assessment of air pollution when incinerating

CHEMICAL AND PROCESS ENGINEERING 2010, 31, 163–179

VIOLETA ČEPANKO*1, PRANAS BALTRENAS1, KĘSTUTIS BUINEVIČIUS2

ASSESSMENT OF AIR POLLUTION WHEN INCINERATING FERMENTED WASTE WITH COMBUSTION GAS COMPONENTS Vilnius Gediminas Technical University, Department of Environmental Protection, Vilnius, Lithuania Kaunas University of Technology, Department of Thermal and Nuclear Energy, Kaunas, Lithuania Agriculture and industry facilities produce large quantities of waste, mainly biomass, which could be used to generate electricity. Promoting the use of such waste could reduce environmental pollution and caused adverse ecological effects. The problem of air pollution by incinerating fermented waste in solid fuel boilers with a fixed grate has been analysed. It was found that during incineration of some fermented waste, CO and NOx concentrations exceed limit values. The main cause of high NOx concentrations are large quantities of nitrogen in the burned wastes. The conversion factors of nitrogen to NOx emission has been estimated for the following types of waste: vegetable/fruit – 0.2247; poultry manure – 0.1433, pig manure – 0.0816, and grain residue – 0.0433. W rolnictwie oraz w obiektach przemysłowych gromadzi się duże ilości odpadów, głównie biomasy, która mogłyby zostać wykorzystana do produkcji energii elektrycznej. Wykorzystanie takich odpadów może zmniejszyć zanieczyszczenie środowiska oraz niekorzystne skutki ekologiczne. Badano zanieczyszczenie powietrza wskutek spalania sfermentowanych odpadów w kotłach na paliwa stałe o stałym ruszcie. Stwierdzono, że podczas spalania niektórych sfermentowanych odpadów stężenie CO i NOx przekracza wartości dopuszczalne, określone dla biopaliw oraz odpadów. Główną przyczyną dużego stężenia NOx są duże ilości azotu odpadach poddanych spalaniu. Czynnik konwersji azotu do emisji NOx oszacowano dla następujących rodzajów odpadów: owoce i warzywa – 0,2247, obornik kurzy – 0,1433, obornika trzody chlewnej – 0, 0816 oraz szlam z produkcji spirytusu – 0,0433.

1. INTRODUCTION Biomass refers to all non-fossil biological materials which are the direct or indirect products of photosynthesis. Chemical energy stored in biomass may be made available for power production through various processing routes, the optimum technological choice depending on the physical and chemical characteristics of the bio____________ *

Corresponding author, e-mail: [email protected]

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mass and economics of various production chains. A bioelectricity production chain starts with cultivation of the biomass fuel or its collection as residues or waste products from other operations. Fuel storage, transport and pre-treatment are usually significant logistical and cost components of production of bioelectricity. Generation of electricity from biomass may involve direct combustion of biomass at a thermal power plant or production of intermediate fuels which are then supplied to power plants. The biomass conversion routes may be classified as thermochemical, physiochemical or biological [1–3]. In addition to the environmental benefits of bioelectricity, power production from biomass provides a number of advantages when compared with other forms of production of renewable electricity and with fossil-based and nuclear power. Biomass, the energy carrier required at the beginning of a bioelectricity production chain, is available in the form of a very wide number of plant and plant-derived materials occurring all over the world. Technical, economic, social and environmental factors mean that certain types of biomass resources are currently most suitable for bioenergy production. Table 1 provides examples of the main types of biomass resources currently exploited [4–6]. Table 1. Examples of biomass resources [4] Category of biomass resource Residues from primary production of biomass By-products and wastes from a variety of processes Dedicated plantations

Examples wood from forestry thinning and felling residues, straw from a variety of cereal crops, other residues from food and industrial crops such as sugar cane, tea, coffee, rubber trees, etc. sawmill waste, manure, sewage sludge and organic fractions in municipal solid waste, used vegetable cooking oil short rotation forestry crops such as eucalyptus and willow, perennial annual crops such as miscanthus, arable crops such as rapeseed and sugarcane

