**4.1. Investigation of the influence of bale quality**

During experimental investigation of the boiler occasionally came to some minor problems in boiler operation. The problem was detected in the poor biomass burning. It is assumed that the main cause of problems is uneven quality of bales. Therefore, it is examined in de‐ tail the quality and moisture in bales that are stored and used in regular plant operation. It is assumed that poor bales quality could come from two reasons: a) Because of the rainy sea‐ son in the period of collection of soybean straw in the fields; b) The increase in moisture con‐ tent during bales storage up to their use.

Part of the bales is stored under the canopy capacity of 1200-1500 pcs bundle (Figure 19). The quantity of bales is insufficient to operate the boiler throughout the season. Therefore it had to accede to the formation of a group bales in the open, again near the boiler where the

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**Number of sample % of moisture Number of sample % of moisture** 14.77 12 13.78 45.17 13 19.44 11.83 14 12.34 15.84 15 59.73 5a 66.70 16 17.59 5b 65.83 17 16.98 17.17 18 20.65 19.63 19 15.75 20.05 20a 68.98 16.74 20b 66.62 62.15 21 67.86

From several groups of bales placed at open space one was chosen for the implementation of a test. Selected group made a bundle so that in a horizontal row was passed four bales (bale lying on the site with the largest surface area). Such orders were five in height. Length of group was determined free space and it corresponded to the width of a few dozen bales. It was decided to analyze the quality of bales (determination of moisture content in bales) per cross-section of group. A special sampler which allows sampling in-depth of the bale was made. Straw sampling scheme in the cross section is given in Figure 20 where from some of

Determination of moisture content in straw samples was performed in an accredited labora‐ tory for testing fuels at the Vinca Institute. Test results of straw samples moisture is given in Table 3. The results show dramatic differences in the quality of the bales at the cross section of bale group. All straw samples from the fifth highest among the group (number of sam‐ ples 5a, 5b, 10, 15, 20a, 20b, 21) show that the concentration of moisture in them is extremely high. It ranged from 60-70%. Such quality straw with so much moisture content, absolutely can not burn in any furnace. Also, if such a bale enters the combustion chamber can cause a

By using the appropriate computer program calculation the adiabatic combustion tempera‐ ture and combustion product composition of soybean straw with different moisture content

bales are placed in the open and covered with nylon.

11 11.97

the bales taken more than one sample.

host of other problems.

**Table 3.** Results of the determination of moisture content in samples of soybean straw

**Figure 19.** The cover and open bales storage near the boiler house

Preparation for use baled straw in boiler is in September. According to official data of the Republic Hydrometeorological Service of Serbia [23] during the month of September at the territory of Belgrade fell more than 3 l/m2 of rain. On this basis it can be concluded that the formed bale of soybean straw were acceptable dry before storing, or it can be said that the weather was ideal for baling straw. Shortly after baling bales were transported near the boil‐ er room so that time needed to bales transport did not affect the increase in moisture.


**Figure 20.** Schematic layout of sampling straw

Part of the bales is stored under the canopy capacity of 1200-1500 pcs bundle (Figure 19). The quantity of bales is insufficient to operate the boiler throughout the season. Therefore it had to accede to the formation of a group bales in the open, again near the boiler where the bales are placed in the open and covered with nylon.

**4. Experimental research**

70 Sustainable Energy - Recent Studies

**4.1. Investigation of the influence of bale quality**

**Figure 19.** The cover and open bales storage near the boiler house

territory of Belgrade fell more than 3 l/m2

**Figure 20.** Schematic layout of sampling straw

tent during bales storage up to their use.

