Integrated vacuum pressure swing adsorption and Rectisol process for CO_(2) capture from underground coal gasification syngas

An integrated vacuum pressure swing adsorption(VPSA) and Rectisol process is proposed for CO_(2) capture from underground coal gasification(UCG) syngas. A ten-bed VPSA process with silica gel adsorbent is firstly designed to pre-separate and capture 74.57% CO_(2) with a CO_(2) purity of 98.35% from UCG syngas(CH_(4)/CO/CO_(2)/H_(2)/N_(2)= 30.77%/6.15%/44.10%/18.46%/0.52%, mole fraction, from Shaar Lake Mine Field,Xinjiang Province, China) with a feed pressure of 3.5 MPa. Subsequently, the Rectisol process is constructed to furtherly remove and capture the residual CO_(2)remained in light product gas from the VPSA process using cryogenic methanol(233.15 K, 100%(mass)) as absorbent. A final purified gas with CO_(2) concentration lower than 3% and a regenerated CO_(2) product with CO_(2) purity higher than 95% were achieved by using the Rectisol process. Comparisons indicate that the energy consumption is deceased from 2.143 MJ·kg^(-1) of the single Rectisol process to 1.008 MJ·kg^(-1) of the integrated VPSA & Rectisol process, which demonstrated that the deployed VPSA was an energy conservation process for CO_(2) capture from UCG syngas. Additionally, the high-value gas(e.g., CH_(4)) loss can be decreased and the effects of key operating parameters on the process performances were detailed.

Nitrogen rejection from low quality natural gas by pressure swing adsorption experiments and simulation using dynamic adsorption isotherms

In order to remove N_(2) from low quality natural gas,a mathematical model has been established by Aspen adsorption,using the CH_(4)-selective sorbent silicalite-1 pellets.The dynamic adsorption isotherm was first simulated by breakthrough simulation of a CH_(4)/N_(2) mixture at different adsorption pressures and feed flow rates based on breakthrough experiments.The resulting simulated CH_(4) dynamic adsorption amounts were very close to the experimental data at three different adsorption pressures(100,200,and 300 kPa).Moreover,a single-bed,three-step pressure swing adsorption(PSA)experiment was performed,and the results were in good agreement with the simulated data,further corroborating the accuracy of the gas dynamic adsorption isotherm obtained by the simulation method.Finally,based on the simulated dynamic adsorption isotherm of CH_(4) and N_(2),a four-bed,eight-step PSA process has been designed,which enriched 75%(vol)CH_(4) and 80%(vol)CH_(4) to 95%(vol)and 99%(vol),and provided 99%(vol)recovery.

Hydrogen Purification Performance of Pressure Swing Adsorption Based on Cu-BTC/zeolite 5A Layered Bed

A pressure swing adsorption (PSA) hydrogen purification model for the four-component gas (H_(2)/CO_(2)/CH_(4)/CO=73/16/8/3 mol%) in a layered bed packed with Cu-BTC and zeolite 5A was established to achieve better hydrogen purification performance.By comparing its simulation results with the experimental data,the adsorption isotherm model was validated and could be used to accurately describe the adsorption process of the gas mixture on the two adsorbents.The breakthrough curves of the mixed gas on the layered bed were studied to verify the correctness of the established simulation models.Based on the validated model,the performance of the PSA system based on the layered bed was carried out,including the hydrogen purity and recovery.The simulation results show that the hydrogen purification system based on the layered bed model can achieve hydrogen purity of 95.469% and hydrogen recovery of 83.219%.Moreover,a parametric study was carried out and its results show that reductions in feed flow rate and adsorption time result in an increase in hydrogen purity and a decrease in hydrogen recovery.A longer equalization time between the two adsorption beds can simultaneously increase the hydrogen purity and recovery.

Comparative study on pressure swing adsorption system for industrial hydrogen and fuel cell hydrogen

In order to improve the design of PSA system for fuel cell hydrogen production,a non-isothermal model of eight-bed PSA hydrogen process with five-component(H_(2)/N_(2)/CH_(4)/CO/CO_(2)=74.59%/0.01%/4.2%/2.5%/18.7%(vol))four-stage pressure equalization was developed in this article.The model adopts a composite adsorption bed of activated carbon and zeolite 5 A.In this article,pressure variation,temperature field and separation performance are stimulated,and also effect of providing purge(PP)differential pressure and the ratio of activated carbon to zeolite 5 A on separation performance in the process of producing industrial hydrogen(CO content in hydrogen is 10μl·L^(-1))and fuel cell hydrogen(CO content is 0.2μl·L^(-1))are compared.The results show that Run 3,when the CO content in hydrogen is 10μl·L^(-1),the hydrogen recovery is 89.8%,and the average flow rate of feed gas is 0.529 mol·s^(-1);When the CO content in hydrogen is 0.2μl·L^(-1),the hydrogen recovery is 85.2%,and the average flow rate of feed gas is 0.43 mol·s^(-1).With the increase of PP differential pressure,hydrogen recovery first increases and then decreases,reaching the maximum when PP differential pressure is 0.263 MPa;With the decrease of the ratio of activated carbon to zeolite 5 A,the hydrogen recovery increases gradually.When the CO content in hydrogen is 0.2μl·L^(-1) the hydrogen recovery increases more obviously,from 83.96%to 86.37%,until the ratio of activated carbon to zeolite 5 A decreases to 1.At the end of PP step,no large amount of CO_(2) in gas or solid phase enters the zeolite 5 A adsorption bed,while when the CO content in hydrogen is 10μl·L^(-1),and the ratio of carbon to zeolite 5 A is less than 1.4,more CO_(2) will enter the zeolite 5 A bed.

