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 is selected. In case the Dump Tube is installed in the condenser then the arrangement of the holes is 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.
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 algorithm has 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 from the pressure transmitter indicates the flow through the dump tube.