Preparation and characterization of fuel briquettes made from dual agricultural waste: Cashew nut shells and areca nuts

Journal Pre-proof Preparation and characterization of fuel briquettes made from dual agricultural waste: Cashew nut shells and areca nuts Thatchapol Chungcharoen, Naruebodee Srisang PII:

S0959-6526(20)30481-9

DOI:

https://doi.org/10.1016/j.jclepro.2020.120434

Reference:

JCLP 120434

To appear in:

Journal of Cleaner Production

Received Date: 18 January 2019 Revised Date:

25 December 2019

Accepted Date: 4 February 2020

Please cite this article as: Chungcharoen T, Srisang N, Preparation and characterization of fuel briquettes made from dual agricultural waste: Cashew nut shells and areca nuts, Journal of Cleaner Production (2020), doi: https://doi.org/10.1016/j.jclepro.2020.120434. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier Ltd.

Credit Author Statement Thatchapol Chungcharoen: Methodology, Validation, Resources, Visualization, Supervision Naruebodee Srisang: Conceptualization, Formal analysis, Investigation, Writing- Original draft, Writing- Reviewing and Editing, Data curation.

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Preparation and characterization of fuel briquettes made from dual agricultural waste:

2

Cashew nut shells and areca nuts a

4

a,*

Thatchapol Chungcharoen , and Naruebodee Srisang

3 a

Energy Engineering Division, Department of Engineering, King Mongkut’s Institute of

5

Technology Ladkrabang, Prince of Chumphon Campus, Chumphon 86160, Thailand

6

* Corresponding author

7 8

Abstract

9

The purpose of this work was fuel briquettes production from cashew nut shells (CNS)

10

and areca nut shells (ANS) with the operating parameters of the compressed screw speed (70 and

11

90 rpm), the mixture of CNS, ANS, and cassava flour (binder) in the unit by weight percent (6

12

proportions), and the CNS size (small and large). The effects of these parameters on the

13

production rate, mechanical properties (hardness and porosity), and fuel properties, i.e., moisture

14

content (MC), calorific value (CV), volatile matter content (VM), ash content (AC), fixed carbon

15

content (FC), and combustion rate (CR), were investigated. The fuel application for cooking was

16

evaluated with the flame temperature (FT), water boiling test (WBT), thermal efficiency (TE),

17

and greenhouse gases (GHG) emission. Experimental results showed that the speed had the most

18

effect on the production rate, while the CR got the least effect from all parameters compared to

19

the other properties. The briquette should be produced using small CNS with the mixture of CNS

20

65%, ANS 25% and, cassava flour 10% (by weight) at speed of 90 rpm which provided the high

21

production rate together with satisfying fuel properties, unless the CR was low. The fuel

22

briquette showed the potential for cooking in acceptable level with the low GHG emission.

23

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Keywords: Fuel briquette; Cashew nut shell; Areca nut shell; Fuel utilizations; Mechanical

25

properties; Fuel properties

26 27

1. Introduction

28

Biomass from agricultural crop transformations such as sawdust (Garrido et al., 2017),

29

bagasse (Lubwama and Yiga, 2017), coffee husk (Lubwama and Yiga, 2018), sugarcane skin

30

(Brunerová et al., 2018) and groundnut shell (Lubwama and Yiga, 2017) have enormous

31

quantities and are utilized as solid fuel for domestic cooking and heating in developing countries

32

(Purohit and Chaturvedi, 2018). These wastes should not be directly used due to poor burning

33

efficiency, non-uniform size, and low bulk density (Ujjinappa and Sreepathi, 2018a), which

34

resulted in the numerous greenhouse gas (GHG) emission during combustion and the high cost

35

for transportation and storage. Hence, residual biomasses are converted the both physical and

36

chemical characteristics to get the fuel with the desirable properties, i.e. the high CV, high

37

durability, and low pollution emission.

38

Densification is a conversion method of biomass feedstocks into briquette which is not

39

complicate process and can adequately respond on the energy requirements for heating and

40

cooking in rural area (Dinesha et al., 2019). The densified biomass had the increased energy

41

density, the ease of storage and conveyance, and the improved combustion efficiency. Fuel

42

qualities from densification method depended on with the aspect of feedstocks (raw biomass and

43

carbonized biomass). Wu et al. (2018) produced the briquette from cotton stalk and wood

44

sawdust through the different methods of carbonized biomass (hydrothermal carbonization, dry

45

torrefaction, and pyrolysis) before briquetting. Their result found that the distinct method for

46

producing carbonized biomass affected the briquette properties (density, compressive strength,

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and CV); the best properties was provided from hydrothermal carbonization process at 200–

48

260°C. Li et al. (2019) compared the solid fuel utilization (thermal efficiency and pollutant

49

emission) from raw biomass and their carbonized biomass (carbonization process at 500–600°C)

50

for household cooking; the solid fuel from carbonized biomass provided the higher thermal

51

efficiency and lower pollutant emission. Wang et al. (2017) investigated the char briquette traits

52

from maize straw after the addition of phosphorus additives in mixture; their results showed the

53

variation of fiber structure after pyrolysis process and led to the worse compaction of carbonized

54

biomass; the additive can amend fuel properties. Ndindeng et al. (2015) demonstrated that the

55

production rate of husk and bran briquette depended on the technology and time of production.

56

Mandal et al. (2019) displayed the briquetting parameters (particle size, pressure, and mixture

57

quantity) affected the physical and combustion properties of pine needles briquette. Olugbade et

58

al. (2019) reported the type and quantity of binder had the effect on combustion characteristics of

59

briquettes. Above researches obviously indicated the relation between the briquette characteristic

60

and preparation process which should be studied to get the desirable attributes of briquette.

