Elevated Temperature Pressure Swing Adsorption Research Articles

Elevated temperature pressure swing adsorption using LaNi4.3Al0.7 for efficient hydrogen separation

The application of LaNi5 based alloys as adsorbent for hydrogen separation and purification has been proposed for a long time. However, the actual utilization is limited by the poor CO tolerance of the alloys at atmospheric temperature. In this study, an elevated temperature vacuum pressure swing adsorption (ET-VPSA) method for H2 separation using hydrogen storage material LaNi4.3Al0.7 is proposed and demonstrated to be energy efficient. Elevating the working temperature results in improved CO tolerance of LaNi4.3Al0.7, making it possible for the alloy to be used in more situations. An ET-VPSA model was built to explore the correlations between product H2 purity, recovery rate, feed gas composition, cycle duration and counter-current blow down (CD) pressure. The results show that H2 recovery rate of ET-VPSA reaches 95% while it is usually 85% or lower for regular pressure swing adsorption (PSA). The energy efficiency of these two separation methods is evaluated by methanol reforming-proton exchange membrane fuel cell system models which contain PSA or ET-VPSA as H2 purification unit. A larger net power generation amount indicates less energy loss during H2 purification process. Although the vacuum pump will lead to extra energy consumption, benefiting from higher H2 recovery rate, the net efficiency of the system with ET-VPSA is 0.475, still higher than that with PSA (0.448).

Warm hydrogen direct adsorptive separation and purification with highly CO/H2S-tolerant rare earth alloys

Direct H2 separation using hydrogen adsorption materials has been gaining research attention for several decades. Rare-earth-metal-based alloys have proved to be feasible hydrogen adsorbents; however, their applications are restricted because of the presence of poisonous impurities, especially CO. Herein, we demonstrate the utilization of fluorinated LaNi5-based materials in elevated temperature pressure swing adsorption (ET-PSA) method for H2 separation is feasible. The adsorbent, fluorinated LaNi4.3Al0.7, maintained satisfactory working capacity at 453 K in poisonous mixed gas, which contained up to 30% CO or 0.5% H2S. During the breakthrough tests performed on a fixed bed reactor packed with, clean separations of H2/CO2+CO+N2+CH4 were observed when the feed gas component was N2/CH4/CO2/CO/H2 (45/10/10/5/30), indicating hydrogen was efficiently separated from the mixed gas in only one step, thereby simplifying the H2 separation process and the device. The mechanism of poisoning of LaNi5 by CO, and the effect of the working temperature on the CO resistance of LaNi5, were investigated using the density functional theory and ab initio molecular dynamics simulation, whose outcomes showed that the presence of CO significantly reduces the adsorption energy of H atoms. Nevertheless, at elevated temperatures (over 453 K), CO molecules was easier to escape from LaNi5 surface and less likely to completely cover the adsorbent surface, resulting in more possibility of H adsorbing on LaNi5 surface.

Simulation and energy consumption comparison of gas purification system based on elevated temperature pressure swing adsorption in ammonia synthetic system

Elevated temperature pressure swing adsorption (ET-PSA) is a novel process for hydrogen purification. By operating steam rinse and purge at conditions beyond the dew point will significantly improve the recovery rate of the product gas. Moreover, since cooling and reheating processes are not needed in ET-PSA, the sensible heat of the incoming gas could also be preserved. In this study, a seven-column 5000 Nm3/h ET-PSA pilot scale model was designed for energy consumption analysis. Product H2 purity, recovery rate, product CO2 purity, CO2 capture rate, unit H2 purification energy consumption and unit CO2 capture energy consumption were set as the criteria for assessing the purification performance. Rinse pressure, rinse media, and desorption method were selected as variables during the design and optimisation of the ET-PSA process. Herein, a high process efficiency (99.98% product gas purity and 99.33% recovery) was achieved. These values increased by 5.38% and 4.44%, respectively, compared to the base case. Meanwhile, the CO2 capture energy consumption was reduced by 59.2 MJ/ton(CO2).

