presentation - coal and biomass combustion
DESCRIPTION
These are slides from my doctoral defense in March 2009. Supply and properties of biomass are discussed. The proposed co-firing and reburing of coal with biomass is then presented. Finally, a conceptualized model of a waste-based biomass disposal system is presented. If you have any interests or questions of this work or if you would like to see this presentation with animated graphics, please e-mail Nicholas Carlin at [email protected].TRANSCRIPT
Optimum usage and economic Optimum usage and economic feasibility of animal manure-based feasibility of animal manure-based biomass in combustion systemsbiomass in combustion systems
Nicholas T. [email protected]
Under the advisement of:Dr. K. Annamalai & Dr. W. Harman
Texas A&M University, Dept. of Mechanical EngineeringMarch 9, 2009
Overview
• Biomass supply and properties• Option 1: Large scale combustion of
biomass– Co-firing coal with biomass– Reburning coal with biomass
• Option 2: Small scale combustion of biomass
• Summary• Acknowledgments
Introduction – CAFOswww.factoryfarm.org
• About 10 million beef cattle on feed in USA• 5 dry kg (11 lb) manure per animal per day (collectable)• Over 18 million dry metric tons of manure per year• 109 million GJ/yr (103 million MMBtu/yr), if 70% ash
Sources:NASS of the USDAASAE standard D384.2 MAR2005
Dairy Cowswww.tnr.com (The New Republic)
• About 9.1 million dairy cows in USA• 6.4 dry kg (14 lb) manure per animal per day (collectable)• Over 21.2 million dry metric tons of manure per year• 255 million GJ/yr (242 million MMBtu/yr), if biomass is 40% ash
Sources:NASS of the USDAASAE standard D384.2 MAR2005
(by mass)
WY Sub-
bituminousa TX Lignitea
Low-ash Dairy
Biomassb
High-ash Feedlot
Biomassb
%Moisture, wet basis 32.9 38.3 25.3c 27.3c
% Ash, dry basis 8.4 18.6 20.0 45.2%Fixed Carbon, dry basis 49.2 41.2 17.4 10.0%Volatile Matter, dry basis 42.5 40.2 62.8 44.7%Carbon, DAF basis 75.7 74.1 58.9 59.1%Hydrogen, DAF basis 4.4 4.2 5.2 7.0%Nitrogen, DAF basis 1.1 1.4 3.2 4.2%Oxygen, DAF basis 18.4 19.1 32.0 28.9%Sulfur, DAF basis 0.4 1.2 0.7 0.8Empirical Formula C3.88H2.68N0.05O0.71S0.008 C3.10H2.09N0.05O0.60S0.019 C2.93H3.08N0.14O1.20S0.013 C1.96H2.76N0.12O0.72S0.010
Normalized Formula CH0.691N0.013O0.183S0.002 CH0.674N0.016O0.194S0.006 CH1.051N0.048O0.410S0.004 CH1.408N0.061O0.367S0.005
HHV, dry basis (kJ/kg) 27,115 23,160 17,183 11,266HHV, dry basis (Btu/lb) 11,658 9,958 7,388 4,844aTAMU Coal & Biomass Lab Fuel BankbSweeten and Heflin, 2006, TAMU Res. & Ext. Center, AmarillocSolar dried before the fuel analysis, typically about 88% moisture as excreted
Fuel Analyses
0
200
400
600
800
1,000
1,200
1,400
0 10 20 30 40 50 60 70 80 90 100
Moisture Percentage, wet basis (%)
Man
ure
Bu
lk D
ensi
ty (
kg/m
3 )
Chen, 1983, for Beef cattle manure with %M > 84%
ρ b,MBB = 998*(1 - 0.00345(100 - %M ))-1
Bulk Density of Manure Biomass
Data from Chen, 1983, Ag. Wastes 6
Curve fit to Chen’s data
2
, 3
3 4
5 6
564.8745 4.373987 % 1.844560 %
1.293383E 1 % 2.800288E 3 %
2.525236E 5 % 8.252736E 8 %
b MBB
kgM M
m
M M
M M
Modeling Particle Distribution and Specific Heat
Porosity:
Specific heat of bone dry biomass solids, adapted from Bohnhoff et al., 1987.
