Vol. 42 2016 No. 3 DOI: 10.5277/epe160308
MAREK JUSZCZAK1
COMPARISON OF CO AND NO
xCONCENTRATIONS
FROM A 20 kW BOILER FOR PERIODIC
AND CONSTANT WOOD PELLET SUPPLY
The impact of the fuel feeding mode (continuous or periodic with various stand-by/operation time ratios) on carbon monoxide (CO) and nitrogen oxides (NO, NOx) concentration values in the flue gas
was analyzed for coniferous wood pellet firing. Experiments were performed using a 20 kW water boiler equipped with an under-fed (retort) wood pellet furnace located in a full scale heat station sim-ulating real-life conditions. Impact of oxygen concentration and temperature in the combustion cham-ber on the concentrations of carbon monoxide and nitrogen oxide have been examined. It was con-cluded that the commonly used periodic fuel supply does not necessarily cause an important increase of the concentrations of carbon monoxide compared to those in the continuous fuel feeding mode. Continuous fuel supply can even imply higher concentrations of carbon monoxide when fuel and air streams are not chosen properly.
1. INTRODUCTION
Low heat output heating boilers (<50 kW), typically used in domestic heat stations, in comparison with high heat output boilers (>1 MW), present a much higher emission of incomplete combustion products (carbon monoxide, hydrocarbons and sooth) per produced energy unit. It is estimated that in Germany in the year 2000 the share of small scale wood combustion systems contributing to the emission of incomplete combustion products was between 16 and 40%, although their total energy production was only about 1% [1]. These numbers have already changed as currently more modern boilers are being used in Germany, it depicts however the scale of the problem. In Poland, this
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1Poznan University of Technology, Institute of Environmental Engineering, Division of Heating, Air Conditioning and Air Protection, Piotrowo 3A, 60-965 Poznań, Poland, e-mail: marek.juszczak@put.poznan.pl
proportion is probably similar or even higher, as customers more frequently use cheap boilers of simple and old design.
The reason behind it is mostly the fact that these boilers, in order to be limited in size and low-cost, are equipped with small combustion chambers. Their walls function directly as heat exchange surfaces and are reached by the flue gas much too fast. As a consequence, the flue gas is cooled and the combustion process is hampered. This problem is especially visible in the case of biomass, as in the first stage of burning it releases as much as 80 wt. % of volatile substances, as opposed to hard coal where it is only 20 wt. %, which makes the flue gas reach the cold heat exchange surfaces and be cooled even quicker. Additionally, biomass is characterized by a smaller lower heating value in comparison with hard coal which leads frequently to a lower temper-ature in the combustion chamber. All these factors create conditions that favor gener-ation of considerable amounts of incomplete combustion products.
The most useful and easily controllable pollutant emission indicator for incom-plete combustion products is CO concentration. The Polish-European law [2] is quite liberal in that aspect as it permits the CO concentration to be even 3000 mg/m3 for high heat efficiency heating boilers with a heating output of less than 300 kW. How-ever, internal legislation of some countries, e.g. Sweden, limit the permitted CO con-centration to 2000 mg/m3. The criteria are even stricter in order for a boiler to be granted an ecological certificate. For example, to obtain the Nordic countries’ Svan Mark certificate it cannot exceed 1000 mg/m3 and for the German Bauer Engel certif-icate it needs to be lower than 100 mg/m3 [3]. Obviously, to reach these values one needs to use high quality deciduous wood pellets with no contamination, such as sand or silicates. The most modern wood pellet furnaces equipped with the oxygen probe
and continuous fuel supply can give as low CO concentrations as 10–50 mg/m3 [4].
These values, however, can only be reached probably in stable laboratory conditions, with a high heat output, and definitely not over a longer period of time in a real-life heat station during operation. In the case of a heat station with conditions resembling the real ones (periodic fuel supply, no oxygen probe air stream regulation) the con-centrations vary from 300 to 800 mg/m3 [5–8]. It does not specify the permitted value for nitrogen oxide concentrations, however, producers of small heating boilers must comply with NOx concentration of below 400 mg/m3, in order to obtain the Polish ecological certificate [10], which facilitates boiler commercialization. All concentra-tions are presented for 10% O2 content in flue gas.