61

In present, there are endeavor in fuel briquette production from distinct biomass materials

62

that promoted the waste utilization and resulted in more choice for the use of feedstocks,

63

however, the difference of chemical configuration inside ingredient affected briquette properties

64

(mechanical and combustion properties). Okot et al. (2019) reported the augmentation of bean

65

straw quantity in mixture can improve the mechanical properties of bean straw- maize cob

66

briquette due to the interlock between the solid bridge bonding of maize cob and fibrous

67

structure of bean straw. Kansai et al. (2018) showed the changed physical properties of

68

carbonized briquettes from rain tree residues and coffee ground/tea waste with the variation of

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feedstocks proportion; this briquette had the CV about 20.17 MJ/kg and shatter index around

70

99% which can use for household cooking.

71

Cashew nut shells (CNS) and areca nut shells (ANS) are residues from the crop

72

transformation in southern Thailand. The yield of cashew nuts of approximately 950,676 kg

73

(DOAE, 2017) generate the residual CNS around 703,500 kg and areca nuts approximately

74

21,399,993 kg (OAE, 2018) provide 3,209,999 kg of residual ANS. The aspect of residual CNS

75

is semi-carbonized while the residual ANS is fiber after the transformation process; these wastes

76

had low bulk density and including varied size and shape; they were usually eliminated through

77

combustion in open air or landfill, and result in GHG emissions (CO2, CH4 and N2O). The

78

information for preparation, properties, utilization, and the pollutant emission of briquettes made

79

from different feedstocks (semi-carbonized and fiber) were still inadequate. These informations

80

were necessary for sustainable waste utilization and could be applied to similar waste from other

81

sources.

82

The aim of this research is the investigation of fuel briquette production from dual

83

materials (CNS and ANS) combined with the binder (cassava flour) through the densification

84

method. The effect of operating parameters on mechanical properties, fuel properties, and

85

production rate of briquette were investigated to determine the proper conditions for production.

86

Then, the briquette got from suitable condition was evaluated the utilization for domestic

87

cooking.

88 89

2. Materials and methods

90

The hypothesis in this research is the different feedstock types (CNS and ANS) and

91

operating parameters (CNS sizes, compressive screw speed, and mixtures) affect the fuel

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properties, production rate, mechanical properties (hardness and porosity), and the fuel

93

utilizations. The fuel properties were determined to indicate the basis characteristics of fuel. The

94

fuel hardness was tested to show the vigor while the porosity was discovered to explain the

95

ingredients compaction which related with the density and affected the stamina and combustion

96

of fuel. The production rate was measured to estimate the potential of fuel production. These fuel

97

attributes were used to determine the suitable condition for briquette production with the good

98

qualities. Finally, the briquette from proper condition was evaluated the fuel utilization as

99

following: FT, WBT, and TE showed the thermal abilities of fuel, GHG emission was presented

100

with the CO2 discharge to point the occurred pollution in environment.

101

2.1. Preparation of raw materials

102

CNS got from a community enterprise group (Watcharee Kayoo Shop, Ranong Province,

103

Thailand) which had MC as 8% (wet basis, w.b.) after pass the roasting cashew nuts process. The

104

CNS aspect was semi-carbonized, i.e. carbonization at low temperature about 300°C (Jian et al.,

105

2016). ANS obtained from a factory that produced dried areca nuts (Ranong and Chumphon

106

provinces, Thailand). The fresh areca nuts were dried and cut to separate the kernels and shells.

107

ANS had MC as 11-12% w.b.

108

2.2. Preparation of mixtures

109

CNS were ground and screened using U.S. sieve No. 3/8 (particle size of 9.51 mm), No. 4

110

(particle size of 4.76 mm), and No. 8 (particle size of 2.38 mm). CNS were separated by size into

111

small (< 4.76 mm) and large (> 4.76 mm), as shown in Fig. 1A and 1B. ANS were chopped into

112

fiber using a wood chip chopper (Velar model No. MA104, Thailand), as shown in Fig. 1C.

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113 114

Fig. 1. Fuel briquette mixture: A) small CNS, B) large CNS, and C) ANS.

115

The cassava flour was mixed with CNS and ANS at 10% and 20% of the total mass of the

116

briquette which were the usual proportions for briquette production (5-25% by weight)

117

(Lubwama and Yiga, 2017). The cassava flour was mixed with a suitable water quantity

118

(approximate 20% of the total mass) and boiled into a uniform paste. The proportions of CNS,

119

ANS, and flour (% by weight) were 65:25:10 (A), 45:45:10 (B), 25:65:10 (C), 58:22:20 (D),

120

40:40:20 (E), and 22:58:20 (F). The CNS size in all mixtures were divided into small and large.

121

2.3 Fuel briquette production machine

122

Fig. 2 shows the fuel briquette production machine which composes of a stirring blade,

123

mixing tank, compressive cylinder, compacted screw, and structure base. A 3 mm thick stainless-

124

steel stirring blade was installed in the mixing tank. The lowest mixing tank had an exit channel

125

to convey all the ingredients after stirring into the compressive cylinder. All ingredients were

126

compressed using a compacted screw within the compressive cylinder. Both the stirring blade

127

and compacted screw were driven using a 3 HP motor. The stirring velocity was fixed at 90 rpm

128

for 5 min while the compressive screw speed was altered at 70 and 90 rpm.

