Agricultural Residues as Biomass Energy

Energy Sources, Part B, 2:123–140, 2007 Copyright © Taylor & Francis Group, LLC ISSN: 1556-7249 print/1556-7257 online DOI: 10.1080/15567240600629401

Agricultural Residues as Biomass Energy H. UNAL K. ALIBAS Department of Agricultural Machinery Faculty of Agriculture University of Uluda˘g Turkey Abstract An evaluation of the production of agricultural residues in Turkey and their conversion to electrical energy via gasification was realized. Agricultural residues were classified into two main categories. The residues in the category A were separated into two sub groups. The residues in the subgroup A1 generally consisted of straw, plant stems, and leaves while the subgroup A2 consisted of pruning residues of fruit trees. Nearly 43 mt/yr residues are produced in category A, or dry basis. As to the subcategories, 10.8 mt/yr residues are produced in the subcategory A1 on dry basis, since 28% of the residues in this category are not utilized; approximately 3.2 mt/yr residues are produced in the subcategory A2, since 80% of the pruning residues in this category are not utilized. The processed product residues in the category B were classified into three subcategories. The subcategory B1 comprises the residues in oil production (i.e., stone, shell), the subcategory B2 comprises the residues resulting from fruit processing (i.e., stalk, peel, stone), whereas the subcategory B3 consists of the residues such as peel, seed, and husk (in tomato and rice). The highest residue quantity in the subcategory B1 was in sunflower in the form of shell with 157.6 thousand tons, the highest residue quantity in B2 subcategory was in grape with 423.0 thousand tons (in the forms of stalk, peel, and stone); in subcategory B3, the highest residue quantity was in tomato (in the forms of peel and seed) with 134.0 thousand tons. Nearly 17% of the national electricity consumption can be met if all of the unused residues (15.3 mt/yr) are converted into energy. One may say that the regions Marmara, Mediterranean, Aegean, and Central South are the suitable regions for electricity, since these are the agricultural regions having the highest intensity of unusable agricultural residues (28.0–43.2 t/km2 ). Keywords agricultural residues, electric, gasification, quantity, regional distribution

1. Introduction Energy, one of the most important inputs of economical and social development, has been a priority of countries around the world since the early 1970s. The fact that fossil energy sources are limited and will be exhausted in a not-to-distant future revealed the necessity of evaluating alternative energy sources. Many countries are struggling to take advantage of new and renewable resources. The most commonly used renewable energy resource in developing countries is the biomass. Biomass is considered a strategic energy resource since it can be grown everywhere, it contributes to environmental protection, Address correspondence to Dr. Halil Unal, Department of Agricultural Machinery, Faculty of Agriculture, University of Uluda˘g, 16059 Bursa, Turkey. E-mail: [email protected]

123

124

H. Unal and K. Alibas

it can be used for generating electricity and chemicals, and is a source of fuel for motor vehicles. Therefore, biomass is of great importance both for developed and developing countries (Unal and Alibas, 2002). Available natural resources play a key role in the success of a thermochemical conversion system for obtaining energy. Natural resources may vary depending on a country’s geographical structure. Agricultural residues involved in the renewable energy resources form a notable potential for the development of bioenergy industry in many countries (nearly 250 mt/yr in Europe) (Blasi et al., 1997). These residues are directly related to the growing and picking of products having nutritional value (straw, stalks, plant leaves, pruning residues, etc.) or processing them industrially (olive stones, hazelnut shells, etc.) in general. When converting these residues, an energy burning method is often used, whereas pyrolysis and gasification methods are only used by researchers in laboratories or a demonstration scale. Nevertheless, destruction methods such as leaving these residues on the land or burning them on the land are being applied in some southern European countries, as well as in Turkey. The former of these two practices may lead to increase in the field traffic during the mixing of the residues of previously grown crops into the soil and growth of the parasitically pests exiting in the residues on the new crops, whereas the latter may cause undesirable and uncontrollable fire events. Although agricultural residues are extensively available in the agricultural regions of Turkey, the type and quantitative analysis of product residues cannot be done in many instances, except for a few analyses especially in some small areas. The estimation of residue types, their geographical distribution and energy contents is important with respect to evaluating the establishment of the facility and defining the residue quantity in a pilot-scale laboratory investigation before commercial applications. Thermochemical features such as density, moisture, and ash contents and ratio of volatile matters, all of which are dependent on the residue type, should be well known. These features of residues affect the conversion process. Hence, the models and operation characteristics of conversion units should be altered and adapted suitably (Blasi et al., 1997). In this study, the results of a comprehensive evaluation related to the type and current situation of agricultural residue that are produced in high quantities in Turkey are given to obtain energy from biomass via thermochemical conversion.

