How to Choose Reagents for Industrial Water Treatment

Water Quality Determines Equipment Lifespan

Industrial equipment in contact with water has one main enemy — the water itself. Incorrect water treatment reduces a boiler's lifespan from 20 years to 5, increases fuel consumption by 15–30 % due to the heat-insulating scale layer, and sooner or later leads to an emergency shutdown.

According to AMPP (formerly NACE International), global losses from corrosion and scaling in industrial water systems exceed $300 billion annually. At the same time, 80 % of these problems can be prevented with the correct chemical regime — that is, the selection and dosing of reagents.

Over the past year, the SVK laboratory performed more than 350 source water analyses for industrial enterprises in the Dnipropetrovsk, Zaporizhzhia, and Poltava regions. In 60% of cases, the current water treatment program did not match the actual water composition — reagents were selected "by inertia," without annual review.

Dozens of water treatment chemistry suppliers operate on the Ukrainian market, but a systematic approach to reagent selection is rare. Usually, an enterprise buys an "antiscalant" without analyzing the source water, system parameters, and compatibility with other reagents. The result is inefficient budget spending or, worse, an accident.

Four Problems of Industrial Water

1. Scaling

Dissolved calcium and magnesium salts in water transition into an insoluble form upon heating and settle on heat transfer surfaces. Calcium carbonate (CaCO₃) begins to precipitate intensively at temperatures >60 °C, calcium sulfate (CaSO₄) — at >95 °C. Silicate deposits (SiO₂) are the most dangerous: they form at a silicon concentration >120 mg/l and are practically immune to chemical removal.

The thermal conductivity of scale is 20–40 times lower than that of steel. A 1 mm thick layer of CaCO₃ reduces heat transfer by 10–15 %, and at 5 mm, the overheating of the boiler wall metal reaches critical values, threatening its deformation.

2. Corrosion

Oxygen (O₂), dissolved in water at a concentration >0.02 mg/l, causes pitting corrosion — pinpoint depressions that eat through the pipe wall. CO₂ lowers the water pH to 5.5–6.5 and causes uniform corrosion of carbon steel at a rate of 0.3–1.0 mm/year. In bimetallic systems (copper heat exchangers + steel pipelines), galvanic corrosion is added — the destruction of the less noble metal.

Corrosion in steam boilers is a separate topic. In the phase transition zone (water → steam), stress corrosion occurs, which can lead to sudden failure without visible warning signs. More details on mechanisms and protection are in the article "Corrosion Inhibitors for Oil and Gas Pipelines".

3. Biological Fouling

Open recirculating systems (cooling towers, irrigation basins) are an ideal environment for microorganisms. Temperatures of 25–40 °C, constant moisture, and organic pollutants from the air all contribute to biofilm formation.

A 25 µm thick biofilm reduces heat transfer more than 250 µm of scale due to its heat-insulating structure. In addition, legionella (Legionella pneumophila) multiplies precisely in cooling towers at 20–45 °C and poses a direct threat to personnel health. According to EU Directive 2020/2184 on the quality of water intended for human consumption, monitoring legionella in cooling systems is mandatory; in Ukraine, it is recommended, but the obligation is growing with the implementation of EU directives. A full overview of biocidal strategies for cooling towers and cooling systems — including biocide type selection, dosing, rotation, and legionella control — is in the specialized article "Biocides for Recirculating Cooling Systems".

4. Suspended Solids and Turbidity

Unfiltered water contains clay particles, rust, and organic suspensions. Suspended solids settle in areas with low flow velocity, forming sludge that becomes a focal point for under-deposit corrosion. For systems with heat exchangers, the maximum permissible content of suspended solids is 5–10 mg/l (plate) or 20–30 mg/l (shell-and-tube).

