Electronic Journal of Polish Agricultural Universities (EJPAU) founded by all Polish Agriculture Universities presents original papers and review articles relevant to all aspects of agricultural sciences. It is target for persons working both in science and industry,regulatory agencies or teaching in agricultural sector. Covered by IFIS Publishing (Food Science and Technology Abstracts), ELSEVIER Science - Food Science and Technology Program, CAS USA (Chemical Abstracts), CABI Publishing UK and ALPSP (Association of Learned and Professional Society Publisher - full membership). Presented in the Master List of Thomson ISI.
2011
Volume 14
Issue 2
Topic:
Environmental Development
ELECTRONIC
JOURNAL OF
POLISH
AGRICULTURAL
UNIVERSITIES
Stolarski M. , Szczukowski S. , Tworkowski J. , Klasa A. 2011. CHARACTERISTICS OF PELLETS MADE OF FOOD PROCESSING WASTES AND OF SHORT-ROTATION WILLOW BIOMASS, EJPAU 14(2), #04.
Available Online: http://www.ejpau.media.pl/volume14/issue2/art-04.html

CHARACTERISTICS OF PELLETS MADE OF FOOD PROCESSING WASTES AND OF SHORT-ROTATION WILLOW BIOMASS

Mariusz Stolarski1, Stefan Szczukowski1, Józef Tworkowski1, Andrzej Klasa2
1 Department of Plant Breeding and Seed Production, University of Warmia and Mazury in Olsztyn, Poland
2 Department of Agricultural Chemistry and Environmental Protection, University of Warmia and Mazury in Olsztyn, Poland

 

ABSTRACT

The subject of the studies was to determine some parameters of pellets produced from waste materials generated during production of the certified seed materials of barley, wheat, red fescue as well as mixed cereal grains wastes, produced from sunflower husk and from short-rotation willow biomass. As a control pellets produced using dry oak or pine woodchips were applied. The following parameters were taken into account: water content, ash content, calorific value and elemental composition (C, N, H and S). Pellets produced from mixed cereal wastes showed the highest moisture content while pellets from other studied wastes manifested moisture content close to oak woodchips pellets. Crude ash content in pellets produced from waste substances was several times higher than in woodchips pellets and considerably exceeded the standard value. Analyses of caloric and heating values showed that pellets from mixed cereal wastes had the lowest values of those parameters. Any of pellets produced from waste materials met demands of first class wood pellet given in German standard DIN 51731 for pellets heating value between 17.5 and 19.5 MJ·kg-1. Sulphur content in waste pellets was sometimes higher by factor of twenty than maximal value for first class pellets (amounting to 0.154% in sunflower husk pellets when allowable level is 0.08% S). Quality parameters of pellets made of short-rotation willow biomass were higher then determined in cereal wastes pellets because of its higher caloric values and lower ash, sulfur and nitrogen concentrations.

Key words: pellets, food processing wastes, willow biomass, quality parameters.

INTRODUCTION

Generation of energy from renewable resources in Poland in a total balance of energy consumption in 2004 amounted to 5.5% and increased to 5.9% in 2005. It was only half of average values for 25 state members of European Community (EU25). In the structure of renewable sources of energy in Poland solid biomass has a predominant position i.e. 91% whereas in EU25 countries this share was relatively lower and amounted to 51.3% (Fig. 1) [2].

Fig. 1. Structure of renewable energy in EU-25 and in Poland in 2005

Biomass for energy generation can be finally utilized in liquid, solid or gaseous form. Solid biomass can be gained from wood industry, agricultural residues, maintenance of green areas and in the smaller amounts from segregated fraction of municipal solid wastes. In the close future above mentioned sources will be supplemented by waste biomass from food processing sector as well by biomass from so called dedicated energy short-rotation plantations. Nowadays, the highest interest in application of the following species for energy generation is noted: willow which is a natural component of Polish vegetation as well as introduced species as Virginia mallow and Miscanthus [1,8,11,10]. According to the data published by the Agency for Restructuring and Modernisation of Agriculture (ARMA) the total area of short rotation willow plantations in Poland in 2006 was 6,700 ha.

An increase of share of renewable sources of energy (including solid biomass) in the total balance of energy consumption seems to be very important because of environmental reasons. Application of biomass for energy generation makes that CO2 maintains in a closed loop in the atmosphere contrary to CO2 from the fossil fuels. Ash which is generated in a relatively small amounts as by-product of biomass combustion can be directly applied as a soil amendment in short-rotation plantations. The other aspects of biomass application should also be taken into account and among them economical and social seem to be most important. The development of renewable sources of energy can be favored by law regulations which can stimulate interest in application of renewable fuels in general public opinion [3]. According to the Law Regulation of Polish Minister of Economy issued on 19th December 2005 the share of biomass which originate out of forestry sector including waste biomass from food processing sector and dedicated energy plantation should amount to not less than 5% and it has to reach the level of 60% in 2014 [6].