Limited availability of high quality and cheap wood pellets in Poland (that are cur-rently used in power plants), aroused interest in agricultural biomass pellets as fuel for heating boilers with low heat output. Agricultural biomass is described by low ash melting temperature which is why it should be fired at a temperature lower than 700 °C [11], in order to avoid the production of slag that hampers furnace operation and the com-bustion process. Also chlorine content is an important factor in biomass comcom-bustion as chlorine can form KCl melting at a low temperature. Therefore, it is recommended
to use additives such as Ca(OH)2 or dolomite that react with chlorine and impede KCl for-mation [12–14]. Interesting results of study in the area of pollutant emission from firing biomass and other fuels can be found in the papers by Musialik--Piotrowska et al. [15, 16] and Hardy et al. [17].
An important factor that could influence pollutant emissions of wood pellet furnaces is the mode of automated pellet supply, namely: whether it is continuous or periodic, which is precisely the topic of this study. The majority of wood pellet furnaces with low heat output, even those produced by renowned manufacturers, do not enable fluent pel-let stream regulation. Instead, they use periodic fuel supply, which means that fuel stream is regulated manually by modifying the operation and stand-by time of the fixed- -speed screw feeder, as well as the stream of air for combustion in the beginning of firing process, in order to obtain the desired heat output of the boiler. The fact that air stream is constant for the required boiler heat output and is not reduced during the stand-by period in pellet feeding causes lowering of the temperature in the combustion cham-ber and excessive increase of oxygen concentration, and as a result an increase of CO concentration. This is why continuous pellet feeding system would seem to be much more beneficial. Nevertheless it is barely introduced as a technical solution in low heat output heating boilers with wood pellet furnaces due to its elevated cost. For periodic fuel supply systems described above, the settings would differ depending on wood type. Furnace producers do suggest recommended settings (operation time, stand-by time, air stream), however only for good quality 100% deciduous wood pellets as deciduous wood is considered to be the best biomass type for firing due to its low nitrogen (0.1–0.2%), ash (1%), and negligible sulfur content. These settings are not always ade-quate for coniferous or mixed wood pellets.
2. EXPERIMENTAL SET UP AND PROCEDURE, MEASURING EQUIPMENT, MATERIAL
In the experimental study, the emission of pollutants has been examined during co-niferous wood pellet firing in a low heat output boiler with under-fed furnace. The aim of performed experimental study was to determine:
whether the concentration of CO is much higher for periodic wood pellet supply than for continuous fuel supply,
at which value of oxygen concentration one can achieve the lowest possible CO
concentration (a parameter which is necessary to determine the adequate air stream for combustion, especially if oxygen probe is to be used in the future),
the fluctuations of concentrations of nitrogen oxides and carbon monoxide
de-pending on the temperature and oxygen concentration in the combustion chamber upon changing one of these parameters,
The experiments were carried out in a full scale heat station equipped with a 20 kW boiler with an under-fed wood pellet furnace (Fig. 1). Unlike many studies performed by accredited laboratories that examine boilers in idealized conditions, in this study, a special attention was paid to ensure conditions similar to the real ones and therefore simulate domestic boiler operation where heat demand is variable. The boiler lacked an automatic device of air stream with an oxygen probe (lambda sensor) in the flue gas downstream the boiler. Air stream was modified manually at the beginning of the firing process by fan speed regulation, ranging from 10 to 100% of its maximum value. Pellets were supplied from the storage to the furnace by means of a fixed-speed screw feeder. The furnace contained a horizontal fixed-speed screw pellet dispenser that subsequently introduced pellets to the burning region. The furnace was equipped with an electric ig-nition device.
Fig. 1. A view of 20 kW pellet supplied boiler (Biomax, Lumo type, Poland) (left), and under-fed (retort) furnace (Bioline 20, Ecotec type, Sweden) (right)
Originally the boiler worked with a periodic pellet supply system. However, for the purpose of this study, a continuous pellet supply system was arranged by installing an inverter that enforced fluent regulation of screw feeder resolutions. The boiler was con-nected to a 900 dm3 water heat storage through a special mixing and pumping device, Laddomat 21 (Swedish production) composed with a pump and three thermal valves that open or close automatically depending on incoming water temperature. This device enabled water flow in the boiler after the temperature of 64 °C was reached. The water at the inlet of the boiler was maintained at temperature over 64 °C in order to keep the combustion chamber walls hot and therefore minimize emission of incomplete combus-tion products.
