Regeneration Air Flow Rate Research Articles

Performance evaluation of an innovative liquid desiccant air-conditioning system directly integrating a heat pump with two membrane energy exchangers

For high moisture removal applications with improved indoor air quality, the use of liquid-to-air membrane energy exchangers (LAMEEs) in liquid desiccant (LD) air-conditioning systems has been suggested in the literature. This study introduces a novel configuration for a heat pump LD system to improve its dehumidification and energy use. The evaporator and condenser coils of the heat pump (HP) are embedded in the LD channels of two LAMEEs; one is an internally cooled dehumidifier (ICD), and the other is an internally heated regenerator (IHR). These LAMEEs are designed to directly use the HP condenser coils for the IHR's regeneration process while also effectively controlling the local temperature rise of the LD solution inside the ICD. An integrated CFD model for both the ICD and the IHR is simultaneously solved, considering the coupling of the HP components and the closed loop of the LD solution. This model, which counts all existing balances of energy, mass, and salt content in various components, determines the condensing temperature employed in the regeneration process at each operational condition. This system-level model, which requires few inputs, is novel and very reliable for evaluating the overall performance of the proposed system in terms of specific dehumidification rates and COP. Case studies were carried out using the annual dehumidification design conditions of five Middle Eastern cities known for their hot and humid climates. For the cities of Sharm El Sheikh and Dammam, respectively, the system achieved promising results with specific dehumidification rates of 130.3 and 172.2 g/(m2.h) and system COPs of 6.38 and 5.67, when the temperature and specific humidity of outside fresh air of (30 °C, 19 g/kg) and (32.8 °C, 23.2 g/kg) were cooled and dehumidified to (20.18 °C, 6.52 g/kg) and (21.0 °C, 6.61 g/kg). Using the regeneration air flow rate as high as possible boosts the performance of the proposed HPLD system, concluding that the system is preferable for all-fresh-air handling units.

Experimental investigation on the dehumidification performance of a parabolic trough solar air collector assisted rotary desiccant system

In areas of high humidity, moisture is a major problem for human comfort and air-conditioning systems. As a green solution to this prevalent problem, a solar assisted rotary desiccant dehumidification system has been proposed for air dehumidification. Through an experimental study conducted, performance evaluation of a parabolic trough solar collector assisted rotary desiccant dehumidification system has been performed based on the parameters including air flow rate, regeneration air temperature, inlet-outlet air temperature, and humidity ratios. Findings indicated that the highest regeneration air temperature supplied by the parabolic trough solar air collector to the dehumidifier was 45.8 °C at a flow rate of 60 m³/h. It was also found that the highest dehumidification efficiency was achieved at a regeneration air flow rate of 80 m³/h. The experimental study clearly proves that parabolic trough solar collectors can successfully provide low-medium temperature thermal energy required during the regeneration process in the desiccant wheel. The findings confirm the potential and explain specific conclusions for the practice of solar thermal driven rotary desiccant wheel system.

Carbon dioxide recovery from a simulated dry exhaust gas by an internally heated and cooled temperature swing adsorption packed with a typical hydrophobic adsorbent

• Internally heated / cooled temperature swing adsorption was tested for CO 2 capture. • Two typical hydrophobic adsorbents were employed for wet emission gas processing. • The separation performance of High Silica Zeolite was explored. • The unique separation behavior of Carbon Molecular Sieves was examined. This study focused on the carbon dioxide (CO 2 ) separation and recovery by an internally heated and cooled thermal swing adsorption process. As part of the preliminary investigation, the CO 2 capture and enrichment performance of carbon molecular sieve (CMS), a typical hydrophobic adsorbent, and high silica zeolite (HSZ), which indicates hydrophobic behavior among zeolites, were examined in a simulated dry exhaust gas. In addition, the hydroscopic adsorbent, CaA type zeolite, was employed for comparison. The effects of the regeneration temperature and the regeneration air flow rate on the separation performance were primarily investigated. In general, the CaA type of zeolite indicated a greater CO 2 concentration performance and recovery ratio due to its relatively larger adsorption capacity. Comparison between HSZ and CMS showed that the CO 2 separation and recovery performance of HSZ were greater than that of CMS. A CO 2 concentration four times higher than that of the feed gas was obtained at a regeneration temperature of 80 °C. Moreover, further enrichment of CO 2 at the desorption outlet was achieved by reducing the regeneration air flow rate to 1/40 of the feed gas of the adsorption process in exchange for lowering the CO 2 recovery ratio. In contrast, CMS could only produce three times greater the concentration of enriched CO 2 when compared to the feed gas. The enriched CO 2 concentration was almost independent of the regeneration air flow rate. This behavior was due to a lower CO 2 adsorption selectivity of CMS; this interpretation was supported by time profiles of desorption gas outlet volume and the CO 2 concentration.

