For steam–methane reforming in ammonia/urea plants, the boiler doesn’t just make steam — it must deliver “dry” vapor with virtually zero contaminants. Think 10–30 ppb total solids in steam, silica ≤0.02 mg/L in feedwater, and oxygen down to a few ppb.
Ammonia and urea producers feed their reformers with high‑pressure steam — often 20–50+ bar — and then spend big to make sure that steam is pristine. The reason is brutal chemistry: any contaminant carried over with the steam can poison the nickel (Ni) reforming catalyst, slash hydrogen yield, and force shutdowns.
The marching orders are unambiguous. The treatment train targets “Type I” demineralized water (very low‑conductivity deionized water), with conductivity on the order of 0.1 µS/cm or less and silica held to a few tens of ppb. In practice, that means zero hardness, chlorides, sulfates, or metals in the feedwater — and steam purity held to 10–30 ppb total solids at pressures exceeding ~300 psig (≈20 bar) (watertechnologies.com).
Ultrapure feedwater targets and case evidence
One case study documented a boiler specification of silica <0.02 mg/L (20 ppb); missing that target led to fouling and higher fuel use. When the plant corrected its demineralizer to hit <20 ppb SiO₂, fuel consumption fell and steam output — and reformer throughput — rose markedly (researchgate.net).
Modern demin plants routinely deliver “infinite” resistivity (~16 MΩ·cm), equivalent to ≪0.05 µS/cm and total dissolved solids (TDS) well under 0.01 ppm. For perspective, even a 1% carryover of feedwater at 0.01 mg/L TDS would load the steam with just 0.0001 mg/L solids — far below harmful levels.
Pretreatment and demineralization train
Typical treatment starts with coarse filtration and softening to strip particulates and Ca/Mg hardness before high‑pressure service. Plants often deploy sand or cartridge filtration upstream; many operators choose a cartridge filter to capture 1–100 micron particles in a compact footprint, and a softener to prevent scale formation from calcium and magnesium ions.
The salt‑and‑organics front also matters. Boiler experts warn that “oil and other organic contaminants…must be removed from the boiler feedwater” because even trace organics trigger foam and carryover (watertechnologies.com). Plants commonly add activated carbon beds for this duty; in many trains, an activated carbon step precedes membrane desalination.
Deep desalting is handled by reverse osmosis (RO) or multi‑stage demineralization. For brackish makeup, a brackish‑water RO is a common first pass, followed by ion exchange. Others standardize on packaged demineralizers — a demineralizer pairing strong/weak cation and anion exchangers, or a continuous EDI unit — to drive ions to trace levels.
Polishing to the last ppb is routine in reformer service. Many plants rely on a mixed‑bed stage, with mixed‑bed resins that deliver <20 ppb silica and very low TDS at the outlet. Resin‑based systems are supported by a full ion‑exchange program and well‑matched regeneration controls.
Deaeration and oxygen control (ppb levels)
Oxygen and carbon dioxide removal is non‑negotiable. Mechanical deaerators typically raise feedwater above 90 °C and drop dissolved O₂ to ~2 ppm or less; chemical scavengers or vacuum deaeration take it down to <0.01 mg/L (forbesmarshall.com).
In practice, that chemistry arrives via metering systems — an oxygen‑scavenger program, dosed precisely through a dosing pump, keeps residual O₂ to a few ppb while minimizing corrosion in condensate and feedwater circuits.
Catalyst poisoning risk from steam carryover
Ni‑based reforming catalysts are unforgiving. Literature lists sulfur, halogens (Cl, F), arsenic, phosphorus, and heavy metals like Cu, Pb, and As as classic poisons (chempedia.info). Veterans note residual sulfur must be <0.2 ppm in natural gas to avoid Ni deactivation (chempedia.info).
The steam path is a hidden risk: “chemicals from the boiler feedwater or the cooling system are poisons to the reformer catalyst, so steam quality must be carefully monitored” (chempedia.info). Any ionic or particulate carryover — copper/iron corrosion products included — can block pores or deactivate active sites. Targets in practice are often stated as 0 mg/L of Fe, Cu, chloride, etc.; even residual Mg/Ca hardness is forbidden.