2. Annual Quantities of Agricultural Residues in Turkey Turkey’s economy is greatly dependent on agriculture, and 35% of its population live in rural areas (SIS, 2003). The majority of the crops grown consist of cereals, legumes, oil-seeds, vegetables, and fruits. Therefore, statistical analysis of the current situation of the residues of these crops should be estimated in obtaining energy. In this study, the agricultural residues were classified into two main categories. Category A consists of the agricultural residues obtained from the crops grown and collected for nutrition. This category comprises straw, stalks, plant leaves and stems, pruning residues, and other agricultural residues. Category B comprises the residues related to processing of some harvested crops in commercial plants by different means before being presented to consumers. Residues such as hazelnut shell obtained from hazelnut kernel production, olive stone in oil production, sunflower shell, etc. are in this category. The residues involved in Category A were separated into two groups: A1 and A2 subcategories according to their physical appearance (Table 1). Subcategory A1 (1st– 17th items) consists of wheat, barley, rye, oat, corn, and rice from the cereals group;

Agricultural Residues as Biomass Energy

125

Table 1 Actual agricultural residue yields of A category in Turkey (means of the years 1999–2002) and residue/product ratios of plants Residue types

Plant types A1 1. 2. 3. 4. 5. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.

Wheat Barley Rye Oat Corn Corn Rice Chickpea Dry bean Lentil Cotton Sunflower Soybean Tobacco Sugar beet Potato Cabbage Tomato

Pear tree Apple tree Plum tree Apricot tree Cherry tree Peach tree Sour cherry tree Lemon tree Orange tree Mandarin tree Pistachio tree Almond tree Hazelnut tree Fig tree Vineyarda Olive tree

Residue/ product ratio

t/ha Straw Straw Straw Straw Stalks Cobs Straw Stems and leaves Stems and leaves Stems and leaves Stalks Stalks and straw Stems and leaves Stems Leaves and collar Stems and leaves Foliage and stems Stems and leaves

A2 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33.

Residue yield

2.82 2.30 2.43 2.57 5.41 1.01 3.30 2.03 1.94 1.51 2.98 3.03 4.93 0.87 16.59 11.78 — —

1.36 1.06 1.45 1.36 1.29 0.24 0.94 2.27 1.45 1.67 2.33 2.06 1.70 1.05 0.40 0.45 2.50 0.30

kg/tree Pruning Pruning Pruning Pruning Pruning Pruning Pruning Pruning Pruning Pruning Pruning Pruning Pruning Pruning Pruning Pruning

a 32nd item residue yield (t/ha).

15.2 34.6 9.4 13.3 26.0 10.5 21.6 25.1 20.9 24.9 4.7 33.1 3.7 12.6 3.95 18.1

0.45 0.47 0.35 0.35 0.83 0.30 0.83 0.28 0.22 0.38 2.70 2.74 1.90 0.45 0.61 1.37

126

H. Unal and K. Alibas

chickpea, bean, and lentil (the total of green and red lentils) from the legumes group; tobacco, sugar beet, and cotton from the industrial crops; sunflower and soybean from the oil seeds group; potato from the tuber plants group; cabbage from the leafy crops group; and tomato from the fruit crops group. Residues in Subcategory A1 are generally straw, stalks, plant stems, and leaves. Subcategory A2 (18th–33rd items) consists of the pruning residues of fruit trees. This category mainly includes pear and apple trees from the pome-fruits group; plum, apricot, peach, sweet-cherry, sour-cherry, and olive trees from the stone-fruits group; pistachio, almond, and hazelnut trees from the nut-fruits group; vineyards and fig trees from the grape and small fruits group; and lemon, orange, and mandarin trees from the citrus fruits group. The residue yields of the crops given in Table 1 are the means of production values in the years 1999 and 2002, based on the data of Turkey’s State Institute of Statistics (SIS, 2004). Total residue values are given for the crops cabbage and tomato in the subsequent evaluations based on their annual production data, since the processed area figures are not defined for these crops. Moreover, since there was not sufficient information about the growing areas of fruit trees in SIS data, the pruning residue values related to these trees were taken as the pruning residue yield per fruit tree. The pruning area residue yield value was given for vines since the area size was determined for the vineyards in item 32. The ratios of residue/product given in Table 1 were determined either by direct measurements or from the Agricultural Technical Offices of the counties and provinces and from farmers. The results were confirmed by comparing with the data obtained from the literature (Blasi et al., 1997; EBN, 2003; Cuiping et al., 2004a; Hay, 1995; Schapaugh and Wilcox, 1980; Raveendran et al., 1995). Turkey is geographically separated into nine agricultural regions (Figure 1). One may see that there are notable differences between the residue yields belonging to the same plant species when the agricultural regions of Turkey are considered (Table 2). This situation may be dependent on the climatic conditions and the soil characteristics of the region, as well as the growing techniques (seed, fertilizers, irrigation, mechanization, etc.) applied by the farmers. The average of the years 1999–2002 related to the magnitudes of the areas on which the agricultural residues of Category A were obtained on the number of fruiting trees. Total production quantities on wet and dry basis and total unusable residue quantities are given in Table 3. Residues of cereal crops in Subcategory A1 comprise a portion of 60%. The product with the highest residue quantity on wet basis was the wheat, with

Figure 1. Geographical distribution of agricultural regions in Turkey.

