Regeneration Of Silica Gel Research Articles

Performance investigation on dual bed adsorption chiller integrated with a partially covered N-PVT collector

The theoretical performance investigation of the adsorption chiller system integrated with a partially covered N-PVT Collector is mathematically modeled and presented in the paper. The study employs a MATLAB-Simulink integrated interface, and the silica gel-water combination serves as the working pair. The average weather conditions of Shiv Nadar Institute of Eminence for the month of May are taken into account the study. The investigation shows that solar energy integrated with an adsorption cooling system could efficiently provide a cooling effect. The results suggested that, due to the direct integration of the PVT with the chiller system, the influence of cycle operation is significant at the minimum and maximum solar radiation times. An optimization research for the optimal number of collectors for silica gel regeneration revealed that using N = 5 collectors results in an outlet hot water temperature range of 110 0C. During operation, the maximum adsorption capacity of 0.21 kg of water/Kg desiccant is obtained, for providing an adequate cooling effect. The system achieved a specific cooling power of between 50 and 200 W/kg during the process, and a coefficient of performance between 0.15 and 0.23.

Regenerated Silica Gel for Isolation of Ethyl p-Methoxycinnamate from Kaempferia galanga rhizome

The main component from Kaempferia galanga rhizome extract is known as ethyl p-methoxycinnamate. Column chromatography using silica gel is one of the commonly used method for obtaining high purity of ethyl p-methoxycinnamate from K. galanga rhizome extract. In this study, the regeneration of silica gel then utilized for checking its reusability to undergo the isolation of ethyl p-methoxycinnamate. The silica gel was regenerated by utilizing two methods: (a) the direct furnace at 600 ⁰C; (b) the stirring process with aqueous solution of sulfuric acid which followed by furnace at 600 ⁰C. K. galanga rhizome extract was obtained under maceration by hexane. Regenerated silica gel was characterized by XRF and FTIR. The ethyl p-methoxycinnamate content was determined by UV-Vis spectrophotometry. The regenerated silica gel showed almost similar characteristic with the original commercial silica gel. The K. galanga rhizome extract after underwent column chromatography with regenerated silica gel showed high stability. This result ensured the utilization of regenerated silica gel can be considered for isolation of ethyl p-methoxycinnamate from K. galanga rhizome extract.

Pressure driven adsorption cycle integrated with thermal desalination

The canned food market is growing at an annually average rate of 3.6% due to easy access and awareness of dietary requirements, leading to a surge in water withdrawal and an estimated supply-demand gap of 40% by 2030. The conventional desalination processes are not sustainable due to high energy requirements and chemicals injection. The adsorption cycle is an emerging technology for desalination due to its temperature operation. It has many advantages over conventional desalination processes including integration synergy to improve overall performance. The conventional AD cycle processes, however, have lower performance due to inefficient packing of adsorbent in the beds and heat transfer losses to their massive heat exchangers. In this article, we propose an innovative pressure driven adsorption (PDAD) cycle to overcome conventional AD cycle limitations. In PDAD, firstly, low pressure steam is used to regenerate the adsorbent which eliminates the huge infrastructure requirement of water circulation and secondly, steam selectively extracts water vapours from pores, reducing energy consumption. We have tested the PDAD pilot and showed successful regeneration of silica gel at motive steam pressure of 2–5 bar. We also demonstrate that discharge steam from the PDAD at 65 °C can be used as a heat source for a multi effect desalination system when operating in hybrid mode to overcome its operational limitations. Our experiments show that the MED + PDAD cycle increases water production by up to 22% as compared to an earlier hybrid MEDAD cycle. The proposed system has excellent thermodynamic synergy with the combined CCGT power and desalination plant, where low-pressure bleed steam can be utilized more efficiently.

