Return to AET Homepage
Reports and Communication ResourcesThe Science of ECFAbout UsEnvironmentally Preferred PaperRegulatory and Market NewsContact UsMembersResponsible Care
 
Join our Listserv
 

 

TCF AND ECF:
Separating Fact From Fiction

Is Retrofitting to TCF Manufacture
Cost-Effective?


An analysis of an article entitled "Effluent-Free Mills Possible with Existing Fiberline Equipment" appearing in the July 1994 issue of Pulp & Paper.



Summary

In a recent article [1] by Richard Albert, Parsons Main Inc., "Effluent-Free Mill Possible with Existing Fiberline Equipment," (Pulp & Paper, July 1994), the headline creates the impression that retrofitting to a TCF "effluent-free" pulp mill is possible with existing equipment. However, scrutiny of the article reveals that retrofitting is hardly discussed at all.

The author fails to inform the industry, government, and interest groups of the significant economic consequences which would face approximately 100 mills in the US if TCF pulp manufacture were required. Analyses have shown the capital cost of converting a typical US mill from ECF to TCF manufacture ranges from $40 to $125 million, and the conversion would incur an operating cost penalty of $20 to 32 per ton. On a US industry-wide basis, conversion from ECF to TCF would cost from $2.7 billion to $8.3 billion with increased annual operating cost ranging from $140 million to as much as $340 million.

Rather than dealing with the real capital and operating cost consequences of retrofitting existing ECF facilities to TCF for the manufacture of high brightness pulp, the article examines the unlikely scenario of new greenfield mills. The article compares a greenfield ECF mill with secondary waste water treatment to unproved technology, i.e. a greenfield "effluent-free" TCF mill.

The greenfield mill comparison asserts that the capital and operating costs will be lower for the TCF "effluent-free mill." Unfortunately the analysis is flawed. Both capital and operating costs are seriously misrepresented. A revised estimate, in agreement with other studies, shows there is no capital or operating advantage to an effluent-free TCF mill.




Capital and Operating Cost Consequences of Converting
to ECF or to TCF

In a recent article by Richard Albert of Parsons Main Inc., "Effluent-Free Mill Possible with Existing Fiberline Equipment," (Pulp & Paper, July 1994), the author argues that mills should convert to TCF bleaching as a logical step towards "effluent-free" operation [1]. However, after making such an argument, the consequences of changing to such technology are not fully addressed, although the difficulty of conversion of existing facilities is recognized:

"... It is unlikely that product quality, capital investment, and operating costs can be optimized when an existing ECF mill is retrofitted for TCF operations..."

A number of studies have shown that conversion of existing mills in North America to TCF operation, as compared to conversion to ECF, would consume substantially more investment capital and incur greatly increased operating cost [2,3]. For example, Lancaster et. al. showed the following cost comparisons for a typical 1,320 ADT/d US mill [3]:

Table A:
Capital and Operating Cost for Converting to ECF or TCF
Process
Option
Capital Cost
$million
Operating Cost
$/ADT
Total Cost
$/ADT
Base Case D50CEopD - - -
ECF DEopD 18.8 9.23 13.37
ECF ODEopD 104.1 2.73 25.68
TCF OZEopP 144.3 13.72 45.54


It is clear from this work that the retrofit cost to convert an existing mill to TCF is substantially higher than for ECF. As shown in Table A above, depending on the ECF option chosen as a base, the increased capital cost to convert from ECF to TCF could range from a low of $40 million (when converting from an existing oxygen delignification ECF mill [ODEopD]) to a high of $125 million (when converting from conventional delignification ECF mill [DEopD]). The operating cost would increase as well, ranging from $20 per ton to $32 per ton.

On a total US industry-wide basis, conversion from ECF to TCF would cost from $2.7 billion to as much as $8.3 billion with increased annual operating cost ranging from $140 million to as much as $340 million.

These figures are in stark contrast to a statement in the article:

"... Based on a specific case for retrofit of a relatively modem BKME, it was found that TCF capital costs would be approximately 5% higher than ECF capital costs, and TCF operating costs would be approximately 15% lower than ECF operating costs..."

This statement is not further supported or demonstrated by any data or discussion.

