Ejector Technology


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Ejector Technology

Ejectors (also referred to as Surface Jet Pumps) provide a simple, robust, and reliable method of pumping and boosting the pressure of fluids. Ejectors use a high-pressure fluid to compress a low-pressure fluid to an intermediate pressure. The provide a simple, robust and reliable method of pumping and boosting the pressure of fluids.

How It Works

The operation is based on Bernoulli’s principle, whereby when you increase the velocity of a fluid as it passes through the nozzle of the ejector, a low-pressure region is created within the Ejector. This region entrains and compresses the secondary low-pressure stream which we call the suction fluid. As the combined High Pressure (HP) and Low Pressure (LP) streams pass through the Ejector’s diffuser section, the velocity decreases and the pressure is regained, resulting in an intermediate pressure, which lies somewhere between the LP and HP inlet pressures.

Advantages of Ejectors over Traditional Gas Compressors

Increase Recovery from Low-Pressure Wells – For Free!

Ejectors are an effective tool to increase production, enhance recovery and extend the life of mature fields. This is achieved by lowering the back-pressure on a well (or a number of wells) imposed by the downstream pipeline and process equipment.

The reduction in the flowing wellhead pressure (FWHP) will result in an increase in production. In many cases, it is also expected that the reduction in the FWHP will help to stabilise production and improve the flow regime of fluids passing through the well bore.

Each well will have its own characteristics. Some high-pressure wells decline very fast, some very much slower. The good news is that even with a fast-declining high pressure well, the economics of an Ejector project are compelling. The energy can be used efficiently and effectively to boost production from a low pressure well, providing a significant payback of extra production.

Click: https://www.transvac.co.uk/production-boosting for more details.

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.

Simple, proven control methods cater for fluctuating flare gas flows, ensuring stable, consistent performance. Flare Gas Recovery Ejectors are often employed as a retrofit solution to replace failing compressor types, such as Liquid-Ring or Screw Compressors.

With no moving parts contacting the often-dirty and sour flare gas, Ejectors are the only sensible, reliable choice.

For more details on how Ejectors can enhance flare gas recovery in your organization.

Click: https://www.transvac.co.uk/flare-gas-recovery

FAQs About Ejector Solutions

All Ejectors are custom designed and built to meet customers’ individual requirements. Thus, there is no specific limit to size in terms of diameter or length. Based on experience, lengths have varied from 0.3m to 8.0m and the Ejector discharge diameter from 1/2” to 36” NB.

Ejectors can be fabricated from any machinable or weldable. Typical materials are Low Temp Carbon Steel, Stainless Steel, Duplex Stainless Steel and Super Duplex Stainless Steel. Materials can be NACE certified for sour application. The internal surfaces can be coated with hard wearing materials such as tungsten carbide, stellite, etc. or lined with ceramics for erosive duties.

All Ejectors are custom designed to form an integral part of the customers’ piping system, thus the pressure/temperature rating of the Ejectors will match that of the interconnecting pipework.

Flanged Connections, rated from class 150# to 2500#. For higher pressure ratings, API 6A or API 17D for subsea applications, are supplied. Compact type flanges or clamp type connections are also possible.

In most cases the Ejectors and Silencers are designed to meet the highest operating pressure, plus an allowance for safety. Normally no pressure relief is needed. It is, however, possible to incorporate a Pressure Relief Valve (PRV) if the LP side piping system is a lower pressure rating than the HP side piping, or to meet site specific requirements such as the site fire case.

Noise applies to gas Ejectors only. The produced noise level may often exceed 85dBA silencers can be installed on the LP inlet and the discharge line of the Ejectors to prevent noise travelling through the interconnecting pipe work. In cases where noise emitted directly through the body of the Ejectors exceeds the acceptable limit, the entire Ejectors can be lagged acoustic insulation materials. The normal acceptable limit is generally 85dBA at 1.0m from the Ejectors. There are, however, exceptional cases where lower noise level is required.

If vibration from the Ejectors is predicted to be a problem, then the Ejectors and silencer supports can be fitted with custom designed anti-vibration mounts.

This is an issue dependent on factors such as HP and LP pressure, temperature and flow rate and the presence of liquids in the LP flow. In general, the theoretical Joule Thomson temperature drop across the Ejectors does not fully materialise, mainly as a result of LP flow mixing rapidly with HP gas and the pressure increasing along the mixing tube and diffuser. Low temperature may be experienced if only HP gas passes through the Ejectors with no LP gas.

In general, the outlet temperature is often lower than the LP or HP temperature by approximately 20% to 30% whichever has the lower value.