Production of electricity from biomass can affect the environment in various ways, with potentially significant impacts that range in scope from local to global ones. Local impacts that must be managed include emissions of particulates and gases from conversion plants, solid waste (ash) disposal, increased demand for local water resources, noise, odour from some types of feedstock, physical intrusion and increased levels of traffic. On the other hand, some bioenergy production chains also present opportunities for improving local environments through reducing erosion and nutrient run-off from agricultural land, providing an effective disposal route for waste products and even increasing biodiversity. Today, the most important environmental benefit of production of bioelectricity results from its almost carbon neutral production cycle, which means that as an alternative to fossil fuel-based electricity, bioelectricity can reduce anthropogenic contributions to global warming [7–9].

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Because carbon dioxide emitted during conversion of biomass to electricity is matched by that sequestered during biomass growth, life-cycle CO2 emissions from bioelectricity are very low, with net emissions resulting from use of fossil fuels for cultivation, harvesting, transport, pre-treatment and processing of the biomass fuel. CO2 emissions from procurement of biomass fuels are also generally lower than those from procurement of fossil fuels [10]. Replacement of fossil fuel based electricity with bioelectricity therefore results in significant reductions in greenhouse gas emissions [11, 12]. The levels of emissions of other gases and particulates from biomass power plants depend on the fuel, conversion technology, plant operational characteristics and the use of emission reduction measures. NOx production from direct biomass combustion is strongly dependent on thermal formation of NOx, which involves nitrogen in the air, and emissions are therefore comparable to those of fossil fuel combustion. It must be noted that modern fossil fuel based power plants use very effective methods to ensure that NOx emissions are maintained below maximum acceptable levels [13–15]. With good planning, design and management of the entire bioelectricity production chain, it is usually possible to limit any negative environmental impacts to satisfactory levels [16]. Fuel nitrogen content has a significant impact on the NOx concentration in the combustion products. Fuel nitrogen conversion factor that shows how the fuel nitrogen is transferred to the nitrogen oxides is very much needed in predicting the NOx concentration of the new, non-traditional fuels [17]. Since large amounts of nitrogen may be accumulated in fermented waste, special studies should be carried out to determine the nitrogen conversion to NOx emission. In the present study, an analysis has been carried out of concentrations of gases, depending on the combustion gas temperature and oxygen concentration in exhaust gas, during combusting of fermented waste in a low-power boiler with grate furnaces and with an automatic feed of fuel flow.

2. EXPERIMENTAL Sampling. Samples of a substrate were taken from various tanks wherein poultry manure, swine manure, swine manure with food waste (the ratio of 1:1), and grain substrate were fermented. The organic waste was anaerobically degraded in bioreactors [18] connected into a joint system, the bioreactors being closed plastic tanks, of 220 dm3 capacity each, wherein anaerobic conditions are created. The tanks were filled up to 90% of their volume, and the remaining part was left for gas to accumulate. Each bio-reactor was fitted up with a mixing system, temperature and sampling place for pH determination. The substrate was mixed manually by rotating the mixer consisting of a shaft and blades allocated at two heights to improve substrate mixing. The body of a bioreactor was equipped with two hermetically sealed thermometers at

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two heights and placed inside holders to prevent the thermometers from being destroyed during mixing operation. Prior to the experiment, the waste substrate was prepared so as to contain 20 wt. % of a dry substance [18, 19]. Sample dehumidification under natural conditions. Samples of the fermented substrate were taken from various tanks of the bio-reactor wherein sewage sludge, fruit and vegetables, poultry manure, piggery slurry, grain and mixtures thereof made at various proportions were fermented. Dehumidification was performed in a drying chamber specially designed for this purpose. The substrate was spread over the mesh of the drying chamber. Drying under natural conditions lasted for 40 days. To speed up the process of dehumidification, the substrate was upturned every day [13, 19, 20]. The elementary analysis of fermented waste samples. The elementary composition of the fermented waste biomass (Fig. 1) was determined at the Institute of Chemistry of Vilnius University. The device EVO 50 XVP (Carl Zeiss SMT AG) with energy dispersion and X-ray spectrometers (Oxford, UK) was used during the experiments. The elementary compositions of the samples analysed were recalculated into the proportion of the dry mass (d. m.) [20–22].