In the last years in Europe as well as in the United States market demands for improved biomass in the form of pellets have constantly increased [4]. In 2006 consumption of pellets in Europe amounted to 5 million of Mg what was higher by 2 million of Mg comparing with 2005. In Poland where production of pellets is a relatively new branch of economical activity the intense development of pellets production has been noted. In 2002 only several thousand Mg of pellets were produced in Poland, in 2003 ca. 20,000 Mg, in 2004 it was 120,000 Mg, in 2005 it amounted to 200,000 and in 2006 this production was equal to value of 280,000 Mg. The total potential of annual pellets production in Poland in 2006 was estimated to be 450,000 Mg [12]. This type of fuel contrary to the raw biomass posses stabile and fixed parameters what makes pellets easy to use and also very convenient for the end user. Presently pellets are produced from wood chips and saw dust as a waste material from wood processing industry. Taking into account rapid development of European market for pellets it should be noted that frequently there was a lack of waste wood raw materials and the other important factor should be mentioned that price of waste wood chips has been constantly growing. For example on Austrian market price of woodchips in two years time has increased from 4 to 15 Euros per 1 m3 what made an increase price of pellets from 160 to 260 Euros per 1 Mg [5]. The similar price level was noted in Sweden. In Poland price paid at the gate of pellet factory was ca. 160 Euros per 1 Mg. Under circumstances of lack of appropriate amount of waste raw material and high market price of pellets application of wastes from food processing sector might be very attractive [7,9].

Our studies were aimed at determination of water content, ash content, caloric value and elemental composition of pellets obtained from different raw materials.

METHODS

Our studies were based on analyses of pellets which were produced using wastes generated during production process of the certified seed materials of barley, wheat, red fescue and mixed cereal grains. These pellets were produced by Swedish company Skånefrö in the framework of BIOAGRO LIFE project (6 FP EU) [13]. Besides them pellets produced from sunflower husk and from short-rotation willow biomass were studied. As a control pellets fulfilling the highest market standards made from dry oak or pine woodchips were taken.

In the laboratory the moisture content values were determined using dryer method with the establishing of constant weight at 105°C. Then the dried material was milled using analytical mill using sieve at the mesh diameter of 0.25 mm. Then the samples were dried again and the next steps of analysis were performed. Ash content was established using muffle furnace at the temperature of 550°C.

Heating value was determined in the calorimeter using dynamics method. Basing into heating value, moisture content and ash content the calorific values of all studied pellets were determined. Contents of carbon, hydrogen and sulphur in biofuels were determined using automatic analyser CHS 500. Nitrogen content was determined using Kjeldahl's method after digestion with concentrated H2SO4.

Results were processed by Statistica® 8,0 PL. For all studied parameters average values were calculated and values of the least significant differences at p = 0.05 were determined using SNK significance test. The coefficient of simple correlations were also calculated.

RESULTS AND DISCUSSION

The average moisture content of all pellets under studies was at level of 9.48% (Fig. 2). The highest value was found in a sample of pellet produced from mixed wastes from cereal grains processing (12.43%). The similar value was found for sunflower husk pellets. The moisture content of other pellets samples was significantly lower and within the range 7.94 and 9.03%, for pellets made of oak woodchips and wastes of barley grain processing, respectively.

Fig. 2. Moisture (% of FM) and ash content (per cent of DM) of studied pellets

Ash content in studied biofuels amounted to 3.95% (Fig. 2) and significantly the lowest value was noted for oak woodchips pellets (0.42% of DM) whereas in pine woodchips its value was twice as high. In pellets from short-rotation willow biomass ash content amounted to 1.81%. In other samples of pellets ash content exceeded value of 2% DM. The relatively high content of ash was determined in pellets produced from mixed wastes of cereals grains and from red fescue seeds wastes and amounted to 9.96 and 9.32%, respectively.

For example in German standard DIN 51731 for first class wood pellets it is indicated that in pellets the highest ash content should not exceed 1.5%. In the light of this regulation only pellets from oak and pine woodchips met this standard. In our earlier studies also ash content in short-rotation willow biomass met demands of this standard [9,10].