Agricultural Residues as Biomass Energy

127

26.5 million tons, while soybean was the crop with the lowest residue quantity with 100.1 thousand tons. The highest residue quantity on dry basis was again in wheat straw, while the lowest product residue was determined in tobacco with 29.2 thousand tons. Although the plantation area of tobacco crop was elevenfold higher than that of soybean, it lowered the quantity of residue on dry basis, since it was the residue with the highest moisture content at the time of harvest. Nearly 90% of 43.2 mt/yr total residue on dry basis consists of Subcategory A1. The highest residue quantities in Subcategory A2 on dry basis belonged to the pruning residues in the vineyards and olive orchards, with 1.69 and 1.65 thousand tons, respectively. As to the residue quantity in Subcategory A2, the highest quantity of pruning residues was obtained from olive trees, and the lowest from sour-cherry trees, with 988.3 and 23.7 thousand tons, respectively. In total, 43.05 mt/yr of residues were obtained from subcategories A1 and A2 on dry basis, and 90% of this quantity is involved in Subcategory A1. Residues with the highest percentage of use in Subcategory A1 were the cereal straws with 85% in Turkey, especially that cereal straw form the basis of animal feed resources and are used in high rates. Straw is also used as animal litter, paper and packaging material, mat, etc. Within the past 20–30 years, developed European countries have abandoned using cereal straws as animal feed (Alibas and Unal, 1995). Utilization of product residues, especially cereals which form the main feeding source for generating energy, will be of great importance. The utilization percentage of the other product residues in subcategories A1 and A2 is about 25% on average, and a majority of this is used for heating, cooking, etc. requirements of the grower. The remaining 75% is either burnt in the field or left on it as organic fertilizer. Basically, 33% of the Category A residues on average is not utilized, and its numerical value is nearly 14.0 mt/yr. As illustrated in Table 3, omission of only the product residues such as wheat and barley, especially from the animal feed ration, will make it more attractive for conversion into energy. This will at least double the annual unusable residue quantity. Twenty years of data (1983–2002) are shown in Figure 2 for the unused quantities of agricultural residues that were obtained from the products grown and collected in

Figure 2. Total quantities of the unused agricultural residues obtained from the products grown and collected in the A category (between the years 1983–2002).

128

1. 2. 3. 4. 5. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.

Wheat Barley Rye Oat Corn Corn cob Rice Chickpea Dry bean Lentil Cotton Sunflower Soybean Tobacco Sugar beet Potato Cabbage Tomato

A1

Plant types

2.69 2.46 2.84 2.43 4.91 0.91 3.64 2.01 1.73 1.46 — 2.08 — 0.74 16.96 10.77 — —

1

3.42 2.62 2.72 2.63 5.10 0.95 3.86 2.10 1.97 1.51 3.00 2.94 5.01 0.81 16.48 12.47 — —

2

4.11 3.46 2.74 3.26 7.50 1.40 3.21 2.58 2.16 1.96 0.84 3.25 3.25 1.31 21.42 8.62 — —

3

3.79 2.36 2.29 3.25 7.99 1.49 2.19 1.73 2.48 1.56 3.00 3.70 5.08 0.95 17.47 11.06 — —

4

1.64 1.50 2.16 4.96 2.37 0.37 1.52 2.63 1.77 1.63 1.83 2.87 5.74 1.09 12.94 7.94 — —

t/ha

5

2.30 2.03 2.06 2.47 5.87 1.09 2.37 2.16 1.89 1.57 3.02 1.71 3.95 1.47 11.36 8.45 — —

6

Residue yields of regions

2.63 2.05 2.08 2.03 2.81 0.52 3.19 2.21 1.00 1.87 — 3.46 4.36 0.86 14.23 6.76 — —

7

2.40 2.32 2.08 2.18 3.98 0.74 3.13 2.38 2.07 1.66 2.68 3.88 4.43 0.91 15.15 9.29 — —

8

Table 2 Yields values of A-category agricultural residues in Turkey with respect to the agricultural regions (means of the years 1999–2002)

(continued)

2.47 2.34 2.41 1.98 3.30 0.61 — 2.00 2.37 1.35 — 2.52 2.46 — 18.23 15.21 — —

9

129

Pear tree Apple tree Plum tree Apricot tree Cherry tree Peach tree Sour cherry tree Lemon tree Orange tree Mandarin tree Pistachio tree Almond tree Hazelnut tree Fig tree Vineyarda Olive tree

15.2 20.3 8.3 27.4 8.9 7.2 8.2 — — — 8.7 32.1 4.1 8.0 2.37 13.6

1

a 32nd item residue yield (t/ha).

18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33.

A2

Plant types

10.4 66.6 9.1 27.4 9.8 10.6 9.7 14.3 10.7 15.6 4.1 26.8 8.0 12.1 6.28 17.1

2

20.1 22.9 11.0 17.3 9.8 10.7 6.9 — — — 28.2 20.7 5.2 18.3 4.86 14.7

3

23.4 34.3 10.4 35.0 9.6 11.6 7.1 27.6 23.9 33.3 5.2 51.9 22.8 13.4 3.24 27.0

4

15.2 20.3 8.8 41.0 10.1 8.7 7.7 2.1 4.7 8.9 4.4 12.2 4.4 6.8 4.51 13.6

kg/tree

5

10.5 15.8 7.0 14.4 4.6 4.9 5.0 — — — 5.1 28.1 6.8 7.1 3.15 11.3

6

Residue yields of regions

Table 2 (Continued)

12.5 13.2 7.0 16.8 8.4 10.5 6.7 1.6 4.5 6.5 7.1 29.3 3.4 11.3 5.05 11.3

7

12.6 23.9 12.9 33.3 18.9 10.1 9.1 — — — 2.0 38.3 3.4 8.7 2.13 10.0

8

15.7 34.0 11.0 23.3 16.5 8.0 12.1 — — — 12.7 36.9 — 10.2 2.83 48.4

9

130

1. 2. 3. 4. 5. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.

