Regeneration of FGD waste liquors: Production of ammonium and potassium sulfate mixed fertilizer. Quarterly technical report, October 1993--December 1993

摘要

In the 2nd quarterly report, we discussed the lime/limestone process which precipitates N-S containing compounds by adding lime/limestone in a narrow pH range, and which can be an alternative to the K(sub 2)SO(sub 4) process. In this report, we focused on investigations of the lime/limestone process. First, we established an overall flow diagram for the lime/limestone process. Based on the diagram, we performed preliminary experimental investigations to outline practical process conditions. Out major investigations concerned about effects of pH on precipitation of the N-S compounds and precipitation characteristics of N-S compounds in a continuous crystallization system. We also performed an experimental investigation to study crystallization characteristic of the ammonium sulfate in the hydrolysis liquor. In studying effects of pH, we performed batch precipitation of the N-S compounds in a broad range of pH and investigated the effects of pH on the amount of required lime, the amount of the precipitate, and the fraction of N-S compounds precipitated. The result revealed the optimum range for precipitation of N-S compounds to be pH = 7.6--8.6. In studying continuous crystallization characteristics of the N-S compounds, a bench scale 4-liter continuous crystallization system was built to compare a typical Mixed-Suspension- Mixed-Product-Removal (MSMPR) crystallizer and Double-Draw-Off (DDO) crystallizer. In a preliminary test, the DDO was shown to be superior by increasing the average size of the precipitated crystals of N-S compounds from 97 (mu)m to 142 (mu)m and thus enhancing the filterability. In order to obtain information for a practical design of the lime/limestone process, we also set up a material balance for a 300 MWe power plant facility. A preliminary calculation showed that a process on the scale could produce approximately 56 tons ammonium sulfate fertilizer per day.