Imperial Chemical Industries Limited

John B Johnson

Alwyn Pinto

Andrew M Haslett

Ammonia synthesis gas is made from a raw gas comprising hydrogen, carbon dioxide and medium boiling point gases including nitrogen in excess of the proportion required an ammonia synthesis gas, by a pressure swing adsorption process characterized by feeding to the absorbent a raw gas in which hydrogen and total medium boiling point gases are present in a volume ratio in the range 1.25 to 2.5, and the medium boiling point gases comprise nitrogen to the extent of at least 90% v/v on the total of such gases. Preferred ways of making the raw gas, of ensuring purity of the product gas and of recovering useful heat are described.

Ammonia synthesis

A raw ammonia synthesis gas, preferably containing an excess of nitrogen, is converted to synthesis ready ammonia synthesis gas by two pressure swing adsorption (PSA) stages operated in succession. If the raw gas contains carbon monoxide this is chemically removed, e.g. by methanation, between the PSA stages. In the first PSA stage, CO.sub.2 is removed and waste gas from the second PSA stage is preferably fed back to the first PSA stage for sweeping, purging or repressurizing. In a preferred system the first PSA cycle includes a sweep with CO.sub.2 -rich gas prior to depressurization and purge with second PSA waste gas. In the second PSA stage inert medium boiling gases, and any unwanted nitrogen are removed as the waste gas.

Gas separation

A pressure control arrangement for a fluid line in a system, particularly a pressure swing adsorption system, wherein, in the event of a valve or control system malfunction, there is a risk of the fluid line being subject to an overpressure in an excess of its maximum design pressure, has a normally open valve, a flow restricting member, and a pressure sensor disposed in the fluid line. The pressure sensor is disposed upstream of the flow restricting member and arranged to sense the pressure in the line and to actuate the valve to close the line in the event of the sensed pressure exceeding a predetermined limit. The predetermined limit is above the normal operating pressure range of the fluid line but below the maximum overpressure to which there is a risk of the line being subject, and that portion of the fluid line upstream of the flow restricting member is constructed to have a maximum design pressure at least equal to the maximum overpressure.

Pressure control

Ammonia synthesis gas is made from a raw gas comprising hydrogen, carbon dioxide and medium boiling point gases including nitrogen in excess of the proportion required in ammonia synthesis gas, by a pressure swing adsorption process characterized by feeding to the adsorbent a raw gas in which hydrogen and total medium boiling point gases are present in a volume ratio in the range 1.25 to 2.5, and the medium boiling point gases comprise nitrogen to the extent of at least 90% v/v on the total such gases. Preferred ways of making the raw gas, of ensuring purity of the product gas and of recovering useful heat are described.

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Sedgefield, United Kingdom

John B Johnson