The aim of this paper was preliminary design of the process for low-temperature coal tar hydrocrackmg m supercritical gasoline based on Aspen Plus with the concept of energy self-sustainability. In order to ensure the...The aim of this paper was preliminary design of the process for low-temperature coal tar hydrocrackmg m supercritical gasoline based on Aspen Plus with the concept of energy self-sustainability. In order to ensure the correct- ness and accuracy of the simulation, we did the following tasks： selecting reasonable model compounds for low-tem- perature coal tar; describing the nature of products gasoline and diesel accurately; and confirming the proper property study method for each block by means of experience and trial. The purpose of energy self-sustainability could be pos- sibly achieved, on one hand, by using hot stream to preheat cold stream and achieving temperature control of streams, and on the other hand, by utilizing gas （byproduct of the coal tar hydrocracking） combustion reaction to provide energy. Results showed that the whole process could provide a positive net power of about 609 kW-h for processing the low- temperature coal tar with a flowrate of 2 268 kg/h. The total heat recovery amounted to 2 229 kW-h, among which 845 kW＇h was obtained from the gas combustion reaction, and 1 116 kW＇h was provided by the reactor＇s outlet stream, with the rest furnished by hot streams of the products gasoline, diesel and residue. In addition, the process flow sheet could achieve products separation well, and specifically the purity of product gasoline and diesel reached 97.2% and 100%, respectively.展开更多
Membrane distillation technology is a new type of efficient separation technology that combines traditional distillation technology and membrane separation technology. In the study, applications of membrane distillati...Membrane distillation technology is a new type of efficient separation technology that combines traditional distillation technology and membrane separation technology. In the study, applications of membrane distillation technology in thermal engineering and refrigerating engineering with typical energy transformation process were presented. Desorption and regeneration process of saline solution by vacuum membrane distillation was proposed on the basis of the concentration and separation properties of membrane distillation. Membrane distillation technology could be used in lithium bromide absorption refrigeration system, energy storage system, and the regeneration process of liquid desiccant solution in temperature-humidity independent control air-conditioning system. The aim of the applications was to use the low-grade energy such as waste heat, solar energy and geothermal energy adequately and to improve the available temperature difference of heat source. According to latent heat transfer and thermal conduction across the membrane in direct contact membrane distillation process, a novel membrane heat exchanger with both heat transfer and mass transfer processes was proposed. The heat exchanger could be used as the solution heat exchanger of lithium bromide absorption refrigeration system and as the special heat exchanger that recovered heat and pure water simultaneously. Some feasible process flows about the applications of membrane distillation technology to energy transformation process were listed and analyzed. Finally, future research emphases were indicated.展开更多
Large reciprocating compressors are important equipment used in a wide range of process industries. Most of these compressors have huge power requirements and their capacity often needs to be regulated. Advanced techn...Large reciprocating compressors are important equipment used in a wide range of process industries. Most of these compressors have huge power requirements and their capacity often needs to be regulated. Advanced technologies in compressor capacity control are effective approaches for saving large amounts of energy in process industries. This paper reviews the basic theories and the state of the art of the capacity control technologies. In particular, a compressor working procedure is first presented using an analogy to the pulse signal concept. Compressor capacity control methods are classified into pulse frequency modulation and pulse amplitude modulation from a perspective of pulse signal processing. The mechanisms and feasibility of some important methods, including dead volume variable control, partial-stroke and full-stroke suction valve opening, are reviewed. Based on the pulse signal concept, a duty cycle regulation method for capacity control is introduced, and the performance and implementation of the new method are compared with those of the existing suction valve opening methods. The duty cycle regulation method has integrated advantages over the other methods in terms of regulating precision, pressure stability, energy saving and reliability. All the suction valve opening methods can cause gas reflux, resulting in the so-called breathing effect. The breathing effect has negative effects on regulation performance and compressor security, which needs further investigation in the future.展开更多
