Design And Research On Baled Straw Fuel Boiler

Nowadays,energy shortage and environmental pollution have become the main factors restricting the development of our country.As a large agricultural country,China has abundant crop straw resources,these straw resources as an important reserve energy have great significance for alleviating China’s energy crisis.The baled straw has the characteristics of moderate density,convenient transportation and storage,and can be used as good fuel.If it is applied to small and medium-sized boilers,it can reduce the dependence on fossil energy and reduce greenhouse gas emissions,and has a good environmental and social benefits.The current domestic biomass boilers are mainly used to burn biomass briquetting fuels,and most of them are modified on the basis of the original coal-fired boilers,or the low mechanized fixed grate boilers that burn single-bundle fuels.There is no real sense of continuous feed baled straw fuel boiler that can be used in production and life.In this paper,the combustion characteristics of typical biomass straw were briefly studied by means of thermal balance,and the combustion weightlessness law and combustion characteristic parameters of biomass straw were researched,and then the combustion characteristics of baled straw fuel were studied on the existing combustion test bench for baled straw fuel.It was concluded that the baled fuel is thick and not easy to burn through.And a boiler suitable for straw baled fuel was designed according to its combustion characteristics.The boiler had a high degree of mechanization,and the furnace and grate were improved according to the combustion characteristics of the baled straw fuel.A suitable inclined reciprocating grate was selected to cooperate with the multi-arch furnace to overcome the disadvantages that large size baled fuel was not easy to burn through and the ash was easily slagging on the grate,the boiler had a high thermal efficiency,and the pollution discharge reached the national standards on the emission of atmospheric pollutants from boilers.The boiler was a single-drum longitudinal reciprocating grate steam boiler equipped with a burnout chamber,a soot deposition chamber,an economizer and a two-stage dust collector device,it was designed to have an evaporation capacity of 1 t/h and a thermal efficiency of 81%.Finally,the thermal performance of the boiler was tested with baled wheat straw fuel.The thermal efficiency,combustion efficiency,smoke composition and other related experiments were carried out under the rated load of 100%,80%and 60%respectively.The main results obtained were as follows:1)The boiler can operate normally under three working conditions,the thermal efficiency was 80.49%,79.35%and 78.42%respectively,which was higher than the evaluation index of GB/T 15317 for 1 t/h boiler efficiency greater than or equal to 65%.2)Under the rated working condition,the steam output reached 970 kg/h,steam pressure up to 0.7 MPa,and the steam temperature up to 170.5℃,which basically met the design requirements and can be used as heat source or power source in production and life.3)Under the optimal working condition,the combustion efficiency of the boiler reached 97.5%,the thermal efficiency of the boiler was 80.49%,the incomplete combustion loss of solids and the incomplete combustion loss of the gas were low,and the efficient and stable combustion of the straw baling fuel was realized.4)Under the three working conditions,the ash slag rate after burning of the baled fuel was 10.1%,9.26%and 7.25%respectively,and the slag bond on the grate was very light,the slag structure was loose,the ash and slag block was fine and had a soft texture.5)The contents of NOx,SO2 and dust in the exhaust smoke of the boiler were 125,42,26 mg/m3 respectively,and the Ringerman blackness was less than 1,and various environmental indicators were far lower than coal-fired boilers,which met the requirements of national industrial boilers for air pollutant discharge.6)Under the rated operating conditions,through the experimental comparison of different excess air coefficients in the furnace,it was concluded that when the excess air coefficient was 1.5,the combustion efficiency of the boiler was the highest,the combustible material burnt completely,at this time the furnace temperature was the highest,the gas and solid heat loss was the least,the boiler was in the best working state.