Turbine motive-steam flow

Figure 17.3 shows a steam turbine with three, rather than one, nozzles. The single, largest, left-hand valve is called the main nozzle. It handles 60 percent of the motive-steam flow. Each of the two smaller nozzles handles 20 percent of the steam. These 20 percent nozzles can be plugged off by a device sometimes called either a horsepower valve, jet valve, speed valve, star (for the handle shape) valve, or port valve. 

An ordinary American-type turbine is designed to run at 3600 rpm. Its overspeed trip will cut off the motive steam flow at about 3750 rpm. But the turbine can be run at any lower speed. There is usually a small knob on the left side of the governor-valve assembly, that is used to... 

This means that if we drop the speed of the turbine by about 3 percent, motive-steam flow will decline by about 9 percent. However, there is an additional benefit. 

The motive-steam flow to the turbine is not known, but won t change. 

The operators were not running the turbine. The turbine was spinning, because it was coupled to the pump, but there was no motive steam to the turbine. The operators reported that the turbine was not needed, as the motor was pulling only 90 percent of its maximum amperage load. The question is, dear reader, whether the pump will run faster if the motive-steam flow is opened to the turbine. And the answer is, no. While the turbine will produce shaft work, and will help... 

If the hot-well pump cannot handle the required condensate flow, the water level in the well will back up. The temperature in the hot well will go down as the lower condenser tubes are submerged. But this will reduce the surface area of the condenser that is exposed to the condensing steam. The condenser outlet temperature will therefore rise and so will the surface condenser pressure. This reduces the horsepower that can be recovered from each pound of the motive steam flowing to the turbine. The turbine will then slow down. 

The offending wildlife were removed. The condenser was reassembled. The motive steam was started to the turbine. Both the turbine and the air blower were running well above critical speed. We lined the flow of combustion air up to the combustion chamber. Everything was finally going my way, except for one minor problem. 

Even if the governor-steam inlet control valve is 100 percent open, it may still be possible to increase the supply of motive steam into the turbine. The position of the governor when it is wide open can often be reset to admit more steam flow. I once increased the flow through a crude tower-bottom pump by pushing hard against the base of the governor, and forced it to actually open to its maximum position. The pump speed came up 300 rpm, and the flow increased by about 15 percent. 

Of course, increasing the motive-steam pressure will greatly increase the horsepower available to the turbine. First, more work can be extracted from each pound of the motive steam and second, increasing the steam pressure will increase the pounds of steam flowing through the governor. 

The SMART and MED-TVC units are connected through the steam transformer. The steam transformer produces the motive steam using steam extracted from the turbine and supplies process steam to the desalination plant. A steam transformer also prevents contamination of the produced water by hydrazine and radioactive material of the primary steam. The steam transformer is made of horizontal tube bundles the primary steam flow is condensed inside the tubes at its saturation temperature. The feed brine is sprayed outside of the tube bundles by the recycling pump. Part of the sprayed water is evaporated and the produced steam is used as the motive steam for the thermo-compressor of the evaporator. Part of the condensate in the first cell of the evaporator is used as make-up for the steam transformer and this makeup water is preheated by the condensate of the primary steam before being fed into the steam transformer. The pre-heater is a plate-type heat exchanger made of welded titanium. 

Turbines (Expanders) High-velocity streams from nozzles impinging on blades attached to a rotating shaft form a turbine (or expander) through which vapor or gas flows in a steady-state expansion process which converts internal energy of a high-pressure stream into shaft work. The motive force may be provided by steam (turbine) or by a high-pressure gas (expander). 

For those of you who work in the liquefied natural gas industry, all of the above principles discussed relating to steam apply to light liquid hydrocarbons as well. The Roto-Flow Turbo Expander, which you use to partially liquefy the natural gas, is much the same as a steam turbine. That is, the motive gas is partially condensed to ethane and propane, as the temperature of the gas is converted to velocity, as the gas flows into the Roto-Flow turbine case. Much of the torque developed by the expander turbine is derived from the latent heat of condensation of the liquefied petroleum fractions. 

The No. 2 main feedwater pump turbine, deprived of steam, was slowly winding down. Since the MSIVs were closed and there was limited steam inventory in the moisture separator reheaters, there was inadequate motive power to pump feedwater to the steam generators. At about 1 40 a.m., the discharge pressure of the pump had dropped below the steam pressure which terminated main feedwater flow. 

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