USING EVAPORATORS TO ACHIEVE ZERO EFFLUENT AT A BCTMP PULP-MILL

Pulp-making is a very water-intensive enterprise, but the water recove ry system at Millar Western Pulp allows the plant to use eight times l ess water than a conventional mill of its type (68 m-3/hr makeup water vs. 568 m3/hr for the same size conventional mill) and eliminates any effluent discharge to the local river. The plant is the first pulp mi ll in the world to operate a successful zero liquid discharge system. Effluent from the thermomechanical pulping process is concentrated fro m 2 percent solids to 35 percent solids by three falling film vapor co mpression evaporators, followed by two steam-driven concentrators whic h further concentrate the effluent to about 70 percent solids. Of the 400 m3/hr of effluent sent to the system, 391 m3/hr is recovered as hi gh purity water for reuse in the pulping process. Solids are burned in the boiler; the smelt is cast into ingots and stored on site for futu re chemical recovery.