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129 130 131

Fig. 2. Fuel briquette production machine. 2.4 Fuel briquette production rate

132

The mixtures were continuously compressed at a screw speed of 70 and 90 rpm and

133

segmented into briquettes with a 50 mm diameter and 100 mm length (Liu et al., 2014), as shown

134

in Fig. 3. One briquette had the weight about 210 g. The number of briquettes and the production

135

time were used to estimate the production rate (pieces/h).

136 137

Fig. 3. Fuel briquettes after A) compression and B) segmentation.

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2.5 Fuel briquette drying

139

The initial MC of briquettes were in the range of 36-38% (w.b.) after ingredient was

140

compressed into briquettes. The briquettes needed suitable drying to reduce the MC < 10%

141

(w.b.) (Missagia et al., 2011). The briquettes were dried using sun drying in the summer period

142

(average ambient around 34-36°C) for 1 week since it was a simple and low-cost method.

143

2.6 Mechanical properties

144

2.6.1 Hardness testing

The hardness of the fuel briquettes was inspected using a Shore D hardness tester (model

145 146

EQUQTIP) which used with composite material (Shalwan and Yousif, 2014).

147

2.6.2 Porosity testing

148

The porosity was estimated from the specific density and unit density. The unit density

149

calculated from the briquette mass divided by the briquette volume (including any pores and

150

spaces within the briquette). The cylindrical fuel briquette was weighed using a digital balance

151

with an instrumental resolution of 0.01 g, and the diameter and length were measured using a

152

Vernier caliper with an instrumental resolution of 0.05 mm (Mitutoyo Corp., Japan). The

153

briquette volume and the unit density were determined according to Equation (1) and (2),

154

respectively. Vb =

155

u=

156

157 158

where

u

m

- Unit density (g/cm3) - Mass of fuel briquette (g)

πD2 L 4 m

V b

(1)

(2)

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Vb

- Bulk volume of fuel briquette (cm3)

160

D

- Diameter of fuel briquette (cm)

161

L

- Length of fuel briquette (cm)

162

The specific density was defined as the ratio of the briquette mass to the true briquette

163

volume (excluding any pores and spaces inside the briquette) and was measured using a gas

164

pycnometer (Micromeritics Instrument Corp., AccuPyc 1340, USA). Both the specific density

165

and unit density were used to calculate the porosity using Equation (3).

Porosity (%) =

166

167

2.7 Fuel properties

168

2.7.1 Calorific value

169

Specific density-Unit density Specific density

× 100

(3)

CVs of the fuel briquettes were determined using an automatic calorimeter (Leco, model

170

AC-500) according to ASTM standard D 5865-11a.

171

2.7.2 Moisture content

172

MCs of the fuel briquettes were determined according to ASTM standard D 3173-87. The

173

procedure started by drying the crucible at temperature of 105°C for 30 min and placing it in

174

desiccator for 15 min; then, the crucible weight was recorded. 1 g of briquette sample was placed

175

in the crucible, and the weight of the crucible combined with the sample was recorded. The

176

crucible that contained the sample dried in oven at temperature of 100°C for 2-3 days. The

177

crucible was put in desiccator for 20 min and its weight was recorded. The recorded weights

178

were used to calculate the MC using Equation (4).

179

MC (% w.b.) =

W2 -W3 W2 -W1

× 100

(4)

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where W1 - Crucible weight (g)

182

W2 - Crucible weight and sample before drying (g)

183

W3 - Crucible weight and sample after drying (g)

184

2.7.3 Volatile matter content

185

VM of fuel briquettes was determined according to ASTM standard D 3175-11. 2 g of

186

briquette sample was smashed and placed in a crucible. The crucible was dried in an oven until

187

the weight was constant. The sample weight was measured. The crucible that contained the

188

briquette sample was baked in furnace at temperature of 550°C for 10 min, and the sample

189

weight after cooling in desiccator was measured. VM was calculated using Equation (5). VM (%) =

190 191

where

Ao

× 100

(5)

Ao - Sample weight after drying in the oven (g) B - Sample weight after baking in the furnace and cooling in the desiccator (g)

192 193

Ao -B

2.7.4 Ash content

194

AC of briquette sample was inspected following ASTM standard D 3174-89. The

195

determination method for AC resembled with VM, but the briquette sample was heated in a

196

furnace at a temperature of 550°C for 4 h. The weight of briquette sample after drying in an oven

197

and after burning in a furnace combined with cooling in a desiccator was used to calculate the

198

AC according to Equation (6). AC (%) =

199 200 201

where

C-D C

× 100

C - Sample weight after drying in the oven (g) D - Sample weight after burning in the furnace and cooling in the desiccator (g)

(6)

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2.7.5 Fixed carbon content

FC was determined according to ASTM standard E711-87 and was calculated from

204 205

Equation (7). FC (%) = 100 – (V +A)

206 207

where

V - The percentage of volatile matter (%) A - The percentage of ash (%)

208 209

(7)

2.7.6 Combustion rate

210

CR showed the burning capability of fuel briquette. One briquette weight was about 210

211

g before combustion (Fig. 4A). The sample was ignited and burned, as shown in Fig. 4B. The

212

combustion time and briquette weight were recorded to calculate the CR (Equation (8)). CR (g/min) =

213 214

where

Wb t

CR - Combustion rate (g/min)

215

Wb - Weight of the burned briquette sample (g)

216

t

- Combustion time (min)

217 218 219

Fig. 4. Fuel briquettes A) before combustion and B) during combustion.

