A Vapour Combustion Unit (VCU) is an "intermediate product", between an Enclosed Ground Flare and an Incinerator, for disposing of liquid & gaseous waste streams in a controlled way and meeting Customer limitations for the emissions. The system receives flare gas through a Knock Out Drum to dry the gas stream, a Water Seal in case of marine applications, and one or more flame arresters. A complete or partial skid-mounted solution is available and customizable to meet project specifications and available Plot Plan.
Applications range from gas plants, petrochemical industries to biogas applications. A typical installation or application for a VCU is at LNG loading terminals where they are used to dispose of the displaced vapour streams coming from the LNG carriers during loading operations.
The VCU receives the vapour from a vent line connected to the ship while its tanks are filled with LNG. Initially the vapour streams from the carrier tanks mainly contain inerts. Then, while the hydrocarbons are being loaded into the tanks of the ship, the inerts are displaced and sent to the VCU. During the initial stage of the ship loading, the VCU receives inert gases plus a small percentage of hydrocarbons, the displaced vapour then needs to be enriched with make-up gas for a high efficiency combustion to take place in the VCU.
Whilst the hydrocarbon stream is being pumped into the storage tanks, the percentage of hydrocarbons in the stream being sent to the VCU increases until the stream is composed mainly by hydrocarbons. During the various loading phases, regulation of flue gas temperature, primary air to burner and secondary air to combustion chamber and make-up gas flowrate is achieved by the PLC. The control system of the VCU monitors the temperature of the combustion chamber and the O2 in the flue gas, to meet emissions and to optimize the addition of the make-up gas stream when required. Operation of the VCU is carried out automatically by the VCU control system. A gas blower may be added to the scope to provide for pressure at the inlet of the gas burner. Where the VCU is also used to dispose of liquids, liquid guns can be installed and used to receive the hydrocarbon liquid from a separate source. All of the streams to be flared (liquids and gases), the utilities and the make-up gas are supplied to the VCU through a skid mounted system complete with valves and instrumentation, included in our scope. With few moving parts and minimal spare parts, our VCUs result in low operating and maintenance costs.