Wheat Barley Rye Oat Corn Corn cob Rice Chickpea Dry bean Lentil Cotton Sunflower Soybean Tobacco Sugar beet Potato Cabbage Tomato

A1

Plant types

9,357.5 3,629.8 144.4 153.2 530.8 530.8 60.5 641.5 176.3 488.0 695.8 549.3 20.4 220.5 391.0 205.7 — —

Cultivated area— fruit bearing trees

26,350.0 8,347.5 350.9 394.1 2,869.6 533.9 198.8 1,301.3 341.5 759.0 2,071.7 1,673.8 100.1 194.6 6,507.9 2,426.6 1,545.6 2,679.1

Residue quantity (wet basis), ×1,000 t

15 15 15 15 60 50 25 15 15 15 45 40 50 85 80 60 85 85

×1,000 ha

Residue moisture, %

22,397.5 7,095.4 298.3 335.0 1,147.8 266.9 149.1 1,106.1 290.3 645.2 1,144.9 1,004.3 50.0 29.2 1,301.6 970.7 231.8 401.9

Residue quantity (dry basis), ×1,000 t

85 85 85 85 85 40 40 10 10 10 40 40 0 0 50 5 5 5

Used ratio, %

Table 3 Total production quantities of the agricultural residues obtained from the A category products in Turkey (average of the years between 1999–2002)

(continued)

3,359.6 1,064.3 44.7 50.2 688.7 160.2 89.5 995.5 261.2 580.6 687.0 602.6 50.0 29.2 650.8 922.1 220.3 381.8

Unused residue quantity, ×1,000 t

131

Pear tree Apple tree Plum tree Apricot tree Cherry tree Peach tree Sour cherry tree Lemon tree Orange tree Mandarin tree Pistachio tree Almond tree Hazelnut tree Fig tree Vineyarda Olive tree

10,682.5 32,482.5 7,348.8 10,791.3 7,517.5 12,502.5 4,292.5 5,363.8 11,681.3 8,437.5 25,981.3 3,573.8 284,142.5 8,980.0 531.3 89,507.5

a 32nd item cultivated area (×1,000 ha).

18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33.

162.1 1,122.1 69.1 342.4 82.3 130.9 39.5 131.6 241.5 201.4 112.5 118.5 1,058.3 112.5 1,693.0 1,647.3

40 40 40 40 40 40 40 40 40 40 40 40 40 40 50 40

×1,000 trees 97.3 673.3 41.5 205.4 49.3 78.5 23.7 79.0 144.9 120.8 67.5 71.1 634.9 67.5 846.5 988.4

Residue quantity (dry basis), ×1,000 t

A2

Residue moisture, % ×1,000 ha

Residue quantity (wet basis), ×1,000 t

A1

Plant types

Cultivated area— fruit bearing trees

Table 3 (Continued)

20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 50

Used ratio, %

77.8 538.6 33.2 164.3 39.5 62.8 18.9 63.2 115.9 96.7 54.0 56.9 507.9 54.0 846.0 494.2

Unused residue quantity, ×1,000 t

132

H. Unal and K. Alibas

Category A in Turkey (SIS, 2002; SIS, 2004). The pruning residues in Subcategory A2 have not exhibited a significant change in the course of 20 years, whereas there were fluctuations in Subcategory A1, although a linear increase was observed. It is estimated that regional climatic conditions and the supply-demand quantities in some products caused this fluctuation. Moreover, there have been no changes in the plantation areas and yields of some products that are the basic nutrient materials such as wheat, barley, oats, rice, corn, sunflower, and cotton within the last 10–15 years. Even the reverse has been observed in some crops, leading to reductions in the residue quantities. Means of the years between 1999 and 2002 for the quantities of residues obtained from the products grown and collecting in Category A, in the nine agricultural regions of Turkey, are given in Figure 3 (SIS, 2004). As seen in this figure, the richest areas for the residues in Subcategory A1 were the Central South, Central North, and Mediterranean regions, whereas the richest areas for the residues in Subcategory A2 were the Aegean, Mediterranean, and Black Sea regions. More detailed information for the product residues in A1 and A2 are given in Table 4. The quantities of residues resulting from the processing of some agricultural residues in agricultural industry plants are classified in Category B, and mean of the years between 1999 and 2002 related to these quantities are shown in Table 5. Since the product residues in Category B require different processing technologies, determining the size of processing facilities and their locations and evaluating their geographical distribution and quantities are more complicated tasks. The processing of agricultural products is largely realized in the facilities located in the harvested sites. Processed product residues in Category B were divided into three subcategories. Subcategory B1 consisted of olive, sunflower, and soybean residues in oil production; Subcategory B2 consisted of the residues of nuts (hazelnut, walnut, etc.), stone fruits (plum, apricot), and grapes in fruit processing; and Subcategory B3 consisted of tomato and rice residues. The product types involved in Category B, their processing percentages, residue types, residue ratios, and total residue quantities are given in Table 5. Yearly production data of the products were provided from DIE (SIS, 2002; SIS, 2003;

Figure 3. Quantities of the unused residues obtained from the products grown and collecting in A category in the agricultural regions of Turkey (on dry basis) (means of the years between 1999–2002).

