Tham khảo tài liệu 'air pollution control systems for boiler and control problems_5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Simpo PDF Merge and Split Unregistered Version - http 5-815-1 AFR 19-6 severe pitting in stainless steels. This condition is frequently encountered in an incinerator which burns large quantities of disposable polyvinyl chloride PVC materials. b. Temperature. Corrosion rates generally increase with increases in exhaust temperatures. This is due to the increased mobility of ions and increased reaction rates. However in cases where the corrosion process is accelerated by the presence of oxygen increasing the acid temperature eventually boils out dissolved oxygen rapidly diminishing corrosion rate. This is the case with Monel a nickel-copper alloy. c. Velocity. Often the corrosion resistance of an alloy depends on the existence of an adhering oxide layer on its surface. A high exhaust gas velocity can remove or erode the surface layer. Once removed this layer cannot be renewed because the oxide film is washed away as it forms. d. State of oxidation. Under reducing condition Monel is very resistant to moderate sulfuric-acid concentrations. Under oxidizing conditions or in the presence of oxidizing ions however very rapid corrosion occurs. The reverse is true of stainless steels which are resistant to oxidizing acid environments but are attached by acids under reducing conditions. The equipment designer should select materials based on individual case conditions including temperature abrasion pH etc. 7-6. Auxiliary equipment a. Gas transport. 1 Ducts and stacks. Large boiler plant stacks have a wind shield of reinforced concrete or of steel with a separate inner flue or numerous flues of steel acid-resistant brick and occasionally stainless steel. The space between the inner flue and the outer wind shield may be insulated with a mineral wool wrapping. This is to prevent the condensation of acid dew on the inside of the metal chimney which occurs below dew point temperature and also to prevent acid smut from being blown out of the chimney. Acid smut is a