Categories of Water Treatment Reagents

Antiscalants (Scale Inhibitors)

They prevent scale formation through two mechanisms: threshold inhibition — blocking crystal growth at a dosage of 2–10 mg/l, which is hundreds of times less than the stoichiometric amount; and dispersion — keeping microcrystals in suspension, preventing them from sticking together and settling on the surface.

Main classes:

Phosphonates (HEDP, ATMP, DTPMP) — classic antiscalants. HEDP is effective against CaCO₃ at temperatures up to 90 °C. ATMP — against CaCO₃ and BaSO₄. DTPMP — broad spectrum, including silicate deposits. Working dosage: 5–20 mg/l. Limitation: phosphonates hydrolyze at pH > 9.5 and temperatures > 95 °C, so they are not suitable for high-pressure steam boilers.

Polymaleates and polycarboxylates — synthetic polymers with a mass of 1000–5000 Da. Effective as dispersants: they keep CaCO₃ and Fe₂O₃ crystals in suspension. Often used in combination with phosphonates for a synergistic effect. Thermally stable up to 150 °C.

Phosphate esters — for medium and high-pressure boilers (up to 60 bar). They form a protective phosphate layer on the surface, simultaneously inhibiting scaling and corrosion. Dosage: 10–30 mg/l in terms of PO₄³⁻.

Corrosion Inhibitors

For steam boilers: the main approach is maintaining the boiler water pH at 10.5–12.0 using alkaline reagents (NaOH, Na₃PO₄, Na₂SO₃). Sodium sulfite (Na₂SO₃) works as an oxygen scavenger — it binds dissolved O₂ according to the reaction: 2Na₂SO₃ + O₂ → 2Na₂SO₄. Dosage: 8–10 mg of Na₂SO₃ per 1 mg of dissolved O₂ (with excess). For boilers with a pressure >40 bar, hydrazine (N₂H₄) or DEHA (diethylhydroxylamine) are used instead of sulfite — they do not increase the salt content of the boiler water.

For cooling towers (open systems): combined formulas based on zinc salts + phosphonates + polymeric dispersants. Zinc (2–5 mg/l) forms a protective ZnO/Zn₃(PO₄)₂ film on the metal surface. Molybdates (MoO₄²⁻) are a safer alternative to chromates (banned due to toxicity), dosage 5–15 mg/l. Tolytriazole (TTA) is a specific inhibitor for protecting copper alloys in condensers and heat exchangers, dosage 2–5 mg/l.

For closed systems: fewer reagents are needed since makeup water is minimal. Sodium nitrite (NaNO₂) 500–1500 mg/l is a classic inhibitor for closed heating/cooling loops. Molybdate + azole — for systems with copper heat exchangers.

Biocides

Oxidizing: chlorine (NaOCl) is the cheapest, effective at a residual concentration of 0.3–0.5 mg/l of free chlorine. Chlorine dioxide (ClO₂) is 2.5 times more effective than chlorine, does not form trihalomethanes (THM), and works in a wider pH range (4–10 vs 6–8 for chlorine). Ozone is the strongest oxidizer, but it requires on-site generation and has no prolonged action.

Non-oxidizing: glutaraldehyde (GA) is effective against sulfate-reducing bacteria (SRB), dosage 50–200 mg/l during shock treatment. DBNPA (2,2-dibromo-3-nitrilopropionamide) is a fast-acting biocide with a half-life of 2–4 hours at pH 8.0, ideal for systems where minimal residual toxicity is required. Isothiazolinones (CMIT/MIT) are for maintenance dosing of 10–50 mg/l, but are limited at pH > 8.5.

Anti-legionella treatment: mandatory for cooling towers. The recommended regime is continuous chlorination (0.5 mg/l of free chlorine) + quarterly shock treatment with a non-oxidizing biocide. Definitions of terms (SRB, THM, scavenger) are in the industrial chemistry glossary.

Coagulants and Flocculants

Used for the preliminary purification of incoming water from suspended solids, colloids, and organics.