Performance assessment of PCM-based solar energy assisted desiccant air conditioning system combined with a humidification-dehumidification desalination unit

In this study, the performance of a new configuration of the solar-based desiccant air conditioning system integrated with a humidification-dehumidification desalination unit was assessed thoroughly. The main novelty of the study stemmed from the fact that the regeneration air was preheated by a photovoltaic/thermal solar collector unit before it entered the desiccant wheel and the considered solar system was improved by the phase change material to satisfy the heating demands of air conditioning system at nighttime. The effects of the regeneration air flow rate and temperature on the cooling COP of the air conditioning system, freshwater production, and thermal and electrical efficiencies of the photovoltaic/thermal system were examined for a typical day in August. Results showed that the maximum COP of the air cooling system and the best value of distillate water, for an air mass flow rate of 0.78 kg/s were about 0.411and 4.9 l/h, respectively. The maximum electrical power generation capacity and electrical efficiency of the photovoltaic collector were obtained 0.72 kWh, and 13.7%, respectively, at 13 : 00. The heat capacity and efficiency were approximately 3.39 kWh and 65%, respectively at 12 : 00. Finally, the maximum thermal energy, which was delivered to the air conditioning system by the phase change material was about 0.89 kWh.

Exergy analysis and performance improvement of liquid-desiccant deep-dehumidification system: An engineering case study

Engineering case studies are important for providing valuable experience and reference for energy conservation in actual industrial factories with deep-dehumidification requirements. In this study, on-site measurements were conducted to reveal the performance of a liquid-desiccant deep-dehumidification system applied in a photographic film factory. The results reveal the current system has a limited exergy efficiency of 17.7%, because the high heat source temperature (120 °C) required for regeneration induces large parameter differences in heat and mass transfer processes, which dominates the exergy loss of the system. To improve the system performance, the limiting value of the required heat source temperature is investigated. It was revealed that the humidity ratio of the exhaust air determines the required heat source temperature and an increase in regeneration air flow rate helps decrease it. Next, a refined system combined with a heat pump cycle is developed with a near-optimal regeneration air flow rate. In the refined system, a low heat source temperature of 45.6 °C is achieved, which helps to significantly improve the exergy efficiency of the system from 17.7% to 28.6%. Operating the refined system, 33.7% of the system’s running cost can be saved to ensure a cost-effective operation compared with the original system.

Separation and enrichment of CH4 and CO2 from a dry biogas using a thermally regenerative adsorbent-packed heat exchanger

Thermal swing adsorption (TSA) using a heat exchanger packed with an adsorbent material was examined as a means of removing CO2 from a simulated biogas. TSA driven by low-temperature waste heat or solar energy represents an environmentally-friendly gas separation process. In this process, the adsorbent material can be heated indirectly by circulating hot water through a heat exchanger and can operate with a smaller amount of regeneration air than in a conventional TSA system to significantly increase the CO2 concentration at the regeneration outlet. In the present work, carbon molecular sieves (CMS) and a high-silica zeolite (HSZ) were examined with regard to their CO2 adsorption from a simulated biogas containing 60% CH4 and 40% CO2. The effects of the hot water temperature supplied to the adsorber and the regeneration air flow rate on the separation performance were investigated. Increasing the regeneration temperature was found to improve the separation performance, and the HSZ was observed to be more selective for CO2 during the adsorption process. However, the CO2 concentration in the desorption outlet gas was not increased when the regeneration air flow was equal to that of the feed gas. Reducing the regeneration air flow rate to one-tenth the original value significantly increased the CO2 concentration at the desorption outlet while only slightly lowering the CH4 concentration in the product gas. A TSA process incorporating an adsorbent-packed heat exchanger is evidently an effective means of processing biogas, based on poor adsorption of CH4 and strong adsorption of CO2.