Study on Pressure Swing Adsorption Removing C_2^+ from Natural Gas as Raw Material for Thermal Chlorination

The experimental investigation demonstrates that a satisfactory result can be expected for pressure swing adsorption (PSA) purification of natural gas as raw material for thermal chlorination process. Using hh-4 molecular sieve as adsorbent for removing C+2 components, the suitable adsorption pressure is 0.4-0.45 MPa, desorption vacuum is 0.08-0.09 MPa and circulation time is 20-21 min.

Analysis of CO₂Pressure Swing Adsorption Simulation by Considering the Transport Phenomena in the Adsorber

This study focused on CO2 separation technology with adsorption. This paper describes the analysis carried out by a CO2 pressure swing adsorption simulation to scale up the absorber. An unsteady one-dimensional balance model was constructed by considering the material, energy, and momentum. In the CO2 breakthrough test, the beginning time and CO2 concentration at outlet of CO2 breakthrough in the calculation were almost equivalent to that of experiment results. The correlation consistency of the calculation results with the analysis model and the experimental results obtained by a bench scale experiment was evaluated. The transport phenomena in the adsorber were investigated at the adsorption, rinse, and desorption steps according to the calculation results. The starting time of CO2 breakthrough obtained by the analysis is equal to that obtained by the adsorption breakthrough experiment. This confirms that the CO2 adsorption, and the temperature and velocity distribution in the adsorber, change as a function of the adsorption, rinse, and desorption steps, respectively. Additionally, the CO2 concentration of the captured gas and the amount of CO2 quantity were 93.4% per day and 2.9 ton/day, respectively. These values are equal to those obtained by the bench scale experiment.

Artificial neural network based optimization of a six-step two-bed pressure swing adsorption system for hydrogen purification

The pressure swing adsorption(PSA)system is widely applied to separate and purify hydrogen from gaseous mixtures.The extended Langmuir equation fitted from the extended Langmuir-Freundlich isotherm has been used to predict the adsorption isothermal of hydrogen and methane on the zeolite 5A adsorbent bed.A six-step two-bed PSA model for hydrogen purification is developed and validated by comparing its simulation results with other works.The effects of the adsorption pressure,the P/F ratio,the adsorption step time and the pressure equalization time on the performance of the hydrogen purification system are studied.A four-step two-bed PSA model is taken into consideration,and the six-step PSA system shows higher about 13%hydrogen recovery than the four-step PSA system.The performance of the vacuum pressure swing adsorption(VPSA)system is compared with that of the PSA system,the VPSA system shows higher hydrogen purity than the PSA system.Based on the validated PSA model,a dataset has been produced to train the artificial neural network(ANN)model.The effects of the number of neurons in the hidden layer and the number of samples used for training ANN model on the predicted performance of ANN model are investigated.Then,the well-trained ANN model with 6 neurons in the hidden layer is applied to predict the performance of the PSA system for hydrogen purification.Multi-objective optimization of hydrogen purification system is performed based on the trained ANN model.The artificial neural network can be considered as a very effective method for predicting and optimizing the performance of the PSA system for hydrogen purification.

Carbon Dioxide/Methane Separation by Adsorption on Sepiolite

In this work, the use of sepiolite for the removal of carbon dioxide from a carbon dioxide/methane mixture by a pressure swing adsorption （PSA） process has been researched. Adsorption equilibrium and kinetics have been measured in a fixed-bed, and the adsorption equilibrium parameters of carbon dioxide and methane on sepiolite have been obtained. A model based on the LDF approximation has been employed to simulate the fixed-bed kinetics, using the Langmuir equation to describe the adsorption equilibrium isotherm. The functioning of a PSA cycle for separating carbon dioxide/methane mixtures using sepiolite as adsorbent has also been studied. The experimental results were compared with the ones predicted by the model adapted to a PSA system. Methane with purity higher than 97% can be obtained from feeds containing carbon dioxide with concentrations ranging from 34% to 56% with the proposed PSA cycle. These results suggest that sepiolite is an adsorbent with good properties for its employment in a PSA cycle for carbon dioxide removal from landfill gases.

Simulation and experiment of six-bed PSA process for air separation with rotating distribution valve

In this work,a six-bed pressure swing adsorption(PSA)process was investigated to produce medical oxygen from air,which uses the combination of six-way rotating distribution valve and PSA and has the main advantage of effectively saving space compared to the traditional two-bed or four-bed PSA process and can obtain greater productivity.The mathematical model of adsorption beds was developed based on the separation mechanism and the interaction among different equipment.Moreover,a pilot-scale device has been constructed to verify the accuracy of mathematical model by experiment.The oxygen product conformed to the medical standard(>93%(vol))with a recovery of over 57%.Some related parameters were also discussed in detail,such as step time,ratio of length to the diameter,flow rate of product.

