| In china, the shortage of coal resources has caused people to focus on the replacement of high-quality coal with lignite. It’s well known that lignite is predominantly distributed in water-deficient area and its moisture content is h igh. So the efficient and clean recycling of moisture in flue gas has become a n ew research direction. At present, the water recovery technology along with the waste heat recovery has been realized by means of flue gas being condensed in heat exchanger. The moisture in lignite combustion can cause fly ash in flue gas deposited on inner surface of heat exchanger, which may reduce the condensatio n efficiency and should be considered in process of condensation.Steam, lignite particles and lignite ash particles were injected into the flue g as generated by the combustion of natural gas, in order to simulate the flue gas of lignite. The experimental system, which used for investigating the condensati on heat transfer and ash depositions of flue gas, is built based on the laboratory original bench. The target of current study is to analyze the influence of flue g as flow rate, cooling water inlet temperature, excess air coefficient and particle s ize on the condensation heat transfer and the ash deposition characteristics of flu e gas, and to compare the condensation behavior between wet flue gas with fine particles and wet flue gas without particles.Based on the heat transfer theory, the mathematical model of the thickness calc ulating of condensate film and the mass of condensate on the surface of fin and ba se pipe are established. The calculation results of the model and the experimental results are in good agreement, which verify the feasibility of the model calculatio n on the process of condensation.The experimental results indicate that as the velocity increased from0.694t o1.081m/s, the inlet temperature of the cooling water decreased from34.3℃to25.5℃, the excess air coefficient decreased from1.82to1.02, the total mass flo w rate of condensate in the experiments with particles increased almost42.56%,35.29%and30.86%, the heat transfer coefficient increased about27.49%,22.06%and31.12%;in the experiments without particles, the total mass flow rate of c ondensate in the experiments with particles increased almost33.96%,43.82%and22.23%, the heat transfer coefficient increased about21.09%27.66%and25.68%,respectively. The mass of condensate increased about7.3%and the condensati on heat transfer coefficient increased almost4.7%as average particle diameter w as from59up to172.5μm. The average Nusselt number and the Sherwood nu mber of flue gas including fine particles over the entire tube bundles was expres sed as Nu=2.683Re0.527· Pr1/3·Co3.976and Sh=2.683Re0.527· Sc1/3· Co3.976.Thickness of the ash deposit on the base of tubes increased gradually along the direction of the flow, and the ash deposition on the top of fins was thicker than that of the root. There were some ash depositions on the windward sides of the base tubes, and on both sides of the fins. Area of ash depositions on the finned tube bundles enlarged with increasing particle diameter.The results of this study for lignite flue gas condensation heat transfer can provide basic data for further research and industrial application. |
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