Fig. 1. Scheme of sample incineration boiler with automatic fuel supply: 1 – fuel bunker, 2 – fuel screw, 3 – immovable grate, 4 – service door, 5 – window to watch fuel combustion process, 6 – gaseous pollutant sampling place

Evaluation of the calorific value of the fermented waste, the air amount required for combustion and the generating theoretical quantity of fume. Based on the results of previous research [17, 21, 23], the dependences to evaluate the theoretical quantities of t air and gas (Voro and Vdt ) ( necessary for combustion of the fermented waste have been derived: t Voro = 0.00026Q + 0.05954 m3 /kg

(1)


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Vdt = 0.00029Q + 0.04886 m3 /kg

(2)

where Q = Qzn is the lover calorific value [16, 17, 21] which may be determined from: Qzn = 348C n + 939 H n + 105S dn + 63 N n − 108O n − 25W

(3)

where Cn is the carbon content in fuel, Hn hydrogen content, S dn sulphur content, On oxygen content, Nn nitrogen content and W fuel moisture content. The values of these parameters determined for the fermented waste based only its calorific value (Eq. (3)) are presented in Table 2. Table 2. Thermal characteristics of fermented waste Waste Poultry manure Swine manure Swine manure/meat waste (at the ratio of 1:2) Grain

Sample 3 t 3 t Qz, kJ/kg Voro , m /kg Vd , m /kg No. 2 3

17 431 13 934

4.59 3.68

5.10 4.09

3a–3*

21 349

5.61

6.24

4

18 921

4.98

5.54

Sample incineration. Incineration was carried out at the Kaunas University of Technology (KTU) Laboratory of Combustion Processes, in a solid fuel burning boiler with helical fuel supply to the incinerator with immovable grate (Fig. 1). To obtain uniform combustion, the fermented waste from the fuel bunker was continuously supplied to the furnace, on oblique grate. To improve the combustibility of some substrates and maintain the process of combustion, substrates were mixed up at different proportions with wood granules.

Fig. 2. Elemental composition of wood granule (1) and fermented waste (poultry manure (2), swine manure (3), swine manure with meat waste at the ratio 1:2 (3a–3*), and grain substrate (4))

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The experimental incineration covered: wood granules (1), poultry manure with wood granules at the ratio of 1:2 (2c), swine manure (3a) with meat waste, the ratio 1:1 (3b), and wood granules at the ratio of 1:2 (3c), grain substrate (4) (Fig. 2). Combustion of gas. Fuel was combusted at a stable traction of 9–9.5 Pa in the incinerator and smooth air supply for combustion and by changing the frequency of fuel supply screw engine from 6 to 20 Hz. The concentrations of carbon monoxide and carbon dioxide, sulphur dioxide, nitrogen oxides and oxygen in fume as well as fume temperature in the measurement places of concentrations were determined experimentally with a mobile gas analyser [7, 23, 24]. Evaluation of conversion factor. To the evaluation, the conversion factor KN was t needed, the theoretical amount of combustion air Voro and the theoretical volume of t combustion products Vd , which can be calculated with Eqs. (1) and (2) and which depend on the fuel lower calorific value [17] KN =

[N] in the NO x emission × 100 [N] in fuel

(4)

where KN is nitrogen conversion factor in %. Statistical analysis. The performed test of repeated experiments shows that the average square error of measurements of concentrations of combustion gases in combustion products during waste incineration is not higher than 15%. The experimental results were processed statistically by using the software package Statistica and presented with the reliability of p = 0.95 [25]. 3. RESULTS AND DISCUSSION The samples of the fermented organic waste had dried nearly to a dry mass (with the maximum average water content of 10% in the samples) after 40 days of drying. A problem arouse, as NOx concentrations were very high due to the enormous initial concentration of nitrogen in substrates, exceeding nitrogen concentration in wood by 50 times and more. The highest contents of nitrogen were determined in the mixture of swine manure with meat waste (1:1) and the grain substrate reaching 9.80 and 4.38% of the dry mass, respectively (Fig. 2). The content of this element in other substrates was 2–3 times lower. The content of nitrogen in wood granules was considerably lower, reaching 0.1% of the dry mass. In addition, the fermented wastes were characteristic of considerably higher (3.84–18.95%) ash content compared to, for instance, that of wood granules (0.89 %) (Fig. 2) and this may influence the operation and depreciation of the incineration installation. When designing the incineration installation for the fermented waste with a big content of mineral incombustible materials, larger amounts of ash against wood burning should be taken into account.


