Introduction
Our client is reviewing/upgrading the primary cooling water system in an existing power plant. The primary cooling water flow can be operated as an open loop or as a closed loop system. In the “closed” loop configuration, the cooling water pumps extract water from the intake basin under the cooling tower and forward the cooling water through the main condenser units back to the atmospheric cooling tower. In the open loop configuration, the main cooling water pumps extract water from the Maas River, forward the water to the condensers, and from the condensers across a spill back to the Maas River.
Analysis
To verify the hydraulic integrity of the system fifteen different load cases have been analyzed. Seven of these cases were related to pump starts and stops. All seven cases have been analyzed for both operation modes i.e. cooling tower operation and open loop operations i.e. from the Maas river into the Maas river.
In addition to the pump start and trip cases, one additional case has been analyzed related to the failure of the damping of the check valves.
It was assumed that halfway through the check valve closure the check valve damping system failed. This load case has been analyzed in particular for cooling tower operation when the back pressure in the system is the largest.
For the pump trip cases, two different conditions have been distinguished:
- One pump trip and
- Both pumps trip simultaneously
Results
The analysis results confirmed that only the final phase of the check valve closure process is important for the maximum pressure built up when the backflow is blocked almost instantaneously. The results also show that the difference between a 2-step and a 3-step damping system is relatively small. For reference, a few analyses for an ideal check valve (a check valve that closes instantaneously when the flow direction is reversed) have been performed.