Hydrates do not normally form within the Ejectors because of high velocity of flow and the combination of HP and LP flow. If the predicted outlet temperature is within the hydrate formation band, then injection of hydrate inhibitor and / or use of heat tracing are recommended. It is usually recommended not to run the HP flow alone (for over a few minutes) without flowing the LP gas in advance.

Changes to the operating conditions will affect the performance of the Ejectors. The Ejectors normally passively responds to such changes by adjusting the LP pressure at its inlet. Its operating range can be extended by simple control and changes of the internals.

Change-out of internals.

This change of internal component within an Ejectors, namely the Hp nozzle and diffuser or mixing tube unit. The internal geometry of these two items is what gives the Ejectors its operating characteristics. Change-out of the internals is only required if there is a significant change one or more key operating key parameters. As the nozzle and diffuser are matched to each other it is usual to change out both internals together, unless the change primarily related to the HP flow. Changing the internals is relatively simple and can be carried out within a few hours: the time needed includes full isolation of the system, venting and draining before the Ejectors can be opened.

Normally no active control is needed on production boosting or pressure boosting applications. In other applications, control of the LP or Discharge pressure would be important, e.g in flare gas recovery applications, control of the LP pressure is generally required to prevent process upsets or to protect the LP separator from exposure to below atmospheric pressure.

The start-up / shut down procedure for the Ejectors is a very simple and easy. Detailed   procedures are provided for each application to ensure all site related and HAZOP issues are considered.

Not directly via the Ejectors. HP gas can only boost LP gas. However, HP liquid (oil or water) can boost LP gas pressure.

Presence of Liquids in the HP or LP gas is tolerated when the liquid rate is less than 1% to 2% of the gas flow rate at the operating P&T (i.e at GVF greater than 98%). Beyond these values separation of the liquid phase is recommended prior to entry to the Ejectors as it begins to significantly affect the performance of the Ejectors. Transient conditions, such as those at start-up when liquids may be swept through pipelines or loaded wells, are acceptable as a temporary condition.

Gas Ejectors are tolerant of liquid slugs passing through them. Liquid slugs will not mechanically damage the Ejectors or Silencers. However, performance will be temporarily affected until the slug has passed through.

Ejectors offer stable LP flow rate turn-down from the design flow rate to near zero LP flow rate without the need of any active control. Hence they are tolerant to sudden changes in LP flow rates. If the HP pressure / flow rate is significantly reduced below the designed value, the nozzle needs changing to match the new HP condition. If the discharge pressure changes, the Ejectors automatically adjusts the LP pressure to match its performance.

An Ejectors can be operated down to zero suction flow rate without causing mechanical damage. However, at zero LP flow conditions and full HP flow only, the temperature effect and possibility of hydrate formation needs to be investigated.

There are a number of ways to protect the LP separation from under pressure. One method is to install a by pass line equipped with control valve which routes fluid from the outlet of the Ejectors back to its LP inlet. This valve will allow recirculation of some gas and will prevent the LP pressure falling below a set point. There may be other viable control strategies.

Peak thermodynamic efficiency of an individual Ejectors device is only around 30%. However, this should not be the basis for selecting or rejecting these devices because they often use energy which was previously being wasted to do useful work. In some cases, the application of Ejectors can bring dead or shut-in-wells back to life. Furthermore, because of the way in which they operate, Ejectors have significantly lower maintenance and running costs.

Ejectors can be installed and operated satisfactorily in any orientation or arrangement. For gas or liquid driven Ejectors installed vertically, there would be a preference for the flow to be arranged vertically downwards, as that provides the best Orientation for liquid drainage. The most appropriate orientation is primarily dictated by site conditions.

Ideally Silencers should be connected directly to the LP inlet and the discharge outlet of the Ejectors. If this is not possible, any pipework between the Silencers and the Ejectors should be acoustically lagged to limit noise emission through these sections.

This depends highly on the site conditions and constraints. It is normally recommended that Ejectors are located as close as possible to the LP source to minimise LP piping pressure loss. Site conditions may, however, dictate otherwise.

Production increase as a result of reducing the back pressure on wells depends on the Productivity Index (PI) of the well, which is outside the control of the Ejectors. If the PI of the candidate wells are not known, the wells could be tested via the test separator to determine their durability and production characteristics.

Yes. There has been a number of successful cases where the Ejectors has revived dead wells or liquid loaded wells.

However, there are cases where the limited HP pressure and flow rate available is insufficient to achieve the initial revival or unloading. In these cases, other techniques should be used for the initial revival of the well before the Ejectors is brought on-line to maintain steady production.

There are no critical upstream / downstream straight pipe length requirements for Ejectors installation. However, sufficient lengths should be allowed with break-in flanges to allow Ejectors internals withdrawals. This is needed mainly on the discharge and HP sides.