The business case is straightforward. Correcting feedwater silica and conductivity to design increased steam generation and cut fuel use in the cited plant (researchgate.net). For scale, a 500 MTPD ammonia plant may contain many tonnes of Ni catalyst at ~$50–100/kg; even small percentage gains in catalyst life are material.
Steam drum separation internals and layout
Designers build separation redundancy into the boiler and steam drum to maximize steam purity. Geometry avoids turbulence: “steam‑carrying riser tubes discharging below the water level…cause severe turbulence” — so modern boilers discharge risers above the water line or through baffles, with tangential entries into separators (watertechnologies.com).
Inside the drum, centrifugal separators (cyclones) split water from vapor: the mixture enters tangentially, water spirals down and steam spirals up. Multiple cyclonic stages (“fore‑separators”) remove bulk droplets; secondary scrubbers — wire‑mesh or vane demisters — polish fines. Boiler handbooks routinely show two to three stages to hit ppb‑level steam purity (watertechnologies.com).
Circulation, dryness fraction, and blowdown
The numbers are stark. For every kilogram of steam, 15–20 kg of water recirculates through the boiler loop; more than 99.97% of that water must be removed from the steam to meet purity targets (watertechnologies.com). In other words, only ~0.03% of drum water can accompany the steam.
With good separators, high‑pressure service expects only parts‑per‑billion solids carryover — 10–30 ppb total solids is typical (watertechnologies.com). In practice, operators run continuous blowdown and keep drum TDS very low (often <1–10 ppm) to limit any eventual carryover, with ABMA‑style guidance indicating that higher blowdown rates can allow higher drum TDS without exceeding steam limits.
Standards, monitoring, and design notes
Key water‑quality targets for reformer boilers converge globally: feedwater silica ≤0.02 mg/L, Na/Cl/SO₄ ≈ 0 (µg/L levels), and oxygen to a few ppb (forbesmarshall.com; watertechnologies.com). Indonesian boiler standards such as SNI 7268:2009 codify similar specifications, mirroring ASME/ABMA norms (m.antpedia.com).
Feedwater is preheated and deaerated to strip gases before entry; chemistry is tightly controlled, often with liberal blowdown to keep impurity cycles low. Where superheat is attemperated, spray placement is carefully managed — often in a closed mud drum or upstream line — so additives cannot leak into the steam path. Some units even employ external steam polishers (cyclones outside the drum) for especially critical purity.
Putting the train together
In reformer service, the reliable pattern is clear: a pretreatment train sized for solids and hardness, deep desalting to “dry” water, and oxygen control to the ppb level. Many operators standardize on modular membrane front ends; a combined membrane system feeds the demin section in industrial layouts, with RO followed by selective ion exchange.
Downstream, a packaged demineralizer or continuous EDI unit closes the ion‑removal gap, and a mixed‑bed polisher ensures silica ~0.01–0.02 mg/L at the outlet via mixed‑bed resin operation. Where organics are suspected, an upstream activated carbon step helps prevent foam and carryover cited by boiler handbooks (watertechnologies.com), and a brackish‑water RO provides the bulk ion knockdown before polishing.
Bottom line for reformer uptime
Producers aim for demineralized/“dry” water so the feedwater TDS is essentially nil, silica sits near 0.01–0.02 mg/L, and the steam drum routinely delivers 99.97% dryness or better. The reward is tangible: higher reformer output, longer catalyst life, and lower operating cost — as shown when one plant cut fuel use and boosted steam generation by eliminating excess silica in boiler water (researchgate.net).
It’s also why the high‑purity targets are among the strictest in industry: steam solids at 10–30 ppb (watertechnologies.com), silica ≤0.02 mg/L, and dissolved oxygen driven to the ppm/ppb level by deaeration and scavenging (forbesmarshall.com). As one authoritative source notes, “steam is another potential source of contaminants…chemicals from the boiler feedwater…are poisons to the reformer catalyst, so steam quality must be carefully monitored” (chempedia.info).
Sources: Boiler water‑treatment and steam‑purity handbooks, process‑textbook data, and case studies (including relevant Indonesian standards). Key references above detail industry targets (e.g., silica <0.02 ppm (lenntech.com; researchgate.netforbesmarshall.com), steam solids 10–30 ppb (watertechnologies.com)) and design measures (steam drum cyclonic separators and demisters (watertechnologies.com; watertechnologies.com)) necessary to achieve them.
