| 摘要 |
Apparatus for recovering vapor during de-pressuring of a vessel, and for those facilities with such a need, for recovering vapor during the liquid filling, or liquid removing, from a vessel. In de-pressuring mode, the vapor and inert gas purging the vessel are processed to recover multiple product vapors with vapor pressures from as low as 0.1 PSIG to about 100 PSIG. Higher values up to 250 PSIG are also processed economically by an optional third-stage, stand-alone system. This system produces overall product recovery rates over 99% and inert gas recovery over 99% at the latter part of the cycle as recycle gas. The system is purged after each use to prevent cross contamination In the liquid filling mode, displaced vapor and pad gas (inert gas added to maintain pressure in tanks during liquid removing) are processed to recover multiple products and the pad gas. Since there is not a continuous flow of inert gas as during de-pressuring from which to extract a large refrigeration load, recovery rates may be lower. The product is returned to the vessel being filled or stored. The pad gas can be stored in a tank and re-used. Actual recovery rates are primarily a function of the actual vapor being displaced, the flow rate of filling, the amount of inert gas present and the type of inert gas. Economics of a particular application determine whether additional compression and/or heat exchangers are needed. In the liquid removing mode, common practice is to release pressurized pad gas from a storage tank through appropriate valves and piping to return pad gas to the vessel compartment being unloaded. Vessel compartments have different pressure ratings and a pressure control system is installed to prevent over or under pressurizing the vessel. Addition of pad gas is normal practice and prevents pulling a vacuum on the vessel compartment and also increases the efficiency of the pump used for liquid removing by increasing head pressure.
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