US3059396A

US3059396A - A device for drawing off gaseous components from a gas-vapour mixture

Info

Publication number: US3059396A
Application number: US785024A
Authority: US
Inventors: Thees Richard
Original assignee: Leybold Anlagen Holding AG
Current assignee: Leybold Anlagen Holding AG
Priority date: 1958-01-07
Filing date: 1959-01-05
Publication date: 1962-10-23
Anticipated expiration: 1979-10-23

Description

Get. 23, 1962 Filed Jan. 5, 1959 R. THEES DEVICE FOR DRAWING OFF GASEOUS COMPONENTS FROM A GAS-VAPOUR MIXTURE 2 Sheets-Sheet 1 Fig. 7

Oct. 23, 1962 R. THEES 3,059,396

DEVICE FOR DRAWING OFF GASEOUS COMPONENTS FROM A GAS-VAPOUR MIXTURE 2 Sheets-Sheet 2 Filed Jan. 5, 1959 Fig. 3

nite T During the operation of a steam-turbine it is necessary to maintain a definite low partial pressure of air in the air outlet junction behind the main condenser. This partial pressure of air influences the optimum efficiency of the turbine and is usually of the order of mm. Hg. To maintain the desired pressure water jet pumps or steam jet pumps have already been used frequently; these, however, are not reliable in attaining the required low partial pressure and also have a high consumption of energy.

Already considerable improvement has been achieved by connecting to the air outlet junction a device containing an auxiliary condenser and a vacuum pump working on the gas-ballast principle (hereafter referred to as gasballast pump for short). In spite of the advantages attained especially regarding the energy consumption, certain drawbacks have become apparent making further improvement desirable. These drawbacks may be summarised as follows:

It is necessary to use cooling water in the condenser having a temperature, much lower than that of the cooling water in the main condenser of the turbine; in practice this condition is very difficult to fulfill and the proposed arrangement will for example be practically of no use for water-power stations, where, from the outset cooling water of low temperature is used resulting in low temperatures of the vapours drawn-off from the main condenser. The same purpose could be achieved by increasing the condensing surface of the auxiliary condenser, however practical limits are soon reached.

The low tolerance of a gas-ballast pump towards water vapour results in the known arrangement having a very narrow middle working-margin between the maximum and the minimum quantity of air that can be drawn off. A larger working range is required for reasons of safety. Besides this, the power consumed is practically always the same as that required for conveying the maximum permissible quantity of air, irrespective of the actual amount of air conveyed.

The present new invention concerns a device for drawing oft gaseous components from a gas-vapour mixture, especially for drawing-01f air from the main condenser of a turbine set by means of a precompression stage and at least one auxiliary condenser and a gasballast pump. The new device is characterized in that the precompression stage is provided with at least one positive rotary or Roots-type compressor which is placed in front of the auxiliary condenser in the direction of gas flow. Such a device has considerable technical advantage over those'known. It is a special advantage that it adjusts itself automatically to the various amounts of air to be drawn off. When there is no air present the rotary compressor having a given delivery compresses very little or not at all. Compression occurs only to such extent that that quantity of vapour is condensed in the intermediate condenser which is delivered by the rotary compressor. When there is air to be pumped off, the gas-ballast pump draws off this amount of air at a definite partial pressure of air, behind the auxiliary condenser. An increase in the partial pressure of air at the outlet of the auxiliary condenser however results in a decrease in the condensing capacity, and the compression of the rotary compressor increases to such an extent that the amount of vapour condensed as a result of the in- States iPate-t ice creased vapour pressure at the inlet of the auxiliary condenser compensates for the increased partial pressure of air at the outlet of the auxiliary condenser so that the quantity of the vapour condensed corresponds to the quantity of vapour delivered by the rotary compressor. With a rotary compressor the Work of compression, and with it the power required increase with rising proportion of non-condensable gas in the gas-vapour mixture. 011 the other hand, with increase in the total pressure only the partial pressure of air increases on the outlet side of the auxiliary condenser; this results in important advantages:

it is now possible to attain the condensing capacity required in the auxiliary condenser without the use of colder cooling-water by increasing the vapour-pressure on the inlet side. The power required by the rotary comprcssor adjusts itself automatically to the desired efliciency and becomes less the colder the cooling Water is which can be supplied to the auxiliary condenser. The increasing total pressure on the outlet side of the auxiliary condenser results in partial pressure of air on the inlet side of the gas-ballast pump which are greater than the total pressure of the gas-vapour mixture at the inlet side of the rotary compressor. This causes a substantial increase in the difference between the maximum and the minimum quantities of air which can be drawn off. The new invented device can also be used for water-power stations and the low temperature of the cooling water and of exhaust-vapour existing there advantageously reduce the power consumption of the rotary compressor.

