UTILIZATION OF THE REGIONAL WOOD BIOMASS RESOURCES
FOR THE CLEAN HEAT ENERGY PRODUCTION BY CO-FIRING
THE WOOD BIOMASS WITH GASEOUS FOSSIL FUELS
Data of Project:
Funding
Number and Title of Priority
Number and Title of Activity
Number of Project
Start Date
Finish Date
Total Cost of Project, LVL
Funding of ERAF, LVL
European Regional Development Funding
2. Promotion of innovation and business
2.5.1. Financial Support of Applied Research in
the State Research Institutions
VPD1/ERAF/CFLA/05/APK/2.5.1./000001/001
07.07.2006
30.07.2008
91833.11
68874.83
Recipient of Finance:
Title of Leading Organization
Number of Registration
Address
Number of Fax
Phone
Manager
E-mail
Institute of Physics, University of Latvia
LV90002112199
Salaspils-1, Miera Street 32, LV-2169, Latvia
+3717901214
+371 7945838
Dr phys. Maija Zake
mzfi@sal.lv
Abstract
The main aim of a project – provide a more effective utilization of the Latvian local energy
resources (wood biomass) for the clean, controllable and stable heat energy production with
application to district heating by co-firing a wood biomass (up to 75%) with fossil fuel propane, natural gas (up to 25%) that allows to combust wet wood biomass faster and more
completely. In fact, the heat and electric power production is responsible for about one third
of greenhouse CO2 emitted to the atmosphere due to the burning of fossil fuels that results in
the global warming and climate change on the Earth. Since the climate change is a key
priority in the Sixth Environment Action Programme of the European Community, different
solutions of this problem are presented. Among them, the co-firing technology of fossil fuel
with renewable is considered to be a very effective way to mitigate the global warming and
reduce harmful emissions along with saving the fossil fuel resources, since the wood biomass
is considered as the CO2- neutral fuel and a release of the greenhouse CO2 emissions at 25%
co-fire is limited by 18%. Hence, the predominant release of CO2 during the burnout of the
wood biomass refers to carbon-neutral emission.
The project activities:
1. Experimental study of co-firing the wood biomass with fossil gaseous fuel and
optimization of the heat production in dependence on moisture content and structure of
wood waste.
2. Calculation and project of a small - scale district heating boiler (10-50kW), providing the
clean, controllable and stable heat energy production by co-firing a wood biomass (up to
75%) with fossil fuel - propane, natural gas (up to 25%).
3. Experimental control and regulation of the working conditions of a boiler (40kW).
Activity Nr.1.
The experimental investigations of co-firing the renewable with fossil fuel were managed
using a small-scale pilot device (Fig.1), designed for co-firing of the discrete portions of
different types of the wet wood biomass pellets with propane flame flow. The pilot device is
composed of the wood fuel gasificator (1) and sectioned water-cooled combustor (3) with
primary air supply below the wood fuel to initiate the wood fuel gasification and secondary
swirling air supply above the wood biomass that enhances the mixing of the flame
compounds downstream of combustor. The total volume of the gasificator can be varied by
varying number of the sections and, hence, can be charged by different total mass of the wet
wood pellets (180 g or 500g), providing the variation of the moisture content in the pellets
from 7% up to 30%.
Testo
10
11
9
8
PC-20
7
3
6
2
5
1
12
5
4
Fig.1. The digital image and schematic view of the experimental set-up:
1- gasifier, charged by the wood granules; 2- swirling propane/air burner; 3- water-cooled channel
sections; 4- primary and secondary swirling air supply; 5- airflow meters; 6, 7- cooling water flow
inlets and outlets; 8- data recording plate PC-20; 9- computers; 10- gas sampling probe; 11. – gas
analyzer TESTO-350XL; 12.- ash container.
Basic characteristics of the propane/air mixture:
 The rate of stoichiometric propane supply is varied from 0,5 to 0,85 l/min.
 The additional heat released rate from the propane combustion is varied from 770 to 1400
J/s
 The additional heat energy supply by the propane flame flow into the wood biomass is
limited by 25% of the total heat amount produced during the co-fire of wood pellets with
propane.
 Total heat output of system is varied from 2,7 up to 5 kWh.
 The mass flow rates of the primary and secondary swirling airflow are varied in a range
from 40 up to 120 l/min.