Coagulants: aluminum salts (Al₂(SO₄)₃ — dosage 20–80 mg/l) or iron (FeCl₃ — 10–50 mg/l). The mechanism is the neutralization of the charge of colloidal particles and their aggregation into flocs. Polyaluminum chloride (PAC) is a modern alternative with a wider working pH range (5.5–9.0 vs 5.5–7.5 for aluminum sulfate).

Flocculants: anionic polyacrylamides (PAM) "collect" coagulated flocs into large aggregates for rapid settling. Dosage: 0.5–3 mg/l. Critical: overdosing the flocculant has the opposite effect — stabilizing the suspension instead of settling.

pH Adjusters

Maintaining the optimal pH is a basic condition for the operation of all other reagents. To increase pH: NaOH (caustic soda), Na₂CO₃ (soda ash), amines (for condensate lines). To decrease: H₂SO₄ (sulfuric acid), HCl (hydrochloric acid). The choice depends on the initial water composition and system limitations — for example, HCl is not recommended for systems with stainless steel due to the risk of chloride corrosion.

Reagent Selection by System Type

Steam Boilers (Boiler Houses)

Specifics: high temperature (up to 350 °C for high-pressure boilers), salt concentration during evaporation, risk of foaming and carryover of boiler water into steam.

Comprehensive chemical regime:

For high-pressure boilers (> 40 bar), phosphonates and phosphates are unsuitable — they decompose to form orthophosphate, which, when concentrated, can cause acid phosphate corrosion. Here, coordination polymers and "all-volatile treatment" (AVT) are used — a regime where all reagents are volatile (amines + oxygen scavenger).

Cooling Towers (Open Recirculating Systems)

Specifics: constant evaporation (concentration factor of 3–6 cycles), contact with atmospheric air (O₂, CO₂, dust, microorganisms), losses through evaporation and blowdown.

Typical treatment program:

1. Antiscalant + corrosion inhibitor — a combined product based on phosphonate + zinc + polymer. Dosage: 80–150 mg/l of the product at 3 cycles of concentration.

2. Biocide — chlorination to 0.3–0.5 mg/l of free chlorine + shock treatment with a non-oxidizing biocide once a week.

3. Dispersant — to keep suspended solids (dust, corrosion products) in suspension and prevent them from settling on heat transfer surfaces.

Control of concentration cycles — via conductivity or chlorides. If chlorides increase > 500 mg/l — increase blowdown.

Closed Loops (Heating, Chillers)

Specifics: minimal makeup water (<1 % of volume per week), stable water composition after initial treatment, risk of microbiological contamination during stagnation.

Program: single injection of an inhibitor (nitrite 1000–1500 mg/l or molybdate 200–500 mg/l) + biocide. Control: monthly analysis for residual inhibitor concentration and microbiology. Reagent makeup — only when the concentration drops below the threshold level.

Heat Exchangers

Plate heat exchangers have narrower channels (2–5 mm) and are more sensitive to deposits than shell-and-tube ones. Water quality requirements are stricter: hardness < 5 meq/l, suspended solids < 5 mg/l, coolant temperature determines the choice of antiscalant.

For stainless steel plate heat exchangers, it is critical to control chlorides (< 200 mg/l) — otherwise, chloride stress corrosion cracking will destroy the plates. For shell-and-tube ones with copper tubes — add tolytriazole (TTA) as a copper corrosion inhibitor. More about types of industrial equipment washing and deposit cleaning is in the article "Industrial Detergents: Types and Selection". A comprehensive program for the chemical protection of heat exchangers — corrosion and scale inhibition, reagent selection, flushing, and monitoring — is discussed in detail in the article "Corrosion and Scale Inhibitors for Heat Exchangers".

Six Parameters to Control

Rule: if the iron concentration in the system water increases, corrosion is progressing, even if everything looks normal visually. An Fe level > 0.5 mg/l in a closed system is a signal to review the inhibitor dosage.

