Every thermal power plant is, in operational terms, a water plant with a turbine attached. Steam-Rankine cycles, condenser cooling loops, and flue gas treatment all depend on precisely conditioned water to protect superheater tubes, boiler drums, turbine blades, and heat exchangers from scale, corrosion, and biological fouling. The economic penalty for cycle chemistry failure — forced outages, tube leaks, turbine deposition — runs from hundreds of thousands to millions of dollars per event before accounting for capacity payments. Every one of those failure modes is dramatically cheaper to prevent through precise chemistry than to remediate after the fact.
The four water systems that follow cover conventional fossil, combined-cycle, and biomass thermal plants. Nuclear, waste-to-energy, and geothermal plants inherit variations on the same treatment logic, with additional constraints noted where they apply.
The steam-water cycle is the most chemistry-sensitive system in the plant. The engineering brief is stable: minimize dissolved oxygen, hold pH in the alkaline range appropriate to the boiler and condenser metallurgy, suppress scale on heat-transfer surfaces, and prevent stress corrosion cracking and flow-accelerated corrosion.
Oxygen scavenging happens at the condensate pump discharge or feedwater, historically with hydrazine and increasingly with safer alternatives such as carbohydrazide, DEHA, hydroquinone, or erythorbate. Dosing is continuous, typically trimmed by a dissolved-O₂ measurement downstream. Amine dosing controls pH: neutralizing amines such as morpholine, cyclohexylamine, ethanolamine, or ammonia volatilize with the steam and set the pH in condensate return lines — the primary defense against flow-accelerated corrosion in carbon steel piping. The choice of amine depends on the distribution ratio between water and steam phases and on the plant's specific layout.
Cooling systems fall into three architectures: once-through (river, sea, or lake water passed through the condenser and returned), closed recirculating (small volume, heat rejected via air or a secondary loop), and open recirculating with a cooling tower. The open recirculating configuration dominates inland thermal plants and is by far the most chemistry-intensive.
Open recirculating cooling loops run three parallel chemistry programs at once — corrosion control, scale control, and microbiological control — each with its own dosing regime. Corrosion inhibitors are typically orthophosphate-zinc, molybdate, or phosphonate blends, with azoles added to protect copper alloys where they are present. Scale inhibitors are polyacrylates, polymaleates, or phosphonates chosen against the specific mineral saturation profile at the plant's cycles of concentration. Biocides are alternated between oxidizing (chlorine, bromine, chlorine dioxide, monochloramine) and non-oxidizing chemistries (isothiazolinone, DBNPA, glutaraldehyde) to prevent microbial resistance from developing. pH is trimmed with sulfuric acid on most sites, or caustic where blowdown chemistry demands it, to hold a corrosion-control setpoint typically in the 7.5 to 8.5 range.
Wet limestone and wet lime FGD scrubbers dose limestone slurry — typically 20 to 30% solids — or milk-of-lime into the absorber vessel to react with SO₂ and precipitate as gypsum.
The dosing chemistry itself is straightforward, but the slurry service is abrasive and demands equipment specifically designed for it: peristaltic hose pumps, wear-hardened progressive cavity pumps, and slurry-specific metering solutions. Wetted-part selection and hose life become the dominant maintenance drivers.
Nuclear plants inherit the same steam-cycle chemistry as fossil units but add distinct primary and secondary circuit programs.
Primary circuit reactivity control requires precise boric acid dosing in PWR units, along with lithium hydroxide for pH control and — in some plants — zinc injection for radiation field reduction. Secondary circuit chemistry follows a modified feedwater and steam chemistry program with enhanced hydrazine or alternative scavenger dosing to protect steam generators and turbine components.