Controller Tuning for a very Random Process

Hey Guys,

I work in a waste to energy plant.

Basically we burn waste and recover the heat to produce steam.

We have a flue gas treatment system that uses lime to neutralize the acid in the flue gas.
The flue gas passes through a lime reaction chamber and lime is fed into the chamber to neutralize to acid.

Currently, the controller measures the HCL concentration at the flue gas stack and controls the amount of lime being fed into the chamber.
However, the waste is very random, we don't know the amount of Cl content in the waste. And we do not have a transmitter to measure HCl content before the chamber.

I would like to ask for advice on what method can I use to tune the controller? Currently, the PV is very random, sometimes high and sometimes low.
Hopefully you are using slake lime, but in regards to effective control, you need to characterize your waste properties such as pH, conductivity, density, temperature, etc. Lacking that, then you need to set up stack gas monitoring. Contact your instrument suppliers for your site.
The problem you share with us is well known. Unstable feed cause unstable flue gas content.
There are several approaches:
- Try to install analyzers in the (earliest possible) key points where the process stream can be characterized (as Dave did recommend!) and build a cascade setup to (try to) catch the variations.
if the above (RECOMMENDED!!!) option is not achievable, for any reason
- Overdose the lime - assuming the penalty for air pollution is higher than the additional lime cost...
I shall be glad to discuss it further directly. [email protected]