– Waste incineration plants
To ensure the cost-efficient operation of a waste incineration plant, the technical reliability and resistance of the plant components used must meet high requirements. For example, during the use of rotary furnaces in the incineration of hazardous waste, operating temperatures of 1300 °C are reached. The heat from combustion at a waste incineration plant can be used for steam generators, the steam then being used with a turbine and electric generator for power generation.
As the chemical composition of the waste generally varies widely, the flue gases and the non-incinerated residues are very different in their composition too. In addition to containing CO2 and H2O, the incineration products regularly consist of CO, Cl- and F-containing and sometimes toxic substances as well as heavy metal compounds in the ash. The technical requirements to be met by the plant components in direct contact with such substances are correspondingly high.
On account of the extreme thermal, corrosive and abrasive conditions prevailing in the waste incineration plant and the downstream steam generator, the use of high-purity, dense-sintered oxide and non-oxide ceramic materials is sometimes the only option to avoid frequent downtime.
Some of the technical properties of such materials (e.g. Al2O3, MgAl2O4, doped ZrO2, Si3N4, SiC, AlN) relevant for operation of the plant are summarized in the following:
- Material density > 98 % of the theoretical value
- Optimized microstructure for high shape and dimensional stability even at temperatures >1000 °C
- Thermal resistance in reducing and oxidizing conditions sometimes well above 1500 °C
- High resistance to thermal shock, especially with the use of non-oxide ceramic materials
- High chemical corrosion resistance
- High mechanical wear resistance
- High thermal conductivity when Al2O3 and especially SSiC, SiSiC and AlN ceramics are used
- High electrical insulation at high temperature in severely corrosive conditions
In recent years, high-purity, dense-sintered Al2O3 ceramics have proven highly corrosion-resistant heat exchanger and container materials in the decomposition of hazardous waste in supercritical water.