Verfahren zur Herstellung von Titandioxid nach dem Sulfatverfahren mit Energieeinsparung

摘要

In Ti02 prodn. by the sulphate process, energy is saved by using the heat of the waste calciner gas (I) for concn. of the waste H2SO4 (II). The unfiltered (I) is cooled by indirect heat exchange to a temp. above the dew point of the impurities present and the heated heat exchange medium (III) is used for heating in evapn. stage(s) for concn. of (II). (I) is pref. cooled to 190-230 deg.C, pref. in a heat exchanger of light alloy steel. (III) is pumped through the heat exchanger and evaporator(s) in a closed cycle and pref. is preheated on start-up. The waste heat from the evapn. stage(s) is used in pre-concn. stage(s). ADVANTAGE - The heat of (I) is used more efficiently than usual and no costly plant is needed. In an example (I) emerging from the calcine at ca. 350-400 deg.C was cooled to ca. 200 deg.C in an indirect heat exchanger, pref. of light alloy steel, and then to ca. 70 deg.C in a cooling tower. (III) was a heat-resistant oil or steam and was preheated to ca. 140 deg.C on start-up. This was heated to ca. 250 deg.C in the heat exchanger and circulated to a last evaporator, then at ca. 140 deg.C to a first evaporator, before recycling to the heat exchanger. (II), with an initial concn. of 23 (wt.)%, was pre-conc. to 28%, 34% and 60% acid in 3 pre-concn. stages operating at 60 deg.C, 85 deg.C and 110 deg.C, which could be heated with steam from the concn. stage(s). It was then conc. to ca. 76% acid in the first concn. stage at 140 deg.C and filtered to remove pptd. metal sulphates before concn. to 86% acid in the last stage at ca. 250 deg.C and recycled to the Ti ore or slag decomposition stage of mfr. Since (I) did not come into direct contact with (II), there was no need to purify (I) before heat exchange or (II) to remove impurities introduced by (I). Most of the heat in (I) was re-used in the process, making the energy balance esp. favourable, the rest of the heat could be re-used as warm water from the cooling tower.