Application of ultrasound in regeneration of silica gel for industrial gas drying processes

Industrial gas dehumidification contributes to a considerable portion of the total industrial energy consumption. Depending on the desired level of dryness, solid desiccants can be a more suitable dehumidification method compared to the conventional dehumidification processes. In this study, the ultrasound-enhanced regeneration of silica gel as a substitute to conventional heating methods is investigated. To analyze the energy-savings effect of applying ultrasound a method of constant total power levels of 20 and 25 (W) corresponding to total specific power levels of 327 and 409 was adopted and for each Watt of applied ultrasonic power, the same amount was deducted from thermal power. The moisture content and regeneration temperature were measured and compared in ultrasound-assisted and non-ultrasound (heat-only) regeneration processes. Experimental results showed that applying ultrasound along with thermal power improves the regeneration process and reduces the energy required to regenerate silica gel by as much as 26%. Various transport modes contributing to mass diffusion in porous media are analyzed and an apparent diffusion coefficient for porous media that includes ultrasonication effects is proposed. Regarding regeneration temperature, with application of ultrasound, regeneration at lower temperatures by as much as ∼11% was achieved.

Numerical simulation of heat and moisture transfer in fibrous porous media dehydration process with ultrasound assisted

In recent decades, the enhancement of ultrasound on heat and mass transfer in the processes of food processing, waste sludge dehydration and silica gel regeneration has been confirmed by experiments and simulations. The effect of ultrasound in the dehydration process of fibrous porous media has been experimentally studied, however, the theoretical simulation is still lacking, which will be presented in this paper. In the first place, the effects of ultrasound frequency and intensity on ultrasound propagation in fibrous porous media are investigated. For the pressure and deformation produced by ultrasound propagation in porous media, ultrasound intensity has an important influence on their magnitude, and their distribution trend is also affected by ultrasound frequency. Then, the fundamental heat and mass transfer process in fibrous porous media with ultrasound assisted dehydration is studied and the mathematical model is validated by experiments in terms of the drying curves under different ultrasound intensity. By numerical simulation, the distribution of liquid transmission velocity, temperature and dry basis moisture content are obtained which is useful to further analyse the mechanism of ultrasound enhancement in fibrous porous media dehydration.

Experimental study of silica gel/water adsorption cooling system using a modified adsorption bed

In the present work, an experimental study of a modified adsorption refrigeration unit is obtained. Silica gel and water are used as a working pair in the adsorption refrigeration unit. Hot air is used for silica gel regeneration. The effect of evaporator pressure, evaporator inlet water temperature, initial silica gel temperature, and hot air regeneration temperature and mass flow rate on the unit coefficient of performance is studied. It has been found that increase of hot air regeneration temperature and inlet evaporator temperature increases the unit refrigeration capacity and coefficient of performance. On the other hand, a decrease of silica gel temperature and evaporator pressure increases the unit refrigeration capacity and coefficient of performance. The results confirm that this kind of adsorption chiller is an effective refrigerating machine; it can be used for air conditioning or producing chilling water since it makes a reduction in the chilling water temperature more than 10°C in minutes.

Mechanism study on the enhancement of silica gel regeneration by power ultrasound with field synergy principle and mass diffusion theory

The enhancement of silica gel regeneration by power ultrasound has been validated by a series of experiments in our previous studies, but there still lacks theoretical basis for illustrating its mechanism. In this paper, the mechanism of ultrasound-enhanced regeneration has been explored. Firstly, the benefit of ultrasonic mechanical effect to the enhancement of regeneration has been illustrated by the field synergy principle. The average synergy degree (κ¯, only considering intersection angle between the velocity and the temperature gradient) and the average overall synergy degree (κ¯overall, considering local values of velocity and temperature gradient based on κ¯) in terms of the near wall region are suggested for analysis, and they are obtained based on the k–omega model which is suitable for the near wall free-shear flow velocity predicting. Results manifest that the ultrasonic mechanical effect can significantly enlarge the synergy degrees between the temperature and the velocity field around the particle, and this can be used to explain the enhancement of convective heat and mass transfer on the gas side due to the mechanical effect of ultrasound. Afterwards, a moisture diffusion model is developed to investigate spatial distributions of moisture ratio and temperature in a silica gel particle as well as its surface equilibrium humidity during the regeneration with and without ultrasound. Results show that ultrasonic heating effect can lead to an increase in the average temperature and moisture diffusivity in the silica gel particle, and this confirms the contribution of ultrasonic heating effect to the enhancement of silica gel regeneration.

