Dry-ice production creates solid CO₂ and return gas. A recycle balance shows how much fresh liquid may be displaced and what the recovery system must handle.
Why a gas stream remains
When liquid CO₂ expands into a dry-ice process, only part becomes solid; another part becomes gas. The split depends on inlet state and equipment. We do not use one universal solid yield for every installation. EIGA Doc 111 describes return gas being collected, compressed and liquefied for reuse. Actual suitability depends on collection, contamination control and the downstream product requirements.
A single-pass balance
In an illustrative hour, a machine processes 1,000 kg of liquid, produces 450 kg of usable dry ice and generates 550 kg of gas. Assume 90% of that gas is successfully returned as accepted liquid: 550 × 0.90 = 495 kg/h. At this steady machine throughput, fresh liquid demand is 1,000 − 495 = 505 kg/h. The remaining 55 kg/h is the unrecovered gas loss. These assumed yields are for arithmetic only.
| Boundary quantity | Illustrative rate |
|---|---|
| Total liquid through the dry-ice machine | 1,000 kg/h |
| Useful dry ice | 450 kg/h |
| Liquid recycled to the machine | 495 kg/h |
| Fresh liquid entering the combined system | 505 kg/h |
| Unrecovered gas leaving the combined system | 55 kg/h |
The combined-system balance closes: 505 kg fresh liquid equals 450 kg dry ice plus 55 kg loss. Do not count the 495 kg recycle as both fresh production and a second saleable product. Fresh-liquid use per kilogram of dry ice falls from 1,000/450 = 2.22 to 505/450 = 1.12 in this example.
What the recovery package actually sees
Define the gas temperature, pressure, instantaneous flow, contaminants, air ingress and machine cycling at the collection boundary. Average machine output can conceal large gas pulses. Buffering and compressor control must fit those pulses without imposing unacceptable backpressure on the dry-ice equipment. Recovery capacity must be checked against the gas stream, not just the dry-ice mass.
What to include in the savings comparison
Value only the fresh liquid genuinely displaced. Subtract electricity, refrigeration, maintenance, quality testing and losses associated with recovery. Confirm whether a measured return rate includes both collection losses and liquefaction losses. If it covers only one of those stages, model the other separately. Compare the same final dry-ice output with and without recycle.
Use the project reference with its proper limits
Our Singapore reference records dry-ice CO₂ return-gas recovery with equipment supply and installation guidance. Its nominal project capacity and design product specification provide scope context. They do not establish the example yields above or a measured energy saving. Site acceptance should verify fresh-liquid displacement and quality at the agreed operating conditions.
Sources and scope
We use these sources for the physical principles or guidance identified in this article. Our examples and decision tables are explanatory calculations, not measured plant results. Industry guidance does not replace the edition, customer specification and local requirements agreed for your project. Publication listings are cited for their public scope; we do not claim to reproduce their full standards.
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