1. STEAM COMPRESSION PROCESS
The steam ejector, or thermocompressor baelz 590, can be used as a variable circulation steam pump or as a compressor for re-evaporated steam / flash steam, for improving condensate return, for condensate cooling, for improving heat transfer and for limiting or restricting steam loses to the atmosphere, etc. The potential energy (motive pressure P01) is converted into kinetic energy (speed) in the steam nozzle (1). This causes a pressure drop and thus a suction effect. The motive flow M01 is mixed with the suction flow M03 at pressure P03 in the mixing tube (2) which expands in the diffuser (3) to mixing pressure P04. The generated flow M04 is the sum of the motive flow M01 and the suction flow M03.
In a system in a Nestlé plant the large condensate tank (15m²) that had been uncovered for 50 years was covered. The re-evaporated steam, mixed with the primary steam, was used to heat the deaerator.
The control valve allows more or less kg/h of steam m01 to flow, depending on the heat exchanger load. The speeds and pressures with which the steam supplies the consumer depend on the opening position of the valve and on the steam pressure. The entire steam flow m01 is motivated by its own pressure and is condensed in the heat exchanger. A float steam trap that only allows the flow of condensate and prevents steam from flowing through is installed at the outlet of the heat exchanger. If the consumer is equipped with a controllable ejector, the speeds and pressures with which the steam is supplied to the consumer also depend on the opening position of the ejector and the steam pressure.
Note, however, the following fundamental differences:
The steam is not “pushed” to the consumer solely by its own pressure, but rather it is also “pulled” by the consumer due to the suction effect of the ejector. There are two flows in the consumer: the motive steam volume m01 and the volume m03 of the steam drawn in, i.e. the circulation. At the outlet, the speed w of the steam is higher than in conventional cases. There is no steam trap at the outlet, which means that steam m03 and condensate m01 leave the consumer and are only separated in the separator. The return steam m03 flows from the separator to the suction inlet 03 of the ejector and condensate m01 flows to the steam trap.
Advantages at a glance
- Higher average steam speed in the consumer
- Better heat transfer coefficient h
- Fully active exchange surface
- Thinner condensate layer
- Reduction of the specific steam ratio (kg steam per kg product)
- Increase in production speed and improvement in drying quality. If the ejector closes during such an application, everything returns to zero: the pressures, the pressure losses, the volumes, because there is only one energy source: the motive steam at 01.
Used as a pressure reducer, a hot steam cooler or as a saturated steam or wet steam generator, this ejector has several advantages over the standard steamers found on the market.
Advantages at a glance
- Saturated steam generation without overheating
- Also for hot steam or wet steam generation
- Precision temperature control within the load range of 2–100%
- Very good (demineralized!) water atomization
- Simplified system structure
The primary steam passes into the nozzle at a speed of 665 m/s. It then expands in the diffuser, resulting in a speed of approx. 300 m/s for the mixture of steam and water droplets. The cooling water is atomized into droplets with a diameter of 0.75 mm. The steam refines these to 0.04 mm. That means that one droplet of 0.75 mm will be atomized into 6592 droplets of 0.04 mm. This increases the heat transfer surface for evaporation by a factor of 19.
This process is similar: The steam flows at a speed of 665 m/s through the almost closed nozzle. At minimum load, the nozzle atomizes the water into drops of 1.3 mm and the steam then further reduces their size to produce 206 droplets of 0.22 mm. This results in an increase in the heat transfer surface which also ensures a good rate of evaporation for such a small load.
With baelz 585 control valves/ejectors, flange design DN 15-125 and baelz 586, socket design DN ¾“-1½“ we offer a system component for low-noise steam-water mixing over a capacity range of 20-100%. Essentially this is an ejector valve.
Steam flowing over a nozzle creates suction in the 3rd path of the water/condensate assembly. Steam and water mix in the assembly, so that heated water/condensate exits at the outlet.
This process is used industrially for the direct heating of water baths, for the production of hot water with storage or in a continuous process. It is also used in the building trade as a compact and inexpensive solution for an indirect steam-water transfer station using a plate heat exchanger with primary-side admixture control without use of a circulation pump.