Calorific value of sunflower husk pellet was the highest whereas for pellet produced from mixed cereals wastes the appeared to be the lowest, 20.09 and 17.88 MJ · kg-1 respectively (Fig. 3). When the heating value of pellets was considered, with taking into account ash and water content, the lowest heating value for pellets produced from mixed cereals wastes was found (13.80 MJ · kg-1). The significantly highest heating value were found for oak woodchips pellet and similar value was determined in pine woodchips pellet sample (17.89 MJ · kg-1). The heating value of pellet produced from short-rotation willow biomass and sunflower husk were slightly lower and amounted to 17.13 and 16.82 MJ · kg-1, respectively. The heating value of other pellets under studies ranged between 15.31 and 16.54 MJ · kg-1. Mentioned earlier German standard DIN 51731 indicates that heating value for pellets should be between 17.5 and 19.5 MJ · kg-1. It appears that similarly to other mentioned pellet parameter i.e. ash content pellets from woodchips met this demand. In our previous studies we have found almost the same values of this parameter [10]. Heating value of pellet produced from oak woodchips, pine woodchips, short-rotation willow biomass and sunflower husk amounted to 18.0, 17.7, 17.1 and 16.88 MJ · kg-1, respectively [9].

Fig. 3. Heating and calorific value of studied pellets (MJ kg-1)

Results of simple correlation coefficients analyses showed that pellets heating value was negatively and significantly correlated with moisture content (r = -0.54), ash content (r = -0.94), sulphur and nitrogen content (r = -0.75 and -0.68, respectively) and significantly and positively correlated with caloric value and carbon content (r = 0.88) (Table 1).

Table. 1. Values of coefficients of simple correlation between parameters of studied pellets

Specification

Heating value

Moisture content

Ash content

Calorific value

C

H

S

N

O

Heating value

1.00

               

Moisture content

-0.17

1.00

             

Ash content

*-0.77

*0.42

1.00

           

Calorific value

*0.88

*-0.54

*-0.94

1.00

         

C

*0.90

-0.27

*-0.81

*0.88

1.00

       

H

-0.34

*-0.45

-0.17

0.02

-0.34

1.00

     

S

*-0.55

*0.57

*0.69

*-0.75

*-0.73

0.10

1.00

   

N

*-0.69

0.23

*0.62

*-0.68

*-0.78

0.38

*0.68

1.00

 

O

*-0.54

-0.03

0.13

-0.33

*-0.68

*0.69

0.34

*0.42

1.00

* significant at p=0.05

Carbon content in studied biofuels on the average amounted to 48.73% (Fig. 4). Pellets produced from oak and pine woodchips contained 54.93 and 53.93% of C, respectively. Relatively high values of this parameter were determined in pellet from short-rotation willow biomass and sunflower husk (52.78 and 52.37%, respectively). In another studied pellet samples value of C content was within the range of 41.29 to 46.00% for pellet produced from different cereals and wheat, respectively.

Fig. 4. Carbon content in studied pellets (% of C in DM)

The highest hydrogen content was shown in wheat pellet 7.68% (Fig. 5). Values of this parameters varied significantly in another studied pellets and the lowest hydrogen content was in pellet produced from sunflower husk.

Fig. 5. Hydrogen content in studied pellets (% of H in DM)

The lowest sulphur concentrations in studied pellets were determined in oak and pine woodchips pellets and amounted to 0.011 and 0.016%, respectively (Fig. 6). Slightly and significantly higher value was determined in pellet from short-rotation willow biomass. Samples of another studied biofuels contained ten times more sulphur by comparison with oak woodchips pellet. The value of S content in other pellets under studies ranged between 0.107 and 0.154%, for pellets from barley and from mixed cereal wastes, respectively. For comparison with given above values it is worth to mention that according to German standard DIN 51731 sulphur content in pellet should not exceed 0.08%. In our earlier studies sulphur content in oak woodchip pellet showed higher value and it amounted to 0.040% [10].

Fig. 6. Sulphur content in studied pellets (% of S in DM)

Nitrogen content in studied biofuels on an average amounted to 1.26% (Fig. 7). The lowest value was found for oak woodchips pellet (0.17%) and the almost the same was determined in short-rotation willow biomass. In pine woodchip pellet relatively high content of nitrogen was detected (1.44%). In pellet produced from cereal wastes value of this parameter was also high and ranged from 1.56 to 2.17, for barley and mixed cereal wastes, respectively. According to German standard DIN 51731 threshold nitrogen content in pellets amounts to 0.03%.

Fig. 7. Nitrogen content in studied pellets (% of N in DM)

CONCLUSION

  1. Parameters of pellets produced from cereal wastes and wastes from food processing industry were differentiated but in general lower than for woodchips pellet.

  2. Generally the quality of pellet produced from short-rotation willow biomass was higher comparing with cereal wastes pellets because of its higher caloric values and lower ash, sulfur and nitrogen concentrations.