The gas pollutant concentrations in the flue gas downstream the boiler as well as the flue gas temperature were measured using a Vario Plus (MRU) flue gas analyzer
(Germany). Concentrations of O2, NO, and NO2 were measured with electrochemical
cells. Gas analyser calculated NOx concentration as a total of NO (transformed to NO2) and NO2 concentration. CO and CxHy concentrations were measured using infrared ra-diation. The flue gas analyser also calculated chimney loss. Temperature in the com-bustion chamber was measured ca. 0.30 m above the flame with a radiation shielded thermocouple PtRhPt. The measurements of temperature in the flame made with a py-rometer showed that the temperature measured with the thermocouple is about 250 °C lower than the temperature in the flame. Unfortunately, it was not possible to make structural changes in the boiler to take flue gas samples directly from the flame area. Dust concentration in the chimney was measured using a gravimetric dust meter equipped with isokinetic aspiration. Heat received by the boiler water and boiler heat output were measured with an ultrasonic heat meter. Fuel stream was measured using a Sartorius lab balance. Pellet lower heating value was measured using the calorimetric method and heat efficiency was calculated as heat transferred to the boiler water divided by fuel mass multi-plied by fuel lower heating value. The obtained values were confronted with heat efficien-cies calculated based on chimney loss and other estimated heat losses.
The study was performed using “Ecopellet” wood pellets certified to the highest European quality standard DIN plus no. 7A105, corresponding with the recent European standard E DIN EN 14961-2:2010-07, ordered from the Polish Company Barlinek. The pellets 6 mm in diameter, up to 40 mm long, were made entirely from coniferous wood sawdust. Their moisture was 10%, ash content 0.7%, lower heating value 18.5 MJ/kg, nitrogen content 0.35%.
In the study, pollutant concentrations were examined for three different fuel streams (3.0, 4.5 and 6.0 kg/h) and related three different speeds of screw pellet dis-penser. For each fuel stream, six different fuel feeding modes (five periodic and one continuous mode) were applied. Each of the feeding modes was performed for 5 con-tinuous hours. Experimental design is presented in Table 1. For fuel stream of 3.0 kg/h, the operation/stand-by time ratio was 2:3, for 4.5 kg/h 2:1 and for 6.0 kg/h 8:1. Such settings result from the necessity of obtaining good furnace operation. Air stream was chosen empirically in order to obtain the lowest possible CO concentration while observing gas analyzer indications in terms of CO concentrations and watching the flame in the combustion chamber through a sight glass. For the examined fuel streams of 3.0 , 4.5 and 6.0 kg/h, the air stream values were set at about 30, 50 and 100% of their maximum, respectively. Gas pollutant concentrations, temperature in combustion chamber and oxygen concentration were measured continuously and transmitted in real time to a personal computer where they got recorded every 2 s, mean values were calculated every 10 s and analyzed on diagrams (Figs. 3–8). For gas pollutant concentrations (CO, NO, NOx), uncertainty intervals were calculated with a 0.95 probability (Table 1).
