Processes » Steam circulation


Depending on the load of the heat consumer (2a), the control valve releases more or less kgs/h of steam m01. The speeds and pressures, with which the steam supplies the consumer (2a), depend on the opening position of the valve (1) and on the steam pressure. The entire steam quantity m01 flows through its own pressure and is completely condensed in the heat exchanger (2a). The steam speed v is 0 m/s at the outlet. A float condensate drainer (3) which permits the passage of condensate only and prevents that steam passes through is fitted to the outlet of the heat consumer.

If the consumer (2b) has been fitted with a controllable jet pump (4), the speeds and pressures, with which the steam is fed to the consumer (2b), also depend on the opening position of the jet pump and on the steam pressure. But, there are the following fundamental differences:

• The steam is pressed to the consumer not only by its own pressure, but it is also drawn in by the consumer (2b) through the suction effect of the jet pump.

• There are two flows in the consumer (2b): the steam pressure quantity m01 and the quantity m03 of the steam drawn in, i.e. the circulation.

• At the outlet, the speed w of the steam m03 is not equal to zero !

• There is no condensate drainer at the outlet, which means that steam m03 and condensate m01 leave the consumer which is separated by the separator (5) only. The return steam m03 passes from the separator (5) to the inlet 03 of the jet pump and the condensate m01 flows to the condensate drainer (3).

• Compared to a consumer provided with a control valve, the consumer fitted with a controllable jet pump has the following best properties:

 - higher medium steam speed in the consumer

 - better heat transfer coefficient K

 - fully active exchange surface

 - thinner condensate layer

 - reduction of the specific steam consumption (kg steam per kg of product)

 - increase of the production speed and improvement of the drying quality

When the jet pump closes in such an application, everything is reset to zero: the pressures, the pressure losses, the quantities because there is only one source of energy: the motive steam at 01.


A simplified comparison between control valve and thermocompressor
(steam jet pump)

This application is known in the paper industry, which has been using this technology for more than sixty years. The good results in this sector has permitted the introduction of the same technology in many other sectors of industry, primarily in the textile industry, agricultural industry and in the chemical industry.

For better understanding of the good results with jet pumps, the illustration demonstrates the differences in behaviour of the control valve and the circulation pump.

Caption of the illustration:

Schematic and simplified explanation as to why a heat consumer (2a, 2b) provides a better output with the controllable jet pump than with a control valve.


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