Modeling,Analysis And Optimization Of Fuel Cell-Based Combined Heat And Power System

The progress of human civilization is closely related to the exploitation and utilization of energy.Currently,fossil fuels are still the main form of energy consumption around the world.The development of society will be increasingly restricted because of the reliance on fossil energy.Therefore,new kinds of energy sources or new ways of energy use are very necessary for people to take the place of traditional fossil energy or traditional methods of energy use.As a new energy,hydrogen has many advantages such as clean,high efficiency and sustainable.It is regarded as the most promising clean energy in this century.Fuel cell is an efficient energy conversion device that can make the good use of hydrogen.It converts chemical energy in the hydrogen into electricity and available thermal energy by electrochemical reaction.The conversion efficiency of fuel cell is much higher than that of other kinds of heat engines,for example,internal combustion engine or thermal power plant which converts the fossil energy into mechanical energy or electricity.The Fuel Cell-based Combined Heat and Power(CHP)system is a kind of distributed energy system that is suitable for home application.Compared to traditional energy conversion methods and other cogeneration technologies,the FC-based CHP system has a greater power generation efficiency and comprehensive energy efficiency.At the same time,it also has unmatched advantages in economy,environmental protection and reliability.The CHP system with a natural gas reformer(hydrogen production)can take advantage of the existing gas pipelines so that the entire equipment could be install on the customer end,which leads to the reduction of energy losses during transmission process.The whole system has a great potential in further research.A complete model of the fuel cell-based CHP system has been developed in this paper,the energy and exergy analysis for whole system were conducted based on the model simulation.Different operational strategies based on the energy supply and demand characteristics of the system was design and optimized.The main research contents and conclusions are as follows:(1)A steady-state model of the fuel processing system was set up in Aspen Plus,which contains natural gas reformer and mixed gas processing devices,the model was tested and verified under real operating parameters.A dynamic model of PEM fuel cell was set up in SIMULINK,which consists of electrochemical model,flow reactant model and energy balance model,the model was tested and verified under real operating parameters.The model of balance of plant(BOP)was set up and simulated in SIMULINK.The steady-state model of fuel processing system was integrated into the fuel cell model to form a completed model of the entire CHP system.(2)The energy and exergy balance equations were built up for the whole CHP system and major reaction components.The energy and exergy analysis were conducted for the whole system and main components in it in order to get the energy and exergy efficiency of each parts in the system.It is found that the PEMFC covers the most parts in energy and exergy loss.The dynamic model of the system was simulated to study the effects of system electric power and fuel cell efficiency on performance of the fuel cell and the whole system.(3)The energy output characteristics of CHP systems was studied.According to the energy supply-demand characteristics,the operational strategies based on electrical load,thermal load and steady power was designed.An energy control module was designed in order to eliminate the mismatch between heat load and system heat output.At the same time,the energy conversion efficiency and exergy efficiency of three operational strategies under different loads are calculated.The advantages and disadvantages of the three operational strategies are compared from the aspects of applicability,system complexity and conversion efficiency.