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When evaluating the thermal characteristics of the dewatered fermented wastes (Table 1) it can be stated that incinerating this waste is beneficial [26, 27]. Knowing that the humidity of non-dewatered fermented waste varies in the range of 70–80% [18], the lower calorific value of such waste considerably decreases. For instance, the proposal is to incinerate the biomass or sewage sludge with the humidity of 50% in the boilers of a boiling layer but not in boilers with a grate [12]. The investigations of incinerating fermented waste together with wood granules were carried out in a wide range of excess air (in the fume of oxygen concentration). In order to determine the values of the optimum incineration parameters, air amount used for incineration was changed so as to obtain the change of [CO] values from high (reduced air quantity) to minimum ones [14, 23]. An instability in the composition of incineration products exists that is preconditioned by the sensitivity of a combustion mode. Due to a low capacity of the installation, even the slightest change in the burning fuel mass and fluctuation of the thickness of the fuel layer had an effect on the composition of incineration products. The higher the capacity (and sizes) of the incineration installation, the lower the influence of fluctuations in the amount of the burning fuel is. To eliminate variations of the compositions of the combustion products, the results of measurements were generalised by describing them using polynomial curves (Figs. 3–8).

Fig. 3. Dependences of fume composition and temperature on the oxygen content during wood granule burning

During burning of wood granules (Fig. 3), [O2] was changed from 12.3 to 15.6%. The minimum of [CO] was reached at [O2] of around 13.2%. However, the best conditions of fuel calcinations were determined when [O2] was between 14.1% and 14.3%. The fluctuations of concentration of nitric oxide were not significant, varying from

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264 to 322 mg/m3. The fact that no strong dependence of [NOx] on the oxygen concentration was determined shows that the thermal constituent of NOx is insignificant and NOx of fuel is prevailing. CO concentration increases upon increasing O2 concentration above 14.3%. Excess air cools the zone of incineration and CO concentration increases to the maximum value, i.e. 1128 ppm.

Fig. 4. Dependences of fume composition and temperature on the oxygen content upon incinerating poultry manure with wood granules (2c) at the ratio of 1:2

Fig. 5. Dependences of fume composition and temperature on the oxygen content upon incinerating swine manure (3a)


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During fermented poultry manure incineration, [O2] was changed from 13 to 18%. As is shown in Fig. 4, NOx concentration varied between 476 and 671 mg/m3. Like in the case of wood burning, no strong dependence, characteristic of the thermal NOx, on oxygen concentration was observed. In this case, NOx constituent of fuel prevails as well, whereas the average NOx level is higher by around 300 mg/m3 than in the case of incinerating wood granules. The lowest concentrations of CO in the interval of 642–673 ppm were achieved when O2 was in the range 13–14%. In the case of higher amounts of excess air in the fuel combustion zone, overcooling of the combustion process occurs and CO concentration reaches its highest value, i.e. 2 470 ppm. Swine manure combustion occurred at the oxygen concentrations of 18–20% (Fig. 5). This type of waste burnt slowly and heavily. This is also confirmed by a low temperature of combustion products. The increased amount of air was supplied for combustion in order the dynamic flow would also perform the function of ash removal from the combustion zone. Rather low concentrations of NOx obtained as a result cannot be considered typical ones, as no quality combustion occurred. However, incinerating pure swine manure in a heated furnace of a low capacity installation would be possible.