A new method for the solution of population balance equations(PBE) describing the micro-processes such as nucleation,growth,aggregation of particle swarms in a multiphase system is proposed.The method is based on the ...A new method for the solution of population balance equations(PBE) describing the micro-processes such as nucleation,growth,aggregation of particle swarms in a multiphase system is proposed.The method is based on the fixed pivot moment and allows arbitrary number of moments to be tracked si-multaneously.By expressing PBEs for both batch and continuous operations in a general form,and using weighted residual method to derive the moment equations,different moments can be tracked directly.The numerical density function is assumed to be a summation of several weighted Dirac Delta functions,and the integral and derivative terms in PBEs are transformed to a summation in order to reduce computational cost.Simulations of a batch nucleation-growth process and a continuous ag-gregation-growth process have demonstrated good agreement with the corresponding analytical solu-tions,with relative errors less than 108%.Simulation of a combined nucleation-growth-aggregation process,which does not have an analytical solution,is also included,so as to reproduce the mi-cro-behaviors of such a complex system,demonstrating the feasibility and reliability of this method.展开更多
The solar energy utilization in built environment has been limited due to its low heat flux, uneven distribution in time and space and temporal difference in day and night. The phase change materials have been used to...The solar energy utilization in built environment has been limited due to its low heat flux, uneven distribution in time and space and temporal difference in day and night. The phase change materials have been used to collect the fluctuant solar energy to form a stable energy source for the terminal equipment of the buildings. In this study, the hybrid organic phase change materials was prepared for the capillary radiant heating system which formed a cascade utilization of solar energy. Firstly, lauric acid and stearic acid were selected as the basic organic phase change materials and the binary equilibrium phase diagram was completed based on the method of step cooling curve according to the experimental tests data. The results showed that the phase transition temperature of the mixed acid at the lowest eutectic point was 31.2℃ and the latent heat value was 264.3 kJ/kg when the mass mixing ratio was 70% for lauric acid and 30% for stearic acid. Secondly, the expanded graphite was used as an additive to enwrap the mixed acid and enhance the heat conductivity. The experimental results showed that when the mass proportion of expanded graphite in the mixed acid was 10%, the mixed acid could be completely enclosed by expanded graphite and the stability of melting and solidification was optimal. Additionally, the phase transition temperature of the hybrid phase change material was 31.5℃ and the latent heat value was 217.4 kJ/kg. The novel hybrid phase change material has a lower eutectic point and a higher latent heat of phase change, so it has a large application space and is quite suitable for the cascade utilization of solar energy with capillary network heating system.展开更多
In this work,the utilization of lattice Boltzmann method(LBM)in the simulation of coupled conduction and radiation heat transfer in composite materials is studied.The novel D3Q30-LBM and D3Q38-LBM models are proposed ...In this work,the utilization of lattice Boltzmann method(LBM)in the simulation of coupled conduction and radiation heat transfer in composite materials is studied.The novel D3Q30-LBM and D3Q38-LBM models are proposed for the simulation of radiative transfer equation(RTE).The LBM-LBM model,coupled finite volume method(FVM)and LBM are compared with the coupled FVM and discrete ordinate method(DOM)for 2D and 3D simulations.The results show that the original D3Q26-LBM is insufficient for the simulation of radiation,and both the D3Q30-LBM and D3Q38-LBM are close to the DOM for the RTE.The LBM can have large errors in the simulation of heat conduction when the relaxation time is large.Thus,its application in the composite materials is limited when the ratio between thermal conductivities of different components is large.The models with LBM for RTE can be more efficient than the FVM-DOM for the simulation of conduction-radiation heat transfer in composite materials.The FVM-D3Q30-LBM model is suggested because of its accuracy and efficiency.展开更多
