The present invention relates to an integrated method and an integrated unit for separating air by cryogenic distillation and for cooling a gas. The cooling makes it possible to cool, or even at least partially condense, a gas originating from a store which contains a liquid; the liquid is produced by a unit supplied with a gas originating from the air separation unit.

It is often necessary to store liquids at low temperature, i.e. at temperatures below ambient temperature. The stores are insulated to prevent the ambient heat from evaporating the liquid but nonetheless defects in the insulation give rise to ingresses of heat and gas is formed at the top of the store. This gas must be either discharged to the atmosphere or recondensed and sent back to the store.

Another possibility, illustrated inFIG. 1, is to dissolve the gas in demineralized water H and to send it to a purification unit. In the figure, a cryogenic distillation air separation unit ASU produces oxygen1which is sent to a methanol production unit MEOH. The methanol produced in liquid form is sent to an insulated store7. The methanol in gaseous form9formed at the top of the store by the ingresses of heat through the insulation is sent to be mixed with demineralized water H in a unit13. The methanol formed15is sent back to the purification section in the methanol production unit MEOH.

In order to condense the gas, another possibility is to use water cooled by an electric refrigerator to a temperature of 10° C. which exchanges frigories with the gas in a heat exchanger via indirect exchange.

In many cases, a cryogenic distillation air separation unit produces oxygen at the request of a customer, but there is no customer for the nitrogen, or even all the nitrogen, which is inevitably co-produced.

According to the invention, the nitrogen produced in excess is used at the outlet of the air separation unit for cooling water in a direct-contact tower fed at the bottom with cold nitrogen gas and at the top by the water to be cooled.

The cooled water is then used to cool, or even to condense a gas originating from a store of a liquid at a subambient temperature, make it possible to reduce the electric power consumption.

A process according to the preamble of claim1is known from EP-A-0 748 763.

According to one subject of the invention, a process as claimed in claim1is provided.