Adsorption of octamethylcyclotetrasiloxane on silica gel for biogas purification

Biogas can be used as a fuel for electricity conversion. However, volatile organic silicon compounds (including siloxanes) in biogas severely damage combustion engines or solid oxide fuel cells. Three adsorbents of different nature were tested for octamethylcyclotetrasiloxane (D4) removal and silica gel (SG) proved to be the most efficient. It was shown that SG adsorption capacity is in the order of 250mgD4/gSG and the adsorbent bed height has little influence on this adsorption capacity. In the presence of water (relative humidity of 70%), the adsorption capacity was lowered by 90% due to competitive effects and preferential adsorption of water. An increase of the temperature of roughly 20°C also lowered the adsorption capacity but the decrease was less than 15%. Moreover, SG regeneration by heating was only partial, probably due to siloxane polymerization on SG.

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.

Separation of ultrasonic contributions and energy utilization characteristics of ultrasonic regeneration

The method of applying ultrasound to silica gel regeneration process has been proved to be able to improve regeneration efficiency and reduce regeneration temperature. The average regeneration rate can be increased by 10% and the benefits should owe to the special “vibration effect” and “heating effect” induced by ultrasound. In this article, a dynamic one‐dimensional mathematical model, validated by experiments, has been developed. It is then used to investigate energy utilization efficiency of the ultrasonic regeneration and respective contribution ratio of the two ultrasonic effects. The results show that the contribution ratio of vibration effect dominates and the energy utilization efficiency of silica gel regeneration with ultrasound can be 1% higher. The ultrasonic regeneration is more energy‐saving when the contribution ratio of vibration effect is greater. The results also show that the enhancement of regeneration brought by ultrasound is not a simple sum of their respective contribution. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1843–1853, 2014

Investigation of the process of regeneration of silica gel by drying it in the super high-frequency electromagnetic field

There were made experimental studies of the drying kinetics of porous silica gel with different initial humidity, and investigated the change in temperature of the material during this process. On the basis of experimental data the parameters of drying process with microwave energy supply, drying time to the equilibrium moisture (≤ 0,5 %), the time limit for processing without disrupting properties of silica gel, as well as temperature adsorbent at the end of the drying process were revealed.

Theoretical model on the heat and mass transfer in silica gel packed beds during the regeneration assisted by high-intensity ultrasound

In the present work, a theoretical model is reported on the heat and mass transfer in silica gel packed bed during the regeneration process by using hot air combined with high-intensity ultrasound. The model consists of two parts: one is about the sound propagation in porous media; the other is about the fundamental heat and mass transfer process in the silica gel (particle) packed bed. The theoretical model is then validated by experiments in terms of the exit air temperature and humidity (kg/(kg dryair)) under different conditions of regeneration. The experimental error due to the measuring instruments is estimated to be within 0.4% and 3.5%, respectively, for the exit air temperature and humidity. The comparison between theoretical and experimental data shows that the mean relative errors (MREs) of the calculated exit air temperature and humidity compared with the experimental ones are mostly within 2.0%, which manifests the model developed in this study has a favorite agreement with the experiments. The theoretical model will help us conduct a further parametric analysis on the regeneration process in the presence of an ultrasonic field, and have a better understanding of the mechanism of enhancement of silica gel regeneration brought by the high-intensity ultrasound.

Effect of applying ultrasonic on the regeneration of silica gel under different air conditions

