Dump Tubes are an important part of a system discharging in a condenser. These devices are primarily deployed so as to minimize the size of the bypass valve outlet where the specific volume of steam dramatically increases at low or sub-atmospheric pressures.
These dump tubes are normally fitted into the condenser inlet duct and are carefully designed to achieve the final pressure reduction stage and allow the steam to expand and cool prior to entering the turbine exhaust or condenser.
It is recommended to ensure that the dump tube is designed properly with respect to size, shape and profile so as to avoid
interference with the turbine exhaust steam path under normal turbine operation. The arrangement and the size of the holes in the dump tube are selected so as to minimize noise generation and direct the steam path away from the duct walls and towards the condenser inlet depending upon the installation.
Depending upon the installation, the arrangement of the holes are selected. In case the dump tube is installed in the condenser then the arrangement of the holes is such that the holes are drilled in two 90 degree sectors.
This does not allow the steam to go up the turbine exhaust or directly down on to the tubes in the condenser. In case the dump tube is installed in the turbine exhaust then the holes are drilled around the complete circumference i.e. 360 degrees.
- Dump tubes are combined with a Steam conditioning valve or Turbine bypass valve for dumping the steam in the Condenser.
- These tubes are deployed so as to reduce the Bypass valve size and thereby reduce the overall cost of the system.
- By installing dump tubes large pipe sizes between the Bypass valve and the Condenser are reduced and made very short.
- Each dump tube is a tailor made device for each application.
The dump tubes are made in single and for special applications double tube versions are available. The material varies as per requirement from alloy steel, carbon steel or stainless steel.
The cooling water required to bring down the temperature is sprayed in the valve or in the dump tube. No water is sprayed in the Condenser. The amount of cooling water quantity is calculated by heat balance calculation. Feed forward logarithm is used in the Distribution Control System.
Inlet steam pressure, temperature, and the position of the valve give the flow rate of steam via the valve characteristics.
The required spray water quantity is calculated as the algorithmhas pre-programmed steam tables and is compared via the FT – Flow transmitter installed in the spray water line or position feed back transmitter.
The result is the control signal given to the valve positioner of the spray water valve. The pressure transmitter installed on
the dump tube measures the steam pressure in the dump tube.
Since the dump tube is a fixed orifice, the signal fromthe pressure transmitter indicates the flow through the dump tube.