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The new multi-nozzle opposed-flow gasifier utilizes domestically produced refractory materials. The refractory brick structure within the gasifier’s combustion chamber consists of three distinct layers: the hot-face bricks, the backing bricks, and the insulating bricks.

Hot-Face Bricks

Since the hot-face bricks are in direct contact with the coal slag, they constitute the most critical section of the gasifier’s refractory lining—the area subjected to the most severe operating conditions. Consequently, 90% Cr-Al-Zr bricks (commonly referred to as “high-chrome bricks”) are selected for this application. The primary raw material used in these Cr-Al-Zr bricks is Cr2O3, which imparts excellent thermal stability as well as superior resistance to high-temperature slag, gas-flow erosion, and chemical corrosion.

Backing Bricks

Positioned behind the hot-face bricks, the backing bricks play a vital role in providing mechanical support to the entire refractory lining structure of the gasifier; therefore, Cr-corundum bricks are chosen for this layer. Cr-corundum bricks exhibit high strength at ambient temperatures, excellent chemical stability, and superior load-bearing capabilities, in addition to possessing outstanding resistance to coal slag corrosion and high-temperature creep.

Insulating Bricks

Situated behind the backing bricks, the insulating bricks serve to provide thermal insulation for the gasifier, thereby minimizing heat loss. For this purpose, alumina hollow-sphere bricks are selected. Alumina hollow-sphere bricks are characterized by their distinct thermal insulation properties and low thermal conductivity; they are a lightweight refractory material that offers excellent high-temperature resistance and energy-saving performance. They demonstrate exceptional stability across a wide range of atmospheric conditions and possess excellent resistance to corrosive gases, as well as a strong capacity to buffer thermal stresses.

Heavy-Duty Castables (Cr-Corundum Castables)

Slag-blocking wool—a ceramic fiber blanket—is a soft, cotton-like felt with very low density and excellent slag-gathering properties. Crucially, it does not contaminate molten steel, and it is a neutral refractory material. When used, it is cut to the appropriate size according to requirements. After being placed on the surface of high-temperature molten steel, it softens and shrinks slightly, but this does not affect its ability to float on the surface and block slag, keeping the molten steel clean for pouring.

Usage Method of Slag-Blocking Wool

During pouring, it forms an insurmountable slag-blocking, slag-filtering, and slag-collecting barrier at the ladle opening, without adhering to the ladle wall. It provides excellent heat insulation, heat preservation, light blocking, and radiation protection. It effectively ensures the purity of the poured molten steel and the safety of the pouring process. After pouring, it can be easily removed.

Alkaline ramming mixes primarily use magnesia refractories, which have advantages such as excellent erosion resistance, high melting point, and non-reaction with alkaline slag. However, magnesia ramming mixes have a large coefficient of thermal expansion and poor thermal shock resistance, which can easily lead to cracking and spalling of the furnace lining during operation. Acidic ramming mixes primarily use silica refractories, which have advantages such as readily available raw materials and low price. However, SiO2 is prone to complex crystal transformations during heating, leading to volume effects. Neutral ramming mixes primarily use corundum refractories, which have advantages such as high temperature resistance, good slag erosion resistance, no impact on molten steel quality, and short construction time. They are widely used in alloy smelting, but corundum ramming mixes also have disadvantages, such as difficulty in sintering and a high coefficient of thermal expansion.

Neutral Alumina-Magnesium Dry Ramming Material for Medium-Frequency Furnace Lining

Chemical Mechanism of AZS Refractory Material and Bubble Formation

Cast AZS refractories contain impurity elements that can be oxidized to form gases, such as carbon, sulfur, zirconium carbide, nitrides, and nitrogen oxides. When AZS refractory bricks are heated to above 1400℃, these impurity elements undergo oxidation reactions, forming corresponding gases such as nitrogen, carbon monoxide, carbon dioxide, and sulfur dioxide.