Fig. 6. Dependences of fume composition and temperature on the oxygen content upon incinerating swine manure with meat waste (3b) at the ratio of 1:1

Experiments of swine manure and meat waste mixture combustion (Fig. 6) were carried out by changing the concentration of oxygen between 16.8 and 19%. The concentration of NOx in this interval varied between 660 and 900 mg/m3, and the average concentration of NOx was ca. 470 mg/m3 higher than in the case of wood. Again, no essential dependence of NOx on the oxygen concentration was noticed, i.e. NOx of fuel obviously prevails. CO concentration increased with excess air increasing. [CO] varied from 430 to 900 ppm.

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Fig. 7. Dependences of fume composition and temperature on the oxygen content upon incinerating swine manure with wood granules (3c) at the ratio of 1:2

Variations in the component concentrations and temperature of the combustion gas of the swine manure with wood granules are presented in Fig. 7. In this case, the average NOx concentration is higher by ca. 240 mg/m3 compared to that of burning wood alone. A high leap in CO concentration, from 1058 to 3892 ppm, actually had no effect on NOx concentration. Such an effect would have been present if NOx was composed of thermal NOx. Thus, these experiments confirm the fact that NOx concentration during the tests was predetermined by the content of nitrogen in the material being incinerated.

Fig. 8. Dependences of fume composition and temperature on the oxygen content upon incinerating grain burning (4)


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Remarkable emission of nitrogen oxides was found during grain burning (Fig. 8), i.e. similarly as in the case of incinerating swine manure with meat waste. NOx concentrations changed from 751 to 1002 mg/m3. Due to a very fine fractional composition, burning of this type of waste was disordered. Upon fuel accessing the zone of combustion, volatile substances burn up quickly and the combustion of the remaining part of fuel is protracted [27, 28]. High instability of combustion was recorded at the concentration of O2 of around 18%. Atypical changes of NOx and CO concentrations were recorded as the concentrations of the both components were increasing and decreasing at the same time. This can be explained by the flashes of more rapid combustibility of fuel as the temperature of combustion products would also increase [7, 17]. The maximum temperatures of combustion products at the boiler outlet were achieved when burning wood granules and grain reached 177.7 °C and 147.8 °C, respectively. In other cases, temperatures were lower because of lower calorific value of the waste. It is common knowledge that the NOx concentration is predetermined by several factors, the major of which being the maximum flame, excess air and the content of nitrogen in fuel. In all the cases the critical influence is attributed to a considerably higher content of nitrogen compounds in the substrate of swine manure and meat waste (9.80%) compared to wood granules (0.10%). These comparative tests show that NOx concentration is predetermined by the presence of nitrogen compounds in waste [12, 13, 17, 20]. No strong dependence on the concentration of oxygen that is characteristic of thermal NOx was recorded. Figures 9–12 show CO and NOx concentrations in fume recalculated at the normative oxygen concentration of 6% and 11% with the aim to compare them with the normative concentrations for standard fuel and waste (Directive 2001/80/EB; Directive 2000/76/EB). Upon incinerating fermented waste, the concentrations of NOx and CO exceed the limit values set out in Directive 2001/80/EB on the limitation of emissions of certain pollutants into the air from large combustion plants and in Directive 2000/76/EB on the environmental requirements for waste incineration.

Fig. 9. NOx concentrations ([O2] = 6%) in combustion gas and the normative limit values

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Fig. 10. NOx concentrations ([O2] = 11%) in combustion gas and the normative limit values

Fig. 11. CO concentrations ([O2] = 6%) in combustion gas and the normative limit values

Fig. 12. CO concentrations ([O2] = 11%) in combustion gas and the normative limit values


