The TOPSOE™ S-50 converter is a single bed radial flow converter, which is added downstream of the main converter in series to increase ammonia conversion.

The S-50 converter is designed in two versions: a hot shell and a cold shell version.

The hot shell version

This design concept is adopted when the upstream converter is designed without an internal feed-effluent exchanger. The heat of reaction from the first converter ensures that the feed to the S-50 converter is sufficiently hot for the ammonia synthesis reaction to continue, and the gas leaving the last bed in the first converter can be utilized for preheating of boiler feed water and/or steam generation. It is the recommended converter design for all new plants.

The cold shell version

This design concept is adopted when the upstream converter is designed with an internal feed-effluent exchanger. No waste heat recovery is foreseen between the two converters and all the heat of reaction is moved downstream of the S-50 converter for generation of steam, superheating of steam and/or preheating of boiler feed water.

The two converters in series configuration can be used to close the overall plant steam balance if the waste heat available for boiler feed water preheating and boiling of steam is not in balance. Additionally, the S-50 converter can be utilized to increase production capacity of the existing loop in connection with plant revamps.