,
% % %
100 100 100BD BD BD
MBB BD ash FC VM
A FC VMc c c c
Specific heat of wet biomass solids
2 ( ),
% %1
100 100 lMBB MBB BD H O
M Mc c c
2 ( )
,,
1 % 100% 1001
l
MBB b MBBH O p MBB
MM
Thermal Energy Conversion of Manure
OPTION 1: Large-scale combustion
OPTION 2: Small-scale, on-the-farm combustion
Power Plant
DryingGrinding and other
processing
Emission and dollar savings (or costs)? Overall economic feasibility?
Waste disposal plus co-benefit of usable energy or thermal
commodities
Design considerations. Gross economic study.
Option 1Large Scale Combustion
Dairy
Dairy
Large feedlot or CAFO
Power Plant
Centralized drying and composting facility
<30 km(<20 miles)
80-320 km(50-200 miles)
Transporting Manure Biomass
Biomass Drying Operations
boilerNatural Gas or Electric
Warm Air
Air
Steam
Capital Costs:•Dryer = f (belt area)•Boilers•Manure Loaders•Land Purchases
O&M Costs:•Dryer•Boilers•Loaders•Gas and/or electric•Labor
Transporting Biomass
• Known Parameters:– Loading and unloading
time– Average speed of the
trucks– Hauling schedule – hours
per day hauling– Number of days per year
hauling– Volume capacity of each
truck• Must find:
– # of trips, # of trucks– Total driving hours (labor)– Diesel fuel consumption
40 cubic yard trailer (www.montonetrailers.com)
Existing coal injection
Biomass stockpile
Transport or hauling vehicle
Front end loader
Metal detector Magnetic
separator
Scale
Screen
Feeder
Grinder
Air intake
Exhaust
Sep
arat
or
Silo
Vent
Scale
Feeder
Pressure blower
Biomass reburn fuel
Biomass co-fired
fuel
•Lower NOx
•Lower nonrenewable CO2
•Better oxidation of Hg
Higher Ash Output
Overall cost estimates for these operations for
reburn and co-fire systems exist in the
literature
Other Processing at Power Plant
[adapted from the DOE, 2004, Fed. Energy Management Program]
CombustionSystemCoal and/or manure
biomass• With a moisture
percentage, %M,• Ash percentage, %A, and• Temperature, Tfuel
Combustion Air• At some excess percentage,
%EA, of stoichiometric level,• At some temperature Tair, and • Some relative humidity
CVref
Qloss
Products of Combustion• At some temperature, Tout
General Combustion Model
22 (l) 2 2 , 2 (g)
2 2 (g) 2 2 2
79 79C H N O S H O Ash O N 1 H O
21 21
CO H O N SO O Ash
C H N O S H O airw a y
b c d e f
2
, ,,
, , ( ), ,,
298 298
298
loss k k fly ash p ash out bottom ash p ash ashproducts out
fuel DAF fuel DAF H O l fuel ash p ash fuel k kair in
Q N h m c T m c T
N h wh m c T N h
Mass balance:
Energy balance:
Direct coal and biomass blend and injection if biomass heat fraction ≤ 2%
Secondary and tertiary air
Additional injection system for biomass if biomassheat fraction > 2%
Secondary and tertiary air
Emissions for MBB blends generally:
• Lower in nonrenewable CO2,
• Higher in SO2, and • Higher in fly ash.
Higher bottom ash levels
CVref
Q
Co-firingBlending coal
with biomass in primary burn
region
Project time (yrs)
Ca
sh
Flo
ws
(D
olla
rs)
3015 20 255 10
Diesel, natural gas, propane fueling costs
Labor & Maintenance
Coal savings
Avoided CO2 and NOx emission allowances New plant equipment and retrofit
Dryer facility and equipment
Transport vehicles
Annual Cash Flows Capital Costs
Project time (yrs)
Ca
sh
Flo
ws
(D
olla
rs)
3015 20 255 10
Operating cost/revenueNew plant equipment and retrofit
Dryer facility and equipment
Transport vehicles
Annual Cash Flows Capital Costs
Operating cost or revenue
, , ,
2 2
& & &n total drying n total truck n cofire n n
n n n n x n
Operating Income O M O M FO M Coal Savings
CO Savings SO Cost Ash Disposal Ash Sale NO Savings
Project time (yrs)
Ca
sh
Flo
ws
(D
olla
rs)
3015 20 255 10
Net Present Value
Net Present Worth
Net Present Cost
OR
1n
nDiscount factor DR
$ n
n presentn
Income after taxDiscounted Income
Discount factor
30
1
$ present n totaln
NPW Discounted Income Investment
Project time (yrs)
Ca
sh
Flo
ws
(D
olla
rs)
3015 20 255 10
Annualized cost or revenue
Annual Cash Flows
30
30
1$/
1 1
DR DRAnnualized Cost Revenue NPW
yr DR
2 2 2 2
22
, , , , ,
$
CO no cofire CO cofiring reported CO drying CO trucks
Specifc CO Reductionmetric ton CO
Annualized Cost
E E E E
Co-firing with BiomassSteps in Analysis
1) Compiled modeling equations into a spreadsheet computer program (Excel).
