How PID tuning impacts furnace control in plants

Posted by Didac Recio on Dec 8, 2020 10:37:45 AM

What if you could increase your return on investment, safety, and overall plant efficiency with just one optimization? Furnace control is often disregarded as furnaces are considered as subunits that are not important to optimize. However, one cannot underestimate the impact of the furnace performance on the overall unit. In this blog, we'll explain what the consequences of bad furnace control are, what the results of optimization will be and how to tune your furnace correctly.

Good furnace control: higher overall plant performance

Good furnace control means that there is proper combustion of the fuel. The main goal of furnace control is to heat fluids or gases and to keep the outlet temperature as constant as possible. For instance, in a furnace of a refinery, you want to transfer energy or heat to the fluids and reach a specific outlet temperature. If that temperature is stable, it means that the units behind the furnace are more likely to be stable as well. More stable operations mean the possibility to increase the overall throughput, more consistent product quality, fewer alarms, higher safety, less downtime etc.

 

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Less emissions and a higher efficiency

When combustion control is suboptimal, operators tend to operate with a large excess of oxygen (up to 10% higher than optimal). It will allow them to have more hands-off operation at the price of less efficiency. More volumes of air mean the plant needs to consume much more fuel to keep the furnace output temperature constant. The extra air heats in the combustion chamber and then leaves via the chimney. Higher fuel consumption by definition also means more emissions (in the best case only CO2).

Bad combustion control also leads to higher CO, SOx, NOx, Cl emissions. Violating the environmental limits will result in penalties. When these violations happen too frequent, the license to operate can be revoked. Waste-to-Energy plants are dealing with these undesired emissions and are good candidates for furnace control optimization. 

Experience has shown that also furnaces in refineries, petrochemical, chemical, fertilizers need attention. Past projects have shown that all these industries can also achieve significant benefits.

Benefits of furnace control

  • Higher fuel efficiency: reduced cost
  • Fewer emissions: reduced penalties, license to operate, environmental responsibility
  • More increased safety in the plant.
  • When furnaces are part of a bigger unit:
    • Operators don't have to spend as much time on this subunit compared to the rest of the unit. 
    • Good furnace performance leads to better overall unit performance.

 

How to properly tune the controllers your furnace?

Proper tuning of the PID loops in your furnace is key for a successful furnace control. Using the trial-and-error method is not recommended in a furnace. Inadequate tuning of fast loops such as fuel gas pressure or oxygen controllers can trip the furnace. In turn, the whole plant is likely to trip as well.

A safer way to properly control your furnace is by using a tuning software. We would always recommend using software that can tune single and multiple interacting PID loops. It's also essential that the tuning is based on engineering specifications like optimal tracking or disturbance rejection with minimal overshoot or a lower bound on the robustness. These specifications are the things that matter for your process stability and efficiency.

 

PID tuning software: furnace control

Are you convinced that you need to take a look at your current furnace control, but not yet sure what PID tuning software to use? We would love to offer you a free, and no-obligation live demo of INCATools AptiTune. So we can show you all the benefits of a proper furnace control tailored to your situation. 

Request your free demo here. 

 

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Topics: PID tuning