Waste incineration is an important industry for purifying the ecological environment, and reducing the volume and harm of waste is an effective way to alleviate waste pollution. Common waste incinerators include plasma decomposition furnaces, rotary kiln incinerators, grate furnaces, chain furnaces, and co-processing kilns in cement plants. Different types of incinerators can achieve a certain level of combustion efficiency and the purpose of purifying and disposing of waste.
Development of Waste Incinerators
Waste incinerators take various forms, with grate combustion being the most common, and a small number of them using rotary kilns and fluidized bed furnaces. They are all single-incineration treatments, belonging to the category of first-generation waste incinerators. The major problem is that they easily produce secondary pollution.
The core of second-generation waste incineration technology is gasification melting integration, which mainly gasifies and high-temperature melts waste for incineration. This overcomes the problems of ineffective decomposition of organic matter in waste caused by low temperatures or short residence times in incinerators, and the possibility of generating chlorinated organic aromatic precursors (which may lead to dioxin formation) in the downstream equipment’s low-temperature area (250-350°C), with the aim of reducing the emission values of dioxins, heavy metals, and other secondary pollutants, as well as improving furnace efficiency and power generation efficiency. Therefore, incinerators using second-generation incineration technology have become the development direction of waste incineration today.
The performance of refractory materials used in waste incinerators is key to promoting waste incineration technology. With the development of waste incinerators in China, it is imperative to develop efficient and economical refractory materials for waste incinerators. Nowadays, with the development of cities, the proper disposal of urban waste and industrial waste has become an urgent issue in contemporary urban management.
Performance of Refractory Materials Used in Waste Incinerators
The performance of refractory materials used in waste incinerators includes resistance to thermal shock, high abrasion resistance, good resistance to alkali erosion and acid erosion, and resistance to various chemical corrosion and peeling.
The working temperature of refractory materials used in waste incinerators generally does not exceed 1300°C, and the chemical erosion of refractory materials by gases (such as CLSOCO) generated during waste incineration is extremely serious. Refractory materials used in waste incinerators can be divided into refractory bricks and refractory castables. Refractory bricks mainly include clay bricks, high-alumina bricks, and silicon carbide bricks. Refractory castables include clay castables, high-alumina castables, silicon carbide castables, and refractory plastics.
Example of Mobile Solid Waste Incinerator for Vehicles
The mobile solid waste incinerator for vehicles is a box-shaped industrial kiln that can be continuously transferred with the working site of garbage processing, using the method of car transport, which is simple and fast. The only limitation is that the solid waste that can be processed is restricted to light industrial waste, and cannot process some household waste and hazardous waste. There is no pollution gas and smoke during the incineration process.
The incinerator’s design can achieve the effect of smoke self-circulation and self-incineration, which changes the previous problem of large amounts of polluting gases and smoke produced by waste incineration. The decomposition temperature is between 1300-1500℃, which promotes the full combustion and decomposition of the waste in the furnace, and the ashes of the incinerated waste are removed manually after sinking through the grate.
Currently, during the use and research of the mobile solid waste incinerator for vehicles, it has been found that the incineration system and the purification system of the kiln are not easily damaged, but the refractory castables and grates inside the pyrolysis furnace have a very high damage rate, which seriously affects the incineration efficiency.
Refractory castables are a kind of water-mixed unshaped refractory material that is solidified with a binder. It has a very wide range of applications and can be used to achieve seamless masonry in the furnace. As the incinerator is used for a longer time, the refractory castables show surface pulverization, cracks, and uneven surfaces. Later, arc-shaped refractory bricks were used, which were built with refractory mud in the furnace. Since the furnace’s shape is cylindrical with a diameter of about 1.8m, arc-shaped refractory bricks were used.
With the use of refractory mud to bond the refractory bricks from bottom to top, the defect of the bricklaying is the worker’s gray seam. About 5 tons of refractory bricks are used for each furnace. During use, the refractory bricks are found to be eroded too quickly by the gas of the incinerated waste, and their service life is shorter than that of the refractory castables.
Later, the refractory materials of the furnace were redefined. High-alumina clinker, corundum powder, and active alumina powder were selected for the refractory castables, and #90 fused alumina cement was added as a binder. The service life of the furnace with the produced refractory castables was extended by nine months compared to the previous refractory materials used, and the effect was obvious. Later, it was analyzed that the key to the use of refractory castables in the furnace was the selection of raw materials, the ratio of raw materials, and the high-temperature strength of the product.
After the successful use of refractory castables in the furnace, the production of the grate was also changed to the same refractory castables. Previously, cast iron was used as the grate, but its weight was large, and its melting point was low. After two months of use, it broke down, and the cost of replacing it was 1,820 dollars, which was expensive.
By analyzing the shape that can be made with refractory castables, the production of the grate was changed accordingly. The grate in the furnace must be able to withstand the weight of the materials and the high temperature in the furnace. The production cost of the new grate is reduced by more than half, and its service life is much longer than that of the cast iron grate.
The garbage incinerator is an important undertaking in the battle for defending the blue sky, and it is also a key component of the incineration system. Therefore, the selection of refractory castables should be defined based on the combustion environment and the reasons for damage. Only by choosing the appropriate refractory castables can the kiln be kept working stably for a long time.
