A few hours of “off” steam chemistry can scar turbine blades for thousands of operating hours. In pulp-and-paper powerhouses, that’s why steam purity isn’t a nice-to-have—it’s the guardrail against 5–20% capacity losses and multi‑million‑dollar damage.
In pulp‑and‑paper plants, steam drives both process heat and high‑efficiency turbines at 300–1500+ psig (psig: pressure in pounds per square inch, gauge). The catch: those turbines demand ultra‑pure, dry steam—essentially no liquid droplets and only trace dissolved contaminants. When boiler water “rides along” (carryover), dissolved solids deposit in superheaters and on turbine blades and valves, cutting output by about 5% and efficiency by about 5%, with capacity losses up to 20% (watertechnologies.com). In the worst case, a slug of boiler water can thermally shock and destroy turbine components.
The operating reality is harsh: plants aim for only 10–30 parts‑per‑billion (ppb) total dissolved solids (TDS: total dissolved solids) in steam for 300–1500 psig service (watertechnologies.com)—roughly 99.97% of the circulating water must be removed from each pound of steam (watertechnologies.com). Industry literature is blunt: “contaminated steam is one of the prime causes of forced and extended maintenance outages and increases maintenance costs” (studylib.net).
Steam purity limits and risk profile
Purity guidelines at the turbine front end are tight: cation conductivity (CACE: cation conductivity measured after cation‑exchange) below 0.2 µS/cm, sodium below 2 ppb, and silica below 10 ppb (chemengonline.com) (ebrary.net). The reason is unforgiving kinetics: “only a few hours of poor steam chemistry can create blade deposits that then take thousands of hours to remove” (scribd.com).
These low‑ppb targets sit alongside upstream water management practices in most mills; related equipment categories include supporting equipment for water treatment (water-treatment-ancillaries).
Steam drum internals: primary separation
Purity is engineered into the boiler’s steam drum. Modern water‑tube units rely on mechanical separation to strip entrained water. Primary devices—centrifugal “cyclone” separators and flow‑direction baffles—remove the bulk of droplets by inertia and density. In tangential cyclone designs, the steam‑water mix enters so water spirals down the drum wall while dry steam rises (watertechnologies.com). This cuts turbulence and water carryunder, setting up the final polishing stage.
Secondary scrubbers: demisters and pads
Because high‑pressure service demands near‑total removal, a secondary “scrubber” stage sits above the primaries: closely spaced wire‑mesh or corrugated‑plate demister pads (also called mist eliminators) to coalesce the remaining micro‑droplets (watertechnologies.com). As the steam weaves through alternating reversing vanes, tiny droplets collide, merge, and drain away—leaving high‑purity steam above.
The payoff is quantifiable: cyclones plus demister pads routinely yield steam >99.9% dry, effectively removing about 99.97% of water per pound of steam (watertechnologies.com) (watertechnologies.com).
Design configuration and drum sizing
Drum geometry, pressure, and total steam flow dictate the number and size of internals. Typical configurations deploy multiple cyclone “cans” with one or more demister pads per drum (watertechnologies.com) (watertechnologies.com). One common “two‑stage” arrangement, shown in Figure 16‑6 of the Veolia Water Handbook, places dual centrifugal separators ahead of corrugated‑plate scrubbers (watertechnologies.com).
Without mechanical devices, a much larger drum would be required for gravity separation alone; internals make high‑pressure drums both compact and cost‑effective (watertechnologies.com) (watertechnologies.com).
Online monitoring and alarm thresholds
Even with robust internals, continuous monitoring is essential. Most modern plants employ steam analyzers and moisture monitors that flag purity losses in real time. Key instruments include cation conductivity (CACE; measured after cation‑exchange) and sodium analyzers on the turbine inlet line (studylib.net). Sodium traces salt carryover; CACE points to chloride/sulfate ingress. Typical practice requires CACE <0.2 µS/cm and Na <2 ppb (chemengonline.com) (ebrary.net), with silica analyzers also targeting ≤10 ppb (chemengonline.com).
Analyzer sensitivity continues to rise: new units can separate chloride and sulfate at ~0.1 ppb resolution (chemengonline.com). Plants trend multiple points—such as condensate pump discharge (CPD: condensate pump discharge) and makeup/feedwater conductivity—to speed diagnosis. EPRI “smart plant” schemes integrate monitors so that if all readings rise, a system leak is likely; if only one spikes, instrument fault is more likely (chemengonline.com). Online steam quality monitors can also trigger increased boiler blowdown or shutdown if limits are exceeded.
Where plants broaden water‑steam chemistry programs, related polishing and deionization technologies are commonly referenced in industry, such as mixed‑bed units (mixed-bed) and demineralizers (demineralizer), alongside condensate side equipment (condensate-polisher).
Economics and availability outcomes
The combination of strict purity standards, well‑designed drum separators, and continuous monitoring is effective. Meeting 10–30 ppb impurity targets and CACE <0.2 µS/cm “virtually eliminates routine turbine fouling” (watertechnologies.com) (chemengonline.com). By contrast, “only a few hours of dirty steam” can lay down multi‑ppm deposits that take “thousands of hours” to shed (scribd.com). Adhering to these practices helps mills avoid the 5–20% capacity losses—or multi‑million‑dollar damage—that unmitigated carryover produces (watertechnologies.com) (studylib.net).
Source notes and references
Engineering data on carryover effects, separator design, and drum internals are drawn from the Veolia Water Handbook (watertechnologies.com) (watertechnologies.com). Purity limits and monitoring practices reflect industry technical literature, including Chemical Engineering (2019) (chemengonline.com) (chemengonline.com). Insurer and OEM guidance on sampling/monitoring appears in sources such as IMIA/ASME/EPRI summaries (studylib.net) (studylib.net). Findings cited above—including the 5% output/5% efficiency losses, 10–30 ppb solids targets, >99.9% dry steam from cyclone+demister trains, CACE/Na/silica thresholds, and diagnostic “smart plant” integration—are from these references.
