Based on recent gas conversion announcements, existing coal units generating a total of approximately 9,000 MW will be converted for natural gas firing. The major drivers of this trend have been Mercury and Air Toxics Standards (MATS) regulations, New Source Review (NSR) settlements, natural gas availability and pricing, and the uniqueness of each project to deliver electricity at the required capacity to make it economically feasible to convert existing coal-fired units to natural gas-firing capability.

The existing coal equipment, material handling systems and air quality control systems (AQCS) are generally left in place to help drive economic feasibility of firing natural gas. In certain cases, coal equipment can be put into long term layup with the uncertainties of fuel costs and environmental regulations but with higher operating and maintenance costs. AQCS equipment, such as electrostatic precipitators, can be de-energized and wet/dry FGD’s can be bypassed.

In some cases, retiring and decommissioning of all coal equipment and AQCS equipment may be more prudent choice to avoid costs of long term lay-up and operating and maintenance of equipment.

Two recent cases studies will be presented in the paper: 1) retiring and decommissioning of all coal equipment and AQCS and its effect on existing balance of plant equipment and 2) long term layup of coal equipment and pollution control and its suggested operating and maintenance procedures.