To decrease the regeneration temperature of silica gel (an excellent desiccant), the non-heating regeneration method with ultrasonic has been proposed and studied in our previous papers in which the effect of acoustic parameters as well as drying air temperature on the regeneration process was investigated experimentally by desiccant-weighing method. In this paper, the effect of drying air temperature and humidity on the ultrasonic-assisted regeneration and the following adsorption features of silica gel will be further studied by measuring the states of drying air. Different inlet air conditions, i.e., 40, 50, 60 and 70 °C in temperature combined with 0.01, 0.015 and 0.02 kg/(kg dry air) in humidity, are designed for the experimental study. The mass of dry silica gel sample used in this study is measured as 175 ± 0.1 g, and the acoustic frequency and power of ultrasound are 23 kHz and 60 W, respectively. The two indexes, AERR (Average Enhancement Ratio of Regeneration) and AERA (Average Enhancement Ratio of Adsorption), are used to estimate the effect of ultrasonic on the regeneration and the following adsorption of silica gel. The experimental results show that the effect of ultrasound on the regeneration will first rise and then decline when the drying air temperature rises from 40 °C to 70 °C, while it decreases with the drying air humidity increasing from 0.01 to 0.02 kg/(kg dry air). Similar regular patterns can be found for the effect of regeneration assisted by ultrasonic on the adsorption of silica gel. Meanwhile, a theoretical model is developed to predict the regeneration rate of silica gel assisted by ultrasound and validated by experiments.

Investigation on the kinetic models for the regeneration of silica gel by hot air combined with power ultrasonic

Regeneration of dehumidizers (a typical drying process) is the most important stage in the working cycle of desiccant system. Ultrasonic technology, as a non-heating method, can enhance drying kinetics and improve energy utilization efficiency in the drying process. This work has made an investigation on five different drying models, i.e., the Lewis, the Henderson & Pabis, the Logarithmic, the Weibull and the Gaussian model, that quantify the drying kinetics of silica gel during the regeneration by hot air combined with power ultrasonic according to the experimental data. The experiments were performed under different drying air temperatures (i.e. 45 °C, 55 °C, 65 °C and 75 °C) plus power ultrasonic with three kinds of frequencies (i.e. 21 kHz, 26 kHz and 38 kHz) and three power levels (20 W, 40 W and 60 W). The models were identified by fitting the experimental data with Matlab’s curve fitting tool, and the suitability of these models for predicting the moisture ratio evolution in silica gel during the regeneration was evaluated by the percent error (PE, %). The results showed that the Gaussian and the Weibull model were much more accurate than the other ones in describing the drying kinetics of silica gel assisted by the power ultrasonic. The parameter, β, in the Weibull model, which is like the drying rate constant ( K) in the semi-theoretical models (e.g., the Lewis, the Henderson & Pabis and the Logarithmic model), can be found to have a regular relation with the drying temperatures, and hence, will be more convenient for modeling.

The energy-saving characteristic of silica gel regeneration with high-intensity ultrasound

The energy-saving characteristic of silica gel regeneration with power ultrasonic was analyzed by introducing the conception of specific energy consumption. For the purpose, the experiments of silica gel regeneration with 21-kHz power ultrasound were performed under different drying air temperatures (i.e., 35, 45, 55 and 65 °C) combined with different acoustic power levels (i.e., 0, 20, 40 and 60 W). And the energy saving ratios of the ultrasonic-assisted regeneration were studied by the method of ANOVA (Analysis of Variance) and compared among different conditions. The influences of acoustic power and drying air temperature as well as the target moisture ratio (at which the regeneration process ended) on the total specific energy consumption (TSEC) and the excess specific energy consumption (ESEC) were also discussed. The results indicate that all the factors (drying temperature, ultrasonic power level and the interaction between the drying temperature and the power level) have a significant ( P < 0.05) influence on the energy saving ratio, among which the influence of drying temperature is the most significant ( P < 0.05). According to the analysis of specific energy consumption, the optimal drying conditions aiming at the minimum energy use can be obtained. For the present experimental conditions, the condition of 55 °C (drying temperature) and 60 W (acoustic power level) can achieve the lowest TSEC and ESEC. In addition, different thresholds of power level are required to achieve the energy-saving effect due to the application of ultrasonic in the regeneration. The method of specific energy consumption can be also used for the energy analysis of the new regeneration technology in the scale-up study.

