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PROJECT REPORT ON

PYROLYSIS OF CARBONACEOUS SOLID WASTES AS A

MEANS OF DISPOSAL AND GENERATION OF VALUE ADDED

FUELS AND CHEMICALS

Submitted to

Department of Science, Technology and Environment,

Govt. of Pondicherry

Prepared by

Dr. K.Subbarayudu,Asst. Professor

Department of Mechanical EngineeringPONDICHERRY ENGINEERING COLLEGE(Sponsored by Govt. of Pondicherry and affiliated to Pondicherry University)

Pondicherry 605 014.

Ph. Nos: 0413-2655281-287 Internet : www.pec.edu

Fax No : 0413-2655101

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ii

PYROLYSIS OF CARBONACEOUS SOLID WASTES

AS A MEANS OF DISPOSAL AND GENERATION OF

VALUE ADDED FUELS AND CHEMICALS

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iii

ACKNOWLEDGEMENTS

The project titled Pyrolysis of carbonaceous solid wastes as a means of

disposal and generation of value added fuels and chemicals is a small step in the

research and development of a promising means of waste disposal. It is my duty to

thank all those who are in one way or other connected with the project.

At the outset, I thank Dr. V.Soundararajan, Head of Department of

Mechanical Engineering, Pondicherry Engineering College, for his support in the

execution of the project and also for allowing me to use the facilities available in the

department.

I am grateful to Dr. T.G.Palanivelu, Principal, Pondicherry Engineering

College, for allowing me to take up the project and for his help in the procurement of

equipments pertaining to the project.

This project was executed with the financial grant from Department of Science,

Technology and Environment (DSTE), Government of Pondicherry. I express my

gratitude to DSTE for selecting the project for funding. I sincerely thank

Dr. P. T. Rudra Goud, Director, DSTE, and Er. S.Sekar, Scientific Officer, DSTE

for their constant support in the successful completion of the project.

I appreciate the assistance rendered by Mr. L.Kumararaja, Sr. Lecturer,

Department of Mechanical Engineering, Pondicherry Engineering College for helping

me in the execution of the project.

Dr. K. SUBBARAYUDU

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iv

C O N T E N T S

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Chapter No. Title Page No.

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Acknowledgements iii

List of Figures v

List of Tables vi

Summary vii

1 Introduction 1

2 Solid Wastes and their Properties 2

3 Literature Review 6

4 Design and Construction 11

5 Experiments 16

6 Results and Discussion 18

7 Conclusions 24

Related Literatures 25

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v

LIST OF FIGURES

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Fig. No. Title Page No.

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4.1 Schematic diagram of pyrolysis system 11

4.2 Pyrolysis Reactor 12

4.3 Schematic View of Heaters 13

4.4 Volatiles condenser 14

4.5 Gas liquid separator 14

4.6 Overall experimental set up 15

6.1 Types of solid wastes and final residues after pyrolysis 18

6.2 Plot of temperature Vs time for pyrolyser without charge 19

6.3 Plot of temperature Vs time for scrap tyre pyrolysis 20

6.4 Plot of temperature Vs time for LDPE pyrolysis 20

6.5 Plot of temperature Vs time for PVC pyrolysis 21

6.6 Yield of pyrolysis products 21

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vi

LIST OF TABLES

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Table No. Title Page No.

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2.1 Composition of tyre samples 2

2.2 Elemental composition of scrap tyres 3

2.3 Elemental composition of Polyethylene 3

2.4 Elemental composition of PVC 4

2.5 Average composition of MSW 5

3.1 Pyrolysis reactor details 9

6.1 Average pyrolytic reactivities of different wastes 22

6.2 pH values of water after pyrolysis of different wastes 23

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vii

SUMMARY

The ever increasing quantity of solid wastes generated in the modern world has

posed several social and health problems. Among the safer methods of waste disposal,

pyrolysis is a technique in which the feedstock is thermally degraded in the absence of

oxygen. The resulting products of pyrolysis are solid char, liquid pyrolytic oil and

gases. Each of the products formed has potential usage as energy carriers and

chemical feed stocks for further processing. In this work, a lab scale semi batch type

pyrolyser was fabricated along with the downstream components like volatiles

condenser, gas-liquid separator etc. General types of solid wastes like scrap tyres,

LDPE, PVC, screened MSW and dry leaves were pyrolysed. Temperature rise,

specific electrical energy consumption for pyrolysis, yields of residual char, pyrolytic

oil and gases, average pyrolytic reactivity for each type of waste were determined.

