- Jet Condenser Definition: A jet condenser is a device that condenses exhaust steam from a turbine using cooling water.
- Low Level Condenser: This type of condenser is placed low and needs pumps to remove condensate and air.
- High Level Condenser: Also known as a Barometric condenser, it uses a long pipe to create a vacuum, removing the need for pumps.
- Ejector Condenser: Utilizes falling water’s momentum to eject air and condense steam, suitable for small power units.
- Counter Flow and Parallel Flow: In counter flow, steam and water flow in opposite directions; in parallel flow, they move in the same direction.
The term jet condensers covers direct-contact equipment that mixes exhaust steam with cooling water. The steam condenses into the cooling-water stream, so the installation cannot recover clean condensate unless the water quality and process permit reuse. Three traditional arrangements are:
- Low level condenser.
- High level condenser.
- Ejector condenser.
Low Level Condenser
In a low-level condenser, the chamber is installed near ground level or below the steam turbine exhaust. Because the chamber operates below atmospheric pressure, a liquid-removal pump discharges the mixed cooling water and condensate. A separate air pump or ejector may remove non-condensable gas, depending on the arrangement.
Low-level jet condensers can be classified by the relative flow directions:
- Counter Flow
- Parallel Flow Jet Condenser.
The following sections explain both arrangements.
Counter Flow Low Level Jet Condenser
In this type of steam condenser, exhaust steam enters near the bottom and rises while cooling water enters near the top and falls. Perforated trays or spray nozzles divide the water into droplets and increase direct-contact area. The coldest water meets the coolest vapour and non-condensable gas near the top, which supports a small terminal temperature difference.
The cooling water and condensed steam collect at the bottom and flow to an extraction pump, which discharges the mixture to a hotwell or cooling system. Direct contact can contaminate the turbine condensate with circulating-water impurities. It should be returned to a steam boiler only when its chemistry and treatment meet the plant requirements. Boiler feed water quality, makeup and blowdown must be managed as part of the complete water cycle.
An air pump or ejector at the gas outlet removes leaked air and other non-condensable gases. In a counterflow jet condenser, the gas stream is cooled before extraction, which reduces its water-vapour content and volumetric load. The device must still be sized for air leakage, released dissolved gas and the required condenser pressure.
- It handles the non-condensable gas and remaining water vapour rather than the main liquid flow.
- Cooling near the water inlet condenses more vapour and reduces the gas-vapour volume presented to the air-removal device.
In this type of steam condenser, condenser vacuum can provide some suction lift for the incoming cooling water. The available lift falls with altitude, warm water, piping losses and lower absolute pressure.
A cooling-water pump is required whenever the available pressure difference cannot deliver the design flow. Vacuum alone must not be assumed sufficient.
Parallel Flow Low Level Jet Condenser
A parallel-flow low-level jet condenser also mixes steam and cooling water directly, but both streams enter near the top and move downwards together. Steam condenses as the mixed flow passes through the contact region.
In one parallel-flow arrangement, a wet-air pump removes cooling water, condensate and the gas-vapour mixture from the bottom. This combines liquid and air removal but gives the pump a larger volumetric load.
Because one pump handles liquid, non-condensable gas and water vapour, attainable vacuum and efficiency depend strongly on pump design and inlet conditions. Condenser vacuum may draw cooling water from a source below the chamber only when the available suction lift exceeds static and friction losses. Other installations need a cooling-water pump.
High Level or Barometric Jet Condenser
A barometric condenser is elevated above a hotwell so its sealed tailpipe can discharge liquid by gravity while the chamber remains under vacuum. The theoretical sea-level water column is about 10.3 m, but the required effective tailpipe height also depends on condenser pressure, water temperature, altitude, friction and operating margin. The tailpipe does not create the vacuum. Condensation and the air-removal system establish it.
The vertical tailpipe outlet remains submerged in the atmospheric hotwell to form a liquid seal. A pump or adequate supply head delivers cooling water near the top of the chamber.
Exhaust steam enters near the bottom and rises against descending water jets, so this is a counterflow jet condenser. The cooling water and condensate drain through the tailpipe to the hotwell under gravity. The liquid column balances the pressure difference between the condenser and atmosphere.
No liquid-extraction pump is needed when the barometric leg has sufficient height and remains sealed. A dry-air pump or steam ejector removes non-condensable gas and residual vapour from the top. It does not handle the main cooling-water and condensate flow.
Ejector Condenser
An ejector or multi-jet condenser uses pressurised cooling-water jets to entrain vapour and non-condensable gas. Exhaust steam enters the body around a central passage fitted with nozzles or mixing cones.
Cooling water accelerates through the converging nozzles at the specified pressure. The jets entrain steam through the side ports and create direct contact. Condensation sharply reduces vapour volume, while jet momentum carries the remaining gas and liquid towards the diffuser.
The reduced pressure draws more exhaust steam into the mixing passages. The combined stream of cooling water, condensate, residual vapour and non-condensable gas then enters the diverging nozzle.
In the diffuser, part of the kinetic energy becomes pressure, allowing the mixture to discharge towards the hotwell at atmospheric pressure. A non-return or relief arrangement protects the exhaust connection from water carryback when flow or vacuum is lost. Its exact design must follow the condenser and turbine manufacturer’s requirements.
An ejector condenser can eliminate a separate air pump, but it needs cooling water at the specified flow and pressure and may use more water than other arrangements. Its compact construction has suited small power generation units and process-vacuum services where mixed condensate can be accepted.
