**4.3. Results of the experimental investigation**



**Figure 21.** Measurements scheme at demonstrating hot water boiler furnace

the fluidized bed.


74 Sustainable Energy - Recent Studies

responding instrument was performed.



Schematic of the experimental tests is shown in Figure 21. Measurement of mass flow of air at inlet cross sections was done indirectly through the measurement of velocity in the chan‐ nels using Pitot-Prandtl's probe. Temperature of the flue gas exiting the fluidized bed of its own ashes, and the temperature at the outlet cross section were measured continuously by thermocouples type K. During experiments the acquisition of measurement data using cor‐

Bales feeding were done discontinuous so that the cycle of 1 min the number of seconds the ball travels to the furnace and the rest to 1 min ball is at rest. Therefore, it is done recording the relative position of the bale in relation to entering the combustion chamber and time, which is based on data received on its secondary mass flow *m*˙ *fu* . Composition of dry flue gas at the exit cross section was measured using a gas analyzer. Based on the measured air flow at the entrance to the ash layer *m*˙ *fu* and the temperature difference Tm3 between inlet and outlet flue gases it is possible to determine the degree of conversion of coke residue, based on the energy balance between the energy of combustion of carbon, which falls on the fluidized bed and the enthalpy difference above the entrance of air and flue gas exit from Experimental tests were carried out at a temperature in the furnace between 850-900o C, which is the optimum temperature for combustion of soybean straw. This temperature is high enough for complete combustion of straw, and safe from the point of ash melting. The stationary measurement regime remain several hours, but here will be presents the results of measurements for 1 h. It is enough to perform the necessary conclusions about the quality of combustion and comparisons with the proposed model. Data whose values are not changed during the experiment are shown in Table 6.

**Figure 22.** Thermocouples on the bale in feeding system

Temperature of air and fuel inputs (T1, T2, T3, T4, Tfu) has not changed during experiments, and for simplicity, adopted their size of 300 K, because any error will not have much impact on the accuracy of the results.


**Table 6.** Data of experimental values

Flue gases temperatures at the outlet section of the model at input 3 were measured continu‐ ously during the experiments and their values in a representative period of time are shown in Figure 23. It can be seen that the average temperature of gases at the outlet section was 889o C, and temperature of flue gases at the entrance to model 3 was ~420o C.

**Figure 23.** Flue gas temperature Tg and Tm3 (Tgav = 889oC and Tm3av = 420oC)

**Figure 24.** Carbon dioxide and oxygen concentration in dry flue gas on the outlet

Graphical presentation of this measurement is shown in Figure 26.

The second part of the experimental research was related to determine the temperature field inside the soybean straw bale on its way from entering the furnace to the combustion zone.

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77

It is important to note that the feeding rate of bale was not continual. In a determined time the bale was traveling to the combustion zone (working interval), and in determined period of time the bale was in pause (interval mode). Here it is clear that the average bale speed, if it is contin‐ uously moving, was less than the speed of movement in the working intervals. This statement is very important from the point of adoption of relevant temperature in the interval mode, be‐ cause it is a case of unsteady heat conduction, so in the diagram can be seen more value of the temperature in one position. If the movement of the bale was uniformly and continuously, then

Based on the known average temperature Tm3, air mass flow and air temperature at the inlet 3, it is possible determined the amount of fixed carbon which burn off in a fluidized bed of its own ashes, according to the methodology presented earlier. This amount essential repre‐ sents a part of unburnt primary fuel that burns in the porous layer, and on the basis of this information can be concluded about the global kinetics of the process based on the mass flow of fuel and the degree of conversion. The mass flow of fictitious components of vola‐ tiles and fixed carbon burning in the porous layer, calculated according to the proposed methodology are shown in Table 7.


**Table 7.** Volatile and fixed carbon mass flow values

The global kinetics of the process is not only defined by the degree of conversion of coke residue, but also by the degree of conversion of combusted gases in volatiles. From that rea‐ son measuring of the concentration of components in dry flue gas at the exit cross section was performed (Figure 21). The values of the measured concentration of CO2, O2, CO and NO are shown in Figures 24 and 25 for a period of one hour.

From Figure 25 it can be seen that the concentration of nitrogen oxides is around 160 ppm, which is converted in mg/m3 for the reference value of oxygen in the flue gas of 11% [29], is approximately 350 mg/m3 . The concentration of carbon monoxide was, at first view, very high, but we should bear in mind the fact that the observed cross section in which the meas‐ ured concentration of the combustion process does not end, but it is continuing inside the chamber for burn of.

Development of the Technology for Combustion of Large Bales Using Local Biomass http://dx.doi.org/10.5772/51095 77

**Figure 23.** Flue gas temperature Tg and Tm3 (Tgav = 889oC and Tm3av = 420oC)

Temperature of air and fuel inputs (T1, T2, T3, T4, Tfu) has not changed during experiments, and for simplicity, adopted their size of 300 K, because any error will not have much impact

**Air mass flow on inlet, [kg/s]**

**Inlet 1 Inlet 2 Inlet 3 Inlet 4** Value 0.2632 0.2263 0.2371 0.05 0.112143

Flue gases temperatures at the outlet section of the model at input 3 were measured continu‐ ously during the experiments and their values in a representative period of time are shown in Figure 23. It can be seen that the average temperature of gases at the outlet section was

Based on the known average temperature Tm3, air mass flow and air temperature at the inlet 3, it is possible determined the amount of fixed carbon which burn off in a fluidized bed of its own ashes, according to the methodology presented earlier. This amount essential repre‐ sents a part of unburnt primary fuel that burns in the porous layer, and on the basis of this information can be concluded about the global kinetics of the process based on the mass flow of fuel and the degree of conversion. The mass flow of fictitious components of vola‐ tiles and fixed carbon burning in the porous layer, calculated according to the proposed

