Thermal conversion technologies like incineration, pyrolysis, and gasification can be used to treat solid waste. Incineration involves high-temperature combustion of waste to produce ash, flue gas, and heat. Pyrolysis converts waste to liquid, gas, and char at high temperatures without oxygen. Gasification converts waste to syngas at high temperatures using air or steam. Each process has advantages like volume reduction and energy recovery, but also challenges for implementation in India like requiring high calorific waste and high capital costs. Fixed bed and fluidized bed reactors are common for gasification.

1. Thermal Conversion Technologies:
Incineration, Pyrolysis and Gasification
Submitted by-
Adarsh Singh (2K19/ENE/07)
MTECH 1st year Environmental Engineering
Delhi Technological University

2. Introduction
• Thermal processing of solid waste can be defined as the conversion of wastes
into gaseous, liquid and solid production with release of heat energy.
The mains objectives in the thermal treatment process of solid waste are the
follows -
• destruction of organic component of wastes, especially dangerous one
• reducing their volume
• obtain solid/gaseous inert products
• Achieve a significant energetic Valorisation.

3. • The thermal methods are a final solution for most of dangerous and no
dangerous solid wastes, when isn’t possible treat them by biological,
physical and chemical techniques .
•

4. Incineration

5. Incineration
Fig.1 inside of a incineration chamber
• Incineration is a waste treatment process
that involves combustion of waste at very
high temperatures in the presence of
oxygen, resulting in the production of ash,
flue gas, and heat.
• It is feasible for unprocessed or minimally
processed refuse besides the segregated
fraction of the high calorific waste.
• About 65%–80% of the energy content of
the organic matter can be recovered as heat
energy, which can be utilized for thermal
applications.

6. Key Criteria For Municipal Solid Waste
Incineration (CPHEEO Guidelines)
• The lower calorific value (LCV) of waste must be at least 1,450 kcal/kg (6 MJ/kg)
throughout all seasons. The annual average LCV must not be less than 1,700 kcal/
kg (7 MJ/ kg).
• The supply of waste should be stable and amount to at least 500 TPD of
segregated waste.
• minimum gas phase combustion temperature of 850°C and a minimum residence
time of the flue gases, above this temperature, of two seconds after the last
incineration air supply.
• optimum oxygen content (lower than 6%) should be maintained to minimise
corrosion and ensure complete combustion
•

7. Flow chart of typical Incineration Process

8. Types of Incinerator
• Grate incinerator
• Rotary kiln incinerator
• Fluidised bed incinerator

9. Grate Incinerator
• Grate incinerators are best suited for incineration of mixed municipal wastes and
can be used for untreated, non- homogenous, and low calorific municipal waste
• Grate incinerators are of two types:
a. Moving grate furnace system : waste enters from one end while ash is
discharged at other
b. Fixed grates: series of steps with drying stage and initial combustion phase,
complete combustion and final carbon burn- out

10. Flow Chart of Grate incineration
• The input material is MSW which is put in a grate-fired boiler as burning
fuel. Steam conditions in regards of pressure and temperature will be
provided depending on the input materials. For the output material, energy
will be delivered as electricity and heat.
Fig.2 Flowchart of grate incineration

11. Overview of Grate Firing System
Fig.3 overview of grate incinerator

12. Enlarged view of Grate firing Combuster
Fig.5 enlarged view of combuster

13. A. Advantages of Grate incinerator-
• There is no need for prior sorting or shredding
• Technology is widely tested and meet standards of technical performance
• Accommodates large variations in waste composition and calorific value
• Allows for an overall thermal efficiency upto 85%
B. Disadvantages of Grate Incinerator-
• Capital and maintenance cost are relatively high
•

14. Rotary Kiln Incinerator
• The rotary kiln incinerator is applied by municipalities and by large
industrial plants
Fig.6 Rotary kiln

15. • This type of incinerator has two
chambers, a primary chamber and
secondary chamber. The primary
chamber consists of an inclined
refractory lined cylindrical tube.
Movement of the cylinder on its axis
facilitates movement of waste.
• In the primary chamber, there is
conversion of solid fraction to gases,
through volatilization, destructive
distillation and partial combustion
reactions. The secondary chamber is
necessary to complete gas phase
combustion reactions.
Fig.7 cross sectional view of rotary kiln incinerator

16. Fluidised bed incinerator
• The basis of fluidized bed combustion systems is a bed of hot inert
particles, such as sand or limestone through which air is blown from below
in these applications, where fuel is burned.
• Fuel represents only a few percent of the bed materials. The combustion air
is injected upwards from the bottom of the combustor in enough amount
and volume and at a high enough pressure to keep the bed in a “fluidized”
state and to trail the small particles of the bed material so that they behave
much like a fluid

17. Fluidised bed incinerator
Fig.8 System description of the process of fluidized bed incinerator

18. Pyrolysis
• Pyrolysis is the conversion of waste and biomass into liquid and gaseous
fuel as well as solid residues and char at 500°C-1000°C in absence of air.
• Pyrolysis, unlike incineration, is an endothermic reaction and heat must be
applied to waste to distil volatile components.
• Process of converting plastic to fuels through pyrolysis is possible, but it is
yet to be proven to be a commercially viable venture.
•

