Models And Efficiency Calculation Of Circulating Fluidized Bed Boiler

Circulating fluidized bed combustion technology,as one type of clean coal technology in line with Chinese national conditions,is widely used in China.The number and amount of circulating fluidized bed boiler in China are the world's first.Currently,calculation of boilers' efficiency in factories is used the standard method.Parameters such as the fly ash carbon content,the ash content of carbon content,the amount of slag and other data are necessary,and these parameters are not control arguments on the stable boiler,thus,critical troubles arises from lack of certain datas and low accuracy of the existing field datas when calculating the efficiency of the boiler by the standard method,furtherly,the calculation of boiler efficiency costs large amount of money.As a result,the check computation of the efficiency of the boiler is seriously lagging behind.Therefore,proposing a method of on-line calculation of boiler efficiency can save the cost for the plant,it is of great practical significance.A process simulation model has been developed using Aspen Plus in this paper,and on the basis of the Aspen Plus model,this paper provides a new method to calculate the efficiency of circulating fluidized bed boiler,in addition to coal industrial analysis and elemental analysis data,other datas used in the model are completely from the plant DCS picture.The innovative method can reflect the overall performance of the boiler operation on-line and display the loss in the process of boiler operation,provide guidance for the optimization of the boiler.In this paper,the main work on a 150 t/h circulating fluidized bed(CFB)combustor with low temperature in separator and low circulating ratio is as follows:(1)Prepared an Excel table to calculate the efficiency of circulating fluidized bed boiler by the standard method,some of the datas were estimated for the lack of field datas.(2)Raised a process simulation model by Aspen Plus,integrating coal pyrolysis,carbon and volatile combustion,gas-solid separation,and heat recovery of fuel gas necessary to simulation coal combustion in CFB,making full use of the device operation data,including outlet temperature of cold streams and hot streams in all heat exchangers,the temperature and pressure of the steam,flow rate of all kinds of stream,etc.(3)According to the conversion of the heat generated by the fuel in the circulating fluidized bed boiler,developed a new method to calculate the efficiency of the circulating fluidized bed boiler based on Aspen Plus model,parameters for the method are the net heat duty of each heat exchange.Through the method,detailed heat losses of the boiler and boiler's efficiency can be calculated directly,and were in good agreement with the results of the standard algorithm.(4)According to the mass conservation,the combustion efficiency can be calculated by the operation data of air flow rate and oxygen content of waste gas.However the field data of air flow and oxygen content in flue gas are not accurate,this method is recommended for the verification of site data,and providing the initialization for Aspen Plus model.(5)In addition,on the basis of the entire model of CFB boiler,the simplified mathematic model executed by a computer program can easily calculate the combustion efficiency.This method uses little field data and provides an estimation combustion efficiency reference for the design phase of boiler.A stable operation condition of the circulating fluidized bed boiler in the paper,the efficiency calculated by Aspen Plus model is 67.47%,while the efficiency calculated by the standard method is 66.02%,the relative error between them is only 2.15%,which means the two methods based on different parameters have very close calculation results.The coal combustion efficiency calculated by the simplified mathematical model is 94.44%,which is close to the design value 95% of the combustion efficiency of the boiler.Therefore,through multiple CSTR reactors in series can accurately simulate the limit combustion efficiency of the circulating fluidized bed boiler at the time of well operating.