Classify streams before combining them
Build an inventory recording source, flow, temperature and potential destination. Distinguish service-steam return, process condensate and water from evaporation. Analyse normal operation, startup, cleaning and exchanger failures. A normally clean stream may experience short contamination events that disappear within the average of a composite sample.
Avoid diluting one contaminated branch into the entire return network simply to simplify analysis. Segregation may allow compliant condensate to return directly while a smaller fraction is assessed. Repairing an exchanger leak deserves consideration before designing permanent equipment to treat the consequences of that failure.
Choose monitoring that detects the actual contaminant
Conductivity can detect certain ionic process ingress and cleaning chemicals. The Spirax Sarco manual states that this mechanism does not detect contaminants such as oils, fats or sugars when they do not change conductivity. A low reading therefore does not establish that the condensate is fully clean.
Depending on the risk, add turbidity, organic carbon, pH or specific analyses. Validate response, temperature, sampling and diversion time. Provide diagnostic points that help locate the source; an alarm only at the final header may protect the boiler while leaving the contaminated branch unidentified and the problem unresolved.
Match separation to contaminant form
UF can separate suspended solids and certain emulsions, while many small dissolved compounds pass through. Ceramic membranes may be assessed where temperature and cleaning constrain selection, with seals and housings checked as well. Material resistance should not be converted into a universal temperature limit for the complete assembly.
RO can reduce salts and certain solutes, with rejection dependent on the compound and conditions. Volatile organics and gases need specific evaluation. Compare treatment with diversion, reuse in a less demanding duty or indirect heat recovery. Contaminated condensate does not necessarily have to return to the boiler.
Close the water, heat and waste balances
Include inlet and outlet temperatures, heat losses, pumping, cleaning and concentrate destination. Cooling to permit filtration and subsequently reheating may dominate the decision. Compare useful water and recovered heat while keeping units distinct and explaining their economic valuation instead of presenting one unexplained recovery percentage.
Agree acceptance with the end user: boiler feed, washing and process applications have different requirements. Test representative variability and measure treated water, residual streams and operational stability. Preserve a means of diverting incompatible events while their cause is investigated and treatment suitability is confirmed.
Common questions
Is condensate always reusable demineralised water?
No. Origin, carryover and process ingress determine quality. Evaporator condensate can contain compounds transferred to the vapour phase rather than remaining in the concentrated liquid.
Can a membrane replace contamination diversion?
Not automatically. The barrier requires validation against the contaminant and expected events. Detecting and diverting off-specification water remains a different function from treating it.
Sources and documentation
- Spirax Sarco — BC3200/BC3210 Installation and Maintenance Instructions, section 10.2, limits of conductivity-based condensate monitoring
- Spirax Sarco — Condensation contamination in steam systems FAQs, contamination sources and recovery
- ASHRAE Handbook 2023 — Water Treatment, deposition, corrosion and treatment mechanisms