Gillian Chew

Condenser Hotwell Level Control The condenser is a key component in any power plant that uses a steam turbine. Its primary function is to increase power by maximizing the pressure drop across the turbine, where efficiency is directly related to the vacuum created by condensing steam. Geothermal condensers are fundamentally different than those found in fossil fuel plants, in that turbine exhaust steam is never recycled to a boiler. Therefore, a direct contact condenser is typically used. In lieu of cooling tower water run through sealed piping, it’s sprayed into the steam, and drains to the condenser hotwell. From there it’s pumped through the level control valve and into the cooling tower, cooled, and collected in the cold-water basin at the bottom of the tower. It is then fed back into the condenser, for the process to repeat. Regardless of plant design, maintaining a proper condenser hotwell level during all phases of operation is critical to generate rated megawatt output. Literature Check out the full Application Spotlight! Download

Meter Balance Valve and Meter Back Pressure Valve In transporting crude oil and pipeline petroleum products to refineries, storage tanks, and other delivery points, metering of the fluid is essential for determining flow rate, volume, and ultimately, cost. In situations where the flow in the input line may vary significantly, multiple meter runs are required in order to maintain flow rates within the optimum accuracy range of each flowmeter. Such meter runs branch off of a manifold and run in parallel, dividing the flow among the individual runs. Meter runs typically consist of the flowmeters and a Meter Balance Valve, which enables control of the flow through the line to ensure that it is within the effective accuracy range of the meter and that it is consistent with the flow through the other meter runs. In Meter Balance Valve applications, ball valves are generally preferred, although globe valves and butterfly valves may be used. Ball valves provide good control characteristics with wide rangeability at moderate costs. Globe valves offer the advantage of better throttling control, while butterfly valves are a lower cost solution, but with reduced control performance. Whatever the type of valve, the actuator controlling the valve must be able to provide quick response and precise control to maintain accurate flow rates through each meter run and avoid possible damage to a flowmeter. The flows from the individual meter runs are combined, and the liquid flows through a Meter Back Pressure Valve before the petroleum enters the refinery or storage tank. The purpose of the Meter Back Pressure Valve is to maintain sufficient back pressure on the flowmeters to ensure there is no phase change as the product flows through the meter. Any amount of phase change can affect the accuracy of the meter. The valve, controlled by an actuator, must provide fast response to main line pressure changes, as well as flow and pressure changes in the delivery line. REXA’s Electraulic Actuation™ provides the quick response and precise level of control required to maintain flow rates within the optimum accuracy range of flowmeters in the meter runs. REXA Actuators are also used to create the back pressures essential for ensuring against phase changes and the possibility of cavitation. Benefits: Ideal for strict environmental requirements Fail-safe capability and surge control options CSA Division 1 and 2 approvals Wide ambient temperature ranges Efficient power consumption No oil maintenance Literature Check out the full Application Spotlight! Download

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 Basis Weight Valve 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