Exhaust steam pressure

On this system, the turbine is speed controlled and passes steam, depending on the electrical demand. The bypass-reducing valve with integral desuperheater makes up any deficiency in the steam requirements and creates an exhaust steam pressure control. Alternatively, any surplus steam can be bypassed to a dump condenser, either water or air cooled, and returned to the boiler as clear condensate. 

The flange leak was taped over, and the exhaust-steam pressure dropped back to 100 mm Hg. The steam required to drive the turbine fell by 18 percent. This incident is technically quite similar to losing the downcomer seal on a distillation tower tray. Again, it illustrates the sort of field observations one needs to combine with basic technical calculations. This is the optimum way to attack, and solve, process problems. 

The 300-psig steam next passes through the steam nozzle. This is an ordinary nozzle. It screws into a hole in the wall, which separates the steam chest from the turbine case. The nozzle is shaped to efficiently convert the pressure of the 300 psig to steam velocity. The pressure of the steam, as soon as it escapes from the steam nozzle, is already the same as the exhaust steam pressure (100 psig). 

Step 3. The exhaust-steam pressure is 17 psia. The intersection of the isoentropic expansion line and 17-psia constant-pressure line together determine point B in Fig. 17.2. 

The higher the exhaust-steam pressure, the drier the exhaust steam. 

Lowering the exhaust-steam pressure always allows us to extract more work from each pound of steam. That is why we often exhaust steam to a condenser. But other than minimizing the exhaust-steam pressure, how else may we increase the amount of work that can be extracted from each pound of steam ... 

SATUR OR TOTAL TEMP. EXHAUST STEAM PRESSURE MOTOR CHARACTERISTICS ... 

Glucose.—One bushel of corn will give about 14 gal. of liquor, and the first concentration is done in a triple-effect evaporator from 15 to 30°B6. with from 5 to 10 lb. of exhaust steam pressure and a vacuum of from 27 to 28 in. The capacity is from 2 i to 3 gal. per square foot. Usually the standard and the horizontal-type evaporators are used also the semi-film. The latter has the advantage that it will prevent foaming and facilitate cleaning. The second concentration from 30 to from 44 to 45°B. is done in a single-effect of the standard or horizontal type. The capacity is from % to. 1 gal. per square foot, and the horizontal type must be of special construction so as to leave sufficient space between the tubes for the discharge of the heavy syrup. On account of the calcium sulphate in the weak liquor, the tubes in the multiple effect will foul very rapidly, and have to be cleaned either chemically or mechanically. The liquors are apt to foam, and special precautions in the form of extra vapor space and separators are to be taken. Evaporators are usually built with cast-iron shells and copper tubes. 

The tower s feed preheat source was exhaust steam of a variable pressure. Flow of steam to the preheater was neither metered nor controlled. A technical investigation revealed that as exhaust steam pressure (and condensing temperature) rose, the ability of the tower to fractionate declined. The problem was resolved by installing a flow.control loop on the exhaust steam to the preheater. The tower instability—which had originally been thought to be an instrumentation failure—proved to be a process problem. 

If high exhaust steam pressure is the problem, increasing the flow of driver steam will not provide much of an increase in refrigeration compressor horsepower. 

You can see quite clearly that it is not the pressure of the steam that is driving a turbine. Place a pressure gauge on the turbine case of a single-wheel machine. The pressure on the turbine case will be quite close to the exhaust steam pressure and certainly not the motive steam pressure. 

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