Bio mass is a form of sustainable energy. This PPT is all about its use and future

1. Urban Waste: A source of Energy
Dr. Lipika Parida

2. Municipal solid waste (MSW)
• MSW are wastes collected from houses, some industries, schools, offices, shops
etc. These wastes include waste like cardboards, newspapers, cartons, fruits,
vegetables, furniture, leftover food, papers, clothes, organic material and non-
renewable items like plastic containers, tin etc. Any useless, unwanted and
discarded materials that resulted from society and normal daily activities are
regarded as MSW.
• It consists of large amount of biodegradable organic waste and cellulosic
materials like paper, cardboard, food etc.
• MSW can be arranged in seven categories, these are food wastes, yard
trimmings, paper and boards, metals, wood, plastics and glass.
• Food scraps and yard trimmings can be composted while other 5 can be recycled
and can be used producing new objects. The compost can be used as organic
manure in agriculture and nondecomposable material is incinerated or sent to
landfill sites.

3. Composition of MSW of World in Year
2009

4. The hierarchy of waste management
1. Waste minimization or reduction which means waste is
prevented from entering the waste stream by the
means of reusing products and first preference is
making every effort to reduce waste.
2. Reusing materials
3. Recycling includes sorting out recyclable material like
plastic, metals, glass and paper from waste and
reprocessing them into new processing. Biological
processing includes composting of degradable waste
components. Making compost of degradable waste
materials.
4. Incineration of waste with or without recovery of energy.
5. Disposal on land (land filling) should be the solution if
waste cannot be treated with above mentioned methods.
Landfills should be designed in such a way to reduce the
impact on environment

5. Benefits of WTE process

6. Benefits of WTE process
• The energy obtained from MSW reduces dependence on fossil fuels for generation of electricity.
• Municipal solid waste can be used as a substituent of fossil fuels.
• Preservation of water can be achieved via advance WtE plants. Latest boiler technology is used in WtE plants which
uses less water from tube wells and rivers to produce same amount of Kwh of energy.
• The carbon dioxide, sulphur dioxide, and nitrogen oxides emissions by WTE using MSW as fuel are 837, 0.8, and 5.4
lb/MWh respectively which is much lower than coal-fired power plants which emits 2249, 13, and 6 lb/MWh of
electricity produced respectively.
• WtE plants provide employment in various stages of construction, designing, planning, commissioning, maintaining
and operating the plant.

7. Methods of generating electricity from
Municipal Solid Waste.

8. Incineration Process

9. Incineration Process
• Incineration consists of burning the whole mass of waste in incinerator. This process of incineration of MSW reduces the volume of
MSW by up to 80–90%.
• Firstly, the collected waste to be burnt is fed into a combustion chamber. During this process gaseous pollutants are released so the
pollution control system needs to be set up along with it.
• Incineration process is operated at 800 C to 1000 C.
• Water is fed into boiler and the heat produced during this process is used for boiling water. Resulting steam is utilized to turn a turbine
generator to produce electricity. Water evaporates then comes down to cooling through natural circulation. Steam is separated from
water through separation line in boiler.
• Then super heated steam is passed high pressure turbine (HPT). The temperature and pressure decreases after discharging from HPT.
Then it is reheated again to attain proper temperature.
• Then steam is passed through intermediate and low pressure turbine. The turbine rotates with high speed.
• The shaft of turbine is coupled with shaft of generator so when turbine rotates the shaft of generator also produces electricity.
• The air contains pollutants which need to be treated. After heating the air, preheated flue gases passes through electrostatic
precipitator scrubber (wet and dry) Chamber with copper chloride and hydrochloric acid, Chamber with sodium hydroxide and passes
through water for toxic filtering.
• Electrostatic precipitators are highly efficient filtration device which removes fine particles like smoke and dust from flowing gas using
force of induced electrostatic charge.
• A wet scrubber is used to clean air flue gas and other emitted gas, dust particles and pollutants.
• To remove acid gases (such as HCl, SO2) primarily from combustion sources, the dry scrubbing system is used.
• To separate carbon dioxide, chamber with CuCl2 and HCl is used.
• Water is used for absorbing solid carbon from flue gases.
• In the end of incineration of MSW, bottom and fly ash is obtained. It can be utilized in construction of roads and cement industry

10. Benefits of incineration of municipal
solid waste
• Large amount of waste is reduced immediately.
• Waste can be incinerated on site.
• Air emissions can be minimized.
• Ashes obtained in the end are aseptic.
• Space requirement is less as compared to landfill.
• Costlier than landfills. But cost can be recovered with power
generation.

11. Disadvantages
• High setup cost.
• Skilled labour is needed.
• High moisture content in municipal solid waste as all materials are not
combustible.
• Environment issues if flue gas is not handled properly.
• According to National Research Council, other potential health effects
from incineration flue gas exposure are chest pain, dizziness, irrelative
symptoms, and poor coordination.

12. Environmental consideration
• An objective of MSWI is to contribute to an overall reduction of the environmental
impact that might otherwise arise from wild dumping, open burning or landfilling of the
waste.
• The volume reduction of waste by incineration helps to save scarce and valuable space
for landfill and protect the environment.
• A fraction of the energy recovered can also be considered to be carbon neutral, due to
the biomass content in MSW. However, MSWI facilities also generate large amounts of
flue gases which must be treated, even when incineration has taken place under
optimum combustion conditions.
• To avoid irreversible health risks to local populations and the environment, compliance
with international emissions standards is essential and continuous monitoring and
reporting of emissions must be guaranteed.
• Pollutants in flue gases take the form of dust and gases such as hydrogen chloride (HCl),
hydrogen fluoride (HF) and sulphur dioxide (SO2). A number of compounds containing
mercury, dioxins or nitrogen dioxide (NO2) may only be removed using highly advanced
chemical processes, which substantially increase project costs.

13. The main environmental aspects to deal with are:
• Control and monitoring of process emissions to air and water (including odour).
• Quality and use potential of slag production (e.g. heavy metal contamination
levels).
• Secure disposal or recycling of hazardous fly ash residues.
• Process noise and vibration.
• Water and other raw material (reagent) consumption.
• Fugitive emissions – mainly from waste storage.
• Storage/handling/processing risks of hazardous wastes.

14. Fluidized bed combustion (FBC)
• Fluidized bed combustion (FBC) is a combustion technology used in power plants.
FBC plants are more flexible than conventional plants in that they can be fired on
coal and biomass, among other fuels.
• Fluidized beds suspend solid fuels on upward-blowing jets of air during the
combustion process.
• The result is a turbulent mixing of gas and solids. The tumbling action, much like
a bubbling fluid, provides more effective chemical reactions and heat transfer.

15. Types
1. Atmospheric Fluidised Bed Combustion System (AFBC)
a. Bubbling fluidized bed combustor
b. Circulating fluidized bed combustor
2. Pressurised Fluidised Bed Combustion System (PFBC).

16. Bubbling fluidized bed combustor
• BFB combustor is one of the most popular designs for biomass gasification,
mainly due to its applicability to medium-scale processes (<25 MWth).
• It consists of a vessel in which the gasifying agent is introduced upward at a
velocity fast enough (0.5–1.0 m/s) to agitate the bed material which sits at
the bottom part of the gasifier and to maintain the required temperature.
• Biomass is fed from the side into the hot bed, where devolatilization occurs.
• Char particles and volatiles are gasified and cracked by contact with the hot
fluidized bed.
• Additional gasifying agent can be supplied in a second zone located above
the bed with the aim of converting entrained unconverted volatiles and char
particles into fuel gas.
• A final flue gas with low to medium tar content is produced.
• Ash is separated from the syngas in gas–solid separation units downstream.
• The gasifying agent can be supplied in two different zones. The first zone is
within the fludized bed in order to maintain the required temperature. The
second zone is located above the bed and it aims to convert entrained
unconverted volatiles and char particles into fuel gas.

17. Circulating fluidized bed (CFB) combustor
• The CFB combustor is arising as a major
technology for medium- (a few MWth) to large-
scale (100 MWth) biomass gasification
processes, mainly due to its long residence time
which makes it applicable to biomass with high
volatile contents.
• In the circulating fluidized bed reactor, the
gasifying agent is introduced upward at a
velocity fast enough (3.5–5.5 m/s) to move the
bed material throughout a circulating loop, full
mixing and long residence times being achieved.
• Biomass is fed from the side and mixed with the
hot bed material which is dispersed along the
tall vessel.
• The solids leaving the riser are separated in a
gas–solid separator (cyclone) and returned to
the bottom of the combustor.

18. Advantages of CFB over BFB
The CFB design overcomes some of the disadvantages
exhibit by the BFB design.
• The gas–solid contact is better due to the absence
of bubbles and prevents the gas from bypassing
the bed.
• In addition, biomass is heated at a higher rate due
to the recirculation of the solids. Consequently
gasification efficiency and carbon burnout are
increased compared to BFB, and tar production
during the heating up of the feedstock decreases.
• CFB can process feedstock with small particle size
(<400 μm) and a wider particle size distribution
without the penalty of the entrainment loss, and
they are reliable over a wider range of feedstock.

20. Pressurised Fluidised Bed Combustion
• The PFBC differs in one important aspect from the atmospheric BFB; it is a
combined cycle plant that uses both gas and steam turbines.
• Operation at high pressure means that the hot flue gases exiting the combustion
chamber, once cleaned, can be used to drive a gas turbine at the same time as
steam produced in the pressurized boiler is exploited in a steam turbine.
• Heat remaining in the exhaust gases once they have exited the gas turbine is also
captured to raise further steam. It is the combination of the two types of turbine
which provides the route to higher efficiency.
• PFBC plants generally operate at 1 MPa to 1.5 MPa (10–15 atm)
• The power production from the generating units in a PFBC is broadly 20% from the
gas turbine and 80% from the steam turbine.