Steam turbines flow-controlled

When automatic-extraction steam turbines have a condensing exhaust, the control system can control pressure as well as power generation by varying flow to the condenser. The amount of power called for by the steam turbine unit control system can be continuously modulated by the plant control system. 

Thus, large let-down flows are usually seen to be a missed cogeneration opportunity but might provide a degree of freedom to bypass bottlenecks in the steam system. Also, flow through let-down stations allows the level of superheat in the lower-pressure mains to be controlled independently of the flow through the steam turbines. 

Figure 17.4 shows a centrifugal pump, driven by a steam turbine. The correct operating speed for the pump and turbine is that speed that puts the process-control valve in a mostly open, but still controllable, position. As we slow the turbine to force open the process-control valve, the turbine s governor valve will close. Steam flow to the turbine will decline in accordance with fan laws ... 

The system shown in Fig. 22.1 has no provision for controlling the evaporator temperature this is controlled solely by the compressor suction pressure. The lower the compressor suction pressure, the lower the evaporator temperature. This is exactly how our home air conditioner works. If the evaporator temperature is too cold, what can we do Well, if this were a steam turbine compressor, gas engine drive, or any other type of variable-speed driver, we could reduce the compressor s speed. This would reduce the flow of refrigerant, and raise both the evaporator and compressor suction pressure. 

It is quite important not to operate a turbine-driven pump by throttling the steam flow to the turbine. Let s assume that the operators have set the turbine speed at 3500 rpm, by adjusting the steam inlet gate valve upstream of a malfunctioning governor. Suddenly, the discharge flow-control valve cuts back, and the pump s flow decreases from 2000 to 1200 GPM. The pump speed will then increase, because fewer pounds of liquid are being pumped, and less horsepower is required to spin the pump. 

The high-pressure steam from the separator is sent to the steam turbine under speed control, and the generated electricity is sent to the grid or to other users. The low-pressure steam is condensed by cooling it with cooling water. The flow of the cooling water is modulated by the turbine exhaust pressure controller. 

PC), serving to make sure that all low pressure steam users in the plant are always satisfied, and a flow controller (FC), which keeps the flow in the turbine bypass at a minimum and increases the HP flow to the turbine as soon as the bypass flow starts to increase. 

If the relative loads are reversed and the LPS availability exceeds the demand for LPS, this will cause the pressure in the LPS header to rise and the PC to reduce the bypass flow. When this let-down flow drops below the set point of FC-1, the previously inactive (saturated) FC-2 becomes active and admits that part of the LP steam which is not needed in the LPS header into the second condensing stage of the turbine. Any number of such bypass flow controllers can be used to sequentially respond to changes in the relative sizes of the work and LP steam loads. These controllers should be provided by integral action only, so that they will be saturated (and their control valves closed) until their set points are reached. 

Figure 7.2c illustrates how a variable-speed drive (a steam turbine) can be used to control throughput. The turbine is driven by high-pressure steam (600 psia) and discharges into a low-pressure steam header (25 psia). A flow controVspeed control cascade structure is used. The output signal from the flow controller adjusts the setpoint of the turbine speed controller, which manipulates the flow of high-pressure... 

Steam turbines with compressors are used for providing process gas flow at a required pressure in high throughput processes. The process demand is determined by a pressure controller, which adjusts the setpoint on the turbine speed controller. In smaller processes, fixed speed compressors may be used by adjusting either an inlet or discharge valve to achieve pressure control. It is more energy efficient to adjust an inlet valve, or better yet to adjust inlet vanes which provide a pre-rotation to the gas. However, adjustment of speed is the most energy-efficient method control. 

Having embarked on the quest of simplification, we show that the steam tables may be represented in the regions of interest to steam turbines by relatively simple approximating functions, examples of which are given. Further, it is shown that small changes in efficiency have little effect on the calculated mass flow, and it will often be sufficient for control engineering purposes to use the isentropic mass flow equation. 

Column pressure is controlled by changing the setpoint of a speed controller on the compressor turbine. The speed controller output sets a flow controller on the high-pressure steam to the turbine. 

Steam to the turbine driving the compressor is flow controlled, reset by a speed controller, which is reset by a distillate composition controller. 

Steam turbine used for the generation of electricity Turbine overspeeding [load disconnection suddenly] /[trip throttle valve stuck] /control valve fault//[extrac-tion valve fault]. Bearings damaged" [turbine overspeeding] /[lube oil] /exces-sive vibration/no lube oil/bearing temperature too hot/insuffident oil because of dogged lines/flow of parasitic currents. 

Steam can get overheated by the superheater if the flow is less due to any reason. This can be harmful to the turbine blades if the temperature of steam is too high. The de-superheaters are used to keep the steam temperature in control. 

Integration of PRT with the Steam Turbine There are two separate opportunities identified so far. On one hand, there is a hot flow gas PRT inFCC, while there is a letdown steam turbine on the other hand. However, if these two opportunities are treated separately, both turbines will require a separate shaft, gear box, and generator, as well as a separate foimdation, piping, electrical infrastructure, and control system. The capital cost could be prohibitive for either opportunity. 

Mechanical design of the turbine blade root and rotor steeple attachments uses optimized contour to significantly reduce operational stresses. Steam flow to the high-pressure turbine is controlled by two floor-mounted steam chests. Each contains two throttle/stop valve assemblies, and two load-governing valves. 

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