Agricultural Residues as Biomass Energy

133

Table 4 The highest quantities of unused agricultural residues provided from the products grown and collected in the category A in relation to the agricultural regions of Turkey (means of the years between 1999–2002) Plant types

The most yields regions of Turkey, ×1000 t A1

1. Wheat 2. 3. 4. 5. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.

Barley Rye Oat Corn Corn cob Rice Chickpea Dry bean Lentil Cotton Sunflower Soybean Tobacco Sugar beet Potato Cabbage Tomato

Central North (678.0), Mediterranean (531.9), Central South (516.9) Central North (298.7), Central South (283.0), South East (154.6) Central South (25.3), Central North (7.5), Central East (3.1) Marmara (17.4), Central South (9.9), Central North (5.8) Mediterranean (300.1), Marmara (150.8), Black Sea (135.2) Mediterranean (69.8), Marmara (35.1), Black Sea (31.4) Marmara (40.4), Black Sea (17.2), Aegean (14.3) Central North (283.6), Central South (187.1), Aegean (151.5) Central South (84.4), Mediterranean (35.8), Central North (31.6) South East (419.2), Central North (55.8), Mediterranean (46.3) South East (285.4), Aegean (226.0), Mediterranean (162.1) Marmara (423.4), Aegean (56.7), Central North (51.3) Mediterranean (42.0), Black Sea (7.3), Central East (0.7) Aegean (16.7), Central East (3.4), Black Sea (3.3) Central South (241.6), Central North (149.7), Central East (76.7) Central South (499.6), Central North (94.0), Aegean (91.9) Black Sea (55.3), Aegean (43.9), Marmara (39.9) Aegean (122.0), Mediterranean (106.0), Marmara (60.9) A2

18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 32.

Pear tree Apple tree Plum tree Apricot tree Cherry tree Peach tree Sour cherry tree Lemon tree Orange tree Mandarin tree Pistachio tree Almond tree Hazelnut tree Fig tree Vineyard Olive tree

Marmara (18.9), Central North (11.6), Aegean (10.2) Aegean (181.8), Mediterranean (62.7), Central North (32.3) Mediterranean (6.7), Aegean (5.9), Marmara (5.0) Central East (102.8), Mediterranean (26.1), Central South (11.6) Aegean (12.5), Central South (6.7), Marmara (5.4) Aegean (20.7), Marmara (18.5), Mediterranean (13.0) Central South (6.7), Central North (6.1), Central East (2.0) Mediterranean (103.5), Aegean (5.2), Black Sea (0.02) Mediterranean (182.9), Aegean (13.0), Black Sea (0.2) Mediterranean (128.0), Aegean (44.4), Black Sea (1.3) Mediterranean (25.0), South East (21.2), Aegean (3.3) Aegean (20.6), Mediterranean (13.2), Central South (7.1) Black Sea (349.6), Marmara (98.1), Central North (54.4) Aegean (43.7), Mediterranean (4.9), Marmara (2.5) Aegean (388.7), Mediterranean (134.2), Central South (108.8) Aegean (340.9), Mediterranean (106.8), Marmara (42.4)

134

846.3 846.3 788.1 58.9 45.0 14.8 43.3 556.3 35.4 417.8 1,719.0 1,031.3 103.1 2,679.1 211.5

70 70 97 100 100 30 100 100 30 30 (70) 37 30 3 30 100

Product quantity, ×1000 t

a Total of plum, apricot, cherry, peach, and sour cherry fruits residues.

B1: Oil production Olive Olive Sunflower Soybeans B2: Fruit process Pistachio Chestnut Almond Hazelnut Walnuts Stone fruita Grape Raisin Raisin juice concentrate, vinegar, grape juice, sausage etc. Wine B3: Others Tomato Rice

Product type

Processed ratio, %

Peels and seeds Husks

Peel, stones and stalks

Grape stalks Peel, stones and stalks

Shells Shells Shells Shells Shells Stones

Stones Peels Shells Integument

Residue type

134.0 42.3

30.9

16.5 + 7.0 + 6.5 (30.0) 5.0 20.0

82.7 309.4

27.0 1.9 21.7 294.8 22.0 71.0

104.9 127.8 157.6 7.4

Total residue, ×1000 t

6.5 16.5 + 7.0 + 6.5 (30.0)

60.0 13.0 50.0 53.0 62.0 17.0

12.4 15.1 20.0 12.5

Residue ratio, %

Table 5 Total residue quantities regarding the processed agricultural products in Turkey (means of the years 1999 and 2002)