**m, [kg/s]**

for the reference value of oxygen in the flue gas of 11% [29], is

. The concentration of carbon monoxide was, at first view, very

**C3H8 CO2 H2O Cfix**

Value 0,0166 0,0185 0,0323 0,0188

The global kinetics of the process is not only defined by the degree of conversion of coke residue, but also by the degree of conversion of combusted gases in volatiles. From that rea‐ son measuring of the concentration of components in dry flue gas at the exit cross section was performed (Figure 21). The values of the measured concentration of CO2, O2, CO and

From Figure 25 it can be seen that the concentration of nitrogen oxides is around 160 ppm,

high, but we should bear in mind the fact that the observed cross section in which the meas‐ ured concentration of the combustion process does not end, but it is continuing inside the

C, and temperature of flue gases at the entrance to model 3 was ~420o

**Fuel mass flow, [kg/s]**

C.

on the accuracy of the results.

**Table 6.** Data of experimental values

methodology are shown in Table 7.

**Variable**

**Table 7.** Volatile and fixed carbon mass flow values

which is converted in mg/m3

approximately 350 mg/m3

chamber for burn of.

NO are shown in Figures 24 and 25 for a period of one hour.

**Variable**

76 Sustainable Energy - Recent Studies

889o

**Figure 24.** Carbon dioxide and oxygen concentration in dry flue gas on the outlet

The second part of the experimental research was related to determine the temperature field inside the soybean straw bale on its way from entering the furnace to the combustion zone. Graphical presentation of this measurement is shown in Figure 26.

It is important to note that the feeding rate of bale was not continual. In a determined time the bale was traveling to the combustion zone (working interval), and in determined period of time the bale was in pause (interval mode). Here it is clear that the average bale speed, if it is contin‐ uously moving, was less than the speed of movement in the working intervals. This statement is very important from the point of adoption of relevant temperature in the interval mode, be‐ cause it is a case of unsteady heat conduction, so in the diagram can be seen more value of the temperature in one position. If the movement of the bale was uniformly and continuously, then the temperature is in a position that corresponds to the interval mode must have been between maximum and minimum measured values. Unfortunately, can not say with certainty whether the value was closer to the maximum, minimum or mean value. For the bale zero position we adopted the position of the combustion zone.

(electricity) production - CHP, which use residual biomass as fuel, and have as least as possi‐ ble power consumption. Proposed facility, analyzed here, meets those requirements in total. This

Development of the Technology for Combustion of Large Bales Using Local Biomass

Agricultural Corporation "Belgrade" - PKB is the largest agricultural enterprise in Serbia (≈ 22.000 ha of arable land), with agriculture and livestock as main domain of work. Crops (≈ 25.000 t/year of corn, wheat, barley, ≈ 5.760 t/year of soya, rapeseed and sugar beet), milk and vegetables are the main products. Each year after the harvest, a huge amount of soy straw (≈ 3.000 t/year) and corn stack (10-15.000 t/year) remain on the fields. The thermal fa‐ cility with 1.5 MW power built for heating 1 ha greenhouses, has been working for five years already, using soy straw as main fuel. In the boiler, an original cigarette type combus‐

The energy efficiency of the straw utilization cycle is mainly affected by process of its prepa‐ ration (balling, chopping, bundling), thus, the most justifiable is to use it close to the place of growing and gathering, and in form in which it is collected from fields. To utilize the re‐ maining balled straw and meet thermal needs of surrounding objects, it is desirable to build a new boiler facility with an efficient and environmentally considerate combustion technolo‐

The planned facility would heat several objects: two greenhouses, the greenhouse office building, a school, and a hospital. An overview of the objects, their installed or required

Greenhouse 1 1 ha Soy straw or light fuel oil 1.5 MW Greenhouse 2 1 ha No heating 1.5 MW Greenhouse office building 130 [m2] Soy straw 25 kW

School 4025 [m2] Light fuel oil 110 t/year (600 kW) Hospital 8600 [m2] Heavy fuel oil 300 t/year (1.3 MW)

The project consists of the substitution of existing boilers fed by fossil fuel by a CHP bio‐ mass facility, to heat public buildings and greenhouses as well as generate electricity. This will contribute to the reduction of CO2 emissions and to the improvement of the general liv‐ ing conditions of the local inhabitants. As a pilot project, it has the potential to serve as an

example for profitable green energy production facilities with replication potential.

**Object Area [m2] Fuel Annual fuel consumption/**

**Thermal power**

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79

gy. The most efficient way is a combined heat and power (CHP) plant [30-32].

thermal capacity and current heating modus are given in Table 8.

is going to be the first CHP facility in Serbia, using residual agricultural biomass.

*a) Present situation*

tion technology has been applied.

**Table 8.** Heating in Padinska Skela - present situation

*b) Projected solution*

**Figure 25.** CO and NO concentration in dry flue gas on the outlet

**Figure 26.** Measurement temperature profiles inside the soybean straw bale

### **4.4. Small scale plant for combined heat and power generation**

The best way for utilizing residual agricultural biomass for energy production in industrial or district heating is to be used close to place of its gathering - in large agricultural companies. That is the optimal solution, from energy, as well as economy point of view. One of the most effi‐ cient ways, recommended by many institutions worldwide, is the combined heat and power (electricity) production - CHP, which use residual biomass as fuel, and have as least as possi‐ ble power consumption. Proposed facility, analyzed here, meets those requirements in total. This is going to be the first CHP facility in Serbia, using residual agricultural biomass.
