Abstract: According to the operation condition of nitrogen-blanketed wastewater tank in petrochemical wastewater plant, the working conditions can be simplified into four types, namely nitrogen supplement working condition, pressure boost working condition, exhaust working condition and pressure reduction working condition in gas phase space. The operating pressure range is given corresponding to nitrogen supplement working condition and exhaust working condition, and the calculation formula of the duration of four working conditions is proposed. The calculation method of organic matter concentration in gas phase is also given. Taking a 10,000m3 storage tank as an example, the operating pressure is maintained in the range of 0.1kPa~ 0.9kPa. Under the most unfavorable condition (full tank), the calculation results of the duration of the four working conditions are given, among which the exhaust working condition takes the shortest time. An optimization scheme is proposed to solve the problem of frequent start and stop of induced draft fan in exhaust working condition.

Key words: nitrogen-blanketed wastewater tank, pressure control, working condition duration