A controlled extraction at various loading conditions of the turbine based on seasonal variations.

In a controlled extraction type, a control valve integrated with the steam path is provided at a predetermined stage and the steam is allowed to escape the turbine at desired constant pressure based on the process requirement. There are two types of control valves a) A Grid Valve, b) Bypass Valve which control the flow of steam at preset pressure accommodating the seasonal variation of turbine load. The control system works on a closed-loop feedback mechanism. The pressure at the user end is measured and feedback is provided to the control system. Based on this error signal the feedback control system actuates a control valve designed to vary the area of the valve aperture and thereby regulate the pressure. This setup is applied for processes, where the steam pressure is a critical parameter. In some cases, a nozzle/port is provided at a predetermined stage and an un-controlled high-pressure steam flow/bleed is drawn out of the turbine. This tap is provided before the controlled extraction in the steam path of the turbine. Its utility is found typically in LP heating requirements like de-aerator, LP/HP Heaters or some processes.