According to a further development of the present invention the delivery of the rotary compressor is chosen to be greater than the condensing capacity of the auxiliary condenser by a factor corresponding to the ratio of partial vapour pressure at the inlet side of the rotary compressor to the maximum permissible partial pressure of Water vapour at the inlet side of the gas-ballast pump. By this means a favourable working range with a greater separation between the maximum and the minimum quantities of air that can be drawn off is attained. In order to prevent accumulation of condensed fluid in the rotary compressor, the latter can be suitably arranged so that its direction of conveyance is vertical or approximately vertical. With this arrangement condensed fluid does not accumulate in the rotary compressor, but is passed directly to the appropriate part of the device, the auxiliary condenser. To reduce the difliculties in sealing the axles of the rotors of the Roots-type compressors evacuated gearboxes are used in a known manner so that the necessary means of sealing can be of relatively simple construction. The low pressure-difference between the interior of the rotary compressor and the evacuated gearbox need not be considered. Until now such gearboxes were directly connected to the outlet of the compressor. Such construction however is not found suitable in the given circumstances, as there is a possibility that particles of the oil used for lubricating the gearwheels become carried along through the evacuation-line and mix with the condensate in the auxiliary condenser.

In turbine-sets an oilfree condensate is required under all conditions. According to the invention this can be easily ensured by connecting the, gearboxes of the rotary compressor to the inlet of the gas-ballast pump by an evacuation-line. Should traces of oil be drawn off from the gearbox they will reach the gas-ballast pump and therefore cannot contaminate the condensate.

It is preferable to use an oil in the gearboxes of the rotary compressor which has a low vapour pressure at the existing temperatures so that the partial vapour pressure of the oil will remain low. In such an arrangement it will be of further advantage to provide a pre-set pressure relief device for the protection of the rotary compressor. This is provided in a pressure relief line connected across the compressor in a known manner. Overloading of the rotary compressor is thus avoided, as a partial equmization of pressure takes place through the pressure relief line when the maximum permissible pressure difference between the inlet and the outlet of the compressor is exceeded. It may be of advantage in various cases to increase the maximum permissible pressure difference for the rotary compressor by the application of a cooling device especially for cooling the rotors.

In a recommended form of construction of the invented device an adjustable air inlet-valve is placed in the connecting line between the auxiliary condenser and the gasballast pump. When there is unusually little air to be pumped away or partial stoppage of the cooling water supply a certain quantity of air is let into the inlet of the gas-ballast pump so that the permissible partial pressure of water vapour is not exceeded and the gas-ballast pump is protected from condensing water.

Apart from this, it is of advantage to connect the drainage pipe for the condensate of the auxiliary condenser to the condensate drain of the main condenser with a syphon-like water loop, while the height of the water loop is so chosen that at least within the permissible limit of pressure difierence for the rotary compressor no pressure equalization can take place between the auxiliary condenser and the main condenser. As, in such a device the rotary compressor will usually be protected against a given permissible pressure difference being exceeded the total pressure in the intermediate condenser cannot become so large that pressure equalisation takes place through the condensate drainage pipes.

The present invention can of course be realized in various technical forms of construction as adapted to definite working conditions. Thus, for example, the precornpression stage may consist of many Roots-type pump units connected in series having intermediate condensers connected in-between them. Further the condensing capacities of these intermediate condensers can be adjusted according to the pressure on the inlet side of the respective rotary compressor.

In this way devices can be made which also operate reliably at very high cooling water temperatures by means of high compression ratios without any one rotary compressor being overloaded because of too high a pressure difference or showing poor volumetric efficiency.

Even the gas ballast pump can be made up from different units having different deliveries. By regulating the deliveries the total pump set can be operated at optimal power consumption when operating conditions change because of different cooling water and exhaust vapour temperatures, e.g. in summer and winter.

Because of danger of corrosion, it is under certain circumstances necessary to render the rotor and the delivery chamber of the rotary compressor corrosion proof by surface treatment or protective covering. For the rotary compressor and the gas-ballast pump a corrosionprotective oil is suitable.

' In the drawing a form of construction of the invented object is shown schematically:

FIG. 1 shows a schematic side-view, partly in section, of a form of construction of the invention in connection with a turbine main condenser.

FIG. 2 is a vertical sectional View along the line AA of FIG. 1 through the casing of a Roots-compressor and FIG. 3 is a schematic side view of a part of the arrangement similar to that shown in FIG. 1 in which, however, the direction of convergence of the rotary compressor is vertical.

In the drawings the same units of construction bear the same reference numbers.

. In FIG. 1 a main condenser 1 is seen, into which the turbine vapours enter in the direction of the arrow A, through the connecting joint 2. In the interior of the main condenser 1 supporting plates 3 carry packages of cooling tubes 4 by means of which the vapours entering the main condenser 1 are condensed and leave the latter as a condensate through the outlet joint 5.

The main condenser 1 also shows an air outlet joint 6 to which a positive rotary compressor 8 acting as a precompressor, is connected by means of a corresponding flange joint 7.

This rotary compressor 8 can be driven by an electric motor 9 and is in turn connected to an auxiliary condenser 13 through a connecting line 10 with

flange joints

11, 12. By means of inlet and outlet pipes 131, 132 a cooling spiral 133 situated inside the auxiliary condenser 13 is connected to a cooling-medium circuit not shown. The outlet of the auxiliary condenser 13 leads through a junction line 15, which is connected by a flange joint 14, to the inlet of a gas-ballast pump 16. An electric motor i7 is provided for driving the gas-ballast pump 16. Both electric motors 9, '17 can be connected to an AC. supply by appropriate means of switching not shown.

