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Steam ejectors use steam or gas instead of moving parts to compress a gas.  In a jet or ejector, a relatively high-pressure gas, like steam or air, expands through a nozzle. The steam or air converts that pressure or potential energy to velocity or kinetic energy.  The jet of high-velocity steam or gas entrains the gas to be evacuated or pumped in the suction of the ejector.  The resulting mixture enters the diffuser where velocity energy is converted to pressure at the ejector discharge.

Steam ejectors use steam as the high-pressure motive fluid to create a deep vacuum. Whereas air jet ejectors are utilized when the required capacity is low or steam is not available or desired. The simple construction and lack of moving parts result in a reliable pump with little maintenance, a low initial cost that is custom-designed with no limit on size, capacity or materials of construction.

Steam ejectors can also be combined with liquid ring vacuum pumps to create a hybrid capable of deep vacuum that ejectors can deliver but with lower energy use.  Nash is globally recognized for assembling the most efficient steam jet and air ejectors and ejector vacuum systems. Application engineers ensure maximum efficiency and performance benefits while optimizing a hybrid system customized to processes, applications, and technology requirements. NASH steam jet and air ejectors minimize greenhouse gas emissions and operational efficiency while improving system stability.

Operating Profile Of Steam Ejectors

Nash Ejector

Steam ejectors pass steam through an expanding nozzle. The nozzle controls the expansion of steam and converts pressure into velocity; thus, creating a vacuum to transfer gases. 
An ejector operates on a mass basis, not by displacing volume. Therefore, ejectors are better suited to handling gases with low molecular weights and when operating at low absolute pressures. These systems are ideally suited to high vacuum applications but are only marginally useful as compressors.

A jet of motive fluid is supersonic velocity entrains the inlet stream and raises its velocity to the speed of sound as the two flows mix. A stationary sonic shock wave forms in the throat of the diffuser, and absolute pressure rises sharply at this point. More pressure rise occurs along the discharge cone as flow slows down. The most common motive fluid is steam at 80 PSIG (6 bar abs.) to 400 PSIG (28 bar abs.). Other fluids can be used whenever there is a good reason to avoid mixing steam with the product.

Steam ejectors or steam jets, ejectors that use steam as motive gas, are by far the most popular type of ejectors.  A single ejector can be designed to create as much as 27 inches Hg vacuum (or about 76 mm HgA).  To create a deeper vacuum, ejectors can be ‘staged’ or installed in series.  Steam ejectors are favored for this because the motive gas – steam – can be condensed between some of the stages to minimize load (and motive steam) to the following stage. Steam ejectors have been used in some industries to reduce the pressure of a vessel to the point that water freezes.  They can be staged to reach a suction pressure of less than 0.1 mm Hg absolute.


NASH Ejectors

Steam Ejectors Are The Ideal Solution 

Steam ejectors and ejector/vacuum pump hybrids are the ideal solutions for the most demanding applications in oil & gas, chemical, electric power, food & beverage. Steam ejectors are used in demanding applications such as:

  • Reactor Vacuum (Chemical Industry) – vacuum can allow the plant to reduce reaction temperature and save energy.  It can also be used to avoid polymerization, undesired reactions and avoid thermal degradation. 
  • Vacuum Distillation (Chemical/Oil & Gas Industries) – pulling vacuum on a product and condensing it allows separation of two or more volatile components with different boiling points.
  • Drying of solids in batch or continuous processes (Chemical/Food & Beverage Industries) – using vacuum allows the solid to be dried at a lower temperature. It can be beneficial when processing heat-sensitive materials, to improve drying rates and to produce very low final moisture concentration.
  • Evaporator vacuum (Chemical/Food & Beverage Industries) – concentrate materials in a liquid state by boiling off solvent (water). Much of the work is done by a condenser. Using vacuum can reduce the energy cost and avoid damaging heat-sensitive products. 
  • Sugar Vacuum Pans (Food & Beverage Industry) -  after the sugar juice is concentrated through evaporation (see above), the vacuum is used to convert the syrup to a state where crystals begin to form
  • Bleaching & Deodorizing (Food & Beverage Industry) – using vacuum to remove color and contaminants from edible oil.
  • Condenser Exhausting (Electric Power Industry) – to optimize the expansion of the steam through the turbine requires the turbine condenser to be maintained at its optimum vacuum. This vacuum must be maintained by removing air that leaks into the condenser.  

Advantages Of Steam Ejectors

  • No moving parts 
  • Simple in construction 
  • Easy to maintain 
  • Available in a wide variety of materials 
  • Low investment, high utility cost
  • Good for MW gases 
 

Installation Of Steam Ejectors

  • Ejectors can be mounted in any direction, precaution must be taken to properly drain the system
  • Barometric condensers/ Shell and tube condenser drain leg must be mounted high enough to gravity drain the water and avoid flooding in the condenser
  • Ejectors can discharge into the hot well
  • If condensers cannot be mounted at the correct elevation, low NPSH pump has to be used
 

How To Improve Ejector System Efficiency

  • Combine ejector strengths with Liquid ring vacuum pump strengths
  • Last stage jet and after-condenser are eliminated and replaced with a high-efficiency liquid ring vacuum pump
  • Interstage condenser pressure is optimized and cooling water load is typically reduced
  • An interstage ejector could be nozzled to optimize interstage pressure and minimize steam flow
 

Highest Quality Standards

Nash designs, builds and tests ejectors at its headquarters in Charleroi, PA, in compliance with HEI Standards for Steam Jet Vacuum Systems, the global standard for steam ejectors.  We are also a proud member of HEI and regularly contribute to the development and improvement of industry standards.

 

Global Provider

Using more than 110 years of experience and expertise, Nash provides a wide range of liquid ring vacuum pump solutions. From pumps and compressors to customer engineered-to-order solutions, we offer a comprehensive portfolio of products that can help you solve the most complex challenges.

Backed by our NASH CERTIFIEDTM  Service Offering, as well as a full range of OEM parts, spare, and aftermarket services, we can act as your trusted partner; protecting your investment and providing you with total peace of mind.

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