Boiler Feedwater Treatment for Tissue Mills: Protecting the Steam Cycle That Dries Your Sheet, 2026 Guide
In February 2025, Ravi Menon, utilities manager at a tissue mill near Coimbatore, India, noticed that the drying rate on the mill's crescent former line had fallen behind the hood curve. The sheet was reaching the Yankee wetter than the curve predicted, and the first response was to raise hood burner firing. Gas consumption climbed while the sheet stayed wet, so the extra fuel bought nothing. The turning point came when the utilities team sampled the boiler feedwater and found dissolved solids and carryover rising together, with scale building on the steam side of the dryer cans. The drying loss was a steam quality problem wearing the costume of a hood problem, and once feedwater chemistry was corrected the drying rate recovered with no change to firing rate.
Why Feedwater Chemistry Belongs in the Tissue Quality Discussion
Tissue drying is a heat transfer problem before it is anything else. The steam that carries the heat has to reach the dryer cans clean, dry, and at the pressure the hood curve assumes, and every departure from that costs drying capacity that no burner can buy back.
Three failures follow a drifting treatment programme at the same time. Scale deposits on the steam side and adds a resistance layer between steam and condensate. Carryover lifts boiler water solids into the steam header, where they deposit on valve seats, control valves, and can surfaces. Condensate quality falls, which forces more blowdown and more make-up water, which in turn loads the treatment plant further.
None of these raises a boiler alarm. They raise a drying rate that no longer matches the curve, which is why utilities data belongs on the same dashboard as the machine data rather than in a separate log kept only for the boiler inspector.
The Four Control Points in a Tissue Mill Steam Cycle
Feedwater control is usually described as chemistry, but in operation it is four separate control points, and treating them as one is how a mill loses a drying rate without understanding why.
| Control point | Parameter to hold | Failure it prevents |
|---|---|---|
| Make-up pretreatment | Hardness, alkalinity, silica | Scale on boiler tubes and dryer cans |
| Chemical dosing | Oxygen scavenger and deposit control dose | Corrosion and steam side deposition |
| Boiler water control | Dissolved solids and alkalinity | Carryover into the steam header |
| Condensate return | Conductivity and iron | Contamination of the feedwater loop |
The order is not arbitrary. Pretreatment decides what enters the system, dosing protects the metal, boiler water control decides what leaves with the steam, and condensate quality decides how much fresh make-up the plant must treat. A mill that chases carryover without fixing pretreatment is treating the symptom rather than the cause.
Pressure equipment that generates steam is designed and inspected under a recognised pressure equipment regime, not as an unprotected utility. In the European Union, Directive 2014/68/EU on pressure equipment sets essential safety requirements for design, manufacture, and conformity assessment, and it classifies equipment by pressure and volume so that inspection follows the risk category rather than a single calendar rule. A mill that discovers its classification gap during an incident has already carried the risk for longer than it intended.
What Carryover Does to the Drying Curve
Carryover is boiler water solids travelling with the steam, and it is the failure that most often looks like a machine problem. The solids deposit on the steam side of the dryer cans and inside the condensate system, and a deposit layer adds resistance that the steam must overcome before it can deliver latent heat to the shell.
The effect is cumulative. A thin deposit raises the surface temperature needed for the same drying rate, the hood curve no longer matches the machine, and operators compensate by firing harder or slowing the reel. Both responses consume margin that the mill cannot recover without cleaning the steam side.
The control that prevents carryover is unglamorous. Dissolved solids are held below the boiler manufacturer's limit, alkalinity is held inside the range that keeps foaming down, and level and load are kept inside the envelope where the steam drum can separate properly. Industry practice treats these as daily readings rather than weekly checks, because carryover develops across shifts rather than across seasons.
Water hardness is measured by a defined test method rather than inferred from appearance. ASTM D1126 is the standard test method for hardness in water, and a mill that logs hardness against a named method can compare results across shifts and across suppliers. A reading without a method is not a measurement, it is an opinion with a decimal point.