The diagnostic tools of the experimental study:
 The measurements of radial and axial temperature distributions in the flame are carried
out using the Pt/Pt-Rh(10%) thermocouples and computer data collecting and recording
system PC-20TR;
 The local measurements effect of the swirling flame velocity compounds are carried out
by using Pitot tube;
 The effect of swirling flame dynamics on the processes of heat/mass transfer and propane
combustion is estimated from the calorimetric measurements of the water-cooled of
channel sections by using PC-20TR;
 The local on-line measurements of the combustion efficiency, temperatures and
composition of combustion products (NOx, CO2, CO, O2, NO2) is registered by the gas
analyzer Testo 350 XL.
The main results of activity Nr.1
a) The effect of propane co-fire on combustion characteristics of the wet wood fuel
The complex measurements of combustion characteristics have shown that the effect of a rate
of propane co-fire on combustion characteristics of the wet wood fuel is quite different at
different stages of the wood fuel burnout. The most pronounced effect of propane co-fire is
detected during the primary stage of unsteady heating and gasification (t<1000s), when
increasing the rate of propane co-fire initiates faster and more intensive wood fuel drying,
gasification and ignition of the volatiles with rapid increase of the flame temperature and heat
production rate up to the peak values (Fig.2). The regression analysis has shown that the
mathematical approximation of the relation between the peak heat production rate during the
propane co-fire (Qsum.max) of the wet wood pellets (MCw), rate of propane co-fire (Qco-fire) and
peak rate of heat production (Qwood.max) during the burnout of the wet wood fuel pellets can be
expressed as:
Q sum. max  (1  MC w / 100)Q co fire  Q wood. max
Temperature,K
a
1200
700
200
0
1000
T2;L=190mm; prop.0
prop.890 J/s
Heat production rate,J/s
1700
Volume fraction,%
Mass fraction,ppm
1000
CO2;prop.0
prop.890J/s
2000
time,s
3000
prop.770J/s
prop.1100J/s
1000
time,s
2000
3000
prop.770 J/s
prop.1100 J/s
140
c
0
1000
Qsum.;prop.0
prop.890 J/s
21
3
2000
0
prop.770 J/s
prop.1100 J/s
9
b
0
time,s
2000
3000
15
3000
d
105
70
35
0
0
1000
2000
time,s
3000
NOx;prop.0
prop.770J/s
prop.890J/s
prop.1100J/s
Fig.2. The effect of propane co-fire on the time-dependent variations of the flame temperature (a),
heat production rates (b), volume fraction of CO2 (c) and mass fraction of NOx (d) during the burnout
of the wet wood fuel (moisture 21%)
The time-dependent measurements of the products composition indicate that the propane cofire provides complete burnout of the volatiles, increasing the volume fraction of CO2 in the
products (Fig.2-c), while decreases the mass fraction of CO and H2. Moreover, the results
show that at the 20-30% of propane co-fire about 85-90% of carbon CO2 emissions are
produced due to the burnout of renewable wood fuel and must be related to the carbonneutral emissions with respect to the greenhouse effect. The effect of propane co-fire on NOx
emissions (Fig. 2-d) indicate that for the stoichiometric combustion conditions in the propane
flame flow the enhanced burnout of the volatiles with an increased rate of heat production
promotes increasing of the flame temperature with correlating increase of the rate of
temperature-sensitive thermal NOx production downstream the flame flow and mass fraction
of NOx emissions in the products- at 30% of propane co-fire the mass fraction of NOx
increases from 65-70 ppm with no co-fire up to 85-90% for the conditions of propane co-fire.
b) The effect of duration time of additional heat input on combustion characteristics
With the aim to improve combustion characteristics of the wet wood fuel, there is essential so
to consider usefulness of propane co-fire duration over the all stages of the wood fuel burnout
(tco-fire). The effect of duration of propane co-fire on the time-dependent variations of the
flame temperature and heat production rates at different stages of the wood fuel co-fire is
illustrated in Figure 3. As one can see, decreasing duration of propane co-fire at constant rate
of co-fire results in pronounced ignition delay with intensive heat consumption from the
propane flame flow and correlating decrease of the flame temperature during the primary
stage of the thermal decomposition of the wet wood fuel. Hence, the time-dependent
variations of the flame temperature and rate of the heat production have shown that, not only
enough heat production rate during the propane co-fire, but also enough duration of propane
co-fire must be provided to prevent an ignition delay. As a consequence of resulting effect of
these two main factors on the rate of wood fuel gasification and ignition of the volatiles, an
ignition time of the volatiles can be decreased by increasing duration of propane co-fire, as
well increasing the rate of propane.
