Steam ejectors use vapor or gas instead of moving parts to compress gas. In an injector, a gas with a higher pressure, such as steam or air, expands through a nozzle. Steam or air converts pressure or potential energy into velocity or kinetic energy. A jet of high-velocity steam or gas entrains the gas to be evacuated or pumped in the suction port of the ejector. The resulting mixture enters the diffuser, whereby the velocity energy is converted into pressure at the outlet of the ejector.
Air-powered ejectors are often referred to as air jets or jets. When no steam is available, air is usually used on small ejectors. When paired with NASH liquid ring vacuum pumps, they can use room air or pump exhaust as a power source to increase the level of vacuum that the pump is capable of. When a vacuum system must be able to pull down to the vapor pressure of the water being degassed, it is often used in applications such as degassing. This type of jet is convenient to use because it does not require a steam or pressurized air source to make it work, but only a vacuum pump.
Steam ejectors can also be combined with liquid ring vacuum pumps to create a combination system capable of creating a high vacuum, which can be provided by the ejector but with lower energy consumption. NASH has a global reputation for assembling more efficient steam and air ejectors, as well as ejector vacuum systems. Experienced application engineers ensure maximum efficiency, performance benefits, and optimized custom composite systems to meet process, application, and technical requirements. NASH steam and air injectors minimize greenhouse gas emissions and increase operational efficiency, while improving system stability.
Operation of the steam ejector
The steam ejector transports steam through an expansion nozzle. The nozzle controls the expansion of the steam and converts the pressure into velocity; Thus, a vacuum is created to transport the gas. The ejector operates on the basis of mass, not by displacement volume. As a result, the injector is better suited for handling low molecular weight gases and operating at low absolute pressures. These systems are ideal for high vacuum applications, but can only be used as compressors.
The jet of the moving fluid is supersonic, and with the mixing of the two fluids, it entrains the inlet air flow and increases its speed to the speed of sound. A fixed sound shock wave is formed in the pharynx of the diffuser, at which point the absolute pressure rises sharply. As the flow rate decreases, the pressure along the discharge cone increases. The most common motive fluid is steam from 80 PSIG (6 bar abs.) to 400 PSIG (28 bar abs.). Other fluids can be used as long as mixing the vapor with the product can be sufficiently avoided.
Steam ejectors, that is, ejectors that use steam as power, are by far the most popular type of ejector. A single ejector can be designed to produce a vacuum of up to 27 inches of Hg (about 76 mm Hg). To create a higher level of vacuum, the ejectors can be “staged” or mounted in series. Steam ejectors are favored because the power gas—steam—can be condensed at certain stages to minimize the load (and power steam) in the next stage. Steam ejectors have been used in some industries to reduce the pressure of a vessel to the point where the water freezes. They can be graded to pressure levels with an absolute suction force of less than 0.1 mm Hg.
How to improve the efficiency of your ejector system
Combine the strength of the ejector with the strength of the liquid ring vacuum pump
The last stage ejector and rear condenser were eliminated and replaced with a high-efficiency liquid ring vacuum pump
Optimizes interstage condenser pressures and generally reduces cooling water loads
Interstage ejectors can be injected to optimize interstage pressure and minimize steam flow
Installation of steam ejectors
The ejector can be installed in any direction, and precautions must be taken to properly drain the system
The drain feet of the pneumatic condenser/shell-and-tube condenser must be installed high enough to drain the water in gravity and avoid condenser overflow
The ejector can be discharged into a hot well
If the condenser cannot be installed correctly at the correct height, a small-capacity NASH pump must be used
Advantages of steam ejectors:
No moving parts
Simple construction
Easy to maintain
A variety of materials are used
Low investment and cost-effective
Solutions for process-demanding applications
Steam ejectors and combined ejector/vacuum pump systems are ideal solutions for the most demanding applications in the oil and gas, chemical, power, and food and beverage industries.
Reactor vacuum (chemical industry) – Vacuum allows the unit to lower the reaction temperature and save energy. It can also be used to avoid polymerization reactions, adverse reactions, and thermal degradation.
Solids drying in batch or continuous processes (chemical/food and beverage industry) – Solids can be dried at lower temperatures using vacuum. When processing heat-sensitive materials, it can help increase the drying rate and reduce the moisture concentration.
Applications for Steam Ejectors
Vacuum distillation (chemical/oil & gas industry) – Vacuuming and condensing a product separates two or more volatile components with different boiling points.
Evaporator vacuum (chemical/food and beverage industry) – concentrates a liquid substance by boiling a solvent (water). Much of the work is done with condensers. The use of vacuum can reduce energy costs and avoid damage to heat-sensitive products.
Bleaching and deodorization (food and beverage industry) – Vacuum is used to remove color and contaminants from edible oils.
be maintained by removing the air leaking into the condenser.
