Selective catalytic reduction catalyst module support system and installation method

A heater, comprising:

• a convection section, including:
• a plurality of columns arranged in pairs of columns spaced from each other along a longitudinal direction of the convection section, and the pairs of columns including a first column and a second column spaced from each other in a lateral direction of the convection section;
• a plurality of tube sheets coupled to the plurality of columns, including pairs of tube sheets coupled to corresponding pairs of columns, the pairs of tube sheets each including a first tube sheet and a second tube sheet;
• a plurality of tube bundles coupled to the plurality of tube sheets;
• a gap between the first tube sheet and the second tube sheet in each pair of tube sheets;
• and
• a structural frame in the gap, including:
• a plurality of beams coupled to corresponding pairs of columns of the plurality of columns and extending through the gap;
• and
• a first catalyst support bed removably coupled to the plurality of beams and positioned in the gap, the first catalyst support bed being slidable with respect to the plurality of beams to enable loading or unloading of a catalyst into the convection section through at least one lateral side of the convection section.