携带流反应器中稻壳气化过程的分析

引言生物质能作为一种可再生的清洁能源,可以减少CO2、NOx、SOx及颗粒物的排放[1],其开发利用受到世界各国的极大关注[2]。生物质气化被认为是生物质利用的最有前途的能源转化方式之一[3],已经成为能源研发与利用的一大研究热点。研究结果表明,气化器或者锅炉是能源转化和利用过程中效率最低的一个操作单元[4],因此,气化器效率的提高能在很大程度上改善整个能源转化过程[5]。

Performance improvement in stepped solar still modified by sponge layer

In this paper,the experimental investigation on the performance improvement of conventional stepped solar still is conducted.The steps are covered by the porous material to improve the performance of the conventional device and increase the evaporation rate.All the parameters,including the temperature on the glass surface,the water temperature inside the evaporation zone,and the amount of water produced in both conventional and modified stepped solar stills are measured and compared.The efficiency of two devices and their exergy efficiency have been calculated.Finally,the economic analysis of both devices has been done to check the economic feasibility of the modified device.The amount of freshwater generated during one day was 2244.4 and 3076.2 mL/m^(2),respectively for the conventional and modified stepped solar stills.As a result,the amount of water produced in one day by modified stepped solar still is 35.5% more than the conventional one.Also,the costs for the conventional and modified stepped solar stills have been calculated as 0.0359 and 0.029$/(L·m^(-2)),respectively.

Exergy Analysis and Retrofitting of Natural Gas-based Acetylene Process

This article presents an acetylene production process by partial oxidation/combustion of natural gas. The thermodynamic performance and exergy analysis in the process are investigated using the flow-sheeting program Aspen Plus. The results indicate that the most important destruction of exergy is found to occur in the reactor and water quenching scrubber, amounting to 8.23% and 10.39%, respectively, of the entire system. Based on the results of thermodynamic and exergy analysis, the acetylene reactor has been retrofitted. The improvement ratios of molar 02 to CH4 and molar CO to CN4 are 0.65 and 0.20, respectively. An improvement of the acetylene production system is proposed. Adopting the improvement operation conditions and using oil to realize the reaction heat recovery, the feedstock of natural gas is reduced by 9.88% and the exergy loss in the retrofitting process is decreased by 19.71% compared to the original process.

Coupling effect of evaporation and condensation processes of organic Rankine cycle for geothermal power generation improvement

Organic Rankine cycle(ORC)is widely used for the low grade geothermal power generation.However,a large amount of irreversible loss results in poor technical and economic performance due to its poor matching between the heat source/sink and the working medium in the condenser and the evaporator.The condensing temperature,cooling water temperature difference and pinch point temperature difference are often fixed according to engineering experience.In order to optimize the ORC system comprehensively,the coupling effect of evaporation and condensation process was proposed in this paper.Based on the laws of thermodynamics,the energy analysis,exergy analysis and entropy analysis were adopted to investigate the ORC performance including net output power,thermal efficiency,exergy efficiency,thermal conductivity,irreversible loss,etc.,using geothermal water at a temperature of 120℃as the heat source and isobutane as the working fluid.The results show that there exists a pair of optimal evaporating temperature and condensing temperatures to maximize the system performance.The net power output and the system comprehensive performance achieve their highest values at the same evaporating temperature,but the system comprehensive performance corresponds to a lower condensing temperature than the net power output.

Exergy Analysis of Single and Multi-Step Thermal Processes

The present paper introduces the concepts of exergy and treats it applications to analysis of the gain in exergy efficiency between one-step and multi-step thermal processes. The analysis, which is carried out with the Excel-based SEPE program, is exemplified with the comparison between single-step and two-steps heat pump setup for providing heat to a floor heating system and for domestic hot water. The paper discusses the use of the concept of exergy efficiency as a measure of success for design of a heat pump application and how the use of information on exergy destruction and temperature levels in different parts of the system add a new perspective to the analysis and the evaluation of the system performance. The paper shows how this information can be used to improve the system configuration and also the operation of the system for given boundary conditions. This is especially useful when the energy from the low temperature sources can be utilized at different temperature or quality levels such as for space heating and domestic hot water.

