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Heated-die Screw-press

Biomass Briquetting Machine: Design, Construction and Operation Manual

Prepared under

Renewable Energy Technologies in Asia: A Regional Research and Dissemination Programme

(RETs in Asia)

Funded by

Swedish International Development and Cooperation Agency

(Sida)

Energy Field of Study School of Environment, Resources, and Development

Asian Institute of Technology Thailand

1

Heated-die Screw-press

Biomass Briquetting Machine: Design, Construction and Operation Manual

Renewable Energy Technologies in Asia: A Regional Research and Dissemination Programme

(RETs in Asia)

Energy Field of Study School of Environment, Resources, and Development

Asian Institute of Technology Thailand

3

RENEWABLE ENERGY TECHNOLOGIES IN ASIA A Regional Research and Dissemination Programme Heated-die Screw-press Biomass Briquetting Machine: Design, Construction and Operation Manual PUBLISHED BY

Regional Energy Resources Information Center (RERIC) Asian Institute of Technology P.O. Box 4, Klong Luang Pathumthani 12120 Thailand E-mail: [email protected] Website: http://www.serd.ait.ac.th/reric/ Copyright © 2003. Regional Energy Resources Information Center (RERIC), Asian Institute of Technology. All rights reserved. No part of this book may be reproduced by any means, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the written permission of the publisher. Printed in Thailand Neither the Swedish International Development Cooperation Agency (Sida) nor the Asian Institute of Technology (AIT) makes any warranty, expressed or implied, or assumes any legal liability for the accuracy or completeness of any information herein provided. References herein to any apparatus, product, trademark or manufacturer do not constitute or imply its endorsement, recommendation or favouring by Sida or AIT.

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Preface This work is a result of adaptive research and development activities carried out within a regional programme entitled “Renewable Energy Technologies in Asia: A Regional Research and Dissemination Programme (RETs in Asia)”. The programme was sponsored by the Swedish International Development Cooperation Agency (Sida), and was coordinated by the Asian Institute of Technology (AIT). Thirteen national research institutes from six Asian countries: Bangladesh, Cambodia, Lao PDR, Nepal, Philippines and Vietnam were involved in the programme. It promoted three technologies: solar photovoltaics, solar drying and biomass briquetting. This booklet contains the design, construction and operation details of an improved heated-die screw-press type biomass briquetting system developed within the biomass briquetting project. The major improvements achieved in the present design compared to existing briquetting systems of similar type are (i) reduction in electrical energy consumption, (ii) enhanced screw life, and (iii) smoke reduction. With these improvements, the system is expected to produce cheaper briquettes, which can effectively replace fuelwood, which are currently the dominant cooking fuel in rural households. With lesser smoke released during the improved briquetting process, it is also less harmful to the operator.

Prof. S.C. Bhattacharya December 2003 RETs in Asia Coordinator

5

Table of Contents Page

No.

1. Introduction 5

2. Design and Construction Details 6 2.1 Briquetting Machine 6

2.2 Biomass Pre-heater 6 2.3 Biomass Die-heating Stove 6 2.4 Smoke Removal System 7

3. Design Drawings 9

4. Operational Details 25 3.1 Effects of Biomass Pre-heating and Screw Speed on Briquetting Energy Consumption

25

3.1.1 Introduction 25 3.1.2 Testing with Wide-pitch Screw 25 3.1.3 Testing with the Close-pitch Screw 26 3.1.4 Performance of the Biomass Stove Die Heater

27

3.1.5 Conclusions 27 3.2 Effects of Raw Material Type on Briquetting Energy Consumption and Screw Life

29

3.2.1 Introduction 29 3.2.2 Rice husk as raw material 29 3.2.3 Mixed Raw Materials of rice husk and saw dust

32

3.2.4 Conclusions 33

7

1. Introduction Biomass briquetting research within the RETs in Asia programme has been conducted with two main objectives: (i) to improve the biomass briquetting system by reducing the electrical energy consumption, enhancing the screw life, and by incorporating a smoke removal system, and (ii) to develop domestic as well as institutional type biomass stoves which can burn briquettes. Towards achieving these objectives, several prototype designs were developed and tested at AIT. Based on the experimental results, final designs of a biomass pre-heater, biomass die-heating stove and a smoke removal system were developed. Additional experiments were carried out to investigate their performance and to find the optimum operating parameters. This report presents the details of the design and the results experiments thus carried out.

