That's a really cool story! I live near a couple of industrial sites like that which have a power plant on site, that were shut down quite a long time ago due to environmental concerns they don't burn cleanly at all as you said!

A transmitter is a sensor in a power plant that very precisely measures the air flow within the combustion chamber, so the fuel burns as clean/efficiently as possible. Relatively new transmitters can read with more precision, so you can dial down the airflow/fuel and the corresponding power output.