1800
1800
Heat production rate,J/s
Temperature, K
a
1300
800
300
0
1000
time,s
T2;L=190mm;tco-fire-2000s
tco-fire-300s
tco-fire-220s
tco-fire-170s
2000
b
1200
600
0
0
1000
time,s
2000
Qsum; tco-fire-2000s
tco-fire-300s
tco-fire=220s
tco-fire-170s
Fig.3. The effect of duration of propane co-fire on the time-dependent variations of the flame
temperature (a) and the heat production rate (b) at constant rate of propane co-fire ( Q co  fire =1,1 kJ/s).
The time-dependent measurements of combustion and emission characteristics have shown
that by limiting duration of propane co-fire and switching out the propane co-fire during the
active burnout stage of the wood fuel promotes the formation of combustion instability,
resulting in the intensive pulsations of the flame temperature, rate of the heat production and
rate of the formation of main product. In contrary, increasing duration of propane co-fire and
the total heat input during the propane co-fire promotes an increase of the average volume
fraction of carbon neutral CO2 in the products (Fig.4-a) with correlating decrease of the
average mass fraction of the flammable volatiles (CO, H2) below 100ppm (Fig. 4-b), so
decreasing the volume fraction of free oxygen and the air excess (Fig. 4-c) in the products,
indicating that increasing duration of propane co-fire is quite desirable to provide cleaner and
more effective burnout of the volatiles. Finally, it should be noticed that the very important
problem of wood biomass co-firing for the stoichiometric combustion conditions of the
propane flame (α=1) is an increased rate of thermal NO production with relative high mass
fraction of NOx emissions in the products (Fig. 4-d). To solve this problem, an excess of
propane supply with α<1 in propane flame is used to promote reburn reactions between
unburned hydrocarbons (CxHy) and NO with correlating decrease of NOx in the products
(Fig.4-d).
1000
a
Mass fraction ,ppm
Volume fraction CO2,%
10
9
8
7
b
750
500
250
0
6
0
0
0,2
0,4
Total additional heat input.,MJ
CO,ppm
H2
100
Mass fraction NOx, ppm
500
c
Air excess,%
0,2
0,4
Total additional heat input, MJ
400
300
200
100
d
90
αprop=1
80
70
αprop=0,8
60
0
0,2
0,4
Total additional heat input,MJ
0
0,15
0,3
0,45
Total additional heat input,MJ
Fig. 4. The effect of total additional heat input on the emission characteristics by co-firing the wet
wood pellets with propane
c) The effects of wet wood fuel of different size and structure co-fire with propane on the
combustion and emission characteristics
The experimental research presents results of the co-firing the wet wood fuel of different size
and structure (wood chips, pellets and logs) (Fig.5) with fossil gaseous fuel by enhancing the
wood fuel gasification and completing the burnout of the volatiles with an additional heat
input, when co-firing of the wood fuel with propane flame flow.
a
b
c
d
Fig. 5. The shapes and sizes of the wood pellets (a), woodchips (b), logs (c) and lignin-hydrolyzed
residues (d).
The raw lignocellulosic non-hydrolized residues are quite different hereupon their structure,
composition and energy content (Tab.1).
Table 1. Composition of non –hydrolyzed residues
Raw
material
Type of
hydrolysis
Softwood
LHR AH
LHR SHF-1
LHR SHF-2
LHR SSF-1
LHR SSF-2
LHR SSF-3
Dilute acid
Enzymatic SHF
Enzymatic SHF
Enzymatic SSF
Enzymatic SSF
Enzymatic SSF
Lignin
Klasson
content, %
28.8
51.7
48.9
54.5
58.2
67.5
71.9
C
49.12
59.4
55.03
57.68
57.96
59.74
60.92
Element content, %
H
N
S-total
5.72
5.95
6.16
6.02
5.86
5.86
5.93
0.326
0.192
0.417
0.396
0.557
0.802
1.13
0.140
0.212
0.220
0.211
0.229
0.200
0.439
S comb.
