Small-Scale ASU for On-Site Liquid and Gas Production

Cryogenic Separation, Cut to Size

Air separation at large plants and air separation at 50 Nm³/h obey the same physics: compress the air, clean it, chill it until it collapses into liquid, then let the boiling-point gap between oxygen (-183 °C) and nitrogen (-196 °C) do the dividing. What changes at small scale is how you make the cold. A 60,000 Nm³/h plant runs turbocompressors and gets refrigeration almost for free; a mini plant like the SKDO can't, so we spin a turboexpander - a turbine that chills air by expanding it, borrowing a trick from the liquefaction world.

The result is a genuine cryogenic plant in a compact, pre-piped, skid-friendly form: 99.5% oxygen at the top of the cold box, 10 ppm oxygen nitrogen out the other side, liquid products drawn off when you specify them.

The Process Line, Walked Once

1. Air compressor pressurizes filtered ambient air.
2. Pre-cooling unit drops the heat of compression with water or air cooling.
3. Purification system - twin molecular sieve adsorbers scrub water, CO₂ and hydrocarbons. One dries while the other regenerates; freeze protection here is the plant's lifeline.
4. Turboexpander expands part of the air stream to generate the refrigeration that liquefies the rest.
5. Fractionation tower separates liquid air into oxygen-rich and nitrogen-rich streams over structured packing.
6. Liquid oxygen pump and storage/withdrawal systems deliver products as gas or liquid, at your pressure.

Control runs PLC with interlocks on cold-box temperature, expander speed and product purity. Trained-for-three-days operators can run it; we prefer to train them for five.

Technical Parameters

Who Runs a Mini ASU

Hospitals and oxygen stations. A SKDO feeding a tank farm and vaporizer replaces cylinder logistics entirely - manifold redundancy, telemetry-ready, no 3 a.m. stockouts during a surge. Medical-grade oxygen at 99.5% comes out of the cold box, not a truck.

Small gas companies. Liquid drawoff turns the plant into a merchant business: fill your own dewar cylinders, sell to neighboring shops, control the margin the distributor used to keep.

Steel, non-ferrous, chemical, paper, laser cutting. Wherever oxygen is a process cost rather than a commodity purchase, a plant paying for itself on the spread between on-site cost and delivered price is the whole argument - usually two to four years.

Design Decisions We Make With You

Gas or liquid mode. A SKDON-150 can pour around a ton of liquid products a day while still supplying gas; a pure-gas plant of the same feed spends its full capacity on the header. Liquid plants earn flexibility, gas plants earn volume. Many buyers run liquid by night, gas by day.

Storage and fill. We pair the plant with CFL vacuum-insulated tanks, welded insulated cylinders or YDS dewars from the same factory - fill headers, venting and safety interlocks arrive pre-engineered.

Altitude and climate. A plant for a 2,000 m site in the Andes is not a plant for a Gulf coast waterfront. Compressor maps, expander corrections and sieve regeneration all shift; we recalculate the cycle instead of oversizing blindly.

Containerized and Skid Options

Need it moving, or needing to clear customs with minimal site works? Cold box, towers and purification skids can ship as single pre-piped blocks or inside container modules with the control room in the corner. Site work becomes civil pads, power and water - weeks instead of months of field erection.

Why This Class of Plant From a 300-Project Builder

The mini plant is where casual assemblers expose themselves. Cold-box contraction management, expander bearing protection, sieve regeneration stability - these come from repetition. Our engineers have commissioned nearly 300 ASU projects, 18 of them at the 30,000 class, and the small plants carry the same discipline of design review, X-ray'd vessel welds and factory test runs. Your 50 Nm³/h unit gets the same cold-box software and the same A1/A2-license fabrication as our largest trains; only the size changes.

Getting Started

Send gas or liquid mode, flow, pressure, altitude and site photos. You'll get a cycle simulation summary, plot plan, power estimate and a firm quote inside 24 hours. One plant is a complete order - the MOQ is your site.

FAQ

Why A Small Cryogenic Plant Instead Of A PSA Box

Buyers cross-shop SKDO units against PSA machines constantly, so put the comparison plainly on the table. A PSA oxygen generator caps out around 93-96% and cannot make a drop of liquid. A small cryogenic ASU at the same flow gives you 99.5% oxygen, a parallel nitrogen stream at 10 ppm, and - this is the business-changer - liquid product you can bottle into cylinders or sell to neighbors.

That liquid capability turns a gas user into a gas business. A 100 Nm³/h SKDON feeding a cylinder filling bench serves a whole district of workshops, hospitals and fish farms. Hospitals in particular land on SKDO units: piped 99.5% oxygen for the ward manifold plus standby liquid reserve, without waiting on a tanker schedule that may be two days of mountain road away.

The trade-off is attention. A cryogenic plant needs trained hands, a pre-start checklist and discipline around hydrocarbons. We price the training honestly into the order and we refuse to sell the plant to owners who intend to run it like a light switch.

What Happens Inside The Cold Box

The flow scheme is classical small-cryogenics engineering, and it fits in a paragraph once you stop selling it:

• Purification. Compressed air passes a molecular sieve bed that strips water, CO₂ and hydrocarbons. These freeze in a cryogenic exchanger and would plug it; the sieve regenerates on a heated cycle.
• Heat exchange. Product streams leave the cold box near ambient temperature through an all-aluminum plate-fin main heat exchanger - the component that defines small-ASU reliability, and one we fabricate with the same care as the towers.
• Refrigeration. A turbo-expander drops part of the stream to liquid in a flash. This is the heart of the SKDO design: bearing-quality turbomachinery we have run on thousands of units.
• Distillation. A low-pressure and a high-pressure column split oxygen from nitrogen. Argon pools between them; on SKDOAr variants it is drawn off as a side stream.
• Product routing. High-purity gas goes to your header at set pressure; liquid goes to storage, a filling pump, or a vaporizer for cylinder barging.

Siting, Utilities, And The Things Owners Get Wrong

Three site facts change everything on a small ASU, and every one of them is free to fix at design stage:

• Ambient temperature and dust. A plant rated at 25 °C design ambient loses yield in a 45 °C summer unless the compressor and sieve were sized for your actual climate, not the datasheet's. We size for your hot-season record.
• Power quality. Turbomachinery dislikes voltage sag. On weak grids we specify soft starters and often recommend a genset interlock - tell us your grid history early.
• Hydrocarbon hygiene. intake air downstream of a refinery vent or a solvent store is a different machine. We will ask where the intake sits and where it will sit in five years.

Commissioning runs two to four weeks with our engineers on site; your crew shadows them for the full duration and signs off the O&M handover. After that, the unit is a daily checklist, a weekly analysis log, and a sieve and turbine service at the intervals in the manual. Owners who keep the log do not call us; owners who lose the log do.

If you are weighing a SKDO against liquid deliveries, send us twelve months of consumption and delivery records. The spreadsheet we run against it will tell you the payback in months, and if the answer is "keep buying liquid," that is the answer we will give you.