Exergy Analysis of a Photovoltaic and an Oven System

The present work deals with the energy end exergy analysis of a system which includes photovoltaic panels providing electricity to a bakery oven. The photovoltaic system （PV） on the bakery unit serves as a model for the installation of PV systems in urbanized areas, which could play a major role in the energy self sufficiency, while at the same time playing a role in the reduction of greenhouse gas emissions. The technology of these systems will be analyzed, as well as the installation of such a system in the building of a bakery unit at the Prefecture of Argolida in Greece with coordinates： latitude 37°34′27″North and longitude 22°50′17″ East. The annual average energy production in horizontal level for 1 kW installed power is 1400 kwh. The Kilowatt peak （kWp） needed for the oven system in the specified area is 29.63 kW. This need of energy can be provided by a PV system that is comprised of 129 PV panels ES-200M60（＋） manufactured by EMMVEE Company at 230 Watts of peak power （Wp） each. The installation of a solar cell is studied with energy storage since the bakery shall be operational at 03.00 am. The exergy of the operating system using electricity from the grid was calculated for the oven temperature of 150 ℃ and up to 220 ℃. The exergy and energy efficiencies were also obtained. The heat lost during the time the oven is not operational was taken into consideration. It was found that 50% of the exergy is being lost, despite the fact that a big amount of heat is being recovered.

An Energy and Exergy Analysis of a Microturbine CHP System

The micro-turbine is known as a producer of high-grade energy （work） and also low energy （heat）. The following low grade heat energy have been modeled under ISO ambient conditions （international standard organization）, i.e. 15 ℃ and 1 bar, to utilize the waste heat energy of a 200 kW micro-turbine combined with a single effect absorption chiller, an organic ranking cycle using R245fa （ORC-R245 fa） as a working fluid, a multi-effect distillation desalination （MED） and a thermal vapor compression MED Desalination unit （TVC-MED）. The thermal comparison was carried out based on an energy and exergy analysis in terms of electric efficiency, exergetic efficiency, carbon footprint, and energy utilization factor （EUF）. The software package IPSEpro has been used to model and simulate the proposed power plants. As a result, utilizing the exhaust waste heat energy in single-effect absorption chillier has contributed to stabilize ambient temperature fluctuation, and gain the best exergetic efficiency of 39%, while the EUF has reached 72% and the carbon footprint was reduced by 75% in MED and TVC-MED Desalination respectively. The results also reveal that TVC-MED is more efficient than traditional MED as its gain output ratio （GOR） is improved by 5.5%. In addition, ORC-245fa generates an additional 20% of the micro-turbine electricity generation.

Transient Exergy Analysis of the Condenser and Evaporator of an Air Source Heat Pump Water Heater

In this study the performance of an ASHPWH （air source heat pump water heater） is assessed from exergy point of view in component wise. In order to investigate the work potential of energy, the destruction on the exergy is analyzed and results are summarized for the components individually. The exergy destruction of the system is studied by considering real paths of the pressure and temperature data which are collected during the experiments of the ASHPWH under varying environmental conditions. In the following step, the evolution of the exergy destruction of the system is calculated by a code which is compiled on MATLAB along these temperature and pressure paths. The obtained results reveal the importance of the transient exergy analysis by providing detailed information about exergy destruction of the system such as where it drives up and reaches up to its max and where it drops down and evolves on a smooth path.

Exergetic Comparative Analysis of Ammonia and Carbon Dioxide Two-Stage Cycles for Simultaneous Cooling and Heating

The paper deals with the comparative analysis of the performance of cooling and heating systems operating with NH3 （ammonia） or CO2 （carbon dioxide）, both natural refrigerants. The study is based on the exergetic analysis that points out the location and the magnitude of a system malfunction. Both systems, with NH3 or CO2 operate in two stages. The exergetic analysis gives the direction of the structural optimization. The exergetic analysis has shown that the best structural schematic is not the same for the two agents. The exergetic analysis points out that the largest exergy destruction in the CO2 cycle is due to the throttling process and offers solutions to diminish it.

Energetic and Exergetic Analysis of Organic Rankine Cycle Powered by Hot Geothermal Water

The paper presents an investigation of energy and exergy analysis of an existing ORC （organic rankine cycle） unit powered by hot geothermal water. The validated model of this unit was used to examine 25 refrigerants belonging to different chemical compositions. The study revealed that R141b and R123 produced the best net power, energy efficiency, and exergy efficiency, whereas R125 was the lowest. Hydrofluorocarbons （except R143a）, hydrocarbons, and inorganic reflected attractive energy and exergy efficiencies. All investigated mixtures gained low performance compared with other studied candidates. The R245ca was the best among the hydrofluorocarbons studied refrigerants, and R501 was the best among the mixture refrigerants. Furthermore, within the ORC system, the evaporator was found to have the highest exergy destruction and the refrigerant pump was the lowest.