Agricultural Residues as Biomass Energy

135

SIS, 2004). The processing percentages of the products were given in the direction of information obtained from the industrial plants processing the products in question. The types and residue ratios of the processed products were determined by the information obtained from the processing facilities as well as by direct measurement in some products, and confirmed by comparing with the references (Blasi et al., 1997; EBN, 2003). The highest residue quantity in Subcategory B1 was obtained in sunflower with 157.6 thousand tons as shells, while the highest residue quantity in Subcategory B2 was obtained in grapes with 423.0 thousand tons. This residue quantity is rather low when compared especially with France and Italy, since the wine production in Turkey is about 3% (FAO, 2002). Nevertheless, since Turkey is one of a few countries producing raisins, there are large quantities of stalk residues. Moreover, processing plants that produce raisin juice concentrate, grape juice sausage, etc. from grapes are widespread. Stalk, peel, and stones are the major residues of processed grapes. The highest residue quantity in grapes was 309.4 thousand tons in the processing section of 30%. Subcategory B3 consists of seeds and peels remained after tomato paste, ketchup, etc. production from tomatoes and husk residues of rice. Here, the highest quantity of residues was obtained from tomatoes with 134.0 thousand tons. It was not possible to determine the net unused ratios of the product residues in Category B, since the processing plants utilize a part or all of the residues of products such as olive, sunflower, nut fruits, and rice for meeting their fuel demands. Also, some plants either sell the residues for commercial purposes or do not use and discard them. Therefore, the probability of utilizing all the residue quantity in Category B for generating energy was taken into consideration. The total quantities of the residues obtained by the processing of agricultural products in Category B grown in Turkey are given in Figure 4, with a linear prediction up to year 2010. Subcategories B2 and B3 showed a linear increase in relation to years, whereas Subcategory B1 showed fluctuations. This may be due to the yearly changes in olive yield owing to the climatic conditions. The distribution of total quantities of processed product residues in Category B into the agricultural regions in Turkey are given in Figure 5. The agricultural regions richest by the product residues in Subcategory B1 were the Aegean, Marmara, and Mediterranean regions; for Subcategory B2, the Aegean, Black Sea, and Mediterranean regions; and for Subcategory B3, the Aegean, Mediterranean, and Marmara regions. The Aegean region

Figure 4. Total quantities of the residues regarding the processing of agricultural products (category B) in Turkey between the years 1983 and 2002.

136

H. Unal and K. Alibas

Figure 5. Total quantity of category B agricultural residues in Turkey regarding the agricultural regions (means of 1999–2002).

is a leading region in Turkey for the production of olive, grape, and tomato in the subcategories of B1, B2, and B3, respectively. For this reason, it is an agricultural region in which there are many industrial plants processing these products. The Northeast agricultural region is processing the lowest quantities of agricultural products and hence agricultural residues, since it is a region with the most severe climatic conditions and the highest altitude in Turkey. Although the total and regional production quantities of agricultural residues are shown in graphics, other information related to distribution of these residues regarding the surface areas of regions may be required. Intensity of residues can be defined at different levels (national, regional, provincial, etc.). Total unused residue density in Turkey exhibited a distribution of 21.3 t/km2 on a national basis (Figure 6). One may see in

Figure 6. Regional intensity of A and B category agricultural residues in Turkey (means of the years 1999–2002).

Agricultural Residues as Biomass Energy

137

the figure that the regions of Marmara, Mediterranean, Aegean, and Central South are convenient areas for the thermochemical conversion of agricultural residues with a surface density of 28.0–43.2 t/km2 .

3. Energy Equivalent of Agricultural Residues The energy value of a biomass can generally be determined through the empirical equation of its higher heating value (HHV), which can be confirmed by its moisture content. When the carbon contents of different firewood types are compared, they give similar heat values. Nevertheless, variations may be observed since the agricultural residues and other types of biomass have higher ash contents. Ultimate analyses of agricultural residues were taken from references in Table 6, and the higher heating values were calculated with the equation below given by Channiwala (Gaur and Reed, 1998). HHV = 0.3491C + 1.1783H − 0.1034O − 0.0211A + 0.1055S − 0.0151N

(1) [MJ/kg]

Table 6 Average higher heating values of the agricultural residues, in relation to the categories Residue category

Higher heating values (moisture-free basis), MJ/kg

A1

17.1

A2

18.5

B1

20.1

B2

20.7

B3

19.7

References (EBN, 2003; Raveendran et al., 1995; Öhman, 1997; Livingston, 1991; Illerup and Rathmann, 1996; Kitani and Hall, 1989; Gaur and Reed, 1995; Demirbas, 1997; Taner et al., 2004; Werther et al., 2000; Ebeling and Jenkins, 1985; ECN, 2004; Annamalai et al., 1987; Jenkins and Sumner, 1986) (EBN, 2003; Raveendran et al., 1995; Parikh et al., 2005) (Demirbas, 1997; Jenkins and Sumner, 1986; Koukis et al., 1999; Cattane et al., 2002; Miles et al., 1995; Arvelakis et al., 1999; Arvelakis et al., 2000) (Raveendran et al., 1995; Gaur et al., 1998; Kitani and Hall, 1989; ECN, 2004; Jenkins and Sumner, 1986; Miles et al., 1995; Antal et al., 2000; Demirbas, 2002; Razvigorova et al., 1993; Petrov et al., 1999; Mason et al., 1985; Sumner et al., 1983; Cuiping et al., 2004b) (Gaur and Reed, 1998; Kitani and Hall, 1989; Kumar et al., 1987)