A Liquid Desiccant Enhanced Two Stage Evaporative Cooling System—Development and Performance Evaluation of a Test Rig

Desiccant technology is found to be a good alternative to conventional cooling systems. It can provide better thermal comfort under hot and humid climatic conditions. The major component of a liquid desiccant cooling system is the desiccant dehumidifier which controls the latent cooling load. In this paper, a newly developed liquid desiccant enhanced evaporative cooling system has been tested experimentally. The effects of ambient conditions and other parameters on the performance of the system are investigated. The system performance curves which help to determine the air outlet conditions and coefficient of performance (COP) of the system are drawn for a wide range of ambient air humidity ratios (0.010–0.026 kg/kg), ambient air temperature (25–40 °C), process air flow rate (1.5–8.0 kg/m2·s), regeneration air flow rate (1.5–4.5 kg/m2·s), and regeneration temperature (55–85 °C). The results showed that better supply air conditions are achieved for hot and humid climatic conditions with effectiveness of the system largely dependent on process and regeneration air flow rates, regeneration temperature, and humidity ratio of process air. The dehumidification performance is increased by 62% for a change of ambient air humidity ratio from 0.01 to 0.025 kg/kg. The thermal coefficient of performance improved by 50% for the above variation in humidity ratio. This shows that such thermally activated systems are feasible options for hot and humid climatic conditions as indicated by better performance under these conditions.

Performance evaluation of a solar energy assisted hybrid desiccant air conditioner integrated with HDH desalination system

In this study, the performances of a solar energy assisted hybrid desiccant air conditioning system integrated with humidification–dehumidification (HDH) desalination system are numerically investigated. The aim of this study is to benefit from the temperature rise of the regeneration air outside of the desiccant conditioning system as well as the water vapor content in this regeneration air by feeding it to the humidification-dehumidification water desalination unit to produce distillate water. The distillate water productivity, human thermal comfort issues, and energy saving represent the main objective of the present numerical study. The simulated results developed for subsystems are validated with the published experimental results. The effects of regeneration air temperature and flow rate on supply cooled air temperature, distillate water productivity, the cooling coefficient of performance and overall daily coefficient of performance of the proposed system are investigated. The results show that (i) the distillate water productivity increases from 3.175 to 5.011L/h and overall daily coefficient of performance decreases from 4.392 to 3.636 with increasing the regeneration air temperature from 75 to 95 as (ii) the increase in the regeneration air flow rate from 70 to 130 m3/h, increases the distillate water productivity from 2.988 to 4.78L/h and decrease the overall daily coefficient of performance from 4.66 to 3.386. The study demonstrates that the proposed system represents the best options in hot and humid regions.

OPTIMIZATION OF PROCESS PARAMETERS OF PRESSURE-SWING ADSORPTION CYCLE IN A SILICA GEL DESICCANT DEHUMIDIFICATION SYSTEM

Parametric study on pressure-swing adsorption cycle desiccant dehumidification system is a continuous engineering task with the aim of analyzing its effects and attains target quality of dry air for an industrial process. An experimental setup is developed with a dehumidification tower, regeneration tower,and flow control valve.The effect of process air inlet moisture content, cycle time ratio, and regeneration air flow rate on the adsorption performance is studied to evaluate the potential of the dehumidification system suitable for drying applications. The optimal dehumidification parameters are found, and a regression equation is also developed for the process. It is concluded that, process air inlet moisture is the most influencing parameter compared to regeneration air flow rate and cycle time ratio for the silica gel desiccant dehumidification system.

Numerical analysis of a desiccant system with cross-flow Maisotsenko cycle heat and mass exchanger

This paper presents a numerical analysis of the desiccant air conditioning system with a cross-flow Maisotsenko cycle (M-Cycle) heat and mass exchanger (HMX). Presented mathematical models of the desiccant wheel and HMX are based on the ε-NTU method. The mathematical model of the desiccant wheel is also supplemented with algorithm allowing the accurate approximation of the initial conditions to reduce the calculation time. The novel system was compared with a conventional solution to show its application potential. The main advantage of the novel system is that it can provide comfort condition even with less effective dehumidification. Also impact of several operational factors (i.e. inlet air temperature and humidity, outdoor and regeneration airflow rate and rotational speed) on the performance of the system were investigated. The analysis of novel system were performed under assumption that the desiccant wheel is regenerated with air heated to the relatively low temperature which can be produced with solar panels in typical moderate climate conditions.