T ab le 1 . M ea n p ara m eter v alu es m ea su re d f o r all f u el fe ed in g m o d es F u el m ass stre a m [ k g /h ] F u el fe ed in g m o d e T im e o f o p era ti o n : sta n d -by m o d e [s ] P o ll u tan t co n ce n trati o n s fo r 1 0 % O 2 in f lu e g as [m g /m 3] T e m p er atu re in c o m b u stio n ch am b er a [° C] O2 co n ce n tratio n [% ] A ir ex ce ss ra ti o He at o u tp u t [k W ] He at eff ici en c y [% ] CO NO NO x 3 .0 co n ti n u o u s 443 32 290 17 446 27 461 9 1 .8 1 2 .6 82 p erio d ic 2 0 :3 0 236 26 242 9 373 14 482 8 1 .6 1 3 .0 84 3 0 :4 5 418 33 257 22 395 36 425 8 1 .6 1 3 .3 86 4 0 :6 0 246 28 239 10 369 16 462 8 1 .6 1 2 .8 83 5 0 :7 5 266 22 273 4 425 8 447 9 .5 1 .8 12 .7 85 6 0 :9 0 284 36 285 10 445 15 430 9 1 ,9 1 3 .1 84 4 .5 co n ti n u o u s 329 49 313 35 423 54 440 10 1 .9 1 9 .2 83 p erio d ic 2 0 :1 0 310 34 272 37 423 58 437 10 1 .9 1 9 .0 82 3 0 :1 5 237 28 247 34 382 53 462 7 1 .5 1 9 .2 83 4 0 :2 0 231 31 254 38 391 5 455 7 1 .5 1 9 .2 83 5 0 :2 5 299 41 256 4 394 6 436 7 1 .5 1 9 .2 83 6 0 :3 0 350 39 240 20 369 33 437 7 1 .5 1 9 .7 85 6 .0 co n ti n u o u s 392 46 241 14 371 22 431 7 .5 1 ,6 2 6 .5 86 p erio d ic 4 0 :5 302 44 267 5 415 8 463 8 1 .6 2 5 .9 84 8 0 :1 0 293 67 279 13 432 20 459 7 .5 1 .6 2 5 .6 83 1 2 0 :1 5 329 38 281 13 435 18 433 7 .5 1 .6 2 5 .3 82 1 6 0 :2 0 335 28 282 18 437 28 439 9 .5 1 .8 2 5 .0 81 2 0 0 :2 5 347 26 254 3 392 5 437 7 .5 1 .6 2 5 .6 83 aT e m p er atu re in th e co m b u stio n c h am b er (m ea su re d w it h a th erm oc ou ple) i s ca . 2 50 ° C lo w er th an th e tem pe ra tu re in th e fla m e (m ea su re d w ith a p y ro m eter).
3. RESULTS AND DISSCUSION
Figures 2, 3, 5, 7 present time dependences of gas pollutant concentrations and of other parameters. All of them seem to display a similar shape. Figures 4, 6, 8 show dependences of CO, NO and NOx concentrations on temperature in the combustion chamber and on oxygen concentration in the flue gas for 3 kg/h continuous fuel feeding and some periodic feeding modes.
Fig. 2. CO concentrations in correlation with fuel mass stream and fuel feeding mode, according to Table 1
Fig. 3. Time dependences of pollutant concentrations and other parameters for 3 kg/h continuous fuel supply 0 50 100 150 200 250 300 350 400 450 500 20:30 30:45 40:60 50:75 60:90 20:10 30:15 40:20 50:25 60:30 40:05 80:10 120:15 160:20 200:25 C O c onc entra ti ons [mg /m 3] for 10 % O 2 conti nuous periodic 3.0 [kg/h] periodic conti nuous conti nuous periodic 4.5 [kg/h] 6.0 [kg/h] 1 10 100 1000 00 :00 00 :34 01 :08 01 :42 02 :16 02 :50 03 :24 03 :58 04 :32 05 :06 05 :40 06 :14 06 :48 07 :22 07 :56 08 :30 09 :04 09 :38 10 :12 10 :46 11 :20 11 :54 12 :28 13 :02 13 :36 14 :10 14 :44 15 :18 15 :52 16 :26 17 :00 17 :34 18 :08 18 :42 19 :16 19 :50 20 :24 20 :58 21 :32 22 :06 22 :40 23 :14 23 :48 24 :22 24 :56 25 :30 26 :04 26 :38 27 :12 27 :46 28 :20 28 :54 29 :28 G as con cen trat io n [m g /m 3] fo r 1 0 % O 2 O2 [%]
Air axcess ratio Flue gas temperature [°C]
Time [mm:ss]
NO [mg/m3] (10% O
2)
CO [mg/m3] (10% O
Correlations obtained for other fuel feedings were similar to those presented in the paper. Rough measurements of dust concentration showed the values between 30 and 50 mg/m3. All pollutant concentrations were calculated for 10% O
2 content in flue gas. The values of uncertainty intervals for CO, NO, NOx concentrations indicate the mag-nitude of fluctuations of these parameters for a certain fuel feeding method.