The temperature rise for scrap tyre pyrolysis is faster than other types. Specific energy

consumption is lowest for tyre pyrolysis. The yields of different products depend very

much on the process variables. The pyrolytic oil can be blended with the conventional

liquid fuels. The pyrolytic waste disposal will also mitigate the problems of

environmental pollution.

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Chapter 1

INTRODUCTION

The generation of solid wastes like waste tyres, plastics, PVC, bio residues etc., is

steadily rising. The local civic bodies like Corporations, Municipalities and

Panchayats face a difficult task in the safe disposal of wastes. The pile up of these

wastes in the land filling sites cause problems such as:

Breeding of insects, mosquitoes etc.,

Emissions of pollutants and obnoxious gases,

Requirement of more land filling sites,

Water contamination

There are several scientific disposal methods like materials recovery and recycling,

thermo chemical methods such as incineration, gasification, pyrolysis, and bio

chemical methods such as composting, anaerobic digestion etc. These are the various

safe disposal methods. Among them, a promising method is pyrolysing the

carbonaceous solid wastes. The benefits resulting from pyrolysis are:

60-90 % of volume reduction and 70-98 % of weight reduction are possible

which means only lesser land area requirement for filling.

Certain products can be recovered and recycled.

There are no health hazards and there is a possibility of clean environment.

Pyrolysis oil can be used directly as fuel or blended with petroleum products.

Pyrolysis oil is a source of various chemicals.

The resulting char can be used as a fuel or it can be activated for a more

valuable purpose.

Pyrolysis is defined as the thermal decomposition of the solid wastes in absence of

oxygen. During pyrolysis, gases, pyrolytic oil and char are produced. The gases are a

mixture of carbon dioxide, methane and hydrocarbons, water vapour etc.; their relative

proportions vary much with the reaction parameters during pyrolysis, and nature of

solid wastes.

The solid wastes selected for testing in this project, were scrap tyres, plastic

wastes like LDPE, PVC, screened municipal solid wastes and bio residues.

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Chapter 2

SOLID WASTES AND THEIR PROPERTIES

The solid wastes are of different types; because they are generated by different

people of various economic statuses, through their various activities involving a

variety of products and commodities. The quantum of solid wastes generated is also

burgeoning as peoples activities have increased very much in this materialistic world.

Among these types of wastes, the properties of some of them are given below.

2.1 Scrap tyres:

The composition of tyre varies with manufacturers. Even in the same tyre, the

composition differs between the tread and side wall portion. Some of the typical

composition of tyres is given in Table 2.1.

Table 2.1 Composition of tyre samples

Sl.

No.

Composition Tyre of

company A

(wt%)

Tyre of

company B

(wt%)

Tyre of

company C

(wt%)

1 Styrene Butadiene Rubber 39.1 - 20

2 Natural Rubber - 41.3 45

3 Butadiene Rubber - 22.3 25

4 Carbon Black 36.9 23.2 -

5 Oil 19.5 4.1 -

6 Others 4.5 9.1 10

Total 100.0 100.0 100

The heat content of rubber is higher than that of coal; tyre rubber could be a

source of alternate fuel for power generation and other usage. For example, the used

tyres can be burn directly in co-fired boilers to generate power. The elemental analysis

of a typical tyre is shown in Table 2.2.

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Table 2.2 Elemental composition of scrap tyres

Sl.

No.

Element Wt%

1 Carbon 84.39

2 Hydrogen 7.13

3 Nitrogen 0.24

4 Sulphur 1.24

5 Other (by diff.) 7.0

Total 100.0

The disposal of used automotive tyres is becoming an ever more pressing

problem as it causes many environmental and economical problems to most of the

countries. Their continuing accumulation is one of the worst solid waste disposal

problems plaguing the countries. The chemical structure of rubber used in making

tyres makes them difficult to recycle.