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NOx generation during fuel combustion is greatly dependent on the content of nitrogen in the fuel itself [27, 29]. During the combustion of poultry and swine manure with wood granules, the minimum concentrations of nitrogen oxides (NOx min) were higher by 2.61 and 1.81 times, respectively, compared to those recorded during wood granule combustion. Comparing these values with the normative values applicable to biomass, the exceedances reached 1.8 and 1.2 times, while comparing with waste – 2.2 and 1.5 times. When the process of combustion becomes steady and under the optimum combustion conditions, the highest values of [NOx], [NOx maks] were determined when burning swine manure (3a) and swine manure with meat waste (3b), reaching 4214 and 2517 mg/m3, respectively, after recalculating [O2] = 6%. The average [NOx vid] values differed from the minimum NOx concentrations from 1.11 (for swine manure) to 2.36 (for grain) times. Comparison of [NOx min.] and [NOx vid.] concentrations with the permissible limit values, determined for the biomass pursuant to Directive 2001/80/EB, show that exceedances reached 1.2–6.5 times and 2.0–7.8 times, while pursuant to the environmental requirements for waste incineration these exceedances varied from 1.5 to 8.0 and from 2.5 to 9.7 times. During the combustion of substrates 3c, 3c and 4a CO concentrations varied in a wide range ([COvid.] in the range 730–4 687 mg/m3 at [O2] = 6%), i.e. carbon monoxide generation and burning were not uniform. In all the cases of combustion of substrates the concentrations of CO exceeded the permissible limit values determined for the biomass and waste according to Directive 2001/80/EB and the environmental requirements applicable to waste incineration (Directive 2000/76/EB). Comparison of COmin. concentrations and the permissible limit values determined for the biomass pursuant to Directive 2001/80/EB shows that exceedances varied in the range 1.5– 4.7 times, while in the case of applying the incineration norms, the exceedances would reach even 20.8 times (3a). The comparison of COmin. concentrations shows that the exceedances vary in the ranges 3.4–7.9 and 15.0–35.3 times, respectively. When burning wood granules, these requirements for biofuel were met with regard to both nitrogen oxides and carbon monoxide. With regard to waste incineration requirements, CO concentrations exceeded the limit values. When designing industrial incineration installations for the fermented waste, technological measures aimed at reducing NOx generation as well as selective noncatalytic treatment of combustion products have to be envisaged. One of the simplest methods is to incinerate fuel with a lower content of nitrogen, for instance wood waste, together with the fermented waste. This would allow reducing NOx concentrations to the required level. The concentration of CO in industrial installations should be lower due to higher temperatures of the flame than that recorded during the experiments. However, to improve the calcination rate of the gaseous combustible components and ensure the normative value of [CO], the technological measures of combustion also have to be

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provided for, e.g. to ensure a longer period of maintenance of the combustion products at high temperature. The ratio of fuel nitrogen conversion to NOx of fermented waste ranged from 0.0433 to around 0.242. KN values obtained experimentally and taken from literature [17] enabled prediction of the conversion factor (Fig. 13).

Fig. 13. Nitrogen conversion dependence on nitrogen content in fuels (0.095, 0.62, 1.05, 2.03, 4.26 – experimental values determined in the present work, 0.1, 0.4, 4.09, 7.5 – values taken from [17]

Analysis of the survey results showed that under totally different nitrogen sources and various types of fuel combustion, fuel nitrogen conversion to NOx can be roughly estimated by the equation (p = 0.05 and R2 = 0.8344): K N = 14.91N n ( −0.854)

(5)

Due to high statistical error (8.65%), estimated and real emissions of NOx obviously differ (from 7% to 40%). To avoid such large discrepancies, some corrections should be made (statistical error should be at least 2%). Applying Eq. (5), the conversion factors of nitrogen to NOx emission are: for vegetable/fruit waste – 0.2247; for poultry manure – 0.1433, for pig manure – 0.0816 and grain residue – 0.0433. Equation (5) is universal for many kinds of waste and independent of the temperature of combustion. The calculations of the conversion factor were based indirectly on the amount of oxygen used during combustion when α = 1.4, i.e. [O2] = 6%, and directly on the calculation of the theoretical value of the theoretical amount of combustion air (Vorot) and the theoretical volume of combustion products (Vdt).