19. • Pyrolysis is carried out at 500°C–1,000°C and produces three component
streams
1. Gas: It is a mixture of combustible gases such as hydrogen, carbon
monoxide, methane, carbon dioxide, and some hydrocarbons.
2. Liquid: It consists of tar, pitch, light oil, and low boiling organic chemicals
like acetic acid, acetone, methanol, etc.
3. Char: It consists of elemental carbon along with the inert material in the
waste feed.
•

20. Fig.8 Municipal solid waste pyrolysis

21. Plasma Pyrolysis
• Plasma pyrolysis vitrification is a modified pyrolysis technology which
employs application of high voltage to decompose inorganic matter in
waste stream
• The system uses a plasma reactor, which generates, by application of high
voltage between two electrodes, an extremely high temperature (5,000°C–
14,000°C).
• This type of plant is used for hazardous waste like biomedical waste.

22. Fig.9 Plasma pyrolysis system installed at
CSIR- CSMCRI Bhavnagar
Fig.10 Plasma pyrolysis system installed at
Agartala medical college

23. Gasification
• Gasification is a process of converting carbonaceous material in MSW into
CO2and syngas (CO, H2 and CH4) at high temperatures in the presence of
controlled air or steam .
• This is achieved at high temperature (650°C and above)
• The process is largely exothermic, but some heat may be required to
initialise and sustain the gasification process. The main product is syngas
having an NCV of 4–10 MJ/Nm
• The other main product produced by gasification is a solid residue of non-
combustible material (ash), which contains a relatively low level of carbon.
3
3

24. Fig.11 Waste gasification plant
• Gasification takes place in two chambers:
a) Primary chamber :
operated below stochiometric air
requirement
b) Second chamber:
under excess air condition
• The waste is fed into the primary chamber
and semi-pyrolyzed, releasing moisture and
volatile components. The heat is provided by
the controlled combustion of fixed carbon
within the waste. The syngas that is driven off
can act as a feedstock for the secondary
chamber
•

25. Types of gasifiers for MSWM
• Gasification technology is selected on the basis of
a) available fuel quality
b) capacity range
c) gas quality conditions
• Two main reactors used for gasification are
a) fixed beds
b) fluidised beds.

26. Fixed bed gasifier
• Fixed bed gasifiers typically have a grate to support the feed material and
maintain a stationary reaction zone.
• They are relatively easy to design and operate, and are therefore useful for
small and medium scale power and thermal energy uses.
• The two primary types of fixed bed gasifiers
a) updraft - highly efficient, wet waste with 50% moisture can be gasified
b) downdraft - not preferred for MSW treatment
•

27. Fig.12 Schematic of updraft and downdraft fixed-bed gasifiers

28. Fluidised bed
• Fluidised bed are preferred for gasification of MSW as it can be used with
multiple fuels, offers relatively compact combustion chambers
and good operational control .Fluidised bed technology is more suitable
for generators with capacities greater than 10 MW
The two main types of fluidised beds for power generation are
a) bubbling fluidised beds
b) circulating fluidised beds

29. • In BFB the gas velocity must be high
enough so that the solid particles,
comprising the bed material, are lifted,
thus expanding the bed and causing it to
bubble like liquid.
• As waste is introduced into the bed, most
of the organics vaporise pyrolytically and
are partially combusted in the bed.
Typical desired operating temperatures
range from 900°C to 1,000°C.
•
Bubbling Fluidised bed
Fig.13 Flow diagram of the
bubbling fluidized-bed system.

30. • In CFB there is no distinct separation between dense solid zone and dilute
solid zones.
• The capacity to process different feedstock with varying compositions and
moisture contents is a major advantage in such systems
Circulating Fluidised bed

31. Plasma Gasification
• Plasma gasification or plasma discharge uses extremely high temperatures in an
oxygen-starved environment to completely decompose input waste material into
very simple molecules in a process similar to pyrolysis.
• Plasma gasification has two variants, depending on whether the plasma torch is
within the main waste conversion reactor or external to it. It is carried out under
oxygen-starved conditions and the main products are vitrified slag, syngas, and
molten metal.
• Vitrified slag may be used as an aggregate in construction; the syngas may be
used in energy recovery systems or as a chemical feedstock; and the molten
metal may have a commercial value depending on quality and market availability.
•

32. Fig.12 Schematic of Plasma gasification reactor

33. Challenges of utilising Pyrolysis And Gasification in
the Indian context
• High calorific value waste, which may otherwise be processed in more
sustainable processes, is required as feedstock.
• Organics can be converted into compost in a much more cost-effective
and environmentally safe process, as against using them as feedstock for
these processes.
• Pre-treatment of waste is a must. Specific size and consistency of solid
waste should be achieved before MSW can be used as feed.

34. THANK YOU