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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:
Recipient of Finance:
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%.
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: Ø
The rate of stoichiometric propane supply is varied
from 0,5 to 0,85 l/min. Ø
The additional heat released rate from the propane combustion
is varied from 770 to 1400 J/s Ø
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. Ø
Total heat output of system is varied from 2,7 up to 5 kWh. Ø
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: Ø
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; Ø
The local measurements effect of the swirling flame
velocity compounds are carried out by using Pitot tube; Ø
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; Ø
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:
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 co-fire 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 carbon-neutral 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.
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 ( 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).
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
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
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 (a<1) are recommendable.
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
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:
Activity Nr.3
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:
Publications 1.
I.
Barmina, A. Desņickis, A. Meijere, M. Zaķe, Development of Biomass
and Gas Co-firing 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 Co-firing 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, 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., 13.
M. Gedrovičs "The
characteristic values of wood fuel, natural gas and propane-butane" referāts 49. International RTU
conferenceEnvironmental protection and heating systems In:
"Enerģētika un Elektrotehnika" Vol. 4., Nr. 21, pp.
63.-69., 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 katls- patent 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. |
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=1,1 kJ/s).
