I'm working on reverse engineering/programming my first bolier control scheme, and have come across a configuration I don't quite understand. I have a master pressure control in the DCS and a local controller in the field. There are two modes of operation for the field controller, remote setpoint which accepts the DCS output and local control. Under both modes of operations the field controller output is sent back into the DCS and is conditioned/characterized before eventually being used to set setpoints for the firing control scheme. Other than the operator having control in the field, what are the pros of this configuration? Has anyone seen this set-up before?

Thanks,
MJ

 

Dear MJ,

Master Pressure Controller finally generates the setpoit for the combustion control. As I am able to understand from your query that The local controller is only having Master Pressure as an input and the output is going to the DCS again for regulating the combustion setpoint. Field operator at most can have an acess to change the setpoint. Two parallel controllers do not make any sense. Are you understanding the scheme correctly?

 

It seems like a dangerous situation to me. In local control, you still need to control steam pressure. Unless there is also a local readout of pressure, the person adjusting the boiler master setpoint is flying blind. Maybe he would use a radio and stay in touch with the operator in the control room. I assure you this is not a normal control configuration. I would talk with operations to see how this controller is used. If they don't have a valid reason, I would remove it.

 

Yes, I think I have described the scheme correctly. However, i don't quite understand its purpose.

The DCS Master Press PID send its output to two local controllers. One for each of two boilers. If the local controller is in Remote SP mode then it uses the DCS PID output it its own algorithm, whatever that is. If the local controller is in local mode, then the field operator has control of that boiler.

Regardless, of what mode of operation is selected for the local controller, its ouput is sent back into the DCS and characterized for firing controls setpoints.

MJ

 

I did get some feedback from operations personnel and they have confirmed that it purpose is to provide the operator control out in the field, and they do have a local indicator of the pressure

Thanks for your input.