Fig. 4. Dependences of CO and NO, NOx concentrations on temperature in the combustion chamber (a),
and on oxygen concentration in the flue gas (b) for continuous fuel feeding and fuel mass stream of 3.0 kg/h
y = 277.27e-3E-04x R² = 0.0017 y = 616.15e-0.003x R² = 0.4491 y = 939.82e-0.02x R² = 0.4498 0 50 100 150 200 250 300 350 400 450 500 400 410 420 430 440 450 460 470 480 490 500
Temperature in a combustion chamber [C]
Po ll u tan t co n cen trat io n [m g /m 3] fo r 1 0 % O 2 NO [mg/m3] for 10% O 2 CO [mg/m3] for 10% O 2 NOx [mg/m3] for 10% O2 a) y = 17.76x2- 298.23x + 1467.4 R² = 0.444 y = -0.6149x2+ 21.936x + 70.631 R² = 0.8519 y = -0.9626x2+ 33.924x + 107.43 R² = 0.8523 0 50 100 150 200 250 300 350 400 450 500 5 6 7 8 9 10 11 12 Po ll u tan t co n cen trat io n [m g /m 3] fo r 1 0 % O 2 O2concentration [%] NOx[mg/m3] for 10% O2 CO [mg/m3] for 10% O 2 NO [mg/m3] for 10% O 2 b)
Fig. 5. Time dependences of pollutant concentrations and other parameters for 3 kg/h periodic fuel supply: operation time 20 s
CO concentrations measured during all tests were below 450 mg/m3 (Table 1). Although it would seem that CO concentrations for continuous fuel supply mode should be lower than those for periodic mode, it was quite the opposite for most cases (Table 1). The highest value of CO concentration was measured for 3 kg/h continuous supply, probably due to too low air stream. Combustion in all cases was performed at low temperatures, and during continuous feeding most probably the pellets had not enough time to be completely fired and CO concentration was relatively high. Table 1 and Fig. 2 show that the increase of stand-by period is not always accompanied by an increase of CO concentration. In order to decrease CO concentration, the air stream for com-bustion needs to be adjusted as well. However, CO concentration decreases upon in-creasing oxygen concentration to a certain minimum value, after which CO concen-tration starts to decrease (Figs. 4, 6, 8). Determining oxygen concenconcen-tration at which CO concentration is the lowest might be helpful in the case when an automatic air stream regulation oxygen probe downstream the boiler is installed. For the studied furnace with periodic fuel supply, it can be assumed that an increase of CO concen-tration above the minimum value is caused also by an important decrease in tempera-ture in the combustion chamber during the stand-by in pellet supply. Nitrogen oxide
(NO and NOx) concentrations depend mainly on the amount of nitrogen introduced
into the furnace. As coniferous wood presents higher nitrogen content than deciduous wood, these concentrations were significant and varied from 239 (NO) and 369 (NOx)
mg/m3 to 313 (NO) and 423 (NO
x) mg/m3. 1 10 100 1000 00 :0 0 00 :3 4 01 :0 8 01 :4 2 02 :1 6 02 :5 0 03 :2 4 03 :5 8 04 :3 2 05 :0 6 05 :4 0 06 :1 4 06 :4 8 07 :2 2 07 :5 6 08 :3 0 09 :0 4 09 :3 8 10 :1 2 10 :4 6 11 :2 0 11 :5 4 12 :2 8 13 :0 2 13 :3 6 14 :1 0 14 :4 4 15 :1 8 15 :5 2 16 :2 6 17 :0 0 17 :3 4 18 :0 8 18 :4 2 19 :1 6 19 :5 0 20 :2 4 20 :5 8 21 :3 2 22 :0 6 22 :4 0 23 :1 4 23 :4 8 24 :2 2 24 :5 6 25 :3 0 26 :0 4 26 :3 8 27 :1 2 27 :4 6 28 :2 0 28 :5 4 29 :2 8 NOx[mg/m3] (10% O2)
Flue gas temperature [°C]
Air axcess ratio O2 [%] G as con cen trat io n [m g /m 3] fo r 1 0 % O2 Time [mm:ss] CO [mg/m3] (10% O2) NO [mg/m3] (10% O2)
Fig. 6. Dependences of CO and NO, NOx concentrations on temperature
in the combustion chamber (a) and on oxygen concentration in the flue gas (b) for fuel mass stream 3.0 kg/h and periodic fuel supply: operation time 20 s, stand-by time 30 s
y = 4105.9e-0.006x R² = 0.2237 y = 886.51e-0.003x R² = 0.2812 y = 1490.1e-0.003x R² = 0.2975 0 50 100 150 200 250 300 350 400 450 500 425 430 435 440 445 450 455 460 465 470 Po ll u tan t co n cen trat io n [m g /m 3] fo r 1 0 % O 2
Temperature in combustion chamber [C]