Solar energy storage is an indispensable and sustainable utilization mode of renewable energy;environment friendly,large-capacity,low heat loss,and long-term storage are critical to improving the integration of solar ...Solar energy storage is an indispensable and sustainable utilization mode of renewable energy;environment friendly,large-capacity,low heat loss,and long-term storage are critical to improving the integration of solar energy supply.Traditional thermal energy storage mode cannot achieve long-term storage due to the heat loss even under the excellent thermal insulation measures.In this work,a solar-powered membrane-based concentration gradient energy storage of liquid desiccant solutions is presented.In the membrane distillation process driven by solar energy under the right solar radiation conditions,the liquid desiccant solution is concentrated gradually and long-term stored as the concentration gradient energy.To this end,the measured temperature of solar hot water is in the range of 40°C to 90°C from May to September,2018,in Xi’an,China.And then,the LiBr solution(50 wt%),the LiCl solution(35 wt%),and the CaCl_(2)solution(40 wt%)were membrane-based concentrated in the temperature range of 42°C to 63°C,separately.The results showed that the water vapor pressure difference decides the water vapor transferred across the membrane pores from the liquid desiccant side to the air side.The energy storage density of liquid desiccant solutions increases along with the increases in temperature and the membrane area.Consequently,when the LiBr,LiCl,and CaCl_(2)solutions are concentrated from 50%to 55%,from 35%to 40%,and from 40%to 45%,separately,the concentration energy storage density is 245 kJ/kg,350 kJ/kg,and 306 kJ/kg,which is equivalent to or even higher than ice storage capacity.Due to the two independent closed cycle of the liquid desiccant solution and air,the liquid desiccant solution’s concentration gradient energy storage can be long-term stored environment-friendly without any insulation measures.展开更多
In this work,a large eddy simulation(LES)model,which includes momentum and heat source(or sink)inside the tree planting layer,is proposed for the simulation of flow in a street canyon with tree planting.Vegetation can...In this work,a large eddy simulation(LES)model,which includes momentum and heat source(or sink)inside the tree planting layer,is proposed for the simulation of flow in a street canyon with tree planting.Vegetation canopy layer simulation shows that this model can be used to simulate the velocity distribution and temperature variation inside the canopy layer.Effects of atmospheric instability on flow and pollutant distribution in a street canyon with tree planting of an aspect ratio of 0.5 are studied.Results show that compared with the canyon with no tree planting(or the exposed street canyon),the canyon with tree planting shows a reduced wind circulation and pollutant exchange rate(PER)at the top layer of the street canyon,which induces the increase in the pollutant concentrations near road surface,leeward wall and windward wall.When street canyon atmosphere is under a strongly unstable condition,wind velocity decreases while pollutant concentration is increased in the areas near the street canyon top,road surface,leeward and windward walls,compared with the wind velocity in the street canyon with the neutral stratification.When street canyon atmosphere is under a weakly unstable condition,wind velocity weakens near the street canyon top and windward wall,but strengthens near the road surface and leeward wall,and pollutant concentration is decreased near the leeward and windward walls and is increased between the two rows of trees.When the street canyon atmosphere is under an unstable condition,PER is lower than that under the neutral stratification.展开更多
Accurate prediction of the evolution of particle size distribution is critical to determining the dynamic flow structure of a disperse phase system.A population balance equation(PBE),a non-linear hyperbolic equation o...Accurate prediction of the evolution of particle size distribution is critical to determining the dynamic flow structure of a disperse phase system.A population balance equation(PBE),a non-linear hyperbolic equation of the number density function,is usually employed to describe the micro-behavior(aggregation,breakage,growth,etc.)of a disperse phase and its effect on particle size distribution.Numerical solution is the only choice in most cases.In this paper,three different numerical methods(direct discretization methods,Monte Carlo methods,and moment methods)for the solution of a PBE are evaluated with regard to their ease of implementation,computational load and numerical accuracy.Special attention is paid to the relatively new and superior moment methods including quadrature method of moments(QMOM),direct quadrature method of moments(DQMOM),modified quadrature method of moments(M-QMOM),adaptive direct quadrature method of moments(ADQMOM),fixed pivot quadrature method of moments(FPQMOM),moving particle ensemble method(MPEM)and local fixed pivot quadrature method of moments(LFPQMOM).The prospects of these methods are discussed in the final section,based on their individual merits and current state of development of the field.展开更多
