EP0588259B1 - Recycling of the axial thrust compensation water - Google Patents

Description

The invention relates to a centrifugal pump.

A wide variety of solutions are known in this technical field. DE-PS 465 383 shows a shared relief water flow. The partial flow having a higher pressure is optionally introduced into the suction chamber or into the pressure chamber by one of the pump stages. In contrast, a partial flow of lower pressure, which emerges after passing a throttle section in front of the gland sealing the shaft, is discharged into the open. The subject of DE-PS 539 225, which is equipped with a multi-stage relief device, functions in a similar manner. Here, too, the partial flow of the relief water that accumulates in the space between the shaft seal and the relief device is discharged outdoors. In DE-PS 681 087, the relief device has a number of stages which corresponds to the number of stages of the pump. Since a partial pressure of 50 bar is to be reduced in each relief stage, a complex piping system is used. According to a selected scheme, this connects the individual relief stages with precisely assigned pump stages, in order to guarantee the specified pressure drop.

From DE-PS 1 094 592 it is known that the water that accumulates directly behind the relief device and in front of the shaft seal formed by a stuffing box the suction nozzle or the inlet tank of the pump is supplied. The subject of DE-OS 1 403 846 makes use of the same principle in a complex control engineering implementation.

If mechanical seals are used as shaft seals instead of the gland seals, additional cooling systems are required for the mechanical seals. Because the mechanical seals cannot be used directly in relation to the pressure and temperature conditions of the relief water and would be destroyed quickly.

A multi-stage centrifugal pump with mechanical seals is known from US Pat. No. 3,999,882, which has a pressure reducing device behind the last pump stage. Any fluid that escapes from this is fed into the suction port of the centrifugal pump with a return line. Further connecting lines connected to the return line cause a feed into a mechanical seal space, with a large number of throttle elements which are complex to adapt serve to guide the flow. The possible cooling of the mechanical seals and the saving of a heat exchanger is only possible at low temperatures.

The invention is therefore based on the problem of developing a less complex solution, with the aid of which a mechanical seal directly acted upon by the relief water can be used in a temperature range> 120 ° C. in multi-stage feed pumps. The solution to this problem is given in the patent claim. The usual and known procedure to connect the space before the shaft seal to the pump suction side, ensures a high pressure drop in this room. This relieves the shaft seal considerably, so that the stuffing boxes usually used only have to prevent steam from escaping. Mechanical seals cannot be used for this, however, since they rely on liquid lubrication of the parts sliding on one another. Under such operating conditions, an additional cooling device for a mechanical seal is unavoidable, so as to avoid evaporation of the relief water located in the mechanical seal space. The invention now goes a completely different way by completely dispensing with the use of cooling devices. Instead, the mechanical seal used is directly exposed to the hot relief water. The risk that, due to the additional frictional heat in the sealing gap, evaporation of the relief water occurs and thus the sliding surfaces are destroyed, the invention prevents. The mechanical seal space is connected to the first pump stage or a pump stage of higher pressure by means of a return line. As a result, a pressure is maintained in the mechanical seal space, which prevents the liquid in the space from evaporating, even at high temperatures. The pressure conditions are designed so that there is always a pressure at the mechanical seal that corresponds to the vapor pressure of a conveying medium temperature that is approximately 20 ° C. above the operating temperature of the conveying medium. Since all components of the mechanical seal are matched to the high temperature range, their reliable use is guaranteed when operating in the desired temperature range. Evaporation in the area of the sliding surfaces is thus prevented in the simplest way.

An embodiment of the invention is shown in the drawing and will be described in more detail below. A multi-stage pump (1) is equipped with a relief device (2), which is followed by a mechanical seal space (3) for sealing the shaft (4). The relief water emerging from the relief device (2) cools and lubricates the mechanical seal (5) directly. In order to prevent evaporation within the mechanical seal chamber (3), this is connected to the pressure chamber (7) of the first pump stage (8) by a return line (6). The pressure prevailing here prevents the hot liquid in the mechanical seal chamber (3) from evaporating. The return line (6) can also open into another, high-pressure space of the first or another pump stage of higher pressure.

This system can be used advantageously for pumps with a drive shaft passage on the pressure side, since the suction side of this machine can therefore be made medium-lubricated. A shaft passage on the suction side would, on the other hand, Mechanical seal always means the application of the inlet pressure or the sealing space would have to be delimited in a complex manner with a throttle system.

Claims (1)

1. A centrifugal pump (1) of the multi-stage type, and more particularly a feed pump, comprising a relief means (2) for the axial thrust, a shaft seal (5) arranged downstream from the relief means, fluid emerging from the relief means flowing directly to a shaft sealing space (3), and the shaft seal is designed in the form of a slip ring seal (5) and a return duct (6) opening from the slip ring seal space (3) is connected with a pressure space of the first pump stage (8) or a pump stage with a higher pressure.

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