FOSSIL-FIRED POWER
Conventional power plants provide baseload power for nearly every country across the globe. Conventional energy sources – such as coal, gas and oil – produce energy at annual rates of more than 15 trillion kilowatt-hours. Environmental regulations increase pressure on plant operators to improve system efficiency. At the same time, production must remain low-cost and widely available.
Turbine Bypass System Control
Parcol 1-5700 Pressure Reducing and Desuperheating stations (PRDS) represent the most universal and compact solution for pressure reduction and desuperheating service of steam turbine by-pass lines, discharging both to intermediate or low pressure sections of power stations.
The spherical body shape design, together with the high quality of construction materials, allow a more uniform wall thickness than the conventional ones, fabricated by welding bodies, reducing P/T fatigue effects and improving welded joints quality.
The pressure reduction is mainly achieved through two stages: the first stage has the function to adjust the flow rate by means of a drilled cage trim, the second stage, designed with fixed throttling section, has the double function to generate a backpressure on the first stage by reducing fluid velocity and generated sound pressure level, and to convey the steam towards the injection chamber, at speed and distribution suitable to optimize the desuperheating process.
The desuperheating section, put immediately downstream the second stage, consists of the injection chamber complete with injection nozzles or a different Parcol desuperheater.
Coupled with REXA’s Electraulic™ Actuation, through responsive and repeatable performance, plants are able to optimize transitions and eliminate nuisance trips during ramp-up, ramp down and emergency response scenarios. Our actuators provide hydraulic control capable of steps to .05% resolution – completely eliminating the effects of stick-slip inherent of pneumatic actuators. We design our actuators for continuous modulating service and provide stiff, stable control even in the harshest environmental conditions (-40°F to +250°F).
Boiler Main Feedwater/Recirculation Valve
Maintaining a minimum flow through the feed pump is critical in preventing cavitation and eventual catastrophic damage. The Feed Pump Recirculation Valve protects the pump at all load conditions, bypassing the boiler and directing feedwater to the deaerator or main condenser. During a boiler trip or other upset condition, the recirculation valve must open quickly, diverting high pressure feedwater away from the pump. As one of the most severe services in the plant, the recirculation valve is subjected to full feed pump pressure on the inlet and a low outlet pressure. At a preheated temperature, cavitation is imminent and is treated with multi-stage valve trims. The recirculation valve is closed for normal boiler operations, resulting in a high pressure drop and the need for Class V or better shutoff. The valve must be capable of remaining tightly closed to prevent major trim/body damage and reduce heat rate.
VARISTEP, an extrapolation of LIMIPHON design, has been engineered by PARCOL in order to better prevent cavitation phenomenon, without limiting the capacity at regimes not subject to cavitation.
Main features are a radial section expansion designed both to minimize the pressure drop at last stage (the most sensitive to cavitation) and, at the same time, to limit the pressure drop at first stage.
Less stages from bottom to top of the stack, resulting in an increase of the incremental Cv along the travel. Capability to comply with the pressure drop decrease at high flow rates, usually occurring in boiler feed water applications.
The plug end close to the seating surface is labyrinth-shaped (CCF design) to provide the best pressure distribution in the clearance flow passage between plug and cage. This to prevent damage at the seat and on guiding surfaces.
All the above features make VARISTEP the ideal solution for start-up and main feedwater combined control valves.
Main Steam System – Superheat and Reheat Desuperheater Stations
The necessity to stabilize the grid from many power generation sources can cause continually varying boiler loads in coalfired plants. Maintaining a constant steam temperature to the turbine during these ramping periods is the goal, which ensures optimum heat rate and protects the boiler. Located between the primary and secondary superheaters, attemperators and Superheater/reheater attemperator spray valves are the final control element before the HP, IP, and LP turbines. They are responsible for controlling steam temperature in accordance with steam turbine design guidelines.
PARCOL 3-4000 series desuperheaters are almost solely used to reduce the steam temperature by directly injecting water inside the superheated steam flow.
The above series includes 3-4100 variable area and 3-4500 fixed area models. LV variable area series, including LVL, LVP and LVM models, allows to solve the most common desuperheating problems without practical limits in flow rate and operating conditions.
Fixed area LF nozzles, on the contrary, are designed for limited power processes with limited load changes.
Superheater/reheater attemperator spray valves experience a significantly high pressure drop across the valve.
Specifically studied for severe service applications, LIMIPHON valves were designed and built by Parcol in 1971. Based on the concept of multi-path and multi-stage labyrinths (velocity controlled trim), LIMIPHON trim divides flow into many streams to minimize the energy levels and it is the ideal solution for all those applications where high pressure drops are the main cause of noise, cavitation, vibrations and erosions.
LIMIPHON control valves are available in Angle, Straight-way or Z-type style.