Hydrophobic activated carbon for elevated-temperature pressure swing adsorption

Elevated temperature pressure swing adsorption is a newly developed gas purification technology, wherein the product gas recovery rate can be significantly improved by adding a steam rinse and purge. Furthermore, high temperature industrial syngas can be directly purified at elevated temperatures, so the temperature variation during purification process is not as large as that in Selexol, Rectisol or some other methods, which benefits to the simplification of heat management and improvement of energy efficiency. At working temperatures of approximately 200 °C, activated carbon is considered to be a promising adsorbent. Nevertheless, activated carbon also adsorbs large amounts of steam during rinse and purge, which affects its adsorption capacity. Herein, hydrophobic activated carbon was synthesized by impregnation and characterized, achieving a contact angle with a water droplet of up to 134°. When exposed to wet air, the weight increase of the hydrophobic adsorbent was 0.3%, whereas it was approximately 12% for the commercial activated carbon, which can be mainly attributed to vapor adsorption. The CO2 adsorption capacity was tested under humid conditions at 200 °C on a fixed bed. The effect of steam on the hydrophobic adsorbent was much smaller than that on the commercial adsorbent. The working capacity decreased from 0.091 to 0.009 mmol/g when the commercial activated carbon was operated under steam at 1 atm, whereas the hydrophobic material exhibited a stable and desired working capacity at the same condition, which was around 0.05 mmol/g. Steam rinse and purge were demonstrated to be feasible for the hydrophobic adsorbent and the introducing of steam rinse could not only compensate for the deterioration of adsorption capacity resulting from impregnation, but further improve the purification efficiency.

Application of elevated temperature pressure swing adsorption in hydrogen production from syngas

A clean and energy-efficient power system can be developed by the combination of hydrogen (as an energy carrier) and fuel cells (as power generation units); such system has the potential to compete with the current energy consumption pattern of direct combustion of fossil fuels. A novel CO/CO2 purification process, called the elevated-temperature pressure swing adsorption (ET-PSA), is coupled into an integrated gasification fuel cell (IGFC) power plant system in this work. A quantitative evaluation standard for the purification energy consumption is developed by considering both the net power efficiency loss of the IGFC after introducing the purification unit, and the total CO/CO2 removal rate. The sensible heat loss of syngas and the thermal regeneration of the saturated adsorbents are avoided; consequently, the calculated energy consumption of the ET-PSA (1.11 MJ/kg) process using the ideal purification unit as the base case is 36.2% lower than of the conventional solvent absorption method. Alternatively, high-temperature steam is consumed in the ET-PSA process during the rinse and purge steps, which leads to a decrease in the output power of the steam turbine. The purification energy consumption of the ET-PSA process can be further reduced either by increasing the hydrogen recovery ratio or by reducing the total steam consumption.

On-site demonstration of an elevated temperature hydrogen clean-up unit for fuel cell applications

Hydrogen from coal-based syngas is usually purified by deep desulfurization and decarbonization scrubbing technologies. Such electricity consuming processes cost a large number of heat exchangers and compressors. In this study, a two-stage demonstration unit had been constructed and demonstrated to purify hydrogen (including useful nitrogen for ammonia synthesis) from on-site sideline shift gas mixture at Yangmei Fengxi ammonia plant. For the first stage, an 8-column hydrogen purification process by novel elevated temperature pressure swing adsorption (ET-PSA, operated at 180 to 220 °C) was developed and demonstrated to capture H2S and CO2 simultaneously by hydrophobic activated carbon (AC) to reduce the impurities compared to that of room temperature PSA. Working condition at elevated temperature was proved to be appropriate and stable for reversible H2S removal by AC. The second stage was a temperature swing adsorption for deep purification of CO to 0.2 ppm by commercial CuCl monolayer dispersed zeolites (PU-1 synthesized by Beijing Peking University Pioneer Technology Co., Ltd.). In order to examine the standard of trace impurities such CO and H2S in product H2, the purified H2 was offered to a 3 kW proton exchange membrane fuel cell (PEMFC) stack to prove that all carbon and sulfur impurities met the demand not only for ammonia synthesis, but for PEMFC as well. Besides, two novel PSA steps: high pressure steam rinse and low pressure nitrogen purge were adopted to improve H2 recovery to above 93%. To demonstrate its stability, over 2500 h of operation had been carried out on the small-scale demonstration rigs by far.

