This kind of design is widely used for services needing a horizontal tube arrangement for specific flow pattern requirements, and duties in the range of 30-120 MW.
In the cabin-shape radiant section, tubes are arranged horizontally along the sidewalls and the sloping roof of the cabin, while on the front wall no tubes are installed. The firebox can be composed of a single-cabin cell or a double-cabin cell, according to the size and number of its passes. Typically, the convection section extends over the entire length of the radiant section.
The horizontal tube arrangement requires an increased plot area for tube extraction but it allows for coil drainability by gravity and easier access to the radiant return bends – seldom located inside the radiant header boxes – for inspection and maintenance purposes. Burners are floor-mounted, installed in a row placed in the center-line of the cabin, and fired vertically.
Instead, for small duties, burners are sometimes located in the front walls on opposite sides, and they fire horizontally toward the center of the firebox.
This kind of design is typically suitable for topping and vacuum services, crude heaters, reboilers, and heavy-feed preheaters.