Condensate pumps of the Ks, KsD, KsV types represent a special group of energy pumps characterized by specific operating conditions: operation in conditions of high vacuum and minimal geometric head. This margin is determined by the difference in the vertical marks of the level of the free surface of the liquid in the condenser and the center of gravity of the inlet opening of the impeller of the first stage of the pump (geometric support) and losses in the inlet path of the pump.
Condensate pumps are designed for pumping condensate in steam-water networks of thermal power plants operating on fossil fuels, as well as liquids similar to condensate in viscosity and chemical activity. The main parameters of the pumps were regulated by GOST 6000-88.
Condensate pumps are divided into pumps of the first and second lifts of the main condensate and drainage ones. The first lift pumps pump condensate from the turbine condenser through a block treatment plant to the inlet of the second lift pumps, which supply the condensate through low-pressure heaters to the deaerator.
Condensate pumps must operate reliably in the presence of initial or developed stages of cavitation in the impeller area, and in some cases, in the presence of supercavitation flow around the impeller elements.
The specific operating conditions of condensate pumps determined the basic requirements for their design:
– ensuring reliable and long-term operation (at least 10,000 hours) with partial cavitation in the pump;
– absence of air leaks through operating and idle pumps;
– a stable, continuously decreasing form of the pressure characteristic in the supply range from 20% to 110% of the nominal to ensure stable parallel operation in the general network.
To expand the range of use of condensate pumps, it is allowed to trim the impellers along the outer diameter by no more than 10% of its original value. In this case, the reduction in efficiency should not exceed 3%.
In order to reduce the harmful effects of cavitation and ensure reliable operation of condensate pumps, the following operating times in the flow ranges are recommended:
– from 0 to 0.2Qnom – no more than 3 minutes;
– from 0.2 to 0.5Qnom – up to 5% of the total pump operating time;
– from 0.5 to 0.85 Qnom – no more than 15% of the total pump operating time;
– from 0.85 to 1.05Qnom – without limitation
– over 1.05 Qnom – according to the load conditions of the electric motor and the cavitation reserve at the input.
All manufactured condensate pumps can be combined into several structurally similar groups. Within each group, pumps have many common design features and solutions with minor differences in the design of individual components.
The materials of the main parts of condensate pumps are gray cast iron, carbon and alloy steels. Chromium steels are used for first-stage impellers and pre-engaged axial wheels.
For small flows, Ks type pumps are used.
As an example of a design of this type, consider the condensate pump Ks 32-150-2.
Condensate pump Ks 32-150-2 (Figure 1) – centrifugal, multistage, horizontal, sectional type with one-sided impellers.
Figure 1
The pump body consists of inlet and discharge covers, between which a set of standardized sections is installed.
One section includes a guide vane, which performs the functions of supplying fluid to and removing it from the impeller, and the section housing. In places where the impellers are sealed in the sections and guide vanes, replaceable sealing rings are installed.
The package of sections and covers are centered together on cylindrical grooves and tightened with pins, forming a pump housing. The tightness of the joints is ensured by the “metal” contact of the sealing bands of the sections and covers, as well as by the installation of rubber sealing rings made of heat-resistant rubber.
The inlet and discharge covers are made of cast parts. Together with the covers, pipes and support legs are cast, with which the pump is installed on the base slab pedestals. The pressure pipe is directed vertically upward, and the inlet pipe is directed horizontally to the side (to the right of the horizontal axis of the pump, when viewed from the drive side). The design of the pipes is flanged. To remove vapors and release air, there is a hole in the upper part of the inlet cover. When the pump is running, the hole is closed with a plug. The pressure cover has a threaded hole for connecting the discharge drum chamber to the inlet pipeline.
End seal housings and bearing housings are attached to the covers.
To ensure directed thermal expansion of the housing along the pump axis, the lower part of the covers is provided with: a longitudinal keyway in the inlet cover, and a hole for installing a pin in the discharge cover.
The pump rotor is a separate assembly unit and consists of a shaft, impellers, an upstream wheel, a discharge drum, bushings, sealing parts and fasteners. To increase the suction capacity of the pump in front of the first stage impeller a pre-engaged wheel is installed. The parts are installed on the shaft using a sliding fit. All impellers, except the first stage, have the same flow path. The impellers, the upstream wheel, the discharge drum, and the bushings are fixed on the shaft with keys, and in the axial one with round nuts. There is a gap between the last stage wheel and the drum, which serves as a compensator for thermal expansion when the impellers are heated by the pumped condensate.
The assembled pump rotor is dynamically balanced.
The axial force of the rotor is perceived by the unloading piston (drum).
The end seals of the pump are stuffing box type with a water seal ring, to which cold condensate is supplied under pressure to cool the stuffing box and prevent air from leaking into the pump. The stuffing box is also cooled by cold condensate entering the chamber made between the seal housing and the bushing.
It is possible to install mechanical seals.
The rotor supports are rolling bearings with grease lubrication. A roller bearing is installed at the end of the shaft on the drive side, and a ball bearing at the free end of the shaft. The inner races of the bearings are fixed on the shaft with round nuts, the outer races with the end caps of the bearing housing, which are secured with through bolts. Tubes are provided in the bearing housings to drain leaks from the end seals.
Alignment of the pump rotor in the stator (pump body) is ensured by moving the bearing housings using adjusting screws. After the rotor is aligned, the position of the bearing housings is fixed with pins.
The pump housing is covered with a protective and decorative casing made of sheet metal, which is attached to the inlet and discharge covers.
An asynchronous motor with a squirrel-cage rotor is used as a drive.
The pump and motor are installed on a common foundation frame and connected to each other using an elastic pin-type coupling. The coupling is closed by a guard.
The pump symbol means: Ks – condensate; 32 – flow rate in m3/h; 150 – head in m; 2 – second modernization.
