Traditionally, in the Oil & Gas industry, waste and surplus gas has been disposed of by flaring to atmosphere. Today this process is becoming increasingly unacceptable as the industry progresses towards eliminating the emission of greenhouse gases into the atmosphere, whilst simultaneously conserving energy. Therefore, the demand for equipment that can safely and
economically compress waste and surplus gas back into the production process is rapidly increasing.
Ejectors are ideally suited to this application because they employ either the available high-pressure gas or liquid energy to entrain and compress waste and surplus gas to a pressure where the gas can be recovered into production or used as fuel gas. With no moving parts and requiring no maintenance, Ejectors are the only sensible choice.
Driving your Ejectors
Ejectors operate with either a gas or a liquid as the high pressure motive fluid. In many cases, only a small compression is required to facilitate waste gas re-entry into the production process. Most commonly, this re-enters the process as fuel gas, is sent to export, or is used as injection/lift gas. Gas motivated Ejectors offer a compression of 7:1 in a single stage. This can be further boosted with the use of a secondary Ejector. Liquid driven Ejectors offer compressions of up to 150:1. Where water is used to drive an Ejector, facilities can often provide available separator capacity to handle the discharge water.
In many cases, the recovery of gas from a separator results in a boost in production from the upstream manifold, as the reduction in backpressure from the separator allows wells to flow more easily.
Liquid Jet Compressors with up to 150:1 compression
Transvac’s LJC solution is a complete, turnkey zero-flare solution for the oil & gas industry. Providing up to 150:1 compression, our latest range of LJC's recover waste gasses with ease and eliminates the need for flaring outside of emergency situations. Using experience gained over 45 years and fine tuned in our state of the art R&D test facility, LJCs offer the very latest in cutting-edge Ejector technology and performance. Waste gasses are compressed and discharged at a specified pressure to suit required the downstream process. In most cases, recovered gas can be returned to production or is used as fuel gas on the facility.
A Liquid Jet Compressor does not interfere with local ESD procedures and is intended to recover gasses continually sent to flare, such as purge, separator and knock-out drum gasses. Simple control philosophies cater for varying inlet (flare gas) flow rates and ensure upstream process is not affected. With no moving parts, Ejectors can handle both solids (such as sand) and sour gasses without issue. Special-grade ceramic internals can be included to resist abrasion and ensure reliability.
Reinjection of waste gas & CO2 Sequestration
Transvac's Liquid Jet Ejectors offer a suitable method of compressing waste gas for reinjection down-hole, eliminating the need for flaring. Existing injection water pumps can be used to supply high pressure water to the LJC which entrains and compresses the waste gas. The Ejector then discharges the compressed gas/HP fluid back down-hole. In many instances, the reinjected fluid is used for resevoir flooding/EOR techniques - an additional benefit.
Carbon Capture & Storage (CSS) / CO2 sequestration can also be achieved with Transvac's Liquid Jet Ejectors. The technique is the same, using HP water to gather, compress and reinject CO2 into the resevoir. If water cannot be reinjected, a separation stage can be added downstream of the Ejector.
Flare Gas Ejector Control Options
It is not uncommon for the flow rate of flare gas to vary and, if not controlled, the suction pressure created by the Gas Ejector will also vary. In order to maintain the desired flare gas operating pressure, a number of control strategies are available. These include:
- Recycling of gas from the discharge side of the Gas Ejector back into the suction (low pressure) side
- Incorporation of an integral HP gas regulating valve which varies the motive fluid consumed.
If the required compressions ratio (discharge pressure / LP pressure) is too high to achieve in a single Ejector, then they can be connected in series to achieve the required discharge pressure. The total flow from the first stage Ejector becomes the LP flow for the 2nd stage Ejector. The consideration with this approach, however, is that the second Ejector may require a higher motive pressure or flow rate.
Where high turndown is expected on the LP (flare gas) flow rate, Ejectors can be placed in parallel. This allows switching one Ejector on or off, depending on the duty demand, thereby allowing motive gas to be saved. This is important in some applications, particularly where HP fluid usage has an associated cost. In some applications, more than two Ejectors have been used in parallel.