2. Design and Construction Details The improved briquetting system developed at AIT consists of the following: a briquetting machine, a biomass pre-heater, biomass die-heating stove and a smoke removal system. 2.1 Briquetting Machine:

The briquetting machine used in this study was a Bangladeshi design, the major components of which were imported by AIT from BIT. All planned improvements were implemented on this machine, and tests were conducted. Table 1 presents the technical specifications of the machine. Figure 1 shows the improved briquetting system configuration; while drawings of the machine, screw and die are given in figures 2, 3 and 4 respectively.

Table 1. Technical specifications of the basic biomass briquetting machine

S. No. Item Description Quantity

1. Induction motor 20 HP at 1450 rpm, 380 volts/ 3 phase 1 unit 2. V-Belts B-90 2 pcs

3. Pulleys (Cast iron) 12.5 cm dia. 47.0 cm dia.

1 no. 1 no.

4 Bearings N 6312 N 6311

1 no. 1 no.

5 Main power transmission shaft (Bright steel) 3" dia. 1 no.

7 Die (Cast iron) 9.7 cm dia., 30 cm long 1 no. 6 Screws (Mild steel) 2 1/4" dia., 45 cm long 1 no.

8 Bush (Cast iron) Dia: 73 mm outside x 59 mm inside Length: 32 mm 1 no.

9

2.2 Biomass Pre-heater:

The biomass pre-heater is essentially a shell and tube heat exchanger. Biomass is passed through the ‘tube’ by a motor-driven screw feeder, while hot flue gases from a biomass gasifier passes through the ‘shell’. Temperature of the flue gases could be controlled by mixing cold air with the hot gases. The preheater was 1.2 m long and 42 cm wide and consisted of a feeder drum placed on a rectangular chamber. The raw material was preheated while being conveyed through the feeder drum by means of a screw. The preheater screw was rotated by a variable speed motor. The hot flue gas from the combustion chamber was passed through the space between the feeder drum and the rectangular chamber and discharged to the atmosphere. Thus, the feeder drum was heated by the flue gas at the bottom. The rectangular chamber was insulated by a 2.5 cm thick layer of rockwool insulation to reduce heat loss to the surroundings. Pre-heated raw material from the preheater exit was fed directly to the briquetting machine. The speed of the preheater screw feeder could be selected based on the required biomass flow rate into the briquetting machine. Electrical energy consumption by briquetting machine, die heaters and preheater motor may be recorded from energy meters installed for the purpose. Figures 5-8 present the detailed design of the pre-heater assembly developed at AIT. 2.3 Biomass Die-heating Stove:

After conducting extensive studies with a biomass gasifier stove and a combustion stove, the later was found to perform better, by offering steady die temperature and better temperature control. The stove was of mild steel (1.5 mm sheet) construction, with a furnace of 20 cm x 35 cm x 40 cm (w x b x h) volume and 2 m long chimney attached to it at the top. The die of the briquetting machine passes through the furnace, exposing its outer surface to the flames inside the furnace. The furnace was insulated with a 30 mm refractory lining at its inner surface. Doors were provided for loading the fuel as well as to remove the ash. An ash scraper was fixed below the grate to remove excess ash from the furnace, which will fall through the grate. Two steel baffles were fixed just above the die, to converge the flames towards the die surface. They were insulated at both sides using refractory cement. The baffles were found to improve the heat transfer from the flames to the die considerably.The design details of the stove has been given in Figure 9. Fuel (briquette pieces of size 40 x 40 mm size) is loaded through the side doors upto the bottom level of the die and ignited using some wood chips and kerosene. When the die temperature reached 350°C, the briquetting machine is started. During production, the temperature drops to 320-330°C, and this

