Report No. PA-95-1
CONTENTS
Page EXECUTIVE SUMMARY
1
1.0 BACKGROUND
4
2.0 TEST PROCEDURE
4 2.1 Process Description 4 2.2 Sampling Description 8
3.0 TEST RESULTS
9 3.1 Pulp Quality
10 3.2 Effluent
Characteristics
11 3.3 Operating
Costs
13
4.0 CONCLUSIONS AND RECOMMENDATIONS
16
APPENDICES
Appendix A Process Flow Diagram
Appendix B Effluent/Sludge Test Results and Polymer Applications
Appendix C TAPPI Test Methods
Appendix D
Operating Cost Data Units of Consumption Unit Cost MajorAssumptions EXECUTIVE
SUMMARY
The lack of affordable, efficient, small-scale technologies for recovery of high-value, low-volume fiber, such as from poly-coated bleached paperboard, poses a significant technological barrier to their recycling. This report details the evaluation of a small-scale system for fiber recovery from milk carton/drink boxes (MCDBs). Pulp characteristics, effluent characteristics, and operating costs were monitored during the system's trial.
Typically, only large-scale paper producers/recyclers are able to sustain the high capital expenditures and low return on investment that are characteristic of most fiber recovery operations. Regenex L.L.C. (a spin-off company of Pellerin Milnor Corporation, a leading manufacturer of commercial laundry equipment) has developed a modular fiber recovery system that is a variation of an established Pellerin Milnor product line known as the continuous batch Tunnel Washer system. Due to the unique material transfer methods of the Tunnel Washer system, several process functions are combined in a single piece of equipment. The new technology also allows reasonable return on investment for value-added processing of MCDBs on a scale significantly smaller than conventional paper mill technology allows (e.g., on the order of 3 bone-dry-tons/day versus 300 bone-dry-tons/day). The modular system is characterized by both low capital cost and low operating expenses, thus making small-scale fiber recovery operations feasible.
Prototype Testing and Evaluation
The prototype system consisted of one seven-module continuous batch Tunnel Washer system. Monitored functions included loading, pulping, separating, reject handling, screening, washing/thickening, clarification of liquid streams, and overall system fluid flow. Post-consumer MCDB material from the Louisiana area was the feedstock for this trial.
Pulp Quality
Selected pulp characteristics were evaluated, including optical properties (brightness, dirt count, debris) and strength properties (freeness, burst index, tear index, tensile strength). These properties were compared to typical deink pulp specifications and historical MCDB recovered pulp.
Effluents
Effluent streams before and after clarification were evaluated for the following characteristics: Biological Oxygen Demand, Silica, Total Suspended Solids, Total Dissolved Solids, Chlorine, Total Metals
CONCLUSIONS
The following is a summary of the conclusions based on the results of the tests conducted on the continuous batch Tunnel Washer system offered by Pellerin Milnor's RE GENEX Division.
· System yield was 63.8% BDT to BDT for post-consumer MCDB.
· For variable costs to be comparable to a state of the art, optimum sized, market deink pulp mill, the yield on milk carton must be about 73% BDT to BDT. This will need to be re-evaluated when quality targets have been achieved.
· Performance/strength properties, with the exception of freeness, did not meet typical deink pulp specifications for fine paper applications, but did fall within typical historical parameters for post-consumer MCDB pulp.
· Strength properties of the post-consumer MCDB may have been influenced by the advanced state of bio-decomposition of the feed stock, which was over 6 months old.
· Loss of fines at the three sequential pulp sampling stages across the system resulted in a progressive reduction in all strength properties except tear index. Freeness increase across system also supports this theory.
· Fiber and poly-coat percentages in the composite system reject stream were 35% and 65% respectively, by dry weight.
· The only optical property to exceed typical deink pulp specifications for printing and writing and tissue grades was brightness.
· When Weyerhaeuser tested the Clarifier Feed Sample, it's pH registered 12.0, which was the same as the target pH.