0.016
0.040
0.032
0.049
0.129
0.130
0.213
The time-dependent variations of the heat production rate and variations of the composition
of the products at different stages of the burnout of wood logs and lignin-hydrolyzed residues
(LHR) indicate that by analogy with effect of propane co-fire on gasification of the wood
pellets and burnout of the volatiles, co-firing of the wood logs and LHRs promotes an
increase of the rate of wood fuel gasification, rate of heat production and peak values of the
flame temperature and produced heat, indicating that propane co-fire completes the burnout
of the volatiles. The enhanced wood fuel gasification promotes faster ignition of the volatiles,
increasing a rate of heat production and flame temperature up to the peak values with an
intensive consumption of free oxygen during the burnout of the volatiles, indicating that
propane co-fire enhances the burnout of the volatiles (Fig.6-a-d).
Moreover, the enhanced burnout of the volatiles with an increase of the rate of heat
production and temperature downstream of the flame reaction zone results in an increase of
the rate of NOx formation and peak mass fraction of NOx in the products. To restrict such
increase in a rate of NOx production during the burnout of the wood fuel fuel-rich conditions
of propane flame flow (<1) are recommendable.
12
Heat production rate, J/s
Heat power, kW
a
8
4
0
0
40
21
O2,%-logs+prop.
0
0
time,min
300
600
time,s
900
Qsum-SHF-2,tprop.=1500s
220s
120s
20s
21
7
40
1000
logs
14
0
2000
time,min 80
c
0
b
3000
Volume fraction O2,%
Volume fraction O2,%
P,kW, logs+prop.
4000
80
O2,%-logs
d
14
7
0
0
300
600
time,s
900
O2-SHF-2, tprop.=1500s
220s
120s
20s
Fig. 6. The effect of propane co-fire on the rate of heat production and the volume fraction of free
oxygen by co-firing of wood logs and LHR SSF-2
The main results of activity Nr.2
The results of experimental research of the wood biomass
(pellets, logs, chips u. c.) co-fire with a small amount of
propane (up to 20-25% from the total heat production) are
used and analyzed to develop a small-scale boiler with
application to private house heating systems for the clean
and effective heat energy production, promoting
stabilization of combustion and emission characteristics
during the burnout of wood fuel at different moisture content
and structure. The main parts of a boiler AK-005S with
simultaneous use of renewable wood and fossil gaseous
(propane) fuels for the heat energy production are: a furnace
with heat surface, a gas burner “BENTON”, and an air
supply fan CAL-120-2T and a wood fuel storage tank
KAPB-100. The boiler is supplied with control panel for
automatic wood fuel, propane and air feeding into a furnace
(Fig.7).
Fig.7. The digital image of the heat and hot water boiler AK-005S
Technical data of the heat and hot water boiler AK-005S:
Characteristics
Parameters
1. Capacity
2. Fuels
40 kW
Wood/propane
3. Heating surface
2,3 m3
4. Water capacity
147 l
5. Maximal water temperature
95oC
6. Water pressure
1bar
7. Cross-section surface of chimney
525 cm2
8. Weigh of boiler
300 kg
9. Boiler efficiency
80%
10. Gas burner “BENTON” BG100
7 – 41 kW
Activity Nr.3
1. Testing and approbation of the small-scale boiler
2. Approbation and testing of the boiler heat production stability and combustion
efficiency
3. Ecological control of the heat production by co-firing the wood biomass with gaseous
fuel (propane)
The main results of activity Nr3:
In accordance with the aims of activity Nr.3 the testing and approbation of the small-scale
boiler is carried out by co-firing the wood biomass with gaseous fuel (propane)
The results of the boiler approbation have shown:
1. In accordance with the aims of activity Nr3 the heat production power of the boiler by
co-firing the wood biomass with propane at the rate of propane co-fire 25-30% has
achieved 50-60kW.
2. Combustion efficiency at the peak rate of heat approaches to 70-75%.
3. At the rate of propane co-fire 25% GHG carbon emission is about 10-12% from the
total amount of carbon (CO2) emission, while the total amount of CO un NOx
emissions refers to the Latvian standards.
Publications
1.
I. Barmina, A. Desņickis, A. Meijere, M. Zaķe, Development of Biomass and Gas Cofiring Technology to Reduce Greenhouse Gaseous Emissions, Springer- NATO
publishing, 2007, pp. 1-10.
