Numerical Simulation And Optimization Design Of Clean Burning Equipment For Straw Bundling Fuel

The production of non renewable energy in China is ranked third,and the energy consumption is ranked second in the world.With the development of social economy,our country has been facing the increasing energy gap and environmental stress.If we can not solve the energy problem well,it will hinder the development of China's economic.Rich,clean and environmentally friendly biomass energy have been found to be one of the renewable energies instead of fossil ones.Biomass energy not only alleviated energy shortage,but also improved atmospheric environmental quality.It has excellent environmental and economic benefits.The resources of the straw are rich in China,but a large number of straw have been burned each year,causing a fair amount of pollutions and wastes.Due to many advantages including moderate density,easy transportation and storage,efficient and convenient production,straw bales fuel has been deemed as the main direction of straw combustion and utilization technology.The research and development of straw bales boilers in China is still in the initial stage.In this paper,a small straw bales combustion test device is set up.A series of deeper studies and analysis upon combustion characteristics,combustion processes and combustion kinetic characteristics of straw bales fuel in entire combustion process are made,which have important theories and practical values to actual designing practices of devices for straw bales fuel.And according to the characteristics of straw bales fuel,the straw bales boiler and the two stage dust removal system are designed through the calculation of thermal power,the calculation of combustion products,the selection and calculation of the grate,the heat balance and the furnace structure.For a long term,the furnace and arches are depended on the experiential design,and the air distribution is often adjusted by experience of the stoker,causing lower combustion efficiency.Notably,the exploration upon furnace structure or combustion optimization by using numerical modeling way to simulate biomass boiler combustion process is not much.In view of the lack of theoretical prediction,the combustion numerical model of a straw bales boiler is established through the basic fluid equation combined with the combustion process of straw bales fuel.The model is composed of two parts,namely,the porous medium model of the bed layer and the gas phase combustion model in the furnace.The former was coupled with the latter by UDF programming.In this paper,the model was applied to the optimization analysis of furnace arch and air distribution.First,the influence of different front arch,rear arch and rear arch length was analyzed,and the best structure of furnace arch was determined.The best plan is the inclination of the front arch is 50 degrees,the inclination of the rear arch is 30 degrees,and the coverage ratio of the rear arch is 50%.Secondly,the effect of two air-distribution ways(pre air-distribution and post air-distribution)is studied.And based on a series of analytic comparisons upon the four air-volume distribution schemes of the above pre air-distribution way,the best air-volume distribution one was fixed.The post air-distribution mode with air ratio of 5%,5%,40%,40% and 10% is most conducive to fuel combustion.And then,based on the results of the simulation analysis of different secondary-air distributions,the optimum ratio of primary-air and secondary-air was obtained.When the primary-air and secondary-air distribution ratio is 6:2:2,the combustion condition of the furnace is better.After completing the above designs,the straw bales fuel combustion equipment is manufactured according to the technology of the boiler,the operation tests of the equipment were carried out.The combustion performances and pollutant emissions of such combustion equipment were tested.The results show that the combustion efficiency of the boiler is above 80%,which meets the design requirements.The structure with inclined reciprocating grate and multi-arch furnace is well matched with each heat-delivery surface.The overall design is reasonable and all the contents of CO,CO2 and NOX in exit flue gases have met the environment protection indexes.It has higher environmental protection benefit.The study lays a theoretical foundations and provids scientific guidance for straw bales fuel applications and disseminations and related technical perfections.