NOx [mg/m3] for 10% O 2 NO [mg/m3] for 10% O 2 CO [mg/m3] for 10% O 2 a) y = 7.0028x2 - 98.034x + 559.8 R² = 0.7654 y = 166.23e0.0485x R² = 0.7394 y = 252.31e0.0509x R² = 0.7604 0 50 100 150 200 250 300 350 400 450 500 6 7 8 9 10 11 12 CO [mg/m3] for 10% O 2 NOx[mg/m3] for 10% O2 NO [mg/m3] for 10% O 2 Po ll u tan t co n cen trat io n [m g /m 3] fo r 1 0 % O2 O2concentration [%] b)
Fig. 7. Time dependences of pollutant concentrations and other parameters for 3 kg/h periodic fuel supply: operation time 60 s, stand-by time 90 s
A slight increase of NO and NOx concentrations was observed when oxygen
con-centration increased and a subtle decrease when temperature in the combustion chamber increased. This means probably that in the same time when temperature in combustion chamber increased combustion process was more intensive and oxygen concentration decreased. For all the cases presented in Table 1 for an almost-real life conditions, a rel-atively high boiler heat efficiency of above 80% was obtained. Throughout the course of the experiments, the presence of hydrocarbons in the flue gas was not detected, whereas soot was observed in the damper. This could mean that the combustion process was being partially hampered on the cool surfaces of the relatively small combustion chamber in spite of applying the Laddomat 21 mixing and pumping device. Dust con-centrations of 30–50 mg/m3 were much below the officially permitted values of 150 mg/m3 [2].
4. CONCLUSIONS
Applying periodic fuel supply instead of continuous feeding mode does not nec-essarily have to come with a radical increase in CO concentration. Actually, the study has shown that in most conditions it was quite the opposite and CO concentrations were lower for periodic fuel supply. Generally, in order to keep CO concentration levels low one has to carefully select appropriate settings: fuel mass stream and air stream for both fuel feeding modes and additionally stand-by/operation time ratio for periodic fuel supply.
1 10 100 1000 00:00 00:38 01:16 01:54 02:32 03:10 03:48 04:26 05:04 05:42 06:20 06:58 07:36 08:14 08:52 09:30 10:08 10:46 11:24 12:02 12:40 13:18 13:56 14:34 15:12 15:50 16:28 17:06 17:44 18:22 19:00 19:38 20:16 20:54 21:32 22:10 22:48 23:26 24:04 24:42 25:20 25:58 26:36 27:14 27:52 28:30 29:08 29:46 NOx[mg/m3] (10% O2)
Air axcess ratio [-]
Flue gas temperature [°C]
O2 [%] G as con cen trat io n [m g /m 3] fo r 1 0 % O 2 Time [mm:ss] NO [mg/m3] (10% O 2) CO [mg/m3] (10% O 2)
Fig. 8. Dependences of CO and NO, NOx concentrations on temperature in the combustion chamber (a)
and on oxygen concentration in the flue gas (b) for fuel mass stream 3.0 kg/h and periodic fuel supply: operation time 60 s, stand-by time 90 s
As boiler producers only indicate adequate settings for pure deciduous wood pellets, in the case of coniferous or mixed wood pellets or any other new kind of fuel these settings need to be determined experimentally for a specific boiler and furnace type.
y = 6851.8e-0.007x R² = 0.1512 y = 424.31e-1E-03x R² = 0.0299 y = 676.99e-0.001x R² = 0.0309 0 100 200 300 400 500 600 420 425 430 435 440 445 450 455 Po ll u tan t co n cen trat io n [m g /m 3] fo r 1 0 % O 2
Temperature in the combustion chamber [C]
NO [mg/m3] for 10% O2 NOx[mg/m3] for 10% O2 CO [mg/m3] for 10% O2 a) y = 16.648x2- 288.74x + 1527.5 R² = 0.7385 y = 184.28e0.0402x R² = 0.5488 y = 278.87e0.0431x R² = 0.585 0 100 200 300 400 500 600 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 NOx[mg/m3] (10% O2) Po ll u tan t co n cen trat io n [m g /m 3] fo r 1 0 % O 2 O2concentration [%] NO [mg/m3] for 10% O2 CO [mg/m3] for 10% O 2 b)
ACKNOWLEDGEMENTS
The author thanks the technical workers and students of Poznan University of Technology for their help during the research. This work was carried out as a part of the research project PB-13/615/08BW sponsored by Poznan University of Technology.
