Energy and Waste Processing

This is where biomass enters the combustion chamber. The main risk factors are thermal effects (up to 750 °C), high humidity, initial gasification, reducing atmosphere, and moderately low temperature. Suitable linings include bricks, prefabricated elements or castables. Typically, a two- or three-layer system is applied: working layer plus one or two insulating layers. Commonly used are high-duty fireclay bricks (45%+ Al₂O₃), with high strength and low iron oxide content.

This zone extends along the boiler grate and is exposed to very high temperatures, thermal shocks, and steep temperature gradients (200 to 1200 °C). Mechanical wear from fuel movement on the grate is also a risk. Two-layer systems are typical; recommended solutions include reinforced prefabricated concrete shapes and insulating protective layers.

This roof separates the combustion zone from the burnout zone. It ensures complete combustion of biomass in the lower zone and directs flue gases to the boiler outlet. It also separates temperature zones: ~850 °C below, >1200 °C above. The combustion side is more aggressive than the burnout side. Due to the temperature difference, andalusite-based products are recommended for their thermal shock and abrasion resistance.

This zone features high temperatures exceeding ash softening points. The oxidizing atmosphere supports complete combustion, and secondary air nozzles may be used to intensify gas mixing. Temperatures range from ~900 °C above the grate to ~1100 °C after the nozzles; drier biomass may cause spikes up to 1400 °C. Linings are made of fired bricks or castables and must resist high temperatures, oxidizing environments, and air nozzle impacts.

This zone, often accompanied by an intermediate roof, finalizes the combustion process at high temperatures in an oxidizing atmosphere. Intense chemical reactions occur here. Solutions are similar to the combustion zone, using fired bricks or castables. Shape and thickness must match 950–1200 °C to ensure process continuity.

Lower temperatures (650–850 °C), but increased friction due to material movement. Post-carbonate burnout may also occur, affecting lining behavior. While thermal demands are lower, abrasion resistance is key. Materials should offer high wear and friction resistance and maintain chemical stability at lower temperatures.

This section transfers heat from the chamber to the waste heat boiler. The outlet and inlet should match geometrically to maintain flow and minimize pressure drops. Castable linings are preferred for ease of application. Adiabatic chamber temperatures can reach 1200 °C. High-alumina castables (sprayed or prefabricated) are suitable.

The ignition roof is a critical element influencing boiler performance. It absorbs heat from the flame and transfers it to the grate below to dry and ignite the fuel. The roof material is exposed to gasification products and reducing atmosphere, as well as rapid temperature increases during startup (up to 1100 °C). It can be made from suspended shapes, poured into formwork, or assembled from prefabricated segments. Poor performance leads operators to maintain the flame directly beneath it, which negatively affects material lifespan, flue gas quality, and overall boiler efficiency

Screen tube deviation boxes (manholes, viewports, pressure and temperature sensors, etc.) require refractory sealing. These areas are typically lined with castables rated at ≥1350 °C.

Boiler walls (on dense linings) are exposed to different conditions depending on placement. In the combustion chamber, temperatures can reach 1100 °C—higher than in the second pass. The purpose of the walls is to contain flue gases and prevent external air from entering (as boilers operate under negative pressure), which would lower efficiency. Walls are exposed to flue gases, flame radiation, and slag buildup (if combustion is suboptimal).

This area is subject to frequent temperature changes and mechanical abrasion due to fuel flow. Solutions are primarily based on fired bricks and occasionally on prefabricated concrete elements. The design must address thermal fluctuations and abrasion, often requiring multilayer lining systems. High mechanical strength and thermal shock resistance are crucial. In case of local blow-through, process temperature may spike up to 1600 °C.

The nozzle bottom is where air, heated to about 220 °C, is injected through multiple nozzles to fluidize the bed. The space between the nozzles is filled with refractory castable. Since the nozzles direct air downward, erosion occurs. A step at the wall transition is also common. Temperatures in this area are relatively low (~600 °C).

These walls are in direct contact with the fluidized bed and include igniter burners, fuel and sorbent inlets, return material inlets from separators, manholes, etc. The main function of the lining here is to protect the pressure parts from bed abrasion. Temperatures do not exceed 900 °C. In discontinuities of the screen, the lining can be thick, while on-screen areas it is usually 50–80 mm above the tube peaks. A dense network of cracks may form here—proper anchor density is essential to maintain durability.

