Cement, lime and paper

The refractory lining of the upper cyclone dome is primarily exposed to gas‐borne abrasion caused by entrained particles in the feed. In this zone, the effects of temperature and mechanical stresses are minimal, resulting in relatively mild service conditions. The dome lining is constructed in multiple layers, with wedge‐shaped bricks forming both the working and insulating layers. This multilayer design provides effective gas protection while minimizing wear of the lining material. Given the low‐demand operating environment, low‐alumina EXTRATON products and lightweight ISOLUX insulating bricks perform exceptionally well in this zone, offering sufficient resistance to gas abrasion while maintaining optimal thermal‐insulation properties.

The lining of the barrel (cylindrical section) of the upper cyclone is subjected to both abrasive and mechanical wear, although these conditions are relatively mild. Mechanical stresses are moderate, allowing for the use of standard refractory solutions. The barrel lining is constructed much like the dome—comprising multiple layers, with wedge bricks dominating both the working and insulating layers. This design permits an even distribution of loads and ensures long‐lasting protection against abrasion. Under these moderate service conditions, the same products used for the dome—the low-alumina EXTRATON series and lightweight ISOLUX insulating modules—are suitable here as well, providing adequate resistance to abrasion and mechanical action while maintaining effective insulation.

The cone is the most mechanically stressed part of the cyclone, although overall the risk to the refractory lining remains low. This is due to the zone’s shape, which influences the intensity of mechanical forces. Because of the cone’s complex geometry, the lining is constructed from castable refractory concrete, allowing the material to conform to the difficult shape and simplifying installation. This design must ensure even distribution of the refractory on the irregular surfaces.

The lining of the lower cyclone dome is primarily exposed to gas-borne abrasion from volatile feed particles. Although the effects of temperature and mechanical forces are relatively minor, service conditions are more demanding than in standard upper cyclones. In addition, the lining must resist chemical attack and accretion from deposits, which increases the risk of degradation. The dome lining is built in layers—several overlapping strata in which wedge bricks play a key role in both the working and insulating layers. This structure allows for gradual load distribution and provides superior protection against both chemical attack and abrasion.

The lining of the barrel (cylindrical section) in the lower cyclone is subjected to a combination of stresses—abrasion, mechanical wear, and aggressive chemical attack, including alkali corrosion. Such multidirectional loading demands a lining that resists both severe mechanical erosion and chemical degradation, making the operating conditions in this zone particularly challenging. Like the dome, the barrel lining is built in multiple layers, with wedge bricks dominating both the working and insulating strata. This multilayer construction ensures even distribution of mechanical and chemical stresses, thereby extending the service life of the lining.

The cone, as the part of the lower cyclone, is the most heavily stressed zone in terms of mechanical, chemical, and abrasive forces. Due to the challenges posed by the cone’s unusual geometry and the complexities of brick installation, the lining in this zone is executed with cast refractory concrete. This approach allows the material to be fitted precisely to the cone’s intricate shape, minimizing the risk of uneven stresses and localized damage. In the cone area, it is essential that the refractory offers resistance to mechanical, chemical, and abrasive loads.

In this zone, temperatures range from approximately 700 – 900 °C. The primary risks to the refractory lining are mechanical abrasion and chemical erosion caused by the ingress of fine particles. Occasionally, accretions—mainly from sulfur and chlorine when using alternative fuels—form on the lining. High-alumina refractory castables enriched with ZrO₂ or SiC are preferred. If a brick lining is used instead, high-alumina bricks with strong abrasion and thermal-shock resistance should be considered.

In this zone, temperatures exceed 1000 °C—and at the burner locations can reach as high as 1200 °C. It is one of the most demanding service areas for refractories in the entire cement plant. The process conditions—typically involving 100 % alternative fuels—subject the lining to aggressive alkali attack. Both castables and bricks used here should be high-alumina grades enriched with additives (such as zirconia or silicon carbide) to enhance resistance to chemical attack and abrasion.

In this zone, temperatures remain high—around 1000 °C. The primary risk, however, comes from alkalis formed during the calcination process in the zone above. Here, low-cement and cement-free high-alumina castables are used. For brick linings, high-alumina bricks with silicon-carbide additives are recommended. The lining often becomes coated with chemical accretions derived from alternative fuels—so severe that they must be removed with air or water during routine maintenance. The refractory must also resist mechanical impact, as chunks of accretion falling from the upper zones strike the inclined surface of the constriction at the bottom of the calciner.

The challenge for the refractory lining in the tertiary air duct lies in its small diameter, which amplifies the effects of the abrasive environment—particles pass through the pipe at high velocity under pressure. To enhance durability, PCO recommends using EXTRATON shaped bricks and chamotte PCOCAST castable with abrasion‐resistant additives such as silicon carbide or zircon. For even harsher operating conditions—higher pressures or temperatures—chamotte bricks with silicon‐carbide reinforcement from the ABRAL line are advised.

