Optimization Design Of Low Temperature Economizer And Simulation Of Flue Flow Field

The heat loss of boiler smoke exhaust is the largest one of boiler heat loss.In order to reduce the heat loss of boiler smoke exhaust and improve unit efficiency,domestic coal-fired power stations have carried out extensive retrofit project of installing low-temperature economizer for waste heat utilization in recent years.With the increase of operating time,many low-temperature economizers have appeared the problem of wear and leakage caused by uneven smoke flow field.Therefore,to ensure the safe operation of low temperature economizer,the problem of uneven smoke flow field must be solved effectively.Based on a practical project of a power plant,this paper optimized the design of low temperature economizer heat exchanger from the aspects of tube material and tube type.By analyzing the mechanism of low temperature corrosion,the acid-dew point temperature was calculated.Corrosion resistant ND steel was used to prevent low temperature corrosion,and H-shaped finned tube was used to enhance heat transfer.The flow chart is compiled to design and calculate the low temperature economizer.Finally,the reasonable structural parameters,heat transfer coefficient and heat transfer of the low temperature economizer were obtained.According to the size of the low-temperature economizer and the layout of the original flue,the numerical model of the low-temperature economizer and the flue were established.The BMCR numerical simulation was carried out for the original scheme without the guide plate.It was found that there were serious deviation of flue gas at the inlet of the lowtemperature economizer and uneven flow in the two-forking flue.Specifically,the error coefficient Cv of velocity distribution on the 300 mm section before the first row of the two flue pipes is 25.5% and 28.4% respectively,the flow deviation rate of the two flue pipes is 3.04%,and the total pressure drop of the flue is 302 Pa.To solve this problem,three optimization schemes are put forward,which can make the smoke flow field uniform and reduce the risk of wear and leakage by installing guide plate at elbow,expanding section and forked flue and changing flue arrangement.Under BMCR condition,the third scheme is determined to be the optimal scheme by comparing and analyzing the velocity cloud diagram,pressure cloud diagram and flow deviation of the three schemes.Under the rated working condition of this scheme,the deviation coefficient Cv of velocity distribution on the 300 mm section before the first row of the two flue pipes is 11.6% and 12.8%,respectively,the deviation rate of flow rate of the two flue pipes is 2.6%,and the total pressure drop of the flue is 360 Pa.Then numerical simulation was carried out for the optimal scheme under 75% and 50% load conditions.By comparing and analyzing the velocity cloud diagram,pressure cloud diagram and flow deviation under different loads,the results showed that the heterogeneity of flow field and total pressure drop all decreased with load reduction,and the optimal scheme could meet the requirements of flow field uniformity under each load.Therefore,the third scheme can effectively solve the local wear and leakage problem of low temperature economizer caused by excessive local flue gas velocity due to flue gas deviation,and improve the safety of low temperature economizer equipment.By comparing and analyzing the economic parameters when the low-temperature economizer is put into operation and removed,the economic analysis is carried out,and the reduced coal consumption rate and standard coal quantity of power generation can effectively save fuel cost and increase economic benefit of power plant.