Parametric study on silica gel regeneration by hot air combined with ultrasonic field based on a semi-theoretic model

To improve the adaptability of the proposed semi-theoretic model in our previous paper (Ref. [1]), the equations of heat and mass transfer coefficient dependent on the regeneration temperature, the air flow rate, the ultrasonic power and frequency are formulated based on a series of experimental data. The semi-theoretic model with the empirical equations of heat and mass transfer coefficient has been validated by experiments. Afterward, the ultrasonic-assisted regeneration for a silica gel packed bed is simulated with the theoretic model under a wide range of conditions, i.e., the inlet air temperature and humidity ranges from 35 to 80 °C and from 0.01 to 0.035 kg/(kg dry air), respectively; the regeneration air flow rate from 0.1 to 1.5 m/s; the acoustic frequency from 20 to 35 kHz combined with the power from 20 to 80 W; the particle size of silica gel in the bed from 1.0 to 7.0 mm. The key variables during the ultrasonic-assisted regeneration are then investigated based on the simulation data, including the acoustic pressure distribution and corresponding oscillation velocity induced in the packed bed, the temperature and moisture ratio distribution in the packed bed and the enhancement of silica gel regeneration brought by ultrasound.

Experimental analysis and regression prediction of desiccant wheel behavior in high temperature heat pump and desiccant wheel air-conditioning system

• The desiccant wheel is regenerated by heat pump without additional heat. • Regeneration temperature and outdoor air humidity ratio influence wheel performance. • Numerical models for wheel are established based on regression theory. • Predicted values and experiment data are compared and agreement is good. The objectives of this study are to evaluate the performance of desiccant wheel (DW) in the running system and obtain the useful data for practical application. The combined influences of multiple variables on the performance of desiccant wheel are investigated based on evaluating the indexes of moisture removal capacity, dehumidification effectiveness, dehumidification coefficient of performance and sensible energy ratio. The results show that higher effect on the dehumidification is due to the regeneration temperature and outdoor air humidity ratio rather than the outdoor air temperature and the ratio between regeneration and process air flow rates. A simple method based on multiple linear regression theory for predicting the performance of the wheel has been proposed. The predicted values and the experimental data are compared and good agreements are obtained. Regression models are established which can easily predict the behavior of DW and also helpful for developing a DW performance map for the further optimization of automatic control of the system.

Experimental analysis on performance of high temperature heat pump and desiccant wheel system

In order to solve the problem of high energy consumption for regeneration of desiccant wheel in the rotary desiccant system, high temperature heat pump and desiccant wheel (HTHP&DW) system and corresponding air conditioning unit is built and tested in the extensive thermal hygrometric environment. When the mixture refrigerant BY-3 is involved in the air source heat pump, the supply air temperatures are in the range as expected except that when in the extreme hot environment (above 36°C), dehumidification capability are satisfied and the regeneration temperatures can satisfy the regeneration requirement of desiccant without additional heat. It is also found that outdoor air temperature, humidity ratio and regeneration air flow rate have great impact on the performance of heat pump based on the coefficient of performance (COP) evaluated. COP is not quite high, as the maximum value is 2.26 for heat pump and 2.08 for whole system respectively. Hence several suggestions are made for optimizing the system which is also helpful for facilitating the development of mature product. As a conclusion, HTHP&DW system could be a potential alternative with effective operation which can be promoted in most areas of China based on the result of our experiment.

Effect of rotational speed on the performances of a desiccant wheel

In recent years, the boost towards the reduction of electrical loads for air conditioning and the decentralization of energy conversion devices are determining an increasing interest in small scale trigeneration systems fueled by natural gas (“gas cooling”), able to shift energy demand in summer from electricity to gas, at the same time allowing the exploitation of natural gas surplus during the warm season. A technology that meets these requirements is represented by desiccant-based dehumidification systems, in which thermal energy for regeneration can be provided by a small scale cogenerator; the main component of these systems is the desiccant wheel, whose performances, in terms of humidity reduction and process air outlet temperature, depend on several operational parameters. The rotational speed of the desiccant wheel is widely recognized as a crucial parameter: if the wheel rotates too fast, the desiccant material does not have enough time to remove the moisture, while if the wheel rotates too slowly, saturation could occur. As a result, there must exist an optimal rotational speed, depending on the operating conditions, that guarantees the best dehumidification performance. Rotational velocity of the desiccant wheel influences the process air temperature exiting the desiccant wheel too; therefore it should be chosen in order to contemporary obtain a high dehumidification performance and an enough low outlet temperature, to reduce the cooling load on the cooling device, in particular if a conventional vapor compression chiller is used, as often occurs in high humidity climates. In this paper, experimental tests on a silica gel desiccant wheel, in order to highlight the effect of rotational speed on its performance, are shown. The adsorbent material is regenerated by thermal energy up to 65°C. The experimental results were used to calculate some of the most representative performance parameters for the wheel, that are the dehumidification effectiveness, the dehumidification coefficient of performance (DCOP) and the sensible energy ratio (SER). Finally, the influence of process air inlet temperature and humidity, regeneration temperature and the ratio between the regeneration and process air flow rates on the optimal rotational velocity is discussed. It was found that, for the analyzed desiccant wheel, the velocity that optimizes the dehumidification performances varies in the range 5–10 revolutions per hour, depending on operating conditions, while SER monotonically increases with rotational velocity.