138

H. Unal and K. Alibas

Here, carbon (C), hydrogen (H), oxygen (O), ash (A), sulphur (S), and nitrogen (N) are the percentage weight ratios of these elements in the ultimate analyses of the fuel. This equation is better than the Dulong, Tilmann, IGT, or Graboski equations at relating the HHV to the ultimate analysis, giving an average absolute error of prediction of 1.45%. Since the ultimate analysis values of some agricultural residues could not be determined, HHV values were directly taken form the references. Energy contents of agricultural residues in categories A and B were calculated, and the means of higher heating values according to subcategories are given in Table 6. The higher heating values and residue quantities are only two basic evaluations that should be confirmed process (ηc ). The conversion productivity of the heat energy for electrical power (ηe ) should also be considered, if not related to heat energy. The conversion yields for obtaining electric power via gasification were given as ηc = 0.7 and ηe = 0.3. The electric power of the agricultural residues in the A and B categories were determined according to the following equation (Blasi et al., 1997).  Qe = 



i=1,2





MAi .HHVi  + 



 MBj .HHVj  .ηc .ηe

[MJ]

(2)

j =1,3

Here, MAi and MBj are the residue quantities in the subcategories Ai and Bj , respectively. Figure 7 gives a comparison of the electricity power that can be obtained via gasification of the agricultural residues evaluated with the equation and the electricity consumption (SIS, 1991; SIS, 2000; SIS, 2003) of Turkey. As can be seen in the figure, the unused parts of agricultural residues would meet nearly 17% of the national electricity consumption, on the basis of predictions (means of the years 1999–2002). Abandoning the use of cereal straws (wheat, barley, etc.) with the highest production potential in Subcategory A1 as animal fodder will be important for the evaluation of these residues in obtaining energy. Therefore, the ratio at which the residues are converted to electrical energy via gasification will be increased as much as threefold. These results are the optimistic predictions that may promote investment research related to the agricultural residues in thermochemical conversion sector.

Figure 7. Comparison of the electricity consumption of Turkey and the energy values that could be obtained from the agricultural residues: 䉭, electricity consumption; 䊊, energy obtained from the unused agricultural residues.

Agricultural Residues as Biomass Energy

139

4. Conclusions A study was conducted to evaluate the potential power production from the agricultural residues in Turkey through gasification. The agricultural residues were separated into two categories, A and B. Category A consisted of the agricultural residues provided from the growing and picking of products with nutritional values; Category B comprised the residues subjected to processing in order to obtain different commercial products. Unused residues (15.3 mt/yr) can meet 17% of the national electricity consumption if they are completely converted via researches to be carried out on the gasification features of agricultural residues. The highest quantities by the agricultural residues in Turkey were found in wheat, barley, chickpea, corn, and cotton stalks as well as in the pruning residues of vine, apple, hazelnut, olive, and orange trees in Category A, and in the production residues of grape, hazelnut, sunflower oil, tomato, and olive oil in Category B. For this reason, it will be suitable to realize the laboratory and pilot-scale experiments related to the gasification characteristics with the aid of these residues. The regions with the highest quantities of agricultural residues are the Marmara, Mediterranean, Aegean, and Central South regions, in decreasing order. The residue density of these regions changes between 28.0–43.2 t/km2 .

References Alibas K., and Unal, H. 1995. Working principals of straw burner and energy potential of straw in Turkey. 16th National Congress of Agricultural Mechanization, September 5–7, pp. 138–146. (in Turkish). Annamalai, K., Sweeten, J. M., and Ramalingam, S. C. 1987. Estimation of gross heating values of biomass fuels. Transaction of the ASAE 30:1205–1208. Antal, M. J., Allen, S. G., Dai, X., Shimizu, B., Tam, M. S., and Grønli, M. G. 2000. Attainment of the theoretical yield of carbon from biomass. Ind. Eng. Chem. Res. 39:4024–4031. Arvelakis, S., Sotiriou, C., Moutsatsou, A., and Koukios, E. G. 1999. Prediction of the behavior of biomass ash in fluidized bed combustors and gasifiers. Journal of Thermal Analysis and Calorimetry 56:1271–1278. Arvelakis, S., Gehrmann, H., Beckman, M., and Koukios, E. G. 2000. Effect of leaching on the ash behavior of olive residue during fluidized bed gasification. Proc. 5th Eur. Conf. on Industrial Furnaces & Boilers 163–172. Blasi, C. D., Tanzai, V., and Lanzetta, M. 1997. A study on the production of agricultural residues in Italy. Biomass and Bioenergy 12:321–331. Cattaneo, C., Palanca, A., Zolezzi, M., Nicolella, C., and Rovatti, M. 2002. Thermovalorization of vegetable and animal biomasses. Proc. 12th European Conference and Technology Exhibition on Biomass for Energy, Industry and Climate Protection, June, Amsterdam. Cuiping, L., Yangongjie, Chuangzhi, W., and Haitao, H. 2004a. Study on the distribution and quantity of biomass residues resource in China. Biomass and Bioenergy 27:111–117. Cuiping, L., Chuangzhi, W., Yanyongjie, and Haitao, H. 2004b. Chemical elemental characteristics of biomass fuels in China. Biomass and Bioenergy 27:119–130. Demirbas, A. 1997. Calculation of higher heating values of biomass fuels. Fuel 76:431–434. Demirbas, A. 2002. Fuel characteristics of olive husk and walnut, hazelnut, sunflower, and almond shells. Energy Sources 24:215–221. Ebeling, J. M., and Jenkins, B. M. 1985. Physical and chemical properties of biomass fuels. Transaction of the ASAE 28:898–902. EBN. 2003. Eubionet biomass survey in Europe—Country report of Greece. European Bioenergy Networks, 38 p. ECN. 2004. The composition of biomass and waste—Composition of single material. Phyllis, Access Date 2004, http://www.ecn.nl/phyllis/