Operating Cost of TCF Compared to ECF

The author makes a number of conflicting statements. Take the following for example:

"... Therefore, many kraft mills may be producing low-brightness TCF pulp with high costs for bleaching chemicals due to digester or other process limitations. The producers now have, and will continue to have, a limited market for their high cost, low brightness pulp..."

and compare it to:

"... And increasingly, it is seen that TCF bleaching costs are lower than ECF bleaching costs..."

The industry is learning that the second quote comes much closer to the truth. The increased operating cost for TCF is now well established. At the 1994 International Pulp Bleaching Conference, delegates learned that TCF pulp production, compared to ECF, increased operating costs $10-20 per tonne in a variety of mill experiments and laboratory investigations [4,5,6].




Analysis of Greenfield Mill Operating Cost Comparison

Process Chemical Losses and Make-up

The author shows chemical losses from different parts of the mill process before crediting recovery of the same chemicals due to effluent recycling. It is asserted that there would be more chemical losses in an ECF mill compared to a TCF mill (before effluent recovery). There is no basis for such a statement. Losses of sodium and sulfur would be comparable from all areas of the mill.

The author suggests washable and bound sodium losses would be greater for the ECF case (Table 5Ý). There is no rationale for such a statement. Brownstock washing would be equivalent in the two cases.

Miscellaneous losses are shown to be much higher for the ECF case compared to TCF. There is no basis for an increase in miscellaneous losses from an ECF mill as compared to a TCF mill. Therefore, the process losses should be equivalent.

Regarding make-up, the author shows that in the TCF case, the losses, for the most part, are recovered from the process. In the ECF case, purchased saltcake make-up is required, though not usually in the amount shown. However, the author fails to recognize that saltcake is a by-product of chlorine dioxide generation and is therefore available for recovery. Based on the chlorine dioxide production, adequate saltcake is available without requiring direct purchase. This of course has an impact on operating cost (Table 10ý)

The following table is a revised estimate of process chemicals makeup and losses for the ECF mill.

Table B:
Revised Process Chemicals - Losses and Makeup for the ECF Mill
Process Chemicals Summary Na
1b/ton
S
lb/ton
Process Chemical Losses (ref. TCF Case)
Recovered from Chlorine Dioxide Generation*
Excess for Disposal (in form of saltcake)
16.8
17.2
~ 0
9.1
12.0
~ 3

Chlorine dioxide production estimated at 38 lb/ton. R8/SVP-lite processes produce 1.4 lb Na2SO4 per lb. of ClO2.

 

Pulping and Bleaching Data

The design basis for calculating bleaching chemical requirements has a number of inconsistencies.

Digester Kappa No.

In the TCF case, the author has assumed the digester system to be capable of extended delignification to a kappa no. of 17. For the ECF case, a standard digester kappa no. is used ~ 25. If the comparison is greenfield, as the author noted, then the capability of extended delignification would also be installed in the ECF mill (as they are now in new greenfield mills). Therefore, to be accurate and fair, the chemical consumption should be compared at the same kappa no. As shown later, comparison at the same kappa no. creates a rather different cost picture to that presented by the author.

If the costs are not compared at the same kappa no., then the ~ 2% yield loss associated with pulping to 17 kappa no. as compared to 25, and the commensurate increase in wood requirement, should both be factored into the overall operating cost comparison. In the article, the author failed to take this into account.

Oxygen Delignification

The author has applied the same operating conditions in the oxygen delignification stage for both ECF and TCF, yet the delignification in the TCF case is 47% and in the ECF case only 32%. No explanation is given for the lower degree of delignification. If this is not adjusted, the chemical consumption for TCF would of course be lower than ECF.

Since there is no reason why both cases should not be able to achieve the same degree of delignification, the kappa no. after oxygen delignification should be the same in both cases.

If the costs are not compared at the same kappa no., then the ~ 1% yield loss associated with oxygen delignification to 9 kappa no. as compared to 17, and the commensurate increase in wood requirement, should be factored into the overall operating cost comparison. In the article, the author failed to take this into account.

ECF Bleaching Chlorine Dioxide Requirement and Cost

The author uses the sequence DEopD as the ECF bleach plant reference. All new greenfield ECF bleach plants are configured as DEop(DE)D. This allows better chemical efficiency between stages.

In the author's sequence, the kappa factor in the first stage is 0.25, the peroxide application in the extraction stage is 0.8% on pulp, and the final brightness is only 88. This is an exaggeration of the chemical requirements of an ECF sequence.