· The TSS particles, in the system effluent stream, are easily floated and removed at the clarifier, visual inspection found a large portion of the TSS to be fiber.
· BOD values reported are questionable due to wide variability of values obtained during testing.
· Total Metals Analysis values show a large decrease from clarifier feed to effluent.
· No concerns were raised about the levels of metals present in the sludge from this trial.
RECOMMENDATIONS
· Need further testing/study to reduce dirt count and increase strength properties.
· Need to increase yield to a minimum of 73% BDT to BDT in order for the system to be economically viable. · Screw press should be sized for the typical load size of 80 to 100 pounds (direct feed of rejects to a screw press for dewatering is currently dependent on running loads of ( 60 pounds).
Analysis, and pH. Effluent characteristics of the MCDB system were comparable to those for a typical mixed office waste (MOW) deink system. The total metal content values from both the system effluent and the system sludge were within acceptable limits.
Operating Costs
Baseline data includes stream flow rates, operating temperatures and times, and chemical dosages. Operating costs are extrapolated to compare a Tunnel Washer system processing MCDBs with a state-of-the-art deink system processing MOW. References to operating costs include only variable cost and labor. Semi-variable costs (operating and maintenance supplies) and fixed costs (depreciation, taxes, salaried labor) are not included. The MCDB system is penalized for labor due to lower production capacity; however, the system is more cost effective than a state-of-the-art deink system for chemicals and energy. Effluent treatment and residual disposal are comparable between the two systems. The test system yield was 63.8% BDT to BDT (bone dry ton of feed stock to bone dry ton of pulp product) for post-consumer MCDB. For variable costs to be comparable to a state of the art, optimum sized, market deink pulp mill, the yield on milk carton would need to be approximately 73% BDT to BDT.
Future Development
Further development work by Regenex L.L.C. has resulted in significant optical property improvements: a dirt count of 10 PPM and debris level of 0.03%. Additional testing must be performed to demonstrate improved strength properties. (Strength properties, with the exception offreeness, did not meet typical deink pulp specifications for fine printing/writing grade paper, but did fall within typical historical parameters for post-consumer MCDB pulp.) Work is currently underway to process other waste paper feedstocks, in addition to MCDBs.
Equipment Availability
Regenex L. L. C. markets modular fiber recovery systems that can be sized to produce from 3 to 250 tons per day. For more information on current product offerings, contact: Dan Mulligan, Regenex L.L.C.; P.O. Box 400, Kenner, LA (504) 467-9591; or (206) 869-8648 (in Washington State).
Acknowledgments
The support of this project by Weyerhaeuser Company and Pellerin Milnor Corporation is gratefully acknowledged.
1.0 BACKGROUND Pellerin Milnor (PM) is located
in Kenner, Louisiana, just outside of New Orleans. They engineer, manufacture, install, and service
industrial size laundry equipment.
It has been proposed that with a few modifications, the continuous
batch Tunnel Washer system offered by Pellerin Milnor’s newly established
RE GENEX Division can be used to recycle milk carton/drink boxes (MCDB’
s). Initial trials for this application were conducted
in September of 1994. Based
on the data generated in that trial, modifications were made to the
Tunnel Washer system to prepare for additional testing. The Clean Washington Center
is engaged in investigating promising recycling technologies for various
types of recovered paper, including poly-coated bleached paperboard. The lack of affordable, efficient, small-scale
technologies to recover high-value, lower volume fiber, such as poly-coated
bleached paperboard led the Clean Washington Center to provide funds
for the evaluation of PM's Tunnel Washer system.
Weyerhaeuser provided the necessary expertise and resources
to evaluate the system prototype for operating costs, effluent characteristics
and pulp characteristics using MCDB feed stock.
During discussions of the data
generated from the September trials, Weyerhaeuser and PM decided to
focus follow-up testing on pulp quality from various stages of the
PM system, and on identifying any additional processing which would
be needed. Rather than the two four-module systems used
in the September trial (one to simulate pulping and separating, one
to simulate cleaning), this evaluation used one seven-module continuous
batch Tunnel Washer system to simulate pulping and separating.