  3. Heating value of cereal wastes pellets was by 8 to 13% lower than pellets produced from woodchips.

  4. Ash content was the lowest in pellet produced from oak woodchips and the highest in pellet produced from mixed cereals wastes, 0.42 and 9.96%, respectively.

  5. Pellets produced from cereal wastes contained 4–6 times more sulphur than fuel produced from short-rotation willow biomass and 10–14 times more sulphur than pellet from oak woodchips.


REFERENCES

  1. Grzybek A., 2006. Zasoby krajowe biopaliw stałych i możliwości ich wykorzystania w aspekcie technicznym i organizacyjnym [National resources of solid bio-fuels and options of their utilization from the organization and technical aspects]. Energetyka, IX: 8–11 [in Polish].

  2. GUS, 2007. Energia ze źródeł odnawialnych w 2006 roku. Informacje i opracowania statystyczne [Statistical Yearbook. Energy from renewable resources in 2006]. Warszawa [in Polish].

  3. Kisiel R., Stolarski M., Szczukowski S., Tworkowski J., 2006. Biomasa pozyskiwana z gruntów rolniczych źródłem energii [Biomass obtained from arable lands as a source of energy]. Zagadnienia Ekonomiki Rolnej, 4, 90–101 [in Polish].

  4. Ljungblom L., 2006. Pellets hotter than ever. Bioenergy International. 23: 9.

  5. Rakos Ch., 2006. Pellet prices. Bioenergy International. 23: 11.

  6. Rozporządzenie Ministra Gospodarki z 19 grudnia 2005 roku w sprawie szczegółowego zakresu obowiązków uzyskania i przedstawienia do umorzenia świadectw pochodzenia, uiszczenia opłaty zastępczej oraz zakupu energii elektrycznej i ciepła wytworzonych w odnawialnych źródłach energii [Regulation of Minister of National Economy dated on 19th December 2005 concerning detailed range of duties of obtaining and presenting to discontinuance certificates of origin, payment of subsidies fees and buying of power and heat from Renewable Resources. Official Register 261, No 2187, Dz. U. nr 261, poz. 2187 [in Polish].

  7. Stolarski M., 2005. Pellets Production from Short Rotation Forestry. World Sustainable Energy Days, European Pellets Conference, 2–4.03.2005, Wels, Austria. – (Proceedings and materials on CD).

  8. Stolarski M., 2008. Willow Short Rotation Coppice. Central European Biomass Conference 2008, Graz (Austria) 16–19 January 2008: 58 (Proceedings and materials on CD).

  9. Stolarski M., Szczukowski S., 2007. Różnorodność surowców do produkcji pelet [Variability of stock materials for pellets production]. Czysta Energia, 6, 42–43 [in Polish].

  10. Stolarski M., Szczukowski S., Tworkowski J., Kwiatkowski J., Grzelczyk M., 2005. Charakterystyka zrębków oraz peletów (granulatów) z biomasy wierzby i ślazowca jako paliwa [Characteristics of woodchips and pellets from short-rotation willow biomass and Virginia mallow as fuels]. Problemy Inżynierii Rolniczej. 1(47), 13–22 [in Polish].

  11. Szczukowski S., Tworkowski J., Stolarski M., 2004. Wierzba energetyczna [Short-rotation willow as a dedicated energy crop]. Plantpress Kraków [in Polish].

  12. Wach E., 2007. Polski i europejski rynek pelet w 2006 r. [Polish and European pellets market] Czysta Energia, 6, 44–45 [in Polish].

  13. http://ww.bioagrolife.com/english/task7.asp#

 

Accepted for print: 18.02.2011


Mariusz Stolarski
Department of Plant Breeding and Seed Production,
University of Warmia and Mazury in Olsztyn, Poland
pl. Łódzki 3, 10-724 Olsztyn-Kortowo, Poland
email: mariusz.stolarski@uwm.edu.pl

Stefan Szczukowski
Department of Plant Breeding and Seed Production,
University of Warmia and Mazury in Olsztyn, Poland
pl. Łódzki 3, 10-724 Olsztyn-Kortowo, Poland
email: stefan.szczukowski@uwm.edu.pl

Józef Tworkowski
Department of Plant Breeding and Seed Production,
University of Warmia and Mazury in Olsztyn, Poland
pl. Łódzki 3, 10-724 Olsztyn-Kortowo, Poland
email: jozef.tworkowski@uwm.edu.pl

Andrzej Klasa
Department of Agricultural Chemistry and Environmental Protection,
University of Warmia and Mazury in Olsztyn, Poland
Oczapowskiego 8, 10-744 Olsztyn, Poland
email: aklasa@uwm.edu.pl

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