(8)

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2.8 Potential of fuel utilization

221

Fuel briquette from the suitable condition was appraised the utilization characteristics

222

(WBT, FT, TE, and GHG emission) and was compared with the wood charcoal (conventional

223

fuel). WBT showed the spent time to boil 1 L of water in conventional cook stove using the

224

briquette of 200 g (Lubwama and Yiga, 2017). FT was the highest flame temperature during

225

WBT which was measured every 5 min using thermoscan camera (FLIR model E series,

226

SINCERE NETWORK, Thailand). TE was estimated during WBT by it calculated from the

227

acquired energy for water evaporation during WBT divided by the obtained energy from

228

briquette as shown in equation (9) (Sawadogo et al., 2018). All experiments were performed in

229

the room size around 4 m (width) x 4 m (length) x 2.5 m (height).

230 231 232 233

TE (%)

where

TE

=

mw x Cw x Twf – Twi + mwe x Le mb x LCV

x 100

(9)

- Thermal efficiency (%)

mw - Initial water mass (kg) w

- Specific heat capacity of water (4.187 kJ/kg.°C)

234

Twf - Final water temperature (°C)

235

Twi - Initial water temperature (°C)

236

mwe - Evaporated water mass (kg)

237

Le - Latent heat of the water evaporation (2,257 kJ/kg)

238

mb - Consumed briquette mass (kg)

239

LCV - Low calorific value of briquette (MJ/kg)

240

GHG emission is a main cause of global warming problem. This study focuses on the

241

discharged amount of carbon dioxide (CO2) from fuel briquette during WBT. GHG emission was

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reported in term of carbon dioxide equivalent (CO2e) by calculated from equation (10) which

243

modified from the article of Ramachandra et al. (2015). GHG emission = mb x LCV x EF

244 245

where

(10)

GHG emission - Amount of CO2 equivalent (gCO2e)

246

mb

- Amount of fuel briquette that used to boil 1 L of water (kg)

247

LCV - Amount of heat released from burning biomass (excluding the latent heat of water evaporation) (MJ/kg)

248 249

EF

- Emission factor (gCO2/MJ)

250

GHG emission of fuel briquette in study was calculated using the EF for stationary

251

combustion in the residential category of solid biomass (100 gCO2/MJ) and wood charcoal (112

252

gCO2/MJ) (Eggleston et al., 2006).

253

2.9 Statistical analysis

254

The research results were obtained from an experiment with a full factorial design

255

(2×6×2) with three main parameters (two CNS sizes, six mixed proportions, and two compressed

256

screw speeds). All experiments were repeated at least triplicate. SPSS software Ver.14 was used

257

to analyze the influence of the operating parameters and their interactions on the mechanical

258

properties, fuel properties, and production rate. The statistical analysis was performed using an

259

analysis of variance with a significance level of 0.05, 0.01, and 0.001 together with Tukey’s

260

HSD test.

261 262 263 264

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3. Results and discussion

266

3.1 Proximate analysis of feedstocks

267

Fig. 5 shows the properties of the feedstock for fuel briquette production. CNS provided

268

the highest CV of approximately 20.18 MJ/kg, followed by ANS (16.77 MJ/kg) and cassava

269

flour (14.93 MJ/kg). These CVs were greater than or equal other biomasses, such as bamboo

270

sawdust, eucalyptus sawdust, rubber wood residue, corn cob, palm fiber; these biomasses had

271

CVs in the range of 15-18 MJ/kg (Thabuot et al., 2015). CV and MC of CNS were similar to

272

those of cashew shell press cakes; meanwhile, AC and FC were lower and VM was higher when

273

collated with the research results of Sawadogo et al. (2018). The lower AC helped to reduce the

274

pollution problem from dust and harmful substances. The higher VM arose from the partial loss

275

of VM within the cashew shell press cakes after the extraction process of CNS liquid. The high

276

VM of the CNS promoted combustion (Rezania et al., 2016). ANS had a CV (16.77 MJ/kg), VM

277

(74.44%), and AC (6.34%) as reported by Ujjinappa and Sreepathi (2018b). Above results

278

indicated the adequate attributes of the feedstock for briquette production (i.e., high CV, high

279

VM, and low AC).

280 281

282

Fig. 5. Proximate analysis of feedstocks.

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3.2 Production rate

284

Fig. 6A and 6B shows the efficiency of the fuel production machine under different

285

conditions. The speed of 90 rpm clearly provided a greater production rate than that at 70 rpm for

286

all mixtures and sizes owing to the faster compression. Mixture B at a speed of 90 rpm and with

287

large CNS provided the maximum production rate of about 353 ± 11 pieces/h (around 73.5 ±

288

2.75 kg/h) which was higher than the conic screw press (50 kg/h) (Sawadogo et al., 2018) and

289

multi-piston briquetting machine (12 kg/h) (Ndindeng et al., 2015). The production rate at 90

290

rpm irregularly changed with the variation in the mixture while 70 rpm was even for each binder

291

content. The production rate from small CNS at a speed of 70 rpm increased with the increment

292

in binder content; the binder content ranged from 10% to 20% and resulted in an increase in the

293

production rate from 151 to 164 pieces/h. The production rate at the same speed and with large

294

CNS decreased with the increased binder content. The increased binder content with larger CNS

295

at a low speed (70 rpm) led to the excess agglomeration of particles and a reduced production

296

rate. Results confirmed the changes in the production rate with the variation in operating

297

parameters and their interactions.

298 299

Fig. 6. The production rate at a speed of 70 and 90 rpm with A) small CNS and B) large CNS.

