CO2 absorption associated with producing fertilizers.

Effect of alkali and alkaline earth metal species on the combustion characteristics of cattle manures

This study investigates the effects of alkali and alkaline earth metal (AAEM) species on the combustion characteristics of cattle manures (CM). Different AAEM species (K, Na, Ca, and Mg) were mixed with CM and deashing CM (D-CM) samples. The combustion characteristics of raw and char samples were compared. The effects of AAEM species on CM char were analyzed based on the structural characteristics of the char sample. Results show that K and Na exert a positive effect, and this effect varies depending on the addition amount. Ca and Mg also exhibit a positive effect, but this effect does not change with the addition amount. The positive effect of K, Na, and Ca is related to the decrease in graphitization degree and increase in specific surface area. However, the positive effect of Mg is negligible. In conclusion, CM can be mixed with fuels containing K or Na in an appropriate ratio. The amount of Ca to be mixed with fuels has no specific requirement, whereas that of Mg to be mixed with fuels should be controlled.

The studies on the methane production with solid state fermentation by mixed the rice straw and swine manures

In this study, an anaerobic dry fermentation system was designed and erected to validate the feasibility and test the performance of dry fermentation by using the mixtures of rice straw and fresh pig manures under the near middle temperature. And during the course of fermentation the leachate was refluxed from the leachate tank to the fermentation tank in order to increase the performance of mass transfer. Some key parameters such as pH value, VFA value, start-up time, gas production and CH4 content were used to reflect the fermentation performance. Experimental results show that after 6 days CH4 content in biogas can be above than 45%, which means that the anaerobic dry fermentation is started up. In addition, the total amount of biogas produced is about 16.55 m3 from 6-day to 22-day, and the maximum volume gas production rate can be about 1.2 m3 biogas/(d·m3 fermentation tank). Furthermore the CH4 content in the biogas after the start-up time can be maintained at about 50%∼70%. These useful results imply that the anaerobic dry fermentation using rice straw and fresh pig manures is viable. On the other side, the germinating index (GI) for cabbage was also experimented to test whether or not the leachate and the fermentation residues can be used to act as fertilizer. Results show that the GI is higher than 70% after 25 days anaerobic fermentation which suggests that these residues can be adopted to act as fertilizer.

Can CO2 Regeneration Heat Consumption Be Reduced by Using the Novel Mass Concentration of Solvent Swing Regeneration (MCSR) Technology

To reduce CO2 regeneration heat consumption inCO2 capture process, a novel concept named ¡°massconcentration of CO2-rich solution swing regeneration(MSCR)¡± was put forward in this study. Experiments were executed to investigate the feasibility and energy reduction potential of MSCR by using MEA as absorbent. Results show that CO2 regeneration performance can be improved greatly when MSCR was adopted. In addition, relatively high but appropriate mass concentration should be recommended to be selected for the initial CO2 rich solution. And experimental results also prove that MCSR technology may be more viable for the bicarbonate-producing systems between the reaction ofCO2 and absorbent or for carbamate-producing systems with high CO2 loading. Finally, evaluation of total regeneration heat consumption shows that the total CO2 regeneration heat consumption can be reduced by at least about 25%for MSCR.