基金the financial support from the National Natural Science Foundation of China(No.2117619)the Shaanxi Province Major Project of Innovation of Science and Technology(No.2008zkc03205,No.2011KTZB03-03-01)
文摘The aim of this paper was preliminary design of the process for low-temperature coal tar hydrocrackmg m supercritical gasoline based on Aspen Plus with the concept of energy self-sustainability. In order to ensure the correct- ness and accuracy of the simulation, we did the following tasks： selecting reasonable model compounds for low-tem- perature coal tar; describing the nature of products gasoline and diesel accurately; and confirming the proper property study method for each block by means of experience and trial. The purpose of energy self-sustainability could be pos- sibly achieved, on one hand, by using hot stream to preheat cold stream and achieving temperature control of streams, and on the other hand, by utilizing gas （byproduct of the coal tar hydrocracking） combustion reaction to provide energy. Results showed that the whole process could provide a positive net power of about 609 kW-h for processing the low- temperature coal tar with a flowrate of 2 268 kg/h. The total heat recovery amounted to 2 229 kW-h, among which 845 kW＇h was obtained from the gas combustion reaction, and 1 116 kW＇h was provided by the reactor＇s outlet stream, with the rest furnished by hot streams of the products gasoline, diesel and residue. In addition, the process flow sheet could achieve products separation well, and specifically the purity of product gasoline and diesel reached 97.2% and 100%, respectively.
基金Supported by the National Natural Science Foundation of China (Grant No. 59806010)Shaanxi Science and Technique Foundation of China ((Grant No. 2005K05-G17)
文摘Membrane distillation technology is a new type of efficient separation technology that combines traditional distillation technology and membrane separation technology. In the study, applications of membrane distillation technology in thermal engineering and refrigerating engineering with typical energy transformation process were presented. Desorption and regeneration process of saline solution by vacuum membrane distillation was proposed on the basis of the concentration and separation properties of membrane distillation. Membrane distillation technology could be used in lithium bromide absorption refrigeration system, energy storage system, and the regeneration process of liquid desiccant solution in temperature-humidity independent control air-conditioning system. The aim of the applications was to use the low-grade energy such as waste heat, solar energy and geothermal energy adequately and to improve the available temperature difference of heat source. According to latent heat transfer and thermal conduction across the membrane in direct contact membrane distillation process, a novel membrane heat exchanger with both heat transfer and mass transfer processes was proposed. The heat exchanger could be used as the solution heat exchanger of lithium bromide absorption refrigeration system and as the special heat exchanger that recovered heat and pure water simultaneously. Some feasible process flows about the applications of membrane distillation technology to energy transformation process were listed and analyzed. Finally, future research emphases were indicated.
基金supported by the National Natural Science Foundation of China (51006077)
文摘Large reciprocating compressors are important equipment used in a wide range of process industries. Most of these compressors have huge power requirements and their capacity often needs to be regulated. Advanced technologies in compressor capacity control are effective approaches for saving large amounts of energy in process industries. This paper reviews the basic theories and the state of the art of the capacity control technologies. In particular, a compressor working procedure is first presented using an analogy to the pulse signal concept. Compressor capacity control methods are classified into pulse frequency modulation and pulse amplitude modulation from a perspective of pulse signal processing. The mechanisms and feasibility of some important methods, including dead volume variable control, partial-stroke and full-stroke suction valve opening, are reviewed. Based on the pulse signal concept, a duty cycle regulation method for capacity control is introduced, and the performance and implementation of the new method are compared with those of the existing suction valve opening methods. The duty cycle regulation method has integrated advantages over the other methods in terms of regulating precision, pressure stability, energy saving and reliability. All the suction valve opening methods can cause gas reflux, resulting in the so-called breathing effect. The breathing effect has negative effects on regulation performance and compressor security, which needs further investigation in the future.
