| 摘要 |
Phosphoric acid having a high polyphosphate content is prepared in a continuous process by feeding orthophosphoric acid and a heating gas into an evaporating zone under conditions such that substantially all the orthophosphoric acid is entrained in the heating gas, and passing the <PICT:1036544/C1/1> heating gas containing the acid into a second zone which is maintained under conditions such that the acid coalesces to form droplets of phosphoric acid having a high polyphosphate content and removing the phosphoric acid and gas from the second zone. The retention time of phosphoric acid in evaporation zone is not more than five seconds. The orthophosphoric acid may be wet process acid containing 50-55% by weight of P2O5. The temperature of the heating gas which enters the evaporating zone at a velocity of 15-75 m/sec. may be 315-980 DEG C. and the temperature of the gas and entrained acid as it leaves may be 245-315 DEG C. The temperature in the second zone should be at least 245 DEG C. The evaporation zone is formed by the inner walls of a vessel and the outer walls of a conduit 14 passing through one wall of the vessel and terminating in an outlet at the opposite wall, the heating gas being fed through the conduit and orthophosphoric acid through the inlet 17 in the opposite wall. The heating gas containing the entrained acid is in heat exchange with the incoming gas and is led out of the evaporation zone through an outlet 19 adjacent to the point at which the conduit enters the vessel. It then passes to inert separator 21 where droplets of phosphoric acid having a high polyphosphate content coalesce and are led away via 24, gases being removed via 25 to a fume scrubber 26 before venting to the atmosphere. The heating gas is prepared by burning fuel gas in a combustion zone 11 and it may be tempered with air supplied through 16 before entry into the evaporation zone via 15. |