These ducts, connecting separators (in CFB boilers) or the combustion chamber (in BFB boilers) with the convective part of the boiler, transport relatively clean and low-eroding flue gases at 850–950 °C.

These ducts connect the combustion chamber to the separators (in CFB boilers). They carry highly erosive flue gases at 850–950 °C. Due to cross-section changes that accelerate gas flow, erosion intensifies. These ducts can be either screened or insulated. In screened ducts, the roof is usually gunned, the floor cast, and the walls may be gunned, cast, or made from prefabricated elements. Lining is typically thin. For thin linings, self-flowing castables like PCOCAST BNAB Fl or MULCAST BN80M Fl are used. In thicker sections (e.g., compensators), vibrated castables such as PCOCAST BMAB160 or PCOCAST BN160AZS (for harsh conditions) are recommended.

Hot gas cyclones (used in CFB boilers) direct pre-cleaned flue gases into the convective section of the boiler. The atmosphere is strongly reducing, with temperatures ranging from 850–950 °C. In screened cyclones, the roof is typically gunned, and the walls are either cast, rammed with plastic mixes, or made of prefabs with thin linings. In insulated cyclones, the roof is also gunned, while walls can be brick-lined with wedges, cast, or prefabricated. The working layer is thicker, and insulation must effectively block heat loss and reduce casing temperature.

This is the core area where gasification and partial combustion of waste occur. Due to rotation, the lining is cyclically heated (when on top) and transfers heat to the waste (as it rolls over it). Lining requirements are determined by process parameters such as environmental aggressiveness and temperature. Most commonly, a single-layer lining is used, made of high-alumina wedge bricks—typically andalusite or corundum-based. Areas around manholes or burner ports are lined with refractory castables rated above 1600 °C.

These sections accumulate carbonate and ash to complete gasification or combustion before the materials leave the kiln. Refractory lining consists of high-alumina fired bricks in the working layer (andalusite or corundum products) and fireclay/insulating products in the protective layers.

The front section delivers the feed/waste to the installation. Depending on the process (co-current or counter-current), it may include a burner and air nozzles. The front plate operates under highly variable thermal conditions and is exposed to strong temperature gradients, as well as evaporated and gasified waste products. It is made from monolithic high-alumina castable or prefabricated concrete elements.

This is a critical transition zone where gases are directed to subsequent stages of the process, while heavier fractions – such as slag, ash, and unburnt residues – fall downward. Operating conditions here are defined by moderate temperatures (typically not exceeding 950 °C) and a slightly oxidizing atmosphere. The zone experiences intense mechanical erosion caused by material movement and impact from heavy particles dropping from the kiln. For biomass-fired units, MULCAST BN50M is recommended. For municipal or medical waste incineration, MULCAST BN80MZr is preferred.

This zone completes the burnout of carbonates—carbon-rich residues from the gasification and combustion of fuel in the rotary kiln. Temperatures do not exceed 950 °C. Though subject to significant mechanical wear from contact with solids and dynamic airflow, the chemical environment is less aggressive, as most reactive compounds are carried away in earlier process stages. Commonly used materials include MULCAST BN50MZr and PCOCAST BNAK160, which are recommended for applications requiring high abrasion resistance and dimensional stability.

In this section, the oxidation process intensifies. Temperatures are generally kept below 1000 °C to prevent lining buildup due to local oxygen deficiency. Here, flue gas compounds mix with tertiary air, causing rapid temperature increases. Refractory linings should consist of ABRAL brick products enriched with silicon carbide or special castables such as BNSiC, which offer excellent chemical and thermal resistance and perform reliably under high-temperature oxidizing conditions.

This zone finalizes the oxidation of flue gases formed during waste combustion. Its main function is to ensure sufficient residence time at high temperature and complete mixing with secondary or tertiary air to eliminate any remaining combustibles. Temperatures can exceed 1050 °C. Similar to the combustion zone, ABRAL bricks and BNSiC castables are recommended.

Mixing baffles plays a critical role in the final phase of combustion. Their function is to prolong flue gas residence time under oxidizing conditions and to intensify mixing with secondary or tertiary air. Temperatures in this section may also exceed 1050 °C. Auxiliary gas burners are often activated to maintain the required thermal profile. Due to the process conditions and oxidizing environment, high-SiC refractory bricks are used in baffles to ensure durability and resistance to both heat and corrosion.