Research On Combustion Characteristics Of Forest Waste Pellet Fuel

In order to utilize forestry waste efficiently,this paper takes forestry waste pellet fuel as the research object.Firstly,the combustion characteristics of forestry waste pellet fuel such as physical and chemical properties,ignition performance and combustion mechanism are studied.Then,the combustion characteristics of forestry waste pellet fuel in combustion furnace are studied.This paper analyzes the factors affecting the thermal efficiency of forestry waste combustion furnace,explores the methods and approaches to improve the thermal efficiency,and provides technical reference for the optimization of forestry waste pellet fuel combustion furnace.(1)In order to study the basic components of forest waste pellet fuel,the elemental analysis and industrial analysis of various forest waste pellet fuel were carried out.The results show that the main elements are C,H,O,N,S and so on.The volatile content of forest waste particulate fuel is more than 70%and the fixed carbon content is 10～20%.In addition,the ash content of forest waste particulate fuel is less.Therefore,forestry waste pellet fuel is easy to catch fire and burn,but the combustion sustainability of forestry waste pellet fuel is poor.The C content of wood pellet fuel is generally higher than that of wood pellet fuel made from branches,bark and leaves,and the O/C atom of wood pellet fuel is lower than that of wood pellet fuel.So wood pellet fuel has a higher calorific value.(2)In order to study the combustion characteristics of forest waste pellet fuel,thermogravimetric analysis was carried out on the pellet fuel prepared by Pinus massoniana,Slash pine and Pinus sylvestris.The results showed that the combustion process of forest waste pellet fuel can be divided into three stages:fuel dehydration and drying stage,volatile matter precipitation and combustion stage,and coke combustion stage.Volatile matter precipitation and combustion stage are the main weightlessness stage of combustion process.Pinus sylvestris pellet fuel has the highest ignition temperature,burning temperature,lowest average burning rate,the largest comprehensive combustion characteristic index is the highest,so the combustion performance is best.(3)In order to study the combustion characteristics of forest waste pellet fuel in combustion furnace,combustion test and heat balance analysis were carried out.The calculation results of heat balance show that the fuel burnout rate is high,but the thermal efficiency of the combustion furnace is low.The calculation results of heat balance show that heat loss of exhaust gas is the main cause of low thermal efficiency.The main reason for the smoke exhaust loss is that the wind velocity of the smoke exhaust machine is too high,leading to the excessive air coefficient is too large,and the excess air takes away a lot of heat.(4)In order to study the combustion characteristics of a variety of granular fuels in the furnace,a simulation model was established by using Fluent software,and the furnace temperature obtained from numerical simulation was compared with the heat balance test value.The results show that the error of the test value is less than 10%,which verifies the reliability of the simulation model.According to the simulation analysis of the flow field characteristics of the combustion furnace,when the air is blown into the forestry waste combustion furnace under positive pressure from the air inlet,the pressure area is larger,and the velocity and turbulent kinetic energy are relatively small.It has little effect on the combustion process of granular forest waste fuel with high volatile content and difficult flame control.(5)The combustion characteristics of a variety of pellet fuels in the combustion furnace were studied.It was found that when the excess air coefficient is 1.5,the burning process of forestry waste pellet fuel is weak and the combustion effect is better.When burning the pellet fuel prepared from slash pine and leaves,the burning flame appears to stick to the wall,and the burning effect is poor.In the combustion process of a variety of forestry waste pellet fuels in the combustion furnace,the concentration distribution area of the intermediate product CO is small,and the concentration at the furnace flue gas outlet is almost zero.The pellet fuel can achieve complete combustion,and the incomplete gas loss is small.