Challenge
A chemical plant in Texas required a 24,000 barrel tank to be degassed during, and following a tank cleaning. The degassing was performed under a nitrogen blanket, with an outside tank cleaning company water washing the tank. The customer’s main concern was to keep the pressure in the tank constant, while maintaining a steady flow of nitrogen into the tank. Tank pressure had been a previous issue for the customer in the past with a different degassing company. The customer wished to keep the pressure within 2” WC of the current pressure.

Solution
Due to the high levels and fluctuations of benzene, the Envent engineers decided to use a thermal oxidizer routed directly to the flame arrestor on the tank. Constant communication was kept between the control room, and Envent personnel throughout the degas to keep the pressure equalized. Envent provided benzene readings to the control room every two hours, per the customer’s request. The benzene concentration was relatively high during the agitation of the tank, about 700 ppm, but dropped significantly after the tank cleaning company had finished. Envent provided a reading of 0 ppm to the control room, which was confirmed by the customer’s lab.

Benefit
To the delight of the customer, Envent was successfully able to degas the benzene tank with a nitrogen blanket during the three days of tank cleaning. With a 24 hour manned watch, the thermal oxidizer outperformed previous competitors, and gave a final benzene reading of zero ppm. Through constant communication with the customer, Envent was able to safely meet the strict requirements set forth by the customer. Envent was also able to save the customer money by significantly reducing costs by shortening the duration of the project.

Degassing Tanks under a Nitrogen Blanket Not a Problem for EMTOS