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Show HIGH EFFICIENCY. LOW EMISSION MARINE VAPOR CONTROL SYSTEM BACKGROUND OF THE EQUIPMENT: The control of emissions of hydrocarbon laden vapors displaced from tank trucks and tankage containers that are being filled with liquid hydrocarbons has been addressed in a variety of ways over the past years. In mid-1991, the U.S. Coast Guard published rules governing the safety aspects of dealing with the hydrocarbon vapors emanating from the loading of vessels at Marine Terminal Facilities. These requirements, made in the name of safety, have a major impact on the design considerations of the required combustion device. Specifically, the vapors, immediately upon being transferred to the loading facility, are analyzed and conditioned, if necessary, to assure they are well outside the explosive limit. As a result, the combustion system must be designed to cope with Air, Nitrogen, or CO2 vapors with Hydrocarbon concentrations varying from 0 to 100 percent. The application is further complicated by sudden changes in the flow rate as compartments are "wetted, loaded, and topped off". Callidus, having been formed around the time the Coast Guard rules were promulgated, enabled the authors to start with a clean sheet of paper and design systems specifically for these applications. The majority of design effort centered on the development of a burner specifically for this application. An anti-flashback flame arrestor type vapor burner is used as the first line of defense in preventing flame propagation back to the vessel being loaded. This flame arrestor functions by exposing adequate cold surface to quench a fuel/air mixture below the ignition temperature. It is, therefore, imperative that the burner tip be kept cool. The most obvious design consideration to accomplish this is to maintain the minimum exit velocity high enough to prevent direct flame contact with the burner flame arrestor element. O n the other hand, the flame must be stabilized to eliminate rumbling and to achieve good destruction efficiencies. Given the large turndown (up to 50 to 1) encountered in Marine Terminals, satisfying the low end velocity criteria makes it impossible (in a single burner configuration) to have stable and efficient combustion at the high flow rates. To accommodate the wide range of vapor flows, multiple burners are used and are brought in and out of service to assure the flame arrestor tips are always kept cool and that exit velocities never exceed the stability limits of the burner. In order to prevent smoking, air assisted flare technology is used and air is brought in with enough energy adjacent to the vapor steam to assure complete combustion of heavier carbon molecules associated with gasoline and crude loading operations. Up to this point, all comments apply equally to elevated burners and burners located near grade that are encircled with a refractory lined enclosure. |