When the cast AZS bricks are cooled and then reheated, oxygen bubbles, or secondary bubbles, are generally generated at the contact point between the molten glass and the cast AZS bricks. This is because, under normal circumstances, cast AZS bricks contain a small amount (<0.3% (mass fraction)) of variable-valence elements, such as iron (Fe, Fe) or titanium (Ti, Ti). These variable-valence elements can change their valence state with temperature changes, thereby absorbing or releasing oxygen, as shown in the following reaction equation.

When the temperature decreases, reaction equation (1) proceeds in the forward direction, favoring the formation of Fe3+. When the temperature increases, reaction equation (1) proceeds in the reverse direction (reverse reaction), favoring the formation of O2.

Another reason for oxygen production is the electrochemical reaction (cell reaction) between the molten glass and the AZS refractory bricks, or a “remote” electrochemical reaction occurring without direct contact between the molten glass and the AZS refractory bricks. Alkali metal or alkaline earth metal ions are responsible for electron transfer. In this cell reaction, oxygen ions (O2-) in the molten glass are oxidized to oxygen (O2), i.e., the anodic reaction. High-valence iron (Fe3+) or titanium (Ti4+) in the refractory is reduced, i.e., the cathodic reaction. The reaction rate of this electrochemical reaction is directly proportional to the difference in the content of alkali metal or alkaline earth metal ions in the molten glass and the cast AZS refractory.

Applications of Magnesia-Iron-Aluminum Composite Spinel Bricks

Magnesia-iron-aluminum composite spinel bricks have been widely adopted in nearly one hundred cement kilns, both domestically and internationally. Based on over three years of application data from various cement enterprises, these bricks demonstrate excellent high-temperature performance and strong adaptability. They surpass the performance levels of the directly bonded magnesia-chrome bricks previously used, thereby fully enabling the realization of chrome-free refractory linings in the burning zones of cement kilns.

Rongsheng Magnesia-Iron-Aluminum Composite Spinel Bricks

Structural Characteristics of Shuttle Kilns

The structural form of a shuttle kiln resembles that of a car-bottom heating furnace or heat-treatment furnace; however, within the ceramics and refractory materials industries, it is specifically referred to as a “shuttle kiln.” As the name implies, the trajectory of the kiln car—as it is pushed into and pulled out of the kiln—resembles the movement of a “shuttle.” It is also sometimes referred to as a “drawer kiln,” a name likewise derived from the action of the kiln car being pushed in and pulled out. Since the shuttle kiln is a batch-type firing device, every firing cycle involves distinct heating and cooling phases. Consequently, the amount of heat stored and subsequently dissipated by the kiln body and the kiln car directly impacts the furnace’s thermal efficiency. Shuttle kilns predominantly utilize lightweight refractory materials to minimize heat storage and heat loss as much as possible. Simultaneously, they are equipped with temperature-regulating, high-velocity burners designed to prevent product defects that might otherwise arise from excessive temperature differentials between the flame and the products being fired. Furthermore, the turbulence and entrainment effects generated by the high-velocity airflow within the kiln serve to enhance convective heat transfer efficiency. The design fundamentally employs a flat-roof structure, ensuring that the kiln roof and side walls remain structurally independent; this allows for free thermal expansion and contraction, thereby facilitating the construction of a lightweight kiln body. At the same time, this design maximizes the utilization of internal kiln space. Additionally, shuttle kilns typically adopt a bottom-exhaust configuration, which creates favorable conditions for achieving uniform temperatures within the kiln and simplifies the layout of floor-level facilities within the workshop.

The aforementioned characteristics constitute the key factors that make shuttle kilns energy-efficient, capable of maintaining minimal temperature differentials, and conducive to short firing cycles; they also represent the critical aspects that distinguish shuttle kilns from standard heating furnaces and heat-treatment furnaces. Currently, the firing chamber volumes of commonly used shuttle kilns vary widely—ranging from as little as a few cubic meters for small units to nearly 200 cubic meters for large ones—and are not bound by a fixed standard series, but rather determined entirely based on the specific requirements of the user. The following section outlines the structural characteristics, design requirements, and construction specifications applicable to large-volume shuttle kilns.