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What Are Condensate Pumps?

Jun 9

Pumps for condensate are centrifugal pumps that are named by the fluid they are used to pump. Using a vacuum to remove water from condensed steam, it is found in many types of condensers (near vapor pressure). Open-circuit condensate pumps transport the condensate into a tank (for example, a feed water tank) and pump the condensate straight into a low-pressure feed heater for the boiler feed pump.

Condensate pump capacity is governed by the maximum mass steam flow rate of the steam turbine.

 

Composition of the cranium:

  • The feed water tank and condenser have water levels that vary by a geodetic head.
  • Pressure differences exist between the feed water tank and condenser in terms of static pressure.
  • As a result of valves and other system components put in the pipeline (such as gate and swing check valves), head losses might occur (e. g. suction strainer, condensate preheater).


In order to meet the low intake head produced by the condenser's placement inside the building, the design of the condensate pump is dictated by the suction side water vapor pressure (approximately 56.2 mbar for pure water at 35°C). It is possible to calculate the input head by subtracting flow losses from the intake line from the geodetic head that exists between standard water level in the condenser and impeller level in the first stage of a cooling system.

To minimize cavitation damage and guarantee optimum performance, the system's available NPSH must be more than or equal to the NPSH required at the first stage's impeller. Everywhere you look, this is the case.

 

To raise the intake head on the system's side, do the following steps:

  • Intake line flow losses may be reduced by adopting larger nominal pipe sizes, for example.
  • Vertical installation, such as a dry installation, which reduces the first-stage impeller's height above the installation floor and raises the geodetic head difference
  • An input "can" below the installation floor holds the suction stage of this "can-type pump," which is vertically configured to optimize the geodetic head difference.
  • Supply and drain pipes may be seen above the installation's ground level.


It is possible to enhance the condensate pump's suction quality in many ways:

  • Proper suction impeller set-up.
  • Installing an inducer.
  • Installing a dual-entry impeller has begun.
  • Reduction in the rotational speed.
  • Improvements to the flow channels of the pump.


Condensate pumps with intermediate extraction are an example of design variations (re-entry). Condensate cleaning system receives all flow from the first or second stage of the pump (condensate booster pump with single or dual entry suction stage).


Additional pressure is provided by the condensate pump, which sits on top of a booster pump and is placed above the floor.

It is important to consider cavitation intensity, velocity conditions, the length of a bubble trail, and flow rates over 150 l/s (540 m3/h) when considering cavitation loads. In order to measure the severity of cavitation, the material loss rate (LM) is utilized.


Longer bubble trails aren't an option due to a lack of control over impeller vane leading edge flow velocity at a constant flow rate.

When a condensate pump is shut off, the shaft seal must be able to withstand a low technical vacuum. The sealing element must be supplied with barrier fluid from the system-side barrier system in order to preclude air intrusion. The lantern ring is used to connect the packing rings in gland packings. Twin mechanical seals are provided for both the inboard and outboard applications. An inboard mechanical seal and an outboard mechanical seal both receive barrier fluid from the lantern ring.

Most often, three-phase motors with a squirrel cage are used to power condensate pumps while operating in a closed loop. The following control options are available to adjust the pump to varied turbine loads and to prevent the condensate pump from running dry.

 

There are many techniques to manage a condensate pump:

  • Adjusting the system's characteristic curve by using a control valve in the exhaust line.
  • Bypass adjustment, which involves returning excess flow to the condenser, aids in modifying the characteristic curve (see Bypass).
  • The H/Q curve may be adjusted by changing the pump speed (speed control).
  • The H/Q curve may be tweaked by letting the flow rate adjust to the input head height. Another word for this kind of self-regulation is cavitation control.


Because of a change in the characteristic curve H(Q) when some condensate evaporates upstream of or in the first stage, the self-regulating condensate pumps may regulate their own heads by decreasing the head H(Q) by a specified amount depending on the degree of steam blockage (Hcav). When the head breakdown curve (Hcav(Q) and the system characteristic Hsys(Q) meet, the operational point is established (OP).

Large cavitation loads in the initial stage of the pump make self-regulation of condensate pumps challenging. Since larger pumps no longer need this control, it has been phased out.