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	European Regional Development Funding
Number and Title of Priority	2. Promotion of innovation and business
Number and Title of Activity	2.5.1. Financial Support of Applied Research in the State Research Institutions
Number of Project	VPD1/ERAF/CFLA/05/APK/2.5.1./000001/001
Start Date	07.07.2006
Finish Date	30.07.2008
Total Cost of Project, LVL	91833.11
Funding of ERAF, LVL	68874.83

 

Recipient of Finance:

 

Title of Leading Organization	Institute of Physics, University of Latvia
Number of Registration	LV90002112199
Address	Salaspils-1, Miera Street 32, LV-2169, Latvia
Number of Fax	+3717901214
Phone	+371 7945838
Manager	Dr phys.  Maija Zake
E-mail	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%.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 (NO_x, 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 (Q_sum.max) of the wet wood pellets (MC_w), rate of propane co-fire (Q_co-fire) and peak rate of heat production (Q_wood.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 NO_x (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 NO_x 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 NO_x production downstream the flame flow and mass fraction of NO_x emissions in the products- at 30% of propane co-fire the mass fraction of NO_x 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 (t_co-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 (=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 NO_x 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 (C_xH_y) and NO with correlating decrease of NO_x 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

 

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.

 

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	Lignin Klasson content, %	Element content, %
			C	H	N	S-total	S comb.
Softwood	-	28.8	49.12	5.72	0.326	0.140	0.016
LHR AH	Dilute acid	51.7	59.4	5.95	0.192	0.212	0.040
LHR SHF-1	Enzymatic SHF	48.9	55.03	6.16	0.417	0.220	0.032
LHR SHF-2	Enzymatic SHF	54.5	57.68	6.02	0.396	0.211	0.049
LHR SSF-1	Enzymatic SSF	58.2	57.96	5.86	0.557	0.229	0.129
LHR SSF-2	Enzymatic SSF	67.5	59.74	5.86	0.802	0.200	0.130
LHR SSF-3	Enzymatic SSF	71.9	60.92	5.93	1.13	0.439	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 NO_x formation and peak mass fraction of NO_x in the products. To restrict such increase in a rate of NO_x 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

 

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	40 kW
2. Fuels	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 NO_x emissions refers to the Latvian standards.

 

 

 

 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, 17^th 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" 7^th 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, 10^th 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, 5^th 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, 5^th 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 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.