As can be seen from FIG. 2 the working space of the rotary compressor, which is essentially determined by the cylinders formed by the rotation of the

rotors

81, 82, is separated from the gearbox 83, in which the gearbox 84, necessary for driving the rotors are situated. Because of the low pressure difference between the evacuated gear housing 83 and the working space of the rotary compressor the axles seals 86, 87 such as rubber sleeves are subjected to only little strain and can therefore be mounted without additional sealing material. The gear housing 83 shows an evacuation line 88 with connected flange 89, and is joined through a connecting-line 90 by means of a flange connector 1&1 to the connector line 15 to the inlet side of gas-ballast pump 16. For returning the liquid condensate formed in the auxiliary condenser 13 a condensate return line connected by a flange connector 134 is provided having a syphonlike tube loop 136, and which enters into the condensate drainage pipe 5 of the main condenser 1 through a flange connector 137.

The arrangement shown in FIG. 3 corresponds essentially to the arrangement according to FIG. 1 with the exception that the rotary compressor 8 is so arranged that the gas mixture drawn off from the condenser 1 is conveyed vertically downwards. Thus no condensate can accumulate within the compressor, but flows off to the auxiliary condenser 13. FIGURE 3 also shows an adjustable air inlet valve 14a which communicates with the conduit joining the auxiliary condenser 13 and the gas-ballast pump 16. This embodiment is also provided with a pressure relief line 18 connected between the air outlet joint 6 of the main condenser and the outlet of compressor 8; This line 18 is provided with a pre-set pressure relief device 18a.

7 The new arrangement and the new method can also be used analogously for other equipment and processes, in which mixtures of various vapours with air or with other gases are to be sucked off whilst a certain partial pressure of gas has to be maintained.

What I claim is:

1. In combination with a main condenser, a device for drawing off gaseous components from a gas-vapour mixture from said main condenser, said device being in communication with said main condenser and comprising: at least one auxiliary condenser, a gas-ballast pump in communication with said auxiliary condenser, and at least one positive rotary Roots-type compressor interposed between said main condenser and said auxiliary condenser and being situated in front of the latter in the direction of conveyance, said positive rotary compressor having a housing divided into separate pumping and gear chambers, and a plurality of rotors each having a driving gear, said rotors being arranged in said pumping chamber and said driving gears being arranged in said gear chamber, said gear chamber being in communication with the inlet side of said gas-ballast pump for reducing the pressure in said gear chamber and removing any oil which would otherwise contaminate the condensate.

2. The device defined in claim 1, wherein said gear chamber of said positive rotary compressor housing is filled with oil having a low vapour pressure at the operat ing temperature of said compressor.

3. In combination, a main condenser and a device for removing gaseous components of a gas-vapour mixture from said condenser, said device being in communication with said main condenser and comprising:

(a) at least one auxiliary condenser;

(b) a gas-ballast pump in communication with said auxiliary condenser;

(c) compressor means interposed between said main condenser and said auxiliary condenser for providing an output which is greater than the condensing capacity of said auxiliary condenser by a factor corresponding to the ratio of partial vapour pressure at the inlet side of said means to the maximum permissible partial pressure of Water vapour at the inlet side of said gas-ballast pump, said means being a Roots-type blower including a housing divided into a pumping chamber and a driving chamber; and

(d) means in communication with said driving chamber and the inlet side of said gas-ballast pump for reducing the pressure in said driving chamber and removing any oil which would otherwise contaminate the condensate.

4. In combination, a main condenser and a device for removing gaseous components of a gas-vapour mixture from said condenser, said device being in communication with said main condenser and comprising:

(a) at least one auxiliary condenser;

(b) a gas-ballast pump in communication with said auxiliary condenser;

(0) means interposed between said main condenser and said auxiliary condenser for providing at most very little compression when no air is present at its inlet which compression occurs only to the extent that that quantity of vapour is condensed in the auxiliary condenser which is delivered thereby, and providing compression, when there is air present which is caused to increase its partial pressure at the outlet of the auxiliary condenser, to such an extent that the amount of vapour condensed compensates for the loss of condensation efliciency caused by the increased partial pressure of air at the outlet of the auxiliary condenser, said means being a Rootstype blower including a housing divided into a pumping chamber and a pump drive chamber; and

(d) communication means between said pump drive chamber and the inlet side of said gas-ballast pump for reducing the pressure in said pump drive chamber and removing oil which might otherwise contaminate'the condensate formed in the auxiliary condenser.

References Cited in the file of this patent UNITED STATES PATENTS 247,691 Roots Sept. 27, 1881 1,053,677 Sutton Feb. 18, 1913 1,372,926 Audouin Mar. 29, 1921 1,684,406 Morgan Sept. 18, 1928 2,512,045 Steinberg et al. June 20, 1950 2,938,664 Hans-George Noller May 31, 1960