Explain The Function Of Condensate Pumps

Nov 9

All condensate pumps are centrifugal and get their specific names from the fluid they move. Many different kinds of condensers use a vacuum to separate the water from the condensed steam (near vapor pressure). Condensate is moved by open-circuit pumps, which collect it in a holding tank (like a feed water tank) before sending it to a low-pressure feed heater connected to the boiler feed pump.

The maximum mass steam flow rate of the steam turbine controls the maximum capacity of the condensate pump.

Structure of the brain:

The geodetic head determines the water level in the feed water tank and the condenser.
There is a static pressure differential between the feed water tank and the condenser.
Head losses may occur as a consequence of pipeline components (such as gate and swing check valves) that are installed in the system (e. g. suction strainer, condensate preheater).

Because of the low intake head created when a condenser is installed within a structure, the suction side water vapor pressure (about 56.2 mbar for pure water at 35°C) must be taken into account during the design phase of the condensate pump. The geodetic head between the standard water level in the condenser and the impeller level may be used to determine the input head, after flow losses in the intake line have been subtracted.

Maximum performance and minimal cavitation damage are only possible if the system's available NPSH is greater than or equal to the NPSH needed at the first stage's impeller. This is the case no matter where one turns.

Follow these instructions to lift the intake head on the system's side:

Larger nominal pipe diameters, for instance, might decrease flow losses in the intake line.
The geodetic head differential is increased in a vertical installation, such as a dry installation, since the height of the first-stage impeller is decreased relative to the installation floor.
This "can-type pump," which is vertically structured to make the most of the geodetic head difference, has its suction stage housed in a "can" under the floor of the installation.
Water and waste pipes are exposed above ground at this structure's installation.

Improvements to the condensate pump's suction quality may be made in a number of ways.

Integral part of a well-functioning suction system is the impeller.
Constructing an inducer and installing it.
Work has started to fit a new dual-entry impeller.
Deceleration of the spinning motion.
Modifications made to the pump's piping to enhance flow.

Variations in design include condensate pumps with intermediate extraction (re-entry). All of the water from the pump's first and second stages is sent to the condensate cleaning system (condensate booster pump with single or dual entry suction stage).

The condensate pump, perched on a booster pump located off the ground, generates supplementary pressure.

When calculating cavitation loads, factors such as flow rates more than 150 l/s (540 m3/h), bubble trail length, and severity of cavitation must be taken into account. The material loss rate (LM) is used to quantify the extent of cavitation.

With no way to adjust the flow velocity at the leading edge of the impeller vanes, increasing the flow rate would result in longer bubble trails.

The shaft seal in a condensate pump has to be able to operate in a technical vacuum when the pump is turned off. In order to prevent air from entering the system, the sealing element requires a constant supply of barrier fluid from the system-side barrier system. If you're familiar with gland packings, you'll know that the lantern ring is what connects the individual packing rings together. There are two of each kind of mechanical seal available for inboard and outboard use. The lantern ring supplies barrier fluid to both the inboard mechanical seal and the outboard mechanical seal.

In a closed loop system, condensate pumps are typically powered by three-phase squirrel cage motors. The following set of controls may be used to adapt the pump to different turbine loads and prevent the condensate pump from drying out.

A condensate pump may be controlled in a number of different ways:

Characteristic curve modification through exhaust valve.
To alter the characteristic curve, bypass adjustment, which entails redirecting the overflow to the condenser, is used (see Bypass).
Changing the pump's speed affects the H/Q curve (speed control).
If the flow rate is allowed to vary in response to the height of the input head, the H/Q curve may be adjusted. The term "cavitation control" may be used to describe this kind of automatic regulation.

Since the characteristic curve H(Q) shifts when condensate evaporates upstream of or in the first stage, the self-regulating condensate pumps may adjust their heads by lowering H(Q) by a predetermined amount based on the amount of steam blockage (Hcav). The operational point is found when the head breakdown curve (Hcav(Q)) and the system characteristic Hsys(Q)) intersect (OP).

Self-regulation of condensate pumps is difficult because of the high cavitation loads they experience early in the pump's cycle. Since this regulation is unnecessary for modern, bigger pumps, it has been removed from service.