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can be maintained by adding fuel periodically (every 5 minutes) to the stove. Primary air for combustion is taken through the ash pit door, which is kept open during operation. Secondary air is taken through the fuel doors, which also are kept open partially. Figures 10 and 11 show the stove during operation. 2.4 Smoke Removal System:

The system has three main components: (i) a smoke collection box, (ii) a suction line connecting the primary air supply port of the biomass stove to the smoke collection box at the top, and (iii) another suction line which connects the exhaust of the die-heating stove to the biomass pre-heater. The metal box traps the smoke during the briquetting process, the deflector mechanism breaks the briquette into certain lengths, and the smoke is sucked through the biomass stove, whose exhaust is connected to a chimney through the biomass pre-heater. The schematic diagram of the system is given in Fig 12. The exhaust from the stove is used for pre-heating the biomass raw material. Smoke produced from briquettes is collected in the box and burnt up in the stove. Unburned gases, along with the exhaust flue gas of the stove, are sucked through the biomass pre-heater using a suction blower, and exhausted through a chimney; Figure 13 presents the system configuration. The smoke collection box is constructed of mild steel sheet of 1.5mm thickness. A circular conduit is fixed at one end of the box, where briquette from the die of the briquetting machine enters the box. The edge of the conduit welded to the metal box serves to snap the briquette which comes out of the die, assisted by the deftector plate as shown in Figure 14. The deflector plate is rigidly fixed to the body of the metal box. A strip of MS sheet is fixed below the path of briquette, and another perforated sheet above, to ‘guide’ the briquette straight. A slider plate is provided below the path of the briquette so that the broken piece of briquette slide through the plate and exits the box at the bottom. A conical cover (hood) is fixed to the box using a water-seal, which prevents smoke from escaping the joint. The exhaust from the smoke collection box is connected to a flexible aluminum duct (commonly used in air condition ducting), the other end of which is connected below the grate of the die-heating stove. The smoke thus enters the stove along with its primary air supply, and is burnt up in the stove. It was found that occasionally, the briquette entering the smoke collection box tends to bend sideways, thus affecting normal operation. Two guide plates, one below and the other above the briquette, fixed along the path of the briquette, eliminate this problem. The top plate is perforated so as not to

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obstruct the flow of smoke upwards. Handles are provided to the metal box for easy handling. Figure 14 presents the detailed drawing of the smoke collection box. The isometric view of the box is given in Figure 15. Figures 16-19 illustrate the design and operation of the system in detail. A suction blower of 150W, fixed at the pre-heater exit provides the required suction to overcome the resistance for the flow of flue gas inside the pre-heater. The capacity of the blower was selected such that the airflow provided the required pre-heat temperature (110-120°C), while maintaining the die temperature at 300-320°C. (It has been found, from experimental results, that a pre-heat temperature of 110-120°C for a screw speed of 370 rpm is the optimum in terms of less briquetting energy consumption for the particular briquetting machine). During operation, the die temperature is maintained at 300-320°C by adjusting the fuel feeding to the stove. The pre-heat temperature, however, fluctuates more (in the range of 90-130°C), as there is no provision in the set-up to control it independently. It is felt that the benefit from such a system to independently control pre-heat temperature will not be economically justifiable. It may also add to operational difficulties and require fairly skilled technicians to operate the briquetting system. Care should be taken while operating the machine using raw material with moisture content in excess of 7%. Briquettes tend to ‘shoot’ through the die as the steam trapped inside the die tries to escape. Raw material should therefore be dried sufficiently before using, so that moisture levels are below 7%. Sufficient protection should be provided to avoid damage that may be caused by flying pieces of briquettes through the mouth of the die in case of ‘shooting’.