Process Study and Exergy Analysis of a Novel Air Separation Process Cooled by LNG Cold Energy

In order to resolve the problems of the current air separation process such as the complex process, cumbersome operation and high operating costs, a novel air separation process cooled by LNG cold energy is proposed in this paper, which is based on high-efficiency heat exchanger network and chemical packing separation technology. The operating temperature range of LNG cold energy is widened from 133K-203K to l13K-283K by high- efficiency heat exchanger network and air separation pressure is declined from 0.5MPa to about 0.35MPa due to packing separation technology, thereby greatly improve the energy efficiency. Both the traditional and novel air separation processes are simulated with air handling capacity of 20t＇h-1. Comparing with the traditional process, the LNG consumption is reduced by 44.2%, power consumption decrease is 211.5 kWh per hour, which means the annual benefit will be up to 1.218 million CNY. And the exergy efficiency is also improved by 42.5%.

Entransy and Exergy Analyses for Optimizations of Heat-Work Conversion with Carnot Cycle

The concept of entransy has been newly proposed in terms of the analogy between heat and electrical conduction and could bc useful in analyzing and optimizing the heat-work conversion systems. This work presents comparative analyses of entransy and exergy for optimizations of heat-work conversion. The work production and heat transfer processes in Carnot cycle system are investigated with the formulations of exergy destruction, entransy loss, work entransy, entransy dissipation, and cfficiencics for both cases of dumping and non-dumping of used source fluid. The effects of source and condensation temperatures on the system performance arc systematically investigated for optimal condition of producing maximum work or work cntransy.

Component Exergy Analysis of Solar Powered Transcritical CO_2 Rankine Cycle System

In this paper,exergy analysis method is developed to assess a Rankine cycle system,by using supercritical CO2 as working fluid and powered by solar energy.The proposed system consists of evacuated solar collectors,throttling valve,high-temperature heat exchanger,low-temperature heat exchanger,and feed pump.The system is designed for utilize evacuated solar collectors to convert solar energy into mechanical energy and hence electricity.In order to investigate and estimate exergy performance of this system,the energy,entropy,exergy balances are developed for the components.The exergy destructions and exergy efficiency values of the system components are also determined.The results indicate that solar collector and high temperature heat exchanger which have low exergy efficiencies contribute the largest share to system irreversibility and should be the optimization design focus to improve system exergy effectiveness.Further,exergy analysis is a useful tool in this regard as it permits the performance of each process to be assessed and losses to be quantified.Exergy analysis results can be used in design,optimization,and improvement efforts.

Combustion Irreversibilities: Numerical Simulation and Analysis

An exergy analysis was performed considering the combustion of methane and agro-industrial residues produced in Portugal (forest residues and vines pruning). Regarding that the irreversibilities of a thermodynamic process are path dependent, the combustion process was considering as resulting from different hypothetical paths each one characterized by four main sub-processes: reactant mixing, fuel oxidation, internal thermal energy exchange (heat transfer), and product mixing. The exergetic efficiency was computed using a zero dimensional model developed by using a Visual Basic home code. It was concluded that the exergy losses were mainly due to the internal thermal energy exchange sub-process. The exergy losses from this sub-process are higher when the reactants are preheated up to the ignition temperature without previous fuel oxidation. On the other hand, the global exergy destruction can be minored increasing the pressure, the reactants temperature and the oxygen content on the oxidant stream. This methodology allows the identification of the phenomena and processes that have larger exergy losses, the understanding of why these losses occur and how the exergy changes with the parameters associated to each system which is crucial to implement the syngas combustion from biomass products as a competitive technology.

Thermodynamic Analysis of Liquefied Natural Gas(LNG)Production Cycle in APCI Process

The appropriate production of liquefied natural gas(LNG)with least consuming energy and maximum efficiency is quite important.In this paper,LNG production cycle by means of APCI Process has been studied.Energy equilibrium equations and exergy equilibrium equations of each equipment in the APCI cycle were established.The equipments are described using rigorous thermodynamics and no significant simplification is assumed.Taken some operating parameters as key parameters,influences of these parameters on coefficient of performance(COP)and exergy efficiency of the cascading cycle were analyzed.The results indicate that COP and exergy efficiency will be improved with the increasing of the inlet pressure of MR(mixed refrigerant)compressors,the decreasing of the NG and MR after precooling process,outlet pressure of turbine,inlet temperature of MR compressor and NG temperature after cooling in main cryogenic heat exchanger(MCHE).The COP and exergy efficiency of the APCI cycle will be above 2% and 40%,respectively,after optimizing the key parameters.