In industry the normal practise is to use stand alone loop controllers for boiler control like 3 element drum level control and for furnace draft control.
What is the real using of using these stand alone controllers? is it reliability orthe cost? or is it the regulation like NFPA or something
Why standard PLC is not accepted for these control? I am working with the PLC for the last 5 years and my personal believe is that PLC are much stronger and reliable that they can be used for critical control as well.

Comments wellcomed

 

if the plc goes down the whole boiler is down. if one of the single loop controllers goes down, you either pop in a spare or run that one loop on manual until the problem is solved.

 

Boiler companies in Australia use PLCs for boiler control all the time. The only restriction is the same as machine control. If an emergency stop is used, it has to be hard wired.

 

Properly you can use a PLC to control any thing, the only consideration you need to keep in mined regarding the regulation is that you do not use the same device for Emergency Shutdown and safeguarding functionality and for general process control.

In the case of the Boiler You will need to have two PLC’s one for the Burner Management System – BMS or the ESD functionality – and another for other functions such as the boiler steam drum three-element control. For the BMS plc please refer to the NFPA 85 standers as it dictates a lot of non slandered PLC design requirements

 

Boiler Automation can be done in the PLC or it maybe advisable to investigate the use a a new scalable process automation system. In either case the true advantages will come in the control implimentation onthe boiler. Typically a system will allow for improved control performance and improved fault handling. A system based solution should be monitoring the status of the inputs and outputs and making automated mode changes. An example: If the airflow steam flow transmitter fails in a three element drum level control solution what happens? In the system world it can switc to a single element mode while the problem is corrected. Typically the loop controllers solutions would only go to manual on the feedwater flow controller.

 

More and more single loop controller manufacturer have network capability built-in to the loop controllers. They can be connected to an HMI and provide visualization and other logic.

I have seen some projects with siemens plc and single loop controllers, SIPART (again siemens). The loop controllers are connected to plc via profibus and all data is available on hmi.

Thanks and Best Regards,
Shahid Waqas Chaudhry

 

ISA has a whole "Standard Practice" document just on boilers. www.isa.org

 

here instead of trying for plc for boiler automation why can't you try for DCS?
DCS is some what advance than plc in some ways

* It can handle more no of analog inputs than a plc
* Though the scan time is less it can provide a reliable performance.
* I am now doing a project in "automation of boiler in YOKOGAWA DCS"

for any more suggestions pls contact the email.id
[email protected]