Coal-Fired (Steam) Plants

A Pure Rankine Cycle Plant

Unlike simple cycle or combined cycle plants, a coal-fired plant runs on a single thermodynamic cycle — the Rankine cycle — with no gas turbine at all. Pulverized coal is burned directly in a boiler to raise steam, that steam drives a steam turbine-generator, and the exhaust steam is condensed and returned to the boiler as feedwater. It's conceptually the oldest and most straightforward power cycle in this course, but the equipment required to burn coal cleanly and reliably at scale is anything but simple.

Where a combined cycle plant's HRSG makes steam from someone else's exhaust heat, a coal plant's boiler is the primary heat source — it has to burn fuel, transfer that heat to water and steam, and manage everything created by combustion of a solid fuel: ash, particulate, sulfur, and NOx. That's the major addition an Auxiliary Operator encounters here that doesn't exist on a gas-fired unit: the entire fuel handling and emissions control train upstream and downstream of the boiler.

From Coal Pile to Boiler

Coal arrives by rail, truck, or barge and is stored in an outdoor stockpile before being reclaimed onto conveyors. Before it reaches the boiler, it passes through pulverizers — mills that grind coal to a fine powder, roughly the consistency of talcum powder, so it can be blown into the furnace and burn almost instantly, like a fine mist of fuel rather than solid chunks.

• Coal yard / handling — stockpiles, conveyors, crushers, and reclaim systems that move raw coal to the plant.
• Pulverizers (mills) — grind coal to a fine powder. Multiple pulverizers typically feed each boiler for redundancy and load flexibility.
• Boiler / furnace — pulverized coal is injected through burners and combusts in suspension, radiating heat to water-wall tubes lining the furnace, then continuing through superheater and reheater tube sections.

Moving Air and Flue Gas Through the Plant

Forced draft (FD) fans push combustion air into the furnace. Induced draft (ID) fans pull flue gas out of the furnace and through the downstream emissions control equipment, maintaining the furnace at a slight negative pressure so combustion products don't leak out into the plant. Getting the balance between FD and ID air flow right — "balanced draft" — is a fundamental part of boiler operation.

After leaving the boiler, flue gas passes through emissions control equipment before reaching the stack:

• Baghouse or Electrostatic Precipitator (ESP) — removes particulate matter (fly ash) from the flue gas stream, either by filtering it through fabric bags or by electrically charging and collecting particles.
• Flue Gas Desulfurization (FGD) / scrubber — removes sulfur dioxide by contacting flue gas with a limestone slurry or other reagent, producing a byproduct (often gypsum) as well as cleaned gas.

Ash: The Byproduct That Doesn't Exist on Gas Units

Burning coal leaves behind ash — roughly 10% of the coal's original weight, split between bottom ash (heavier particles that fall to the bottom of the furnace) and fly ash (lighter particles carried out with the flue gas and captured by the baghouse/ESP). Ash handling systems continuously remove both, typically to storage silos for truck/rail loadout or to a landfill. This entire fuel-in, ash-out logistics chain simply doesn't exist on a simple cycle or combined cycle gas plant — it's one of the defining differences an Auxiliary Operator will notice moving between plant types.

The Steam Side Looks Familiar

Once steam leaves the boiler's superheater, the rest of the plant will look familiar from BTA-106: a steam turbine (HP/IP/LP sections) drives a generator, exhaust steam is condensed using circulating water and a cooling tower, and condensate returns through a deaerator and boiler feed pumps back to the boiler. The water/steam chemistry, condenser vacuum, and feedwater concerns from the combined cycle module apply here just as much.