Problem Statement
The control valve is required for a low load feed water service, for a boiler in a large polyester plant located in Southern India, where the pressure drop is high, 90bar at low flow rate. At the same time, the same valve must allow a higher flow at a low pressure drop of 2.5 bar on load pick up of the boiler.
Once the boiler is started the pressure drop reduces and large flow occurs which is generally met by a full load valve. In power plants with drum-type boilers and constant-speed main boiler feed pumps, the feedwater control valve (drum level control valve) provides the means for controlling flow to the boiler.
The feedwater control valve is in critical and severe service in both cases.
It should be sized and designed to provide adequate drum level control and cope with varying drum pressures expected over the range of plant operating conditions.
If improperly sized and designed it will affect the performance of the boiler reducing process efficiency of the plant.
Solution
For meeting this low flow with high pressure drop at low load condition and high flow with low pressure drop in full load condition, we offered a HFT (Triple) cage and a seat diffuser.
In HFT cage, holes were drilled for up to 30% lift, in a manner to effectively have 3 steps of pressure reduction, where pressure drop is high, and after that for 30%-100% lift, through holes were drilled, to obtain large flow with low pressure drop.
Benefit
Single Control Valve Solution with for two different sets of operating conditions – Hugely economical. The delivery of the custom engineered control valve, including design and engineering, done within 10-12 weeks.
