Low-temperature sintering

The production process for crockery and technical porcelain was optimized in the joint project "Low-temperature sintering". Raw material mixes were processed in such a way that porcelain can be produced at a sintering temperature of 1,220 °C. Sintering at a lower final temperature saves considerable amounts of natural gas. In addition, domestic rather than imported raw materials can be used as well as recycled materials.

Producing technical porcelain and crockery is a very intensive process in terms of the raw materials and energy used. The prices of all ceramic raw materials are rising and reserves of the natural gas required are declining. This is why it is essential to use resources optimally and sustainably.

The project partners investigated which of the imported raw and auxiliary materials can be substituted by domestically-sourced substances. Raw material costs can be lowered by 20 percent due to the resulting shorter transport routes. In addition, resources can be conserved by using recycled materials. The use and costs of raw materials are reduced by grinding porcelain shards and rejects to porcelain powder and reprocessing it. This also saves landfill costs and avoids dumping materials which may be hazardous to groundwater. In order to use the raw materials more efficiently, product quality was also improved through the targeted use of "fireproof" clays so that there are fewer rejects.

In addition, the project partners developed ultra-light and highly porous firing shelves. Because the sintering temperature was able to be reduced by 60 °C from 1280 to 1220 °C, the use of this kiln furniture is possible even with the lower stability resulting from the high porosity. The reduced material use for the kiln furniture means that less gas is required to heat it.

Lowering the firing temperature opens up the possibility to substitute the fossil fuel natural gas by renewable wood gas as the fuel for the sintering furnaces.

In total, the new process can save up to 60 percent raw materials due to the use of recycled materials. Material costs can be reduced by about 50 percent and energy costs by about 20 percent. An additional CO₂ saving results from reducing the volume of natural gas used or replacing this with wood gas.

The technologies studied can be used throughout the ceramics industry. Substituting natural gas by wood gas can be transferred to other gas-fired installations in the medium term.