Experimental Study On The Coupling Mechanism Between Dew Point Corrosion And Ash Deposition Of The Low-temperature Heat Exchanger System

Safe and efficient operation of the low-temperature heat exchanger system can achieve the requirement of "energy-saving and emission-reduction" which aim at the electricity industry, but the system runs at high dust areas and below acid dew point, therefore, it is necessary to study the coupling mechanism between dew point corrosion and ash deposition put forward to prevent measures、look for safe operating temperature and corrosion resistant materials, in order to provide protection for safe operation, and better guide engineering practice.To study the corrosion resistance of steel, which commonly used in thermal power plants, by artificially accelerating corrosion test from three aspects:temperature, concentration, ingredient (sulfuric acid, hydrochloric acid, hydrofluoric acid were mixed in different concentrations). The results show that:the higher the temperature, the faster the rate of corrosion; with increasing concentration of sulfuric acid, the corrosion rate first increased, then decreased; the rate of corrosion is proportional to the concentration of hydrochloric acid and hydrofluoric acid. Three kinds of acid mixed will make the metal passivation in advance. The order of five kinds of corrosion-resistance materials is:316L> ND>corten>20#>q235。Insert the homemade experimental equipment of corrosion and fouling stick into the outlet of the air preheater and desulfurization tower, control the wall of temperature during the operation of the low-temperature heat exchanger, in order to simulate a real furnace operating conditions, explore the coupling mechanism of the dew point corrosion and ash deposition, and investigate the effects of temperature and corrosive materials. The results show that, the cooling exchanger runs at80～100℃, the corrosion lighter, five kinds of materials can meet the requirements, but the heat transfer coefficient will decrease; the heating exchanger tubes in the first row when running at45℃, suffered severe corrosion. Corrosion layer has two parts, the inner layer is thick and dense, combined with metal, which is iron of sulfides; the outer layer is sulphate and chloride, which is the reactants of ash and acid. In this case only316L can meet the requirements of corrosion.The experiment of the low-temperature heat exchanger system in the600MW unit show that:the cooling exchanger causes lighter corrosion, at the same time, it reduces the operation temperature, narrow temperature difference, and lower heat transfer efficiency, therefore, selecting the proper extended surface to optimize heat transfer and reduce wear and tear is crucial. The heat exchanger fouling is less, but corrosion is serious, which selecting corrosion-resistant materials is able to prevent corrosion. For optimum type selection of cooling heat exchanger, comparative analysis of H finned tube and spiral finned tube on the characteristic of heat transfer, ash deposition and attrition were made with thermodynamic calculation and numerical simulation methods. The results show that, the spiral finned tube is better on the performance of heat transfer, but H finned tube is better on the performance of ash deposition and attrition resistance.