Exponential correlations to predict the dependence of effectiveness parameters of a desiccant wheel on the airflow rates and on the rotation speed

The desiccant wheel is a key component in solid-desiccant systems. At present, it is difficult to access a component model that can represent the behaviour of commercialised desiccant wheels with enough accuracy.In this work, it is investigated the feasibility of a simplified simulation method based on the effectiveness concept. The pair of independent effectiveness parameters based on the changes of enthalpy and of the ratio of the partial to the saturation vapour pressures is adopted instead of the combined potentials.Extensive parametric studies are conducted using the software of a manufacturer and a detailed numerical model to generate reference data. Exponential-type correlations are investigated to account for the influences of the process and regeneration airflow rates, balanced or unbalanced, and of the rotation speed on the effectiveness parameters. The predicted results provided by the correlations are compared with reference data, separately or combined with the recently developed interpolation approach that accounts for the influence of variable inlet states of both airflows. Cases are identified with an acceptable agreement demonstrating that the correlations can be used with great advantages in the generalised dynamic analysis of systems integrating a desiccant wheel.

Experimental analysis on the dehumidification and thermal performance of a desiccant wheel

The advantages of desiccant-based air conditioning systems, compared to conventional ones based on the dehumidification by cooling, have been highlighted in many research papers. The energy saving and the reduction of the environmental impact are higher when the desiccant material is regenerated by using “free” thermal energy (for example, waste heat from cogenerators or solar energy). Further investigation on the performance of the desiccant wheel is useful: therefore, in this paper, an experimental analysis on this component is presented, with particular attention to the variation of the performance as a function of the process and regeneration air flow rates. The desiccant material is regenerated by means of low-temperature thermal energy (about 65 °C) from a microcogenerator. Both the experimental results obtained by the authors and the data provided by the manufacturer have been used to calculate some performance parameters, and a satisfactory agreement has been obtained. The performance parameters have been evaluated as a function of the regeneration temperature, the inlet process air humidity ratio and temperature and the ratio between the regeneration and process air flow rates, in both the cases of fixed regeneration temperature and fixed regeneration thermal power: the results show that higher influence on the dehumidification process is due to the regeneration temperature rather than to the regeneration air flow rate. Moreover, the process air humidity ratio and regeneration temperature influence the desiccant wheel performance more than the process air temperature.

Effectiveness Parameters for the Heat and Mass Transfer in a Desiccant Wheel

The desiccant wheel is the key component in a solid-desiccant system for air dehumidification. The heat and mass transfer phenomena occurring within the porous channel walls of the wheel and with the airflow are strongly coupled, and some properties of the airflow and of the desiccant medium exhibit important changes during the sorption/desorption processes. The dynamic analysis of such devices integrated in non-conventional HVAC&R systems can be easily done by a project designer using the NTU-effectiveness method, provided that appropriate correlations for two independent effectiveness parameters are available. In this work, the performance of a desiccant wheel was evaluated by numerical modelling the cyclic behaviour of a representative channel of the hygroscopic matrix. The physical model adopted takes into account the gas-side and solid-side resistances, as well as the simultaneous heat and mass transfer coupled with the water adsorption/desorption process in the channel wall domain. Two phases co-exist in equilibrium inside the desiccant porous medium, the equilibrium being characterized by sorption isotherms. The desiccant medium considered is silica gel RD. In the numerical model, the airflow is treated as a bulk flow, and its interaction with the wall channel matrix is represented by appropriate convective heat and mass transfer coefficients. Two independent effectiveness parameters were defined. A set of cases was numerically simulated and the results were analysed to assess the dependence of those effectiveness parameters on the process and regeneration airflow rates and on the channel length. As a conclusion, novel empirical correlations are here purposed.

