Experimental Study On The Device Of Water Film Dust Removal Coupling Heat Transfer Of Flue Gases

Improving thermal efficiency of boilers through technical innovation is one of the important measures to improve the productivity,energy saving and emission reduction of sugar mills.With moisture content of about 50%,bagasse as the boiler fuel is burned to form a large number of water vapor mixed in the flue gases,resulting in the high specific heat enthalpy of the flue gases.On the other hand,the dust removal of flue gases currently prevailed in sugar mills is the water film scrubber which has low dust removal efficiency.With the implementing of new standards promulgated by the national environmental protection department,the sugar factories will face greater challenge.Based on the characteristics of flue gases with high moisture enthalpy,A scheme of coupling heat exchange with dust scrubber of boilers was proposed,which employs the hot water from sugar process for the scrubbers,thus to saturate the flue gases at around 70 ℃which is used to heat the air for boiler burning with heat exchangers.The scheme is to intensify dust removal through the effect of moisture condensation with the dust as the nuclei,while recovering the vapor heat of the flue gases.In order to simulate the proposed scheme,an experimental rig of corrugated plates intensified coupling heat exchange with dust scrubber of flue gases was devised.Experiments were performed to investigate dust removal and heat exchange properties,as well as the convective heat transfer of saturated flue gases with water film and the properties of fluid flows.Research contents and results are as following:1.A heat exchange devise in which the air was heated by flue gases saturated by spraying hot water was established.The device consists of five units,namely:flue gas generating unit,water heating and spraying unit,dust addition device,heat transfer-dust removal unit and measuring unit.Calibrated the measuring instruments,insulated the heat transfer-dust removal unit,and debugged the experimental device before the experiment.2.Based on the heat exchange devise,the preliminary experiment of heat exchange and dust removal was carried out.The results showed that:The device had good heat transfer and dust removal performance.The flue gas saturation temperature about 70 ’C,wet flue gas outlet temperature dropped by about 9 ℃,which indicts that steam was condensed phase transition.The removal efficiency of smoke and dust was increased from 70%to 90%when the average particle size increases from 2 μm to 4 μm.When the dust concentration increases from 62 mg/Nm3 to 222 Mg/Nm3,the dust removal efficiency increased by 20%.3.Based on the heat exchange devise,the convective heat transfer coefficient with different parameters of the corrugated plate and the operating parameters of the device were studied.The results showed that:When the liquid-gas ratio was 3.3～4.2 L/m3,the convective heat transfer coefficient reaches the maximum value,which indicated that flue gas was saturated.Under the condition of optimum liquid-gas ratio,the convective heat transfer coefficient increased with the increasing of the flue gas flow rate,but the velocity reaches a certain value,the increase trend was slowed down.The influence of the height of the corrugated section on the convective heat transfer coefficient was relatively small,while corrugated plate height and corrugated plate section had a great impact.According to the experimental data regression.the quasi-correlation of the corrugated plate parameters and the flue gas flow rate to the convective heat transfer coefficient was fitted as follows:Nu = 0.240Re0.702Pr0.333(de/D)-0.395(Ls/D)0.059 n0.2964.Based on the heat exchange devise,the experimental study of hydrodynamics is carried out.The results showed that:The pressure drop was significantly increased by improving of liquid-gas ratio,flue gas velocity,corrugated section height and corrugated plate section,while decreased by increase of corrugated peak.According to the experimental data regression,the quasi-correlation of the corrugated plate parameters and the flue gas flow rate to the resistance coefficient was fitted as follows:f = 1.469Re-0.390(de/D)-0.780(Ls/D)1.149n1.3445.Based on the experimental results,the economic and social benefits were carried out.The results showed that:With sugar mill of 75 t/h steam boiler as an example.Each crop can save about 11520 tons of bagasse,the direct economic benefits reached 2.25 million yuan.At the same time,it has great social benefits that decreased emissions of CO2 and NO2 is 5425 tons and 20 tons respectively.