Research On Fire-side Corrosion Of Heat Exchanger Of Instantaneous Gas Water Heater

Our country began to produce Water Heater,Since in the late 1970 of the 20 th century,after more than 40 years of development,gas instantaneous water heater with production of up to tens of millions of sets.The gas water heater uses a heat exchanger to achieved heat transfer between the high temperature flue gas with cold water When flue gas runs on the heat exchanger,condensation occurs,thus forming acid electrolyte environment,copper tube corrosion may occur,making pipe wall thinning.Corrosion products Build-up on the finned heat exchanger surface,which obstruct the flow of gas,led to increased emissions.Not only will the corrosion,fouling,reduces heat transfer properties but also lead to flue gas temperature and energy consumption increase,resulting in a security incident and economic loss.So,it is very significant to Study on corrosion of the heat exchanger for the safe operation of gas instantaneous water heater.Gas water heater will prone to corrosion and corrosion from corrosion in the environment of high temperature flue gas,this paper focus on Corrosion mechanism and corrosion testing,efficiency test and fluid simulation system,the main content as follows:(1)Using metal corrosion hot mechanical and dynamics research found copper business heat exchanger and high temperature flue gas in the of excess oxygen occurred chemical reactions produced CuO;and vapor of the flue gas encountered water wall condenses to form acidic condensate,which occur electrochemical reaction with the outer surface of the heat exchanger metal forming sulfate;the acid gas CO2,and NO,and NO2 in the flue gas without corrosivity in gaseous,but when dissolved into condensation water in the will generated carbonate,they turn out to be nitric acid,dilute acid mixed solution,causing hot corrosion of the heat exchanger.(2)By macroscopic examination found that the green solid particles on the walls of the heat exchanger wall produced by cumulative burning 2000 hours are more than that of 1000 hour,and light green attachments cover a wide range,they began to fall from the coil wall series and spread to the entire wall.Also,corrosions in the pipe surface of Heat exchanger under the lateral and uopper are more than that of 1000 hours.A part of clearance in the fins are blocked.The surface of lead-coated heat exchangers finned have been corroded,it can be seen the copper-colored surface.Through microscopic examination found that walls of the not lead-plated heat exchanger corrosion products are mainly(Cu4(OH)6SO4).Corrosion products of Heat exchanger up the lateral are mainly(CuSO4(H2O)5)and(Cu3(OH)4SO4),but which of the Heat exchanger under the lateral are mainly(Cu4(OH)6SO4)and(Cu3(OH)4SO4).Corrosion products in the walls of the Lead-plated heat exchanger are mainly(PbSO4)and(Cu4(OH)6SO4),Corrosion products of Heat exchanger up the lateral are mainly(PbSO4),but which produced by the Heat exchanger under the lateral are mainly(PbSO4)and(CuSO4(H2O)5).(3)The corrosion product accumulating on the surface of the heat exchanger in flue gas side,which will obstruct heat transfer performance of heat exchanger,leading the thermal efficiency decrease of the water heaters.Only the efficiency of the 40 kW water heaters decreased significantly when operate in high load,other water heater efficiency declines nearby 4%.After 2000 hours of the experiment,there are only the lead-coated water heater(28kW)and lead-coated water heater(32kW)meeting the national secondary energy consumption standard.The efficiency of the non-lead-plated water heaters(28kW and 32 k W)meet the National the third level energy consumption standard.The efficiency of the non-lead-plated water heaters(40kW)less than the three levels of energy consumption standards.(4)During the test cycle,the corrosion rates can be calculated by the quality changes of the heat exchanger,the maximum corrosion rate is 28 kW lead plated heat exchanger,and the minimum corrosion rate is 28 kW lead plated heat exchanger,it can be concluded that the corrosion rate do not have relation with power and the lead plating of heat exchanger.(5)Using numerical simulation methods to analyze finned flue gas temperature distribution,velocity distribution and pressure distribution between found that finned heat exchanger under the side when compared to the upper temperature is high,fast speed,high pressure,lower side are more likely to corrode.Finned heat exchanger of the four side tube in the middle of the two tubes compared with two near the heat exchanger wall tube,the contact area between two tube with high temperature flue gas,flue gas flow is fast,finned heat exchanger of the four side tube in the middle of the two tubes are more likely to corrode.It can be mitigate the severity of corrosion of the heat exchanger by improving air quality,reducing excess air ratio,changing the water inlet and outlet of the heat exchanger and coating methods.