Hie Chemrec Process
Chemrec has built a number of small demonstration plants, including a 75 tDS/d (tons dry solids per day) as well as one commercial unit of 300 tDS/d (Chemrec, see Figure 5-41). These are all based on quench technology, and most use air as an oxidant. One of the pilot plants was converted to oxygen gasification, and a second oxygen-blown unit is under construction at the Energy Technology Centre (ETC) at Pitea, Sweden, close to the Kappa Kraftliner pulp and paper mill.
The Chemrec reactor is a refractory-lined entrained-flow quench reactor operating at a temperature of 950-1000°C. The organic material is gasified in the reaction zone. The inorganic material is decomposed into smelt droplets consisting of sodium and sulfur compounds. Carbon conversion is greater than 99.9%; tar formation is low.
The smelt droplets are separated from the gas phase in the quench zone, after which they are dissolved in the quench liquid to form a green liquor solution. The synthesis gas leaving the quench zone is scrubbed to remove particulate matter, primarily entrained alkaline particles in a countercurrent condensing tower.
In the booster configuration in which the gasifier is installed in parallel to an existing black liquor boiler as a de-bottlenecking measure, air is used as oxidant. The syngas is burnt untreated in a boiler to raise steam. Sulfur removal is effected by scrubbing the flue gas with oxidized white liquor.
Alternatively, a black liquor gasification combined cycle (BLGCC) can be used to replace the conventional black liquor boiler. In this configuration the gasifier is
oxygen blown at about 30 bar. A syngas cooler is installed for maximum heat recovery. Sulfur removal is then from the synthesis gas using conventional acid-gas removal technologies (see Chapter 8). A full BLGCC configuration can double the electric power production per ton of black liquor compared with a new recovery boiler.
The first commercial-sized booster unit was built for the Weyerhaeuser Company at New Bern, NC in 1996. Initial problems, particularly with respect to the refractory lining, were overcome, and in 1999 the plant achieved an availability of 85%. However, chloride-induced stress corrosion cracking has developed in the stainless steel reactor shell, and this will be replaced using a different metallurgy during 2003.
The use of a BLGCC can bring the same environmental advantages to pulp processing as other IGCC systems, as described in Chapter 7.