UPM / Closed
UPM is seeking innovations how to utilize green liquor dregs from pulp production
Green liquor dregs from three UPM pulp mills in Finland is the main waste stream to the landfill and innovative utilization ideas are needed for the use of the dregs.
- industry innovation and infrastructure
- responsible consumption and production
Green liquor dregs from three UPM pulp mills in Finland is the main waste stream to the landfill. Dry solids amount is about 25 000 t/a. Only some dregs are used for instance in soil construction and as desulphurising agent in solid fuel power plants. More useful utilization ideas are needed.
The kraft pulping process (also known as sulphate process) is a technology for conversion of wood into wood pulp consisting of almost pure cellulose fibres. In the process wood chips are cooked in high temperature and pressure with a mixture of sodium hydroxide and sodium sulphide, (known as white liquor), that break the bonds that link lignin to the cellulose. About half of wood is dissolving in the process. In the washing stages the used cooking liquors (black liquor, containing dissolved wood material and cooking chemicals) are separated from the cellulose fibres. After concentrating of black liquor by evaporating water from the liquor black liquor is burned in recovery boiler. Black liquor firing in the recovery boiler generates sodium carbonate (Na2CO3) and sodium sulphide (Na2S) as inorganic fuel products, which flow in the form of chemical smelt from the bottom of the boiler furnace into water in the dissolving tank (green liquor). Green liquor insoluble compounds are separated as green liquor dregs. The composition of dregs is quite near of wet wood ash and water content is about 50 %. Depending on separation method dregs contain also even 50 % (of dry solids) lime, if pre-coat drum filter is used and it contain also some alkaline (green liquor residuals).
Ca concentration is high and the main source is the lime mud added in pre-coat filter. The concentration of Mg and S are high, Concentrations of Mn, Si, Al, K and P are also relatively high. Zn is the only trace metal that has a relatively high concentration. See typical composition of green liquor dregs (pre-coat filter, pre-coat is lime) attached.