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3. Design Drawings

Figure 1: Schematic DBiomass Pre-heater,

Figur

1. Biomass Pre-heater 7. Flexible pipe

2. Screw feeder 3. Biomass stove for die heating 4. Smoke collection box 5. Main bearing for screw 6. Motor of briquetting machine

8. Flue gas suction blower 9. Raw material hopper 10. Motor for feeder screw 11. Conduit pipe

iagram of the Improved Briquetting System incorporating the Biomass Die-heating Stove and the Smoke Removal System

All dimensions are in centimeters

16015

67

100

125

e 2. Design details of the briquetting machine

13

3

Grooving: R7

All dimensions are in

Figure 3. Briquetting Die (Bangladeshi Design)

6

37

All dimensions are in

Figure 4. Briquetting Screw (Bangladeshi Design)

14

FEEDING HOPPER

OUTER PIPE INNER PIPE

SCREW

Preheated biomass

FromGasifier

740

43

Raw material

Note: All dimensions are in millimeter

Figure 5. Biomass Preheating System: General View

15

BAFFLE

II

3

φ 160

500 500 500

D1=210 D2 =350

FLUE GAS EXIT (L100 GI PIPE)

φ 60

500

I

Figure 6. Biomass Preheating System: Outer Pipe

16

WELDING LINE

D2 =R:170

R:10

BAFFLE

WELDING LINE

SECTION I SECTION II

Note: - Material: Mild Steel Sheet, δ = 3 mm - Welding of two end flanges will be done after fixing the inner pipe inside the outside tube - All dimensions are in millimeters

Figure 7. Outer Pipe: Details of sections I and II

17

φ 100 3

φ 24

D 210

FLANGE

φ 250, 8 HOLES

BEARING φ 30

φ 250

Note: All dimensions are in millimeterφ 80

φ

BEARING φ 30

A

A

2,300 2.4

A - A

Figure 8. Biomass Preheating System: Inner Pipe

18

66 66

66 66 66 66

φ 23φ 30

20

2,400

R = 35

R = 100

BAFFLE 40

A - A

Figure 9. Biomass Preheating System: Feed Screw

19

Note: All dimensions are in millimeter

Refractory insulation

3 thick

Die dia. + 0.2 10

12

10

12

2

Chimne

15

35

15

Rods for grate

Ash pit door 20 x 13

22

115

Figure 10. Die Heating Stove for Briquetting Machine

20

Figure 11. Biomass Die Heating Stove in Operation

Figure 12. Combustion inside the stove

21

Smoke Collection

Box

Biomass Die-heater

Stove

Suction Blower

Chimney

Smoke Exhaust

Biomass Pre-

heater

Figure 13. Schematic diagram of the Smoke Removal System

Die of Briquetting Machine

Die-heating Stove

Conical Hood

Smoke Collection

Exit for briquette

To PreheatingSystem

Conduit Grate

Flexible Aluminium Duct

Chimney

Figure 14. Schematic diagram of the Smoke Removal System

22

Circular opening, 9 cm dia.

R12

8

B

AA

Section A-A

B

View B-B

Briquette

Die of Briquetting Machine

BriquetteSheet Metal Box (59x45x52

59

52

Slider

Deflector Plate

Briquette Exit

14

8

Smoke Collection Box

Top View

Handles

Conduit, 9∅

45

Perforated guide plate

Figure 15. Final Design of the Smoke Collection Box

23

Conduit 9 cm Ø

Water seal (2 cm wide x 2cm deep)

Deflector Plate

Connection to stove primary air inlet

8

Hood

52

45 59

Figure 16. Isometric view of the smoke collection box

Figure 17. Smoke collection box - inner details

24

Figure 18. Smoke collection box - assembled view

Figure 19: Smoke Removal System in Operation

25

4. Operational Details

4.1 Effects of Biomass Pre-heating and Screw Speed on Briquetting Energy Consumption 4.1.1 Introduction A detailed analysis was done on the improved briquetting system to study the effects of biomass pre-heating and screw speed on the energy consumption of the briquetting process. The electrical coil heaters were used for die heating since measurement of energy consumption is easier and more accurate than if a biomass stove die-heater is used. Two designs of briquetting screws were developed by BIT, for higher and lower screw speeds. The design variation was only on the pitch of the screw, which was wider in one design than the other. Experiments were conducted on both the designs, to analyse their technical performance. This report presents the experimental data, results and analysis. 4.1.2 Testing with the Wide-pitch Screw First, the briquetting experiments were performed using the wider pitch screw with and without biomass preheating. Ricehusk was used as raw material. Tables 2 and 3 present the summary results of the experiments. Average total electrical energy consumption by the briquetting machine without biomass pre-heating was 0.20 kWh/kg at an average production rate of 85.4 kg/hr (Table 2) whereas, briquetting with biomass preheating consumed an average of 0.178 kWh of electrical energy for each kg of briquettes produced (Table 3).