In the upper section of the riser duct, where temperatures do not exceed 700 °C, chamotte refractories are used for the working layer. PCO Żarów recommends EXTRATON or ABRAL products, which offer enhanced abrasion resistance. Under more severe conditions, this zone can also be lined with high-alumina bauxite bricks—BAUXITEX—to provide additional protection.

In the lower section of the riser duct, where operating conditions are more severe, the lining must withstand higher temperatures—up to 1100 °C—and intensive chemical attack. Typically, high-alumina refractories based on andalusite or bauxite raw materials are used here, enhanced with additives to boost both mechanical and chemical resistance. PCO Żarów recommends ABRAL or ANDALUX grade products, or ultra-low-cement castables such as NxGel, specifically designed for rapid heat-up processes, to ensure optimal protection of the lining in this demanding zone.

The inlet chamber (flue‐gas chamber) is where the lining is primarily subjected to chemical attack from hot exhaust gases and mechanical impact as the charge falls from the riser duct into the chamber before being fed into the rotary kiln. This causes significant abrasion of the ceramic lining. A common issue is accretion build-up from the feed material, leading to local blockages. The refractory lining should include silicon‐carbide or zirconia additives to enhance resistance to mechanical impact and prevent sticking (imparting low porosity and non-wettability to the bricks and castables). This minimizes accretion formation and allows the lime fines to flow freely into the rotary kiln.

Here, the refractory lining is exposed to very high temperatures and the aggressive action of alternative fuels, necessitating frequent repairs. Installing the lining in the flame zone is challenging, especially when casting concrete directly onto the burner; it requires not only appropriate technology but also highly skilled masons. Achieving a homogeneous concrete consistency is critical to ensure even material distribution and rapid heat-up, which is essential for maintaining uninterrupted furnace operation. Due to these extreme conditions, the refractory material must offer exceptional resistance to thermal shock and aggressive fuels.

The ending zone of the kiln—known as the “nose ring”—experiences conditions similar to the outlet zone. Here, temperatures fluctuate and the processed charge exerts high mechanical pressure, requiring materials with excellent mechanical strength. The rotary kiln design calls for monolithic products cast in place from refractory concrete during maintenance. The key properties of these materials are compressive strength and abrasion resistance, ensuring structural integrity under intense loading. Recommended products include high-alumina concretes of the MULCAST class and low-cement concretes from the PCOCAST line.

In the cooling zone, the primary challenge for refractory materials is mechanical impact caused by cracking clinker, which changes its volume due to sudden temperature fluctuations. Temperatures in this area vary between 900–1100 °C. The lining consists of a single layer of wedge bricks, and the key properties required of the refractory materials are high resistance to thermal shock and exceptional mechanical strength against impact and abrasion.

In the lower transition zone, the clinker sintered in the previous zone gradually cools down, with temperatures dropping to around 1200 °C. Despite the reduced temperature, refractories with high resistance to dynamic temperature changes are still used. At this stage, magnesite–spinel products predominate, ensuring continuous lining protection while limiting thermal stresses.

The firing zone is the area of highest temperatures—up to 1500 °C—where complete chemical transformations occur. The limestone charge undergoes intense reactions that form the clinker minerals. In this zone, magnesite refractories are recommended, as their properties provide the necessary resistance to the extreme thermal and chemical conditions encountered during firing.

In the upper transition zone, very intense thermal exposure occurs, with temperatures exceeding 1200 °C. This zone is characterized by unstable and fluctuating conditions, and the lining—made of a single layer of wedges—must resist rapid temperature changes. Magnesium–spinel products are typically used here, while at the boundary leading into the safety zone, top‐grade aluminosilicate refractories are installed to provide optimal protection against thermal shocks.

In the safety zone, temperatures exceed 1000 °C, which promotes the decomposition of limestone. Conditions here are variable and heavily dependent on the process—especially when the share of RDF in the fuel increases. The lining, built as a single layer of wedge bricks, is exposed to alkalis, liquid eutectics, unstable stresses, and aggressive chemical and thermal attack from the charge and alternative fuels. Refractory material selection must be flexible to meet these changing operational conditions. In this zone, high-alumina products with SiC—such as ABRAL or ANDALUX—and chemically bonded BAUXITEX refractories should be used.

In the calcination zone of the rotary kiln, in addition to intense mechanical abrasion caused by the movement of the charge, there is exposure to alkali compounds originating from raw materials and fuels. Temperatures in this part of the kiln are maintained between 1000–1100 °C. The lining consists of a single layer of wedge bricks. The key requirements for refractory materials in this zone are high mechanical strength and corrosion resistance, ensuring uninterrupted system operation under variable process conditions. Depending on the specific conditions, products from the ABRAL group—known for their enhanced corrosion and abrasion resistance—are well suited for this application.

