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Coal Power Plant Coordinated Unit Control
Basic types of unit control in a coal fired power plant

Dear control experts,

by reading other posts here, I learned a lot and I can see that there are a lot of experts in area of power plant control.

I have read the following article about basic boiler tuning:

This article describes so called Boiler Follow, Turbine Follow and Coordinated control of a unit with steam turbine. In the article when both Boiler master and Turbine master controllers are in automatic mode, there must be coordination between these two in such way that turbine controller controls turbogenerator load (electric power), while boiler master controller control main steam pressure.

In the "turbine follows" mode, turbine controller maintaining constant throttle pressure of main steam, while boiler controller is in manual mode. It is stated that this control mode is favorite among operators because this is as stable control since turbine control valves are very fast to react to the changes.

I wonder if it is possible to tune boiler master controller to work in automatic mode when turbine controller is already in auto controlling main steam pressure. In that case, the difference between desired load (output power) and actual load would go to the boiler controller. I don't see any reason why this couldn't be properly tuned.

For example, in steady state turbine's Cvs are open in some percentage and quality of coal starts going down. Boiler controller is in manual and total coal feeders' speed is constant.This will reduce produced steam flow and decrease output pressure. Decreased steam flow and pressure wil caused output power to decrease (power = enthalpy*steam flow). Since pressure in front of the turbine is decreasing, turbine controller will close CVs a little bit in order to keep the steam pressure at desired level. Closing of control valves will decrease turbo generator power even more. So, in this case it would make perfect sense that boiler master controller is in auto mode too. When produced steam flow starts decreasing, this controller would speed up coal feeders a little bit in order to restore the steam flow.

Did you see any application in coal fired power plants where both boiler and turbine controllers were in automatic mode but turbine control system worked as a load controller?

I couldn't find such applications. In my opinion in multiunit power plats, it makes senste that one or two units work in "pseudo coordinate control" that exploits all good sides of Turbine follows control mode.

Looking forward to your replies.