Filtration Properties of Green Liquor Sludge, 1997 Minimum Effluent Mills Symposium Proceedings

In this study, the filtration properties of green liquor sludge were investigated. Two different experimental set-ups were used: one for low pressure differences (50 - 300 kPa) and one for high pressure differences (2-10 MPa). Green liquor sludge from four different pulp mills were investigated in the low pressure tests. The influence of pressure and the addition of calcium, magnesium and aluminium ions were investigated. The high pressure tests investigated the influence of the applied pressure. The low pressure filtration tests showed that green liquor sludge is quite compressible material (the compressibility coefficient is approx. 0.6) and that the specific filtration resistance could differ by one order of magnitude between different mills (10 12 - 10 13 m/kg). It was found that the addition of aluminium, as well as calcium, ions improved the filtration properties, whilst the addition of magnesium makes them deteriorate. Furthermore, it was found that there was a reasonable agreement between the data obtained in laboratory tests and that used in mathematical models and in measurements made at a pulp mill. The high pressure tests showed that a considerable amount of water can be squeezed out of the filter cake at high pressures.