基金Supported by the National Basic Research Program of China (Grant No.2004CB720208)National Natural Science Foundation of China (Grant Nos.40675011 and 10872159)Key Laboratory of Mechanics on Disaster and Environment in Western China (Grant No.200707)
文摘A new method for the solution of population balance equations(PBE) describing the micro-processes such as nucleation,growth,aggregation of particle swarms in a multiphase system is proposed.The method is based on the fixed pivot moment and allows arbitrary number of moments to be tracked si-multaneously.By expressing PBEs for both batch and continuous operations in a general form,and using weighted residual method to derive the moment equations,different moments can be tracked directly.The numerical density function is assumed to be a summation of several weighted Dirac Delta functions,and the integral and derivative terms in PBEs are transformed to a summation in order to reduce computational cost.Simulations of a batch nucleation-growth process and a continuous ag-gregation-growth process have demonstrated good agreement with the corresponding analytical solu-tions,with relative errors less than 108%.Simulation of a combined nucleation-growth-aggregation process,which does not have an analytical solution,is also included,so as to reproduce the mi-cro-behaviors of such a complex system,demonstrating the feasibility and reliability of this method.
基金The work was supported by the Innovation Chain of Key Industries of Shaanxi Province under Grant(No.2018ZDCXL-GY-10-03)the National Natural Science Foundation of China(No.51478386).
文摘The solar energy utilization in built environment has been limited due to its low heat flux, uneven distribution in time and space and temporal difference in day and night. The phase change materials have been used to collect the fluctuant solar energy to form a stable energy source for the terminal equipment of the buildings. In this study, the hybrid organic phase change materials was prepared for the capillary radiant heating system which formed a cascade utilization of solar energy. Firstly, lauric acid and stearic acid were selected as the basic organic phase change materials and the binary equilibrium phase diagram was completed based on the method of step cooling curve according to the experimental tests data. The results showed that the phase transition temperature of the mixed acid at the lowest eutectic point was 31.2℃ and the latent heat value was 264.3 kJ/kg when the mass mixing ratio was 70% for lauric acid and 30% for stearic acid. Secondly, the expanded graphite was used as an additive to enwrap the mixed acid and enhance the heat conductivity. The experimental results showed that when the mass proportion of expanded graphite in the mixed acid was 10%, the mixed acid could be completely enclosed by expanded graphite and the stability of melting and solidification was optimal. Additionally, the phase transition temperature of the hybrid phase change material was 31.5℃ and the latent heat value was 217.4 kJ/kg. The novel hybrid phase change material has a lower eutectic point and a higher latent heat of phase change, so it has a large application space and is quite suitable for the cascade utilization of solar energy with capillary network heating system.
文摘In this work,the utilization of lattice Boltzmann method(LBM)in the simulation of coupled conduction and radiation heat transfer in composite materials is studied.The novel D3Q30-LBM and D3Q38-LBM models are proposed for the simulation of radiative transfer equation(RTE).The LBM-LBM model,coupled finite volume method(FVM)and LBM are compared with the coupled FVM and discrete ordinate method(DOM)for 2D and 3D simulations.The results show that the original D3Q26-LBM is insufficient for the simulation of radiation,and both the D3Q30-LBM and D3Q38-LBM are close to the DOM for the RTE.The LBM can have large errors in the simulation of heat conduction when the relaxation time is large.Thus,its application in the composite materials is limited when the ratio between thermal conductivities of different components is large.The models with LBM for RTE can be more efficient than the FVM-DOM for the simulation of conduction-radiation heat transfer in composite materials.The FVM-D3Q30-LBM model is suggested because of its accuracy and efficiency.
基金This work is financially supported by National Natural Science Foundation of China(No.51478386).