Influence of ultrasonic frequency on the regeneration of silica gel by applying high-intensity ultrasound

Abstract Ultrasonic frequency is the key parameter considered in ultrasonic applications. In order to provide a basic knowledge about the influence of ultrasonic frequency on the regeneration of silica gel assisted by power ultrasound, the experiments about silica gel regeneration under the radiation of constant-power (60 W) ultrasound with different frequencies (i.e., 23, 27, and 38 kHz) and that without ultrasound were carried out at different regeneration temperatures (i.e., 35, 45, 55, and 65 °C). The experimental results showed that the lower frequency was beneficial for the application of power ultrasound in the regeneration of silica gel. The fact was theoretically explained by the ultrasonic power attenuation model which indicates that the ultrasound of lower frequency will lead to more uniform energy distribution and hence achieve higher efficiency of utilization. Meanwhile, the effect of ultrasonic frequency on silica gel regeneration would be influenced by the regeneration temperature and the moisture ratio in silica gel. As investigated in this study, the effect of ultrasonic frequency on the regeneration would be more significant at the lower regeneration temperature or at the higher moisture ratio in silica gel. In addition, the mean regeneration speed model of silica gel dependent of the regeneration temperature and the ultrasonic frequency was established according to the experimental data.

Parametric Study of High-intensity Ultrasonics for Silica Gel Regeneration

The use of ultrasonic power in the regeneration of silica gel may be very promising because it helps to improve the regeneration efficiency at the lower regeneration temperature. This work is to study experimentally the effects of ultrasonic power and frequency on the regeneration of silica gel using the ultrasound at different regeneration temperatures (i.e., 45, 55, 65, and 75 °C). Three kinds of frequencies (i.e., 21, 26, and 35 kHz) combined with different power (i.e., 0, 20, 40, and 60 W) of ultrasound were employed to perform the experiments. The moisture change in the silica gel during the ultrasonic regeneration was modeled by the Page equation, and the effective moisture diffusivity was estimated through the diffusion equation that is based on the Fick’s second law. Three parameters, including the enhanced rate (ER) of regeneration, the conditioned regeneration time (CRT), and the energy-saving rate (ESR), are suggested to evaluate the effect of ultrasonic power and frequency on the regeneration....

Feasibility study on power ultrasound for regeneration of silica gel—A potential desiccant used in air-conditioning system

A new regeneration method using power ultrasound was put forward to overcome the limitations of silica gel in air-conditioning applications, such as high regeneration temperature and low regeneration efficiency. The technical feasibility of the new method was validated experimentally and demonstrated in detail from different sides. The experiments were performed under different regeneration temperatures, i.e. 45 °C, 55 °C, 65 °C and 75 °C. The power and frequency of ultrasound applied in this experimental study was set as 40 W and 26 kHz, respectively. The three indicators, including the regeneration degree (RD), enhanced rate of regeneration (ER) and energy-saving rate (ESR), were suggested to evaluate the effect of power ultrasound in the regeneration. The Crank’s diffusion model was used for the calculation of the moisture diffusivity in silica gel, and the Arrhenius equation for the determination of energy activation of moisture desorption on silica gel. The analysis results prove that the introduction of high-intensity ultrasound to the regeneration of silica gel can help to improve the regeneration efficiency and reduce regeneration energy. The benefits should owe to the special ‘heating effect’ and ‘micro-vibration effect’ caused by power ultrasound that can enhance the moisture diffusivity in silica gel and lower the activation energy of moisture desorption on silica gel.

Regeneration of Silica Gel Using High-intensity Ultrasonic under Low Temperatures

This paper presents the experimental study on the regeneration of silica gel using ultrasonics under low-temperature conditions. Four kinds of regeneration temperatures, including 35, 45, 55, and 6...

Integration of a rotary desiccant wheel into a hot-air drying system: Drying performance and product quality studies

A desiccant rotary wheel was coupled with a hot-air drying system and used to dry coarsely chopped coconut pieces. Silica gel was selected as the desiccant material. The drying performance and end color of the dried coconut were examined and compared with coconut dried in a pure hot-air drying system. The results showed that the desiccant dehumidification system can work properly in removing water vapor from humid drying air, resulting in significantly shortened drying time and a higher drying rate than a pure hot-air system. However, energy consumption was higher, mainly due to the energy required for silica gel regeneration. The color of the dried coconut was affected by all drying conditions, but the most important parameter causing the product to become considerably darker was the relative humidity of the inlet drying air.