Refinery cooling towers do not get easy duty cycles. They run hot, recirculate aggressively, and face periodic hits of hydrocarbons and process chemicals. High thermal loads, re‑circulated water, and contamination combine to drive mineral scaling, corrosion, and explosive microbial growth, each of which torpedoes heat transfer and reliability (epcmholdings.com) (invirotec.co.id).

Calcium bicarbonate in groundwater that’s stable at ambient conditions re‑crystallizes as calcium carbonate (CaCO₃) when heated; the result is insulating scale on heat‑exchange surfaces (epcmholdings.com) (epcmholdings.com). Chemistry matters: high pH (>8.5) favors carbonate scaling, while low pH (<6.5) attacks metal parts (epcmholdings.com).

Microbes thrive in warm, stagnant zones; biofilm acts like glue for solids, accelerates fouling, and triggers localized corrosion (watertechusa.com) (epcmholdings.com). Untreated makeup sources quickly concentrate hardness and TDS (total dissolved solids), degrading performance and forcing cleanouts — the kind of “organic growth, contamination, scaling, and corrosion” that “reduce productivity, cause downtime, and require costly equipment replacement” (invirotec.co.id).

Refinery realities add more risk: oil vapors and chemicals such as glycol, amines, and solvents can enter the tower and interfere with chemistry and biocide action. And regulations — including Indonesian discharge limits — tighten the screws on blowdown composition and Legionella control; “setiap pembuangan…harus memenuhi semua persyaratan peraturan” (all discharges must satisfy regulatory quality requirements) (invirotec.co.id).

Scaling risk and inhibitor blend

As water evaporates, TDS — Ca, Mg, CO₃²⁻, SO₄²⁻ — concentrate, and many salts drop out more readily at higher temperatures (epcmholdings.com). Without chemistry, exchangers foul with CaCO₃ or CaSO₄, cutting heat‑transfer efficiency and increasing blowdown. The job of the scale program is to “disrupt mineral precipitation” and keep surfaces clean (epcmholdings.com).

Formulations typically combine phosphonates/polyphosphates with advanced organic polymers. Phosphonates such as HEDP or NTMP sequester Ca/Mg, but under oxidizing conditions they degrade to orthophosphate, which can precipitate as Ca₃(PO₄)₂ — a reason modern programs limit phosphate or pair small inorganic phosphate with organics (chemengonline.com). Multifunctional polycarboxylate and acrylate/sulfonate copolymers, including co‑/ter‑polymers that distort crystal lattices, broaden protection to calcium carbonate, calcium sulfate, iron hydroxide, magnesium/calcium silicates, phosphates, and fluoride scales (chemengonline.com) (chemengonline.com). Dispersants at threshold levels help keep micro‑crystals suspended so blowdown can remove them.

Programs are metered against cycles of concentration (the ratio of recirculating TDS to makeup TDS). A move from ~4× to 6–8× cycles can cut blowdown by roughly 25–40% — savings that only land if inhibitors hold the hot end below saturation, monitored by Langelier or Ryznar indices (scaling tendency metrics) and continuous pH, conductivity/TDS, and Ca²⁺ measurements. The field data track with this: “scale inhibitors…preserve heat transfer efficiency” (epcmholdings.com), and one refinery analysis showed cooling tower load/water consumption falling ~40% through redesign and reuse (researchgate.net).

Environmental pressure is reshaping formulations. Cooling Technology Institute trends and producer data point to rising demand for non‑phosphorus options to avoid eutrophication risk (chemengonline.com). Zinc is constrained for aquatic toxicity. The latest blends lean zinc‑free, phosphate‑free, sometimes using organic nitrates or molybdates as safer metal substitutes, and are credited with “performance advantages, including reduced fouling tendency and better corrosion performance” versus legacy programs (chemengonline.com). In practice, this means selecting complementary scale inhibitors and polymers, engineered for performance and environmental compliance.

Dosing precision underpins the chemistry, which is why many operators pair control logic with metering via a dosing pump.

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Pengertian dan Pengaruh TDS dan TSS Terhadap Kualitas Air

Corrosion inhibitor selection and pH

Carbon steel, stainless, and copper alloys all face attack from dissolved oxygen, CO₂, and chloride/sulfate in recirculating water. Corrosion inhibitors “assemble on the metal surface… [forming] a passivation layer that limits contact between the metal and the process water,” slowing metal loss and reducing downtime (environmental-expert.com).

Programs typically combine anodic/barrier inhibitors (silicates; molybdate or phosphate passivators; organic amines) with cathodic inhibitors for copper alloys (e.g., benzotriazole, mercaptobenzothiazole). Some modern treatments use filming amines to build hydrophobic layers across mixed‑metal systems. Where discharge rules tighten, molybdate can be replaced by organic nitrite or azole blends; non‑chromate, zinc‑free, non‑phosphate systems are increasingly standard (chemengonline.com).

pH is kept in the ~7.0–8.0 window to balance steel passivation against copper sensitivity (epcmholdings.com), and performance is verified via corrosion coupons or probes, aiming for ≤0.05–0.10 mm/year (≈2–4 mpy). “Corrosion inhibitors…extend the life of the cooling tower, ensuring structural integrity and operational reliability,” with dosing controlled to avoid over‑concentration (epcmholdings.com). A refinery case moving from chromate to a non‑chromate blend achieved corrosion rates below targets and eliminated hexavalent chromium discharge. The corrosion chemistry must be integrated with scale control to balance passivation and deposition. When selecting formulations, many teams source proven corrosion inhibitors tailored to their metallurgy.

