An Engineering Design Of The Air Pollution Control For A Stainless Wire Enterprise

Stainless steel is one of the most important industries in Chinese national economy. The processes of production include annealing and sealing, so that the sinters were produced in the surface of the steel. Sinters not only affected the appearance but also had adverse effects on the subsequent procedures. So sinters had to be removed by acid-washing or polishing before entering the next process. The acid-washing of stainless steel usually includes three steps:first, the oxide layer was washed off by pre-pickling by sulfuric acid; then, it was washed by the mixture of nitric acid and hydrofluoric acid; finally, it was passivated by nitric acid to produce a stable layer of passivation film which could enhance the corrosion resistance of stainless steel. But during the processes above, large quantities of waste gases containing HF, NOx and the waste gases from stainless steel nickel-chromium pickling sludge treatment containing particulate matter, sulfur dioxide and fluoride. If these waste gases discharge to the environment directly without any treatments, they will cause serious impacts on the surrounding environment.This paper is based on surface treatment transformation projects of stainless steel wire (ie the removal of acid-washing workshop and reduction of stainless steel nickel-chromium pickling sludge) for one limited machinery company in Zhejiang Province. Because of low collection efficiency of the existing treatment facility for the waste gas from picking, veneer efficiency can not meeting the original design requirements, and treatment facilities for the exhaust gas from the rotary kiln not being equipped, design a waste gas treatment system for the waste gases from picking and for exhaust gases from the rotary kiln respectively.The depth of pickling bath increased to 2600mm and the collecting efficiency of waste gas augmented from 30% to 80% using air draft all around. The waste gases from picking were treated by classified collection. The design technique of sulfuric acid mist was "first stage of absorption of alkaline liquor", which had three pieces of rotational plate and one piece of defogging plate. The treatment technology for the waste gases from the mixed acid pickling and nitric acid pickling was "second stage of absorption of sodium hydroxide and sodium thiosulfate liquors", which using six pieces of rotational plate, one piece of blind plate in the bottom and one piece of defogging plate. The investment and operating cost of the treatment system for pickling waste gases was 549 thousand,4042 yuan/d respectively.We used the methods of baghouse filter and lye spray to treat the waste gases from rotary kiln. The type of baghouse filter was LCM-1350, a long bag pulse filter. The tower of lye spray was composed of six pieces of rotational plate, one piece of blind plate in the bottom and two pieces of defogging plate. The investment and operating cost of the treatment system for the waste gases from rotary kiln was 1220 thousand and 5189 yuan/d respectively.