Post consumer MCDB material, collected from areas around Louisiana,
were used in this trial. Five
100 pound batches were processed to assure that the system would reach
a steady state. 2.0 TEST PROCEDURE This section describes the
work completed by Weyerhaeuser and PM to test the Tunnel Washer system
for its potential to process MCDB's.
Section 2.1, Process Description, provides a description of
the Tunnel Washer system and the feedstock processing methodology.
A description of the tests and sampling methodology used to
evaluated the pulp and effluent quality of the MCDB feedstock is provided
in section 2.2, Sampling Description.
2.1 PROCESS DESCRIPTION This section describes the
batch system used to process MCDB's.
Rather than the two four-module systems used in the September
trial (one to simulate pulping and separating, one to simulate cleaning),
this evaluation used one seven-module continuous batch Tunnel Washer
system to simulate pulping and separating.
The MCDB processing system includes the following component
parts: loading; pulping and
separating; rejects handling; screening; washing/thickening; clarification
of liquid streams; and flow rates. Post consumer MCDB material, collected from areas around Louisiana,
were used in this trial. Five
100 pound batches were processed to assure that the system would reach
a steady state. Figure 1,
in Appendix A shows the process flow diagram for the system under
test. 2.1.1 Loading Five 100 pound batches of Milk
Carton (MC) material were weighed and placed in plastic bags. A bag of MC was dumped onto a scoop that was
hydraulically raised to deliver the material to module 1. In a commercial installation, bales of MC material
would be broken and dumped onto a weight sensitive conveyor that would
carry the material to the first module.
The conveyor is sensitive to +/-10 pounds. 2.1.2 Pulping and Separating A seven-module continuous batch
tunnel washer system was used to achieve pulping and separating (Figure
1). The entire system is enclosed,
therefore no sampling can take place until after these two operations
have been completed. As can
be seen in Table 1, the first four modules have baskets with ribs
to provide additional mechanical action to facilitate poly/fiber separation.
A change from 0.25 inch holes to 0.03 inch screen is made between
modules 1 and 2 to prevent loss of fiber that has already broken down
in module 1. The change from
0.03 inch screen to 0.25 inch holes from module four to modules five,
six, and seven insures removal of all pulp that has been separated
from the poly-coating.
Pulping pH is controlled by
the addition of sodium hydroxide (caustic), target pH which is monitored
at each of the four pulping modules was 12.
The pH measured, on site, at the clarifier, was 10.7. This pH value was less than the target of 12
because the drain trough effluent is diluted by reject water, very
dirty water from module one (R), and what normally would be counter-flow
water from module two to module one (W), (in this trial this water
went to the trough). By the time this water gets to the clarifier,
it is thoroughly mixed and diluted, resulting in a lower pH. Fresh chemicals (bleach H2O2 and caustic) are
added to modules 1-4 only, any chemicals associated with modules 5-7
occurs due to the chemical residue in the clarified water recirculated
to these modules. As seen
in Table 2, pulping temperatures are higher than separation temperatures. The system is capable of maintaining different temperatures and
chemical compositions in each module.
As the number of modules in the system increases the residence
time in each module decreases, keeping the overall time for pulping
and separating constant.
Modules 1-4 are pre-dosed with
bleach (H2O2) and caustic upon start-up of the equipment. During operation, each of these pulping modules
that contains material receives and additional half pound of H2O2
(1 pound of caustic in module 1, 3/4 pound in module 2, 3, and 4)
every time a load is transferred
forward. By the time each 100 pounds of MC enters Module
5, it has received a total of 2 pounds of H2O2 and 3.25 pounds of
caustic. The amount of caustic
addition will drop off considerably the longer the system is run due
to re-circulation of chemically rich water from the clarifier. 2.1.3 Rejects Handling Rejects from the pulping/separating
system dump out of Module 7, at location (M) into a perforated dumpster,
each time a load is transferred. Due to the limitations of the existing screw press used in the system
under test, if loads of material ( 60 pounds are run, rejects from
the system and the vibrating screen can be fed directly to a screw
press and dewatered to 25-30% consistency.
For the 100 pound loads run in this trial, rejects were removed
from the perforated dumpster by hand and fed to the screw press.
This restriction could be eliminated by the installation of
a larger capacity screw press. Screw
press effluent (V) flows into the effluent trough underneath the pulping/separating
system and is pumped to the clarifier.
Screw press solids (poly and fiber) are collected in a dumpster
for disposal at a landfill (S). 2.1.4 Screening Pulp flows through the 0.25
inch holes of the separation section (Modules 5-7) and is pumped onto a vibrating screen at 0.540 % consistency, at
location (A). The vibrating
screen is equipped with 0.059 inch slits for removal of remaining
poly-coat. Rejects move along the top of the vibrating
screen and pile up in a trough at the end, at location (N), they then
slide down a tube to combine with system rejects from Module 7. 2.1.5 Washing/Thickening Pulp from the vibrating screen,
at location (B), is fed to a side hill screen at 0.37 % consistency.
As the pulp flows down the screen dirt is removed and the pulp
is thickened to 6.20 % consistency. The finished pulp “product” accumulates, at
location (C), in a trough at the bottom of the screen where it is
diluted and pumped to a holding tank.
Effluent from the screen, at location (F), flows to a concrete
trough underneath the pulping/separating system where it mixes with
the other system effluents before being pumped to the clarifier. 2.1.6 Clarification of Liquid
Streams System effluents are mixed
in a trough, at location (F), underneath the 7 module system and then
pumped to a Krofta clarifier at 53.89 gpm.
Clarifier Filtrate is pumped, at location (J), from a tank
adjacent to the clarifier to a tank adjacent to Module 1 where it
is mixed with fresh make-up water.
Clarifier sludge is deposited into a tank adjacent to the clarifier
before being pumped to a dumpster, at location (L).
A Cytec Chemicals representative was on hand to monitor chemical
application, and a Krofta representative monitored the clarifier operation. A copy of the report and data on the polymer
usage are included in Appendix 3. 2.1.7 Flow Rates The letters in Table 3 correspond
with the process flow diagram in Figure 1, and Appendix 4. Fresh water enters the system at K, all other
water used by the system is clarified water from the Krofta. Water loss from the system occurs in the clarified
sludge, final pulp product, and screw press rejects.
2.2 SAMPLING DESCRIPTION Samples were taken after each
of the three stages of the PM system (A, B, and C) to evaluate the
improvement in pulp quality after each stage, and to determine the
necessity for supplementing the PM system with conventional cleaners
or screens. Small samples were taken at each stage, every
20 minutes, and deposited into a 5 gallon bucket to generate composite
samples. The Vibrating Screen Feed sample
represents the accepts from the 7 module pulping/separating system. Pulp was collected into a cup, then emptied
into a bucket, as it flowed onto the vibrating screen (A). Vibrating Screen Accepts/Side Hill Feed samples
were taken at the side hill before the pulp was deposited onto the
top of the side hill (B). Side
Hill Accepts were sampled by scooping the pulp off of the bottom of
the side hill screen before they fell into the trough.
This sample represents the “final product” (C). Clarifier Feed (I), Filtrate (J), and Sludge (L) samples were also
composite samples. Clarifier
feed samples were taken from the trough underneath the 7 module system. Clarifier filtrate samples were taken from
the pipe coming out of the clarifier.
Sludge samples were taken from the tank adjacent to the clarifier. Strength testing includes:
TAPPI brightness, basis weight, caliper, density, burst index, tear
index, tensile index, tensile energy absorption, elongation, and breaking
length (Table 4). Environmental
testing on the sludge consisted of a total metals analysis.
Clarifier Feed and Filtrate were tested for BOD, Silica, Total
Suspended Solids, Total Dissolved Solids, Chlorine, Total Metals Analysis,
and pH.
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