Table 2. Briquetting with wider pitch screw, without biomass pre-heating

Run Average die Production Electricity consumption (kWh/kg)

No. Temp. (°C) rate (kg/hr) Heater Motor Total

1 440 84.6 0.077 0.128 0.206 2 430 84.0 0.074 0.126 0.200 3 440 81.4 0.070 0.140 0.210 4 410 85.0 0.071 0.123 0.194 5 410 92.0 0.065 0.126 0.191 Average 85.4 0.0714 0.1286 0.2002

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Table 3. Briquetting with wider pitch screw, with biomass pre-heating

Run No.

Average die

temp,

Avg. biomass

temp,

Production rate

Electricity consumption kWh/kg

°C °C kg/hr Heater Motor Total 1 420 110 87.7 0.068 0.106 0.179 2 410 120 81.0 0.059 0.115 0.178 3 410 125 78.5 0.064 0.104 0.176 4 410 130 80.6 0.061 0.112 0.179 5 410 150 83.9 0.061 0.109 0.177 Average 82.34 0.0626 0.1092 0.1778

Average savings in the electrical energy consumption due to pre-heating were 12.3% at heater and 15.1% at motor respectively. The average total energy saving (electrical heater and motor) was about 11.2%.

For briquetting with preheating, the highest and lowest electrical energy input to the system were found to be 0.18 kWh/kg and 0.17 kWh/kg of briquettes produced, respectively. The highest and lowest electrical energy consumption for briquetting without biomass preheating was found to be 0.21 kWh/kg and 0.19 kWh/kg of briquettes produced, respectively. Production capacity was in the range of 80 - 90 kg/hour and good quality briquettes could be produced at a die temperature of around 410-440°C. Nevertheless, electrical energy was saved at the heater, motor and overall system. When the die temperature was below 400°C, the quality of briquettes produced was poor, as indicated by many cracks on the briquette surface. 4.1.3 Testing with the Close-pitch Screw Briquetting experiments were also carried out with the screw having closer pitch. The results of the experiments are presented in Table 4 and 5.

Table 4. Briquetting with close-pitch screw, without biomass pre-heating

Run Average die Production Electricity consumption (kWh/kg) No. temp. (°C) rate (kg/hr) Heater Motor Total 1 390 91.6 0.060 0.112 0.172 2 390 87.7 0.071 0.113 0.184 3 365 85.9 0.071 0.110 0.181 4 380 88.3 0.070 0.110 0.180 Average 88.38 0.068 0.111 0.179

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Table 5. Briquetting with close-pitch screw, with biomass pre-heating

Run No.

Average die

temp:

Average biomass

temp:

Production rate

Electricity consumption kWh/kg

°C °C kg/hr Heater Motor Total 1 390 100 82.2 0.058 0.094 0.168 2 370 115 81.2 0.053 0.105 0.165 3 390 130 80.0 0.045 0.097 0.150 4 390 140 84.5 0.052 0.101 0.161 Average 82.0 0.052 0.099 0.161

In the case of closer pitch screw, average electrical energy savings at the heater, motor, and overall system were 23.5%, 10.8%, and 10.2% respectively. The production capacity was also slightly higher than that for the wider pitch screw. 4.1.4 Performance of the Biomass Stove Die Heater The briquetting machine was tested with a biomass stove die-heater as well, the fuel for the stove being ricehusk briquette chips. The briquette quality was very good at a temperature of around 320°C, in the beginning of the operation. With the passage of time, the temperature gradually came down to 250°C and briquettes could still be produced only with a change of color of briquette surface from black (at higher temperature) to gray (at lower temperature). It takes around 35 minutes to bring the die temperature to 320°C, when briquetting could be started. The die temperature was noted to often go out of control, irrespective of primary air supply control. It was found that this was due to fuel blockade inside the pyrolysing chamber. An ash scraper was then introduced, which could be operated at regular intervals (once in 15-20 minutes) to clear the accumulated ash. The stove performed remarkably well after this modification. 4.1.5 Conclusions Experiments were conducted to investigate the effect of raw material pre-heating, screw speed and screw pitch on the overall energy consumption. Two screws - a wide-pitch screw and a close-pitch screw - were used in the experimentation. It was observed that the close-pitch screw design performed better than the wide-pitch screw. It consumed lower electrical energy for both with and without biomass pre-heating compared to the other. Moreover, in the case of close-pitch screw, the briquetting could be accomplished at comparatively lower temperature. The following observations were made while using ricehusk as briquetting raw material:

28

♦ Average savings in the electrical energy consumption due to pre-heating were 23.5% at heater and 10.8% at motor respectively, with close-pitch screw. The average total energy saving was about 10.2%.

♦ The lowest electrical energy consumption for rice-husk was

0.172 and 0.150 kWh/kg of briquettes produced, without and with preheating respectively.

The above results do not take into account the electrical energy consumed by the motor, which feeds the raw material through the biomass pre-heater. If that is taken into account, the net energy saving due to pre-heating ricehusk may not be significant. It was found that the moisture content of ricehusk should not be more than 7-8% for smooth operation of the machine. At higher moisture levels, shooting occurs from the die outlet while the briquetting operation was on, and briquettes could not be produced both with and without biomass preheating. 4.2 Effects of Raw Material Type on Briquetting Energy Consumption

and Screw Life 4.2.1 Introduction Experiments were conducted on the final design of the improved briquetting system, integrating the biomass pre-heater, die-heating stove and smoke removal system, to investigate the effect of raw material type on the performance of the integrated system. This section presents the test results and operating parameters of the improved briquetting system based on the experiments conducted. A set of experiments were carried out without pre-heating the biomass, and another set with pre-heated biomass, to measure the energy savings due to pre-heating as well. Other parameters such as screw speed and die temperature were maintained constant in both cases, to the possible extent, for a consistent comparison. Biomass stove was used in both the cases for die heating. Two sets of experiments were conducted: (1) with ricehusk, and (2) with mixed raw materials, of ricehusk and sawdust, at 1:1 ratio, to investigate the energy consumption of the briquetting process as well as the life of briquetting screws.

29

4.2.2 Ricehusk as raw material The briquetting machine was run at three different screw speeds, 370 rpm, 465 rpm, and 560 rpm, and its performance evaluated. Tables 6 and 7 present the experimental results at a screw speed of 370 rpm, with and without pre-heating.

Table 6. Briquetting without preheating. Screw speed: 370 rpm

Expt. No. Production rate (kg/hr)

Total energy consumption

(kWh/ kg)

Moisture content (%)

Average Die Temp. (°C)

1 68.5 0.107 9.6 260 2 64.8 0.103 9.3 237 3 68.0 0.103 9.1 248

Average 67.1 0.104 248

Table 7. Briquetting with preheating. Screw speed: 370 rpm



(kWh/ kg)



1 63.0 0.121 9.3 266 2 66.0 0.088 9.3 273 3 68.9 0.137 9.7 226

Average 66.0 0.115 255 It may be noted that the total electrical energy consumption of the briquetting process actually increased with pre-heating the ricehusk, indicating a possible mis-match between the screw speed and optimum loading of the electrical motor. The screw speed was therefore increased to 465 rpm, and the experiments were continued. Tables 8 and 9 present the results of the experiments.




(kWh/ kg)



1 66 0.152 9 224 2 70 0.133 9 251 3 84.5 0.116 11 253

Average 73.5 0.133 243

30



Total energy consumpn. (kWh/ kg)

Moisture content

(%)


1 73.0 0.131 8.5 253 2 76.3 0.133 6.1 248 3 69.6 0.115 9.1 271

Average 73.0 0.126 257 At a screw speed of 465 rpm, the total electrical energy consumption slightly decreased with pre-heating the ricehusk. The decrease was however not significant. Also, there was a general increase in energy consumption at this screw speed, both with and without pre-heating, when compared to screw speed of 370 rpm. No significant difference was noted in the production rate. The screw speed was further increased to 560 rpm and the results analysed. Tables 10 and 11 present the results of the experiments at 560 rpm.