During experimental investigation of the boiler occasionally came to some minor problems in boiler operation. The problem was detected in the poor biomass burning. It is assumed that the main cause of problems is uneven quality of bales. Therefore, it is examined in de‐ tail the quality and moisture in bales that are stored and used in regular plant operation. It is assumed that poor bales quality could come from two reasons: a) Because of the rainy sea‐ son in the period of collection of soybean straw in the fields; b) The increase in moisture con‐

Preparation for use baled straw in boiler is in September. According to official data of the Republic Hydrometeorological Service of Serbia [23] during the month of September at the

formed bale of soybean straw were acceptable dry before storing, or it can be said that the weather was ideal for baling straw. Shortly after baling bales were transported near the boil‐

er room so that time needed to bales transport did not affect the increase in moisture.

of rain. On this basis it can be concluded that the


**Table 3.** Results of the determination of moisture content in samples of soybean straw

From several groups of bales placed at open space one was chosen for the implementation of a test. Selected group made a bundle so that in a horizontal row was passed four bales (bale lying on the site with the largest surface area). Such orders were five in height. Length of group was determined free space and it corresponded to the width of a few dozen bales. It was decided to analyze the quality of bales (determination of moisture content in bales) per cross-section of group. A special sampler which allows sampling in-depth of the bale was made. Straw sampling scheme in the cross section is given in Figure 20 where from some of the bales taken more than one sample.

Determination of moisture content in straw samples was performed in an accredited labora‐ tory for testing fuels at the Vinca Institute. Test results of straw samples moisture is given in Table 3. The results show dramatic differences in the quality of the bales at the cross section of bale group. All straw samples from the fifth highest among the group (number of sam‐ ples 5a, 5b, 10, 15, 20a, 20b, 21) show that the concentration of moisture in them is extremely high. It ranged from 60-70%. Such quality straw with so much moisture content, absolutely can not burn in any furnace. Also, if such a bale enters the combustion chamber can cause a host of other problems.

By using the appropriate computer program calculation the adiabatic combustion tempera‐ ture and combustion product composition of soybean straw with different moisture content (Table 4). Results of proximate analyze of soybean straw was used as input data for calcula‐ tions. In the case of combustion of soybean straw, with a total moisture content of Wt = 68%, the theoretical calculation shows that the combustion temperature is not possible to achieve satisfactory gas temperature for a real excess air to be used in the process of bales burning. The theoretical combustion temperature of soybean straw for excess air of 2.80 would be 572o C. In the case of combustion of the same composition biomass, but reduced the moisture content of Wt = 15%, the calculation shows that it is possible to achieve significantly higher gas temperature for a real excess air. In this case, the theoretical combustion temperature was 903o C for the excess air of 2.80. Note that this is mathematical calculated theoretical combustion temperature of soybean straw, which in real terms of furnace can not be ach‐ ieved so that the actual combustion temperature significantly lower. This is caused by the fact that the combustion of CO to CO2 achieves at the minimum temperature of 680o C. When burning soya straw with high moisture content in the flue gases products is a large amount of CO which is due to low temperatures (below 680o C) can not be transformed into CO2.

20.65%. This shows that such bales, with such quality, can satisfy needs of combustion in a boil‐ er with a cigarette burning like that installed in PKB Corporation. This means that careful bales choosing avoid many problems in the boiler operation, would reduce the number of delays, to facilitate the boiler operators and that, most importantly, and would provide a safer produc‐

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We will point to another very important effect of increased baled biomass moisture, which is reflected in the flow, and thus indirectly on the kinetic characteristics of the biomass combus‐ tion in a boiler furnace. As is well known soybean straw baled is a porous medium, and as such unless the porosity is characterized by another feature of flow, which is permeability. Permea‐ bility is flowing layer in some fluid flow. Experiments have shown that as the permeability of

Bearing all this in mind, we can conclude that the bales moisture is essential for the applied concept of biomass combustion. During designing this boiler we calculated that the mois‐ ture content of bales shall not be greater than 25%. This is why we made this concept that the boiler is the simplest and cheapest solution for the user. For the case when one wants to burn fuel with a high content of moisture applied to the concept of boiler furnaces with higher volume and with additional support of liquid or gaseous fuel which satisfy necessary heat required for continuous combustion of fuel in the boiler furnace. It is more expensive and complicated option for users, both in design and manufacture of the boiler as well as its