In this zone, which marks the start of the kiln lining, the primary hazard is intense mechanical abrasion caused by the advancing charge. To address this challenge, abrasion-resistant castables are employed. It is essential to use high-alumina concrete; the recommended products are medium-cement MULCAST concretes or cement-free GELCAST concretes, both of which provide the necessary strength and resistance to mechanical wear.

In the hot zone of the cooler, temperatures can reach up to 1000 °C and then drop sharply toward the moving grate. These conditions produce severe thermal shocks, and on the clinker bed the primary threat to the refractory lining is intense mechanical abrasion resulting both from the charge movement and from dynamic flows of air and dust. The lining in this zone is built using precast concrete modules—so-called retaining wall elements—which provide not only effective thermal insulation but also mechanical stability under fluctuating temperatures. A key factor in ensuring reliable performance is the use of high-alumina castable, which offers outstanding resistance to thermal shock and severe abrasion. This ensures the material retains its operational properties even under rapid temperature declines and mechanical stresses.

In the cold zone, thermal conditions are very stable, and temperatures do not exceed 500 °C. Due to the gentler temperature exposure and fewer dynamic changes, this part of the cooler experiences low thermal and mechanical stresses—making relines relatively infrequent. In this zone, the lining is made from shotcrete, which provides a uniform, continuous refractory surface. Additionally, along the grate, prefabricated retaining‐wall modules are installed, using lower‐grade refractories such as MULCAST BN45M S5.

The roof, which spans both the hot and cold zones, is subjected to abrasion from volatile dusts and to rapid temperature fluctuations along the cooler’s entire length. The refractory lining must resist mechanical wear as well as variable thermal stresses. For the roof, it is crucial to use materials with outstanding mechanical and thermal properties—particularly in the hot zone, where the inclusion of SiC additives enhances the lining’s strength. In the cold zones, the priority is maintaining a cohesive, durable lining at lower temperatures, allowing for prolonged service without frequent relining.

The primary function of the kiln hood is to recover the clinker and transfer it into the cooler, all under severe mechanical and thermal stresses. Special attention must be paid to the area known as the bullnose ring—a vertical wall that is most susceptible to damage. In this zone, the refractory lining endures mechanical loads from falling clinker combined with rapid temperature changes, placing extremely high demands on the materials. In the kiln hood, the lining is typically made of shaped refractory bricks that provide thermal stability and sufficient insulation, minimizing heat losses and the influence of external factors. In the bullnose ring, however, the extreme mechanical loads call for high-grade refractory castable or precast concrete modules.

The heating zone is the area where limestone mixed with fuel is loaded cyclically. This process generates intense abrasive wear due to the mechanical movement of the charge, while also exposing the lining to high temperatures. Materials used in the heating zone must offer high abrasion resistance—hence the choice of EXTRATON aluminosilicate refractories. To reduce heat losses, an insulating layer based on ISOLUX products combined with mineral wool provides excellent thermal‐insulation performance. The key is to balance mechanical durability with insulating properties to ensure the lining’s longevity while maintaining the kiln’s optimal thermal parameters.

The firing zone—often synonymous with the calcination zone—is where the intense thermal treatment of the charge (such as limestone or dolomite) takes place. The firing temperature and the charge composition dictate the specific chemical and thermal stresses, including the risk of hydration. Under normal operating conditions, alumina (Al₂O₃) and silica (SiO₂) are chemically stable, which limits their reaction with water. However, it remains essential to use refractories that maintain stability even in the presence of moisture. In this zone, it is critical to employ products that offer high resistance to hydration and chemical stability at elevated temperatures. MULITEX, ANDALUX, and BAUXITEX refractories meet these requirements, ensuring long service life despite the variable chemical environment of the charge.

In the cooling zone, the lining is subjected to a gradual reduction in temperature, resulting in less severe thermal stress but still requiring abrasion resistance. In a single‐shaft kiln, uniform cooling occurs along the entire height of this zone, allowing for a consistent insulating approach. For the cooling zone, chamotte refractories perform best, offering good compressive strength and abrasion resistance. In particular, SUPERTON‐grade products are recommended for this area. In single‐shaft kilns, the insulating layer throughout this zone is constructed with ISOLUX modules supplemented by mineral wool, creating a continuous thermal barrier and minimizing heat losses.