Table 10. Briquetting without preheating. Screw speed: 560 rpm Expt. No. Production

rate (kg/hr) Total energy consumption

(kWh/ kg)



1 78.0 0.131 11.0 237 2 80.6 0.150 9.0 238 3 87.4 0.130 9.5 230

Average 82.0 0.137 235


Expt. No.

Production rate (kg/hr)


(kWh/ kg)



1 79.6 0.113 8.7 230 2 73.7 0.135 9.2 225 3 61.0 0.163 8.6 246

Average 71.4 0.137 234 Figure 20 illustrates the relationship between the screw speed, production rate and energy consumption, with ricehusk as raw material.

31

Screw Speed Vs Production Rate and Power Consumption(100% rice husk)

40

50

60

70

80

90

100

370 465 560

Screw speed (rpm)

Prod

uctio

n ra

te (k

g/ h

r)

0.000

0.020

0.040

0.060

0.080

0.100

0.120

0.140

0.160

Pow

er c

onsu

mpt

ion

(kW

h/kg

)

Production rate Power consumption

(a) Without pre-heating

Screw Speed Vs Production Rate and Power Consumption (100% Rice husk)

40

50

60

70

80

90

100

370 465 560Screw speed (rpm)

Prod

uctio

n ra

te(k

g/hr

)

0.100

0.105

0.110

0.115

0.120

0.125

0.130

0.135

0.140

Pow

er c

onsu

mpt

ion

(kW

h/K

g)


(b) With preheating Figure 20. Screw speed Vs. Production Rate and Specific Energy Consumption,

with ricehusk as raw material

Energy Consumption:

With ricehusk as raw material, the energy consumption figures with and without pre-heating show inconsistent results, with no direct correlation between energy consumption, production rate and screw speed. While pre-heating results in a slight reduction in energy consumption by the electrical motor driving the screw, the saving, in most cases, is more than offset by the energy consumed by the motor driving the conveyor screw in the biomass pre-heater. Thus, the experimental results so far indicate that pre-heating ricehusk does not seem to offer definite energy saving advantages. Briquetting Screw Life:

It has been noted that a higher briquetting screw speed reduces the screw life and therefore is not a preferred option to increase production rates. Screw life was found to be highest at a screw speed of 370 rpm while it was lowest at 560 rpm. Pre-heating the ricehusk seems to decrease the screw life by about 25% for screws made of mild steel, and tempered in oil. Briquette Quality:

Briquette quality is inspected visually, and judged in terms of the smoothness, cracks, and colour of the briquette surface. Without pre-heating, the quality of ricehusk briquettes is generally better than that with pre-heating. This may be due to drying of the ricehusk during the pre-heating process to below a minimum level of moisture, which is required for good binding of the ricehusk particles.

32

It was found that fresh ricehusk is a better raw material than that which is kept in storage for prolonged periods, in terms of briquette quality, production rate and energy consumption. The ‘old’ ricehusk releases a powdery dust around the machine during the briquetting process, which may be harmful if inhaled. Also, ‘old’ ricehusk produces low quality briquettes, with cracked surfaces and small pieces of briquettes. 4.2.3 Mixed raw materials, of ricehusk and sawdust, at 1:1 ratio by volume. Ricehusk and sawdust were mixed at 1:1 ratio by volume, and the briquetting experiments were continued. Tables 12 and 13 present the results for a screw speed of 370 rpm while Tables 14 and 15 furnish the test results at a screw speed of 465 rpm.






