Any industrial process involving high temperatures requires refractories in order to operate. Heat is not, however, the only issue that these materials face. In most chemical processes, refractories will be exposed to a range of other stresses, including mechanical (abrasion), thermal (wide swings in temperature), and chemical stress.
With any industrial operation, the first step in refractory selection is to identify the operating conditions that will determine the origin of the refractory wear. These will differ depending on the industry process in question: in some conditions, certain types of wear will be more relevant than others. Refractory properties should therefore be optimised to the specific process environment in order to maximise refractory life at the lowest cost.
Within the growing hydrogen economies, specialised equipment such as autothermal reforming (ATR) and other reformers will be in demand for flexible and more efficient hydrogen, and for producing blue hydrogen and green ammonia with a lower carbon footprint.
When considering refractories for hydrogen production units, chemical corrosion is the main concern. Although process temperature is high, it is constant, reducing the risk of thermal shock caused by large fluctuations in the thermal profile. Meanwhile, processing units only contain gas; there are no solids or liquids. As a result, abrasion is minimal and does not represent a major concern.
Case study: pre-cast, pre-fired catalyst support domes
Catalyst support domes are installed in various chemical production processes (such as ammonia and syngas) that contain secondary reformers.
The conditions experienced by these domes are severe: environments comprising significant percentages of carbon monoxide (CO), carbon dioxide (CO2), hydrogen (H2), water (H2O), and nitrogen (N2), at maximum temperatures of about 1300°C and high pressures of approximately 35 bar, are common. In such conditions, the performance of the refractory lining is critical. Aluminous refractories, which are low in both silica and iron oxide, are typically recommended. These are usually as pre-fabricated, sintered bricks, from which the dome is constructed.
The major consideration when selecting the support dome is the compressive stress that is placed on it by the weight of the catalyst bed. Combined with the high-pressure conditions inside the secondary reformer, and high process requirements of the plant, the dome would be liable to crack over time. However, novel solutions that extend refractory lifetime and reduce turnaround time for replacement offer key benefits. The first pre-cast, pre-fired (PCPF) catalyst support dome has been demonstrating these benefits over the past six years of operation.
Improved quality and delivery time of a PCPF catalyst support dome
This first dome was supplied to a US chemicals manufacturer by Calderys in 2015 as a significant part of the refractory construction. The faster fabrication time of the PCPF dome compared to traditional refractory brick construction meant that it could be delivered just before installation, without causing any delays to the project.
In fact, that same year, another PCPF catalyst support dome was ordered from Calderys based on quick delivery, as there was no spare dome available, and the original brick supplier was not able to produce and supply the spare dome within the delivery time required to hit the onsite installation date. This meant that Calderys had to produce the monolithic and prepare moulds, as well as pre-cast, pre-fire and pack the dome blocks in its workshop for shipment...
Written by Joost Meeuwissen, Calderys, the Netherlands.
Read the article online at: https://www.globalhydrogenreview.com/special-reports/05082022/reaching-new-heights/