4. SUMMARY The highest contents of nitrogen were in the substrates of swine manure and meat waste mixture (at the ratio of 1:1) and grain reaching 9.80 and 4.38% of the dry mass,


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respectively. In other substrates, the content of this element was 2–3 times lower. The content of nitrogen in wood granules was considerably lower compared to that in waste and accounted for 0.1% of the dry mass. The fermented waste was characteristic of considerably higher ash content (3.84–18.95%) compared to wood granules (0.89%), which may have an influence on the operation and depreciation of an incineration installation. This feature of the waste should be considered when designing incineration installations. Fuel humidity did not have a significant impact on the fuel combustion process as it varied within minor limits (1.31–2.54%). When the fermented waste was incinerated in a low capacity unit, the concentrations of CO and NOx in the products of combustion exceeded the limit values set out in Directive 2001/80/EB and Directive 2000/76/EB. Low concentrations of NOx are predetermined by a high content of nitrogen compounds in fermented waste. NOx concentration in the products of combustion is predetermined by fuel NOx. When designing industrial incineration installations for the fermented waste measures aimed at reducing NOx generation as well as selective non-catalytic treatment of combustion products have to be envisaged. To maintain the process of full fuel combustion, a certain proportion of the quantity of the incinerated fermented organic waste and wood has to be established for each type of the waste. This allows reducing of NOx concentration in the products of combustion. Due to higher temperatures of the flame, the concentrations of CO in industrial installations may be lower than those recorded in a low capacity unit. However, when designing industrial installations additional technological measures of combustion to improve CO calcinations must be envisaged. SYMBOLS n z

Q, Q

– lower calorific value, kJ/kg

V

– theoretical amount of combustion air, m3/kg

Vdt

– theoretical volume of combustion products, %

Cn Hn S dn

– carbon content in fuel, % – hydrogen content in fuel, % – sulphur content in fuel, %

On Nn W On KN

– – – – –

t oro

oxygen content in fuel, % nitrogen content in fuel, % fuel moisture content, % oxygen content in fuel, % conversion factor, % REFERENCES

[1] CARPENTIERI M., CORTI A., LOMBARDI L. En. Conv. Man., 2005, 46, 1790. [2] BALTRENAS P., VASAREVIČIUS S., MASILEVIČIUS R., PETRAITIS E., Atmosferos apsauga šilumineje energetikoje,Vilnius, Technika, 2003. [3] BALTRENAS P., ZAGORSKIS A. J. Env. Eng. Land. Man., 2008, 16, 113.

