Liquid jet gas Compressors for Vapour Recovery from Crude Oil Tanks

Oil Production sites and Refineries use large tanks for storing Crude Oil. Crude Oil is a mixture of various hydrocarbons. When stored in a tank, the lighter fractions in the crude mostly Methane and Ethane flash off from the crude oil. These Methane & Ethane in vapour form occupy the space between the floating roof and the Tank liquid level.
The vapours are flashed continuously and keep on the collecting over the liquid level. This leads to increase in pressure inside the tank. This pressure increase is hazardous as increases gas leakage through the floating roof and also raises fire concerns.
To avoid any mishaps the tanks need to be periodically vented to keep the pressures within limits. During the venting process, some amount of vapour are released from the tank into the flare gas header. The vapour may then be flared or recovered from the flare system.
The storage tanks are very large in size and contain huge crude oil quantities. Naturally the amount of vapour vented throughout the day is considerable. These vapours are actually a fuel rich gas and has significant value if recovered.

But recovery of vapours is not an easy task and fraught with below challenges
• Availability at low Pressure
Generated vapours are typically at atmospheric pressures and need to be compressed in order to reuse them in the plant’s fuel gas network
• Sour Service
Crude Oil tends to have high concentrations of H2S. H2S possess a risk to the plant infrastructure and hence needs to be separated or neutralized during recovery

Liquid jet gas Compressors operate on the basis of jet Venturi principle and utilize energy in pumped water for their operation. During operation the Liquid jet gas Compressor displays a special ability to create vacuum at its inlet and at the same time creating a compressive effect between its inlet and outlet.
This enables the Liquid jet gas Compressor to utilize the vacuum to suck vapours from the storage tanks and then compress it to the required pressures. The water + vapours mixture is then separated in the gas-liquid separator and the compressed vapours can be reinjected into the fuel gas grid after appropriate treatment.

Liquid jet Gas Compressors are able to deliver very high compression ratios and compress the vapours to very high pressures. This makes it possible to directly inject the recovered vapours into the fuel gas grid without any additional compression by a mechanical compressor.

The system is similar to an Ejector based Flare Recovery but has following advantages:
• Each tank or set of tanks can be provided with its independent recovery system, thus reducing the load on the flare recovery system.
• The vapour generated in crude storage tanks are very rich in Methane & Ethane and if recovered independently, mixing with other gases in the flare headers can be avoided.

Liquid jet gas Compressors are suited for Vapour Recovery from Crude Oil tanks due to their inherent characteristics
• The vapour generation in each Crude Storage facility varies drastically. Liquid jet gas Compressors can be easily customized and hence are designed as per each facility.
• Can be manufactured in materials compatible with the sour service requirements.
• Liquid jet gas Compressors do not contain any moving parts and have large internal passage areas, hence are not vulnerable to liquid entry or clogging by solid particles.
• As they have no moving parts, maintenance requirements are very less. Also it reduces largely the risk of abrupt breakdowns, helps in maintaining the regular production schedule
• Water is available at high pressures in all Oil & Gas Facilities and hence no additional infrastructure is typically required.