The heating zone in a Maerz furnace extends from the lower burner level to the upper part of the shaft, where limestone mixed with fuel is loaded cyclically. This process generates intense abrasive and thermal stresses due to the direct contact between the charge and the lining, as well as fluctuating temperature conditions. Therefore, in this zone it is critical to provide materials with high abrasion resistance and to minimize heat losses, which in turn maximizes the efficiency of the entire furnace. The lining design in the heating zone is based on using different materials selected according to the temperature profile. In the lower section around the burners, the working layer is made of magnesite–spinel refractories, which offer high abrasion resistance and withstand the aggressive compounds formed during combustion. In the upper part of the shaft, high‐abrasion aluminosilicate products from the EXTRATON line are employed.

To ensure a smooth transition between the magnesite–spinel layer and the aluminosilicate layer, a transitional lining made of high-alumina (andalusite) refractories is introduced. Additionally, the space between the steel shell and the working lining is filled with an insulation system that includes ISOLUX insulating boards and mineral-wool insulation blankets. In some designs, an extra insulating layer of SUPERTON or EXTRATON products is placed between the working layer and the main insulation system. The entire shaft lining is finished with a conventional castable layer, providing the final protection and sealing of the structure.

The firing zone extends from the lower level of the supporting arches up to the lower level of the burners (gas lances). In this part of the kiln, the charge undergoes an intensive firing process that generates both very high temperatures and aggressive chemical conditions, depending on the type of raw material—such as limestone or dolomite. PCO Żarów supplies the protective and insulating materials for this zone. The entire lining of the shaft, from the expansion‐joint area upward, is built using specialized shapes—types AS1, AS2, and similar—manufactured from MULITEX or ANDALUX refractories. This approach ensures not only structural stability but also reliable performance under fluctuating firing conditions.

In the Maerz furnace construction, there are elements such as columns, inter-column arches, flat arches, and the connecting duct, all made from low-cement or cement-free castables. Building the columns in a Maerz furnace requires a combination of so-called nose-shaped blocks (VK-76x and WL-76), which ensure exceptional structural stability. In a pillar-less Maerz furnace, the base of the suspended cylinder is also made from high-strength castables, and the flat arch is lined with an insulating layer of lightweight castables—such as ISOCAST or ISOGUN—supplemented with mineral wool.

The cooling zone in a Maerz furnace extends from the level of the first refractory lining down to the lower level of the inter-column arches. In this section, the temperature gradually decreases, which is critical for stabilizing the cooling process. Despite the drop in heat, the lining remains subject to intense abrasive and mechanical stresses caused both by the movement of the charge and by the thermal-stress cycles generated during cooling. The working layer is made from chamotte refractories – SUPERTON or EXTRATON series are recommended, as they perform exceptionally well under these conditions. The inter-column space is typically lined with EXTRATON shapes. The insulating layer in the cooling zone is based on ISOLUX modules, installed in combination with calcium-silicate boards and mineral-wool blankets to complete the thermal barrier.

The heating zone of the rotary lime kiln covers the temperature rise from 200 °C to 1100 °C. Here, the slurry is dried and initially calcined. The refractory lining is subjected to abrasion and chemical erosion. The slurry contains alkali salts, sulfur compounds, and chlorides, which pose a risk of chemical infiltration into the lining. Another hazard is that the slurry can be wet (up to 20 % moisture), so the refractory must resist water penetration into its pores. For the working lining, high-grade chamotte refractories with low porosity and alkali resistance—such as EXTRATON—are recommended. In the section closer to the firing zone, where temperatures are higher, high-alumina or chemically bonded refractories—such as ANDALUX—should be considered.

Temperatures in this zone range from 1100 °C to 1300 °C along its entire length. Operating conditions here are variable; the main risks are thermal stresses from the burner flame and chemical attack by the process gases. The lime slurry is sintered, converting the carbonate-bearing mud into pure CaO (quicklime). The refractory lining must resist thermal shock, sustained high temperatures, and both chemical and mechanical corrosion. The lining is two-layered; for the working layer in this zone, chemically bonded andalusite bricks of the ANDALUX grade are recommended.

This is the shortest section of the rotary kiln and spans a few meters before the inlet to the cooler. Here, temperatures drop rapidly—from 1000 °C to around 200 °C—creating severe thermal shocks. At this point, the fully reacted lime acts abrasively on the lining as it moves with the charge. The kiln’s rotation and the converging construction (reduced shell diameter) impose mechanical stresses that are hazardous to the refractory. The lining is two-layered: at the constrictions, a high-alumina refractory castable is used for the working layer, while the insulating layer employs ISOLUX shaped boards with enhanced compressive strength.

The charging threshold is made of refractory ceramic and is designed to even out the distribution of the charge at the rotary kiln outlet. In this zone, the lining is subject to significant abrasion and mechanical stress. The recommended installation uses the most durable andalusite bricks, which help regulate the movement of the charge.