The Mercury and Air Toxics Standards (MATS) put forth by the Environmental Protection Agency (EPA) in 2011 is forcing power plants to reduce their emissions of toxic pollutants. For many older coal burning power plants, the cost of air quality control systems (ACQS) is prohibitively high, but maintaining their generating capacity is still crucial. These regulations coupled with predicted continued availability of low-cost natural gas is pushing some coal-burning plants to convert their coal boiler to fire natural gas.
Is it time to convert from coal to natural gas?
It might make practical and economic sense to switch from coal to gas. However, changing fuel requires major control system changes and presents significant control and safety logic challenges. Unless you address these factors before startup, the cost of your fuel conversion project in the form of rework, delays, overtime, and unit trips could become much more significant than anticipated.
How to reduce the downtime and generate revenue more quickly
Several leading utilities have addressed these concerns by pre-commissioning control system changes with a high-fidelity simulator. While DSC virtual commissioning can help keep your project on track, there are other factors to consider when modifying an existing coal-fired simulator for the new fuel type.
As a result, you will have to incorporate the following model changes into your simulator:
1. Gas Supply
Because you are adding fuel gas, you must install a pressure-reducing valve station and modify the gas supply and vent piping.
Using natural gas as fuel changes the heat absorption characteristics in the boiler and convection pass. Therefore, you must modify the radiation and/or convective area to help achieve proper steam temperatures. You will also need new burners and igniters, and windbox modifications.
3. Flue Gas Recirculation (FGR)
You will need an FGR unit to control NOx and steam temperatures by recycling a portion of the flue gas from the economizer outlet back into the windbox. This helps achieve the low emission goals associated with gas plant conversion projects.
4. Flue Gas System
Finally, you must modify the air and gas system, forced-draft/induced-draft fan, and other control functions to maintain furnace pressure. These modifications will enable you to meet designed steam temperatures and full boiler output.