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3.3 Drying kinetics of fuel briquettes

301

MC of the fuel briquettes after mixing and compressing into fuel briquettes (shown in

302

Fig. 7) was in the range of 36-38% (w.b.) under every condition owing to the equal water

303

quantity in the binder (20% of the total mass). MC of all briquettes needs to be decreased below

304

10% (w.b.) (Missagia et al., 2011). The briquette was dried to reduce moisture and the drying

305

kinetics was determined. Mixture A was selected to determine the drying kinetics because it had

306

the maximum MC compared with that of the other mixtures. MC of the briquette rapidly

307

decreased in the first period of drying (3 or 4 days) and slowly decreased in the subsequent

308

drying time for all CNS sizes and screw speeds. The quick reduction in primary drying period

309

caused the fast evaporation of moisture at the briquette surface; the moisture within the briquette

310

was removed, and more time was required to remove the interior moisture to the briquette

311

surface when the surface dried, thereby allowing a slow drying rate. The drying time to obtain a

312

desirable briquette MC (< 10% w.b.) was 6 days. The trend of the change in moisture was similar

313

for every size and speed. Result indicated that the CNS size and screw speed did not affect the

314

decrease in MC.

315

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Fig. 7. Drying kinetics of fuel briquettes for mixture A with speeds of A) 90 rpm and B) 70 rpm.

317

3.4 Mechanical properties

318

3.4.1 Hardness

319

The hardness of the fuel briquette was reported in terms of the Shore D value in unit HB,

320

as represented in Fig. 8. The smaller size of the CNS caused the hardness of the briquette to be

321

higher than large CNS for mixtures A, B, D, and E with a speed of 70 rpm. The smaller particles

322

allowed more compact aggregation and led to the increase in hardness of the briquette. The

323

increase in binder content from 10% to 20% increased the hardness value, as shown in mixtures

324

A, B, D, and E with both CNS sizes and a speed of 70 rpm. The higher binder content made a

325

harder briquette (Ndindeng et al., 2015). The influence of CNS size and binder content on the

326

hardness was not clear when the quantity of CNS was lower than 40% and 45% (mixtures C and

327

F), which may have arisen from the deficient CNS content. The speed of 90 rpm provided the

328

maximum hardness value of 141 HB (62.7 N), which was intermediate when compared with that

329

of briquettes from rice husk char (21 N) and rice husk mixed with bran (101 N) (Ndindeng et al.,

330

2015). The hardness was unevenly changed with the variation in mixtures and speed.

331

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Fig. 8. Hardness of fuel briquettes at speeds of 70 and 90 rpm with A) small CNS and B) large

333

CNS.

334

3.4.2 Porosity

335 336

Fig. 9. Specific density of fuel briquettes at speeds of 70 and 90 rpm with A) small CNS and B)

337

large CNS.

338

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Fig. 10. Unit density of fuel briquettes at speeds of 70 and 90 rpm with A) small CNS and B)

340

large CNS.

341

Fig. 9 and 10 show the specific density and unit density of the fuel briquettes, respectively.

342

The specific densities of the briquettes under all conditions were more than the unit densities

343

owing to the lower volume from the exclusion of any pores and spaces inside the briquette. The

344

briquette was produced from both sizes of CNS showed an increasing trend in porosity following

345

the increase in ANS content at a speed of 70 rpm (as shown in Fig. 11); the increased porosity

346

implied a diminished density owing to the additional fiber content (Yank et al., 2016). The ANS

347

content increased to the maximum value for mixture C and reached the highest porosity value of

348

82.98%; the high porosity supported efficient combustion owing to the contact between air and

349

the briquette (Thabuot et al., 2015). The increase in porosity or reduction in density within the

350

briquette distinctly appeared when the CNS size increased, except for mixture C with a speed of

351

70 rpm. Muazu and Stegemann (2017) explained that the smaller particle had a higher density

352

owing to their lower compressible intraparticle porosity. The screw speed did not affect the

353

porosity.

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354 355

Fig. 11. Porosity of fuel briquettes at speeds of 70 and 90 rpm with A) small CNS and B) large

356

CNS.

357

3.5 Fuel properties

358

3.5.1 Calorific value

359

The CV of the briquettes is reported in Fig. 12. The average CV of the briquettes was in

360

the range of 18-21 MJ/kg. Sawadogo et al. (2018) reported the CV of cashew shell charcoal as

361

27.73 MJ/kg that was higher than the cashew press cake (20.78 MJ/kg) due to the augmentation

362

of fixed carbon after pass the complete carbonization process. On the other hand, the CNS aspect

363

in this study was the partial carbonization due to the roasting the cashew nuts and resulted in the

364

lower CV than the research of Sawadogo et al. (2018). However, the CV of the briquettes passed

365

the DIN51731 standard (at least 17.5 MJ/kg) (Faizal et al., 2018).

366

The decreasing proportions of CNS in each experimental condition resulted in the

367

decrease in CV. The decreased CV with the reduction in CNS content could be explained by the

Word count = 7995 368

CV of the CNS before transformation into briquettes. The CNS had the highest CV compared

369

with that of other materials within the mixture; thus, the change in CNS content directly affected

370

the CV of the briquette. The smaller CNS provided a higher CV. The maximum CV of 21.78

371

MJ/kg was provided from small CNS with speeds of 70 or 90 rpm with mixtures A or D; these

372

results confirmed that the speed did not influence the CV while the CNS size did. The increase in

373

binder content from 10% to 20% slightly reduced the CV for mixtures with every size and speed.

374

The decrease in CV with the addition of binder occurred because of the greater heat loss for the

375

elimination of added VM from the increase in flour quantity (Sawadogo et al., 2018).

