| Biomass briquette technology has been greatly developed recently,and biomass briquette has been recognized as an alternative fuel.While,several problems exist when burning biomass briquette with industrial coal-fired boilers,such as incomplete combustion of volatile matter and fixed carbon content in furnace,easy slagging,excessive discharge of pollutants,and so on.Hence,the boiler has low thermal efficiency and pollutes environment seriously.In order to realize high efficiency combustion and environmental protection of biomass briquette boiler,in this paper chain boiler structure and air-flue gas system were designed that applied to biomass briquette fuel.The design of air supply system(primary air and secondary air)plays an important role in the efficient and complete combustion of biomass.Thermal efficiency of the boiler and emissions-reduction technology were also investigated in this paper.The main research contents and results were showed as below:(1)Physical chemical characteristics,combustion characteristics and pollutant emission characteristics of biomass briquette were analyzed.Several important characteristics of biomass fuel were also analyzed when taken biomass as a fuel for industrial boilers.Problems that existed in biomass burning equipment were also summarized.The above analysis provided theoretical and computational basis for the design improvement,combustion efficiency improvement and pollutant control of biomass briquette combustion equipment.(2)According to the characteristics of biomass briquette fuel and purpose of using industrial boiler,chain steam boiler was designed.The boiler was single cylinder vertical type water fire tube with rated evaporation for 1 t/h,and steam pressure was 0.7MPa.The overall layout of the boiler and novel multi-arch structure of the furnace was designed,the air-flue gas system was designed on the basis of furnace structure.Design features of primary air were: four isobaric closed air chamber is provided and air in bilateral positions,primary air was used to send the wind by the way of wind distribution and the proportion of each wind room is adjusted according to the working condition;Secondary air design features: 8 secondary air outlet were provided on the front of arch and the mid-arch,and secondary air outlet angled and offset each other.Air-flue System and furnace structures complement each other to achieve full combustion furnace volatile and fixed carbon combustion of low intensity,and the formation of different local materials rich combustion zone and oxygen-rich combustion zone within the furnace,to reduce NO_X and particulate generation and emissions.The total pressure drop flue was 943.053 Pa and the total pressure drop of the air channel was 968.743 Pa of the boiler by calculated.The model of induced draft fan was Y5-47-4C and the model of air supply fan was 4-72-No3.6A.Fans were equipped with frequency converter and access control cabinet.(3)After the boiler was designed and manufactured,the thermal performance test and the main pollutant emission test of the boiler were carried out.Firstly,the heat loss of boiler was calculated under the condition of 6.5% of the flue gas oxygen content in boiler design,and heat loss of boiler was the smallest when the two wind rate was 40%.Secondly,pollutant emission test was carried out under the two wind rate of 40%,and the relationship between the pollutant emission and the oxygen content in flue gas and the relationship between the thermal efficiency of the boiler and the oxygen content of the flue gas were studied.Finally,optimal thermal efficiency of the boiler was 83.5% when rated with a secondary air was 40%,the smoke flue gas containing oxygen in 7%,the thermal efficiency of the boiler for 82.9%~83.5%,air pollutants of boiler(particulate matter,nitrogen oxides,sulfur dioxide)based on containing the maximum emission concentration of oxygen conversion were lower than that of the GB 13271-2014 the boiler air pollutant emission standards’ limit value,when the oxygen content in flue gas in the range of 6% to 8%.The boiler has good environmental benefits and economic performance. |
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