The recovery of heat from the synthesis gas exiting an ammonia converter gives specific challenges due to the high pressures and the high hydrogen and ammonia contents. The gas cooling and heat recovery are best taken care of in a loop boiler and the design of this boiler must address the special challenges effectively. The loop boiler is both used to initiate the final cooling of the ammonia-rich gas or as interstage cooling between two converters, for instance, an S-200/300 followed by an S-50 converter.

The TOPSOE™ proprietary loop boiler is based on a patented bayonet tube design. With this design, all low alloy metal parts are kept out of temperature zones where nitriding is a concern without the use of sleeves or ferrules. At the same time, the temperature difference across the tube sheet from the inlet side to the outlet side is zero. The thermal stress is therefore drastically reduced compared to a conventional layout. Furthermore, the tube sheet is kept at a low temperature close to the boiling water temperature, which significantly differentiates this boiler from what is otherwise offered to the ammonia industry.

Benefits

Efficient heat recovery

• The TOPSOE™ proprietary bayonet U-tube loop boiler provides efficient heat recovery

Design for reliability and long life

• The unique features of the TOPSOE™ loop boiler has eliminated all nitriding concerns
• The low temperatures and the absence of thermal stress induced by differential temperatures ensure a very high degree of mechanical robustness
• Strict manufacturing requirements and quality control ensures a loop boiler which is reliable during a long life

Layout flexibility

• The loop boiler is offered with a horizontal layout for hook-up to a common steam drum
• Alternatively and in case of space constraints or in revamping cases, the loop boiler can be of the vertical type with or without an integrated steam drum