376 377 378

Fig. 12. CV of briquettes at speeds of 70 and 90 rpm with A) small CNS and B) large CNS. 3.5.2 Moisture content

379

MCs from all experimental conditions were below 10% (w.b.) (as shown in Fig. 13). MC

380

within the CNS was lower than that of the ANS. MC inside the briquette significantly increased

381

with the increase in ANS content, except for mixtures D (90 rpm; small CNS) and C (70 rpm;

382

large CNS). The additional fiber content caused the increase in porosity and led to remaining

Word count = 7995 383

water in the inter-particle void (Yank et al., 2016). The decrease in screw speed influenced the

384

reduced MC for the same mixture and CNS size, except for mixtures B and F with large CNS.

385

This result may have arisen from the lower speed, which regularly compressed the particles and

386

led to increased moisture removal. The smaller CNS adsorbed more moisture than that of the

387

larger CNS with the same mixture and speed of 90 rpm. The effect of CNS size unclearly

388

appeared when the speed was reduced to 70 rpm.

389 390

Fig. 13. MC of fuel briquettes at speeds of 70 and 90 rpm with A) small CNS and B) large CNS.

391

3.5.3 Volatile matter content

392

Fig. 14 shows the VM of the fuel briquettes, which was in the range of 70-75%.

393

Sawadogo et al. (2018) reported that the VM of cashew shell charcoal briquettes is in the range

394

of 40-58%. These distinct VMs were caused by the significant loss of VM during the intensive

395

carbonization process into charcoal, while the CNS in this study were residual waste after

396

roasting cashew nuts with a weak carbonization process, which led to the small loss of VM. The

Word count = 7995 397

high VM of the briquettes promoted combustion but made a smokier blaze owing to the

398

combustion of volatile gases (e.g., methane and other hydrocarbons) (Pandey and Dhakal, 2013).

399

VM decreased with increased speed for every mixture, especially with large CNS. The higher

400

speed may have caused rapid squeezing of particles and resulted in greater VM discharge. The

401

mixture slightly affected the VM at similar speeds and CNS sizes. VM changed little with the

402

increase in binder content, and gradually decreased with the decrease in CNS content.

403 404

Fig. 14. VM of fuel briquettes at speeds of 70 and 90 rpm with A) small CNS and B) large CNS.

405

3.5.4 Ash content

406

Fig. 15 shows that the AC of the fuel briquettes under all experimental conditions was in

407

the range of 2.4-5.8%. The European standard (EN 14775) recommends an AC < 3% (Sawadogo

408

et al., 2018), while the ISO 18122 standard requires an AC ≤ 5% (Faizal et al., 2018).

409

ANS had the highest AC compared with that of the other materials in the mixture. The

410

increase in ANS content mainly influenced the additional AC under every condition, except for

411

mixture B at a speed of 70 rpm with small CNS. The increase in CNS size affected the reduction

Word count = 7995 412

in AC under all conditions, except for mixture F (90 rpm and large CNS). The larger CNS

413

provided more porosity in the fuel briquette than that with smaller CNS; thus, air could

414

thoroughly contact the briquette in both the internal and external area, so the fuel combustion

415

was better and led to the decreased AC (Thabuot et al., 2015).

416 417

Fig. 15. AC of fuel briquettes at speeds of 70 and 90 rpm with A) small CNS and B) large CNS.

418

3.5.5 Fixed carbon content

419

The FC, as shown in Fig. 16, was in the range of 17.23-20.62%, which was similar to that

420

of sawdust charcoal briquette (20%) (Akowuah et al., 2012). The low FC indicated rapid

421

combustion of the fuel briquette. The additional content of ANS reduced the FC under all

422

conditions, except for mixtures B (70 rpm; large CNS) and E (90 rpm; small CNS). The increase

423

in screw speed distinctly affected the FC in all mixtures with large CNS. The increase in the size

424

of CNS clearly caused a decrease in the FC in the identical mixtures with a speed of 70 rpm. The

425

effect of CNS size on FC was not clear when the speed increased to 90 rpm.

Word count = 7995

426 427 428

Fig. 16. FC of fuel briquettes at speeds of 70 and 90 rpm with A) small CNS and B) large CNS. 3.5.6 Combustion rate

429

Fig. 17 show that the CR of the fuel briquettes was in the range of 1-1.5 g/min, which

430

was very low when compared with that of rice husk char briquettes (7-9 g/min)

431

(Wongwuttanasatian and Sakkampang, 2016) and the fuel briquettes made from corn cob mixed

432

with palm fiber (2.9-3.2 g/min) (Thabuot et al., 2015). These different CR results may have been

433

caused by the distinct FC within the raw material, as the lower FC caused the briquette to burn

434

more quickly and led to a higher CR. The maximum CR of about 1.5 g/min showed in mixture

435

C, which had the maximum porosity. The high porosity stimulated the mass and heat transfer

436

during combustion and resulted in the high burning rate (Thabuot et al., 2015). The CNS size and

437

screw speed did not clearly influence the CR. The reduction in ANS content showed an

438

increasing trend in CR.

Word count = 7995

439 440

Fig. 17. CR of fuel briquettes at speeds of 70 and 90 rpm with A) small CNS and B) large CNS.

441

3.6 Relative importance of operating parameters

442

The CNS sizes, mixtures, and compressed screw speeds were the operating parameters

443

for producing briquette in this research. The effect of these parameters and their interactions on

444

the production rate, mechanical properties (hardness and porosity), and fuel properties (MC, CV,

445

VM, AC, FC, and CR) were evaluated. The production rate and mechanical and fuel properties

446

responded differently to the parameters, as shown in Fig. 18 and 19. The level of influence

447

indicated by the sum of squares value, as shown in Table 1. The higher sum of squares value

448

indicated a higher influence.