REFERENCES
[1] KNAUS H.,RICHTER S.,UNTERBERGER S.,SNELL U.,MAIER H.,HEIN K.R.G., On the application of
different turbulence models for the computation of flow and combustion process in small scale wood heaters, Exp. Therm. Fluid Sci., 2000, 21, 99.
[2] PN-EN 303-5:2004. Heating boilers. Part 5. Heating boilers for solid fuels, hand and automatically
stocked nominal heat output of up to 300 kW. Terminology, requirements and marking.
[3] FIEDLER F., The state od art of small-scale pellet-based heating systems and relevant regulations in
Sweden, Austria and Germany, Renew. Sust. Energ. Rev., 2004, 8, 201.
[4] OLSSON M.,KJALLSTRAND J., Low emissions from wood burning in an ecolabelled residential boiler, Atmos. Environ., 2006, 40, 1148.
[5] VERMA V.K.,BRAM S.,GAUTIER G.,DE RUYCK J.,Performance of a domestic pellet boiler as a func-tion of operefunc-tional loads. Part 2, Biomass Bioenerg., 2011, 35, 272.
[6] BOMAN C.,ESBJORN PETTERSSON S.,WESTERHOLM R.,BOSTROM D.,NORDIN A., Stove performance
and emission characteristic in residential wood log and pellet combustion. Part 1. Pellet stoves,
Energy Fuels, 2011, 25 (1), 307.
[7] FIEDLER F.,PERSSON T.,Carbon monoxide emission of combined pellet and solar heating system, Appl.
Energ., 2009, 86, 135, 2009.
[8] OLSSON M.,KJALLSTRAND J., Emission from burning of softwood pellets, Biomass Bioenerg., 2004, 27, 607.
[9] JOHANSSON L.S.,LECKNER B.,GUSTAVSSON L.,COOPER D.,TULLIAN C.,POTTER A.,Emission charac-teristic of modern and old-type residential boilers fired with wood logs and wood pellets,
Atmos. Environ., 2004, 38, 4183.
[10] KUBICA K., Energetic and ecological efficiency criterions of low heat output and solid fuel boilers
used in towns. Certificates established for criterions of ecologic security, Institute of Chemical Coal
Transformation, 1999 (in Polish).
[11] WERTHER J.,SAENGER M.,HARTGE E.U.,OGADA T.,SIAGI Z., Combustion of agricultural residues, Prog. Energ. Combust. Sci, 2006, 26, 1.
[12] POSKROBKO S.,ŁACH J.,KRÓL D., Experimental investigation of hydrogen chloride bonding with
cal-cium hydroxide in the furnace of a stoker-fired boiler, Energ. Fuel., 2010, 24, 948.
[13] POSKROBKO S.,ŁACH J.,KRÓL D., Experimental investigation of hydrogen chlorine bonding with
lime-stone and dolomite in the furnace of a stoker-fired boiler, Energ. Fuel., 2010, 24, 5851.
[14] POSKROBKO S.,ŁACH J.,KRÓL D.,Hydrogen chloride bonding with calcium hydroxide in combustion and two-stage combustion of fuels from waste, Energ. Fuel., 2012, 26, 842.
[15] Musialik-Piotrowska A., Kordylewski W., Ciołek J., Mościcki K., Characteristics of fair pollutants
emitted from biomass combustion in small retort boiler, Environ. Prot. Eng., 2010, 2, 123.
[16] MUSIALIK-PIOTROWSKA A.,KOLANEK C., Emission of volatile organic compounds from diesel engine
fuelled with oil-water emulsion, Environ. Prot. Eng., 2011, 1, 39.
[17] HARDY T.,MUSIALIK-PIOTROWSKA A.,CIOŁEK J.,MOŚCICKI K.,KORDYLEWSKI W.,Negative effects of biomass combustion and co-combustion in boilers, Environ. Prot. Eng., 2012, 1, 25.
