| 摘要 |
A process for concentrating dilute phosphoric acid, in which dilute phosphoric acid is heated by an indirect heat exchange to a temperature below its boiling point and is subsequently sprayed and directly contacted with hot gases, whereafter water vapor and fluorine compounds are withdrawn with the exhaust gas and the fluorine compounds are removed from the exhaust gas. The process is characterized in that the dilute phosphoric acid is heated by an indirect heat exchange with heat to be extracted from the absorption system of a sulfuric acid contact process plant, the heated dilute phosphoric acid is sprayed into and phosphoric acid is circulated through two successive concentrating stages and in said stages is sprayed and directly contacted with a heated gas mixture consisting of the tail gas of the sulfuric acid contact process plant and of admixed air, the gas mixture is heated by an indirect heat exchange with surplus gas heat of the gases which have left the first contacting stage of the sulfuric acid contact process plant and have partly been converted to SO3 and have not yet entered the high-temperature interstage absorption system, the heated gas mixture is conducted through the first and second concentrating-stages in succession and the exhaust gas is subjected to a plurality of scrubbing stages for removing the fluorine compounds by absorption. The process of the invention avoids the use of primary energy or steam for producing the hot gases and also enables one to minimize the operating costs as well as the acid fume content of the exhaust gas. |