Characteristics of activated carbon in elevated-temperature pressure swing adsorption desulfurization

Elevated-temperature pressure swing adsorption could potentially replace wet methods in the field of syngas purification. However, the reversibility of sulfur removal in this technique needs to be validated. In this study, the H2S adsorption reversibility of two types of activated carbon sorbents were evaluated on a fixed-bed reactor. The effects of desorption method and desorption temperature were studied. Elevated-temperature vacuum desorption was found to be effective for regenerating adsorbents saturated with H2S. The necessities of both vacuum desorption and elevated temperature were reported. The findings were explained on the basis of the characterization results obtained using pore distribution analysis, inductively coupled plasma, and X-ray photoelectron spectroscopy. The oxidative functional groups or adsorbed O2 reacted with H2S on the surface of the adsorbents and the resultant, i.e., elemental sulfur, damaged the pore structure. The richness of the pores with a diameter range of 0.7–0.8 nm decreased by nearly 50% after several adsorption–desorption cycles. At high temperatures and under vacuum atmosphere, element sulfur could be easily distilled and removed from the fixed bed. Thus, element sulfur would not accumulate on the adsorbent, thus ensuring the reversibility of H2S.

Two-train elevated-temperature pressure swing adsorption for high-purity hydrogen production

The trade-off between hydrogen recovery ratio (HRR) and hydrogen purity (HP) is one of the main drawbacks in normal temperature pressure swing adsorption (NT-PSA) for producing high-purity hydrogen from shifted gas. In this paper, a two-train elevated-temperature pressure swing adsorption (ET-PSA) process that achieved 99.999% HP and over 95% HRR is proposed, which has wide application potentials in fuel cells and chemical industries. Potassium-promoted layered double oxide (K-LDO), which shows reasonable working capacity and fast adsorption/desorption kinetics at elevated temperatures (200–450 °C), is adopted as the CO2 adsorbent. CO in the shifted gas is co-purified by high-temperature water gas shift (WGS) catalysts added to the columns. The first-train ET-PSA adopted an eight-column thirteen-step configuration with shorter step time to remove most of the CO/CO2 in the shifted gas, and the second-train ET-PSA adopted a double-column seven-step configuration with longer step time to purify the residual gas impurities. The introduction of co-current high-pressure steam rinse and counter-current low-pressure steam purge is the key to achieve both high HRR and HP. The high-temperature steam is the main energy consumption of ET-PSA rather than low HRR in NT-PSA, and the total steam consumption is reduced by adopting the tail gas from second-train ET-PSA as the purge gas for first-train ET-PSA. The optimal results achieved 97.51% HRR and 99.9994% HP with only 0.188 rinse-to-feed ratio and 0.263 purge-to-feed ratio, which are the highest values reported for PSAs producing high-purity hydrogen from carbon-based fuels.

Elevated temperature pressure swing adsorption process for reactive separation of CO/CO2 in H2-rich gas

Purification of CO and CO2 to the ppm level in H2-rich gas without losing H2 is one of the technical difficulties for fuel cell power systems. In this work, a two-column seven-step elevated temperature pressure swing system with high purification performance was proposed. The concept of reactive separation by adding water gas shift catalysts into the columns filled with elevated temperature CO2 adsorbents was adopted. The H2 recovery ratio and H2 purity were greatly improved by the introduction of steam rinse and steam purge, which could be realized due to the increasing operating temperature (200–450 °C). An optimized operating region to both achieve high efficiency and low energy consumption was proposed. The optimized case with 0.09 purge-to-feed ratio and 0.15 rinse-to-feed ratio could achieve 99.6% H2 recovery ratio and 99.9991% H2 purity at a stable state for a feed gas containing 1% CO, 1% CO2, 10% H2O, and 88% H2. No performance degradation was observed for at least 1000 cycles. The proposed (ET-PSA) system possessed self-purification ability while the columns were penetrated by CO2. It is however suggested that periodical heat regeneration should be adopted to accelerate performance recovery during long-term operation.