Cigarette baled biomass combustion is a relatively new and unexplored technology. For this reason a complex Computation Fluid Dynamics (CFD) simulation of the combustion process at a specific procedure may be of importance for further investigation of the process of ciga‐ rette combustion. Numerical simulations process of this type of facility involves modeling the transfer of momentum, heat and substances during combustion of biomass bales, which composition is a porous medium [24, 27]. To form a mathematical model of thermo physical parameters except combustion in a porous medium, it is necessary knowledge inputs as

This paper describes experimental studies performed on mentioned boiler in order to deter‐ mine the necessary model input parameters. When performing experiments measured the all parameters necessary to determine the global kinetics of the combustion process, the composition and temperature of flue gases at the outlet section of the space being modeled, and estimates the amount of fuel which is unburnt and which post combustion performed in a fluidized bed of its own ashes. In order to compare with the model made the determina‐ tion or measurement of the temperature profile in soybean bale on its way from entering the

Experimental investigation on the demonstration boiler implies the measurements of the fol‐

tion in the greenhouse that uses heat produced by combustion of soy bales straw.

porous biomass layer is less, the pressure drop i.e. flow resistance higher [24-26].

subsequent exploitation.

thresholds model.

**4.2. Experimental investigation in boiler furnace**

combustion chamber to the combustion zone.

lowing input parameters [28]:


**Table 4.** Theoretical (adiabatic) combustion temperature of soybean straw (<sup>o</sup>C)

Also was made a bale straw moisture test on the basis of statistical data on the amount of rains on the territory of Belgrade in September, October and November. In September fell 3.9 kg rain/m2 of soil, in October 98.8 kg rain/m2 , while in November fell 62 kg rain/ m2 . This means that the total per bale could fall about 386 kg of water, taking into account data from October and November. If we accept that the initial bale moisture was 10% and the average weight of bales after baling was about 200 kg by the calculation is to the point that one rain bales after October and November had a moisture content of ≈ 70%, which agreed quite well with the obtained moisture analysis of samples. So the increase of moisture in the bales stor‐ ed in groups is a consequence of atmospheric rains.

Information about the theoretical combustion temperature (Table 4) confirmed the facts of bales combustion impossibility from the upper row of the crowd with such high moisture con‐ tent in it. On the other hand, the vast majority of straw samples from bales, which were in the middle of the crowd (except than bale no. 2), has a moisture content ranging from 11.83 to 20.65%. This shows that such bales, with such quality, can satisfy needs of combustion in a boil‐ er with a cigarette burning like that installed in PKB Corporation. This means that careful bales choosing avoid many problems in the boiler operation, would reduce the number of delays, to facilitate the boiler operators and that, most importantly, and would provide a safer produc‐ tion in the greenhouse that uses heat produced by combustion of soy bales straw.

We will point to another very important effect of increased baled biomass moisture, which is reflected in the flow, and thus indirectly on the kinetic characteristics of the biomass combus‐ tion in a boiler furnace. As is well known soybean straw baled is a porous medium, and as such unless the porosity is characterized by another feature of flow, which is permeability. Permea‐ bility is flowing layer in some fluid flow. Experiments have shown that as the permeability of porous biomass layer is less, the pressure drop i.e. flow resistance higher [24-26].

Bearing all this in mind, we can conclude that the bales moisture is essential for the applied concept of biomass combustion. During designing this boiler we calculated that the mois‐ ture content of bales shall not be greater than 25%. This is why we made this concept that the boiler is the simplest and cheapest solution for the user. For the case when one wants to burn fuel with a high content of moisture applied to the concept of boiler furnaces with higher volume and with additional support of liquid or gaseous fuel which satisfy necessary heat required for continuous combustion of fuel in the boiler furnace. It is more expensive and complicated option for users, both in design and manufacture of the boiler as well as its subsequent exploitation.