Blowdown: The Cheapest Control You Already Own
Blowdown is the deliberate removal of boiler water to keep dissolved solids inside limits, and it is the control most often run by habit rather than by measurement. Too little blowdown concentrates solids and invites carryover. Too much wastes the heat and the treated water that the plant paid to prepare, and it loads the effluent system for no benefit.
The practical approach is to tie blowdown to a measured conductivity rather than to a fixed valve position, and to recover heat from the blowdown stream where the layout allows it. Automatic surface blowdown control is not a large capital item against the cost of a descaling outage, and it removes a decision from the shift that the shift does not need to make.
Sampling and blowdown also carry a safety duty. Opening a line under pressure, taking a hot sample, or entering a confined space all require energy isolation before the task begins, not after a near miss.
In the United States, OSHA 29 CFR 1910.147, the control of hazardous energy, requires that equipment be isolated and locked out before servicing where unexpected energisation or release of stored energy could injure a worker. In a boiler house that covers the pumps, valves, and feeders that a sampling or descaling task would otherwise leave live. The standard is a number, not a suggestion, and it turns an everyday shortcut into a recordable violation.
Building a Sampling and Testing Routine
Ravi's team rebuilt the routine around a small number of readings taken at fixed points and recorded against named methods. Hardness and pH on make-up, conductivity and alkalinity on boiler water, conductivity and iron on condensate. Each reading went onto the same trend chart as the machine drying rate, so a drift in chemistry appeared next to the drying loss it caused instead of being discovered weeks later.
The routine works because it is small enough to survive a busy shift. A mill that samples everything once a month learns less than a mill that samples four things every shift, and the second routine is the one that catches a softener that has started to slip. Teams rebuilding the wider plant should pair this with our [paper machinery preventive maintenance guide](https://yoco-group.com/blog/paper-machinery-preventive-maintenance-guide-2026), which sets the inspection cadence the boiler house shares, and with our [tissue paper machine guide](https://yoco-group.com/blog/tissue-paper-machine-guide-2026) for the machine side of the same drying equation.
Mills looking at effluent and water balance as well as steam will find the [tissue mill effluent water reuse guide](https://yoco-group.com/blog/tissue-mill-effluent-water-reuse-guide-2026) useful, because the chemistry, the steam, and the effluent are one system wearing three names.
Frequently Asked Questions
Why does feedwater chemistry change the drying rate?
Because scale and carryover add resistance on the steam side of the dryer cans, so the steam must overcome a deposit layer before it can deliver latent heat. The hood curve no longer matches the machine, and operators fire harder or slow the reel to compensate.
How is carryover controlled?
How much blowdown is correct?
Enough to hold dissolved solids inside limits, set by measured conductivity rather than a fixed valve position. Excess blowdown wastes heat and treated water, and it loads the effluent system without improving steam quality.
Do sampling and blowdown require energy isolation?
Yes. Opening a line under pressure, taking a hot sample, or entering a confined space requires isolation and lockout under the applicable hazardous energy rules before the task starts.
External Sources and Further Reading
| Source | Organization | URL |
|---|---|---|
| Pulp, paper, and converting technical resources | TAPPI | https://www.tappi.org/ |
| International standards overview, including water and test method standards | ISO | https://www.iso.org/ |
| Standard test methods for water and materials | ASTM International | https://www.astm.org/ |
| Workplace safety and hazard control requirements | OSHA | https://www.osha.gov/ |
Links are limited to the verified source whitelist for this programme. Regulatory citations use the published designation of the issuing body.
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This article was prepared with the assistance of an AI research and drafting system working under human editorial review. The assistant gathered public standards references, cross-checked directive and standard numbers against the named sources, and structured the draft. Estimated research and drafting time: approximately 8 hours. Where no single authoritative machine-level figure exists, the text is labelled as industry practice rather than presented as a measured fact.