FI81967C - OVER ANALYZING FOR SEPARATION OF OAKING CONDITIONERS GASER AND AONGA. - Google Patents

Description

1 81967

Method and apparatus for separating uncondensed gases from steam.

This invention relates to a method and apparatus for separating uncondensed gases from steam by isothermal absorption. It can be used to increase the efficiency of the condenser deaeration and to reduce the pumping energy required for it.

The removal of uncondensed gases from the condensing steam 10 is a key problem in all steam handling processes. The most common problem of this type is the removal of leaking air from the condenser of a condensing power plant. Similarly, in seawater distilleries, the removal of dissolved air is a prerequisite for the process to work. The importance of this problem 15 increases as the steam is condensed at a lower pressure.

It is known that the non-condensing gases entrained in the condenser with the steam can be separated from the steam by cooling the mixture of steam and these gases. In this case, the vapor pressure decreases and the partial pressure of the non-condensing gases increases accordingly. In this way, the proportion of steam in the mixture is reduced, which in turn reduces the total amount of gas pumped out of the vacuum during deaeration.

Cooling the steam requires a very careful design of the condenser so that the flow rate of the gas mixture remains sufficient at all times to prevent the accumulation of uncondensed gases and, on the other hand, the flow losses remain sufficiently low. For example, if the gas mixture is cooled from 2 ° C to 25 ° C, the vapor pressure drops from 31.7 mbar to 28.1 mbar. If at the same time the total pressure decreases by 1 mbar due to flow losses, the partial pressure of the non-condensed gases is 2.6 mbar. Uncondensed gases then have to remove more than ten times the volume flow of steam.

2,81967

According to the invention, the partial pressure of the non-condensing gases can be increased by means of isothermal absorption. The gas mixture leaving the condenser can be brought into contact with an absorption medium in which the vapor pressure is low compared to the vapor pressure in the gas mixture. Such absorption media may include aqueous solutions of many highly soluble salts, such as sodium hydroxide, lithium bromide, lithium chloride, calcium chloride, potassium carbonate, and potassium acetate. Steam is then absorbed from the gas mixture into such an absorption medium and the partial pressure of the uncondensed gases increases accordingly. When uncondensed gases are removed from this space, only a small amount of steam has to be pumped from the vacuum with them.

As the steam is absorbed into the solution, it transfers to it its absorption heat, whereby the temperature of the solution tends to rise and its vapor pressure increases accordingly. To prevent this, the absorption medium is cooled in an indirect heat exchange with a coolant, for example cooling water, as is done in the absorber of an absorption heat pump. In this case, the vapor absorption takes place substantially isothermally and the vapor pressure of the solution remains low.

For example, if the absorption medium is a 30% sodium hydroxide solution at 25 ° C, its vapor pressure is about 14 mbar. When water vapor is absorbed into this solution at the same temperature of 25 ° C and the flow loss is assumed to be the same 1 mbar as in the previous example, the partial pressure of the non-condensed gases rises to 16.7 mbar. With non-condensed gases, only 0.8 times the volume flow of steam has to be removed.

The absorption medium dilutes as steam is absorbed therein. 35 It is concentrated by evaporating an equivalent amount of steam from this absorption medium at a slightly higher temperature, in the same way as in the steam generator of an absorption heat pump. The released steam can be condensed in a separate condenser. The temperature can also be adjusted so that the pressure of the released steam is the same as that of the original absorbed steam, whereby this re-vaporized steam can be condensed in the same condenser from which the mixture of steam and non-condensed gases was removed.

In order for the steam and the absorption medium to have a sufficient heat and mass transfer surface and on the other hand for efficient cooling and heating of the absorption medium, both the absorber and the generator can in practice be constructed of horizontal tubes on the outer surface of which the absorption medium flows as a thin film.

Claims (4)

4,81967 A method for separating non-condensed gases from steam, characterized in that a mixture of non-condensed gases and steam 5 is brought into contact with an absorption medium having a vapor pressure lower than that of the vapor in the gas mixture. , A gas mixture containing more condensed gases than the original gas mixture is pumped out of the process in some known manner. A method according to claim 1, characterized in that an amount of steam corresponding to the amount of steam absorbed therein is evaporated at a temperature higher than the absorption temperature and this steam is condensed in a separate condenser or in the same condenser from which the uncondensed gases and condensed gases were removed. Apparatus for applying the method according to claim 1 or 2 for the removal of non-condensable gases from a condenser, characterized in that said apparatus comprises an absorber, a steam generator and a known pumping device arranged so that the gas space of the absorber is connected to the condenser. to the gas outlet connection and on the other hand to said pumping device and the gas space of the steam generator is connected to the steam space of said condenser 30 or to a separate condenser. Device according to Claim 3, characterized in that the absorber and the steam generator have heat exchangers constructed of substantially horizontal tubes, on the surface of which the absorption medium is made to flow in the form of a thin film. Il 5 81 967