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SEPARATION METHODS FOR CLOSED-LOOP TECHNOLOGY IN BLEACHED KRAFT PULP MANUFACTURE

Objective



The pulp and paper industry has a great potential to develop its operation into a
truly ecocyclic production system. A higher degree of system closure of the
pulping process leads to problems due to the accumulation of different substances.
It is therefore necessary to introduce internal separation techniques which clean the
liquid flow in the mill. Another issue of great importance is to solve the water
balance in an reasonable way which means reuse of evaporator condensates. The
overall objective in this project proposal is by new separation techniques find
solutions to 'bottlenecks' earlier identified in closed-loop manufacture of bleached
chemical pulp. The reach the main objective, the project is divided into four parts
with their corresponding objectives :

1. Reuse of condensates from the black liquor evaporation : Condensates from
the black liquor evaporation have to be reused in a closed-loop process. The
smell is a critical parameter in products used in food packages. Bad smell
in process water can be transferred to pulp and paper. Consequently, the
black liquor condensates need further treatment to remove the smell-creating
substances. We intend to develop methods to produce washing water from
condensates for use in the bleach plant when filtrates are recycled.

2. Handling of accumulating inorganic elements : Inorganic non-process
elements, NPE's, will accumulate in a closed-loop process and cause very
severe negative effects such as scale, deposits, high content of inerts in lime
cycle and negative effects in TCF-bleaching. NPE's such as Al, Si, P, Ca,
Ba, Mn, etc can today only be purged in very limited ways or not sufficiently
effective. We suggest a technology which enables these elements to be
purged in a precipitation/separation-step from a flow of acidic or neutral
bleach plant filtrate which would offer an alternative way to solve the water
balance from the mill and at the same time purge accumulated substances.
However, it is not yet known how a high increase of dry solids content in
liquor affects the efficiency of NPE's precipitation and the separation of
precipitate. This will be clarified.

3. Handling of accumulating organic substances : We will develop and compare
two alternative ways to achieve a tight internal closure of a bleaching stage
possible - membrane filtration and biological treatment. Today we know that
this type of integration of a bleaching stage usually result in high chemical
consumptions and a lowered pulp brightness.

4. Process integration of separation technologies : The different separation
technologies studied in this project proposal will affect the water balances
in a closed-loop mill when they are integrated into the process. The main
objective is to study these consequences by mass balance calculations with
simulation programme, e.g. MOPS, PULPSIM or GEMS. Changes in the
water balance, scaling in the evaporation, and build up of organic substance
in the bleach plant are examples of consequences which will be illustrated
by an analysis of the whole process.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

S.T.F.I.
Address
Drottning Kristinas Väg, 61 - P.o. Box 5604
114 86 Stockholm
Sweden

Participants (3)

CENTRE TECHNIQUE DE L'INDUSTRIE DES PAPIERS, CARTONS ET CELLULOSES
France
Address
Domaine Universitaire - B.p. 251
38044 Grenoble
OY KESKUSLABORATORIO
Finland
Address
P.o. Box 70
02151 Espoo
TECH-SEP S.A.
France
Address
Chemin Du Pilon, 5 - Saint Maurice De Beynost
01703 Miribel