PIPER PROCESS SYSTEMS LTD

The Problem

Tanks are used throughout the Energy Industry to store product prior to pumping it to a plant or pipeline. The common types used are fixed roof and floating roof tanks.

Of these, fixed roof tanks reduce the environ-mental impact as the gas/vapour padding between the liquid and roof can be positively contained (see figure 1).

Seamless integration

of design, engineering

and fabrication.

www.piperprocess.com

A gas blanket fills the void between the liquid and tank roof. The blanket is typically a few ounces above atmospheric pressure to prevent air and consequently oxygen from entering the system and possibly creating a more explosive mixture.

As the tank fills, the liquid rises and compresses the gas blanket thereby raising its pressure. This increase in pressure must be relieved to pre-vent tank damage. It is drawn off the tank by the Vapour Recovery Unit or VRU (see figure 2).

The Solution-Reliable and Efficient VRUs

If the VRU becomes inoperable, or does not provide sufficient capacity, the increase in pressure will be relieved directly to atmosphere through relief valves on the tank. It is essential that the VRU be reliable and capable of han-dling the varying capacities and compositions of the vapours flowing from the tank.

The vapour coming from the tank consists of blanket gas (typically natural gas) and constit-uents from the liquid that have migrated into it. These constituents could be water vapour, light hydrocarbons, H2S, CO2 and asphaltines. The VRU takes the resulting vapour and raises it to a usable pressure for further processing.

Vapour Recovery

In heavy oil applications there are often el-evated temperatures and the potential of high concentrations of the constituents mentioned above. Liquid ring compressors have been found to be extremely reliable when incorpo-rated into a VRU module.

Liquid Ring Compressors

PIPER PROCESS SYSTEMS LTD 1.403.212.5750 sales@piperprocess.com www.piperprocess.com

Competing Products

Vapour

Recovery

It could be as an incompressible fluid, with an asphaltine build-up, or the hydrocarbon liquid diluting the lubricating fluid of the compressor.

An added advantage of the liquid ring compressor is the low temperature rise ex-perienced during compression. This allows for the liquids condensed to be captured in the VRU and transferred by pumps on the VRU module to the plant for use in the pro-cess. The condensed hydrocarbons can be separated in the VRU, which is particularly useful for diluent recovery.

FunctionWhen a tank is emptied, blanket gas is added (see figure 3) and the VRU capacity is reduced accordingly. For this application, a VRU with liquid ring compressor(s) will have the following capabilities.

• Fullyautomatedstopstartononeormul-tiplecompressorswithoutoperatorinter-vention

• 0%to100%fullyautomaticcapacitycon-trol

• Handleawidevarietyofpotentialinletva-pourcom-positions

• Provideeasymaintenanceandservice-ability

• Completelyintegratedmodulardesignal-lowingfullcontrolfunctions.

• 100%redundancyprovidingcontinuousoperationsevenduringmaintenance.

Advantages – Liquid Ring Compressor

• Ruggedandreliablemachinewithnotouchinginternalparts

• Significantlyreducedscheduledmain-tenance-reducingcosts-deliveringin-creasedproductiontime

• EliminatesGasconditioningbeforecom-pression

• Cooleroperatinganddischargetempera-tures(Isothermal)

• Oilfreedischargedgas• Singleortwostagecompressioncapability

usingonemachine• Canmanagesolidparticulatewithout

damage• Canoperateusingdifferentliquidstoactas

theringseal• Canacceptcondensingliquidsinthe

compressorwithoutaffectingthemachinesperformance

• Isexcellentforcompressingdirty,wet,andhighlycorrosivegasseswithoutaffectingmachinesperformance

• CanprocessH2SandCo2withoutanyis-sues

Other types of compressors, like vane and screw, have difficulties compressing a wet, dirty gas. During the compression cycle liquid may condense that can be damaging to the com-pressor.