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[4] Biofuels in the European Union. A Vision for 2030 and Beyond. Final draft report of the Biofuels research Advisory Council, 14 March 2006. [5] PEHNT M., Ren. En., 2006, 31, 55. [6] WARNECKE R. Biomass Bioen., 2000, 18, 489. [7] GIMBUTAITE I., VENCKUS Z. J. Env. Eng. Land. Man.,, 2008, 16, 97. [8] Applied resesearch report. Analysis of bioenergy development prospects and tools necessary to ensure research and development of bioenergy coordination. Lithuanian University of Agriculture, 2007, p. 82 (in Lithuanian). [9] ŠTREIMIKIENE D., BUBELIENE J., Env. Res. Eng. and Manag., 2005, 2, 63 (in Lithuanian). [10] VRUBLIAUSKAS S., Consumption of solid biofuel in Lithuania and perspectives, Proc. 3rd Int. Sci. Conf., Rural Development 2007, 3, 318. [11] JANKAUSKAS V., Energetika, 2004, 4, 1. [12] KAVALIAUSKAS A., KATINAS V. Energetika, 2004, 3, 12. [13] THUNMAN H., LECKNER B. Fuel, 2001, 80, 473. [14] REVOLDAS V., DENAFAS G., Env. Res. Eng. and Manag., 2002, 1, 43 (in Lithuanian). [15] VRUBLIAUSKAS S., PEDIŠIUS N. Energetika, 2005, 1, 16. [16] Manual for Biofuel Users, Villu Vares (Ed.), Tallinn University of Technology, 2005, 56. [17] BUINEVIČIUS K., Agr. Eng., 2009, 41, 180 (in Lithuanian). [18] BALTRENAS P., KVASAUSKAS M., Ecology, 2007, 54, 57. [19] STRUSEVIČIUS Z.,Sewage, Waste and Manure Management in Agriculture, Vilainiai, 1996, p. 157 (in Lithuanian). [20] ČEPANKO V., BUINEVIČIUS K., PSZCZOŁA J., Investigation and Estimation of Exhaust Gas Emission from Fermentable Waste Combustion, Proc. 7th Int. Conf. Environmental Engineering, May 22–23, 2008, Vilnius, Vilnius Gediminas Technical university Press, 2008, 100. [21] DEMIRBAS A., Fuel, 1997, 76, 431. [22] RAVEENDRAN K., GANESH A., KHILAR K.C. Fuel, 1996, 75, 987. [23] BUINEVIČIUS K., PUIDA E., J. Env. Eng. Land. Man., 2005, 13, 91. [24] ČEPANKO V., BALTRENAS P., BUINEVIČIUS K., Environmental Dimensions of Fermented Waste Incineration, Proc. Conf. Thermal Energy and Technology, February 5–6, 2009, Kaunas, Kaunas University of Technology Press, 2009, p. 61 (in Lithuanian). [25] GASKA K., WANDRASZ A. J. Waste Man., 2008, 28, 973. [26] ECN, Phyllis, database for biomass and waste: Composition of a single material, 2007. [27] GORT R., On the Propagation of a Reaction Front in a Packed Bed, Thesis, University of Twente, 1995. [28] OWEN A., En. J., 2004, 25, 127. [29] WANDRASZ, A. J., PIKON K., Formed Fuels of Animal and Organic Origin, Proc. 26th Int. Conf. Incineration and Thermal Treatment Technologies, Phoenix, AZ, USA May, 2007, 14. OCENA ZANIECZYSZCZENIA POWIETRZA GAZAMI ODLOTOWYMI PODCZAS SPALANIA SFERMENTOWANYCH ODPADÓW Przedstawiono wyniki badania zanieczyszczenia powietrza wskutek spalania sfermentowanych odpadów w kotłach na paliwa stałe o stałym ruszcie. Stwierdzono, że najwięcej azotu zawierają mieszanina ze świńskiego obornika i odpadów mięsnych (w stosunku 1: 1) oraz odpady spirytusowe, gdzie zawartość azotu sięga 9,80 i 4,38 % suchej masy. W innych substratach zawartość N jest 2–3 razy mniejsza. Zawartość azotu w granulowanym drewnie była znacznie mniejsza w porównaniu do jego ilości w odpadach sfermentowanych i stanowiła zaledwie 0,1 % suchej masy. Dla sfermentowanych odpadów jest również charakterystyczne to, że zawartość popiołu jest znacznie większa (3,84–18,95 %) w porównaniu z granulowanym drewnem (0,89 %). Może to mieć wpływ na działanie i amortyzację instalacji do spalania odpa-


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dów, więc zawartość popiołu należy uwzględniać już w procesie projektowania. Ustalono, że wilgotność paliwa nie miała znacznego wpływu na proces jego spalania, ponieważ wahała się ona w niewielkich granicach, od 1,31 do 2,54%. Podczas spalania produktów fermentacji odpadów stężenie CO i NOx w produktach spalania przekraczała wartości dopuszczalne, określone w dyrektywach 2001/80/EB i 2000/76/EB. Ustalono, że stężenie NOx zależy od zawartości związków azotu w sfermentowanych odpadach. Podczas projektowania spalarni przemysłowych sfermentowanych odpadów należy przewidzieć środki mające na celu redukcję emisji NOx, jak również oczyszczanie gazów w sposób selektywnie katalityczny. Aby uzyskać wydajne i pełne spalanie paliw z odpadów po fermentacji, należy najpierw określić dla każdego rodzaju odpadów stosunek ich ilości do ilości drewna. Umożliwi to zmniejszenie stężenia NOx w produktach spalania. Podczas spalania sfermentowanych odpadów w instalacjach przemysłowych, gdzie osiąga się wyższą temperaturę płomienia oraz istnieje możliwość regulacji ilości doprowadzanego powietrza potrzebnego w procesie spalania, można uzyskać lepsze warunki spalania i zmniejszyć stężenia NOx w produktach spalania. Received 1 February 2009