Product - Two-stage Dump Tube
​​​​​​​​​​The dump tube is used together with a steam conditioning valve in applications such as turbine bypass where steam is dumped into a condenser. The process can, in case of high pressure drops between the steam conditioning valve outlet and the condenser, be a source of high levels of noise. In order to remedy this, IMI CCI has developed a multi-stage dump tube which splits the pressure drop over a series of pressure reducing stages, thus reducing the noise level. IMI CCI has experts in the field of dump tubes, with experience from thousands of plants, that can provide support at the design stage.​


​Key features

  • The dump tube is welded to the steam pipe downstream of the bypass valve
  • The dump tube is a fixed orifice, which reduces the bypass steam pressure down to the pressure of the condenser
  • Our dump tubes are carefully calculated to allow it to be used as a flow meter
  • There are two main applications for the dump tube:
    • Water cooled condenser, where the dump tube is mounted in the condenser
    • ​Air cooled condenser, where the dump tube is mounted in the bypass line connected to a header going from the turbine outlet to the air-cooled condenser

Benefits​

  • The two-stage dump tube allows for reduced noise levels thanks to its multi-stage pressure-reducing design
  • Each dump tube is specifically designed for each application. The steam entering the water-cooled condenser from the bypass valve can be directed to avoid damage to the condenser internals or to the steam turbine internals
  • The expensive large diameter pipe between the bypass valve and the condenser can be reduced and made very short
  • Accurate steam temperature control
  • Optimised size of bypass valve and dump tube gives low investment cost​
  • Dump tubes are sized together with the bypass valve to minimise cost while maximising performance

​​Applications



Installation example

Dumping steam into the condenser is a delicate operation with a large number of elements that must be properly considered during the design stage. The condenser is a very costly component in the system that is sensitive to both pressure and heat. Not only is the design of the individual components (the turbine bypass valve and the dump tube) important, but so is the control system used. IMI CCI provides a complete system with turbine bypass valve, dump tube, spray water control valve and control algorithm for controlling the spray water injected into the steam.
The example shown below is a feed-forward control scheme in a bypass to air-cooled condenser application. Feed-forward control  calculates the required water injection flow based on the following data:
  • Inlet enthalpy
  • Inlet steam flow
  • Spray water enthalpy
  • Required enthalpy of the fluid dumped into the condenser

The algorithm developed by IMI CCI is to be used in customer’s Distributed Control System - DCS. Inlet steam pressure, temperature, and bypass valve outlet pressure give the actual steam flow into the valve. The required spray water flow to reach the desired outlet temperature is calculated and compared with the actual spray water flow, measured via a flow-meter. The result is a control signal to the positioner on the spray water valve. A pressure transmitter measures the steam pressure before the dump tube. Since the dump tube is a fixed orifice, the signal indicates the flow through the dump tube.
Design

The dimensions of the dump tube stages and the orientation of the orifice are determined by the following factors:
  • Operating conditions of the steam conditioning valve (pressure, temperature, flow, pipe dimensions and percentage of free water through the dump tube.
  • Operating conditions of the condenser (pressure, temperature).
  • Condenser design.
Alloy steel is always used for our dump tube design, as carbon steel is unsuitable. Stainless steel is available upon request.

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Product - Two-stage Dump Tube