Operating data from a 168 tube reformer before and after its brick tunnels were replaced with StaBlox and orifice inserts sized by BD Energy Systems.
The new tunnels went in during a 2018 outage.
The tube thermocouples showed the difference within weeks
In an ammonia plant reformer with 168 catalyst tubes and eight flue gas tunnels, replacing the brick tunnels with StaBlox in 2018 cut the standard deviation of tube metal temperatures from 42 °F to 21 °F and the spread between coolest and hottest tube from 222 °F to 116 °F. With the hot tubes closer to the average, the plant raised its reformer outlet temperature, methane slip fell from 9.94% to 6.94%, and production rose by 3.3%, comparing 2.5 months before with 3.5 months after the installation.
The reformer is down-fired, with seven rows of 24 catalyst tubes. Flue gas leaves the radiant box through openings in eight tunnels on the furnace floor.
In the brick tunnels, every opening was a half brick of the same size. The only way to change the open area along a tunnel was to leave out openings, so the flow changed in steps instead of gradually. Buttresses and expansion joints left stretches with no openings at all. Flue gas then crossed over near the bottom of the tubes, where tube metal is already at its hottest.
Once the hottest tube was no longer far above the rest, the plant could fire the whole reformer harder without crossing its tube metal limit, and that margin is where the extra production came from.
The tunnels were rebuilt with StaBlox, interlocking hollow blocks of mullite bonded high alumina set without mortar. The design needs no buttresses and no discrete expansion joints, so there are no blind stretches in the walls. Every block carries openings for orifice inserts. BD Energy Systems modeled the furnace and assigned an insert diameter to each opening, varying both along the tunnel and from top to bottom. On average the crew completed three tunnels per 12 hour shift.
| Measured value | 2.5 months before | 3.5 months after |
|---|---|---|
| Average tube metal temperature | 1,556 °F (847 °C) | 1,545 °F (841 °C) |
| Standard deviation | 42 °F (23.3 °C) | 21 °F (11.7 °C) |
| Coolest to hottest tube | 222 °F (123 °C) | 116 °F (64 °C) |
| Methane slip | 9.94% | 6.94% |
| Production | +3.3% | |
| Production to feed ratio | +3.7% |
The author, from BD Energy Systems, calls the 3.3% relatively high for this size and estimates 1.3 to 1.8% for larger reformers.
A narrower band of tube temperatures protects the tubes that used to run hottest, and those tubes set the limit for the whole furnace. The same reformer now makes more ammonia from the same feed. If the firing pattern changes later, the inserts can be swapped at a shutdown without touching the walls.
Interlocking precast tunnels with an orifice insert in every opening.
How the reformer works and where its refractory decides tube life.
How crews at two US ammonia plants built the tunnels in 2018.
Operating data from 2.5 months before the new tunnels was compared with 3.5 months after them.
Only by 11 °F. The gain is in the spread: the hottest tubes came down toward the average, which is what limits the firing.
The author expects less, about 1.3 to 1.8% for larger units, and calls the 3.3% of this 168 tube reformer relatively high.
In World Fertilizer, January and February 2020, in an article by BD Energy Systems.
Send the tube metal temperatures, the tunnel layout and the firing pattern. A Blasch engineer and BD Energy Systems look at what new tunnels could change in your reformer.
