Steam ejectors use a motivating fluid and pressure-to-velocity energy conversion to create vacuum. Nozzles convert high-pressure steam to high-velocity steam in the mixing chamber to create a low-pressure region. As the steam and entrained air travels down the diffuser, kinetic energy is lost and pressure increases again. Steam ejectors handle high volumes of gasses, including wet, corrosive, or particulate-laden vapors, and operate in the rough or medium vacuum range, with operating pressures to 0.003 torr. Multiple-nozzle designs, a Croll-Reynolds specialty, improve efficiency. Steam ejectors mount in any orientation and have a low maintenance design with no moving parts. Multi-stage systems offer improved vacuum, and can contain up to six ejector stages. The number of ejectors is determined by the level of vacuum required. Condensers are included to remove steam from the system and reduce load on later stages.
Steam Jet Ejectors For The Process Industries Pdf 20
Shell and tube condensers, such as the one shown here, cool the steam down using arrays of cooling tubes. Condensate is drained from the system, allowing more steam to be added at the next ejector. Each system is a custom design and multiple condensers can be used as well. Steam ejector systems provide the lowest capital costs among vacuum process pumps.
Thermocompressors are designed for applications in the food, petroleum, chemical, power, and paper industries. Thermal recompression is typically applied in the dairy and juice industries to recapture and reuse steam from evaporators during the concentration process.
In the ejector, the velocity of the motive fluid becomes very high as it expands across the converging and diverging nozzles from motive pressure to the operating pressure of process fluid. The expansion of the motive fluid through the motive nozzle causes supersonic velocities at the exit of the nozzle. Velocity coming out from a motive nozzle is 3 to 4 times the Mach number. In the actual scenario, the motive fluid expands to a pressure lower than the suction process fluid pressure. This causes the driving force to draw the suction fluid into the ejector. High-velocity motive steam entrains and mixes with the suction fluid.if(typeof ez_ad_units!='undefined')ez_ad_units.push([[300,250],'whatispiping_com-large-leaderboard-2','ezslot_15',635,'0','0']);__ez_fad_position('div-gpt-ad-whatispiping_com-large-leaderboard-2-0');Main Parts of an EjectorThere are five main parts of an ejector which are as follows,
A multi-stage ejector is normally used when a generation of high vacuum is required that is normally from the atmosphere to in the range of 30 torrs to 0.05 torr. For the generation of such low pressure, up to six stages of the ejector can be used.What is Motive Fluid?Motive fluid is the fluid that motivates the process fluid to draw into the ejector. Normally high- pressure steam is used as a motive fluid but compressed air or gas can also be used as the motive fluid. The choice depends on the availability of the utility, operational feasibility, etc. A minimum pressure of the motive fluid is required to maintain a stable operation & thereby for designing a stable ejector system. If the pressure of the motive fluid falls below the design pressure then the nozzle will pass less amount of steam than required. If it happens, the ejector is not provided with sufficient energy to compress the process fluid to the design discharge pressure. A similar problem occurs when the supply temperature of motive fluid rises above its design value which results in increased specific volume, and consequently, less steam passes through the motive nozzle.
Steam ejector is the ejector which utilizes high-pressure steam as the motive fluid. It has a converging and diverging nozzle across which pressurized motive fluid is passed. In the diffuser section, the velocity of the mixed fluid is recovered to pressure energy greater than suction pressure but it is lower than the inlet pressure of the motive steam. This pressure should be greater or equal to the backing pressure for smooth operation. For low vacuum, multiple-stage ejectors are used. Table 1 shows the probable suction pressure vs total steam consumption in an ejector.No. of stageOperating suction pressure (Torr)Total Steam consumption per kg of air pumped (kg)1200-1004-8260-40015-20320-518-2543-0.520-100Table 1: probable suction pressure vs total steam consumption in an ejectorThe steam jet ejector capacity is directly proportional to the weight of the motive fluid. Motive gas to process gas pumped is high, especially under low vacuum, and results in the huge requirement of steam in multi-stage systems. Operating parameter of motive steam such as inlet steam pressure, and discharge pressure has a significant impact on overall ejector performance.Fig. 2: Different Sections of a Steam EjectorPurpose of Inter-condenserInter-stage condensers & ejectors are staged in series with each other. The purpose of the inter-condenser is to condense hydrocarbon & steam as much as possible. The load of the downstream ejector can be reduced by condensing steam & hydrocarbon. So for proper maintaining of motive steam consumption condenser is highly recommended.
Vapor recompression relies upon a mechanical compressor or steam jet ejector to increase the temperature of the latent heat in steam to render it usable for process duties. Recompression typically requires only 5% to 10% of the energy required to raise an equivalent amount of steam in a boiler.
Consider a petrochemical plant that vents 15-psig steam to the atmosphere. At the same time, a process imposes a continuous requirement on the boiler for 5,000 lbs/hr of 40-psig steam. If 15-psig waste steam is recompressed to 40 psig by an electrically driven compressor, the compression ratio is:
The NASH condenser exhauster saves energy when air leakage increases SEE HOW MUCH MONEY IS INVOLVED INVOLVED Steam cost per million These dollar figures are computed on the pages that follow for a typical utility power generating unit. The same calculations can be applied to actual generating units now in service or projected. The analysis reveals the impressive energy savings of the NASH condenser exhauster. You lose Or this much this much with a NASH NASH with steam condenser jet ejectors exhauster Btu So you save this much with NASH NASH Dollars per 24-hour day $1 $550.80 $194.40 $356.40 $2 $1,101.60 $338.80 $712.80 $4 $2,203.20 $777.60 $1,425.60 $8 $4,406.40 $1,555.20 $2,851.20
System design assumes air leakage Venting equipment is installed on a steam condenser to prevent non-condensable gases from accumulating in the vapor space. Small amounts of non-condensables inhibit heat transfer. Large amounts can virtually block the condensation process. Some of these gases are released from solution in the liquid condensate. Some arrive with the exhaust steam, having been dissolved in the boiler water. The major non-condensable component in a fossil fueled system, though, is air in leakage that finds its way into the sub-atmospheric condenser system. A NASH AT-2006E...
Graphite multi-stage steam jet vacuum pumps are used in various industries to remove gas molecules from a volume in order to leave behind a partial vacuum. They are a reliable alternative to vacuum pumps. GAB Neumann offer graphite single and multi-stages steam jet vacuum pumps for ultra-corrosive applications. They consist in several graphite steam ejectors and graphite condensers in series.
If the condensation temperature is too low at the intermediate temperature, several ejectors might be installed in series without condensers in between. Multi-stage steam jet vacuum pumps can be designed for suction pressures down to 1 mbar or lower. The maximum compression ratio for a steam jet vacuum pump depends on the suction pressure and the pressure of the available motive steam. For steam jet pumps for suction pressure of less than 6 mbar the head and the mixing nozzle shall be heated to prevent the formation of ice.
GAB Neumann designs and manufactures graphite single and multi-stage steam jet vacuum pumps for ultra-corrosive applications. They consist in several steam ejectors and condensers in series. It is possible to reach a vacuum level of 150 mbar and less with a single steam ejector and a condenser. With 2 ejectors and condensers a vacuum level of 20 mbar and less can be reach, 3 mbar or less with three, 1 mbar or less with four and 0.2 mbar or less with 5 in series. 2ff7e9595c
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