Лако-красочные материалы — производство

The doped hydrate is filtered with rotary vacuum filters (s) to remove water until a TiO2 content of ca. 30-40% is reached. Pressure rotary filters or automatic filter presses can also be used to obtain a TiO2 content of ca. 50%. Some of the water — soluble dopants are lost in the filtrate and can be replaced by adding them to the filter cake before it is charged into the kiln. Calcination is performed in rotary kilns (t) directly heated with gas or oil in countercurrent flow. Approximately two-thirds of the residence time (7-20 h in total) is needed to dry the material. Above ca. 500 °C, sulfur trioxide is driven off and partially decomposes to sulfur dioxide and oxygen at higher temperatures. The product reaches a maximum temperature of 800-1100 °C depending on pigment type, throughput, and temperature profile of the kiln. Rutile content, particle size, size distribution, and aggregate formation are extremely dependent on the operating regime of the kiln. After leaving the kiln, the clinker can be indirectly cooled or directly air-cooled in drum coolers (u).

The exhaust gas must have a temperature of >300 °C at the exit of the kiln to prevent condensation of sulfuric acid in the ducting. Energy can be saved by recirculating some of the gas to the combustion chamber of the kiln and mixing it with the fuel gases as a partial replacement for air. Alternatively, it can be used for concentrating the dilute acid (see Section 2.1.З.5.). The gas then goes to the waste-gas purification system.