In 2008, a 250m3/hr hydrogen plant was constructed in Europe to supply a Borcelik steel facility with hydrogen (H2) for annealer and coating line operations.
Unique was the plant’s utilisation of a novel catalyst-coated metal foil structure developed by Catacel Corporation (Garrettsville, Ohio, US) in place of catalyst-impregnated ceramic pellets, to sustain Steam Methane Reforming (SMR) processes.
Expected performance was achieved at start-up on 24th July 2008, with minimal correction; reactions were observed to operate at exact equilibrium. As anticipated, furnace temperatures registered lower than a comparable older plant operating at the Borcelik location with conventional ceramic media.
Shortly thereafter, the old plant was shutdown when the new plant demonstrated sufficient hydrogen yield to sustain all necessary operations.
Plant performance was again evaluated in April 2009. No discernable change from initial performance was observed. At the same time, the old plant was restarted to perform a similar evaluation. Furnace temperatures and fuel consumption rates were observed to be considerably higher than the new plant.
Today, after two years and 17,500 hours of problem-free operation, the performance of Catacel’s catalyst-coated metal foil structure – the Stackable Structural Reactor (SSR®) – remains indistinguishable from new. While principally anecdotal with respect to confidentiality constructs, the Borcelik installation suggests Catacel’s SSR® as a viable alternative to ceramic catalyst en route to lower-cost hydrogen production.
Hydrogen production: Ceramic catalyst
Steam Methane Reforming of hydrogen has traditionally utilised alloy steel tubes filled with catalyst-impregnated, pellet-shaped ceramic media. These tubes are suspended vertically in a furnace and heated to typically between 1000°C-1100°C.
Steam and hydrocarbon fuel are then fed to the top of the tubes and syngas – containing between 50% and 70% hydrogen – is extracted from the bottom. Although this conventional production method has been in use for nearly a century, there are drawbacks.
Ceramic media tends to crush to powder after start-up and shutdown cycles, due to different thermal expansion rates between the tube and media. The tube expands when heated, but the media does not. Instead, the media settles. After shutdown, the tube cools and contracts – crushing some of the media to powder.
Accumulation of this powder leads to clogging of the tube, so the media must be removed and replaced, on average, every three to five years. This recurring event has negative impact on plant lifecycle cost; besides material replacement, there are associated expenditures for labour and downtime as well as hazardous waste disposal of the catalyst.
A second shortcoming of ceramic media is heat transfer. As an endothermic reaction, SMR requires a constant supply of heat from the furnace through the tube wall. Media near the wall picks up heat readily but heat transfer to the centre of the tube is less efficient, meaning the catalyst is less effective. Reaction efficiency is thus compromised due to imbalanced heat transfer throughout the tube.
Hydrogen production: SSR®
Catacel designed the SSR® with the express intent of resolving the deficiencies of ceramic media. The company surmised that a catalyst material that could last (at least) twice as long, while continuing to deliver superior heat transfer, would present compelling economic benefits for hydrogen plant operators.
The SSR® is a honeycomb made from a special grade of high temperature stainless steel foil coated with a reforming catalyst. Individual reactors are roughly the size and shape of a coffee can and are stacked – one upon another – inside the reformer tube.
As a durable metal foil structure, the SSR® is not subject to ‘crushing’ as occurs with ceramic media when tubes expand and contract. Also, Catacel’s reactor exposes approximately 2.5 times more catalytic surface area to the reaction process than does an equivalent volume of catalyst-impregnated pellets.
Furthermore, tests conducted in collaboration with the NASA Glenn Research Center (Cleveland, Ohio) have demonstrated 30% heat transfer improvement over ceramic media.
Catacel quantifies the cost-benefit of its stackable reactor technology to hydrogen plant operation in four ways:
1) Improved heat transfer permits lower furnace temperatures to sustain SMR reactions – hence less fuel consumption, hence less fuel cost
2) Durable metal foil design in tandem with increased catalytic surface area extends effective media life, necessitating fewer change-outs – hence less material and associated downtime costs
3) In retrofit scenarios, improved heat transfer permits throughput yield increase from existing equipment – hence avoidance of additional capital investment
4) In new plant scenarios, combined performance/durability advantages warrant fewer and/or shorter reformer tubes – hence reduced construction expense.
An unexpected benefit: Borcelik installation
In October 2009, a process upset dramatically reduced the Borcelik plant’s hydrogen generating ability. What triggered the failure is undetermined, though it is Catacel’s presumption that sulphur, mistakenly introduced with furnace fuel, coated the catalytic surface of the SSR® with a ‘paste’ that impaired SMR reactions.
Sudden increases in plant methane yield – as would be expected should hydrocarbon gas pass through a reformer tube without fully catalysing – served to evidence Catacel’s supposition.
While undesirable, the occurrence exposed a previously unexpected benefit of SSR®. Plant engineers endeavored to clean the sulfur paste from the SSR® inserts by steaming the reformer tubes rigorously. This measure proved extremely time efficient, as it did not require removal of Catacel’s reactors from the tubes.
Hydrogen production resumed after only two days at acceptable performance levels. It was noted by engineers that ceramic media would likely not have survived either the failure event or corrective action – the consequence being an unscheduled, unbudgeted catalyst change-out.
For More Information: SSR® White Paper
Available from Catacel Corporation is White Paper No. 102 – Stackable Structural Reactor (SSR®) Technology – authored by company president William A. Whittenberger, BSME, MBA, PE.
To obtain a copy, contact firstname.lastname@example.org or visit www.catacel.com.