The secondary reformer in an ammonia plant is one of the most thermally hostile environments in the process industry. Gas temperatures at the top of the vessel can exceed 1000°C, and the refractory lining system — of which insulating bricks form a critical layer — must perform without failure for years between planned shutdowns.
If you are involved in the specification, procurement, or maintenance of refractory systems in secondary reformers, this blog will give you a clear understanding of what to look for in insulating bricks and why cutting corners on material specification is not a risk worth taking.
What Does a Secondary Reformer Do?
In the ammonia synthesis process, the primary reformer converts natural gas and steam into a synthesis gas mixture. The secondary reformer then reacts that mixture with air — introducing nitrogen needed for ammonia synthesis — through a partial combustion process. The outlet gas from a secondary reformer is hot, and the internal refractory lining must contain and manage that heat efficiently.
The refractory system in a secondary reformer typically comprises multiple layers: a hot face castable or brick layer, a backup insulating brick layer, and sometimes an additional ceramic fibre or lightweight castable layer before the vessel shell. Insulating bricks sit in the intermediate or backup role — their job is to reduce heat flux to the steel shell while maintaining structural integrity.
Why Insulating Bricks — Not Just Any Refractory?
Standard dense refractory bricks are excellent at handling mechanical loads and abrasion. But in a secondary reformer, the primary challenge at the backup lining level is thermal management — keeping the shell steel below its design temperature limit, typically below 350°C.
Insulating bricks achieve this through their structure: they contain controlled porosity (air pockets) that drastically reduces their thermal conductivity compared to dense refractories. The trade-off is lower cold crush strength, which is why insulating bricks are never used on the hot face without a protective working layer.
The Alumina Content Question
Insulating bricks are available in a wide range of alumina contents: from low-duty firebricks at around 30% Al₂O₃ up to high-alumina grades at 70%, 80%, or even 90%+ Al₂O₃. The alumina content directly determines:
Maximum Service Temperature
Higher alumina content raises the pyrometric cone equivalent (PCE) and, correspondingly, the maximum continuous service temperature the brick can sustain. For secondary reformer backup lining applications, where backup layer temperatures can still reach 700–900°C in some designs, specifying an inadequate alumina grade risks permanent deformation or flux-induced failure.
Refractoriness Under Load (RUL)
This is the temperature at which a brick begins to deform under a specified compressive load. Low-alumina bricks have lower RUL values, meaning they soften and creep at lower temperatures. In a reformer lining that sees thermal cycling over decades of operation, a brick that creeps progressively closes joints, builds stress, and eventually spalls.
Chemical Resistance
The gases in a secondary reformer contain hydrogen, carbon monoxide, methane, and nitrogen at high temperatures. Bricks with significant silica (SiO₂) content can be vulnerable to reduction atmospheres and alkali attack over long service periods. Higher alumina content means lower silica, which improves long-term chemical stability.
Thermal Shock Resistance
Insulating bricks endure thermal cycling during every plant start-up and shutdown. Higher alumina bricks typically have better resistance to thermal shock compared to silica-rich alternatives, though this also depends on the specific mineralogy and manufacturing process.
Why Dimensional Tolerance Is Not a Secondary Concern
This is where many procurement teams — under cost pressure — make a significant error. Insulating bricks that do not meet tight dimensional tolerances create problems that compound over time in a reformer lining:
Joint Integrity
A secondary reformer lining relies on tight mortar joints between bricks for both thermal efficiency and structural coherence. Bricks that vary significantly in dimension create variable joint widths. Wide joints allow hot gas bypass, increase heat flux to the shell, and weaken the lining structure. In a high-pressure reformer, gas infiltration through lining joints is a serious operational concern.
Fit-Up and Installation Quality
Dimensional inconsistency slows installation because masons must select, sort, or modify bricks on-site. This increases shutdown time and labour cost, and introduces the risk of improper installation when bricks are cut or modified to fit.
Long-Term Lining Stability
A lining built from dimensionally inconsistent bricks is more susceptible to differential thermal expansion effects. Some bricks fit tightly while others have excess gaps, creating stress concentration zones that initiate cracking during thermal cycling.
What Dimensional Tolerance Should You Specify?
For insulating bricks used in secondary reformers, a dimensional tolerance of ±1% or ±1mm (whichever is smaller) is considered appropriate for standard shaped bricks. For specially shaped bricks — arches, wedges, keys — tolerances may need to be tighter depending on the design geometry.
Your refractory design contractor or plant licensor may have specific tolerance requirements. Always request a dimensional inspection report with your brick delivery, and spot-check on-site before installation begins.
Key Specifications to Include in Your Purchase Order
- Al₂O₃ content (minimum %)
- Bulk density (kg/m³)
- Cold crush strength (CCS, minimum in MPa)
- Modulus of rupture (MOR)
- Permanent linear change on reheating (at specified test temperature, %)
- Refractoriness under load (RUL T0.5 or T1.0, minimum temperature)
- Maximum service temperature
- Dimensional tolerance (per face, in mm or %)
- Test certificate requirements — mill test report with each batch
India-Specific Considerations
Fertilizer plants in India — particularly those operating under the New Pricing Scheme or connected to strategic production targets — often face tight turnaround schedules during planned maintenance shutdowns. Secondary reformer refractory relining is a critical-path activity in most ammonia plant turnarounds.