1 89.5 0.0849 10.5 225 2 98.2 0.0678 6.85 241 3 93 0.0785 8.8 229

Average 93.6 0.0771 232





Average Die Temp.(°C)

1 81.1 0.0877 5.9 282 2 74.33 0.0867 6.6 264 3 72 0.095 5.6 258

Average 75.81 0.0898 268






1 66.4 0.0864 8.6 258 2 87.69 0.0877 9 211 3 96 0.0778 10 225

Average 83.36 0.0839 231

33



Total Energy consumpn. (kWh/kg)


Average Die Temp.(°C)

1 100.5 0.0955 8.5 263 2 99.8 0.0804 7.6 247 3 98 0.1008 8.4 235

Average 99.43 0.0922 248 Figure 21 illustrates the relationship between the screw speed, production rate and energy consumption, with mixed raw material, of ricehusk and sawdust, at a ratio of 1:1 by volume.

Screw speed Vs Production Rate and Power Consumption (50% rice husk-50% sawdust)

40

50

60

70

80

90

100

370 465 560

Screw speed (rpm)

Prod

uctio

n ra

te(k

g/hr

)

0.072

0.074

0.076

0.078

0.080

0.082

0.084

0.086

Pow

er c

onsu

mpt

ion

(kW

h/kg

)


(a) Without pre-heating

Screw speed Vs Production Rate and Power Consumption (50%rice husk-50%sawdust)

40

50

60

70

80

90

100

370 465 560

Screw speed (rpm)

Prod

uctio

n ra

te(k

g/hr

)

0.088

0.088

0.089

0.089

0.089

0.089

0.089

0.090

0.090

0.090

Pow

er c

onsu

mpt

ion

(kW

h/kg

)


(b) With preheating

Figure 21. Screw speed Vs. Production Rate and Specific Energy Consumption, with mixed raw material, of ricehusk and sawdust.

Energy Consumption:

Mixing sawdust with ricehusk has resulted in an overall reduction in energy consumption by the briquetting process, when compared to pure ricehusk as raw material. While the specific energy consumption without pre-heating dropped by about 25%, energy consumption with pre-heating also came down by about 22%, for a screw speed of 370 rpm. Similar trend was also noted for the screw speed of 465 rpm. Briquetting Screw Life:

In general, the screw life with the mixed raw materials was significantly higher compared to that with pure ricehusk. A 25% increase in screw life was

34

realised for a screw speed of 370 rpm, while the increase was 60% for a screw speed of 465 rpm. Briquette Quality:

Unlike in the case of pure ricehusk, pre-heating offers better quality briquettes with the mixed raw materials. The production rate is lower at 370 rpm, while it is higher at 465rpm. 4.2.4 Conclusions Several experiments were carried out to evaluate the effect of raw material type on the performance of the integrated biomass briquetting system, consisting of the biomass pre-heater, die-heating stove and smoke removal system. Results indicate considerably less energy consumption when mixed raw materials (ricehusk and sawdust, at 1:1 ratio by volume) are used in comparison with pure ricehusk as raw material. Significant reductions in electrical energy consumption have been realised with the introduction of the die-heating stove to replace the electrical coil heaters. The smoke recycling system has also improved the working environment at the briquetting plant, by significantly reducing smoke in the vicinity.

35

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About RETs in Asia …

The project ‘Renewable EnergyTechnologies in Asia: A Regional Researchand Dissemination Programme’ (RETs in Asia)was initiated in 1997 with the broad aim ofcontributing to sustainable development ofthe Asian region through promoting theutilization of renewable energy resources formeeting indigenous energy needs of thecountries in Asia. The project promoted thediffusion of selected renewable energytechnologies in a group of six Asian countriesthrough a regional research anddissemination program. Regional approachand institutional co-operation remained inthe forefront of strategies adopted by theproject. Photovoltaics, solar and biomass-based drying, and biomass briquetting arethe technologies selected for promotion. Theproject is supported by the SwedishInternational Development CooperationAgency (Sida) and coordinated by theAsian Institute of technology (AIT).

For further information, please contact:

mme

ology

nd

c.th

Prof. S.C. Bhattacharya Coordinator, RETs in Asia PrograEnergy Field of Study Asian Institute of TechnP.O. Box 4, Klong Luang Pathumthani 12120, ThailaTel: +66-2-524 5403 Fax: +66-2-524 5439 E-mail: [email protected]

A publication of RETs in Asia

http://www.retsasia.ait.ac.th/

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