2.2 Polyethylene (PE):

Polyethylene of different density ranges are obtained by chain polymerization

of ethylene. Commercial categories are

(a) Low Density Poly Ethylene (LDPE) of density range 915 940 kg/m3

and

(b) High Density Poly Ethylene (HDPE) of density range 945 960 kg/m3

LDPE is more branched i.e., 25 50 branches per 1000 linear carbon atoms. It has

lower melting point of 110 117C. HDPE are linear having only 2 5 branches per

1000 linear carbon atoms. It has higher melting point of 125 130 C. HDPE is more

resistant to chemicals than LDPE; LDPE is permeable to gases than HDPE. The

factors contributing to widespread use of polyethylene are low cost, easy

processability, chemical inertness, electrical insulation properties, low temperature

toughness, flexibility, clarity etc. The elemental composition of PE is given in table

2.3.

Table 2.3 Elemental composition of Polyethylene

Sl.

No.

Element Wt%

1 Carbon 85.7

2 Hydrogen 14.3

Total 100.0

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2.3 Polyvinyl Chloride (PVC):

Its monomer is CH2 = CHCl. PVC is a hard plastic that is made softer and

more flexible by the addition of plasticizers, the most widely used being phthalates.

It has a chlorine content of 53.8%. On heating, HCl is liberated as volatile. PVC is

used in chemical plant equipments, pipes, sheets, window frames, transparent roof

sheeting. In the temperature range of 200 400C, PVC decomposes into HCl and a

coke like residue. This residue can be burnt at higher temperatures without any

chlorine related limitation. The elemental composition of PVC is given in table 2.4.

Table 2.4 Elemental composition of PVC

Sl.

No.

Element Wt%

1 Carbon 40.1

2 Hydrogen 5.1

3 Chlorine 53.8

4 Other (by diff.) 1.0

Total 100.0

2.4 Municipal Solid Wastes (MSW):

MSW is the most heterogeneous substance with the quantity of any particular

constituent varying widely with location. However, for a general idea a normal

composition of MSW is given in table 2.5.

C == C

H H

HCl

C C C C

H H H H

Cl H Cl H

Vinyl Chloride monomer Poly Vinyl Chloride polymer

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Table 2.5 Average composition of MSW

Sl.

No.

Constituent Wt (%)

1 Paper 37.8

2 Plastics 4.6

3 Rubber and leather 2.2

4 Textiles 3.3

5 Wood 3.0

6 Food wastes 14.2

7 Yard wastes 14.6

8 Glass and ceramics 9.0

9 Metals 8.2

10 Miscellaneous 3.1

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Chapter 3

LITERATURE REVIEW

An extensive survey of technical journals, internet and books related to

pyrolysis was done before embarking on the project. This was done to keep ourselves

abreast with the latest developments in the field. A brief summary of the technical

articles collected from the technical journals are given below.

1. Soo Hyun Chung, et.al, [1] in their paper Pyrolysis of Waste Plastics using

Synthesized Catalysts from Fly Ash proposed that waste plastics can be converted

into fuel oil by pyrolysis using suitable catalysts. These synthesized catalysts were

more effective for PP than for PE which is difficult to pyrolyse. Experimental

results showed that synthesized catalysts from fly ash can be used for the pyrolysis

of most of waste plastics including the olefin series to make fuel oil.

2. Yang Yongrong, et.al, [2] authored a paper titled Technical Advances on the

Pyrolysis of Used Tyres in China. The objective of their work is to give an

outline of the research activities on the pyrolysis of tyre rubber. They also describe

the kinetics of pyrolysis, pyrolysis mechanism and design of pyrolysis reactor.

3. M.T.Gonullu, E.Arslankaya, et.al, [3] in their paper titled An Experimental

Research on Pyrolysis and Gasification of Scrap Tyres described that pyrolysis is

a method to get valuable new materials and energy. It has been reported that

experimental research was conducted to get optimum operating parameters for

pyrolysis of rubber scrap tyres. In their experiments, heating was done upto

600C; thermal decomposition of waste tyres began at temperature 150C and

almost finished by 550-580C.

4. Masemore, et.al, [4] authored a paper titled Process for pyrolyzing tyre shreds

and tyre pyrolysis systems. They have reported that tyre pyrolysis systems and

processes were developed which include feeding tyre shreds to a pyrolysis reactor,

pyrolyzing the shreds in the pyrolysis reactor to produce a hydrocarbon rich gas

and carbon rich solid fuel.

5. Ron Zevenhovena and Ernst Petter Axelsenb, [5] described their work in the paper

Pyrolysis of waste derived fuel mixtures containing PVC. This paper describes

the experimental analysis of pyrolysis of PVC and mixtures of PVC with wood

(Finnish pine) and LDPE (Low Density Poly Ethylene) in nitrogen at 250400oC.

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Results are presented for various process temperatures for PVC, PVC/wood and

PVC/LDPE mixtures.

6. P. T. Williams [6]described their work in the paperHigh Value Products from the

Pyrolysis of Scrap Tyres. They have reported that pyrolysis of tyres produced

oil, carbon and gaseous products, in addition to the steel cord, all of which have the

potential to be recycled. In this paper, process routes have been described for the

production of high grade activated carbon and high value aromatic chemicals from

the pyrolysis of scrap tyres which may improve the commercial viability of tyre

pyrolysis.

7. F. Pinto et.al, [7] have written a paper titled Pyrolysis of plastic wastes - Effect of

plastic waste composition on product yield. They opined that accumulation of

enormous amounts of plastic waste produced all over the world has negative

implications on the environment. Pyrolysis of plastic waste can have an important

role in converting this waste into valuable hydrocarbons.

8. A.A. Zabaniotou et.al, [8] have written a paper titled Pyrolysis of used automobile

tyres and residual char utilization. In their study, the rubber portion of used car

tyres was transformed by atmospheric pyrolysis into oil, gas and char. The

experiments were performed in a captive sample reactor at atmospheric pressure

under helium atmosphere. The effect of temperature on the products yield was

investigated by them.

9. A. Chaala et.al, [9] described their work in their paper Vacuum pyrolysis of

automobile shredder residues: use of the pyrolytic oil as a modifier for road

bitumen. The physicochemical properties and the rheological behavior of the

pyrolytic oil residue obtained from the vacuum pyrolysis of automobile shredder

residues have been studied. The pyrolysis experiments were performed batch wise

in a large retort.

10. Paul T. Williams et.al, [10] described their work in the paper Catalytic pyrolysis

of tyres: influence of catalyst temperature. Two stage thermal decomposition i.e.,

pyrolysis-catalysis of used tyres was done by them. The tyres were first pyrolysed

in a fixed bed reactor and then the evolved pyrolysis gases were passed through a

secondary fixed bed reactor containing Zeolite catalyst. The pyrolysis reactor was

maintained at 500C and the influence of catalyst temperature between 430C and

600C on the yield and composition of the derived oils were examined.

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11. Jian-Bing Zhao et.al, [11] have written a paper titled Pyrolysis of Waste Tyres

with Copper Nitrate. They studied the influence of copper nitrate on the pyrolysis

of waste tyres in a 50 cm3

static batch reactor in nitrogen atmosphere. The results

showed that the gaseous mixture contained H2, C2H6, C3H8, CO2, CH4, C3H6, CO

in the sequence of their yields.

12. L.Sorum et.al, [12] in their paper titled Pyrolysis characteristics and kinetics of

municipal solid wastes, have observed that the large variety in municipal solid

waste (MSW) composition and difference in thermal degradation behaviour of

MSW component makes modelling, design and operation of thermal conversion

system a challenge.

13. EPA, 1992, [13] Pyrolysis Treatment, Engineering Bulletin. This bulletin

describes that pyrolysis could transform hazardous organic materials into gaseous

components, small quantities of liquid, and a solid residue (coke) containing fixed

carbon and ash. Pyrolysis of organic materials produces combustible gases,

including carbon monoxide, hydrogen and methane, and other hydrocarbons.

14. Fagbemi et.al, [23] have written a paper titled Pyrolysis products from different

biomass: application to thermal cracking of tar. Their work involved conducting

experiments in a small capacity pyrolyser provided with external heaters. The

heating is achieved either by dropping the biomass basket into the heated section or

by placing a small quantity of biomass on a wire mesh and passing required current

through it or by feeding at slow rates in to the heated reactor. During the trials,

inert gas was used to sweep the volatiles produced during the pyrolysis.

The pyrolysis reactor details which have been compiled from the different articles

collected from international technical journals are given in Table 3.1.

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Table 3.1 Pyrolysis reactor details

Title of paperDiameter

(cm)

Height

(cm)

Temperature

(C)

Type of

reactor

Sample used

and quantity

Material

used for

reactor

Heating r

(C s-1

)

Pyrolysis of used

automobile tires and

residual char utilization[8] 7 12 390-800

Captive

sample

reactor

Used tyres

of

500 g

Stainless

steel70-90

Experimental studies on

pyrolysis of Dantong coal

with solid heat carrier in

fixed bed reactor

[13]

12 45 350-500Fixed bed

reactor

Datong coal

of

1,3,5,8mm

Stainless

steel

__

Characterization potential

application of pyrolytic

char ablative pyrolysis of

used tires[14]__ __

550

Continuou

s ablative

reactor

(CAR)

Used tiresStainless

steel

__

Hardware component

waste pyrolysis energy

recovery and liquid

fraction valorization[15] 4 70 600

Tubular

quartz

reactorHardware

component

__ __

Vacuum pyrolysis of

automobile shredderresidues:

use of the pyrolytic oil as

a modifier for road

bitumen [9]

60 300 450

VacuumPyrolysis

in a pilot

plant

Automobileshredder

residues:

130 kg

__ __

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Table 3.1 : Pyrolysis reactor details (Contd.)

Title of paperDiameter

(cm)

Height

(cm)

Temperature

(C)

Type of

reactor

Sample used

and quantity

Material

used for

reactor

Heating r

(C s-1

)

Charecterisation of

pyrolytic light napha

from vacuum Pyrolysis

of used tyres

comparition with

petroleum naphtha [17]

60 300 500Horizontal

reactor

Used tyres

(SBR)

19 kg

__ __

Charecteristion of

product from the

recycling of glass fibre

reinforced polyesterwaste by pyrolysis[18 ] 0.6 202

450 Fixed bed

reactor

Polyester/gla

ss fibre ,

30wt%,7wt%1.5 kg

Stainless

steel

__

Catalytic pyrolysis of

tyres: influence of

catalyst

temperature[10]10 15 500

Fixed bed

reactor

Used tyres

200 gm of

sample

Stainless

steel10

Production of biocrudes

from biomass in fixed

bed tabulated reactor:

product yields and

compositions [21 ]

1.1 80 400-700

Fixed bed

tubular

reactor

SunflowerStainless

Steel 3167 Kmin

Characteristics of

evolution of tar from

wood pyrolysis in a

fixed- bed reactor

[13 ]

2 30 700Fixed bed

reactorWood

Inconel

600

alloy

__

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11

Chapter 4

DESIGN AND CONSTRUCTION

4.1 System components:

On the basis of literature survey conducted, it was found that most of the

researchers had developed only lab scale model for their investigation on pyrolysis

This is because, the solid wastes pyrolysis must be analyzed first in the lab scale

reactor, before the establishment of any large scale pyrolyser plant. The essential

components of the pyrolysis system have thus been identified from the literatures

collected. The schematic diagram of solid waste pyrolysis system is shown in fig.4.1.

1. Pyrolysis reactor 4. Scrubber

2. Volatiles condenser 5. Sucking blower

3. Gas-liquid separator 6. Gas burner

Fig.4.1 Schematic diagram of pyrolysis system

4.2 Pyrolysis reactor:

The reactor which has been designed for the solid waste pyrolysis is a

cylindrical shell. Refer fig.4.2. It is a semi batch type, fixed bed reactor made up of

mild steel sheet. The net volume of the reactor is about 5.3 l. The thermal degradation

of the waste is caused by electrical resistance heating. There are three heaters arranged

inside the cylindrical shell vertically protruding into the reactor from the bottom closed

side. Refer fig.4.3. They form the three vertices of a virtual equilateral triangle inside

the shell. Each heater is rated 1 kW; all the three heaters are connected in parallel to

the applied external power supply, so that the total rate of heating comes to about 3

kW. The total resistance has been measured as 16 ohms. The heater is made up of 20

SWG nichrome wire wound in the form of a coil. The top side is open through which

solid wastes are fed at the beginning and the solid residue is removed after pyrolysis.

During the reaction, the top side is kept closed by a cover plate tightly secured to the

12 3 4

56

Water Waterin out

Pyrolytic

oil

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12

flanged opening. This prevents ingression of atmospheric air into the reactor, thereby

achieving pyrolysis. The reactor weighs approximately 17 kg. The pyrolyser is

provided with ceramic wool insulation on the outer side. An exit pipe at the side

carries away the evolved gases during pyrolysis. The temperature inside the reactor is

measured by a thermocouple.

All dimensions are in mm

Fig.4.2 Pyrolysis Reactor

152

380

250

350

Top lid

Heater

Exit pipe

Thermocouple

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4.3 Volatiles condenser:

The condenser is provided to cool and condense the gases evolved out from the

pyrolyser. As a result of cooling, the condensable gases become liquid which is called

pyrolytic oil. The condenser is a vertical shell and tube type heat exchanger as shown

in fig.4.4. The evolved gases from the pyrolyser pass through the tubes and the cooling

water is circulated on the shell side. It has 1- shell pass and 1- tube pass counter flow

type of arrangement. The cooling water is circulated by a water pump. As the evolvedgases may contain particulate matter and tar, they are passed on the tube side, so that

cleaning would be easier after the experiments. Instead of room temperature water

being circulated from the water pump, chilled water from a water chiller can also be

supplied to increase the pyrolytic oil yield. However, a certain fraction of gases cannot

be condensed and they are termed as non condensable gases.

152

All dimensions are in mm

Fig.4.3 Schematic View of Heaters

42

Heater

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14

Fig.4.4 Volatiles condenser

4.4 Gas-Liquid Separator

The pyrolytic oil formed in the volatiles condenser drips down and get collected at

the bottom of the gas liquid separator. Besides, those liquid droplets borne by the

gases can also be separated out due to differential inertia as the velocity is very much

reduced in the separator. Refer fig.4.5. The separator has two chambers separated

Fig.4.5 Gas liquid separator

by a segmented baffle. The oil laden gases enter the separator from the top into the firstchamber; flow downwards and then rise up in the second chamber. During the flow,

the liquid oil gets collected at the bottom and the non condensable gases rising up in

the second chamber leaves through a hole at the top. The non condensable gases are

taken through a pipe and bubbled into water kept in a pan.

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15

4.5 Instrumentation:

The instrumentation panel consists of a fuse unit, MCB, on-off switch,

voltmeter, ammeter and single phase energy meter. The temperature of the pyrolyser

is measured by a K- type thermocouple connected to a digital temperature indicator of

1C accuracy. The time is measured by a digital timer of 0.01 second accuracy. The

weights of input feedstock and residue after pyrolysis are measured by a digital

weighing balance of 1 gm accuracy. The pH is determined in Deluxe pH meter

(Model 101E).

The overall arrangement of the components is shown in fig.4.6.

Fig.4.6 Overall experimental set up

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16

Chapter 5

EXPERIMENTS

The experiments were conducted by maintaining the pyrolyser under non-

isothermal conditions by heating. During the experiments, pyrolysis was carried out

only in the range from slow to moderate rate of heating. The following quantities

were involved in the experimental studies.

5.1 Variables changed:

Type of raw feedstock (Scrap tyre, LDPE, PVC)

Rate of heating

For each type of raw feedstock, tests were conducted for three different heating rates.

5.2 Parameters observed:

Initial weight of raw feedstock

Initial weight of water in bubbling tank

Temperature of pyrolyser at regular time intervals

Voltage at regular time intervals

Current at regular time intervals

Heater energy consumption at regular time intervals

Time period to attain 600C in every trial

Final weight of solid residue

Final weight of liquid oil collected

Final weight of water in bubbling tank

pH value of water in bubbling tank

5.3 Parameters calculated:

Rate of temperature rise

Reactivity

Yields of pyrolysis products

5.4 Procedure:

5.4.1 Heating without any charge:

Initially, the rate of temperature rise of the pyrolyser without containing any

charge was observed when heated. The time to reach 600C was also noted. This was

done to compare the electrical energy consumption for the pyrolysis of feed stocks

with that of the uncharged pyrolyser.

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17

5.4.2 Pyrolysing scrap tyre:

Scrap tyre of a two wheeler was obtained and cut into pieces so that they can be

easily fed into the pyrolyser to occupy its full volume. The initial quantity of scrap

tyre pieces was weighed before charging into it. The top lid was tightly secured to the

pyrolyser by bolts and nuts. Cooling water was circulated in the volatiles condenser by

means of a pump. A measured quantity of water was taken in the bubbling tank. In

the first test, only one heater was energized ON. During the heating process,

temperature, voltage, current, heater energy consumption were observed at regular

time intervals. This was continued till the pyrolyser temperature reached 600C; the

heating was stopped at this condition.

The system was allowed to cool up to room temperature naturally. Then the

top lid of the pyrolyser was opened; solid residue remaining in the pyrolyser was taken

out and weighed. The stopper at the bottom of the gas-liquid separator was also

opened and pyrolytic oil was drained into a jar. The pyrolyser was cleaned with

acetone and made ready for the subsequent test. The same procedure was followed for

the cases of a) when two heaters ON and b) when all the three heaters ON.

5.4.3 Pyrolysing LDPE:

LDPE roll of virgin grade was procured and cut into pieces and then fed into

the pyrolyser till it covers the entire volume of the reactor. The procedure detailed in

Section 5.4.2 for scrap tyre was followed for LDPE also.

5.4.4. Pyrolysing PVC:

PVC pipes were procured and cut into pieces so that they could be easily

charged into the pyrolyser up to the brim. The procedure detailed in Section 5.4.2 for

scrap tyre was followed for PVC also.

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18

Chapter 6

RESULTS AND DISCUSSION

6.1 Physical observation:

The photographs of raw feed stocks and the solid residues obtained after

pyrolysis are shown in fig. 6.1.

Type of Solid wastes

Scrap tyres

Final residues

Polyethylene

PVC pipes

MSW

Fig. 6.1 Types of solid wastes and final residues after pyrolysis

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6.2 Heating without any charge:

Without taking any solid wastes in the pyrolyser, the temperature rise of the

reactor when it had been heated was observed. The temperature Vs time graph for that

case is shown in fig.6.2.

Pyrolyser without charge

0

100

200

300

400

500

600

700

0 5 10 15 20 25 30 35

Time (min)

Temperature(C)

Fig. 6.2 Plot of temperature Vs time for pyrolyser without charge

It is observed from the graph, that the temperature rise is faster initially up to a

temperature of 400C; after which it becomes slower due to increased heat loss by

radiation.

6.3 Pyrolysis of scrap tyre:

The temperature variation of the pyrolyser with respect to time in the case of

scrap tyres when all the three heaters were ON is shown in fig.6.3. The rate of

temperature rise is higher in the case of scrap tyre pyrolysis than that for uncharged

condition of the pyrolyser. This may be due to certain exothermic reactions occurring

during pyrolysis of scrap tyres.

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Tyre Pyrolysis

0

100

200

300

400

500

600

700

800

0 5 10 15 20 25 30 35

Time (min)

Temperature

(C)

Fig.6.3 Plot of temperature Vs time for scrap tyre pyrolysis

6.4 Pyrolysis of LDPE:

Low Density Poly Ethylene sheets of virgin grade were pyrolysed in the

reactor. It was observed that the rate of temperature rise was slower for LDPE. This

may be due to the occurrence of a number of endothermic reactions. The temperature

Vs Time chart is shown in fig.6.4.

LDPE Pyrolysis

0

100

200

300

400

500

600

700

800

0 20 40 60 80 100

Time (min)

Temperature(C)

Fig.6.4 Plot of temperature Vs time for LDPE pyrolysis

6.5 Pyrolysis of PVC:

The pyrolysis of Poly Vinyl Chloride was carried out under the same

conditions similar to LDPE. The temperature rise is faster when compared to LDPE.

The variation of temperature Vs time for PVC pyrolysis is shown in fig.6.5. But the

evolution of HCl vapours contributes very much to environmental pollution. It also

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converts the water in the pan through which the gases are bubbled out to become

strongly acidic.