2) Generated a base case reference run of the program.
3) Conducted a sensitivity analysis of the net present worth of the co-fire system by varying each individual parameter, while holding all other parameters constant.
Base case Inputs for Co-firing
• Plant base inputs:– Plant Capacity: 300 MWe (35% efficiency)– Burning WY sub-bituminous– FGD is installed, 20% of ash is sold
• Co-firing Biomass– 5% (by mass) low-ash dairy biomass– Each biomass dryer has a 2 dry metric ton
capacity (fueled with natural gas)– Biomass transported 80 km (50 miles)
Base case Inputs for Co-firing
• Pricing– Coal: $30/ton (3.77% annual escalation)– CO2 value: $3.50/ton (5.25% escalation)– SOx value: $880/ton (4% escalation)– Natural gas: $7.76/MMBtu (5% escalation)– Electricity: $0.09/kWhe (3.70% escalation)– Diesel: $3.00/gallon (5% escalation)
• Economics:– 5.3% non-inflated discount rate– 4% inflation 9.5% inflated discount rate– 12.1% capital charge rate– 34% tax rate (MACRS of depreciation)
Year 1 CostsCoal Combustion
onlyCo-firing Coal with
BiomassFixed O&M Cost 0 (67,261)
Variable O&M Costa 0 (2,155,166)Biomass Delivery Cost 0 (620,100)
Coal Delivery Cost (43,878,448) (42,265,847)CO2 Penalty (7,800,913) (7,574,966)
SO2 Penalty (314,864) (329,081)
Ash Revenue 368,704 368,601Ash Disposal Cost (1,769,781) (1,993,493)
Annualized Capital Cost 0 (594,887)TOTAL COST (w/o capital) (53,395,301) (54,637,314)aFor MBB, variable O&M includes the cost of drying the biomass
Year One Comparison
Total Operating Cost @ Y1 = $1.2 million
(6.0)
(5.0)
(4.0)
(3.0)
(2.0)
(1.0)
0.0
1.0
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Project Year
Mill
ion
Do
llars
Total Operating Cost (real dollars)
Discounted Operating Cost (present dollars)
Total Initial Investment:$5.9 million
Annual Cash Flow for Base Case
NPW = -$22.6 million
Base Case Results
• Total investment for plant equipment, dryers, and trucks = $5.9 million
• NPW = -$22.6 million– Annualized cost = $2.30 million per year
– Cost of reducing CO2 = $35.68/ton CO2
– Cost of co-firing = 0.11 ¢/kWhe
• If avg. household consumes 940 kWhe per month, co-firing with manure biomass would increase electric bills by about $1.03 per month.