Recent published information of an oxygen delignified softwood in an DEop(DE)D sequence showed the kappa factor to be 0.19 in the first stage with peroxide addition of 0.4% [7]. Moreover, in a further publication, optimum utilization of chlorine dioxide in an ECF sequence was achieved at a kappa factor of 0.12-0.15 [8].

The cost of chlorine dioxide @ $0.55 per lb. is high for a modern R8 or SVP-lite plant. Typical chemical cost is in the range of $0.32 per lb. [9]. Hydrogen peroxide is also somewhat overstated at $0.50 per lb. A more reasonable price is $0.38 [10].

Table C:
Revised ECF Chemical Consumption--Changes from Article Only
ECF BKME
ref. Article
ECF BKME
Revised
Washed Pulp
Kappa No.

25

17
Oxygen Delignification
Kappa Number

17

9
Chlorine Dioxide Stage 1
Total Active Chlorine, %
ClO2, as ClO2, %
ClO2, lb/ton
Kappa No.

4.25
1.63
33
4

1.8
0.7
14
2
Oxidative Extraction Stage
NaOH, lb/ton
H2O2, lb/ton

34
16

14.4
10
Total Chemical Required
Chlorine Dioxide, lb/ton
Sodium Hydroxide, lb/ton
Hydrogen Peroxide, lb/ton

57
59
16

38
40
10


Table D:
Revised ECF Greenfield Pulp Bleaching Cost
Chemical
Prices*
$/lb.
ECF BKME
ref. Article
$/ton
ECF BKME
Revised
$/ton
Chlorine Dioxide 0.32** 31-35 12.16
Sodium Hydroxide 0.14 8.26 5.60
Oxygen 0.05 3.00 3.00
Magnesium Sulfate 0.25 1.00 1.00
Hydrogen Peroxide 0.38** 8.00 3.80
Sulfur Dioxide 0.13 0.65 0.65
* Calculated from article
** Per ref. 9,10
Total 52.26 26.21




Analysis of Greenfield Mill Capital Cost Comparison

The capital cost analysis, (Table 9ÝÝ in the article), compares proven technology, a greenfield ECF mill with waste water treatment, to unproved technology, a greenfield TCF mill without waste water treatment. To a certain extent, this is an "apples and oranges" comparison. There is no TCF bleached kraft pulp mill in operation that does not discharge effluent. Therefore, either waste water treatment facilities must be included in the TCF case or the analysis should compare an ECF mill that does not discharge bleach plant effluent, an equally feasible design [11,12].

However, since the capital cost comparison is "apples and oranges" the following shortcomings should be noted and accounted for:

  • The capital cost for TCF does not include any investments for spill control or management of water volumes between the many coupled processes such as:
    • pulp machine - bleach plant
    • bleach plant - brown stock screening/washing

  • The capital cost for TCF does not include allowance for ozone generation at the mill. However, the ECF capital cost includes an allowance for chlorine dioxide generation. It is equally valid for the ECF case to have "over-the-fence" chlorine dioxide as it is to have "over-the-fence" ozone. Therefore, the capital cost for ozone should be included in the TCF case or the chlorine dioxide generation capital cost removed from the ECF case. (It is noted that the capital cost for ozone is reflected in the chemical cost used by the author. Therefore if ozone capital is to be included the operating charge for ozone should be adjusted.)

  • The capital cost for ECF includes requirements for environmental studies and engineering for effluent treatment. It is inconceivable that a mill proposing a TCF effluent free mill would not require environmental studies. Furthermore, such a mill will require additional design engineering for water management.

  • Water treatment costs are substantially higher for the ECF case. However, no mill water balance is shown to justify the capital cost difference. The only water replaced by the "effluent-free" TCF case is fresh water for brown stock washing. The capital cost to treat this extra water is unlikely to be $9.5 million if the total water treatment cost is $14.5 million.

Table E:
Adjustments to Capital Cost Estimates (Changes Only)
Cost Center ECF
$ million
TCF
$ million
Water Treatment (Equivalent to ECF Case) - +9.5
Pulping (Add Extended Delignification Capability) +2.0 -
Ozone Generation - +10
Bleaching (Add additional (DE) stage) +2.0 -
Water Management and Spill Control, Tanks etc. - +15.0
Environmental Studies - +3.5
Contingency (required in ECF Case) +4.0 -
Sub-Total +6.0 +28
Total Capital Cost Estimate 631 623


Based on the above table, the capital cost estimate for the ECF and TCF cases are comparable. Accounting for all cost centres, the difference is $8 million in favour of the TCF case. However, in a budget capital cost estimate, with a total cost estimated at ~ $625-630 million, the difference is 1% and is well within the error of the estimate. Therefore it would be improper to assert that TCF effluent-free is less capital intensive than a modern ECF mill.

