Jared Thompson

Boiler Feedwater Recirculation Valve Background A Net Positive Suction Head (NPSH) is available for a boiler feed pump, specific to the design and piping layout of every plant. This defines the inlet pressure at the suction side of the pump, due to the effects of gravity and system design. If the pump draw exceeds the NPSH, the inlet line pressure would drop below the vapor pressure, therefore resulting in flashing and cavitation. Not only would the cavitating feedwater physically damage the pump, but the reduced flow rate would also allow the pump to overheat.  To prevent this, a minimum available flow must be maintained to circulate through the pump, regardless of downstream boiler load requirements. To protect the boiler feed pump from damaging conditions, plants have a recirculation line bypassing the boiler and recirculating feedwater directly back to the deaerator or condenser. This recirculation line ensures that the boiler feed pump has the required flow available to protect the pump at all boiler load conditions.  Responsive and repeatable control of the Boiler Feedwater Recirculation (BFR) Valve protects a plant’s investment in the boiler feed pump while allowing it to deliver the required flow to the boiler. The feedwater recirculation valve is responsible for taking almost a full pressure drop across the valve. This valve is typically designed for Class V shutoff and to fail-open on loss of power since it is usually closed during normal operations.  Most plants still utilize pneumatic spring and diaphragm actuators for their BFR valves. Unfortunately, pneumatic actuators lack the necessary rigidity to accurately control small steps. REXA actuators, however, offer repeatable, stiff, and accurate valve control performance – allowing for tight shut-off.  Literature Read more in-depth about Boiler Feedwater Recirculation Valves in our Application spotlight! Download

REXA installed an Electraulic™ Actuator on a basis weight valve at a paper mill in the Northeast United States. We performed an extensive benchmark test to verify the REXA basis weight solution meets or exceeds the performance of the existing actuator. After eight months of run time, we collected process data to verify actuator performance.  What is a Basis Weight Valve? The basis weight valve is the most critical component on the wet end of a paper machine producing fine paper. This valve modulates the flow of stock as it is mixed with white water on its way to the head box, as well as forming wire where the sheet begins to take shape.  What’s the Key to a Successful Process? Paper making is a complex process involving a variety of operations. From wood preparation, to pulping, to bleaching, to the paper machine, many variables affect the finished product. In addition, the type of wood available and the type of paper produced significantly affect each paper mill’s operation.  Each paper machine is designed for a specific basis weight range and roll speed. Therefore, reliably producing quality paper requires precise control of the basis weight valve. Fluctuations in the basis weight result in uneven drying, a poorly finished product and/or waste. Consequently, this leads to a rejection of the whole roll. Mills need a high-performing, reliable, responsive actuator capable of making fine position changes without overshoot while maintaining this performance level at a high duty cycle.  Solution Check out our full Application Spotlight below to learn more about the mill’s application and see how REXA provided the best-fit solution!  Literature Check out the full Application Spotlight! Download

Furnace Draft Pressure Control Background Increased regulatory pressures to reduce emissions along with a declining generation demand create challenges for a plant’s operating practices. Plant operators are forced to adopt new practices and advanced technologies to improve efficiency and increase reliability.  Within a furnace draft pressure control application, Primary Air (PA) fans deliver the required fuel from the pulverizers to the furnace to meet generation demand. Force draft (FD) and Induced Draft (ID) fans control air and combustion gas flow through the boiler.  The precise control required to maintain furnace draft can be a difficult proposition – particularly for plants that are cycling. Inadequate FD/ID damper operation negatively affects performance of low NOx burners, while poor damper performance and inadequate pulverization leads to increased fly ash.  REXA actuators offer a rugged, repeatable and responsive solution for combustion optimization and accurate furnace draft pressure control. Check out the full Application Spotlight below to learn more!  Literature Download the full Application Spotlight! Download