This new type of valve for pressures from 140 to 250 bar is developed for systems with frequent operation in the minimum flow range. It will especially be in use with boiler feed water circuits in gas and steam combined cycle power plants (CCPP) for the protection of centrifugal pumps. In fact, initial projects in pulp mills and other power plants are already being implemented.
In the past decade, the operating mode of power plants has changed considerably. Historically, process operation was almost exclusively carried out close to the nominal load point of the plants; an area in which the bypass of the minimum flow valve is closed. Today, cases are increasing rapidly with significantly varying load conditions – down to the single-digit percentage range of the nominal load – which then have to be compensated. This applies particularly to combined cycle power plants and is also due to the increasing use of renewable energies.
Previously, it was difficult to prevent cavitation during regular operation and increasingly difficult when operating just below the minimum flow rate in the critical range. Now, the SIP will be able to operate in this range, even in the area of the switch point hysteresis.
In the main process direction, the volume flow controlled cone utilizes a special design. In the bypass, the valve controls the bypass with a multi-stage piston, which enables a defined multi-stage pressure reduction at all flow rates and always ensures cavitation-free operation. The piston is actuated directly by the plug via a lever. The actuating forces are reduced enough by pressure compensation that a supporting pilot system is not required. This provide the unit with optimum protection against wear and cavitation over the entire operating range from 0 % to 100 % flows.
This pump protection valve is available in standard nominal diameters from DN80 (3”) to DN250 (10”), and in nominal pressures from PN250 (ASME1500) to PN400 (ASME2500) as per EN 1092 normative. Larger diameters and higher pressures are possible.