Incineration And Pyrolysis

Incineration
Akash Tikhe
M.Sc. Environmental Science
Bharati Vidyapeeth, Pune

Incineration
MSW is burnt in a properly designed furnace under suitable
temperature and operating conditions. This process is called as
incineration.
It is one of the most effective method of reducing the volume and
weight of municipal solid waste.
The process consists of controlled burning of waste at high temp
(1200- 1500°C).
It sterilizes and stabilizes the waste with reduction in the volume.

Incineration
It is a process in which carbon, hydrogen and other elements in the
waste mix with oxygen in the combustion zone and generates heat.
This reaction is called as oxidation.
For complete oxidation the waste must be mixed with appropriate
volume of air. Approx. 5000kg of air is required for each tone of
solid waste burned. It differs with moisture content, heating values
of waste and type of combustion .
Proper temp must be maintained for suitable length of time.

Incineration
The process can reduce MSW by about 90% in volume and 75% in
weight.
Temperature ensures good combustion and complete elimination of
odour.
The combustion process is based on 3T’s
1. Time
2. Temperature
3. Turbulence (gas velocity)

Objectives of Incineration
1. Volume Reduction- To combust SW to reduce their volume to
1/10th
without producing offensive gases and ash.
 Volume reduction depends upon the MSW composition. General
volume reduction is by 90% and weight by 75%.
2. Stabilization of waste– output from incinerator is more inert
than input due to oxidation of organic components of waste
stream.

Objectives of Incineration
3. Recovery of energy from waste – Energy recovered from burning
of waste is used to generate steam for on site electricity generation or
export to local heating schemes.
Combined heat and power plants increase the efficiency of energy
recovery by producing electricity as well as utilizing residual heat.
It reduces demand on fossil fuels.
4. Sterilization of waste– Important for incineration of
clinical/biomedical waste. It ensures pathogen destruction prior to
final disposal.

Advantages of incineration
The volume and weight of the waste are reduced to a fraction of its
original size.
Waste reduction is immediate, does not require long term
residence.
Waste can be incinerated on site without carted to a distant area.
Air discharge can be effectively controlled for minimal impact on
the atmospheric environment.

The ash residue is usually non putrescible or sterile.
Technology exists to completely destroy even most hazardous
material in a complete effective manner.
Requires relatively small disposal area compare to land burial.
Particularly popular in countries such as Japan where land is a
scarce resource.
By using heat recovery techniques the cost of operation can often
be reduced or offset through the use or sale of energy. (resource
recovery/ waste to energy facility)

Denmark and Sweden have been leaders in using the energy
generated from incineration for more than a century, in localized
combined heat and power facilities supporting district heating
schemes.
A number of other European countries rely heavily on incineration
for handling municipal waste, in particular the Netherlands, Germany
and France.

Disadvantages of incineration
The capital cost is high.
Skilled operators are required.
All materials are not incinerable (construction and demolition
waste).
Supplemental fuel is required to initiate and at times to maintain
the incineration process.
 The most publicized concerns from environmentalists about the
incineration of municipal solid wastes (MSW) involve the fear that
it produces significant amounts of dioxin and furan emissions.

 The solid residue remaining in the furnace after incineration is called as
bottom ash which ultimately go for land disposal. The bottom ash may
contain metals like lead and cadmium, can be treated prior to disposal.
 Dioxins occur as in the incineration of chlorine-containing substances
such as PVC (polyvinyl chloride)
Health effects such as
 Developmental of abnormalities in the enamel of children's teeth.
 Central and peripheral nervous system
 Thyroid disorders
 Damage to the immune systems
 Endometriosis
 Diabetes

Fly ash is the incinerator ash carried along in the combustion
airstream. So air pollution control devices are installed to remove
fly ash and potentially harmful gaseous contaminants.
Thus, Installation of air pollution control equipment make the
process expensive.
These equipments are located after the furnace and before the
stack.

Important Factors For Incineration
1. waste moisture content– The greater the moisture content , more
fuel is required to destroy the waste.
2. Heating Value–With no significant heating value incineration
would not be a practical disposal method.

Important Factors For Incineration
3. Inorganic salts– waste rich in inorganic, alkaline salts are
troublesome to dispose of in a conventional incineration system.
A significant fraction of the salt get collected on furnace surface,
creating a slag or cake which severely reduces the ability of an
incinerator to function properly.
4. High sulfur or halogen content– The presence of chlorides or
sulfides in waste will normally result in the acid forming compounds
in the off gas.

Pyrolysis
Pyrolysis is a thermochemical decomposition of organic material at
elevated temperatures in the absence of oxygen.
It involves the simultaneous changes of chemical composition and
physical phase, and is irreversible.
Pyrolysis is a type of thermolysis and is most commonly observed
in organic materials exposed to high temperature.

Pyrolysis
Pyrolysis of organic substances produces gas and liquid products
and leaves solid residue richer in carbon content, char.
Pyrolysis is used heavily in the chemical industry for example to
produce charcoal, activated carbon, methanol and other chemicals.
It is also a tool of chemical analysis, for example in mass
spectrometry and in carbon-14 dating.

Pyrolysis
Pyrolysis occurs whenever food is exposed to high enough
temperatures in a dry environment such as roasting, toasting or
grilling, baking, frying, grilling and caramelizing.
In normal cooking, the main food components that undergo
pyrolysis are carbohydrates (including sugars, starch, and fiber)
and proteins.
Pyrolysis of fats requires a much higher temperature and it
produces toxic and flammable products.

Pyrolysis
In many industrial applications, the process is done under
pressure and at operating temperatures above 430º C.
For agricultural waste typical temperature range is 450º-550º
C.

Management of Biomedical Waste
The goals of biomedical waste treatment are to reduce or eliminate
the waste’s hazard, and usually to make the waste unrecognizable.
Biomedical waste if often incinerated. An efficient incinerator will
destroy pathogens and sharps.
An autoclave may also be used to treat biomedical waste. An
autoclave uses steam and pressure to sterilize the waste or reduce its
microbiological load to a level at which it may be safely disposed off.

Biomedical waste is a waste that is either putrescible or potentially
infectious. It is generated from hospitals, health clinics, nursing
homes, medical labs, research centers, funeral homes and
veterinarians.
Biomedical waste may be solid or liquid. Examples are discarded
blood, sharps, unwanted microbiological cultures and stocks,
discarded body parts, human and animal tissues, used bandages,
discarded gloves, etc.

For liquids and small quantities a 1-10 % solution of bleach
can be used to disinfect biomedical waste.
Solution of NaOH and other chemical disinfectants may also
be used depending upon the waste’s characteristics.

Management of Hazardous Waste
Hazardous waste is waste that poses substantial or potential
threats to public health and the environment.
Hazardous wastes are material that are known or tested to exhibit
one or more of the following four characteristics:
Ignitability (flammable)
Reactivity
Corrosivity
Toxicity

Hazardous wastes may be found in different physical states such as
gaseous, liquids or solids depending upon the source of generation.
Many types of businesses generates hazardous waste. For example
dry cleaners, automobile repair shops, hospitals and photo
processing centers, etc.
Some larger companies such as chemical manufactures,
electroplating and oil refineries generates some hazardous waste.

Historically, some hazardous wastes were disposed of in regular
landfills.
This resulted in unfavorable amounts of hazardous materials
seeping into the ground and eventually entered into natural
hydrological systems.
Many hazardous waste undergo different treatments in order to
stabilize and dispose of them.
These treatment can be recycling, incineration, pyrolysis and
secure landfilling.

Recycling of Hazardous waste
Many items that can become HW disposal problems can be
recycled into new products or sometimes reclaimed.
Some reclamation processes are the recovery of acetone from spent
solvents and lead from metals.
Lead acid batteries or electronic circuit boards can be recycle.
Zinc can be gathered from smelting furnaces.
Most flammable materials can be recycled into is industrial fuel.

Incineration of Hazardous Waste
Flammable HW can sometimes be burned as energy sources. For
example many cement kilns burns HW like used oils or solvents.
Incineration treatment not only reduce the amount of HW but also
they generate energy from the gases released in the process.
Incineration of particular waste releases toxic gases produce by the
combustion of byproducts or other materials and this can affect the
environment.

Pyrolysis of Hazardous Waste
Some HW may be eliminated using pyrolysis in an ultra high
temperature electrical arc, in inert condition to avoid combustion.
This treatment method may be preferable to high temperature
incineration in some circumstances such as in the destruction of
concentrated organic waste types, including PCBs, pesticides and
other persistence organic pollutants.

Landfilling of Hazardous Waste
Land disposal of HW contains the waste in a landfill, waste
pile, injection well or other land based disposal area.

Incineration And Pyrolysis

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