Steam Turbines

Dear Norm – From an operator’s point of view, what is the best way to operate a steam turbine? What are the two valve handles on either side of the speed governor for? How do we operators know what speed to set the turbine to operate at? Our engineer just tells us to operate at the turbine’s design speed. Is this right?

--James, Oklahoma

            James – Operate turbine speed to keep downstream process control valve in a mostly open but still controllable position. Alternately, connect the governor directly to the process variable to be controlled. That is, control an upstream level by directly varying turbine steam supply flow. The two valves you refer to are called horsepower or port valves. If the governor was a delta P of more than 5% of the motive steam pressure, close one of the port valves until the governor is mostly open.

-Norm

Steam Turbines

Mr. Lieberman – I read in your book, “A Working Guide to Process Equipment,” that the steam chest pressure of turbines should not be less than 10 or 20 psi of the supply pressure. But how to measure the steam chest pressure when a turbine is in operation?

--Prabu, India

            Prabu – If there is no connection on top of the steam chest, then you may use the small (½”) condensate drain to the sewer from the bottom of the steam chest. I just place my gauge on this drain. Closing a port valve will cause this pressure to increase which will save steam. Run at the maximum steam chest pressure by closing port valves or until governor is 100% open. Good to hear from you again.

--Your friend, Norm

Steam Turbines

To Norman Lieberman – Can we safely operate a topping steam turbine if the governor speed control valve is out of service and the over-speed trip is working correctly?

--Carl, Texas

            Carl – No. If you are controlling the turbine speed manually, then a reduced load to the turbine will cause the turbine to over-speed and trip. Sooner or later, operators will tire of the repeat trips and “wire-up” the over-speed trip mechanism (i.e., disable the over-speed trip protection). It’s an industry wide problem that has resulted in injuries and death. The only answer is that both the governor and trip must both be working. See my book, “Troubleshooting Process Plant Control,” Wiley Publications.

--Regards, Norm