Model‐Based Energy Efficiency Optimization of a Low‐Temperature Adsorption Dryer

AbstractLow‐temperature drying is important for heat‐sensitive products, but at these temperatures conventional convective dryers have low energy efficiencies. To overcome this challenge, an energy efficiency optimization procedure is applied to a zeolite adsorption dryer subject to product quality. The procedure finds a trade‐off between the improved drying capacity due to dehumidification and energy expenditure due to regeneration while incorporating product drying properties. By optimizing the regeneration air inlet temperature, drying air, adsorbent, and regeneration air flow rates as well as sensible and latent heat recovery from the regenerator exhausts, the energy efficiency is improved by up to 45 % compared to the state‐of‐the‐art. The high mass transfer effect of high temperatures is utilized in the regenerator to boost dehumidification while isolating the heat‐sensitive dried product from the quality‐degrading effect.

Experimental investigation on a solid desiccant system integrated with a R407C compression air conditioner

In the present work, experimental performance data of a solid desiccant based hybrid air conditioning system are presented. The system consists of a packed bed solid desiccant integrated with a R407C conventional vapor compression refrigeration system. Experiments are carried out during dehumidification operation mode for various operating parameters such as; desiccant mass on shelves (5, 10 and 15 kg), air mass flow rate (7.4 and 10.2 kg/min), shelves number (1, 2 and 3) and three values of shelves span (7, 14 and 28 cm) at evaporator air inlet conditions of 28 °C DBT and 66% RH, condenser air inlet volume flow rate of 850 m 3/h and temperature of 35 °C. The reactivation of the desiccant at different regeneration temperatures and air flow rates as well as desiccant masses is also investigated. During the dehumidification mode, the average system coefficient of performance increases by 6.2% and 1.61% when the mass of desiccant increases from 5 to 10 kg and from 10 to 15 kg, respectively. The enhancement in the coefficient of performance is 6.2% due to increasing the air mass flow rate from 7.4 to 10.2 kg/min. Increasing both shelves number and span yields to a reduction in the adsorption rate that can be extracted by the desiccant material in the ranges of considered operating conditions. The regeneration temperature and the air flow rate of regeneration have significant effects on the reactivation process. It was found that, with increasing the mass flow rate of regenerated air from 7.4 to 10.2 kg/min produces a reduction in regeneration time by 87.5% and an augmentation in the desorption rate by 16% after 10 min of regeneration. In addition, with escalating the regeneration temperature from 45 to 55 °C, the reactivation time reduces by 25%. Reported results revealed that solid desiccant based hybrid air conditioning system reduces the compressor electric power and the number of electric unit (kW h) by 10.2%.

Investigation on a new liquid redox method for H2S removal and sulfur recovery with heteropoly compound

An innovative approach to H2S removal and sulfur recovery involving the use of heteropoly compounds was investigated systematically in this study. The favorable redox potential of sodium phosphomolybdate (HPAS) makes it thermodynamically feasible for it to oxidate H2S to elemental sulfur and to be regenerated by air. The presence of Na2CO3 in HPAS system can improve the absorption rate of H2S, and the contribution of NaCl lies in its catalytic effect on HPAS regeneration. The absorption efficiency of HPAS decreases slightly with the increase in operation temperature and good absorption effect can be achieved at room temperature. The regeneration time decreases with the increase in absorbent concentration, temperature and regeneration air flow rate, and it increases with the increase in feed gas H2S concentration. HPAS is still much stable in its chemical property during multiple absorption–regeneration cycles, the desulfurization product is confirmed to be elemental sulfur. The chemical reaction between HPAS and H2S was proposed to be: H2S+Na3PMo(VI)12O40→S ↓+Na3H2PMo(VI)10Mo(V)2O40 i.e. there are two Mo(VI) atoms reduced to Mo(V). As a further work, the characteristic and efficiency of H2S removal with HPAS solution systems were investigated in a counter-current packed column. The effects of absorbent concentration, operation temperature, inlet H2S concentration, flow rate of inlet gas stream and absorbent spray density on the absorption of H2S are presented. The absorbent consisting of HPAS and additives including NaVO3, Na2CO3 and NaCl shows better performance than that of HPAS only. Although the H2S removal efficiency of HPAS absorbent system is several percentage lower than that of Fe–EDTA during 12 absorption–regeneration cycles, the sulfur content (i.e. elemental sulfur) in the sedimentation product of the former was confirmed to be much higher than the latter with the aid of energy Spectrum. In addition, the absorbent loss of the former is much lower too.