140

H. Unal and K. Alibas

FAO. 2005. Faostat—Agriculture, Crops Primary, 2005 Data, http://www.faostat.fao.org/ Gaur, S., and Reed, T. B. 1995. An atlas of thermal data for biomass and other fuels. NREL/ TP-433-7965. Gaur, S., and Reed, T. B. 1998. Thermal data for natural and synthetic fuels. New York: Marcel Dekker, 259 p. Hay, R. K. M. 1995. Harvest index: A review of its use in plant breeding and crop physiology. Annals of Applied Biology 26:197–216. Illerup, J. B., and Rathmann, O. 1996. CO2 gasification of wheat straw, barley straw, willow and giganteus, Rosoe, Denmark, Risoe-R-873(EN), 32 p. Jenkins, B. M., and Sumner, H. R. 1986. Harvesting and handling agricultural residues for energy. Transaction of the ASAE 29:824–836. Kitani, O., and Hall, C. W. 1989. Biomass Handbook. New York: Gordon and Breach Science Publishers. Koukios, E. G., Arvelakis, S., and Georgali, B. 1999. Physico-chemical upgrading of agro residues as solid biofuels. Proc. 4th Biomass Conference of the Americas, pp. 99–304. Kumar, K., Bal, S., and Ojha, T. P. 1987. Methods of determining heat potentials of agricultural biomass. AMA 18:71–73. Livingston, W. R. 1991. Straw ash characteristics. Babcock Energy Limited DE92 519748, 23 p. Mason, N. B., Hyde, G. M., and Waelti, H. 1985. Fruit pomace as a fuel. Transaction of the ASAE 28:588–591. Miles, T. R., Baxter, L., Bryers, R. W., Jenkins, B. M., and Oden, L. L. 1995. Alkali deposits found in biomass power plants. A preliminary investigation of their extend and nature, NREL/TP433-8142, 82 p. Öhman, M. 1997. A new method to quantify fluidized bed agglomeration in the combustion of biomass fuels. Licantiate Thesis, Umea University, 23 p. Parikh, J., Channiwala, S. A., and Ghosal, G. K. 2005. A correlation for calculating HHV from proximate analysis of solid fuels. Fuel 84:487–494. Petrov, N., Budinova, T., Razvigorova, M., Ranzi, R., Björmbom, E., and Minkova, V. 1999. Preparation of activated carbon from cherry stones, apricot stones, and grape seeds for removal of metal ions from water. 2nd Olle Lindström Symposium on Renewable Energy-Bioenergy, Royal Institute of Technology, June 9–11, Stockholm, Sweden. Raveendran, K., Ganesh, A., and Khilar, K. 1995. Influence of mineral matter on biomass pyrolysis characteristics. Fuel 74:1812–1822. Razvigorova, M., Goranova, M., Minkova, V., and Cerny, J. 1993. On the composition of volatiles evolved during the production of carbon adsorbents from vegetable wastes. Fuel 73:1718–1722. Schapaugh, W. T., and Wilcox, J. R. 1980. Relationships between harvest indices and other plant characteristics in soybean. Crop Science 20:529–533. SIS. 1991. Statistical Indicators 1923–1990. State Institute of Statistics Prime Ministry Republic of Turkey, Public. Number: 1472, 429 p. SIS. 2000. Statistical Yearbook of Turkey 1999. Public. Number: 2390, 721 p. SIS. 2002. The Summary of Agricultural Statistics 1981–2000. ISSN 1300–1213. SIS. 2003. Statistical Yearbook of Turkey 2002. Public. Number: 2779, 721 p. SIS. 2004. Agricultural Statistics of Agriculture Regions of Turkey 1999–2003. State Institute of Statistics Prime Ministry Republic of Turkey. Sumner, H. R., Sumner, P. E., Hammond, W. C., and Monroe, G. E. 1983. Indirect-fired biomass furnace test and bomb calorimeter determinations. Transaction of the ASAE 26:238–241. Taner, F. I., Ardic, B., Halisdemir, B., and Pehlivan, E. 2004. Biomass and agriculture: Sustainability, markers and policies. Paris: OECD Publication Service, September, pp. 439–453. Unal, H., and Alibas, K. 2002. Determination of quantities of combustion air and chimney gas essential for burning wheat straw and sunflower stalks. UTES 2002, IV. National Clean Energy Symposium (II. Volume), October 16–18, pp. 841–851. Werther, J., Saenger, M., Hartge, E. U., Ogada, T., and Siagi, Z. 2000. Combustion of agricultural residues. Progress Energy Combustion Science 26:1–27.