1-805-484-2992
Quotes - Engineering - SalesSteam from steam
The generator is a heat exchanger with a level control and a blowdown valve
A clean steam generator has no burner. Plant steam at 75 to 150 psig flows through a U-tube bundle submerged in feedwater on the shell side, the feedwater boils, and a separator above the bundle delivers dry steam at 30 to 60 psig to the header. The design keeps the two steams apart with a double tubesheet, holds the bundle covered with level control, and removes what the feedwater left behind with blowdown.
The parent page sizes the generator on the SIP peak. This page is about the generator as a machine: the plant steam pressure it needs, 3-A 609 culinary and USP pure steam as the two targets, and the blowdown arithmetic.
Designing the generator
Plant steam pressure and the approach
To make clean steam at 45 psig, saturation 292 F, the plant steam in the tubes must boil water at that pressure through a tube wall with a film on it. That takes 30 to 50 degrees of approach, so 100 psig plant steam at 338 F is the usual minimum and 125 to 150 psig gives a smaller bundle. A site with only 50 psig plant steam can make 15 psig clean steam, enough for barriers and low-pressure SIP but not for a 250 F sterilization at any speed. Hot oil or 350 F hot water works where there is no high-pressure steam, with a larger bundle.
Feedwater preheating pays: plant steam condensate leaving the tubes at 300 F warms feedwater from 70 F to 180 F in a small 316L exchanger and cuts the plant steam by 10 to 15 percent.
Culinary steam to 3-A 609 and pure steam to USP
The feedwater and finish set the grade. Culinary steam under 3-A Accepted Practice 609 can contact food: potable feedwater, only boiler compounds the FDA lists as acceptable, a stainless header with a separator and a filter at the use point. A generator fed with softened, filtered water and no treatment chemicals makes 609 steam directly. Pure steam is the pharmaceutical grade: its condensate must meet the USP monograph for Water for Injection on conductivity, TOC and endotoxin, so the feed is WFI or qualified purified water, the shell side is electropolished 316L, and the separator delivers a dryness of 0.95 or better with non-condensables under 3.5 percent.
- Culinary: softened, filtered feed, no amines, 32 Ra shell, stainless header, separator and filter downstream
- Clean steam: RO or purified feed, chloride under 1 ppm, 316L, quality tested at the use point
- Pure steam: WFI feed, 20 to 25 Ra electropolished shell, sampling condenser, condensate to USP WFI
Blowdown, level and the feedwater system
Whatever the feedwater brings in stays in the shell when the steam leaves. RO permeate at 10 microsiemens concentrates ten times in a shell blowing down at 10 percent of the steam rate, and the shell water sits at 100 microsiemens carrying ten times the permeate's chloride, hot, against 316L tubes. The blowdown rate is set from the feedwater conductivity at 10 to 20 cycles of concentration and held by a continuous blowdown valve on a conductivity controller; intermittent bottom blowdown removes what settles. The feedwater pump is sized for steam rate plus blowdown.
Level control keeps the bundle covered under a swinging load: a 3,000 lb/h SIP draw on a small shell can uncover the top tubes in a minute, superheating the steam and scaling the tube. A shell sized for the swell, a modulating feedwater valve and a low-level cutout on the plant steam are the answer.
The common mistake
Feeding a clean steam generator with softened water because the plant boiler uses it. Softening swaps hardness for sodium and leaves silica and chloride, so the shell water climbs to several thousand microsiemens, silica carries over, the condensate fails conductivity and the tubes pit. Clean steam takes RO or purified water; only culinary steam tolerates softened feed. Call and talk it through with an engineer: 1-805-484-2992
Steam generator conditions
These rows describe the generator we size, from capacity to the quality of steam delivered. Use them to check the match with your use, and send the steam demand and feedwater details with the quote request.
| Condition | Detail |
| Fluid | Feedwater: softened and filtered for culinary; RO or purified water for clean steam; WFI for pure steam |
| Capacity | 100 to 5,000 lb/h; SIP peaks three to five times the hold load |
| Temperatures in / out | Feedwater 60 to 200 F in; clean steam saturated at 30 to 60 psig, 274 to 308 F |
| Hold | Shell water at saturation; blowdown continuous plus intermittent |
| Utility | Plant steam at 75 to 150 psig in the tubes; hot oil or high-temperature hot water on some sites |
| Approach | Plant steam 30 to 50 degrees above clean steam saturation |
| Construction | Vertical or horizontal U-tube reboiler, double tubesheet, integral or separate separator |
| Finish / class | 316L shell side, 20 to 25 Ra electropolished for pure steam; 32 Ra for culinary; ASME stamped |
| Steam quality | Culinary to 3-A 609; clean steam tested for dryness and non-condensables; pure steam condensate to USP WFI |
| CIP / SIP | Shell side drained and flushed on schedule; passivated after any repair |
Common FAQs
Roughly 30 to 50 degrees of saturation temperature above the clean steam it makes. For 45 psig clean steam that means 100 psig plant steam at minimum; 125 to 150 psig gives a smaller generator.
Culinary steam under 3-A 609 is food-contact steam from potable feed with approved chemicals and a filter. Pure steam is pharmaceutical steam whose condensate meets USP Water for Injection, made from WFI in an electropolished generator.
Enough to hold the shell water at 10 to 20 times the feedwater conductivity: usually 5 to 10 percent of the steam rate on RO feed, less on WFI, held by a conductivity controller.
Yes, with a larger bundle. Hot oil at 400 F or hot water at 350 F in the tubes makes clean steam at 30 to 45 psig; the film coefficient is lower than condensing steam.
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