Near the Jingzhu Small and Micro Park in Wenzhou, Zhejiang Province, the two residential quarters delivered in 2021 are only a few hundred meters apart. The technical team of the Engineering Center of Nanjing Institute of Environmental Science and Technology of the Ministry of Ecology and Environment rose to the challenge and used its own technical advantages to overcome the problem of waste gas odor in the precision casting industry.
As of the end of June this year, all 27 enterprises in the park have completed the improvement of odor and gas, which not only achieved zero complaints of exhaust gas pollution, but also created opportunities for enterprises in the park to reproduce.
Wenzhou Precision Casting Small and Micro Park was established in 2020. The leading industry is the foundry industry. 26 wax film precision casting and 1 sand casting enterprise are combined into 8 group companies, with an annual output value of more than 800 million yuan.
Previously, the Longwan District of Wenzhou City issued the “Wenzhou Precision Casting Small and Micro Park Comprehensive Renovation Implementation Plan”, which required a comprehensive solution to the problem of the odor of industrial waste gas disturbing the people in the small and micro park. Although the small and micro park has repeatedly hired experts and governance units to carry out rectification and invested a lot of waste gas treatment facilities, the rectification effect is not good, and the park faces the risk of closure.
In August 2021, experts conducted in-depth research on the front line and found that the odorous gases in various precision casting workshops mainly come from the waste gas of hot wax, dewaxing and roasting. The workshops of each company are equipped with exhaust gas treatment facilities on the roof of the factory building, and the exhaust gas is discharged at high altitude after treatment. Among them, there are a total of 70 high-altitude emission cylinders for odor gas, which are the main source of air odor in the surrounding areas of Xiaowei Park.
In order to solve the problem, the Nanjing Institute of Environmental Science of the Ministry of Ecology and Environment proposed a source-process-end odor control improvement plan, including source control, process reduction, and end-end optimization measures.
Specifically, the roasting furnace was upgraded to a regenerative sintering furnace with secondary combustion function, and the removal rate of residual wax in roasting exhaust gas was increased from 75% to 95%. Secondly, the coil heat exchange condensation depressurization process is adopted to reduce the dewaxing steam, thereby reducing the amount of wax-containing waste gas. The use of spray facilities to replace the cyclone dust collector, multi-pipe air cooler, lime dosing device, bag filter and other equipment for dry dust removal can shorten the treatment process. Wait.
After the treatment, the number of high-altitude exhaust pipes in the park was reduced from 70 to 25, and the exhaust gas volume was reduced by more than 50%. After treatment, most of the organic matter, nitrogen oxides, sulfur dioxide and particulate matter in the exhaust gas are converted into carbon dioxide, washing wastewater and some inorganic salts, so as to achieve full coverage and ultra-purification of desulfurization, denitration, dust removal and deodorization, so that the exhaust gas is odorless.
Not long ago, public representatives of the residential community climbed up the ladder, opened the air outlet of the exhaust pipe, and personally sniffed the exhaust gas after treatment. “We are relieved to smell it ourselves,” said the resident.