Effect of Coal Prices
(5.0)
(4.5)
(4.0)
(3.5)
(3.0)
(2.5)
(2.0)
(1.5)
(1.0)
(0.5)
0.0
0 10 20 30 40 50 60 70
coal price at year 1 ($/metric ton)
An
nu
aliz
ed C
ost
/Rev
enu
e o
f C
o-f
irin
g(m
illio
n $
/yea
r)
(45)
(40)
(35)
(30)
(25)
(20)
(15)
(10)
(5)
0
30-y
ear
Net
Pre
sen
t W
ort
h (
mill
ion
$)
Coal price escalates annually by 3.77%
Effect of CO2 Value
(3.0)
(2.5)
(2.0)
(1.5)
(1.0)
(0.5)
0.0
0.5
1.0
1.5
2.0
0 10 20 30 40 50 60
CO2 value at year 1 ($/metric ton CO2)
An
nu
aliz
ed C
ost
/Rev
enu
e o
f C
o-f
irin
g(m
illio
n $
/yea
r)
(30)
(25)
(20)
(15)
(10)
(5)
0
5
10
15
20
30-Y
ear
Net
Pre
sen
t W
ort
h (
mill
ion
$)
CO2 credit values increase annually by 5.25%
Co-firing with biomass becomes profitable
Cost components of co-firing vs. transport distance
0
10
20
30
40
50
60
70
80
90
100
0 16 80 161 241 322
average distance between plant and animal feeding operation (km)
Per
cen
tag
e o
f M
anu
re-b
ased
Bio
mas
sC
o-f
ire
O&
M C
ost
at
Yea
r 1
Co-fire O&M Transportation Cost Drying O&M
70 – 80% of drying cost due to
natural gas
0.76
1.76
3.95
2.02
1.22
0.0
1.0
2.0
3.0
4.0
5.0
TX Lignite WY Sub-bituminous LA Dairy BiomassDried off the Plant(with natural gas)
LA Dairy BiomassDried at the Plant
(i.e. no natural gas)*
LA Dairy Biomass ifNo Drying Needed
(already < 30%moisture)
As-
del
iver
ed F
uel
Co
st (
$/G
J)
--300 MW Plant--80 km (50 mile) transport distance--Natural gas: $7.76/MMBtu--Diesel: $3.00/gal--Drying from 60% to 20% moisture*Not accounting for investment cost of installing heat exchanger at power plant
Cases where natural gas may not be needed
May be the case for dairies and feedlots
in the Texas Panhandle Region
NPW = -$22.6 million
NPW = +$2.1 million
Waste heat utilized from power plant
Primary Coal Injection• Along with primary
combustion air
Reburn Fuel Injection• Usually natural gas or coal, but
could be manure biomass,• 10-20% of the plant heat rate• Rich mixture, ER = 1.05 – 1.2• Temperature: 1300-1500 K
High NOx emission
Lower NOx emission60 to 90% reduction
Over Fire Air• Completes the combustion
process
Exhaust Gases• With acceptable NOx
emission• Lower CO2 emission from
nonrenewable sources
Higher bottom ash levels
CVref
Q
Reburning to reduce NOx
Different base case inputs for Reburning
• Tangentially fired boiler using low-NOx burner with closed coupled over fire air– Primary NOx control can achieve levels of 0.20
lb/MMBtu
• Reburn fuel is pure low-ash dairy biomass– 10% heat contribution to overall heat rate
• (13% by mass)
– Reburning achieves levels of 0.06 lb/MMBtu
• Alternatively, SCR can also achieve levels of 0.06 lb/MMBtu
• NOx value: $2,600/ton NOx (4.5% escalation)
Effect of NOx Value
(10000)
(8000)
(6000)
(4000)
(2000)
0
2000
4000
6000
8000
10000
0 1000 2000 3000 4000 5000 6000 7000 8000
NOx credit value at year 1 ($/metric ton)
Sp
ecif
ic N
Ox
Re
du
cti
on
Co
st/R
even
ue
($/m
etr
ic t
on
NO
x)
annual escalation of NOx value 10.0%
1.0%
4.5%
Section 1:The cost of reducing NOx by
reburning is greater than the current value of a metric ton of NOx.
Section 3:The revenue from reducing NOx by
reburning is greater than the current value of a metric ton of NOx.
Section 2:The cost of reducing NOx by reburning is less
than the current value of NOx
Effect of NOx Value
(8)
(6)
(4)
(2)
0
2
4
6
8
0 1000 2000 3000 4000 5000 6000 7000 8000 9000
NOx credit value at year 1 ($/metric ton)
An
nu
aliz
ed C
ost
/Rev
enu
e (m
illio
n $
/yea
r) SCR
Manure-based biomass
reburning
NOx credit values escalate annually by 4.5%
Option 2Small-scale, On-the-farm
Combustion
Solids Separator
Pump
Process (e.g. space heating, hot water generator,
etc.)
Flushed Manure Slurry
90-99% moisture
Semi solids50-70% moisture
Vapor Exhaust
Biomass Solids 15-30% moisture
Bottom Ash
Exhaust Products
Wastewater 1-6% solids
Condensate for continued flushing
Recycled wastewater for flushing or treatment lagoon
Saturated Steam
Remaining solids%M=??
