The Blue Ridge Paper Products (formerly Champion), Canton mill, NC, recycles both the Eop and D₀ filtrates to meet strict permit requirements, for water use and effluent colour. As part of Champion International, the mill undertook an aggressive bleach filtrate recycle strategy (the BFR process). This strategy incorporates a metals removal process (MRP, i.e., based on ion-exchange technology) and a chloride/potassium removal process (CRP, i.e., based on evaporation-crystallization of ESP dust) into the recycling operation [1]. BFR uses oxygen delignification followed by three stages of post-oxygen washing and ECF medium consistency bleaching (OD₀EopD), with recycle of bleach plant filtrate to the recovery system. To optimize bleach plant operation, the chlorine dioxide charge in the D₀ stage was reduced from a kappa factor of 0.28 to between 0.18-0.22 before the recycle began [2]. Eop filtrate is recycled to the showers of the last post-oxygen washer, and D₀ filtrate is processed through a metal removal process before being recycled to the D₀ washer. A portion of the final D-stage filtrate is sewered, because of the minimal environmental effect and the higher chloride load that would have to be recovered.

The degree of closure for D₀+Eop filtrates was reported as >80% in 1998. During periods of substantial recycle, the bleach plant COD discharge was reduced by about 75-80%. The colour discharged from the pine operation decreased from about 9070 to 2270 kg/d. Several measures were taken to reduce the amount of tramp water entering the fiberline, which increased the amount of filtrate that can be recycled at a given evaporator load. Specific changes included using filtrate for washer wire cleaning showers, replacing a water doctor on the screen decker with an air lift take-off, and removing air compressor seal water from the air used to pressurize the compaction baffle washers [1].

In 2001, about 75% of the D₀ filtrate was being processed through the MRP prior to recycle. Some scaling had been observed in the bleach plant washers. The degree of recycle was based on a target of 80%, but varied because of process variability. Most of the filtrate from the final D stage was also recycled. The energy cost was within the expected range. The BFR process was used with the softwood operation, although some recycle was done on the hardwood line as well, but without the MRP. The CRP met expectations. Over 90% Cl and K removal was achievable, but the CRP system was run to provide a Cl concentration of 3.5 g/L in white liquor. No problems were observed with plugging or corrosion in the recovery boiler [3].

1. Caron, J.R. and Delaney, G., Initial Learning from the BFR Demonstration, 84th Annual Meeting, Technical Section, CPPA, Montreal, QC, January 27-28, Book A, pp. 379-384, (1998).

2. Stratton, S.C. and Ferguson, M., Process Report on the BFR^™ Technology Demonstration – December 1996, 1997 TAPPI Environmental Conference and Exhibits, Minneapolis, MN, May 5-7, Book 1, pp. 423-428, (1997).

3. Personal communication with the mill (July 2001).