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International Journal of Coal Preparation and UtilizationPublication details, including instructions for authors and subscription information:http://www.informaworld.com/smpp/title~content=t713455898

Briquetting of Coal Fines and Sawdust Part I: Binder and Briquetting-Parameters EvaluationsD. Taulbeea; D. P. Patila; Rick Q. Honakerb; B. K. Parekhaa Center for Applied Energy Research, University of Kentucky, Lexington, Kentucky, USA b

Department of Mining Engineering, University of Kentucky, Lexington, Kentucky, USA

To cite this Article Taulbee, D. , Patil, D. P. , Honaker, Rick Q. and Parekh, B. K.(2009) 'Briquetting of Coal Fines andSawdust Part I: Binder and Briquetting-Parameters Evaluations', International Journal of Coal Preparation andUtilization, 29: 1, 1 22

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BRIQUETTING OF COAL FINES AND SAWDUST

PART I: BINDER AND BRIQUETTING-

PARAMETERS EVALUATIONS

D. TAULBEE1, D. P. PATIL1, RICK Q. HONAKER2,AND B. K. PAREKH1

1Center for Applied Energy Research, University of

Kentucky, Lexington, Kentucky, USA2Department of Mining Engineering, University of

Kentucky, Lexington, Kentucky, USA

Various technical and economic aspects relating to the briquetting offine coal with sawdust have been evaluated with the results for two

segments of that study presented here: binder and briquetting-

parameter evaluations. Approximately 50 potential binder formula-

tions were subjected to a series of screening evaluations to identify

three formulations that were the most cost effective for briquetting

fine coal with sawdust. Two of the binders, guar gum and wheat

starch, were selected as most suitable for the pulverized coal market

while the third formulation, lignosulfonate=lime, was targeted for thestoker market. Following binder selection, a number of briquetting

parameters including binder and sawdust concentration, sawdusttype, briquetting pressure and dwell time, coal and sawdust particle

size, clay content, moisture content, and cure temperature and cure

Received 4 June 2008; accepted 14 October 2008.

Funding for this research was provided in part by the U.S. Department of Energy,

State Industries of the Future (DE-FC07-02ID14273). The authors gratefully acknowledge

the support of TECO Coal, James River Coal, and Cooke & Sons Mining for the fine-coal

samples and H&S Lumber and Sandy Gaye Lumber for the sawdust samples. We also wish

to acknowledge the provision of binder materials from a number of sources including

ADM, Meade-Westvaco, Northway Lignin, Omni Materials, ABC Coke, US Sugar Corpo-

ration, Marathon-Ashland, Anheuser-Busch, Hase Petroleum, PQ Corp., Akzo-Nobel, the

Heritage Group, and Bob Rooksby.

Address correspondence to D. Taulbee. E-mail: [email protected]

International Journal of Coal Preparation and Utilization, 29: 122, 2009

Copyright Q Taylor & Francis Group, LLC

ISSN: 1939-2699 print=1939-2702 online

DOI: 10.1080/19392690802628705

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time were evaluated. Briquetting pressure and dwell time have the

least impact while binder and sawdust concentrations, sawdust type,

and curing conditions exerted the greatest influence on briquettequality.

Keywords: Binders; Biomass; Briquetting; Fine coal; Fuel; Waste

INTRODUCTION

During the past several years, an increasing consumer demand for the

production of renewable green energy has been realized. Such interest

stems mostly from the potential for reductions in net emissions of carbondioxide (CO2), a suspected agent of global warming, reduced SOx, NOx,

and mercury emissions as well as a lessening of the problems associated

with the mining and utilization of the coal that would be displaced.

Of the green energy options, the generation of power via co-firing of

biomass could be the more quickly implemented of the short-term solu-

tions to meeting required CO2 reductions and perhaps the more eco-

nomical as well. However, despite its advantages, biomass utilization

suffers from a number of economic and practical limitations including

high transportation costs, seasonal availability, high-moisture content,

increased boiler-volume requirements, and the capital investment needed

to handle, store, and process. Before biomass can play a significant

role in our green energy=CO2-reduction strategy, there are certain

economic issues that must be addressed. Namely, how can biomass be

economically transported from where it is available in abundance to

the utility site where it can be used? Once there, how can it be stored,

handled, and ground to the required particle size, all with a minimal

capital investment?In addition to the large amounts of biomass that goes unused, each

year between 70 and 90 million tons of coal fines [1] are discarded in

slurry impoundments in the United States. This represents enough

energy to provide electrical power to an industrialized country of about

15 million people. Even more striking is that this material is being added

to an existing inventory of approximately 2.5 billion tons of coal waste

that is stored at active and abandoned sites. It should also be noted that

most of these sites are located within the Appalachian coal fields thatalso happens to be home to a vibrant timber industry that produces a

significant quantity of energy-containing wood waste, about one third

of which is in the form of sawdust. Methods to clean and recover a

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high-Btu product from waste coal fines are known and reasonably

inexpensive. However, similar to biomass, the utilization of recovered

fine coal poses problems associated mainly with its high- and difficult-to-remove moisture content that lowers its heating value and makes

handling and transport difficult. Thus, substantial energy in the form

of fine coal and biomass is discarded each year and despite past efforts

[26] a significant commercial coal=wood-waste recovery industry has

not developed.

This wasteful practice is being reevaluated as a number of factors

such as higher market prices for coal, increased waste-disposal costs,

tax incentives, potential legislative controls on CO2 emissions, and theconsumers willingness to pay premium prices for green energy have

impacted the economics of utilizing coal and wood wastes and spawned

renewed interest in finding ways to use these waste materials in a ben-

eficial manner. One promising avenue for moving these materials into

the market is to compress blends of cleaned fine coal and sawdust into

briquettes that would provide a reduced-moisture product that can be

transported as dense, free-flowing solids and then stored, crushed, and

conveyed in existing equipment. In other words, the briquetting of bio-

mass with cleaned coal fines would not only produce a premium fuel pro-

duct from waste materials but could offer a near-term, practical means to

generate green energy in existing utilities without requiring a substantial

additional investment in processing and handling equipment.

Accordingly, a concentrated research effort has been directed at the

development of an economical process for producing a low-ash, high-

Btu, premium briquetted fuel from cleaned fine coal and timber wastes

(Figure 1). This research has focused on several topic areas including

the evaluation of binders that could double as frothing agents, advancedfine-coal drying technologies, an extensive binder evaluation to identify

the more cost-effective formulations, optimization of briquetting para-

meters, blending of clean coal from spiral (coarse) and flotation (fine)

circuits to optimize the coal particle size, and combustion testing of

the briquetted product. Effective binders for coal briquetting have been

known for some time and, in fact, were used quite extensively in com-

mercial briquetting operations in the mid-1900s [1]. However, there is

a shortage of published information on effective binders for fine coaland sawdust agglomeration requiring that a comparative binder evalu-

ation be undertaken. This manuscript will focus on results from the

binder and processing parameters studies.

BRIQUETTING OF COAL FINES AND SAWDUST 3

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EXPERIMENTAL

Binders

The literature survey for binders was not only limited to binders used for

the briquetting of coal but also included other agglomeration techniques

(e.g., pelletizing and extrusion), as well as materials used to agglomerate

other feedstock (e.g., charcoal and pharmaceuticals). From this survey,

coupled with discussions with equipments and binder suppliers, approxi-

mately 50 binder formulations were identified and procured. These mate-

rials were evaluated with an ultimate goal of identifying one or more

formulations that would be most cost effective for producing fuels for

pulverized coal boilers and to identify one more appropriate for the

production of stoker fuels.

Sawdust Samples

Eleven sawdust samples from varying sources were evaluated during the

study. These included (a) a larger particle-size sawdust generated by a

circular saw at an Eastern Kentucky mill (Gaye Bros.) that was a mixture

Figure 1. Schematic of the proposed concept of coal=sawdust premium fuel production.

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of tree species; primarily white oak with lesser amounts of red oak and

poplar; (b) a smaller particle-size chestnut-oak sawdust generated by a

band-saw near Clay City, Kentucky (H&S oak); and (c) a poplar sawdustfrom the same mill (H&S poplar). In addition, eight pure saw dusts from

different tree species common to Eastern Kentucky (red oak, white oak,

poplar, willow, ash, maple, beech, and hickory) were obtained with a

chain saw from a log yard in Breathitt County, Kentucky. Each of the

saw dusts was screened to 6.3mm (1=4 inch) prior to use with the

exception of the H&S oak, which was screened to 9.5 mm (3=8 inch).

Each was thoroughly mixed, split, and frozen in sealed quart jars to

minimize drying and oxidation.

Fine-Coal Samples

The two fine-coal samples used in this study were all of bituminous rank

and were obtained as high-ash, fine-coal waste streams (thickener feed)

from preparation plants in Eastern Kentucky. One of the sample was

obtained from Leatherwood Kentucky, referred to as JR, and the second

was obtained from a preparation plant in Letcher County and is referred

to as Cooke and Sons. Each sample was collected in 208 liter (55 gallon)drums and returned to the laboratory where they were cleaned using the

Jameson flotation cell, vacuum filtered and reduced to approximately

2025% moisture by spreading and drying on plastic sheets. Each sam-

ple was then homogenized, split, sealed in one-liter containers and frozen

to suppress further drying or oxidation during the study.

Table 1 lists the analysis of two clean coal samples. The ash

contents of Cooke and Sons and Leatherwood products were 8.32%

and 5.91%, respectively. The volatile matter and fixed carbon contentswere similar for the two products. The median (d50) particle size of the

Cooke and Sons and Leatherwood samples were 44.30 mm and

36.89 mm, respectively.

Table 1. Proximate analysis of the clean coal samples

Coal sample Ash % Volatile matter% Fixed carbon %

Cooke and Sons 8.32 32.69 58.99

Leatherwood (JR) 5.91 33.84 60.24

On moisture free basis.


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Procedures

Sample Handling and Briquette Formation. To obtain meaningful

results when conducting binder comparisons, briquetting parameters

must remain constant or at least repeatable for the duration of the study.

Examples of the variables to be controlled include briquetting pressure

and dwell time, feedstock oxidation and moisture, the weight of material

briquetted, temperature and humidity during cure, sample mixing, and

briquette crushing speed. Precautions were taken to minimize these

variations in the values of and other parameters during the study.

Blends to be briquetted were prepared by mixing sawdust, coal, and

binder at a fixed time and speed with a laboratory blender. An automatedhydraulic press (Carver Ind.) with a selectable dwell time and briquet-

ting pressure (45.4 kgf) was used to press 17.0 0.05 g of each coal=

sawdust=binder blend in a 28.6-mm diameter cylindrical die. This

method of making briquettes is tedious but provides for tighter control

of the briquetting parameters than can be obtained with a continuous

briquetter. Disadvantages are that the dynamics of briquette formation

and the briquette shape differ from those of a continuous, roller-type

briquetter. For the purposes of comparing binder performances, it wasassumed that the ability to maintain a more stringent control of briquet-

ting conditions more than offset potential disadvantages. It should be

noted that this assumption may not hold for binders that are activated

by the heat imparted in a continuous roller.

Unless otherwise noted, standard conditions of 1815 kgf briquetting

pressure, 3-s dwell time, and 10% sawdust addition were used through-

out the study. After forming, briquettes were stored in a Caron Model

6010 environmental chamber at a constant temperature (22.2C) and

relative humidity (RH) to ensure constant-curing conditions. Initially,

briquettes were cured at 80% RH but were cured later in the study at

90% RH to more realistically simulate stockpile conditions.

Briquette Testing

Compressive strengths were determined at a crushing speed of

25.4 mm=min with a 25.4-cm diameter disk attached to a Mark 10 Model

EG-200 compressive-strength meter that was mounted to an automatedChatillon TCM 201 test stand. Compressive strengths were measured

along the same axis as used to apply force during formation. Each

reported compressive strength value represents the average of five

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determinations and were normally conducted at 30 minutes, 24 hours,

and 7 days after the briquettes were formed. In two binder-screening stu-

dies, compressive strengths were used to identify the ten more promisingbinders for further evaluation.

The expanded evaluations included water resistance, shatter resis-

tance and attrition and were conducted on briquettes following a

seven-day cure. Water resistance was determined by weighing four bri-

quettes, after submerging them in water for eight hours, removing (if still

intact) and curing overnight in an environmental chamber, and measur-

ing the compressive strengths. Shatter resistancewas reported as the aver-

age number of times to failure for four briquettes dropped from a heightof 0.46 m onto a steel plate. Attrition indiceswere determined by record-

ing the mass of 78 briquettes ($100 g), placing the briquettes into a

30.5-cm diameter Plexiglas cylinder equipped with three, 5-cm lifters,

tumbling for five minutes at 40 rpm, and then determining the weight

of0.297 mm (50 mesh) material. The attrition index was reported

as the percent of the briquette weight retained by the 50-mesh screen.

Higher test values equate to better performance for all four of the

physical tests.

RESULTS AND DISCUSSIONS

Binderless Briquetting

The first scoping study was an attempt to produce acceptable binderless

briquettes as has been reported for dried coal fines [7]. Briquettes were

prepared with the JR coal and Gaye Brothers sawdust (10%) at 1815,

4536, and 9072 kgf. This approach generated briquettes with seven-day

strengths of 3.6, 14, and 19.5 kgf, respectively. While higher pressuresproduced better strengths, these values were unacceptably low, the bri-

quettes were highly friable, and such high pressures would increase

energy costs while lowering throughput. Hence, further study with

binderless briquetting was not pursued.

Initial Binder Screening

An initial round of binder comparisons was conducted to reduce thepotential materials to a more manageable number. Approximately 50 for-

mulations were blended at 5 wt% with JR coal and the Gay Brothers

sawdust (10%). Average green, one-, and seven-day compressive


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strengths were determined. Those formulations that did not provide a

13.6 kgf green strength, 18 kgf one-day strength, or 22.7 kgf seven-day

strength were eliminated from further study.

Sawdust Particle Size. A sawdust particle-size study was initiated after

noting that many of the briquettes containing the circular-saw sawdust

formed horizontal cracks during curing. The larger-sized sawdust parti-

cles from the circular saw were suspected as being responsible. To test

this hypothesis, a sample of Gaye Brothers sawdust was divided into

four fractions of 1.19, 1.19 0.84, 0.84 0.595, and 0.595 mm

(16, 16 20, 20 30, and 30 mesh) and briquetted with the JR coaland an emulsified asphaltic binder (5%). This study revealed an inverse

relation between briquette strength and sawdust particle size. For

example, the average seven-day strengths were determined to be 10,

13, 18, and 37 kgf for briquettes prepared with the 16, 16 20,

20 30, and 30 mesh sawdust, respectively. Visual inspections of the

briquettes revealed a decrease in the extent of the horizontal cracks in

briquettes formed with smaller sawdust particles (Figure 2) prompting

a switch to the two band-saw sawdust for subsequent studies (H&S

oak and poplar).

Binder-Performance Comparisons

Addition of Binders on an Equivalent-Cost Basis. An effort to iden-

tify the more effective binders was conducted for the approximate 30

materials that remained following the preliminary screening tests.

Figure 2. Briquettes formed with different particle-size sawdust showing increased cracking

with larger sawdust particles (16, 16 20, 20 30, and 30 mesh sawdust added at

10wt%).

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Compressive strengths were again used to assess binder performance. In

order to compare binder performance on a cost-equivalent basis, each

binder was added to the coal fines=sawdust blends on at an equivalentcost of briquetted product, i.e., $8=short ton (907 kg). To calculate the

equivalent-cost application rate, a market price for each binder was

obtained to which was added a $25=short ton delivery cost. Although

this approach does not consider potentially significant binder-price fluc-

tuations, differences in delivery costs, or differences in the cost of appli-

cation equipment, it nonetheless provides a practical starting point. The

results from this study are shown in Table 2. While no single binder pro-

vided both the highest green, one- and seven-day strengths, some of the

Table 2. Compressive strengths (kgf) of briquettes prepared with an $8=short ton binder-

application rate, JR Coal, and 10% Gaye Bros. oak (better performers shown in bold)

Binder Binder wt%

Green

strength (kgf)

1-day

strength (kgf)

7-day

strength (kgf)

Peridur 300 0.4 15.6 16.2 81.8

Western bentonite 6.7 15.7 15.9 32.2

Wheat flour, Walmart 3.4 17.8 17.1 57.2

Spring wheat flour 7.2 19.3 19.3 73.2

Lavabond 6.7 13.8 18.1 32.2

Corn starch 2.9 17.7 23.1 55.0

Black strap molasses 6.4 15.0 16.8 22.6

Coal loading tar 5.0 19.7 18.1 33.4

Paper sludge 17.8 18.6 13.2 15.3

Lime 8.0 20.7 14.8 30.4

RS-2 4.8 14.9 10.3 10.5

Sodium silicate 8.0 14.2 31.2 33.4

Polybond 300G 6.2 13.7 15.3 25.1

Polybond 9.4 11.6 15.5 20.8

Guar gum 1.0 19.8 32.0 64.8

Bleached softwood pulp 1.5 24.8 16.3 15.6

Brewex 17.8 18.8 18.5 33.5

Wheat starch 7 1.0 16.2 17.1 42.3

Wheat starch 6 2.9 20.5 24.3 64.1

Reax 4.8 14.3 15.7 27.7

Cola syrup 12.3 15.0 12.9 Asphalt-SS 4.8 17.8 14.1

Asphalt-MS 4.8 13.4 12.2

No binder (control) 0.0 14.0 8.8


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materials exhibited better than average performance at all three time

intervals and were selected for further evaluation.

The Impact of Lime Addition. A second round of binder comparisons

was again performed at a binder application rate of $8=short ton of

briquetted product, this time with a focus on evaluating the impact of

lime addition. Lime is often used for agglomeration as it is relatively

inexpensive and generally improves agglomerate properties, particularly

green strength. However, lime alone, even at relatively high concentra-

tions, does not produce coal briquettes that can withstand the rigors of

shipping and handling. Furthermore, depending on the coal-ash compo-sition, excessive lime may enhance slagging and fouling in pulverized

coal-combustion boilers as it may lower the ash-fusion temperature.

On the other hand, lime can enhance the performance of some binders

resulting in improved briquette properties at a reduced cost. Lime

addition can also be attractive in certain applications such as in slagging

boilers, where a lower ash-fusion temperature is desirable, or in

fluidized-bed boilers where limestone is added for SO2 capture. While

hydrated lime is more normally used to briquette dry feed materials,

unhydrated lime (CaO) was used in this study because of the relatively

high-moisture content of the fine coal. The logic behind selecting

unhydrated lime was that the high moisture of the fine coal would

suppress spontaneous combustion in product stockpiles and the

unhydrated lime would serve to reduce the surface moisture to some

extent.

The evaluation of lime addition was conducted with blends of

binder, H&S oak sawdust (10 wt%), and Cooke and Sons coal. Each

blend was split into two portions with one split briquetted without limeand the second briquetted after adding 2% lime by weight. Results for

selected binders, with and without added lime, are given in Table 3 where

the higher strength values are shown in bold. Briquettes containing lime

generally exhibited higher green strengths than briquettes prepared with-

out lime from otherwise identical blends. While results with the Cooke

and Sons coal did not precisely track those obtained with the JR coal

(Table 2), the best results for both coals when briquetted without lime

were obtained for guar gum and the starch-based binders. The perfor-mance of guar gum and starch generally declined following lime addition

while the performance of molasses, paper sludge, and the three REAX

(lignosulfonate) binders exhibited notable improvements.

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Table 3. Compressive strengths (kgf) for briquettes prepared with and without 2 wt% added

lime ($8=ton binder application rate, cooke and sons coal, and 10% H&S oak sawdust

(better performers shown in bold)

No lime 2 wt% lime

Binder ID

Binder

wt%

Green

strength

1-day

strength

7-day

strength

Green

strength

1-day

strength

7-day

strength

Wheat starch 7 1.01 9.5 11.3 37.0 13.5 14.0 30.9

Wheat starch 6 2.90 14.2 19.9 92.3 19.9 20.1 58.9

Polybond 9.40 6.9 9.3 13.4 16.8 21.0 21.9

Paper sludge 17.89 12.5 15.0 19.1 22.2 25.1 45.2

REAX-N-EF 4.32 10.0 11.5 47.8 16.3 22.4 90.7

REAX-N-DK 4.28 9.4 12.5 19.6 14.8 18.9 50.5

REAX-A 4.95 10.4 12.7 22.4 18.0 21.8 53.6

Peridur 300 0.42 10.5 10.8 40.2 12.6 9.3 19.7

Peridur 330 0.51 9.5 10.1 58.5 12.0 8.3 21.1

Puridur 300-repeat 0.40 14.4 12.8 33.4 21.8 16.5 20.6

Black strap molasses 6.64 9.5 10.7 12.8 20.3 23.4 40.8

Black strap

mol.-repeat w=lime

6.38 21.3 27.6 49.4

Peridur 300-repeat 0.41 10.2 8.3 28.0 13.2 8.3 21.2

Brewex 17.75 11.9 12.5 22.5 13.4 15.2 48.2

Asphalt-MS 4.83 12.5 9.3 10.8 17.2 17.6 27.8

Hardwood pulp 1.94 11.8 8.8 8.7 16.7 15.6 28.4

Softwood pulp 1.52 15.7 10.2 12.6 21.5 25.6 36.3

Guar gum 1.00 12.2 10.8 78.1 13.9 9.6 25.2

Coal tar 5.11 10.4 7.8 16.6 12.7 11.8 35.0

SS-1 asphalt emulsion 4.78 13.0 9.8 11.7 17.1 16.1 31.0

RS-2 asphalt emulsion 4.84 11.4 7.5 8.8 13.6 14.4 21.1

Corn starch-polymerized 2.90 16.7 19.9 47.9 22.9 22.8 44.5

Corn starch-unpolymerized 2.90 13.6 11.2 12.8 17.2 14.5 35.5

Slack wax (212) 2.10 14.8 12.3 11.3 20.8 21.4 27.4

Phenolic resin-unheated 0.80 9.9 6.0 7.8 14.1 15.0 27.7

Cola syrup 10.80 9.5 9.8 13.2 15.4 15.2 28.4

Polybond 300G 6.20 9.4 10.8 5.5 17.8 19.8 24.4

Promo-1 5.00 8.9 7.3 9.0 10.7 17.1 23.3

Wheat flour-Walmart 3.12 14.6 17.6 69.4 18.3 19.6 45.5

Wheat flour-high gluten 2.89 17.2 22.6 91.2 17.9 19.0 57.4

Wheat flour-high starch 2.89 15.1 17.6 75.9 16.9 14.9 54.4

Tall oil 2.50 11.5 8.3 8.7 18.7 19.3 32.0 No binder (control) 0.00 11.0 5.4 6.9 14.2 12.7 25.5


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Testing of the More Promising Formulations. Based on the

compressive-strength data, the list of potential binders was further

reduced to about 10 materials. Briquettes were prepared with these for-mulations for more extensive testing with the aim of identifying (a) the

most effective lime-containing formulation for stoker or fluidized-bed

applications and (b) the most effective combustible binder targeted for

pulverized-coal boilers.

Briquettes were prepared as before using JR fine coal and H&S oak.

In addition to compressive strength, tests of shatter resistance, water

resistance, and attrition indices were conducted following a seven-day

cure in an environmental chamber (22

C and 80% RH). For each physi-cal test, higher test values equate to better performance. The results,

shown in Table 4, indicate that the guar gum and wheat-starch binders

(Hi-gluten and wheat starch) provided the best overall performance for

Table 4. Comparison of physical properties for selected binder formulations ($8=ton binder

application rate, JR coal, & 10% H&S sawdust (compressive strengths in kgf)

Binder ID

Binder

wt%

Green

strength

1-day

strength

7-day

strength

Drop test

(# drops)

H2O

resist

(kgf CS)

Attrition

index

Black strap

molasses6.70 41.6 46.4 79.3 17.8 Disintegrated 55.5

Hi-gluten

wheat flour

2.90 29.3 35.6 >100 46.8 10.9 67.5

Guar gum 1.00 28.8 39.1 >100 51.3 18.9 81.1

Hi-Starch

wheat flour

2.89 23.3 28.0 >100 27.3 8.1 56.8

Corn starch 2.9 22.9 30.0 77.0 24.8 16.7 46.0

Paper sludge 17.90 35.6 38.0 61.6 4.3 38.5 36.0

Wheat starch 6 2.90 26.4 NA >100 NA NA 71.7

Control w=lime

only

2.00 26.1 NA 20.6 1.0 16.3 31.1

Tall oil

emulsion5.3 20.8 17.2 29.2 2.8 19.3 34.1

Molasses 5.7 25.4 32.4 68.7 9.0 Disintegrated 55.2

REAX 4.3 19.8 40.4>

100>

100 Disintegrated 91.1

REAX &

ASPHALT2.5&1.2 27.0 39.7 88.5 28.0 35.6 50.4

indicates addition of 2 wt% lime.


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rates for all three binders, particularly shatter resistance, attrition indi-

ces, and seven-day compressive strengths. On the other hand, little or

no difference was noted in the green strength or water resistance as afunction of binder concentration. Interestingly, the briquettes formed

with REAX, which contained a constant 2 wt% lime, showed better

water resistance at the lower REAX application rates. It is believed that

when REAX (lignosulfonate) was applied at higher concentrations, its

solubility resulted in a low resistance to water damage whereas when

applied at lower concentrations, water resistance may have been more

controlled by the constant 2% lime concentration.

Sawdust Concentration and Particle Size. The impact of sawdust

addition was evaluated at sawdust concentrations of 0%, 5%, 10%,

and 25% of the coal weight (Table 6). Both green and one-day strengths,

water and shatter resistance, and the attrition indices declined signifi-

cantly with increasing sawdust concentrations for both guar gum and

wheat starch. On the other hand, sawdust concentration had little impact

on the compressive strengths of the briquettes containing the REAX=

lime binder. The briquettes formed with Reax also exhibited excellent

shatter resistance, attrition indices, and, to some extent, water resistance

up to 10% sawdust addition but declined substantially with the higher

Table 6. Variation of sawdust concentration (0, 5, 10, & 25 wt% addition rates; strengths

given in units of kgf)

Binder ID

Green

strength

1-day

strength

7-day

strength

Drop test

(# drops)

H2O

resist

(kgf CS)

Attrition

index

Sawdust

(wt%)

Guar gum 49.9 87.2 >100 88.0 54 83.2 0

Guar gum 32.9 66.9 >100 18.3 19 64.7 5

Guar gum 28.8 39.1 >100 51.3 19 81.1 10

Guar gum 27.2 31.2 >100 23.3 9 65.8 25

Wheat starch 6 53.2 76.8 >100 >100 39 93.2 0

Wheat starch 6 38.4 55.7 >100 83.8 25 92.2 5

Wheat starch 6 29.4 NA >100 40.0 NA 73.9 10

Wheat starch 6 27.5 35.3 >100 17.5 Disintegrated 68.1 25

REAX

2 wt%

lime 24.4 40.0 >100 >100 52 93.9 0REAX 2 wt% lime 24.6 41.4 >100 >100 54 92.1 5

REAX 2 wt% lime 19.8 40.4 >100 >100 Disintegrated 91.1 10

REAX 2 wt% lime 26.9 43.3 183.5 10.5 Disintegrated 48.5 25


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25% sawdust addition. These results suggest that guar gum and starch

may provide better briquettes when little or no sawdust is blended with

the coal fines but that REAX may be preferable at higher sawdustconcentrations.

The impact of the sawdust particle size was evaluated by screening

sawdust to either 9.5, 0.84, 0.595, or 0.84 0.595 mm (3=8-inch,

20 mesh, 30 mesh, or 20 30 mesh) and forming briquettes using

10wt% of each particle-size range (Table 7). There was some minor

improvement in green and one-day compressive strength tests for guar

gum and REAX for briquettes prepared with the 20 30 mesh sawdust.

Otherwise, there were little or no clear trends in briquette performanceas a function of the sawdust particle size over the range evaluated.

Briquetting Force and Dwell Time. The impacts of the force applied

during briquetting (907, 1,814, and 4,536 kgf) and of the time over which

Table 7. Variation of sawdust particle size (10% SD addition rate; strengths given in units

of kgf)

Binder

Binder

wt%

Green

strength

1-day

strength

7-day

strength

Drop

test

(# drops)

H2O

resist

(kgf CS)

Attrition

index

Sawdust

size

Guar gum 1.0 28.8 39.1 >100 51.3 18.9 81.1 As recd

Guar gum 1.0 25.3 43.8 >100 35.5 13.1 62.5 20 mesh

Guar gum 1.0 26.9 42.5 >100 52.0 17.6 78.2 30 mesh

Guar gum 1.0 34.1 47.5 >100 20 30 mesh

Wheat

starch 6

2.9 29.4 NA >100 40.0 NA 73.9 As recd

Wheat

starch 6

2.9 24.4 31.3 >100 20.3 Partial

disint

61.4 20 mesh

Wheat

starch 6

2.9 22.2 28.9 98.0 22.5 Partial

disint

59.9 30 mesh

Wheat

starch 6

2.9 16.1 26.5 >100 20 30 mesh

REAX 2%

lime

4.3 19.8 40.4 >100 >100 Disintegrated 91.1 As recd

REAX 2%

lime

4.3 22.3 37.7 >100 >100 38.3 88.3 20 mesh

REAX 2%

lime

4.3 21.3 35.5 >100 >100 32.1 87.9 30 mesh

REAX 2%

lime

4.3 29.9 42 >100 20 30 mesh

As recd 6 mesh.


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the applied force was maintained (1, 3, and 8 sec) are shown in Tables 8

and 9, respectively. Some improvement in green and cured compressive

strengths was noted for the briquettes as a function of higher briquetting

pressures. Otherwise, the impact of this parameter on briquette perform-

ance was relatively minor. Likewise, little or no correlation was observed

Table 9. Variation of briquetting dwell time (1, 3, and 8 sec; strengths given in units of kgf)

Binder

Binder

wt%

Green

strength

1-day

strength

7-day

strength

Drop

test

(# drops)

H2O

resist

(kgf CS)

Attrition

index

Dwell

time

Guar gum 1.0 27.3 42.5 >100 54.8 22.3 72.71 1 sec

Guar gum 1.0 28.8 39.1 >100 51.3 18.9 81.06 3 sec

Guar gum 1.0 27.4 42.7 >100 54.3 23.3 79.36 8 sec

Wheat starch 6 2.9 23.0 26.9 >100 36.3 15.4 64.38 1 sec

Wheat starch 6 2.9 26.4 N=A >100 71.71 3 sec

Wheat starch 6 2.9 29.4 N=A >100 40.0 73.92 3 s ec

Wheat starch 6 2.9 23.7 26.9 >100 14.3 13.2 60.88 8 sec

REAX 2 wt%

lime

4.3 18.1 37.4 >100 1 sec

REAX 2 wt%lime

4.3 19.8 40.4 >100 >100 Disintegrated 91.10 3 sec

REAX 2 wt%

lime

4.3 19.6 40.0 >100 8 sec

Table 8. Variation of briquetting force on briquette properties

Binder

Green

strength

1-day

strength

7-day

strength

Drop test

(# drops)

H2O resist

(kgf CS)

Attrition

index

Briquetting

force (kgf)

Guar gum 20.6 32.5 >100 57.25 14.83 79.43 907

Guar gum 28.8 39.1 >100 51.25 18.92 81.06 1814

Guar gum 26.7 31.3 >100 62.00 17.60 78.88 4536

Wheat starch 6 20.2 28.6 >100 43.75 68.90 907

Wheat starch 6 26.4 NA >100 71.71 1814

Wheat starch 6 29.4 NA >100 40.00 n=a 73.92 1814

Wheat starch 6 38.2 50.0 >100 40.50 75.88 4536

REAX 2 wt%

lime

18.3 35.0 >100 907

REAX 2 wt%

lime

19.8 40.4 >100 >100 Disintegrated 91.10 1814

REAX 2 wt%

lime

21.3 42.0 >100 4536


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between the briquetting dwell time and briquette performance. Both

findings are favorable with respect to commercial operation as they sug-

gest that it should be possible to use a lower energy input and fasterthroughput without a significant sacrifice in briquette quality.

Moisture. To evaluate the impact of moisture content, briquettes were

prepared with either 0%, 5%, or 10% added water. The master sample

of JR coal used in this study had an initial moisture content of 20.7%,

meaning that this study was conducted roughly over the range of

20%30% moisture. A constant weight of dry blend was used in each

briquette by correcting for the differences in the amount of water added.The results, shown in Table 10, reveal no clear trends in briquette per-

formance as a function of moisture content over the range evaluated.

The higher compressive strengths for guar gum were obtained with either

0% or 5% water addition. In contrast, briquettes formed with wheat

starch showed higher strengths with increasing water addition.

Briquettes formed with REAX showed mixed results with 5% water

addition giving the lowest green and one-day compressive strengths but

the highest compressive strengths at seven days.

While not quantified, it was noted throughout the project that some

water addition appeared to improve briquette performance. It was

believed that this improvement stemmed from a more uniform coating

of the coal and sawdust particles; as without sufficient moisture, many

of the binders, particularly the powders or viscous liquids, were difficult

to disperse. However, when the water content was too high, the excess

Table 10. Effect of moisture content (0%, 5%, and 10% added water) on compressive

strength (kgf)

Binder Binder wt %

Green

Strength

1-day

strength

7-day

strength

Water

addition (%)

Guar gum 1.0 24.3 37.8 >100 0

Guar gum 1.0 24.7 42.6 >100 5

Guar gum 1.0 14.2 21.7 >100 10

Wheat starch 6 2.9 18.1 24.2 78.8 0

Wheat starch 6 2.9 24.2 33.4 >100 5

Wheat starch 6 2.9 27.3 38.7 >100 10REAX 2 wt% lime 4.3 28.8 46.0 69.7 0

REAX 2 wt% lime 4.3 19.8 40.4 >100 5

REAX 2 wt% lime 4.3 26.9 44.8 75.7 10


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water was squeezed out during compression, carrying away some of the

binder, especially the more water-soluble binders. It should also be noted

that the blends were manually loaded to the die in this study so that excesswater was not a problem. However, this would likely be a problem in a

continuous briquetter as blends with excess water tend to bridge and feed

more erratically than dried blends. While not reported here, subsequent

continuous-briquetting experiments showed slight improvements in bri-

quette strengths with increasing water content up to the point at which

the blends began to stick in the hopper and could no longer be fed uni-

formly. These results suggest that in general terms, the optimum water

content is the maximum at which the blend can be fed steadily and thatlow-moisture content is not a prerequisite for good briquette strengths.

However, it should be noted that the optimum moisture content is

expected to be dependent on the nature of the binder being used and

would have to be determined for each site-specific set of conditions.

Cure Temperature. The impact of cure temperature was evaluated by

curing briquettes for 30, 60, and 120 minutes at either 50C or at 80C

before crushing (Table 11). For comparison, a set of control briquettes

prepared from the same feed blends were cured for two hours at ambient

temperatures prior to crushing. Briquette strength following a 30-minute

cure at 50C was similar to that obtained for the control briquettes.

Curing for two hours at 50C resulted in some, but not radical, improve-

ments in briquette strengths relative to the control. At 80C, some

improvement was noted after 30 minutes relative to the control but after

two hours, these latter briquettes exhibited compressive strengths compa-

rable to those of briquettes cured for one week at ambient temperature.

Table 11. Compressive strength (kgf) as a function of cure temperature and time

Binder

Binder

wt%

Cure

temp (C)

30-min

strength

One-hour

strength

Two-hour

strength

Control

(2 hr ambient

temp strength)

Guar gum 1 50 25.4 30.6 39 24

Wheat starch 6 2.9 50 27.9 29.8 39.7 29.8

REAX

2 wt%

lime 4.3 50 26.7 35.8 46.3 24.5Guar gum 1 80 22.8 40.5 >100 24

Wheat starch 6 2.9 80 33.5 54 >100 29.8

REAX 2 wt% lime 4.3 80 27.7 39.5 >100 24.3


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Sawdust Type. The relation between briquette strength and the species

of tree from which the sawdust was derived was examined using eight

different sawdust sources from trees common to eastern Kentucky. Each

sawdust was screened to 4.76mm (4 mesh) and briquetted as before

using guar gum as the binder (1 wt%). The compressive strength values

obtained from briquettes cured for the time periods of 0.5, 24, 48, and 72hours are shown in Table 12a. While some differences in strength were

anticipated as a function of sawdust type, the magnitude of these differ-

ences was surprising. Much higher compressive strengths, particularly at

48- and 72-hour curing times, were obtained with the higher density saw-

dust (red oak, beech, white oak, and hickory) relative to the softer and lower

density wood types (poplar, willow, ash, and maple) as shown in Figure 3.