CO2 residual concentration of potassium-promoted hydrotalcite for deep CO/CO2 purification in H2-rich gas

Elevated-temperature pressure swing adsorption is a promising technique for producing high purity hydrogen and controlling greenhouse gas emissions. Thermodynamic analysis indicated that the CO in H2-rich gas could be controlled to trace levels of below 10 ppm by in situ reduction of the CO2 concentration to less than 100 ppm via the aforementioned process. The CO2 adsorption capacity of potassium-promoted hydrotalcite at elevated temperatures under different adsorption (mole fraction, working pressure) and desorption (flow rate, desorption time, steam effects) conditions was systematically investigated using a fixed bed reactor. It was found that the CO2 residual concentration before the breakthrough of CO2 mainly depended on the total amount of purge gas and the CO2 mole fraction in the inlet syngas. The residual CO2 concentration and uptake achieved for the inlet gas comprising CO2(9.7 mL/min) and He (277.6 mL/min) at a working pressure of 3 MPa after 1 h of Ar purging at 300 mL/min were 12.3 ppm and 0.341 mmol/g, respectively. Steam purge could greatly improve the cyclic adsorption working capacity, but had no obvious benefit for the recovery of the residual CO2 concentration compared to purging with an inert gas. The residual CO2 concentration obtained with the adsorbent could be reduced to 3.2 ppm after 12 h of temperature swing at 450 °C. A new concept based on an adsorption/desorption process, comprising adsorption, steam rinse, depressurization, steam purge, pressurization, and high-temperature steam purge, was proposed for reducing the steam consumption during CO/CO2 purification.

Integrated gasification combined cycle with carbon dioxide capture by elevated temperature pressure swing adsorption

This paper investigates the CO2 capture energy consumption via elevated-temperature pressure swing adsorption (ET-PSA) for CO2/H2 separation. IGCC power plants with ET-PSA, with the conventional Selexol process and without CO2 capture are built in Aspen Plus. The CO2 capture energy consumption of ET-PSA is evaluated by the specific primary energy consumption for CO2 avoided (SPECCA), which is a function of the net electrical efficiency and the specific CO2 emission rate. The ET-PSA unit with different processes simulated in gPROMS is coupled into the IGCC model, the operation parameters of which are analyzed to achieve the lowest SPECCA. The results show that the CO2 capture energy consumption has a tendency to decrease by increasing the adsorption time, the residence time, and the purge-to-feed ratio; reducing the purge ratio; and adding the CO2 reflux. The SPECCA of ET-PSA with the 5–3–1 process is 2.79MJ/kgCO2 with a 90.5% CO2 capture ratio, which is 11.71% lower than that of the Selexol process. An effective way to further reduce the SPECCA of ET-PSA is to add rinse and purge steps, whose energy loss mainly comes from the consumption of high-temperature steam. The calculated SPECCA of ET-PSA with rinse and purge steps is 2.32–2.52MJ/kgCO2, which is 20.3–26.6% lower than that of the Selexol process.

Layered double oxide/activated carbon-based composite adsorbent for elevated temperature H2/CO2 separation

A layered double oxide/activated carbon-based composite adsorbent for H2/CO2 separation at elevated temperatures is presented for the first time. The CO2 adsorbent is synthesized from commercially available activated carbon, which is loaded with Mg–Al hydrotalcite using the urea or co-precipitation methods. Samples are comprehensively characterized using various techniques, including XRD, BET and SEM. The results show that the co-precipitation method is more efficient for the synthesis of the composite adsorbent. Compared with activated carbon and hydrotalcite as single-composition adsorbents, the composite adsorbent has a comparatively larger adsorption capacity and faster kinetics at elevated temperatures. The adsorption capacity of the composite adsorbent reaches 0.185 mmol/g at 200 °C and 1 atm for the second adsorption/desorption cycle, and 86% of the total CO2 is adsorbed within 20 min. Additionally, K2CO3 is loaded on the surface of the composite adsorbent via impregnation to further promote the adsorption performance. The adsorption isotherm data show that the K2CO3-promoted composite adsorbent has an adsorption capacity of 1.741 mmol/g at 200 °C and 3 MPa, which is higher than that for activated carbon (1.410 mmol/g) and for the composite adsorbent without K2CO3 (1.638 mmol/g). This result further proves that the developed adsorbent is a promising candidate for H2/CO2 separation within the elevated temperature pressure swing adsorption process.

