Pollution Prevention and Environmental Benefits
Out-of-service inspections of petroleum storage tanks currently require cleaning and degassing of the tanks. These processes are necessary to allow workers to enter the tank to conduct the inspection manually. Degas emissions are released from the tanks’ vapor space prior to cleaning, and sludge emissions are removed from the tank during cleaning for processing elsewhere at increasing cost.
Robotic inspections eliminate the need for degassing as well as the requirement to collect the emissions and waste materials. These reduced emissions and waste are considerable when evaluating the costs of the current standard inspection techniques. One of the papers published in Independent Liquid Terminals Association (ILTA) annual operating conference (1999) states:
“According to the Texas Natural Resource Conservation Commission, substantial greenhouse gas emissions occur during tank cleaning operations. The use of in-service inspections reduce these greenhouse gas emissions by eliminating the need to drain, vent and clean tanks prior to inspection. In order to avoid releasing greenhouse gases, such as benzene and other chemicals on the Toxic Release Inventory, operators will typically burn the evacuated fumes with methane and other gases to eliminate the VOC release. Nevertheless, incineration generates significant CO2 emissions.”
The above table represents typical pollution prevention and energy savings that are associated with an in-service robotics inspection of a 30 m (100 ft.) diameter 13.8 m (45 ft.) tall tank containing diesel. These calculations assume best practices are being used to ventilate and thermally treat VOCs.
The U.S. EPA also estimates large volumes of liquid wastes are produced when a tank is cleaned for an out-of-service inspection. (U.S. EPA, Office of Air and Radiation, Emission Standards and Engineering Division, Research Triangle Park, NC: Alternative Control Techniques Document for Volatile Organic Liquid Storage in Floating and Fixed Roof Tanks, EPA-453/R-94-001, pp., 5-6, 1994.) This document states:
“Another possible source of secondary emissions is the treatment, storage or disposal of tank sludge and the rinsate from tank cleaning. The regulatory status of the sludge and rinsate depend on the composition of tank contents. The sludge generated from the tank cleaning process may be up to 90 percent liquid. Independent of any VOC emitted from the liquid portion of the sludge, 3,000 gallons of solid waste will be produced from cleaning a 200,000 gallon tank. This material may be RCRA hazardous wastes.”
As shown above, in-service tank inspections have proven to reduce emissions and environmental impacts. The costs associated with handling these emissions and waste products are pushing the industry towards more environmentally friendly methods of tank inspection.