449

The production rate was influenced most by the screw speed, as it increased from 151 to

450

245 pieces/h when the speed increased from 70 to 90 rpm, respectively. The factors of size and

451

mixture did not significantly affect the production rate. The interaction of the three main factors

452

(mixture, size, and speed) affected the briquette hardness. The hardness showed an increasing

453

trend with the increase in speed and reduction in size (Ndindeng et al., 2015). The porosity was

Word count = 7995 454

most affected by the mixture factor, and particularly by the additional ANS content. The high

455

porosity affected the strength of the briquette (Muazu and Stegemann, 2017).

456

457

458 459

Fig. 18. The effect of operating parameters on A) production rate, B) hardness, and C) porosity.

460

The fuel properties were less influenced by the operating parameters than the production

461

rate and mechanical properties, as indicated by the lower sum of squares values. The speed

462

influenced the MC more than other factors because the slower particle movement from the lower

463

speed discharged more moisture. The mixture had the second greatest influence on the MC; the

464

additional fiber content caused the increase in porosity and resulted in the increase in MC owing

465

to the residual water in the void (Yank et al., 2016). VM was affected most by the mixture. CV

Word count = 7995 466

and AC were equally affected by the mixture. The interaction between size and speed had a

467

greater effect on the FC than the main effect. The CR was least affected by the operating

468

parameters compared with other properties, and the mixture affected the CR the most. Overall,

469

the properties mentioned above were used to determine the appropriate conditions for briquette

470

production. The desirable conditions for production were comprised of a high production rate of

471

approximately 50 kg/h (Sawadogo et al., 2018), a high hardness of 31-132 N (Ndindeng et al.,

472

2015), intermediate porosity to balance between the improvement in combustion efficiency

473

(Thabuot et al., 2015) and decreasing strength (Muazu and Stegemann, 2017), a CV ≥ 17.5

474

MJ/kg (Faizal et al., 2018), MC < 10% (w.b.) (Missagia et al., 2011), AC ≤ 5% (Faizal et al.,

475

2018), high VM (approximately 60%) (Sawadogo et al., 2018), low FC (approximately 38-54%)

476

(Sawadogo et al., 2018), and high CR (approximately 2-4%) (Thabuot et al., 2015).

477

The fuel briquette produced from the operating parameters in study had the following

478

qualities compared with the required criteria: the average production rate was in the intermediate

479

range (151-245 pieces/h), the average hardness was in the intermediate range (103-123 (HB)),

480

the porosity was in the intermediate range (52-65%), the average CV was higher than the lowest

481

criterion (18.9-21 MJ/kg), the average MC passed the criterion (3.5-4.5% (w.b.)), the average

482

VM was in the high range (71.2-73.2%), the average AC was close to the standard value (3.3-

483

5.2%), the average FC was low (18.8-20%), and the average CR was low (1.1-1.2%).

484

Briquette production from CNS combined with ANS should be conducted with mixture A

485

because this mixture provided fuel properties that met the standard levels, especially the

486

maximum CV and the lowest VM. The size of CNS should be small because they provided lower

487

porosity and lower AC, while other properties were similar except for a higher FC. The screw

Word count = 7995 488

speed of 90 rpm should be used because it provided a high production rate even though it

489

obtained a lower VM and higher FC; the other qualities did not differ with the speed of 70 rpm.

490

491

492

493

494

Word count = 7995

495 496

Fig. 19. Effect of operating parameters on A) MC, B) CV, C) VM, D) AC, E) FC, and F) CR.

497

Table 1 ANOVA of the briquette properties and production rates as affected by the operating

498

parameters (mixture, CNS size, and screw speed). Sum of squares (P-value) Properties Mixture (M)

Size (S)

Speed (s)

MxS

Mxs

Sxs

MxSxs

19384(NS)

9023(NS)

144184***

36960***

20855***

5512***

31215***

Hardness (HB)

2818**

1932*

1891*

1583(NS)

2394*

165(NS)

3006**

Porosity (%)

2442***

1191***

325(NS)

1244***

874***

75**

1698***

MC (%w.b.)

6*

0.6(NS)

7***

6***

2***

6***

2***

CV (MJ/kg)

33***

1(NS)

4(NS)

14***

12***

6***

15***

VM (%)

35***

39***

25***

15***

6***

8***

4***

AC (%)

33***

5**

0.02(NS)

4***

2***

4***

2***

FC (%)

14**

15***

10***

2**

2*

17***

2*

0.62***

0.001(NS)

0.01(NS)

0.05(NS)

0.03(NS)

0.02(NS)

0.35***

Production rate (pieces/h)

CR (g/min)

499

The levels of statistical significance of the mean values are * ≤ 0.05, ** ≤ 0.01, *** ≤ 0.001, and NS = not significant.

500

3.7 Potential of fuel utilization

501

The relationship between operating parameters and fuel briquette characterization in

502

previous section indicated that the proper condition for fuel production. The suitable condition

503

(mixture A, a screw speed of 90 rpm, and small CNS) was chosen to evaluate the fuel utilization

504

compared with the charcoal as represented in Fig. 20. The average FT of briquette was about

505

570°C which was lower than the charcoal (645°C); result corresponded with the lower CV of

Word count = 7995 506

fuel briquette (21.5 MJ/kg) as collated with the charcoal (29.6 MJ/kg); the higher CV caused

507

from the low MC inside charcoal (Anca-Couce, 2016); the charcoal had the eradication of

508

hydroxyl groups due to the carbonization process and provided the decreased moisture

509

adsorption (Jiang et al., 2013). WBT result agreed with the FT result by the water boiling

510

duration of charcoal (44.3 min) was less than the fuel briquette (55.7 min). Sawadogo et al.