Elevated temperature hydrogen/carbon dioxide separation process simulation by integrating elementary reaction model of hydrotalcite adsorbent

An elementary reaction kinetics model related with Elovich equation is developed to predict the CO2 adsorption capacity and adsorption kinetic behavior for potassium promoted hydrotalcite-like compound (K-promoted HTlcs). The elementary reaction kinetics model is comprehensively validated by experimental data from both atmosphere pressure thermo gravimetric analysis (TGA) and a high pressure adsorption apparatus. The elevated temperature pressure swing adsorption s(PSA) system modeling framework is then developed on the gPROMS commercial simulation platform by further considering comprehensive coupling effects from mass, momentum and energy transport processes, integrated with dynamic boundary condition and realistic operating procedures. The effects of adsorption time, residence time, purge to feed ratio, working pressure and adsorbents capacity on PSA cycling gas separation performance are studied with the proposed modeling framework based on a four-bed two-pressure-equalization PSA process.

Experimental Characterization and Mechanistic Simulation of CO2 Adsorption/Desorption Processes for Potassium Promoted Hydrotalcites Sorbent

Abstract The elevated temperature pressure swing adsorption (PSA) based on potassium promoted hydrotalcite-like compounds (K-HTlc) is one of the most promising technologies for pre-combustion CO 2 capture. K-HTlc could achieve a fast part of reversible CO 2 capacity under desorption conditions of low inert purge flow rate and short purge time. The CO 2 breakthrough capacity is 1.01 mmol/g and 0.6 mmol/g at 1.2 MPa (CO 2 partial pressure) for 400 °C and 300 °C, respectively. A one-dimensional isotherm column model was developed to describe the K-HTlc performance and CO 2 transportation in a single column during PSA process. The results indicated that the simulation results agreed well with the experimental results. The CO 2 desorption process of K-HTlc should be characterized as a fast and a followed slow process which is origin from the chemisorption characteristics and was validated by the model results. The presented model could be further applied in the practical industrial PSA.

Techno-economic Evaluation of an Elevated Temperature Pressure Swing Adsorption Process In A 540 MW IGCC Power Plant with CO2 capture

Abstract Pressure swing adsorption at elevated temperature (ET-PSA) is one kind of widely studied acid gas clean up technology. In this study, a system scheme for a 540 MW IGCC system with CO 2 capture is proposed by integrating the current developing ET-PSA process. The modeling framework is developed and implemented in process simulation platform (Aspen Plus) by considering 90% of CO 2 removal rate and 99% of H2S removal rate. The system performance is simulated for comparing the effects with adopting Selexol process on the system efficiency and integration characteristics. The simulation is based on the same coal feed rate, gas turbine combustion temperature and stack gas temperature. The simulated results show that with the H2 recovery rate increases from 75% to 100%, the net plant efficiency for IGCC with ET-PSA process increases linearly from 23.1% to 34.4%, and when the H2 recovery rate exceeds 93.5%, the estimated efficiency can be higher than that for IGCC with Selexol process (31.5%).

Mechanism Modeling of Elevated Temperature Pressure Swing Adsorption Process for Pre-combustion CO2 Capture

The elevated temperature pressure swing adsorption (PSA) is a promising technology for pre-combustion CO2 capture in Integrated Gasification Combined Cycle (IGCC) power plant by taking the advantages of high partial pressure (1.0-2.0MPa) of CO2 in the syngas after water-gas shift reaction. An elementary reaction kinetic model was developed to predict the CO2 adsorption capacity and adsorption kinetic behavior for potassium promoted hydrotalcite-like compound (K-promoted HTlcs). Thermo gravimetric analysis (TGA) and a high pressure adsorption apparatus were respectively used below atmospheric pressure and above atmospheric pressure. The results indicate that the modeling results agreed well the experimental results. The elevated temperature PSA system modeling framework is developed by considering comprehensive coupling effects from mass, heat, and momentum transport mechanisms. The modeling framework is implemented in the gPROMS commercial simulation platform by integrating adsorption bed with dynamic boundary condition and realistic operating procedures. The presented modeling framework can be further applied for the system optimization and controller design for multi-column elevated temperature PSA processes.