One concern in attributing the observed differences in strength solely

to the sawdust type was that the different tree species likely produced saw-

dust with different particle-size distributions due to inherent differences in

Table 12a. Briquette strengths for various wood species

Type of wood SD bulk densities

Compressive strength (kgf)

30 min 1-day 2-day 3-day

Beech 0.797 64 83 > 100 > 100

Ash 0.694 32 37 67 > 100

Maple 0.694 38 49 76 > 100

Hickory 0.900 49 71 91 > 100

Poplar 0.579 37 57 80 > 100

White Oak 0.878 36 61 > 100 > 100

Red Oak 0.893 64 93 > 100 > 100

Willow 0.485 24 23 45 76

Table 12b. Briquette strength for various wood species using equivalent sawdust particle-

size distributions

Compressive strength (kgf)

Type of wood Briquette height (mm) 30-min (kgf) 1-day (kgf) 2-day (kgf)

Beech 24.5 73 83 >100Poplar 24.9 42 52 65

Red oak 23.0 65 89 >100

Willow 25.1 18 27 45


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hardness. To determine if the observed differences were due to differences

in sawdust type instead of sawdust particle size, samples of the two betterperforming sawdust (red oak and beech) along with two of the lesser

Figure 4. Green and one-day briquette strengths as a function of the fine-coal ash content.

Figure 3. The relation between sawdust density and the one-day briquette strengths.


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performers (poplar and willow) were screened to the same six particle-size

ranges. Each size range was then recombined at the same ratios to ensure

particle-size uniformity with the four reconstituted sawdust used to formbriquettes for testing (Table 12b). The red oak and beech sawdust again

significantly outperformed the willow and poplar sawdust providing

evidence that the differences in performance were related to sawdust type

and not differences in particle-size distributions.

Fine-Coal Ash Content. To evaluate the impact of ash content, a sam-

ple of relatively high-ash fine coal (14.2%) was collected from a commer-

cial flotation facility, was split into representative lots and was cleaned by

froth flotation under different conditions to obtain samples that varied in

ash content (2.78%, 4.66%, and 10.4%). Each of these samples was bri-

quetted with 1% guar gum and subjected to compressive strength, water

resistance, and attrition measurements. Briquettes produced with the

higher ash samples exhibited better green and one-day strengths

(Figure 4) as well as a higher attrition index. While a higher ash content

is generally not desired, these data suggest that the briquetting of a

higher ash coal might equate to a reduction in binder cost along witha higher weight recovery of fine coal during cleaning.

CONCLUSIONS

The fine waste materials of two industries commonly located within

the same proximately can be potentially combined by briquetting to

produce a premium utility fuel source. To be commercially successful,

the briquettes formed from cleaned fine-coal waste and sawdust mustpossess sufficient strength to resist breakage during transportation

and handling while meeting economical constraints. Over 50 binder

reagents were evaluated to identify a binder that economically

achieves the desired goal. After determining the most promising

binders, other briquetting parameters were evaluated for their

effects on compressive strength, attrition, and weatherability. Guar

gum, wheat starch, and Reax=lime were identified as the best perform-

ing binders for briquetting coal and sawdust when applied on anequivalent-cost basis. The parameters that exhibited the greatest

impact on briquette performance were binder concentration; sawdust

concentration, particle size, and type; cure temperature; and ash


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content. Parameters that had the least impact on briquette properties,

at least over the limited ranges studied, were moisture content, bri-

quetting force, and briquetting dwell time.

REFERENCES

1. National Research Council, Coal Waste Impoundments: Risks, Responses,

and Alternatives, National Research Council, National Academy Press,

Washington, D.C., 2002.

2. K. V. S. Sastry, Pelletization of Coal Fines, United States Department of

Energy Report No: DOE=PC=89766-T4, 1991.

3. C. A. Holley and J. M. Antonette, Agglomeration of Coal Fines, Proc. of the15th Biennial Conf. of the Inst. of Briquetting and Agglomeration, Montreal,

Canada, Vol. 15, pp. 112, 1977.

4. P. Burchill, G. D. Hallam, A. J. Lowe, and N. Moon, Studies of Coals and

Binder Systems for Smokeless Fuel Briquettes, Fuel Processing Techn.,

Vol. 41, pp. 6377 (1994).

5. J. T. Cobb and D. J. Akers, Co-Processed Fuel Pellets from Coal, Biomass,

and Waste, Prepr.: Div of Fuel Chemistry, Vol. 46, pp. 715716 (2001).

6. A. Given, Briquetting in the Present Energy Picture, Proc. of a Coal Briquetting

Conference, Superior, Wisconsin, August 23, 1951.7. J. W. Davidson and G. W. Kalb, Current Status-Binderless Briquetting of

Thermally Dried Coal, Proc. of 23rd Biennial Conf. of the Inst. of Briquetting

and Agglomeration, Vol. 23, pp. 5164, 1993.


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