Analysis of Operating Cost Comparison

Table F combines the revised chemical losses, bleaching costs, and capital cost estimates into a total operating cost. The operating costs in the revised analysis are essentially the same and within the errors of such estimates.

Table F:
Revised Operating Cost Estimate
Cost Item ECF
$/ton
TCF
$/ton
Bleaching Chemicals 26.21 36.27*
Steam for Bleaching 4.37 3.75
Incremental Steam for Black Liquor Evaporation - 3.92
Cooking Chemical Make-up
Saltcake
- -
Sulfur
- 1.16
Effluent Treatment 9.00 -
Subtotal 39.58 45.10
Incremental Capital Cost
8 million for 15 yrs @ 10%
3.00
Maintenance on Incremental Capital
1.20
Total Comparative Cost 43.78 45.10
*Bleaching cost revised to reflect ozone generation on-site. Ozone charged at
$0.29/lb [9]. Also adjusted to reflect revised hydrogen peroxide price.




References

  1. Albert, R., "Effluent-Free Mills Possible with Existing Fiberline Equipment". Pulp & Paper. July 1994.

  2. "An Assessment of Industry Costs to Meet British Columbia's New AOX Regulations". H.A. Simons Ltd. June 1992.

  3. Lancaster, L., C. Yin, J. Renard and R. Phillips, "The Effects of Alternative Pulping and Bleaching Processes on Product Performance - Economic and Environmental Concerns." Proceedings, 1992, EPA International Symposium on Pollution Prevention in the Manufacture of Pulp and Paper.

  4. Helander, R., B. Nilsson and Bohman, "Development and Progress in Ozone Bleaching at the Skoghall Mill." 1994. Proceedings, International Pulp Bleaching Conference.

  5. Mokfienski, A. and B.J. Demuner, "Pilot Plant Experience with Ozone in TCF Bleaching of Eucalypt Pulp." 1994. Proceedings, International Pulp Bleaching Conference.

  6. Dillner, B. and P. Tibbling, "Optimum Use of Peroxide and Ozone in TCF . Bleaching." 1994. Proceedings, International Pulp Bleaching Conference.

  7. Young, J., G. Start and J. Lazorek, "Utilization of an Eop Stage During 100% Chlorine Dioxide Bleaching at Weldwood, Hinton." Proceedings, 1993 International Non-chlorine Bleaching Conference.

  8. Malinen, R., T. Rantanen and R. Rasimus, "ECF Bleaching of Oxygen Delignified Softwood Pulp with the Minimum Charge Of ClO2." Proceedings, 1993 Tappi Pulping Conference.

  9. Nutt, W. E., B. F. Griggs, S. W. Eachus and M. A. Pikulin, "Development of an Ozone Bleaching Process." Proceeding, 1992 Tappi Pulping Conference.

  10. Govers, T. R., "Ozone in the Pulp Mill: Alternatives and Cost." Proceedings, 1994 International Non-Chlorine Bleaching Conference.

  11. Nykanen, T. and Ryham, R., "Comparison of ECF- and TCF- Based Solutions for a Minimum Impact Mill (MIMTM)." Proceedings, 1994 International Non-chlorine Bleaching Conference.

  12. Maples, G., R. Ambady, J. R. Caron and R. Vega Canovas, "BFR: A New Process Toward Bleach Plant Closure." 1994. Proceedings, International Pulp bleaching Conference.




ÝTable 5 - Pulp & Paper, July 1994: p.83-89.

ÝÝTable 9 - Pulp & Paper, July 1994: p.83-89.

ýTable 10 - Pulp & Paper, July 1994: p.83-89.




Acknowledgment

This report was reviewed by David Forbes, Vice President, Process and Staff Engineering, BE&K Engineering Co. and Don Manolescu, Zerotech Technologies Ltd. Their comments were incorporated into the document. The Alliance for Environmental Technology (AET) gratefully acknowledges their contribution.

Return to Table of Contents