On-line determination of green-liquor with FT-NIR

The use of Fourier-transform Near-Infrared spectrometry (FT-NIR) has been made for on-line measurement of green liquor compositions, such as TTA, EA, carbonate, sulphide, sulphate, thiosulphate, and reduction efficiency (RE) in raw green liquor. The technical feasibility of using this analyzer as an on-line monitoring system for dissolving tank TTA control as well as for reduction efficiency monitoring has been demonstrated during normal mill operation as well as for simulated upset conditions. FT-NIR data for TTA has tracked well with dissolver density values. In addition, FT-NIR reduction-efficiency data has been correlated to changes in black-liquor solids content; primary air flow and black-liquor firing rate. Online TTA control could help stabilize TTA which will stabilize recausticization operations. The ability to monitor reduction efficiency online will provide operators with better understanding of boiler conditions that lead to “poor” conditions with high TRS and dead-load.( PAP-TAC Online news July 2010)