SSR® versus Conventional Steam Reforming
Although it has been in use for many years, the conventional steam reforming process using packed ceramic catalysts has two significant drawbacks:
- The ceramic media tends to crush to powder after several startup and shutdown cycles. This is a result of differential thermal expansion rates between the metal tube and the ceramic media. When the tube heats, it expands, but the media does not. Instead, the media settles a bit. When the reactor is shut down, the tube cools and contracts, crushing some of the ceramic media to powder. Accumulation of this powder in the tube leads to plugging of the reactor. Because of this plugging, the media must often be removed and replaced in as little as every three to five years. This recurring event has a significant negative impact on plant life cycle cost. It creates a material replacement cost, and associated labor cost, hazardous waste disposal cost (nickel catalyst is a listed hazardous material), and downtime for replacement. Also, the initial equipment cost is higher than it might otherwise be due to built-in design provisions for changing out the catalyst.
- Steam reforming is an endothermic reaction, requiring considerable heat. This heat is provided to the catalyst media from the furnace through the wall of the container tube. The catalyst media near the tube wall picks up heat readily. However, heat transfer to the media near the center of the tube is more difficult, and the catalyst at the center is largely ineffective. Thus, reaction efficiency is compromised due to poor heat transfer through the catalyst particles.
The ceramic media in conventional steam reformers can be directly replaced with SSRs. This reactor is a honeycomb made from a special grade of high temperature stainless steel foil, which is coated with a reforming catalyst. Individual reactors are about the size and shape of a 1lb coffee can, and stack one upon another to fill the vertical tube.
Because the SSR is made from metal foil, it solves the primary problem of the conventional ceramic media – that of crushing the media, plugging, and replacement. The foil has an expansion rate similar to that of the tube, and will expand and contract in unison with the tube, and, therefore, will not crush. Because of unique Catacel coating know-how developed over 25 years, the catalyst, once applied to the metal foil, adheres tightly to the foil during these thermal events.
The corrugation/flow channels in the SSR are unique. They are positioned such that conductive, convective, and radiant heat from the reformer tubes can easily be transferred to ALL the working catalytic surfaces. By contrast, catalyst near the center of the conventional ceramic system is not well heated, and is largely ineffective. The special SSR flow geometry leads to improved overall catalytic performance, resulting in increased capacity and/or lower system cost.
With a simple catalyst change-out, the heat transfer increase from SSR can enable about a 25% throughput increase for any given reformer. Of course, plant balance must be adjusted to deliver the additional flow to the reformer and to process the output. Even if additional capacity is not needed in an existing plant, catalyst changeover to SSR can provide significant benefit. The increased heat transfer of SSR allows the reformer furnace temperature and the tube temperatures to be reduced. This results in an energy savings of about 20% and extended lifetime for the expensive tubes. In new plant designs, SSR will allow a reformer that is at least 25% smaller, with consequent capital cost savings.