Discussion
605
The authors objected to the large addition of fuel necessary to incinerate sludge for lime recovery.
In American practice as previously described, the "sludge" is just a portion of the slaked lime and is
reburned only after it has become lime mud. The extra energy required is almost negligible.
Another objection to the use of the massive lime process (not given in the paper) was the fear that
an increase of chlorides would result in excessive corrosion. On this supposition the designers were
willing to separate the lime sludge recovery process from the rest of the mill, and thereby to add all of
the equipment shown in Figure 1, but by integrating massive lime precipitation into the mill process,
the only equipment really needed is settling tank No. 1 and perhaps the vacuum filter.
During a 16-month demonstration project by International Paper Company
4 at Springhill,
Louisiana, it #as shown that green liquor normally contains approximately 80 mg/1 chloride. The
addition of the massive lime process added only 20 mg/1 to give a total of 820 mg/1. This increase of
chloride is negligible. If the increase of chloride in the lime sludge is feared, it would be easy to wash
the sludge on the vacuum filter to eliminate all but traces of chloride. Hence, it seems unreasonable to
base costs for massive lime precipitation on a non-integrated process, because integration is the major
appeal of massive lime precipitation. On the other hand, the cost of alum precipitation must be based
upon all of the process equipment shown in Figure 4, because it cannot be integrated into the pulping
process.
Alum Recovery
Apparently the authors were able to recover only 92 percent of the alum in the laboratory.
Considering the massive doses used it appears that about 500 mg/1 of alum is not recovered and this,
together with the sulfuric acid required, represents a significant cost. Furthermore, laboratory
experience with alum sludge is deceptive. Alum sludge is quite difficult to treat under full-scale
conditions.
Costs
The comparative costs should have been based on the most economical feasible practice for each
process. It is regrettable the authors did not give complete information on sizes of reactors and all
other factors used in estimating comparative costs. It is not easy to compare costs in one country with
costs in another unless these data are provided.
REFERENCES
1 BERGER, H.F., GEHM, H.W. and HERBET, A.J., "Decolorizing kraft waste liquors" - U.S.
Patent 3,129,464 (Feb. 4, 1964).
2 Rohm and Haas Company - "Decolorization of kraft pulp bleaching effluents using Amberlite
XAD-8 polymeric adsorbent" - Philadelphia (1967).
3 WILEY, A.J., AMERLAAN, A.C.F. and DUBEY, G.A., "Application of reverse osmosis to
processing of spent liquors from the pulp and paper industry" - TAPPI 50, No. 9, 455-460 (1967).
4 International Paper Company - "Evaluation-demonstration of the massive lime process for the
removal of color from kraft pulp mill wastes" - EPA Project No. 12040 DYD (in press).
Reply
The essential part of the criticism made by my two discussers is based on an economical
comparison between lime and alum processes. However, Mr Gould surprises me by refering to Dence's
studies on lime precipitating process since I gave a summary of the conclusions of this study and
included it as a reference. It is a matter of fact that if just a partial color removal from bleached kraft
pulp waste waters is wanted, it is possible to simplify the lime process, avoiding recarbonation,
integrating calcination of sludge in the lime manufacturing works and so obtaining a very competitive
treatment cost.
But in our case, the research which a French group of papermills asked us to carry out had to be a
very elaborate process allowing — thanks to final treatment with activated carbon - a high quality
water fit to be reused to be obtained.
In these conditions, we devised a process giving very high color removal efficiency, more than 90%
both with the sodation effluent and the chlorination - sodation mixed effluent.
The favourable pH for treatment with activated carbon being near 5,4 one sees that the comparison
can be done only with a very complete lime process including recarbonation step.
In contrast to American practice French pulp mill owners asked us not to integrate sludge
calcination systems with devices existing in the mill for fear of corrosion by chlorides.
So in answer to Mr. Sanks we employed the following materials:
605
The authors objected to the large addition of fuel necessary to incinerate sludge for lime recovery.
In American practice as previously described, the "sludge" is just a portion of the slaked lime and is
reburned only after it has become lime mud. The extra energy required is almost negligible.
Another objection to the use of the massive lime process (not given in the paper) was the fear that
an increase of chlorides would result in excessive corrosion. On this supposition the designers were
willing to separate the lime sludge recovery process from the rest of the mill, and thereby to add all of
the equipment shown in Figure 1, but by integrating massive lime precipitation into the mill process,
the only equipment really needed is settling tank No. 1 and perhaps the vacuum filter.
During a 16-month demonstration project by International Paper Company
4 at Springhill,
Louisiana, it #as shown that green liquor normally contains approximately 80 mg/1 chloride. The
addition of the massive lime process added only 20 mg/1 to give a total of 820 mg/1. This increase of
chloride is negligible. If the increase of chloride in the lime sludge is feared, it would be easy to wash
the sludge on the vacuum filter to eliminate all but traces of chloride. Hence, it seems unreasonable to
base costs for massive lime precipitation on a non-integrated process, because integration is the major
appeal of massive lime precipitation. On the other hand, the cost of alum precipitation must be based
upon all of the process equipment shown in Figure 4, because it cannot be integrated into the pulping
process.
Alum Recovery
Apparently the authors were able to recover only 92 percent of the alum in the laboratory.
Considering the massive doses used it appears that about 500 mg/1 of alum is not recovered and this,
together with the sulfuric acid required, represents a significant cost. Furthermore, laboratory
experience with alum sludge is deceptive. Alum sludge is quite difficult to treat under full-scale
conditions.
Costs
The comparative costs should have been based on the most economical feasible practice for each
process. It is regrettable the authors did not give complete information on sizes of reactors and all
other factors used in estimating comparative costs. It is not easy to compare costs in one country with
costs in another unless these data are provided.
REFERENCES
1 BERGER, H.F., GEHM, H.W. and HERBET, A.J., "Decolorizing kraft waste liquors" - U.S.
Patent 3,129,464 (Feb. 4, 1964).
2 Rohm and Haas Company - "Decolorization of kraft pulp bleaching effluents using Amberlite
XAD-8 polymeric adsorbent" - Philadelphia (1967).
3 WILEY, A.J., AMERLAAN, A.C.F. and DUBEY, G.A., "Application of reverse osmosis to
processing of spent liquors from the pulp and paper industry" - TAPPI 50, No. 9, 455-460 (1967).
4 International Paper Company - "Evaluation-demonstration of the massive lime process for the
removal of color from kraft pulp mill wastes" - EPA Project No. 12040 DYD (in press).
Reply
The essential part of the criticism made by my two discussers is based on an economical
comparison between lime and alum processes. However, Mr Gould surprises me by refering to Dence's
studies on lime precipitating process since I gave a summary of the conclusions of this study and
included it as a reference. It is a matter of fact that if just a partial color removal from bleached kraft
pulp waste waters is wanted, it is possible to simplify the lime process, avoiding recarbonation,
integrating calcination of sludge in the lime manufacturing works and so obtaining a very competitive
treatment cost.
But in our case, the research which a French group of papermills asked us to carry out had to be a
very elaborate process allowing — thanks to final treatment with activated carbon - a high quality
water fit to be reused to be obtained.
In these conditions, we devised a process giving very high color removal efficiency, more than 90%
both with the sodation effluent and the chlorination - sodation mixed effluent.
The favourable pH for treatment with activated carbon being near 5,4 one sees that the comparison
can be done only with a very complete lime process including recarbonation step.
In contrast to American practice French pulp mill owners asked us not to integrate sludge
calcination systems with devices existing in the mill for fear of corrosion by chlorides.
So in answer to Mr. Sanks we employed the following materials: