1
ENGG*4230
Energy Conversion
University of Guelph, Fall 2022
• 1 Overview
• 2 Review
• 3 About the Final Exam
Review- 01/12/2022
1.2 Energy Conversion (ENGG* 4230)
•
The course introduces the technical criteria for the design of efficient
energy conversion processes and systems.
– Lectures provided theory and examples
– Laboratories/Tutorials provided hands-on experience
You should now have a better understanding on the following:
1. Introduction to energy conversion and sustainability
2. Fundamentals of Energy Conversion: Energy forms, conversion systems
and energy intensity
3. Emission intensity, climate change and energy conversion planning
4. Biomass properties, Various conversion processes
5. Fuel and Combustion Calculations
6. Introduction to Thermal Power Plant
7. Design of Thermal Power Plant:
pulverized, fluidized bed, integrated gasifier combined cycle systems,
8. Biochemical biomass conversion
9. Solar energy system design: Thermal and PV
10. Wind Energy system design
11.Geothermal Energy
12.Energy Storage
Final
Review- 18/10/2022
•
2
1.
3
Energy Production in Canada
2018
3
4
Energy Production in Ontario
2021
4
5
Energy Emissions
5
6
Electricity Emissions
6
7
Coal Plants
Wikimedia Commons [Online].
Available: http://upload.wikimedia.org/wikipedia/commons/thumb/4/4a/Coal_fired_power_plant_diagram.svg/1280pxCoal_fired_power_plant_diagram.svg.png
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Coal Plants 1
• Coal plants obviously burn coal
• Burning coal produces nitrogen oxide (NOx)
and sulfur (SOx)
• It will also leave particle pollution
– Dust, dirt, smoke,
– Sometimes arsenics and other matter
• Coal plants can also pollute water
– In China, 1/5 of the water is used in “coal washing”
– However, “coal washing” reduces the ash content
of the coal which means less air pollution
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9
Coal Plants 2
• The last coal plant in Ontario closed in
2014
•
•
•
•
There are 9 coal-fired plants in Canada
Most of these plants are phasing out of coal into natural gas
Globally there are about 8500 coal plants
Quick research – how many coal plants are in your native
country?
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10
Natural Gas Plants
• Natural gas is an colourless and odourless gas that burns easily
• In Canada, Natural gas is used for heating, hot water heaters,
gas burning stoves and BBQs, and even fireplaces
10
11
Natural Gas Plants 1
1. Wikimedia Commons [Online],
Available: https://upload.wikimedia.org/wikipedia/commons/4/4c/Jet_engine.svg
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12
Natural Gas Plants 2
• They operate much like a jet engine
• Some plants, called Combined Cycle, will use the
heat to produce steam for a steam turbine
• Some plants use the excess heat to industrial plants
– This is called Co-generation or Co-Gens
• Gas is cleaner than coal, however, it does still
produce emissions than can be harmful to the
environment
• According to the US EIA, Gas plants produce 114
pounds of carbon dioxide for every million BTU,
while coal will produce 200 pounds and more than
160 pounds of distillate fuel oil
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13
Hydro Plants
Source: https://www.energy.gov/eere/water/types-hydropower-plants
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Hydro Plants 1
• Use the mechanical energy from water and turns it into electrical
energy
• They can be found at dams, on rivers, and at waterfalls
• The water needs to drop from a certain elevation (the head) and
drop to spin the turbine
• Canada has the second most hydro plants in the world
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15
Hydro Plants 2
• While hydro plants do not produce any harmful emissions, the
dams and reservoirs can cause issues for the aquatic life
around them
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16
Nuclear Plants
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Nuclear Plants 1
• During operation, nuclear plants do not produce any
greenhouse gas emissions
• The fuel rods are highly radioactive and must be
disposed of carefully
• In Canada, the used rods are stored in deep pools of
water for 7-10 years and then stored in dry storage
for …well…a very long time
• There are 3 nuclear plants in Ontario – Pickering,
Darlington and Bruce
– They are all on the great lakes due to their need of immense
amounts of water
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18
Wind Power
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Wind Power 1
• Wind power also does not produce any emissions
• Due to the laws of physics (or Betz Law), wind is only
capable of 59.3% efficiency
• Surprisingly, wind power can only be produced when
there is wind! (Usually at a minimum speed of 5 m/s)
• While the use blade can be recycled, currently they
are just being buried in landfills
• The blades can move at speeds of 200 km/h, this has
been known to be deadly to birds and bats
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Solar Power
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Solar Power 1
• Does not produce any emissions
• Does not produce energy at night?!?!?!
• Converts sunlight into electrical energy through photovoltaic
(PV) panels
• First solar panel was invented in 1883 (but was only 1%
efficient)
• In 1954 solar panels were used to power satellites and were
less than 10% efficient
• Today most solar panels are around 20% to 27% efficient
• The most efficient solar panel is 47% efficient (just not cost
effective yet)
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1. Overview
22
Energy Conversion
•
The course introduces the technical criteria for the design of efficient
energy conversion processes and systems. It includes the review of boilers
and cycles, fuel and combustion calculations, and fundamentals of both
traditional and emerging energy conversion processes and systems for
production of thermal, mechanical, and electrical energy. Topics include
fossil, biomass and nuclear fuels, as well as wind, solar, geothermal
energy and fuel cells. Mechanisms for storing energy generated from each
of these are also studied. The course also explores conversion of
automobile systems, renovation of old fossil fuel fired plant technology, cofiring of opportunity fuels, waste to energy technology, emissions, and
economics of energy projects.
Review- 18/10/2022
1.1 Course Overview
• 2. Review
23
2.1 Introduction to Thermal Power Plant, Design of
Thermal Power Plant: pulverized, fluidized bed,
integrated gasifier combined cycle systems
• Heat Balance and Design of a Boiler
• State of Biomass Combustion Technologies:
Coal/Waste Combustion Technologies
• Torrefaction and Gasification Technologies for
Biomass Conversion
Introduction to Thermal Power Plant
24
Schematic Diagram of a Power Plant
Heat Balance
25
Direct Method
This is also known as ‘input-output method’ due to the fact that it
needs only the useful output (steam) and the heat input (i.e.
fuel) for evaluating the efficiency. This efficiency can be
evaluated using the formula
Q--Quantity of steam generated per hour in kg/hr.
q--Quantity of fuel used per hour in kg/hr.
GCV--gross calorific value of the fuel in kCal/kg of fuel
Heat Balance
26
Heat given to steam in a boiler
• Heat delivered to water Q1 = m (Hsteam –Hfeed)
where
Hsteam = Enthalpy of superheated steam (kJ/kg)
Hfeed = Enthalpy of feed water (kJ/kg)
Heat Balance
27
HEAT BALANCE
• HEAT INPUT = HEAT UTILIZATION +LOSSES
• Q = Q1+ Q2+ Q3+ Q4+ Q5+ Q6+ Q7 + Q8
• Q = Available heat of fuel
• Q1= Heat utilized by steam and water
• Q2 = heat lost through stack gas
• Q3 = Unburned carbon
• Q4 = Moisture in fuel
• Q5 = Hydrogen in fuel
• Q6 = Moisture with air supplied
• Q7 = Loss from boiler surfaces
• Q8 = sensible heat in ash
Heat Balance
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29
Losses from combustor
Dry flue gas
loss (Q2)
Fuel moisture
loss (Q4)
Loss due
to H2 (Q5)
Energy generated from
combustion of fuel – Heat
delivered to water (Q1)
Radiation
loss (Q7)
Moisture in
air loss (Q6)
Sensible heat loss
due to ash (Q8)
Heat Balance
Unburned carbon
loss (Q3)
Equations to Estimate Heat losses
• Dry flue gas loss: (Mg*Cpex*tex-Mwa*Cpair*tair)/HHV*100
• Unburned carbon loss: Unburned carbon content*ash*heating
value of carbon/HHV*100
• Fuel moisture loss: Mf*(hfg@ex.temp-hwl@in.temp)/HHV*100
• Air moisture loss: Xm*(hfg@ex.temp-hwl@in.temp)/HHV*100
• Moisture from H2 in fuel: 9H*(hfg@ex.temp-hwl@in.temp)/HHV*100
• Sensible heat loss due to ash: Ash*Cpash*tash/HHV*100
• Thermal efficiency of a boiler = 1-sum of all losses
Heat Balance
30
Design of a boiler: Steam enthalpy and
parameters
• Once the pressure schedule of the steam/water circuit is made,
the steam/water parameters (Enthalpy) can then be estimated
from the available steam table.
• The heat duty of each segment (EC, Evaporator, SH, RH etc)
can then be calculated once mass flow of steam/water is known.
• The total heat duty is the sum of heat duty of all the segments
• The fuel consumption can them be calculated by the following
equation
– Fuel consumption (kg/s) = Total heat duty (kJ/s)/(Thermal efficiency
of the boiler*HHV of fuel (kJ/kg))
• The air requirement (kg/s) and flue gas produced (kg/s) can then
be calculated afterwards.
Heat Balance
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How to Improve efficiency of boiler
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•
•
•
•
•
•
Oxygen Trim Systems
Flue gas outlet temperature
MS temp
HRH temp
Feed Water Temp
Blowdown control
Blowdown heat recovery
Flash Steam Recovery
Steam Trap Leaks
Exhaust Draft Control
The effect of coal blending on combustion performance
Air to fuel ratio control
Heat Balance
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Factors Affecting Boiler Performance
The various factors affecting the boiler performance are listed
below:
• Periodical cleaning of boilers
• Periodical soot blowing
• Proper water treatment programme and blow down control
• Draft control
• Excess air control
• Percentage loading of boiler
• Steam generation pressure and temperature
• Boiler insulation
• Quality of fuel
Heat Balance
33
Design Problem
A biomass boiler uses Miscanthus as a fuel with following elemental analysis
Element
Weight (%)
Carbon, C
46.82
Hydrogen, H2
6.14
Nitrogen, N2
0.30
Sulfur, S
0.03
Oxygen, O2
43.40
Ash
3.31
Moisture, Mf
5.78
HHV (kJ/kg Fuel)
19276
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a. Calculate the boiler efficiency if fuel feed rate is 12.65 kg/s and output of the boiler is
200MWth?
b. Find the volumetric capacity (m3/s) of the combustion air fan (forced draft) for the boiler if air
is handled at 27 C. Assume excess air (EAC)=20%, moisture in air (Xm) is 1.3%, specific
volume at standard temperature and pressure (STP) = 0.7734 m3/kg, Cp air@27C =0.97 kJ/kg.0C
and Cp flue gas@150C =1.1 kJ/kg.0C.
c. Estimate the flue gas produced in kg/s if the unburn carbon loss is 1.5%
Equation:
Stoichiometric air required, Mda = [0.1153C+0.3434(H-O/8)+0.043S] kg/kg of dry fuel
Here C, H, O, and S to be used in percentage form (For example, C=46.82 and so on)
The actual air including excess air (EAC) and moisture (Xm), in air is
Mwa = (1+EAC)Mda(1+Xm) kg/kg of dry fuel
Here EAC, and Xm to be used in absolute form (For example EAC=0.20 and so on)
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Estimation of higher heating value (HHV)
• Channiwala and Parikh (2002) developed the
following correlation for HHV based on 15
existing correlations and 50 fuels including
biomass, liquid, gas and coal
HHV=349.1C + 1178.3H + 100.5S – 103.4O – 15.1N – 21.1ASH
Unit: kJ/kg
3
0<C<92%;
0.43<H<25%;
0<O<50%;
0<N<5.6%;
0<ASH<71%;
4745<HHV<55345 kJ/kg
Stoichiometric Calculations for Complete
Combustion
Noting that dry air contains 23.16% O2, 76.8% N2 and
0.04% inert gases by weight, the dry air required for
complete combustion of a unit weight of dry
hydrocarbon, Mda is given by
Mda = [0.1153C+0.3434(H-O/8)+0.043S] kg/kg of dry fuel
The actual air including excess air (EAC) and moisture (Xm), in
air is
Mwa = (1+EAC)Mda(1+Xm) kg/kg of dry fuel
3
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State of Biomass Combustion Technologies
Also Coal/Waste Combustion Technologies
39
Why Biomass?
➢ Enormous Resources- Biomass ranks second after large hydro in
producing renewable energy in Canada, and creates almost three
times as much energy as wind.
➢ Political benefits - e.g. reduced dependency on imported fossil
fuels; rural development; energy diversification;
➢ Employment creation- biomass fuels create up to 20 times more
employment than fossil fuels.
➢ Stable fuel Price- it has been stable historically and are not directly
linked to national or global energy markets. Biomass pricing is not
subject to monopolistic control.
➢ Environmental benefits- e.g. mitigation of greenhouse gas
emissions, reduction of acid rain, and soil improvement
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Biomass Conversion Technologies Options
Combustion Systems are the
only commercially available
bioenergy technologies with
a size ranges from 2 kW to
500 MW
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Basic process flow
Biomass/
Coal/
WasteAir
Furnac
e
Boiler
Hot
Flue
Exhaust
flue gas
gas
Ash
Thermal
energy
Furnace type: Mainly Fixed bed types and fluidized bed
types
Fixed bed systems include manual-fed systems, spreader41
stoker systems, under screw systems, through-screw
systems, static grates, and inclined grates
Fluidized bed systems include bubbling and circulating
varieties.
Size Ranges for Combustion
Equipment
Ref: Preto 2011
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Commercialization Status of Biomass Combustion Systems
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Biomass Boilers—Different types
Advantages:
• Low cost
• Small fuel inventory makes
for very rapid response to
load changes
Underbed Stokers
Disadvantages:
• Moisture content (MC)
preferably <30%, not more
than 35%
• Lack of provision for
primary and secondary air
supply limits fuel flexibility
• Consistent particle size and
MC for stable fire
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Wood Combustor Evaluations
• Grate Type
– Fixed bed
• Pin-hole grate
• Slopping grate
–
–
–
–
Travelling grate/chain
Reciprocating/stepping grate
Vibrating grate
Pre-combustor (Two-stage)
Grate
Evaluation
• Better Control
• Fuel Flexible
• Lower
emissions
• Higher thermal
efficiency
• Fluidized bed boilers
– Bubbling bed
– Circulating bed
• Suspension burners
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46
Fixed Bed Grate
• Manual Ash Removal limits size and
requires “down time”
• Refractory maintenance can be costly
• Low air flow rates (overfire air does
not penetrate chamber at low flow
rates and may cause too much
dilution/cooling at low fire leading to
increased emissions)
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Steeping Grates
ADVANTAGES:
➢ Some tolerance of fuel type,
moisture and particle size
➢ A positive movement of fuel down
grate reduces blockages
➢ Better controlled air distribution
leads to high efficiency
➢ Modern systems can have a split
of 40:60 for undergrate and
overfire air distribution
DISADVANTAGES:
❖ Large fuel inventory slows response to
load changes and increase emissions at
low loads
❖ Poor mixing especially when co-firing
different fuels
❖ Problems with high moisture fuels
(>45% moisture)
❖ Moving elements have problems with
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rocks and metal
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Fluidized Bed Technology
• “Fluidization is the operation by which solid particles show fluidlike
properties through suspension in a gas or liquid” (Kunii and
Levenspiel, 1991).
• An essential characteristic of a fluidized bed is the liquid-like
behavior. With this behavior, a gas-solid mixture bears a linear
static pressure distribution, denser objects sink and lighter objects
float.
• Under the fluidized state, the gravitational force on granular
particles is offset by the fluid drag.
• The fluidized beds have improved gas-solid mixing and more
uniform temperature distribution compared to fixed bed
reactors.
Fluidization
48
Basics of Fluidization
•Static pressure at any height equals weight of bed solids
P h = − g  p (1 −  ) +  g    − gp
•Bed surface is always horizontal
•May be drained like a liquid
•Particles are well mixed such that a nearly uniform temp is maintained
Fluidization
49
Fluidized Bed Principles
Features:
Ref:Fluidized bed
➢Excellent mixing,
➢High thermal inertia
➢Higher residence time
➢Higher heat transfer
➢Moderate operating temp.
➢Uniform temp. distribution
50
Fluidizations regimes
The pressure drop through a fixed bed of loose material, as a
function of velocity. It also shows the pressure drop for other
fluidization regimes
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BUBBLING REGIME
Freeboard: the entire region between the bed surface and the gas outlet.
Splash zone: the region just above the bed surface, in which coarse particles fall back down.
Disengagement zone: the region above the splash zone, in which both the upward flux and the
suspension concentration of fine particles decreases with increasing height.
Dilute-phase transport zone: region above the disengagement zone, in which all particles are carried
upwards; particle flux and suspension concentration are constant with height.
Dilute transport
Freeboard
H
TDH
Splash zone
Bed (bubbling zone)
Fluidization Suspension density
What is a CFB Boiler
53
•A type of steam generator
where fuels burn in a special
hydrodynamic condition called
the fluidized state and transfers
the heat to the boiler surface
via some inert solid particles. It
comprises of
•CFB loop (combustion
chamber, gas-solids separator
and standpipe)
•Convective loop (back pass
heat exchangers)
The fluidization is achieved by blowing relatively low-velocity air
into a medium such as sand. It exhibits core-annulus structure
53
Circulating Fluidized Bed - Hydrodynamics
fast fluidization regime
Particle Velocity
solids volume
fraction
wall
wall
Time-averaged behavior
bubbling fluidization regime
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Solids Distribution (CFB)
U
=
5
m
/
s
,
S
A
/
P
A
=
0
o
6
3
0
2
G
(
k
g
/
m
s
)
s
5
2
5
Average Suspension Density (kg/m3)
Bed Height (m)
8
1
5
2
5
4
3
2
2
0
1
5
1
0
5
1
0
0
0
0
1
0
2
0
3
0
4
0
5
0
3
S
u
s
p
e
n
s
i
o
n
D
e
n
s
i
t
y
(
k
g
/
m
)
6
0
5
1
0
1
5
2
0
2
5
2
S
o
l
i
d
s
C
i
r
c
u
l
a
t
i
o
n
R
a
t
e
(
k
g
/
m
s
)
3
0
56
Fluidized bed Systems
Courtesy of Metso Power Oy
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Features (continued)
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Benefit of Fluidized bed boiler
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Biomass Boiler Efficiency Comparison
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Comparison of Stokers with Fluidized Bed
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Dust or Suspension Burners
To ensure higher combustion efficiency
• Moisture content of dust <10%
• Particles sizes of dust <1 mm.
• The volatile matter content ≥ 80%
• Particles should be of flake-like and narrow shape.
• Low ash with lower Cl, K, and Na content in ash.
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Pulverised fuel technology
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Technology comparison of CFB versus pulverized
fuel firing for utility power generation
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Why do we select CFB?
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Why should Utility consider Fluidized bed boilers
➢
➢
➢
➢
➢
➢
➢
➢
Fuel supply is more uncertain and more diverse than ever
before
Great opportunity for taking advantage of non-traditional fuels
Pollution standards are changing. FB boilers are more suited
for the change
Air pollution norm without combustion penalty makes it ideal for
years to come
Price of CFB boilers are competitive with bare bone PC boilers
Capacity is no longer a barrier. CFB boilers rising to 660 MW
CFB can maintain its efficiency and availability with off-design
fuels better than PF units
More suitable for supercritical operation than PF boilers
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TORREFACTION AND GASIFICATION
TECHNOLOGIES FOR BIOMASS
CONVERSION
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BACKGROUND
Depleting fossil fuel resources and GHG/Global Warming
Renewable energy, sustainable fuels
Biomass  Carbon-neutral, local
fuel; energy security
Technology barriers to their utilization as energy
source
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Promising pre-processing technology
69
Ref: UMEA, 2010
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Torrefaction
➢
A thermochemical treatment process,
similar to roasting or mild pyrolysis
➢
Energy density increases as ~70% biomass remains
with 90% of its original energy content
Cellulose
Cellulose
Lignin
Lignin
Hemicellulose
Hemicellulose
1.3 E/M
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Indicative Fuel Properties (Cont.)
Parameters
Dust
Hydroscopic
properties
Biological
degradation
Milling
requirements
Handling
properties
Product
consistency
Transport cost
Wood
Wood
pellet
Average
Limited
Hydrophilic Hydrophilic
Torrefaction Charcoal
Coal
Pellets
Limited
High
Limited
Hydrophobic Hydrophobic Hydrophobic
Yes
Yes
No
No
No
Special
Special
Classic
Classic
Classic
Special
Easy
Easy
Easy
Easy
Limited
High
High
High
High
High
Average
Low
Average
Low
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The added value of torrefaction
Higher co-firing Torrefied biomass can directly milled and co-fired with coals.
percentages
Product is dry (<5%) and has a calorific value of 20-22 MJ/kg.
Cost savings in
handling and
processing
The product is brittle and easily breaks down in small
particles. Dedicated biomass equipment (hammer mills, silo
storage, biomass feeding systems, biomass burners are not
needed. Also it is less sensitive to degradation due to
hydrophobic nature.
Cost savings
long in
transport
The volumetric energy density of torrefied pellets is 16 GJ/m3
compared to 10 G/m3 of wood pellets
Torrefaction alone will NOT:
Significantly reduce sulfur, chlorine and alkali
concentrations of the biomass
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TORREFACTION-PELLETIZATION
Moisture: 8%
Bulk density: 700 kg/m3
Energy density: 10 GJ/m3
Bulk density: 800 kg/m3
Energy density: 16 GJ/m3
Torrefied Pellets
Wood Pellets
Biomass
collection
Moisture: 35%
Bulk density: 225 kg/m3
Energy density: 2.5 GJ/m3
Torrefaction
Pelletizing
Wood
Pelletizing
Tree logs
Chipping
Torrefied
wood chips
Moisture: 4%
Bulk density: 300 kg/m3
Energy density: 7.5 GJ/m3
Transportation
Torrefaction
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TYPICAL TORREFACTION PROCESS FLOW
Raw Material
Infeed (chips)
Advantage: Two marketable products:
Pellets & Torrefied pellets
Classifier
Rotary Drum
Dryer
Hammer
mill
Pelletizer
Torrefier
Cooler
Classifier
Rotary Drum
Dryer
Torrefier
Hammer
mill
Pelletizer
Cooler
Raw Material
Infeed (chips)
Advantage: Lower energy cost for
hammer mill
74
Torrefaction technologies
75
•Most reactor configuration/technologies applied for torrefaction are proven
in other applications (drying, pyrolysis, gasification, combustion).
Screw conveyor
•All ofdrum
them have their own advantages
and disadvantages
Rotary
Belt conveyor
reactor
reactor
reactor
•Overall efficiency depends on
their design configuration
in heat integration
in the form of either direct or indirect
•Process control (temperature, residence time, particle size, mixing) is the
key for better performance of the reactor
Moving bed
Torbed
TurboDryer
reactor
Microwave
75
reactor
Technology status
76
Biomass Conversion Pathways
Thermal
Excess air
Partial air
Biological
Gasification
Physical
No Air
Pretreatment
Combustion
A/D
Hydrolysis
Pyrolysis
(Heat & Pressure)
Fermentation
Heat
Fuel Gases
(CO + H2)
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Liquids
H2
Ethanol
CH4
Liquids
78
Biomass Conversion Pathways
Biomass conversion to Biochemicals,
Biofuels, and Bioenergy
Thermal
gasification
Chemical
looping
gasification
Dry
torrefaction
Multi stage
gasification
Bio-carbon
for various
application
Wet
torrefaction
/liquefaction
Supercritical
gasification
Anaerobic
digestion
Dry/steam
reforming
Syngas fermentation to
renewable liquid fuels
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Samples of Torrefaction of agri-residue
Tests performed at 2500C temperature and 1 hour residence time
Rice husk
Sawdust
Peanut husks
Bagasse
A water hyacinth
Ref: Dutta, 2010
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Hydrothermal Carbonization
30-80%
15-50%
2-5% 80
81
HTC Inputs and Outputs
Biochar
Woody
Biomass
Hog
Fuel
• Soil amendment
Willow
Purpose
Grown
Biomass
Miscanthus
Hydrochar
• Heat and power
production
Charcoal
• Metallurgy
applications
Wet
Biomass
Agricultural
Biomass
Switchgrass
Wheat
Straw
Corn
Stover
Biocarbon
Tomato
Vines
Corn
Husks
Activated
Carbon
• Wastewater
treatment
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van Krevelen Diagram
1.8
1.6
H:C (ATOMIC RATIO)
1.4
1.2
1
0.8
Increased
Heating Value
0.6
0.4
0.2
0
0
0.2
0.4
O:C (ATOMIC RATIO)
0.6
Feedstock(Treatment)Temp-Time-Pressure
CS(raw)
CS(HTC)-200-5-Sat.
CS(HTC)-200-15-Sat.
CS(HTC)-200-30-Sat.
CS(HTC)-200-45-Sat.
CS(HTC)-230-5-Sat.
CS(HTC)-230-15-Sat.
CS(HTC)-230-30-Sat.
CS(HTC)-230-45-Sat.
CS(HTC)-260-5-Sat.
CS(HTC)-260-15-Sat.
CS(HTC)-260-30-Sat.
CS(HTC)-260-45-Sat.
CH(raw)
CH(HTC)-260-15-Sat.
CH(HTC)-260-15-6
CH(HTC)-260-15-7
CH(HTC)-260-15-8
CH(HTC-NW)-260-15-7
0.8
Coal
82
83
83
Biomass gasification process
84
One of the best way to optimize the extraction of energy from biomass
and to obtain a standardized gas from very different materials
Air,
Steam,
CO2,
and/or O2
CO, H2, CO2, H2O, CH4, C2H4
BIOMASS
Low Calorific Value:
Medium Calorific Value:
+
unconverted tars
(all organic compound with mass > C6H6)
4 - 6 MJ/Nm3
12 - 18 MJ/Nm3
Using air and steam/air
Using oxygen and steam
The main challenges of biomass gasification are:
• Good control of temperature in the reactor
•High heating rate (hundreds of degrees per second) and high temperatures (around 800°C) are
necessary to maximize the gas yield
•TARS conversion
•TARs condense in the cold parts  plugging of tubes or agglomeration phenomena
•TARS removal by filtration  lost of efficiency since they still contain energy
85
Biomass gasification reactors
Fixed bed technology
Updraft gasifier
Downdraft gasifier
Fluidized bed technology
Bubbling
fluidized bed
Circulating fluidized bed
Cyclone
: Bed hot
particles
: Biomass
and char
: grid
Advantages: simple design, good
maturity.
Drawbacks: low calorific value gas
with a high tar and fines content.
Advantages: good gas and solid mixing, uniform
temperatures and high heating rates, greater
tolerance to particle size range and safer operation
due to good temperature control compared to fixed
bed gasification
Drawbacks: low density biomass fuel (with respect to
the bed particles) segregates to the surface of the
bed. This segregation phenomenon is increased by the
formation of volatiles and gaseous species bubbles
around the fuel particle, reducing the conversion rate.
Fused ash and tar condensation provokes
defluidization.
Gasification based process scheme
Gasifier Types - III
86
Ref: BTG, 2005
Selected commercial Gasification demonstration
Plant
ENAMORA,
Spain
Greve-inChinti, Italy
Gussing,
Australia
Lahti,
Finland
Tech.
BFB
CFB
Feedstocks
Almond shell, industry
residue
RDF
Dual FBCHP
CFB, Cofiring
Wood chips, wood
residues
Wood, board, paper,
plastics, RDF
Rudersdorfe CFB
r, Germany
SVZ,
Fixed,
Germany
Slagging,
Entrained
Varnamo,
CFB-IGCC
Sweden
Vermont,
Indirect
USA
CFB
DTU,
Two stage
Denmark
fixed bed
Biomass
Power
Fuel: 3500 kW; Electrical: 750
kWe
Fuel: 2X15 MW; Electrical: 6.7
MWe
Fuel: 8 MW; Heat: 4.5 MWth;
Electrical: 2 MWe
Fuel: 40-70 MW; Heat: 40-70
MWth; Power: 20 MWe of 176
MWe coal power plant
Fuel: 100 MW
RDF, oil slurries,
mixture of tar and
sewage sludge
Wood chips, pelletised
wood, bark,
Wood chips, residue
wood, pellets,
Wood chips (45%
moisture)
Fuel: 420 MW; Electrical: 75
Mwe; Chemical: 120 kt/a
Methanol
Fuel: 18 MW; Heat: 9 MWth;
Electrical: 6 MWe
Fuel: 44 MW; Heat: n.a;
Electrical: 9 MWe
Fuel: 70 MW; Heat: 39 MW;
Electrical: 17.5 kWe
87
Costs
Funding
Euro: 1.1 Private
million
Euro: 20 Own
million
Euro: 8.7 Public: 60%
million Private: 40%
Euro: 12 25% by EU
million
N/A
Own
Euro:
335
million
Euro: 25
million
U$: 14
million
N/A
N/A
Public: 23%
Private: 77%
DOE, FERCO
87
Tar conversion:
88
It can be done thermally or catalytically (a lower process
temperature improves control of exhaust species)
Cleaned gasification gas contains mostly gas phase
(light hydrocarbons + H2, CO2, CO, H2O)
1)
2)
Tars and
gasification
products
Biomass
feeder
system
Gasifying gas (air, O2, H2O or CO2)
The catalytic tars conversion can both decrease tar
production and modify gas composition.
There are two ways for catalytic tar rem
1: Primary method:
the catalyst is mixed
with biomass directly
inside the gasifier.
Single-stage process
2: Secondary method:
the catalyst is placed
down stream the
gasifier.
Dual-stage process
Primary methods are more difficult to set up (multiphase catalysis), but reduce the
costs of the overall process (reactor set up is simplified).
89
Anaerobic Digestion
BOD and COD
• Biochemical (or Biological) Oxygen Demand (BOD) and Chemical
Oxygen Demand (COD) are both indices of the amount of organic
material in a sample of waste liquid.
• BOD: is the amount of dissolved oxygen needed (i.e., demanded)
by aerobic biological organisms to break down organic material present in
a given organic materials sample at certain temperature over a specific
time period. It is calculated from the change of dissolved oxygen from the
mixtures of waste, aerated water and micro-organisms. BOD depends on
the temperature and duration of incubation. It is usually expressed as gm
(O2)/m3 of waste water. Accepted standard conditions are 5days at 200C.
• COD: Estimates the amount of organic matter by measuring O2
required for complete oxidation of the sample. It gives total organic
mater whether it is biodegradable or not.
• Therefore, ratio of BOD/COD will give the proportion of
biodegradable organic matter in the waste sample.
Anaerobic Digestion
90
90
Anaerobic digestion is
91
• a complex biochemical process of biologically mediated reactions (in
the absence of air) by a consortia of microorganisms to convert
organic compounds (biomass) to methane and carbon dioxide.
During the process a part of
organic material is removed by
the micro-organisms and used
to support both life and growth
functions
• a stabilization process achieving odor, pathogen, and mass reduction.
Anaerobic Digestion
91
92
Steps in the Anaerobic Process
Biodegradable Particulates
1
1
Proteins and Carbohydrates
Lipids
1
1
Volatile Acids
(propionic, butyric)
1
Amino acids and
simple sugars
2
2
2
Acetic acid
3
H2 and CO2
4
5
Anaerobic Digestion
Long chain fatty acids
CH
4 and CO2
92
Steps in the Anaerobic Process
Biodegradable Particulates
Proteins and Carbohydrates
Volatile Acids
(propionic, butyric)
Lipids
Amino acids and
simple sugars
Acetic acid
Anaerobic Digestion
Long chain fatty acids
H2 and CO2
CH
4 and CO2
93
93
Steps in Anaerobic Digestion
Hydrolysis
Acidogenesis
Acetogenesis
Methanogenesis
Anaerobic Digestion
94
94
Steps in Anaerobic Digestion
95
Particulates solubilized and large polymers
Hydrolysis
converted to simpler monomers
Acidogenesis
Simple monomers converted
to volatile fatty acids
Volatile fatty acids converted to acetic acid,
Acetogenesis
CO2 and H2
Acetate converted into CH4 and CO2
Methanogenesis
while H2 consumed
Anaerobic Digestion
95
Steps in Anaerobic Digestion
Anaerobic Digestion
96
96
Step 1 - Hydrolysis
Anaerobic Digestion
97
97
Hydrolysis
• Particulates made soluble and large polymers
converted to simpler monomers
– Carbohydrates, fats, and proteins
• Large molecules (polymers) broken down into
smaller molecules (monomers)
– Allow passage through bacterial cell wall
• Facultative arobes and anaerobes
• May be rate limiting step in process if high
concentration of particulate organic matter.
Anaerobic Digestion
98
98
99
Step 2 – Acidogenesis
Anaerobic Digestion
99
Step 2 - Acidogenesis
• Sugars, amino acids, and fatty acids
converted to C3 and C4 volatile fatty acids
(76%), H2 (4%), and acetic acid (20%)
• Optimum growth rate occurs near pH 6
• Volatile fatty acids generally not significant
consumer of alkalinity
• CO2 significant consumer of alkalinity
• NH3 produced from amino acids
Anaerobic Digestion
100
100
Acetogenesis
Anaerobic Digestion
101
101
Step 3 - Acetogenesis
• Volatile fatty acids converted to acetic acid (68%) and H2 (32%)
• Sensitive to H2 concentration
• Syntrophic (mutually beneficial) relationship with the
methanogens
Anaerobic Digestion
102
102
Step 4 - Methanogenesis
Anaerobic Digestion
103
103
Methanogenesis
• Obligate anaerobes – methanogens
– Tend to have slower growth rates
• H2 utilizing methanogens use H2 to produce
methane removing H2 from system
• Limited pH range 6.7 to 7.4 (sensitive)
– importance of alkalinity in system
• Sensitive to temperature change
Anaerobic Digestion
104
104
Routes to Formation of Methane
Hydrogenotrophic methanogens
CO2 + 4 H2 → CH4 + 2 H2O
Acetotrophic methanogens
CH3COOH → CO2 + CH4
Methylotrophic methanogens
CH3OH + H2 →
Anaerobic Digestion
105
CH4 + H2O
105
Background Concepts
•
•
•
•
Enzymes
Environmental Conditions
Alkalinity
Toxicity
Anaerobic Digestion
106
106
Catalysis & Enzymes
• Catalysis - the acceleration of a chemical reaction by
some substance which itself undergoes no
permanent chemical change.
• Catalysts of biochemical reactions are enzymes.
– Responsible for bringing about almost all of the chemical
reactions in living organisms. Without enzymes, the
reactions take place at a rate far too slow for metabolism.
– Extracellular and intracellular
• Note: Bacteria have specific enzymes for specific
tasks and not all bacteria have all enzymes.
Anaerobic Digestion
107
107
Bacteria : Environmental
Conditions
strict
tolerant
anaerobes anaerobes
facultative
anaerobes
108
strict
aerobes
Dissolved Oxygen
mesophilic
thermophilic
Temperature
30 – 35 oC
5.0
acidogens
50 – 60 oC
6.2
pH
6.8 - 7.2
methanogens
Toxicity (NH3, H2S, metals)
Functional
Anaerobic Digestion
Inhibitory
108
Fatal
109
Bacteria
Hydrolysis
Acidogenesis
Acetogenesis
Methanogenesis
Anaerobic Digestion
109
Important Note:
• Not all bacteria have same environmental tolerance.
• Not all bacteria have same optimum environmental conditions.
• Optimum gas production depends on types of substrates.
Anaerobic Digestion
110
110
Toxicity
111
• Oxygen: is inhibitory to methanogenic bacteria. Highly
reduced atmosphere should be maintained.
• Volatile acids: pH should be held constant near
neutrality. Neither acetic nor butyric acids have
significant effect on hydrogen-utilizing methanogenic
bacteria. Propionic acids has a little effect.
• Ammonia: Nitrogen from protein released as ammonia
[amonium ion, NH4, dissolved free ammonia (more
toxic), NH3]. A pH below 7.2 is preferable.
• Sulfide: Only soluble sulfide exhibit toxicity. Addition of
metal like iron precipitates sulfide and reduces soluble
sulfide concentration.
Anaerobic Digestion
111
Phased (Staged) Digestion
• Digestion process separated into multiple reactors to optimize
process
• Environmental conditions optimized for specific microorganism
population
–
–
–
–
acid-forming
methane-forming
thermophilic
mesophilic
Anaerobic Digestion
112
112
Acid / Gas Phased Digestion
• Digester 1
– Low solids retention time to promote growth of acidogens (acid
forming bacteria)
– pH < 6.0 (optimum growth rate)
• Digester 2
– High solids retention time to promote growth of methanogens
– pH = 7.0
Anaerobic Digestion
113
113
Temperature Phased Digestion
• Thermophilic generally 4 times faster than mesophilic
• Mesophilic phase enhances stability
Anaerobic Digestion
114
114
Anaerobic digestion
115
Anaerobic digestion is employed to stabilize the sludge
produced during wastewater treatment. The sludge may
be primary, secondary or mixture of both. Anaerobic
digestion is equally applicable to other solids such as
animal manure, industrial wasted sludge, etc.
During anaerobic digestion the organic matter present in
the sludge is biologically converted into CH4, CO2 and
NH3.
The sludge may be applied continuously or
intermittently to the reactor and is allowed to remain in the
reactor for a given time. The organic and pathogen
content is reduced.
Why do we need to stabilize the sludge?
1.
2.
3.
4.
Reduce pathogens
Eliminate or reduce putrescent matters
Eliminate offensive odor
Reduce the solid concentration
Reduction
of organic
fraction
Anaerobic digester
116
Anaerobic digester is an airtight reactor in which digestion
of solid such as sludge and animal manure is carried out.
Types of anaerobic digester
Standard rate
anaerobic digester
(Low rate)
High rate anaerobic
digester
Single-stage
Two-stage
Standard rate anaerobic digester (Low rate)
117
• In standard rate anaerobic digester, the content (sludge)
of the digester is usually unheated and unmixed.
• The active zone of digestion only occupies 50% of total vol.
• Because of no mixing, stratification takes place inside the
reactor during digestion. The digested sludge forms a
bottom most layer and supernatant above digestion zone
Biogas
• Operated in batch
mode.
Gas storage
• The sludge detention
Scum layer
Supernatant
layer
time is about 30-60
days.
• The process is not so
popular these days.
Sludge
inlets
Supernatant
outlets
Actively digesting
sludge
Digested
sludge
Sludge
outlets
Single-stage high rate anaerobic digester
118
• In single-stage high rate anaerobic digester, the contents
(sludge) of the digester is heated and mixed completely.
• Because of complete mixing and heating , much higher VS
loading (kg VS/m3-day) can be applied.
• Because of mixing, the supernatant cannot be separated
from the digested sludge. About 50% of the applied VS
loading transforms to gas. The digested sludge is ½ conc.
• Operated in continuous
mode or cyclic feeding.
• The sludge detention
time is about 15-20
days.
• The process is operated
in mesophilic temperature.
Two-stage high rate anaerobic digester
119
• In two-stage high rate anaerobic digester, there are two
tanks with the first tank being for actual digestion while
the second tank is for separation of digested sludge and
supernatant.
• The first tank is heated and completely mixed while in the
second tank no heating and mixing is done. Both the tanks
are usually of same size.
•
Major gas production
takes place in the first
tank. However second
tank also produces
some CH4
•
The process is operated
in mesophilic
temperature.
Design of anaerobic digester
120
Anaerobic digesters are simple completely mixed reactors for
which SRT and HRT are the same. Hence digester design
consists of selecting an appropriate SRT and calculating
reactor volume directly from the known sludge flow rate.
The selection of appropriate SRT depends on:
• Degree of stabilization required
• Pathogen inactivation
• Digester mixing efficiency
Also others factors of importance in selecting minimum SRT are
Washout of methanogens, hydrolysis rate of particulate
organic matter, etc.
.
For primary solids, 8-10 days of SRT is reasonably enough for
stabilization where as 15-20 days is required to achieve substantial
stabilization for waste activated sludge because hydrolysis of waste
activated sludge occurs at a slower rate than that of primary solids.
Design Factors
121
Anaerobic digester is designed in terms of size by using
various approaches. Some approaches are outlined below:
1.
2.
3.
4.
Solids retention time (SRT) : denoted by C (days)
Volatile solids loading rate : kg VS/m3-day
Volume reduction
Loading factors based on population
Important design parameters for anaerobic digesters
Parameters
Solid retention time, SRT in days
Volatile solids loadings, kg VS/m3-day
Digested solids concentrations, %
Volatile solids reductions, %
Gas production, L/kg VS destroyed
Methane content, %
Standard rate
30 – 60
0.5- 1.6
4–6
35 – 50
500 - 650
65
High rate
15-30
1.6 – 6.4
4 –6
45 – 55
700-1000
65
Solids retention time (SRT)
Anaerobic digester is a completely mixed reactor for which
solid retention time (SRT) & hydraulic retention time (HRT)
is the same.
Influent flow rate
(Q), m3/day
V, m3
Volume
HRT, days =
V (m3)
=
day
Flow rate
Q (m3/day)
For a given SRT (HRT), the size of reactor can be
easily determined since flow rate (Q) is known to us.
Digester volume, V (m3) = Flow rate (Q) x SRT (C )
122
Volatile solids loading rate
123
The size of an anaerobic digester can also be estimated
based on volatile solids loading rate expressed as
kg VS/m3-day.
Influent VS
kg/day
V, m3
Volatile solids
loading rate, =
(kg VS/m3- day)
Influent VS (kg/day)
Reactor volume (m3)
For a given volatile solids loading rate, the size of reactor can
be easily determined since influent VS (kg/day) is known to us.
Digester volume, V
(m3)
=
Influent VS (kg/day)
Volatile solids loading rate,(kg VS/m3- day)
Example:
124
A high rate anaerobic reactor is employed to stabilized primary and
secondary sludge at mesophilic temperature. The primary sludge flow
rate is 500 m3/day with total solids content of 5% of which 68% is
volatile. The secondary sludge flow rate is 1250 m3/day at a total
solids content of 1% of which 75% is volatile fraction. Assume the
specific gravities of primary and secondary sludge are 1.02 and
1.01 respectively. The minimum SRT of the digester should be 12
days and allowable VS loading rate is 2.5 kg VS/m3-day. What is the
total VS in kg/day? Determine the volume of digester in m3.
Solution:
(a) Find mass of sludge produced:
Wt. of dry solids (kg/d), W = V x  x S x P
(m3/d)
V = Volume of sludge produced
 = Density of water (kg/m3)
S = specific gravity of sludge
P = % of solids expressed in decimal
125
Primary sludge dry solid mass, kg/day
= 500 x 1000 x.05 x 1.02 = 25500 kg/day
Volatile solids in primary sludge , kg VS/day
= 25500 x 0.68 = 17340 kg VS/day
Secondary sludge dry solid mass, kg/day
= 1250 x 1000 x.01 x 1.01 = 12625 kg/day
Volatile solids in secondary sludge , kg VS/day
= 12635 x 0.75 = 9468.75 kg VS/day
Total Volatile solids = 17340 + 9468.75
= 26808.75 kg VS/day
126
.
(b) Size of digester
Based on SRT:
Total volume of sludge = 500 + 1250 = 1750 m3/day
Given SRT = 12 days
Digester volume = 1750 x 12 = 21000 m3
Based on volatile solids loading:
Total Volatile solids = 26808.75 kg VS/day
Given VS loading = 2.5 kg VS/m3-day
Digester volume = 26808.75/2.5 = 10723.5 m3
Since the volume based on SRT is much higher than that based
on VS loading rate. SRT governs the design of digester. Thus By
choosing higher volume, the possibility of biomass washed could
.
Digester Shape
• Rectangular
• Cylindrical
127
• Egg-shaped
Sludge outlet
Sludge inlet
Biogas recirculation
Rectangular digesters are not so common because of
difficulty of mixing the content uniformly. This type of
shape is suitable for low rate digesters in remote areas
where resources are scare (energy) and land is available
at cheaper price.
Cylindrical shape anaerobic digester
Cylindrical shape digesters are quite common. The mixing is
much better than rectangular shape digester. The digesters
diameter could be more than 6 m but less than 38 m and
depth as high as 14 m. The bottom is conical in shape to
(slope 1:4) facilitate sludge draw off.
128
Egg-shaped digester
Egg-shaped digesters have
many advantages:
• Better mixing
• No cleaning required as
there is no accumulation
of grit
• Better control of scum layer
• Smaller land area
requirement
129
Gas production
130
The anaerobic digestion of organic waste produces biogas
which contains 65-70% CH4, 25-30% CO2 (by volume)
and small amount of N2, H2, H2S etc.
Gas production can be estimated from the percentage of
volatile solids reduction. 0.75- 1.12 m3 of gas is produced
for every one kg of VS destroyed.
Gas production depends on types of sludge as primary
sludge usually have higher gas production rate than
secondary sludge, also on the biological activity in the
digester.
Gas production rate indicates whether the digester is
well operated.
Optimum C/N=20-30
Gas production
131
 a b 3c 
 n a b 3c 
 n a b 3c 
Cn H aOb Nc + n − − +  H 2O →  + − − CH 4 +  − + + CO2 + cNH 3
 4 2 4
2 8 4 8 
2 8 4 8 
Primary solids:
C10H19O3N + 4.5 H2O → 6.25 CH4 + 3.75 CO2 + NH3
Secondary sludge:
C5H7O2N + 2 H2O → 2.5 CH4 + 2.5 CO2 + NH3
Digester Mixing
Smooth functioning of digester depends of proper mixing
of its contents. Mixing is important for the following reasons:
• Mixing helps to maintain the better contact between
substrate and microorganisms
• Maintains uniform temperature within the digester
• Prevents settling of grit matters
• Avoids excessive built-up off scum layer
Digester mixing can be achieved by:
1. Bio-gas recirculation
2. Mechanical stirring
3. Mechanical pumping
132
Digester heating
133
High rate anaerobic digesters are operated at mesophilic
temperature range which therefore requires heating the
digester. The heat requirements for digesters consist of:
1. To raise the temperature of incoming sludge to digestion
tank temperature.
2. To compensate the heat losses through walls, floors, and
roof of the digester
3. To make up losses that might occur in the piping between
the source of heat and tank.
Solar Thermal Energy
135
Energy balance on a solar collector
absorber / receiver
136
Performance of a typical flat-plate thermal
collector (ambient temperature 25°C)
The resulting plot will be a straight line only if conditions are such that
FR, UL and (τ α) are constants. )
137
Example
⚫ A flat place collector
measuring 2m X 0.8m has a
loss resistance rL (1/UL) = 0.13
m2kW-1 and a plate transfer
efficiency of 0.85. The glass
cover has transmittance of 0.9
and the absorptance of plate is
0.9. Water enters at a
temperature of 40C. The
ambient temperature is 20C
and the irradiance in the plane
of the collector is 750 Wm-2.
Calculate the flow rate needed to produce a temperature
rise of 40C.
138
139
Example:
The figure below provided the results of a performance test for a single-glazed flat-plate collector.
The transmissivity of the glass is 0.90, and the absorptivity, α, of the surface is 0.92. For the collector,
find:
(a)The collector heat removal factor, FR
(b) The overall conductance, UL in Btu/ft2°F.
(c)The rate at which the collector can deliver useful energy when the irradiation incident on the
collector per unit area is 200 Btu/ft2h, the ambient temperature is 30°F, and the inlet water
temperature is 60°F
(d) The collector temperature when the flow rate is zero.
Fig.: Flat-plate solar collector performance
data
140
SOLAR PHOTOVOLTAICS AND SYSTEM DESIGN
PV CELLS
Single crystal Si
Amorphous Si
Polycrystalline Si
Polymer
141
Dye-sensitized cell
Cd
Te
CuInSe2
HOW A PHOTOVOLTAIC CELL WORK
How a photovoltaic cell work in 3 stages is shown in this figure
numbered 1, 2 and 3
142
PHOTOVOLTAIC EFFECT
143
The photovoltaic effect produces free electrons that must travel through conductors in
order to recombine with electron voids, or “holes.”
144
SOLAR PHOTOVOLTAIC
❖
Direct conversion of radiation to electricity
– Not all are designed for it…………………
❖ Semiconductor technology
– Similar to diode or transistor
– Combination of positively and negatively doped silicon
– Radiation provides energy to allow electrons to move
– Generates an electric potential
❖ Each solar cell generates ~0.5 V
• Put many in series to get 12 or 24 V panels
• If shade one cell, acts as diode, entire series stops
generating
144
145
SOLAR PHOTOVOLTAIC
145
146
SOLAR ELECTRICITY GENERATION
❖ Standard test conditions
– 1000 W/m2
– Defined spectrum
– 25°C
Solar Photovoltaic
❖ Power output depends on load
– Many combinations of voltage
and current possible
– Good charge controllers
optimize load
146
SILICA SAND TO SOLAR PV SYSTEM
+
=
Solar module PV inverter
147
FUNDAMENTAL SOLAR CELL PARAMETERS
148
(a) Short circuit state
p
dark current
J
photocurrent
electron
light
Vmax
Maximum-power
rectangle
photo current
n
V
Open circuit voltage
Voc
hole
(b)Openpcircuit state
Jmax
Short circuit current
Jsc
light
n
Voc
Typical quantum efficiency patterns for a-Si and μc-Si
1
Q.E.
Jsc Voc FF η QE(λ)
μc-Si
0.8
Jsc: short circuit current
Voc: open circuit voltage
0.6
Fill factor FF
Conversion
efficiency η
0.4
a-Si
0.2
0
400
600
800
Wavelength (nm)
1000
1200
FF =
=
Quantum efficiency
QE(λ)
Vmax  J max
Voc  J sc
Voc  J sc  FF
 100 (%)
Pin
QE ( ) =
1 hc I sc ( )
q  P ( )
Pin, P(λ): incident irradiation
149
SOLAR CELL CHARACTERISTICS
Maximum power point (MPP)
depends on:
• Temperature
• Irradiance
• Solar cell
characteristics
Fill factor
→ Performance of solar cell
Wilson s. 209
Efficency coefficent
PV PERFORMANCE CURVE (I-V)
150
An I-V curve illustrates the electrical output profile of a PV cell, module, or
array at a specific operating condition.
PV PERFORMANCE CURVE (P-V)
A power versus voltage curve clearly shows the maximum power point.
151
PV PERFORMANCE
152
(I -V RESPONSE TO SOLAR RADIATION)
Voltage increases
rapidly up to about 200
W/m2, and then is
almost constant.
Current and maximum
power increase
proportionally with
irradiance.
PV PERFORMANCE
TEMPERATURE RESPONSE OF SOLAR CELL
Increasing cell temperature decreases voltage, slightly increases current, and
results in a net decrease in power.
153
PV PERFORMANCE
I-V RESPONSE TO NUMBER OF CELLS
154
155
TECHNIQUES TO IMPROVE CELL EFFICIENCY
•
•
•
•
•
Stacking (Multi-junction)
Concentrating PV (Mirrors or lenses)
Reflectors
Si spheres
Cylindrical modules
Source: www.waoline.com
Source: Sharp Solar
Source: Solyndra
155
156
Example:
The specification of a SILFAB SLA-P polycrystalline PV module (SLA 245 P) is given below:
Electrical Specifications-Standard Test
Units
Values
Module Power (Pmax)
Wp
245
Maximum power voltage (Vpmax)
V
30.2
Maximum power current (Ipmax)
A
8.11
Open circuit voltage (Voc)
V
37.3
Short circuit current (Isc)
A
8.65
Module efficiency
%
15.0
Maximum system voltage (UL)
VDC
1000
Series fuse rating
A
15
Power tolerance
Wp
-0/+5
Temperature Coefficient Isc
%/K
0.06
Temperature Coefficient Voc
%/K
-0.34
Temperature Coefficient Pmax
%/K
-0.40
NOCT (+/- 2 °C)
°C
41
Operating temperature
°C
-40/+85
Conditions, STC
(Solar Irradiance: 1000 W/m2, Air Mass, AM 1.5,
Temperature 25°C)
Temperature Ratings
Find the temperature dependence of solar cell efficiencies at maximum power point
(mpp) for the temperatures of 45°C and 65°C.
157
WIND ENERGY SYSTEM DESIGN
157
CLASSIFICATIONS OF WIND ENERGY
CONVERSION SYSTEMS
Wind Mills
If the mechanical energy is used directly by
machinery, such as a pump or grinding stones,
the machine is usually called a windmill.
158
Wind Turbine
If the mechanical energy is then
converted to electricity, the machine is
called a wind generator
158
TYPES OF WIND TURBINES
Vertical Axis Wind Turbine
(VAWT)
Compared with the horizontal
are available commercially.
159
Horizontal Axis Wind Turbine
(HAWT)
axis
type,
very
few
vertical
axis
159
160
SIZES AND APPLICATIONS
Small (10 kW)
• Homes
• Farms
• Remote Application
Intermediate
(10-250 kW)
• Village Power
• Hybrid Systems
• Distributed Power
Large (660 kW - 2+MW)
• Central Station Wind Farms
• Distributed Power
• Community Wind
160
L05.2 Wind Resources
161
Where,
U*: Friction Velocity
•
K: Von Karman’s Constant (e.g. 0.4~0.41)
Z, Z0: Height
U: Wind speed
161
•
L05.2 Wind Resources
162
162
•
L05.2 Wind Resources
163
163
164
Example 1:
L05.2 Wind Resources
The anemometer at the Elora weather station is at a height of 10 m
above ground, surrounded by a large flat expanse of open grass-filled
hay field. It is reading a steady wind speed of 5 m/s. The time is 12
noon solar time, and the sun is shinning brightly.
•
Calculate the maximum possible power per swept area (e.g. P/A) that a
wind turbine could produce in these conditions if the turbine had a hub
height of 50 m. Clearly state and explain any assumptions you use to
make your estimate.
164
•
L06.1 Wind Turbines 1
165
165
TURBINE MECHANICAL POWER
VERSUS WIND SPEED CURVE
166
166
EFFICIENCY IN EXTRACTING WIND POWER
167
Betz Limit & Power Coefficient:
Power Coefficient, Cp, is the ratio of power extracted by the turbine (PT)to the total
contained in the wind resource(PW), Cp= PT/PW.
Turbine power output
PT = ½ * ρ * A * v3 * Cp
For utilization of wind power, wind turbine
should take as much power from the wind as
possible. The turbine slows the speed from v1 to
v2 and uses the corresponding power differences.
PT =
(
1
m v12 − v 22
2
)
Power utilization efficiency is defined as PTactual/PTideal = Cp/Cpmax
The Betz Limit is the maximal possible Cp = 16/27
59% efficiency is the BEST a conventional wind turbine can do in extracting power
from the wind.
167
•
L06.1 Wind Turbines 1
168
168
Example 2:
169
Assume
• Turbine: 2 blades, 10 m rotor diameter
• Wind: T= 293 K, Pressure=101.3 kPa, U=12 m/s
Find
a) Power of incoming wind
b) Maximum power theoretically available in wind
c) Reasonable value for attainable power
d) Rotor speed required
e) Torque produced by rotor
169
170
Geothermal Overview
171
What is geothermal energy
❖ The term geothermal comes from the Greek geo
meaning earth and therine meaning heat thus
geothermal energy is energy derived from the natural
heat of the earth
❖ High-temperature underground reservoirs of water or
steam, heated by an upwelling of magma
❖ We tap these reservoirs which heats the water, which
turns the turbines and creates electricity
171
Heat from the Earth’s Center
• Earth's core maintains temperatures in excess of 5000°C
– Heat from gradual radioactive decay of elements
• Heat energy continuously flows from hot core
– Conductive heat flow
– Convective flows of molten mantle beneath the crust.
• Mean heat flux at earth's surface
– 16 kilowatts of heat energy per square kilometer
– Dissipates to the atmosphere and space.
– Tends to be strongest along tectonic plate boundaries
• Volcanic activity transports hot material to near the surface
– Only a small fraction of molten rock actually reaches surface.
– Most is left at depths of 5-20 km beneath the surface,
• Hydrological convection forms high temperature geothermal
systems at shallow depths of 500-3000m.
http://www.worldbank.org/html/fpd/energy/geothermal/technology.htm
172
GEOTHERMAL RESOURCE TYPES
173
Different Geothermal Energy Sources
❖ As the name implies these are reservoirs of hot underground
water. There is a large amount of them in the NA, but they are
more suited for space heating than for electricity production.
❖ In this case a hole dug into the ground can cause steam to
come to the surface. This type of resource is rare in the NA.
❖ In this type of reserve, brine completely saturated with
natural gas in stored under pressure from the weight of
overlying rock. This type of resource can be used for both heat
and for natural gas.
173
GEOTHERMAL RESOURCE TYPES
174
Different Geothermal Energy Sources
❖ At any place on the planet, there is a normal temperature
gradient of +300C per km dug into the earth. Therefore, if one
digs 20,000 feet the temperature will be about 1900C above
the surface temperature. This difference will be enough to
produce electricity.
❖ This type of condition exists in 5% of the NA. It is similar to
Normal Geothermal Gradient, but the gradient is 400C/km dug
underground.
❖ No technology exists to tap into the heat reserves stored in
magma. The best sources for this in the NA are in Alaska and
Hawaii.
174
Methods of Heat Extraction
http://www.geothermal.ch/eng/vision.html
175
176
Types of Geothermal
Direct use
Indirect use
• Residential Heating
• Dry Steam
• Industrial and commercial • Flash Steam
building heating
• Binary System
• HDR
• Combined Power Plant
– Binary and Flash
Alternate
•Combined System: Uses Power Plant with Direct Use
•Coproduced System
Geothermal Heat Pump
http://www.worldenergy.org/wec-geis/publications/reports/ser/geo/geo.asp
177
Heat Pumps
• Residential and
commercial/industrial heating or
cooling
• 3 separate closed loop systems
http://www.nextenergy.ca/how-it-works-flash.htm
• 30 000 homes with geothermal
heat pumps
• Over 3000 commercial and
industrial buildings
http://www.nextenergy.ca/how-it-works-flash.htm
178
Residential Economic Factors
• Reduce the heating costs of
a home by 60 to 70%
• Dependent upon vertical or
horizontal system
• Dependent upon size of
house and where it is
located geographically
http://www.newenergynexus.com/473/geothermal-pump-cost
179
Geothermal District Heating
Southhampton geothermal district heating system technology schematic
Boyle, Renewable Energy, 2nd edition, 2004
180
Direct Heating Example
Boyle, Renewable Energy, 2nd edition, 2004
181
In-direct Use
http://www.bbc.co.uk/scotland/learning/bitesize/standard/physics/energy_matters/supply_and_demand_r
ev4.shtml
182
Reservoirs
• Hot water reservoir
– Direct heat
• Natural steam
reservoir
– Electricity and
direct heat
• Geo-pressure
reservoir
– Brine solution of
water and steam or
http://www.springerlink.com/content/u633m624r2j3p452/fulltext.html
CH4
• Created from rain water
– Energy and CH4
reserve
– Penetrates earths crust and
stored between two
impermeable rock layers
183
184
Dry Steam
http://www.infinityturbine.com/ORC/Geothermal.html
• Steam travels directly from production well to injection well at
roughly 56 m/s with a temperature of 180-225⁰C at 4 to 8 MPa
• To produce 1 KWhe need about 6.5 kg of steam, 55MW plant
uses 100 kg of steam per second
• Reservoirs maintained naturally and with controlled flow rate
185
Flash Steam
Single Flash
• Brine mixture
containing mainly
water above 182⁰C
• Most common
• Can use 6 to 9 tonnes
of steam per hour
• Output range 5 to 100
MW
http://mitraco-surya.com/contents/geothermal/techniques/
http://www.infinityturbine.com/ORC/Geothermal.html
186
Double Flash
• Same procedure as single flash with additional
turbine and flash tank
• Brine remaining flows into injection well
• Second pressure drop produces lower pressure
steam
• Increases efficiency by 20 to 25%
• Costs only increase by 5%
Double Flash Schematic
Boyle, Renewable Energy, 2nd edition, 2004
187
188
APPLICATIONS OF GEOTHERMAL
Binary Cycle Electric Power Generation
❖
Used in geothermal areas where geothermal
fluid is at moderate temperatures
❖
Hot geothermal fluid and a binary fluid pass
through heat exchanger
❖
Binary fluid has much lower boiling point
than water, thus heat from the geothermal
fluid causes binary fluid to flash
❖
Flash steam drives turbine/generator
188
Binary Cycle Power Plants
• Low temps – 100o and 150oC
• Use heat to vaporize organic liquid
– E.g., iso-butane, iso-pentane
• Use vapor to drive turbine
– Causes vapor to condense
– Recycle continuously
• Typically 7 to 12 % efficient
• 0.1 – 40 MW units common
http://www.worldenergy.org/wec-geis/publications/reports/ser/geo/geo.asp
189
Binary Cycle Schematic
Boyle, Renewable Energy, 2nd edition, 2004
190
Binary Plant Power Output
http://www.worldbank.org/html/fpd/energy/geothermal/technology.htm
191
Combined Power Plant
• Uses combination
of binary with
additional system
• Can produce 10 to
100 MWe
• Increases
efficiency of binary
• 2 configurations
http://mitraco-surya.com/contents/geothermal/techniques/
192
Direct and Indirect (cogeneration)
http://mitraco-surya.com/contents/geothermal/techniques/
193
Single Flash Plant Schematic
http://www.worldbank.org/html/fpd/energy/geothermal/technology.htm
194
195
http://www.worldbank.org/html/fpd/energy/geothermal/technology.htm
Binary Cycle Power Plant
http://www.worldenergy.org/wec-geis/publications/reports/ser/geo/geo.asp
196
Flash Steam Power Plant
http://www.worldenergy.org/wec-geis/publications/reports/ser/geo/geo.asp
197
Efficiency of Heat Pumps
Boyle, Renewable Energy, 2nd edition, 2004
198
199
ENERGY STORAGE
Energy Storage
⚫ Energy is stored to use it at a different time than when it was
generated
⚫ The process of converting the energy to storable form means that
some energy is lost due to inefficiency and heat
⚫ Additional energy is lost when the energy is released or recovered
due to a second inefficiency
⚫ Ideally, storage is avoided to have a more efficient process
⚫ Time-of-day metering is likely in the future as metering becomes
electronic and inexpensive (like a thermostat)
⚫ Shifting the energy from usage peaks to low-use times helps the
utility, and customers would be rewarded by lower charges
200
Energy Storage
201
⚫ Renewable energy is often intermittent (like wind and
sun), and storage allows use at a convenient time
⚫ Compressed air, flywheels, weight-shifting (pumped water
storage) are developing technologies
⚫ Batteries are traditional for small systems and electric
vehicles; grid storage is a financial alternative
⚫ Energy may be stored financially as credits in the
electrical “grid”
Electrochemical Batteries
⚫ Batteries (groups; from artillery guns) of cells are
used separately or in a case containing several cells;
a 12V car battery has six 2V cells inside the case
⚫ Large batteries are often use separate 2V cells
placed next to each other in a rectangle
⚫ Various cell chemistries are used
◆ Lead-acid; Nickel-cadmium; Lithium
◆ Nickel-metal hydride
◆ Zinc-air
⚫ Best suited to storage periods of 1 second to 60 days
⚫ Self-discharge and sulphation occur with time
⚫ Desulphator circuits can reduce sulfates for longer
life
070403
202
Mechanical Energy Storage
Three Types of Storage
⚫ Pumped hydroelectric
storage (PHS)
⚫ Compressed air energy
storage (CAES)
⚫ Flywheels
203
Ultracapacitors
204
⚫ Ultracapacitors are very high capacitance units
⚫ Best suited to storage periods of 0.1 second to 10
seconds
⚫ Stored energy is 0.5 C V2
⚫ Capacitances now reach 2.7 kF (kilofarad)
⚫ Carbon electrode surface areas 1000m2 to 2000m2 per
gram provide high capacitance
⚫ Electrolytes are sulfuric acid or potassium hydroxide
030331
http://aries.www.media.mit.edu/people/aries/portable-power/
205
Supercapacitors
• Ultracapacitors = Supercapacitors
• Two metal plates that are coated with a sponge-like, porous materi
called activated carbon
• Immersed in an electrolyte made of positive and negative ions
dissolved in a solvent
• One electrode is positive, and the other is negative
• During charging, ions from the electrolyte accumulate on the
surface of each carbon-coated plate
205
Image from e-motec.net
206
Supercapacitors - Pros
• Fast energy storage
• Very long lifespan (upwards of
1 million life cycles)
• Charge and discharge very
quickly
• Lighter than a battery
• Can work in extreme
temperatures (-40°to 65 ° )
• Does not contain harm acids or
metals
• Won’t explode
206
207
Supercapacitors - Cons
• Low energy density (it doesn’t
run for very long)
• High self-discharge rate
• Can only store about 5% of the
energy of a Li-Ion battery
• If an ultracapacitor was
used for your cell-phone,
your battery would
basically last forever,
however, it would need to
recharged every 90
minutes
207
208
Supercapacitors - Future
• Currently, ultracapacitors are
great for short bursts of energy
• Great for the acceleration of an
electric vehicle
• Peugeot, Lamborghini and
Mazda are currently using them
for start/stop systems
• Ultracapacitors may be used in
conjunction with batteries –
used for regenerative braking
and periods of acceleration
• Video:
• https://youtu.be/-7T-6XdiRTw
Lamborghini Sian – image from Forbes
208
Superconductors
⚫ New technology uses high temperature superconductors
(HTSC)
⚫ HTSC operate at -1960C or -3210F
⚫ Diamagnetism- creates a field of opposition to a
magnetic field
⚫ Hybrid systems use conventional magnets to levitate
and superconductors to stabilize
209
Superconductors
⚫ Since a superconductor has essentially zero resistance, a
current once started will flow “forever”
⚫ At a later time, energy could be extracted from the
superconductor
⚫ Since the superconductors must be kept far below usual
air temperature (~20K to 80K), energy must be used to
compress the gas and make it liquefy
⚫ Newer superconductors are being investigated to find
ones with a higher critical temperature near room
temperature
080331
http://www.accel.de/pages/2_mj_superconducting_magnetic_energy_storage_smes.html
210
Superconductor Example
211
⚫ A current is induced in the superconductor toroid by inserting a magnet
briefly
⚫ Once replaced in the liquid nitrogen, the current circulation can be detected
by a compass
⚫ Current decay is on the order of 50% in 1020 years
030331
http://www.imagesco.com/articles/supercond/08.html
Ice Thermal Energy Storage
212
⚫ Air conditioning systems have a high afternoon load to
offset the sun heating of the building and the higher
outside temperature
⚫ Freezing ice during the night provides a latent heat
absorber at lower energy prices, assuming demand
charges or time-of-use rates are imposed
⚫ During the day, the ice is melted as the refrigerant is
condensed as it passes through pipes in the ice
⚫ The overall process thus provides air conditioning at a
lower cost
⚫ Bayside High School in Palm Bay FL uses this method
080331
Issues and Trends
213
⚫ Energy storage provides energy at a different time than
when it was generated (time-shifting)
⚫ Conventional storage systems such as batteries and
pumped hydro continue to dominate due to cost
⚫ Short-term storage or energy-smoothing devices like
flywheels and ultracapacitors work well in the 10-second
time range
⚫ Unneeded generators are often kept in “spinning
reserve”, motoring without load to act as generators if
additional power is required (air and bearing losses)
◆ This also stores reactive power (v.a.r.s or vars)
⚫ Energy storage will smooth peaks and valleys of
availability, but load shifting by the users is more useful
070403
Energy Storage
⚫ Energy storage is to be avoided due to the losses, but
may be economic when load time-shifting is possible
⚫ Energy must be stored in vehicles since they cannot
obtain sufficient power from wind or sun on the vehicle
◆Special student SunRayce PV cars are fragile and
light, and cannot be used in normal highway traffic
without a significant death rate
◆ Protected by team cars travelling with them
⚫ Newer technologies may increase energy storage density
at a lower cost; both are needed for a viable product
080331
214
215
❖ Fuel and Combustion Calculations
❖ Introduction to Thermal Power Plant
❖ Design of Thermal Power Plant:
pulverized, fluidized bed, integrated gasifier
combined cycle systems
❖ Biochemical biomass conversion
❖ Solar energy system design: Thermal and PV
❖ Wind Energy system design
❖ Geothermal Energy
❖ Energy Storage
1.
Review- 18/10/2022
Final Exam ( Topics)
216
• Good Luck with your Final Exam