Membrane applications in the pulp and paper industry: Experience on lab, pilot and industrial scale

Abstract

1. IntroductionIn the last two decades the pulp and paper industry has put significant efforts into improving its productivity and reducing its fresh water consumption. Among the different approaches, recycling close to the source has been identified as one of the most effective ways to reduce water consumption and recycle valuable components. The focus of this paper is thus on the different opportunities of membrane technology in the water, by-product and utilities/chemicals loop. The development of membrane technology for use in the pulp and paper industry will be reviewed and the development of new applications from lab to industrial scale will be presented. 2. Membranes applications in the loops of the pulp and paper industryMembrane applications have established themselves three main loops of the pulp and paper industry: the water, the by-product and the utilities/chemical loop. In the following key applications in each of these loops will be highlighted. For the water loop, the use of membrane technology in the pulping and paper making process will be presented, e.g. white water recirculation at the paper machine. Further, the combination of a membrane bioreactor (MBR) with ultrafiltration/nanofiltration /reverse osmosis for end-of-pipe treatment as an alternative to production integrated recycling will be discussed. In the by-product loop, the membrane applications will cover amongst others the concentration of lignin and black liquor and the recycling of the permeate back to the pulp mill. Finally, for the utilities/chemicals loop, the focus will be on applications of membrane technology for the recovery and recycling of e.g. coating colour and bleaching effluent. 3. Application development from lab to industrial scaleThe polishing of evaporator condensate is one of the more recent applications for membrane technology in the pulp and paper industry. Ultrafiltration, nanofiltration and reverse osmosis are often suitable process alternatives to polish evaporator concentrate. Thus these processes separate the evaporator condensate into (1) a retentate stream containing most of the COD/BOD, which has to be treated separately, and (2) a permeate stream, which might be suitable for recycling/discharge. In this application study, important aspects at the different stages of scale-up from lab to industrial scale will be highlighted leading to the design of the full-scale plant. In this final design ultrafiltration with a ETNA10PP membrane (Alfa Laval Nakskov, Denmark) was used to concentrate the COD/BOD by a volume concentration factor (VCF) of 50, while the COD/BOD in the permeate was in line with discharge limits. The operating pressure of the plant was set to 3-4 and the temperature was 60 oC. At the operating conditions the flux decreased from 55-60 l/(m2h) at VCF of 10 to 45–50 l/(m2h) at a VCF of 50. The proposed ultrafiltration system to treat 50 m3/h was divided in four loops and contained a total of 800 m2 of membrane area. The resulting streams from the plant are a permeate stream of 49 m3/h and a retentate stream of 1 m3/h. 4. ConclusionsOverall, this paper will show that the integration of membrane technology can have a significant impact on productivity and water consumption in the pulp and paper industry.