Clean steam (sometimes called “pure steam”) is widely used in sterile processes: humidifying clean rooms, sterilizing equipment, and providing process steam that comes into direct contact with products or primary packaging.

The equipment that produces it is therefore a “clean-steam generator” (CSG).

Below is a concise checklist engineers normally follow when they have to size, specify or purchase one.

1. Clarify the real demand

·Maximum instantaneous flow (kg h⁻¹) – record the sum of all users that can open simultaneously, then add 10–20 % safety margin.

·Pressure (barg) – most autoclaves and SIP skids need 2–3 barg; HVAC humidifiers can accept 0.5–1 barg.

·Load profile – continuous, batch, or peak-shaving? A flat 24 h base load can use a small generator with large buffer; short, sharp peaks (e.g., 15 min every 2 h) justify an accumulator or an oversized generator.

·Condensate return – if 70–80 % of the steam is returned as WFI-quality condensate, feed-water pre-heating and running cost drop sharply.

·Redundancy philosophy – N+1 is normal for cGMP plants; decide whether the standby unit must be “hot” (ready in <5 min) or “cold”.

2. Select the heating source

·Industrial steam (plant steam) – simplest and cheapest; a double-plate or shell-and-tube exchanger is used with a falling-film column.

·Electric – no plant steam available; higher OPEX but zero boiler house; good for <500 kg h⁻¹.

·Gas-fired – rare; needs burner management and stack; only justified when gas is very cheap and plant steam is absent.

3. Check feed-water quality

·Pharmacopoeial WFI or at least Purified Water (PW) is mandatory.

·Conductivity <1 µS cm⁻¹, TOC <500 ppb, endotoxin <0.25 EU ml⁻¹.

·Hardness must be zero; any residual will coat the tubes and drop output within weeks.

4. Material & surface finish

·Product-wetted parts: 316L stainless steel; Ra ≤0.8 µm mechanical polish or 0.4 µm electropolish.

·Double-tube-sheet (DTS) exchangers eliminate cross-contamination between plant steam and clean steam.

·Elastomers: USP Class VI, FDA 21 CFR 177; EPDM or PTFE are standard.

5. Validation & documentation

·The generator is treated as “direct-impact” under GAMP 5.

·Expect DQ, IQ, OQ and PQ templates; FAT protocol; material certificates 3.1.B; weld logs, orbital weld radiographs, passivation record, roughness certificates.

·Instrumentation must be calibrated; 21 CFR Part 11 data integrity if connected to MES/SCADA.

6. Instrumentation & control

·Minimum sensors: feed flow, feed conductivity, clean-steam pressure/temperature, column drop, condensate conductivity, level in separator.

·Auto-sanitisation cycle (80–90 °C for 30 min) keeps endotoxin low.

·Capacity control: ON/OFF for small units, 3-step or modulating pneumatic valve for 0–100 % turndown.

7. Utilities & footprint

·Plant steam consumption ≈1.2 kg per kg clean steam (allow 10 % radiation loss).

·Cooling water for sample condenser: approx. 100 L h⁻¹ per 100 kg steam capacity.

·Power: <5 kW for controls; 50–100 kW for electric models (500 kg h⁻¹).**

·Typical skid: 1.2–1.8 m L × 0.8–1.0 m W; allow 1 m service access on all sides.

8. Life-cycle cost snapshot (1000 kg h⁻¹, 8000 h y⁻¹, 3 barg)

Note: electric looks attractive when cheap hydro power (<0.05 € kWh⁻¹) is available; otherwise plant-steam heated wins.

9. Common pitfalls

·Undersizing the feed pump – a 10 % drop in feed pressure can cut output 20 %.

·Ignoring altitude – at 2000 m the boiling point is 93 °C; the generator must be de-rated.

·Using softened instead of de-ionized water – white dust will appear in humidifiers within days.

·Forgetting a sample condenser – regulatory audits always ask for endotoxin data.

10. Quick selection matrix

Follow the ten points above and the generator will meet both process needs and regulatory expectations without over-spending.