PVC Pyrolysis

0

100

200

300

400

500

600

700

800

0 10 20 30 40 50 60

Time (min)

Temperature(C)

Fig.6.5 Plot of temperature Vs time for PVC pyrolysis

6.6 Products yield:

The products of pyrolysis are solid residue, liquid pyrolytic oil and gaseous

volatiles. Better the cooling of gases, more the quantity of oil collected. The typical

yield of products of pyrolysis for a) scrap tyre, b) LDPE and c) PVC are shown in

fig.6.6.

Yield

0%

20%

40%

60%

80%

100%

Tyre LDPE PVC

Material

%byweight

Gas

Oil

Char

Fig.6.6 Yield of pyrolysis products

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6.6 Reactivity of feed stocks:

In order to analyze a more practical kind of waste, a type of MSW was

obtained from Garbage Compost Production Centre, Arasur, Villianur Commune,

Pondicherry. The Centre is run by PASIC an Undertaking of Pondicherry

Government. In this centre, raw MSW from Pondicherry Municipality is segregated

mechanically in the process of composting. One of the segregations is the MSW

containing more amount of plastics; this segregation is dumped in landfills. This type

of MSW which is rich in plastics called hereinafter as screened MSW was collected

from the centre and analysed in the pyrolyser.

Experiments were also conducted to determine the average reactivity of

different feed stocks such as scrap tyres, LDPE, PVC, screened MSW and dry leaves.

The average pyrolytic reactivity r of a feedstock during a time period of t minutes is

given by

r = W1-W2 x 1 min-1

W1 t

Where W1 = initial weight of raw feed stock taken in the pyrolyser

W2 = final weight of residue after pyrolysis

The average reactivities of various types of feedstock are shown in table 6.1.

Table 6.1 Average pyrolytic reactivities of different wastes

Sl.

No.

Solid wastes Avg. pyrolytic

reactivity (min-1

)

1 Scrap tyre 0.01843

2 LDPE 0.019

3 PVC 0.02201

4 MSW 0.00909

5 Dry leaves 0.02105

6.7 Nature of collection water after pyrolysis:

The non-condensable pyrolysis gases coming from the gas-liquid separator are

bubbled through water kept in a pan. This was done to prevent ingression of outside

air into the reactor. As a result of passage of gases through water, it gets contaminated

and its nature changes. The pH value of the pan water was measured after pyrolysis of

each feed stock. The results are shown in table 6.2.

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Table 6.2 pH values of water after pyrolysis of different wastes

Sl.

No.Solid wastes pH value of water

1 Scrap tyre 9.2(Moderately alkaline)

2 LDPE 2.78 (Acidic)

3 PVC 0.1 (Strongly acidic)

4 MSW 3.9 (Moderately acidic)

5 Dry leaves 3.8 (Moderately acidic)

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Chapter 7

CONCLUSIONS

It is very much essential to scientifically dispose the ever increasing solid

wastes generated by the growing population. Pyrolysis of solid wastes is one of the

safe methods of disposal. From the experiments conducted on various types of solid

wastes, the following conclusions are derived.

The hydrocarbon part of any solid wastes can be pyrolysed.

Pyrolysis of solid wastes will yield solid char, liquid oil, and gases; all of them

have considerable heating values.

The pyrolysis of scrap tyres has produced solid char containing steel wires

which can be recycled and the percentage of liquid oil collected is more than

that of gases. The temperature rise of the pyrolyser is faster due to better heat

transfer inside the reactor.

The pyrolysis of LDPE has produced only a little char, but the percentage of

volatiles is high which can be largely converted to liquid oil, theoretically up to

100 %. The temperature rise is slower when compared to that of scrap tyres

and PVC due to poor heat transfer characteristics and drastic physical changes

taking place during pyrolysis.

The pyrolysis of PVC has produced more solid char than LDPE, but the

evolution of HCl vapours requires pretreatment as they are strongly acidic. The

temperature rise of the pyrolyser is faster than that for LDPE.

The average specific reactivity of screened MSW is very low when compared

to that of scrap tyres, LDPE, PVC and dry leaves due to the presence of inert

materials in it.

The specific electrical energy consumption during pyrolysis is lowest for scrap

tyre, and highest for PVC.

The pyrolysis of PVC can be safely done only with the integration of adownstream treatment process for HCl vapours.

A real pyrolyser plant can be operated by deriving heat from a portion of the

feed stock itself, instead of the electrical heating practiced in the case of lab

scale pyrolyser.

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