Effects of micropore structure of activated carbons on the CH_(4)/N_(2) adsorption separation and the enrichment of coal-bed methane

In the process of enriching CH4 from coal-bed methane,the separation of CH_(4)/N_(2)is very difficult to accomplish by an adsorption process due to the similar physico-chemical properties of the two molecules.A series of coconut-shell-based granular activated carbons(GACs)with different pore structures were prepared,which were characterized by different methods.The influence of the pore structure on the separation properties was investigated in detail.The results show that one of the carbons prepared(GAC-3)has high CH4 equilibrium adsorption capacity(3.28 mol·kg–1)at 298 K and equilibrium separation coefficient(3.95).The CH_(4)/N_(2)separation on the GACs is controlled by adsorption equilibrium as compared with the dynamic effect.Taking the specific surface area,for example,the common characterization index of the pore structure is not enough to judge the separation performance of the GACs.However,the microstructure of carbon materials plays a decisive role for CH_(4)/N_(2)separation.According to the pore-structure analysis,the effective pore size for the CH_(4)/N_(2)separation is from 0.4 to 0.9 nm,with the optimum effect occurring in the range of 0.6–0.7 nm,followed by the range of 0.7~0.9 nm.Also,a four-bed vacuum pressure swing adsorption process was adopted to evaluate the performance of GACs for the separation of CH4 from nitrogen.

Efficiency analysis of sorption-enhanced method in steam methane reforming process

The sorption-enhanced method can change the thermodynamic equilibrium by absorbing CO_(2).However,it also brings about the problems of high regeneration temperature of adsorbent and large regeneration energy consumption.In order to study the impact of enhanced adsorption methods on the overall energy cost of the system in the hydrogen production process,this paper analyzes and compares steam methane reforming and reactive adsorption-enhanced steam methane reforming with the energy consumption of hydrogen production products as the evaluation index.The results showed that the energy consumption per unit hydrogen production decreased from 276.21 MJ/kmol to 131.51 MJ/kmol,and the decomposition rate of H2O increased by more than 20%after the addition of adsorption enhancement method.It is proved that the advantage of sorption enhanced method on pre-separation of CO_(2)in the product makes up for the disadvantage of energy consumption of adsorbent regeneration.In addition,the ability of the process to obtain H element is improved by the high decomposition rate of H2O,which realizes a more rational distribution of the element.

Bioenergy recovery from landfill gas:A case study in China

Landfill gas(LFG)utilization which means a synergy between environmental protection and bioenergy recovery was investigated in this study.Pressure swing adsorption technology was used in LFG purification,and laboratory experiment,pilot-scale test,and on-site demonstration were carried out in Shenzhen,China.In the laboratory experiment,A-type carbon molecular sieve was selected as the adsorbent by comparison of several other adsorbents.The optimal adsorption pressure and adsorption time were 0.25 MPa and 2 min,respectively,under which the product generation rate was 4.5 m^(3)/h and the methane concentration was above 90%.The process and optimization of the pilot-scale test were also reported in the paper.The product gas was of high quality compared with the National Standard of Compressed Natural Gas as Vehicle Fuel(GB18047-2000),when the air concentration in feed gas was under 10.96%.The demonstration project was composed of a collection system,production system,and utilization system.The drive performance,environmental protection performance,and economic feasibility of the product gas—as alternative fuel in passenger car,truck,and bulldozer—were tested,showing the feasibility technology for LFG utilization.

Fundamentals and developments of compressed biogas in city gas distribution network in India:A review

Biogas is a significant renewable source as well as an alternative energy carrier provided by Anaerobic Digestion(AD)of biodegradable food wastes and other organic materials.This paper describes some major facts about biogas along with the barriers and adaptation of CBG in society,it also narrates the types of feedstocks available for biogas generation and what are the major sources in India.In this study,different stages of anaerobic digestion are discussed such as hydrolysis,acidogenesis,acetogenesis and methanogenesis for biogas production.After its purification,the biogas can be used as a fuel for domestic as well as transportation purposes.A glimpse of biogas like purification techniques like biological desulphurization,iron chloride dosing,pressure swing adsorption,chemical scrubbing and water scrubbing is given,the major additions of national policy of biofuels in 2018 is also highlighted.It has been found that in India,majorly pressure swing adsorption and water scrubbing methods are used for biogas purification,currently,the country has 12 commercial CBG plants with a total CBG output capacity of 18,461.7 tonnes per year,which is just 0.06 percent of the total ability.The details of the plants along with their CBG production capacity are described,and sustainable alternative towards affordable transportation(SATAT)launched by MoPNG is introduced in this study,furthermore,the features and types of models suggested by Ministry of Petroleum and Natural Gas(MoPNG)to introduce compressed biogas(CBG)in city gas distribution(CGD)network are discussed.