511

(2018) reported that the boiling time of water about 47 min for combustion using cashew shell

512

charcoal (CV of 27.73 MJ/kg). Their results showed the lower boiling time than fuel briquette in

513

study due to the higher CV. The fuel briquette and wood charcoal were tested the TE during

514

WBT using a conventional cook stove. Both fuels showed the same TE in the range of 37.1-

515

38.8%; whereas the cashew shell charcoal presented low TE at 33.9% (Sawadogo et al., 2018).

516

The low TE may rise from the low performance of cook stove which affected to conserve heat

517

during water boiling and resulted in the rapid heat loss from cook stove to the environment

518

(Lubwama and Yiga, 2018). GHG emission was evaluated from fuel combustion during WBT.

519

Fuel briquette from CNS and ANS obviously provided the lower GHG emission (250 gCO2e)

520

than charcoal (460 gCO2e). Results due to the less fuel consumption with low CR at 1.3 g/min

521

whereas the charcoal presented with high CR at 120 g/min (Ndindeng et al., 2015). This CO2e

522

emission of briquette was compared with the other widely used fuels such as LPG and kerosene

523

through the same calculation (eq.10); the fuel consumption was similar as 0.152 kg; the heating

524

value of LPG and kerosene were 47.3 and 43.8 MJ/kg, respectively (Ramachandra et al., 2015);

525

CO2 emission factor of LPG and kerosene were 63.1 and 71.9 gCO2/MJ, respectively

526

(Ramachandra et al., 2015); the calculation results of CO2e emission were 453 gCO2e for LPG

527

and 478 gCO2e for kerosene. The fuel briquette in study demonstrated the good result for the

528

lower GHG emission (only CO2 emission) as compared with the above fuels, however, the GHG

Word count = 7995 529

emission may change with the combustion efficiency which chiefly associated with combustion

530

apparatus (Roy and Corscadden, 2012). Pilusa et al. (2013) studied the flue gas emission from

531

eco-fuel briquette using the database of occupational safety and health agency (OSHA) was the

532

benchmark for toxic gas exposure limits. The OSHA defined the maximum exposure limit of

533

CO2 about 5000 ppm or 5000 g/m3 which was the safety level for human. SRREN (2011)

534

reported the renewable energy technology had the principal role on the stability of CO2

535

concentrations in atmospheric which affect the global warming situation. The CO2

536

concentrations should be stabilized at a level ≤ 440 ppm or 440 g/m3. The CO2 emission from

537

fuel briquette was 250 g with the air volume of 40 m3 which it could be converted into 6.25 g/m3.

538

This result indicated the low GHG emission corresponded with the environmental criterion.

539

Therefore, these results indicated the possibility of fuel briquette utilization in term of domestic

540

cooking which translates into savings in energy usage and reducing in GHG emission.

541 542

Fig. 20. The potential of fuel utilization in term A) FT, B) WBT, C) TE, and D) GHG emission.

Word count = 7995 543 544

4. Conclusion

545

CNS and ANS can produce into fuel briquette using the densification process. The results

546

revealed the relationship between the briquette characteristics and operating parameters, and

547

including the fuel utilization. The main results were as follows:

548 549 550 551 552 553

1. The increased speed from 70 to 90 rpm clearly improved the briquette production rate. The average production rate was 245 pieces/h (52 kg/h). 2. The increased ANS content was related to the increase in porosity. The maximum CNS quantity (65% by weight) obtained the highest average CV (21 MJ/kg). 3. The CNS size reduced from large to small that mainly increased the FC (18-20%) and AC (3-5%), but decreased the VM.

554

4. The operating parameters slightly affected the MC variation and hardly affected the CR,

555

while the interaction of the three main factors largely influenced the hardness. The

556

suitable condition for briquette production was the mixture A with a screw speed of

557

90 rpm and small CNS. These operating conditions provided an adequate briquette

558

production rate (245 pieces/h) with acceptable fuel properties (i.e., porosity, hardness,

559

VM, and FC) and passed the standard (i.e., CV, MC, and AC), except when the CR

560

was low.

561

5. The fuel utilization in domestic cooking had the feasibility as pointed the moderate FT

562

(570°C), the boiling duration < 1 hour, the TE equated with wood charcoal (37%),

563

and the low GHG emission (250 gCO2e).

564

Results showed the use of simple and clean processes compared with those for briquette

565

production from cashew shell charcoal, which is a difficult method owing to the carbonization

Word count = 7995 566

process. The understanding of the relationship between the operating parameters and briquette

567

characteristics could be adapted to obtain desirable briquette qualities that correspond with the

568

utilization requirements. The interesting potential of fuel briquette utilization for cooking could

569

be used to the guideline for other applications.

570 571

Acknowledgements This research project was supported by King Mongkut’s Institute of Technology

572 573

Ladkrabang (A118-0460-013).

574 575

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Highlights •

Shell of cashew nut and areca nut can reuse into the renewable energy source.

•

Operating parameters affected the fuel briquette characteristics.

•

Briquette production rate obtains the most effect from the compressed screw speed.

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Briquette has the high quantities of calorific value and volatile matter.

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Briquette utilization can use household cooking with low CO2 emission.

Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: