Sizing the Turbine

Power is torque multiplied by angular velocity, and angular velocity is related to the poles on the generator and the frequency needed for the outgoing supply. In order to generate more power from a larger generator, more torque will be needed from the turbine.

There is a limit to the torque that any rotating equipment shaft can sustain and in order to increase the torque for a similar machine, the shaft has to be made larger. In order to produce and sustain the larger torque, the machine has to get bigger. The size of the machine is determined by experimental activity during the design proving phase of the equipment and from what is learned during the commissioning phase of equipment that is installed on site. QED.

If the load increases then the equipment has to work harder and, just like a vehicle going from level to travelling up a slope, if the steam rate is not increased the thing will slow down; slowing down will cause the thing to trip off the local grid due to speed mismatch. Fortunately, speed regulation is straightforward and any number of ways of automatically regulating the speed can be found.

Wikipedia has an article on speed governors. Bedtime reading, perhaps?

Dear Mr. ntr,

You have given the the steam inlet condition only. You have not mentioned the following. Unless these details are furnished sizing of the Turbine is not possible.

1. The Exhaust Steam condition - whether it is working in vaccuum - condenser as condensing Turbine or working as Back-Pressure Turbine, going to the Process and the condition of the Exhaust Steam such as Pressure, Temperature etc.

2. When the Turbine is working as Back-Pressure Turbine, whether the entire steam goes to the process or partly going to process and balance to the Condenser.

3. Whether any steam is bled for Boiler Feed Water Heater, if so the Quantity and Steam Conditions to be specified.

The Basic philosophy is the Steam required per KW energy will decide the Turbine sizing, which is also linked NETT HEAT DROP per Kg. of Steam.

One KW of Power requires 860 K.Cal of Heat or 3600 Kilo Joules per Hour. Knowing/Calculating the Heat Drop per Kg. of Steam, the total steam flow per KW can be calculated

i.e., Steam/KW.Hr = 860/Nett Heat Drop per g. of Steam will be known. Since total power is known the steam flow required can be calculated and then sizing of the Turbine will be decided, considering a Steam Entry Velocity of 2200 Ft./Sec or 670 to 675 M/Sec.

DHAYANANDHAN.S