We are about to be engineering a power & desalination plant, in which one boiler with two turbines in each unit. What problems should be addressed as an I&C engineer at an early stage? For example, will it be OK when one of two turbines trip on normal condition? How about the function and capacity of bypass system? It is so confusing, please help me.

 

I do not know your system but if one boiler is feeding two turbines, you will need a proper bypass control scheme. If the turbines are feeding two separate LP headers than you will need two bypass systems.

Depending on your process objectives, you might choose to design your bypass system so that it matches the maximum rated steam flow rate of your turbine. If the LP header demand is higher than the max flow through your turbine than the bypass control valves will have to be sized to accomodate the max LP steam demand.

2. The Bypass control valves need to be fast acting, good resolution. You might want to go for pneumatic but I would recommend going electro-hydraulic (it costs more but you will be happy when the turbine trips during startup and your bypass system works well!).

3. You will need to tune your system very well (drum level and combustion controls). The bypass control needs feedforward to work (feedback and good tuning is simply too slow)

4. Make sure your DCS controls the steam turbine through the speed SP. You should not treat the turbines as a separate system and the turbines should be very well integrated with your DCS.

Good luck,

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