文摘Solar energy storage is an indispensable and sustainable utilization mode of renewable energy;environment friendly,large-capacity,low heat loss,and long-term storage are critical to improving the integration of solar energy supply.Traditional thermal energy storage mode cannot achieve long-term storage due to the heat loss even under the excellent thermal insulation measures.In this work,a solar-powered membrane-based concentration gradient energy storage of liquid desiccant solutions is presented.In the membrane distillation process driven by solar energy under the right solar radiation conditions,the liquid desiccant solution is concentrated gradually and long-term stored as the concentration gradient energy.To this end,the measured temperature of solar hot water is in the range of 40°C to 90°C from May to September,2018,in Xi’an,China.And then,the LiBr solution(50 wt%),the LiCl solution(35 wt%),and the CaCl_(2)solution(40 wt%)were membrane-based concentrated in the temperature range of 42°C to 63°C,separately.The results showed that the water vapor pressure difference decides the water vapor transferred across the membrane pores from the liquid desiccant side to the air side.The energy storage density of liquid desiccant solutions increases along with the increases in temperature and the membrane area.Consequently,when the LiBr,LiCl,and CaCl_(2)solutions are concentrated from 50%to 55%,from 35%to 40%,and from 40%to 45%,separately,the concentration energy storage density is 245 kJ/kg,350 kJ/kg,and 306 kJ/kg,which is equivalent to or even higher than ice storage capacity.Due to the two independent closed cycle of the liquid desiccant solution and air,the liquid desiccant solution’s concentration gradient energy storage can be long-term stored environment-friendly without any insulation measures.
基金supported by the interdisciplinary project of XVan Jiaotong University(No.2009xjtujcl0)the National Natural Science Foundation of China(Grant No.10872159)
文摘In this work,a large eddy simulation(LES)model,which includes momentum and heat source(or sink)inside the tree planting layer,is proposed for the simulation of flow in a street canyon with tree planting.Vegetation canopy layer simulation shows that this model can be used to simulate the velocity distribution and temperature variation inside the canopy layer.Effects of atmospheric instability on flow and pollutant distribution in a street canyon with tree planting of an aspect ratio of 0.5 are studied.Results show that compared with the canyon with no tree planting(or the exposed street canyon),the canyon with tree planting shows a reduced wind circulation and pollutant exchange rate(PER)at the top layer of the street canyon,which induces the increase in the pollutant concentrations near road surface,leeward wall and windward wall.When street canyon atmosphere is under a strongly unstable condition,wind velocity decreases while pollutant concentration is increased in the areas near the street canyon top,road surface,leeward and windward walls,compared with the wind velocity in the street canyon with the neutral stratification.When street canyon atmosphere is under a weakly unstable condition,wind velocity weakens near the street canyon top and windward wall,but strengthens near the road surface and leeward wall,and pollutant concentration is decreased near the leeward and windward walls and is increased between the two rows of trees.When the street canyon atmosphere is under an unstable condition,PER is lower than that under the neutral stratification.
基金Supported by the National Basic Research Program of China(Grant No.2004CB720208)the National Natural Science Foundation of China(Grant Nos.40675011&10872159)the Key Laboratory of Mechanics on Disaster and Environment in Western China
文摘Accurate prediction of the evolution of particle size distribution is critical to determining the dynamic flow structure of a disperse phase system.A population balance equation(PBE),a non-linear hyperbolic equation of the number density function,is usually employed to describe the micro-behavior(aggregation,breakage,growth,etc.)of a disperse phase and its effect on particle size distribution.Numerical solution is the only choice in most cases.In this paper,three different numerical methods(direct discretization methods,Monte Carlo methods,and moment methods)for the solution of a PBE are evaluated with regard to their ease of implementation,computational load and numerical accuracy.Special attention is paid to the relatively new and superior moment methods including quadrature method of moments(QMOM),direct quadrature method of moments(DQMOM),modified quadrature method of moments(M-QMOM),adaptive direct quadrature method of moments(ADQMOM),fixed pivot quadrature method of moments(FPQMOM),moving particle ensemble method(MPEM)and local fixed pivot quadrature method of moments(LFPQMOM).The prospects of these methods are discussed in the final section,based on their individual merits and current state of development of the field.
