View
39
Download
0
Category
Preview:
Citation preview
SOLID BIOMASS FOR ENERGY
WOOD - AGRO- RESIDUE - MSW
COMBUSTION PRINCIPLES - FUEL
PREPARATION - FURNACES
Comparison of Bio-fuel with Coal-1
• Biofuel is useful near forests / woodlands and
villages for decentralized and small / medium
scale operation over coal / char. Coal which is
useful for Thermal Power Plants.
• Biofuel restricts the emission of green house
gases and air pollutants (like SO2).
• In rural areas, available biofuel lessens the
dependence on transported fossil fuels like
coal and oil & gas.
2
Comparison of Bio-fuel with Coal-2
• Biofuel is location specific and limited in
availability; suitable for small applications
• Lower calorific value; variable particle size
• Preparation like drying, briquetting etc., needed
for wood /agro-residue
• Price depends on production system like
energy plantation, social forestry, saw mills,
paddy processing mill etc.
3
USES OF SOLID BIOFUEL
COMBUSTION
• RURAL DOMESTIC: COOKING, WATER, ROOM
HEATING
• HEAT & STEAM: SMALL FURNACES, KILNS,
BOILERS
• ELECTRIC POWER GENERATION:
SMALL SCALE: DECENTRALISED, RURAL
MEDIUM SCALE: COFIRING, COGENERATION /
COMBINED CYCLE
4
Sources of Solid Bio-fuels
(Agriculture, Plantation, Forestry)
WOOD - [Forestry, Trees outside Forests]
BAGASSE - [Agro-industry residue]
RICE HUSK- [Crop residue]
PROSOPIS ETC.- [Energy crops]
NEEM ETC.- [Multi-purpose trees]
5
Biomass Power Potential (MW):
Source
Potential (MW)
From surplus Biomass
16,000
From bagasse based
co-generation in the
existing sugar mills
3,500
Total
19,500
Ref: MNES Annual Report, 1999
6
Important Fuel Properties
• MOISTURE CONTENT
• ELEMENTAL ANALYSIS
• CHEMICAL COMPOSITION
• PARTICLE SIZE & DISTRIBUTION
• BULK DENSITY, SPECIFIC GRAVITY
• POROSITY
7
Test Data needed for Combustion
• Proximate Analysis:
(1) Moisture, (2) Volatile, (3) Fixed carbon
(4) Ash. [Weight %]
• Ultimate Analysis:
C, H, O, N, S. [Weight %]
• Higher Heating Value, MJ / Kg
• Flue Gas Analysis: H2O,CO2,N2, CO, SO2
8
Draft-pressure drop for air flow
P required to make the air flow through the fuel
bed and to the flue gas discharge height is called
‘draft of air’ in a furnace and is expressed in
millimeters of water. Natural (by means of a
chimney). Forced: The fan is used to suck the
gases away from the furnace [induced draft], or to
force the air required [forced draft] through the
grate.
9
COMBUSTION PROCESS-1
• Combustion: Oxidation of reduced forms of
carbon and hydrogen by free radical processes at
higher temperatures.
• Chemical properties determine the higher heating
value & the pathways of combustion.
• Bio-fuel: A wet (50% moist), dirty, light in weight,
heterogeneous in particle size, and quite reactive
condition.
11
COMBUSTION PROCESS-2
• Biomass fuels are highly reactive, volatile,
oxygenated fuels of moderate heating value.
• Moisture content lowers the combustion efficiency
and affects the economics of the fuel utilization.
• Drying, pyrolysis of solid particle, release of volatiles
and formation of char are followed by pre-
combustion gas phase reactions and char oxidation
reactions. 12
Requirements of efficient
combustion:
o Sufficient air to provide oxygen needed for
complete burning; higher than theoretical air.
o Distribution of air supply: mix with fuel
o Secondary air to burn the volatile
o Volume of furnace; Flow path for flue gas
o Minimize heat losses
14
Factors influencing thermal
efficiency in wood combustion
o Enthalpy of the fuel
o Moisture content of the fuel
o Level of excess air employed
o Final stack temperature
o Note: Theoretical flame temperature depends
on moisture content, % excess air and
preheating of air 15
BRIQUETTING
[PELLETIZATION]
o IMPROVES STORAGE AND
o TRANSPORT CHARACTERISTICS
o SCREW PRESS AND
o RAM PRESS
Fuel Preparation:
Briquetting in India
• Indian briquettes made from: groundnut shell,
cotton stalk, saw dust, coffee husk, bagasse,
mustard stalk and press mud.
• Southern region: groundnut shell and saw dust
• Western and Northern regions: bagasse,
groundnut shell, cotton stalk, mustard stalk and
press mud briquettes.
17
Briquetting continued
A recent addition: Municipal solid waste
densified for use as fuel in process
industries (tea, tobacco, textile,
chemical, paper, starch, tire re-
treading, tiles, etc.) for thermal
applications.
18
Screw and Ram Press
• Both the machines give briquettes with a density
of 1-1.2 gm /cc, suitable as industrial solid fuels.
• The screw type machines: briquettes with a
concentric hole-- better combustibility- a preferred fuel.
• These briquettes can also be more conveniently
deployed in small furnaces and even cook-stoves
than solid briquettes generated by a ram press.
19
FURNACE FOR COMBUSTION OF BIOFUEL
• Horizontal grate furnace
• Inclined step grate furnace
• Spreader-stoker system
• Suspension burning system
• Cyclone firing system
• Fluidized bed combustion system 22
Inclined step grate furnace-1
• Fuel is fed to the top of the grate
• heating and drying can occur very near to the
fuel feed shoot.
• Solid phase pyrolysis can occur as the fuel is
sliding down the grate.
23
Inclined step grate furnace -2
• Char oxidation can occur at the base of the
grate and on the dumping grate.
• Gas phase reactions can be controlled by
over-fire air distribution and separated
completely from solid phase reactions
24
Spreader stoker-1
• Fuel particles are fed into the firebox and flung,
mechanically or pneumatically across the grate
• Some heating and drying and possibly some
pyrolysis occurs while the particle is in
suspension
• Solid phase pyrolysis and char oxidation occur on
the grate. 25
Spreader stoker-2
• Pre-combustion gas phase reactions occur
between the grate and the zone where
secondary air is introduced.
• Gas phase oxidation occurs either throughout
the firebox or in the vicinity of the zone where
secondary air is introduced if the under-grate
air is limited to sub-stoichiometric quantities.
26
Suspension burning system:
horizontal cyclone furnace
• A horizontal or slightly inclined cylinder lined
with firebricks into which air is ejected
tangentially at a velocity of 6000- 7000 m/min.
• The flame in the furnace revolves at a rpm of
1200 to 1800
• The fuel introduced at the cyclone tip is
entrained by the revolving mass and is thrown
against the cyclone walls where it burns.
27
Horizontal cyclone furnace
• The flue gases that escape at high velocities
through the aperture at the other end of the
cyclone are substantially free from fly ash.
• The heat release rate of (2-5 )X 106 kcal/m2-
hr can be achieved for pulverized coal in a
cyclone furnace
28
Fluidized Bed Biofuel
Combustion: Boiler
• Bio-fuel is dispersed and burned in a gas
fluidized bed of inert particles.
• Temperature [750 to 1000 o C ] to avoid
particle sintering .
• 50% of the heat transferred directly to
surfaces immersed within the bed.
• Remaining heat with gases leaving
29
COMBINED HEAT & POWER
• STEAM INJECTED GAS TURBINE
• INTERCOOLED STEAM INJECTED GAS
TURBINE
• COMBINED CYCLE
30
Cogeneration with biomass fuel
• SUITABLE FOR SMALL SCALE (<10 MW)
GENERATION
• PRODUCES LESS AIR POLLUTANTS AND
SOLID WASTES
• AUGMENTS POWER SUPPLY TO
INDUSTRY
31
BIOMASS INTEGRATED GASIFIER /GAS
TURBINE (BIG/ GT) TECHNOLOGY
HIGH THERMODYNAMIC CYCLE
EFFICIENCY
GAS TURBINES TECHNOLOGY IS MADE
AVAILABLE NOW AT REASONABLE COSTS
LOW UNIT CAPITAL COST AT MODEST
SCALES FEASIBLE
IT IS EXPECTED THAT THIS TECHNOLOGY
WILL BE COMMERCIALLY SUCCESSFUL IN
THE NEXT TEN YEARS.
32
Reference Books
• A. Chakraverthy, “Biotechnology and Alternative Technologies for Utilization of Biomass / Agricultural Wastes”, Oxford & IBH publishing Co., N. Delhi, 1989.
• Samir Sarkar, Fuels and Combustion, 2nd Edition, Orient Longman, 1990
• Chapters on Combustion process Stoichiometry and Thermodynamics, Combustion Kinetics and Combustion Appliances. pages 217 to 326
35
Reference Books / journals
Journal—‘Biomass and Bio-energy’,
a) 1996, 11(4): 271-281 ‘Biomass Combustion for power generation’
b) 1998, 14(1): 33-56 ‘De-centralized biomass combustion: state of the art and future development’
4. Wood Combustion, D A Tillman, Ch. 5 ‘Heat production & release from wood combustion’,
5. Progress in biomass Conversion, vol 3, Edited by K V Sarkanen, D A Tillman and. E C Jahn, Academic Press, 1982
36
Recommended