A precast, interlocking tunnel system for top-fired steam methane reformers, set without mortar.
Interlocking precast blocks replace brick and mortar at the bottom of the radiant section.
The flue gas leaves through openings sized for each position in the furnace.
StaBlox is a reformer flue gas tunnel system made of interlocking, precast ceramic blocks that are stacked without mortar on the floor of a top-fired steam methane reformer. Each opening carries an orifice insert sized for its position, so flue gas is drawn evenly along the tunnel and the catalyst tubes see more uniform temperatures. In two US ammonia plants, a 43 ft tunnel was set in about 4 hours and nine tunnels in about three days.
Flue gas tunnels, often called coffins, are 4 to 10 ft high and 40 to 100 ft long. Most are still laid course by course in firebrick and mortar.
A reformer is only as even as its tunnels: when every opening draws the right share of flue gas, the hottest tube is no longer the one that decides the firing rate.
The base spans the tunnel floor, sets the spacing of the side walls and spreads the load over roughly five times the area of a brick footing.
The side wall blocks are hollow, 18 by 9 inches, each with two 4.5 inch openings, tongue and groove joints and a fiber seal. One block replaces about six bricks and weighs under 50 lb.
Tie rods connect both walls where the tunnel is tall relative to its width, and can be removed for inspection.
The hollow lid closes the tunnel with a shiplap joint against gas bypass and ties the wall tops together.
Orifice inserts lock into each opening. Their bores come from a model of the furnace developed with BD Energy Systems, and they can be swapped later if the firing pattern or capacity changes.
The sequence from the first installations in 2018, with a refractory contractor and no masons on the crew.
Level the floor, lay the insulating brick and check the full tunnel length on a line.
Place all base blocks with the correct gaps, which decide the expansion allowance of the tunnel.
Stack the side blocks with their fiber seal, usually fed in on a roller conveyor.
Set the lids and tie rods, then fit the numbered orifice inserts to the opening plan.
An ammonia plant with 168 catalyst tubes compared tube metal temperatures for 2.5 months before and 3.5 months after its tunnels were replaced with StaBlox. The study was published in World Fertilizer in 2020.
| Measured value | Before | After |
|---|---|---|
| Standard deviation of tube metal temperature | 42 °F | 21 °F |
| Spread from coolest to hottest tube | 222 °F | 116 °F |
| Methane slip | 9.94% | 6.94% |
| Production | +3.3% |
With the hottest tubes closer to the average, the plant could raise the reformer outlet temperature, which lowered methane slip and raised production.
The blocks are cast from mullite bonded high alumina. In published tests it keeps a hot modulus of rupture of 1,700 psi, where super duty brick stays under 600 psi, and it deflects 1.11% under creep load at 1,649 °C, against 7.86% for super duty brick at 1,427 °C.
The lid is where most brick tunnels fail first. A finite element analysis of a lid at 1,900 °F shows only about 10 psi from its own weight, but 1,500 psi from a top to bottom temperature difference of just 10 °F. That is why the StaBlox lid is hollow and the joints are designed to move.
Many plants keep running with a damaged or missing tunnel. A published CFD study of a theoretical reformer with eight tunnels found up to 9.7% less hydrogen next to a missing outer tunnel and 0.95% less across the furnace. For a 2,000 t/d ammonia plant limited by its primary reformer, the authors estimated a loss of about 19 t/d. A single collapsed tunnel can be rebuilt with StaBlox on its own, without waiting for a full revamp.
StaBlox works with the components around it. How steam methane reformers work
Rebuild one collapsed brick tunnel with stocked blocks, lids and bases, in hours instead of days.
Ceramic ferrules protect the tubesheet of the boiler that follows the reformer.
Ceramic tips for burners and flares that see flame and thermal cycling.
Yes. StaBlox can replace a single tunnel and run beside brick tunnels, so one failed tunnel does not force a full rebuild.
No. The blocks are set dry, without mortar and without curing, by a general refractory crew following the opening plan.
At two US ammonia plants in 2018, one 43 ft tunnel was set about every 4 hours and nine tunnels in about three days, including inserts and the connection to the outlet.
Yes. The tie rods lock with a quarter turn and can be taken out, and the system can be taken apart and rebuilt.
The orifice inserts are replaceable. A new firing pattern needs new insert sizes, not new walls.
Send the tunnel dimensions and the furnace layout. A Blasch engineer works out the blocks and the opening plan for your reformer.
