Drying apparatus and use thereof and process for producing an isocyanate using the drying apparatus

A drying apparatus configured to perform a drying operation of a starting material to be dried to obtain a dried material and a vapor phase, comprising:

• a dryer comprising a heatable drying space having a feed opening for the starting material, a discharge opening for the dried material and a passage for the vapor phase, wherein the passage opens into a vapor dome comprising a discharge opening for the vapor phase;
• a condenser connected downstream of the discharge opening for the vapor phase;
• and
• an unheated vapor conduit connecting the discharge opening for the vapor phase with the condenser;
• wherein
• (i) the vapor dome, but not the unheated vapor conduit, is configured so that partial condensation of the vapor phase occurs in the vapor dome, but not in the unheated vapor conduit, during the drying operation, or
• (ii) the unheated vapor conduit, but not the vapor dome, is configured so that partial condensation of the vapor phase occurs in the unheated vapor conduit, but not in the vapor dome, during the drying operation, or
• (iii) the vapor dome and the unheated vapor conduit are configured so that partial condensation of the vapor phase occurs in the vapor dome and the unheated vapor conduit during the drying operation,
• wherein a drainage means for constituents of the vapor phase liquefied in the partial condensation is arranged:
• (1) inside the vapor dome in the case where the vapor dome, but not the unheated vapor conduit is configured so that partial condensation of the vapor phase occurs in the vapor dome, but not in the unheated vapor conduit, or
• (2) inside the unheated vapor conduit in the case where the unheated vapor conduit, but not the vapor dome is configured so that partial condensation of the vapor phase occurs in the unheated vapor conduit, but not in the vapor dome, or
• (3) inside the vapor dome and inside the unheated vapor conduit in the case where the vapor dome and the unheated vapor conduit are configured so that partial condensation of the vapor phase occurs in the vapor dome and the unheated vapor conduit, and
• wherein the drainage means is configured such that the constituents liquefied in the partial condensation are discharged via a discharge opening (i) from the vapor dome, or (ii) from the unheated vapor conduit, or (iii) from the vapor dome and from the unheated vapor conduit, thereby separating the liquified constituents from constituents of the vapor phase not liquefied in the partial condensation.