2.
M. Zaķe, I. Barmina, A. Meijere, A. Desņickis, Control of Pollutant Emissions by Cofiring the Renewable with Fossil Fuel, 17th International Congress of Chemical and
Process Engineering, Praha, Czech Republic, CHISA 2006, CD-ROM of Full Texts,
Nr.0699, pp.1-15; Summaries 4, System Engineering, p. 5.095.
3.
M. Zaķe, I. Barmina, A. Desņickis, Electric Control of Combustion Dynamics and
Polluting Emissions from the Swirl Stabilized Premixed Combustion" 7th International
Congress of Chemical and Process Engineering, Praha, Czech Republic, CHISA 2006,
CD-ROM of Full Texts, Nr.0727, pp.1-13; Summaries 4, System Engineering, p. 5.096.
4.
I. Barmina, A. Desnickis, M. Gedrovics, M. Zaķe, Experimental study of Combustion
Dynamics by Cofiring the Renewable with Fossil Fuel, RTU, In: Power and Electrical
Engineering, International Scientific Conference, Vol.17, N4, 2006, pp.174-187.
5.
M. Zaķe, I. Barmina, M. Gedrovičs, A. Desņickis, Effective Technique of Wood and
Gaseous Fuel Co-firing for Clean Energy Production, LFTZ, 2007, N2, pp. 41-56.
6.
I. Barmina, A. Desnickis, M. Gedrovics, M. Zake, Co-firing of Renewable with Fossil
Fuel for the Cleaner Heat Energy Production, 10th Biennial Conference on
Environmental Science and Technology (CEST -2007), Greece, pp. B44-B51.
7. I. Barmina, A. Desnickis, M. Zake, The effect of Combustion Dynamics on the
Formation of Pollutant Emissions by Co-firing the Wood Biomass with Gaseous Fuel,
Proceedings of 5-BHTC, Sankt-Peterburg, 2007, 589-597.
8. A. Arshanitsa, I Barmina, G Telysheva, M. Zake, Combustion and emission
characteristics of the wood fuel pellets, “World Bioenergy-2008”, Jonkoping, Sweden,
pp.244-248.
9. I. Barmina, M. Zake, Wood biomass co-firing for the clean heat energy production,
“World Bioenergy-2008”, Jonkoping, Sweden, pp.249-253.
10. I. Barmina, M. Zaķe, M. Purmals, The effect of wood biomass co-firing with fossil
gaseous fuel on the combustion and emission characteristics, Rīga, 2008, 5th UEAA
General Assembly and the associated Workshop on “Renewable Energy Resources,
Production and Technologies”, Zinātne, 2008, pp.54-62.
11. A.Arshanitsa, I. Barmina, T. Dizhbite, G. Telisheva, M. Zake, Combustion of
Granulated Plant Biofuel, Rīga, 2008, 5th UEAA General Assembly and the associated
Workshop on “Renewable Energy Resources, Production and Technologies”, Zinātne,
2008, pp.37-46.
12. I. Barmina, A. Desņickis, M. Gedrovičs, M. Purmals, M. Zake, "Experimental study of
multi-fuel firing for effective and environmentally friendly heat production" paper 49.
International RTU conference "Environmental protection and heating systems”, RTU
"Enerģētika un Elektrotehnika" Vol. 4., Nr. 21, pp. 11.-18., Rīga
13. M. Gedrovičs "The characteristic values of wood fuel, natural gas and propane-butane"
referāts 49. International RTU conference”Environmental protection and heating
systems” In: "Enerģētika un Elektrotehnika" Vol. 4., Nr. 21, pp. 63.-69., Rīga
14. A. Arshanitsa, I Barmina, T.Dizhbite, G Telysheva, M. Zake, J.Rizhikov, Combustion
and emission characteristics of the plant biofuel pellets 2008, Spain, Valencia, pp. 10.
15. I. Barmina, M.Gedrovičs, P. Meija, A. Meijere-Līckrastiņa, M. Purmals, M. Zaķe,
Atjaunojamā kurināmā un gāzveida kurināmā vienlaicīgas sadedzināšanas apkures katlspatent announcement, 2008, pp.1-16.
16. M. Zaķe, Co-firing of renewable with fossil fuel for the clean and effective heat energy
production, "High Tech in Latvia", 2008, pp. 31.