A recorded presentation by Blasch and BD Energy Systems on tunnel structure, flue gas flow and NOx reduction.
Three topics in one talk: structure, flow and NOx.
All three come back to the flue gas tunnels.
The new technology for steam methane reformers in this presentation is a flue gas tunnel built from interlocking precast blocks, combined with a flow design that sizes every wall opening. It addresses three things at once: tunnels that crack and collapse, catalyst tubes that heat unevenly, and ammonia injection for NOx control that mixes poorly inside a conventional tunnel.
| Format | Recorded presentation |
| Presenters | Blasch Precision Ceramics and BD Energy Systems |
| Topics | Tunnel structure, flue gas flow uniformity, NOx reduction |
Conventional side walls are built up from the floor in mortared brick with discrete expansion joints, support buttresses and half brick openings. Mortar turns long sections into single bodies, and when expansion is not allowed for, the wall snakes.
The lids are often solid slabs set on freestanding walls. They fail individually from falling burner tiles or people walking on them, or all at once from static stress, thermal stress and the wrong material. A finite element model of a 9 by 9 by 42 inch slab at 1,900 °F shows about 10 psi from weight and about 1,500 psi from a 10 °F temperature difference.
The tunnel that holds up the floor of the furnace also decides how evenly the tubes heat and how well the ammonia mixes for NOx control.
The presentation walks through the StaBlox parts, all in mullite and hollow to reduce mass and thermal stress. The base sits on insulating castable or brick and spreads the tunnel load over roughly five times the floor area. Side wall blocks are set without mortar and have uniform expansion allowances that prevent snaking. Tie rods in the wall openings replace buttresses and shorten the free span of the wall. Hollow covers interlock with the walls, seal with a shiplap joint and carry a walkway support. Orifice inserts in the openings tune the flow.
Without mortar or dry out, with fewer and lighter parts, the tunnel work leaves the critical path of the turnaround.
Along a tunnel, gas velocity rises from zero at the closed end, so the open area should shrink gradually. Brick walls change it in large steps and leave no-flow zones at buttresses and joints. The tubes respond with hot spots that recur in loose groups, mostly below the tunnel tops. The TOP design from BD Energy Systems spreads openings evenly over the whole tunnel and varies their diameters instead. In the plant data shown, the spread of tube metal temperatures fell by about half, which is summarized in a new kind of tunnel vision.
Selective non-catalytic reduction injects ammonia or urea into the flue gas, with lower capital cost than a catalytic system but results that vary from reformer to reformer. The presentation shows a CFD case of a poorly performing SNCR system. Moving the injection point upstream gave longer residence time, but the mixing stayed poor: the gas entering through the wall openings pushed the ammonia upward. A three point nozzle did not solve it either. With evenly distributed openings, a single injection point achieved better mixing and longer residence time, with a more even exit velocity and lower pressure losses.
If NOx control, tube life and tunnel repairs are on separate lists in your plant, this talk argues that they share one cause. The parts are on the StaBlox flue gas tunnel system page. More reformer topics are on hydrogen and ammonia production.
Mostly from thermal stress. A small temperature difference between top and bottom stresses a solid slab far more than its weight does.
In the CFD case shown, ammonia injected into a conventional tunnel mixed poorly because gas entering through the wall openings pushed it upward. Evenly distributed openings improved the mixing.
Tie rods set into the wall openings connect both walls and shorten the free span.
BD Energy Systems developed the method for sizing the openings. Blasch designs and makes the precast blocks that carry it.
Describe your reformer and what you are trying to fix. A Blasch engineer will show you where the tunnels come in.
