Furnace tunnels and assembly system

A furnace tunnel assembly system comprising:

• a plurality of interlocking refractory blocks adapted to form a longitudinal wall of a flue gas flow channel in a firebox;
• at least some of the blocks comprising ports formed therein, wherein the ports are arranged in regular rows and columns;
• and
• respective inserts for the ports, wherein at least some of the inserts comprise plugs comprising imperforate plates, and wherein some of the inserts comprise perforated plates.

A method comprising:

• positioning a plurality of interlocking refractory blocks to form a longitudinal wall of a flue gas flow channel in a firebox, wherein at least some of the blocks comprising ports integrally formed therein;
• arranging the ports in regular rows and columns;
• plugging some of the ports with plugs comprising imperforate plates having a profile matching the ports to inhibit flue gas entry from the firebox to the flow channel;
• and
• providing some of the ports with flow passages for the flue gas to enter the flow channel from the firebox.