Reagent Dosing Methods

Proportional dosing — supplying the reagent proportionally to the water flow (via a pulse meter). The most accurate method for boiler and cooling tower makeup systems. The dosing pump receives a pulse from the flow meter and supplies the exact amount of reagent per cubic meter of water.

Continuous dosing — continuous supply at a fixed rate. Suitable for systems with a stable load (closed loops, recirculating systems). Easier to set up, but less accurate during load fluctuations.

Shock dosing (slug dose) — a single injection of an increased dose. Typical application: biocidal treatment of cooling towers (50–200 mg/l of glutaraldehyde for 2–4 hours), initial treatment of closed systems, boiler flushing before commissioning.

For any dosing method, it is critical: the reagent injection point must be before the problem zone. The antiscalant is injected into the incoming water before heating, the biocide — into the zone with maximum circulation, the oxygen scavenger — into the deaerator tank or at the suction of the feedwater pump.

FAQ

Can the same antiscalant be used for a boiler and a cooling tower?

No. Boiler antiscalants work at pH 10–12 and temperatures of 100–200 °C, cooling towers — at pH 7–9 and 25–45 °C. The chemical bases are different: for boilers — coordination polymers or phosphate buffers, for cooling towers — phosphonates + zinc + dispersants. A formula effective in a boiler may be unstable in a cooling tower, and vice versa.

How often should source water analysis be done?

At a minimum — a full analysis once a quarter (hardness, alkalinity, chlorides, sulfates, silicon, iron, pH, conductivity). When changing the water supply source or during seasonal quality fluctuations (artesian wells) — monthly. The analysis results are the basis for adjusting dosages. Up-to-date information on regulatory requirements for chemicals is in the article "UA-REACH: What Manufacturers Need to Know".

What is more dangerous — scale or corrosion?

Corrosion. Scale reduces efficiency and increases energy costs, but rarely leads to a sudden accident. Corrosion is the loss of wall metal, and at a rate of 0.5 mm/year, a boiler with a wall thickness of 8 mm will exhaust its lifespan in 10–12 years instead of the estimated 25. Pitting corrosion is more dangerous than uniform corrosion — it can "eat through" the wall locally in 2–3 years.

What budget should be allocated for water treatment reagents?

Estimated costs: a boiler house with a capacity of 10 Gcal/h — 800–2000 UAH/month for reagents. A cooling tower with a recirculation volume of 500 m³ — 3000–8000 UAH/month (the main item is the biocide). A closed system of 100 m³ — 500–1500 UAH for initial treatment, then 200–500 UAH/month for maintenance. These figures are for typical conditions with water hardness of 5–7 meq/l. At a hardness > 10 meq/l, costs increase by 1.5–2 times.

SVK Water Treatment Reagents

SVK develops and manufactures a full line of reagents for industrial water systems: antiscalants for boilers and cooling towers, corrosion inhibitors for closed and open loops, biocidal programs, coagulants, and pH adjusters.

Our approach is not selling a "universal remedy," but selecting a treatment program for a specific system:

1. Source water analysis — laboratory testing of 15+ parameters

2. System audit — equipment type, materials, temperature regimes, capacity

3. Program selection — a combination of reagents with dosage calculation

4. Test Drive — a trial batch of reagents to verify effectiveness on your system for 2–4 weeks

5. Support — dosage adjustment based on monitoring results

Order water analysis and reagent selection: svk.com.ua/vodopidgotovka

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Read also:

• Corrosion Inhibitors for Oil and Gas Pipelines — protection mechanisms, inhibitor types, HPHT conditions
• Industrial Chemistry Glossary — definitions of terms: scavenger, coagulant, PAM, THM, and others
• Industrial Detergents: Types and Selection — detergent classification, CIP washing, degreasing
• UA-REACH: What Manufacturers Need to Know — regulatory changes for industrial chemistry in Ukraine