Refractory Materials Used in Waste Incinerator Equipment

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Besides daily household waste such as urban garbage, sewage sludge, and other pollutants, industrial waste constitutes the largest volume of waste generated. All of these wastes require harmless treatment. Waste treatment begins with urban waste incineration for sanitation purposes.

Waste Treatment Equipment and Furnace Types

Incineration equipment mainly consists of incinerators, including grate-type, moving bed type, and rotary kiln type.

Refractory Materials Used in Waste Incinerator
Refractory Materials Used in Waste Incinerator

Grate-type incinerators introduce combustion gases from below the grate, driving the grate and continuously burning the waste. Because this method is suitable for many types of waste, it is widely used in first-tier cities.

Moving bed incinerators use regenerable sand as a heat carrier and are used for instantaneous incineration of waste. Because the equipment is very easy to stop and is also very suitable for incinerating liquid waste, it is used for incinerating garbage, sewage sludge, and industrial solid waste in small and medium-sized cities.

Rotary kiln incinerators are widely used for treating difficult-to-burn industrial solid wastes such as sludge and waste liquids because they can fully incinerate waste through radiant heat within the furnace.

Incineration ash melting furnaces mainly include: surface melting furnaces and rotary melting furnaces that use burners as heat sources; plasma melting furnaces and electric arc melting furnaces that utilize electrical energy. All of these melting furnaces melt and slag the incineration ash at high temperatures of 1400-1600°C.

Gasification melting furnaces mainly include: pyrolysis gasification melting furnaces and direct gasification melting furnaces. These are waste melting devices without an incinerator, thus minimizing the generation of dioxins.

  • Pyrolysis gasification melting furnaces use a pyrolysis furnace to thermally decompose waste in a low-temperature reducing atmosphere, while simultaneously igniting the resulting combustible gases and char (carbonaceous residue) for slag formation. Therefore, this treatment method helps reduce dioxins and suppress CO2 emissions. In some cases, pyrolysis furnaces are combined with rotary melting furnaces.
  • An immediate gasification melting furnace is a type of furnace that immediately melts waste together with fuels such as coke, and the resulting combustible gas is used for power generation. This melting method also helps reduce dioxins and allows for efficient energy utilization.
  • Waste melting furnaces (including incineration ash melting furnaces and gasification melting furnaces) melt and liquefy incineration ash at high temperatures of 1400~1600℃, and the residue (slag) is in a liquid state (liquid phase).

Selection of Refractory Materials for Melting Furnaces

Generally, the C/S ratio of molten furnace slag is 0.3~1.0. However, to improve melting efficiency and achieve the goals of lowering the melting point and solidifying (slagging) heavy metals and harmful substances, the composition of the molten material is usually adjusted (commonly by adding CaO and SiO2). This results in changes in basicity, requiring corresponding adjustments to the adaptability of the refractory material.

Therefore, the selection of refractory materials for melting furnaces cannot solely consider corrosion resistance. There are instances where changes in operating conditions, alterations in slag composition, and fluctuations in melting temperature can significantly shorten the service life of refractory materials, and a universal material suitable for these conditions does not exist. Therefore, the selection of refractory materials must be based on the main factors causing refractory material damage. It is now confirmed that the corrosion of refractory linings in melting furnaces is primarily controlled by slag composition and operating conditions (temperature, atmosphere, etc.).

Therefore, the main criteria for selecting refractory materials for molten furnaces are:

1. When the slag basicity is not less than 1.0 or the Fe2O3 content is high, basic (MgO, Spinel) and carbonaceous refractory materials should be selected. When the slag basicity C/S < 1.0, Al2O3, Cr2O3, and SiC refractory materials should be selected.

2. Depending on the operating conditions (temperature, atmosphere, etc.), the following factors need to be considered when selecting refractory materials for molten furnaces:

  • (1) Since the erosion of refractory materials will increase sharply when the temperature exceeds 1450~1500℃, it is necessary to comprehensively consider the application location, cooling conditions, and furnace structure.
  • (2) The erosion loss of refractory materials is not only caused by the slag composition, but also easily affected by the furnace atmosphere and slag flow.
  • (3) C and SiC refractory materials, which have good corrosion resistance and wettability, are prone to oxidation loss.

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