Dual‑mode biocide regimen

Uncontrolled biology can incapacitate a tower. Slime layers become anchor points for solids and drive under‑deposit corrosion (watertechusa.com). The industry standard is a robust program pairing continuous oxidizing biocide with periodic non‑oxidizing shocks, monitored by HPC (heterotrophic plate count) and Legionella targets.

Oxidizers — chlorine, chlorine dioxide, bromine, iodine, ozone, hydrogen peroxide — are fed continuously to maintain a small residual (e.g., 0.2–0.5 ppm Cl₂) in recirculation. “Oxidizing biocides…require constant feeding,” often via fractionating or pulse feeds to sustain coverage (watertechusa.com). Residuals or ORP (oxidation‑reduction potential) controls track effectiveness.

Non‑oxidizers — glutaraldehyde, DBNPA, THPS, isothiazolinones, quaternary amines — are dosed weekly as “shock” treatments, commonly ~5–20 mg/L glutaraldehyde per ASHRAE and Bosch practice. Pilot work shows weekly 10 mg/L glutaraldehyde with continuous chlorine “greatly reduced planktonic and biofilm bacterial counts immediately after injection,” but regrowth appeared 4–5 days later — a reminder that suppression, not eradication, is the operating goal (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). WaterTech notes that “non‑oxidizing biocides…do not require constant feeding because residual chemical can last in a system for several days” (watertechusa.com). Alternating biocide classes helps prevent resistance.

Hydrocarbons and organics can shield biomass, so programs often include oil separation and antifoam measures. Where shocks are applied, operators may co‑dose a dispersant/surfactant to break biofilm, all while tracking environmental limits; intermittent ozonation or UV may supplement chemistry under strict rules (epcmholdings.com). For hydrocarbon ingress, some sites add upstream oil removal to protect the biocide program.

Typical performance indicators: HPC <1000 CFU/mL and Legionella <1000 CFU/L, with 3–5 log (99.9–99.999%) reductions after shocks (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Precision matters: “the injection of [biocides] is meticulously regulated…balance effective microbial control and avoid developing resistant strains” (epcmholdings.com). For sourcing, facilities typically standardize on proven biocides compatible with their oxidant and metallurgy, and many pair shocks with a dispersant chemical to maximize biofilm breakup.

Baca juga: Pengolahan Limbah Secara Kimia

Monitoring, cycles, and outcomes

Integrated programs ride on automation and continuous monitoring. Typical setpoints: pH ~7.0–8.0 (epcmholdings.com); conductivity/TDS to manage cycles and trigger blowdown; corrosion coupons/probes targeting ≤0.1 mm/yr; biological counts for HPC/Legionella; and residuals like ORP for chlorine or HPLC confirmation for glutaraldehyde.

The payoffs are measurable. Less than 1 mm of CaCO₃ scale can halve a loop’s heat‑transfer coefficient; conversely, a tuned program sustains design capacity. Plants report tangible run‑length gains: upgrades extended cleaning cycles from quarterly to annual in one refinery, and a phosphonate/polymer blend increased cycles by ~50%, saving ∼100,000 m³/year of water. In broader optimization, researchers quantified ~40% reductions in tower load and water use with improved reuse/treatment (researchgate.net). Chemistry choices also influence oxidant demand: after removing phosphates from treatment, experts reported a 70% reduction in bleach usage for microbial control (chemengonline.com).

Regulatory compliance and blowdown treatment

Blowdown must meet local discharge limits on pH, TSS, oil and grease, metals, and pathogens — particularly stringent in Indonesia — which is why many towers route effluent to clarification or RO ahead of outfall (invirotec.co.id). A non‑phosphate, zinc‑free, low‑tox biocide/corrosion approach aligns with global best practice and evolving eco‑toxicity rules (chemengonline.com). For solids control, many facilities pair upstream clarifiers with downstream RO for polishing; when RO is used on blowdown, teams often specify reverse osmosis units sized to cycles and TDS. Where chemical residuals are capped tightly, supplemental UV disinfection can be considered as a non‑chemical adjunct.

In Indonesia, the mandate is explicit: “setiap pembuangan…harus memenuhi semua persyaratan peraturan” (invirotec.co.id). Chemistry, dosing, and monitoring are therefore structured to maintain thermal reliability while meeting environmental obligations.

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Penerapan Sistem Biofilter dalam Pengolahan Limbah Air

Sources and references

Guidance and data cited here include Duvenhage’s maintenance overview, which details scale control, microbiological control, and corrosion practices in towers (epcmholdings.com) (epcmholdings.com) (epcmholdings.com); an Indonesian industry explainer on contaminants and treatment steps, including the discharge requirement quote (invirotec.co.id) (invirotec.co.id); WaterTechUSA’s primer on oxidizing and non‑oxidizing biocides (watertechusa.com) (watertechusa.com); Liu et al.’s pilot‑scale tower biocide efficacy (Biofouling 2011), documenting weekly glutaraldehyde shocks with continuous chlorination, immediate reductions, and regrowth after 4–5 days (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov); Matijašević et al. on refinery cooling‑water optimization (∼40% load/water cuts) (researchgate.net); Buecker & Post on evolving non‑P chemistries and polymers, with notes on fouling and corrosion performance and bleach reduction when removing phosphates (chemengonline.com) (chemengonline.com) (chemengonline.com) (chemengonline.com); and a Hydrocarbon Processing case on non‑phosphorus corrosion inhibitor performance (environmental-expert.com).

Taken together, the playbook is clear: blend complementary inhibitors, meter with precision, and verify with data — a strategy that protects plant reliability and maximizes efficiency while staying inside tightening environmental lines (epcmholdings.com) (pmc.ncbi.nlm.nih.gov).