This makes the quality of insulating bricks doubly important: not just for long-term performance, but for installation efficiency during the shutdown window. Bricks that fail dimensional inspection on-site, or that arrive with a significant proportion of damaged units, compress the available installation window and add cost.
Sourcing insulating bricks from a manufacturer with consistent production quality, reliable delivery timelines, and the ability to supply test certificates aligned with BIS or equivalent international standards is essential for Indian fertilizer plant operators.
How Refshape Approaches Insulating Brick Manufacturing
Refshape produces insulating bricks for secondary reformer applications with controlled raw material blending and standardised firing profiles designed to maintain consistency across production batches. Our dimensional checks are performed on every batch prior to dispatch.
We supply across multiple Al₂O₃ grades and can assist your team in confirming the correct specification for your specific reformer design and operating conditions. We also work with customers on non-standard shapes when the reformer geometry requires specially profiled bricks.
Closing Thoughts
Insulating bricks are a relatively small line item in a reformer refractory budget. But the consequences of under-specified or dimensionally inconsistent bricks can include premature relining, unplanned shutdowns, and shell overheating. Taking the time to specify correctly — and sourcing from a manufacturer who can prove compliance with those specifications — is straightforward risk management.
The Refshape team is available to assist with specification review and product selection for your secondary reformer refractory project.
10 FAQs — Insulating Bricks for Secondary Reformers
| Q1: What alumina content is recommended for secondary reformer insulating bricks?
For secondary reformer backup lining applications, insulating bricks with a minimum Al₂O₃ content of 45% to 70% are commonly used, depending on the design temperature at the backup layer. Your licensor or refractory design engineer can confirm the appropriate grade for your specific reformer design and operating temperature profile. |
| Q2: How is dimensional tolerance checked before insulating bricks are dispatched?
Reputable manufacturers check dimensional tolerance using calibrated gauges on a statistical sampling basis from each production batch. Key dimensions checked include length, width, height, and straightness. Customers should request a dimensional inspection report and are advised to perform spot-checks on-site before installation. |
| Q3: What is the difference between insulating bricks and dense refractory bricks in a secondary reformer lining?
Dense refractory bricks have high bulk density, high cold crush strength, and low porosity — suited for hot face applications where abrasion and chemical attack are primary concerns. Insulating bricks have controlled porosity and significantly lower thermal conductivity, making them ideal for backup lining layers where heat flux management is the priority. |
| Q4: Can insulating bricks be used on the hot face of a secondary reformer?
No. Insulating bricks lack the mechanical strength and abrasion resistance needed for direct hot face exposure in a secondary reformer. They are designed as backup or intermediate lining layers behind a more robust hot face castable or dense brick layer. |
| Q5: What does Refractoriness Under Load (RUL) mean for insulating bricks?
RUL is the temperature at which a refractory brick begins to deform under a specified compressive load in a standard test. For insulating bricks, the RUL value indicates how well the brick maintains its structure at elevated temperatures under the weight of the lining above it. Bricks with low RUL values will creep and deform at temperatures that may be within normal operating range. |
| Q6: How many brick grades are typically used in a secondary reformer lining system?
A typical secondary reformer lining might use two to three grades of insulating brick across the backup and intermediate lining layers, with different grades corresponding to different temperature zones from the hot face toward the shell. The exact layering depends on the reformer design, heat balance, and operating temperature profile. |
| Q7: What causes insulating bricks to fail prematurely in a secondary reformer?
Common causes of premature failure include: selection of an alumina grade below the actual service temperature, excessive thermal cycling from frequent plant trips, gas infiltration through wide mortar joints caused by dimensional inconsistency, alkali or steam attack on bricks with high silica content, and poor installation practice during the refractory relining. |
| Q8: Does Refshape supply non-standard shaped insulating bricks?
Yes. Refshape can supply specially shaped bricks — including arch, wedge, and key profiles — to meet specific reformer geometry requirements. Non-standard shapes require detailed drawings and dimensional specifications, and lead times may be longer than for standard shapes. Contact us early in your project planning to ensure availability. |
| Q9: Are Indian BIS standards applicable to insulating bricks for secondary reformers?
BIS standards cover refractory bricks broadly, and some fertilizer plant specifications reference IS standards alongside international norms. However, many plant licensors have proprietary specifications that supersede generic standards. Refshape can align test certification with your specified reference standard, whether BIS, ASTM, or licensor-specific. |
| Q10: How can I estimate the quantity of insulating bricks needed for a secondary reformer relining?
Quantity estimation requires the reformer vessel dimensions, the lining design (layer thicknesses, brick sizes, mortar joint allowance, and wastage factor). Your refractory design contractor or Refshape’s technical team can assist with quantity takeoff if you share the vessel drawings and lining design specification. |