Condensate for continued flushing
Proposed Manure Waste Disposal Combustion Proposed Manure Waste Disposal Combustion System for on-the-farm disposalSystem for on-the-farm disposal
Combustion Air
Air
Air
Disposal Efficiency
1 8, 5
1
ew adisposal
m m m
m
Mass of flushed manure leaving the animal housings
Mass of wastewater not vaporized in the boiler
Mass of remaining ash
Tracking Results in Spreadsheet
Overall System Results: Mass Flow (kg/s) and Temperature (K)
Dry air 0.1995Moisture 0.0019 Steam 0.2097Temp 298 Temp 417
Dry exhaust 0.2130Moisture 0.0114 Steam 0.0114 Moisture 0.0216
Solids 0.0131 Temp 417 Temp 417 Temp 420Moisture 0.4233Temp 298
Solids 0.0106Moisture 0.3421Temp 298
Solids 0.0237Moisture 0.7655Temp 298 Vapor 0.1010
Temp 385Steam 0.0964
Solids 0.0447 Temp 417Moisture 0.8496 Dry air 0.1995Temp 298 Moisture 0.0019
Temp 416Solids 0.0316Moisture 0.1089Temp 298
Ash 0.0063Solids 0.0210 Temp 1,993Moisture 0.0842 Moisture 0.0964 Solids 0.0316Temp 298 Temp 417 Moisture 0.0079
Temp 370 Extra fuel 0.0000Boiler Press. 300 kPa (gage) Moisture 0.0000Flame Temp 1,993 K Temp 298
Solids 0.0106Moisture 0.0247Temp 417
Solids Separator
Pump
Air Pre-heater
Dryer Design
Vapor Exhaust
Solids into Dryer
Saturated Steam
Dried Solids
Condensate3
9d
10
11
2
Vapor Exhaust
Solids into Dryer
Saturated Steam
Dried Solids
Condensate3
9d
10
11
2
0
500
1,000
1,500
2,000
2,500
01020304050607080
moisture percentage of dried solids for combustion, %M 3
Was
tew
ater
Mas
s F
low
(kg
/hr)
0
500
1,000
1,500
2,000
2,500
Ad
iab
atic
Fla
me
Tem
per
atu
re (
K)
not vaporized
vaporized
flame temperature
(10% excess air)
Drier Solids
Effect of Ash Percentage
0
500
1,000
1,500
2,000
2,500
0 10 20 30 40 50
ash percentage in biomass (dry basis)
Rem
ain
ing
Was
tew
ater
(kg
/hr)
30
35
40
45
50
55
60
65
70
Dis
po
sal
Eff
icie
ncy
(%
)
disposal efficiency
remaining wastewater
Additional Fueling
40
50
60
70
80
90
100
0.00 0.05 0.10 0.15 0.20
additional fuel, mf EF (kg of extra fuel / kg of total fuel burned)
Dis
po
sal
Eff
icie
ncy
(%
)
CH4 C3H8 Texas Lignite
Summary
• Bottom line:– Large scale combustion of
manure-based biomass can be profitable, but a lot has to happen.1. Manure must be low in
ash2. Coal prices must be high
3. NOx and CO2 values must be high and expected to escalate
4. Using high-grade fuels to dry the manure should be avoided
5. Reburning is theoretically more profitable than co-firing, but there are many feasibility issues and simply not enough possible applications for reburning in the US.
– Small scale combustion is highly dependant on two things1. Avoided manure waste
disposal costs2. Earning profit from
electricity or thermal commodity (e.g. steam) production
Summary (cont.)
• Currently, given the high cost of transporting manure and preparing it for combustion in coal burners, as well as the lack of available low-ash manure and the lack of real dollar benefits, small-scale combustion is preferable.
• Future carbon taxes or cap-n-trade programs can greatly improve the possibility of burning manure biomass in coal-fired power plants.
Summary (cont.)
• As for drying and transporting:– Rotary dryers were found to consume slightly
less heat energy than conveyor belt dryers– Due to the relationship between manure
density and moisture percentage, there seems to be little difference in costs between transporting manure with 20% moisture and manure with 60% moisture.
– Although transporting liquid manure, >90% moisture, is significantly more expensive.
Acknowledgments
• DOE--Golden, Colorado, Grant #DE-FG36-05GO85003 and
• Texas Commission on Environmental Quality (TCEQ), Grant #582-5-65591 0015