Research On Wet Desulfurization-Collaborative Dust Removal And Heat Loss In Coal-Fired Bulk Curing Barn

Tobacco leaf roasting is a typical field of use of scattered coal.There are hundreds of thousands of coal-fired bulk curing barns scattered in the tobacco leaf growing area in the country.The bulk curing barns uses a small hot air stove with coal added manually,direct combustion and direct exhaust,leading to serious pollution.And the thermal efficiency of the bulk curing barns is low.Research on reducing the emissions of flue gas pollutants from the curing barns and improving the thermal efficiency of the curing barns is of great significance to the comprehensive management of scattered coal in China.Because tobacco leaf roasting is produced in the form of households or agricultural cooperatives,the flue gas treatment of coal-fired bulk curing barns needs to fully consider the investment and operating costs.At the same time,existing researches only use the"coal consumption per kilogram of dry tobacco"as an indicator to evaluate the thermal efficiency of the bulk curing barns.The lack of in-depth analysis of the losses that cause the thermal efficiency of the bulk curing barns cannot guide the improvement of the heating system.In view of the problem of flue gas pollution,this paper directly used the flue and selected spray wet desulfurization as the flue gas treatment process,and reversely sprayed the Ca(OH)₂slurry reaction in the flue to remove SO₂.This method does not change the main structure of the barn.It has the advantages of low operating cost and high desulfurization efficiency,and has a synergistic dedusting effect,which can simultaneously remove SO₂ and smoke.First,the nozzle height and Ca/S ratio under different flue gas flow rates were optimized through experiments to improve the desulfurization efficiency.Then,the numerical simulation of Fluent was used to further study the effect of adjusting the nozzle height and spray liquid flow on the flue residence time of the droplet.Finally,On-site tests were conducted to analyze the SO₂removal effect and synergistic dust removal effect of the wet desulfurization device under real operating conditions.At the same time,the operation effect of automatic coal feeder was studied.In addition,in view of the problem of low thermal efficiency of the coal-fired bulk curing barns,this paper measured the heat loss of the heating system of the bulk curing,combined the local coal characteristics and the combustion conditions of the furnace to analyze the loss distribution and changes in the flue-cured tobacco process.The experimental optimization results show that the desulfurization efficiency increases with the increase of nozzle height at low flue gas velocity(1m/s),and decreases with increasing nozzle height at high flue gas velocity(5m/s).The Ca/S ratio should choose 1.5 at low gas velocity.At high gas velocity,desulfurization efficiency and operating cost should be considered comprehensively.The numerical simulation results show that the nozzle height increases at low gas velocity,the average residence time of the droplets leaving the flue from the top and the droplets falling at the bottom of the flue will increase.At high gas velocity,all droplets leave the flue from the top,and the average residence time decreases as the nozzle height increases,which explains the experimental optimization results well.Adjusting the spray liquid flow has little effect on the flue residence time of the droplet,and the nozzle height is the main factor affecting the droplet residence time.During the field test,the nozzle height was set to 0.9m,and the mass concentration of Ca(OH)₂ slurry in the small-fire period was 10%.The spray flow was 60m L/min,and it increased to 120m L/min after entering the middle-fire period.The test results showed that for the curing barn with flue gas flow rate in the range of 1?5m/s,the device maintained more than 80%of the desulfurization efficiency during the entire flue-cured tobacco cycle.When the gas velocity of the curing barn reached 8m/s,the desulfurization efficiency was still low after increasing the mass concentration of Ca(OH)₂ slurry and the spray flow.The cooperative dust removal effect of the device can have a higher dust removal efficiency at the initial stage of increasing the spray liquid flow rate,and the dust removal efficiency decreased as the flue gas flow rate further increases.The operation result of the automatic coal feeding device shows that the automatic coal feeding barn can reduce the emission concentration of flue gas pollutants.Among the heat losses of the heating system,the exhaust smoke loss is the most important loss.It will increase significantly during the large-fire period.Reducing the exhaust smoke loss is the key to improving the thermal efficiency of the barn.During the period from small-fire to large-fire,generally due to the operation of the combustion-supporting fan and the opening of the furnace door and the cleaning door,the furnace has sufficient oxygen supply,and the chemical incomplete combustion loss is reduced,but the excessively high moisture content of coal will cause the chemical incomplete combustion loss to increase.The mechanical incomplete combustion loss is mainly affected by the coal characteristics in different regions.The physical heat loss of ash and slag accounts for a very small proportion and can be ignored.