**3.1. An efficient boiler burning small straw bales**

The experimental boiler burning small soya, corn, rape seed or wheat straw bales, with 0.8x0.5x0.4 m in size, has been designed and built [10, 14-16]. The combustion has been or‐ ganized on the principles of cigarette burning [17]. Thermal power of the boiler is around 75 kW. In Figure 1, the scheme of the experimental boiler is shown. Baled straw is introduced through the inlet (3) into the combustion zone (7). The inlet is supplied by devices for con‐ tinuous bale feedings and provides stable combustion conditions (Figures 2 and 3). Furnace walls (4) have been made of refractory material – chamotte, with thermal insulation (5).

Under the original solution fresh air is injected through two channels, the primary air through channel (8), and secondary air through channel (9), and they are divided using compartment (11). The tertiary air is supplied through the inlet (12), and is previously heat‐ ed by flowing inside the walls (13). In the zone (14) is carried out the process of final com‐ bustion of the bale.

After the first examination of the boiler some changes were carried out in the distribution of air so that after this change the air for combustion is inserted into the space through the dis‐ tributor (26) which is connected to a fan of fresh air (27). By changing the position of the air distributor can be regulated the part of the bale involved in combustion and thus indirectly is regulated the heat output of the boiler.

The heat produced by combustion of biomass is transferred by the gas-to-water heat ex‐ changer (15). After passing through the channels (16) to the flue gases collector (17), the flue gases leave the boiler through the smokestack (18), equipped with the valve (19) and flue gas fan (28), and through the cyclone-type particle precipitator (29). Ash is collected in ash collectors (20, 21, and 22). A mobile tube for ash removal (23) has been placed inside the fur‐ nace, as well as a tube for pneumatic transport of ash (24). The boiler has a revision opening (25) for manual ash removal.

**Figure 1.** Scheme of the small agricultural biomass bale combustion boiler

was used for heating 1 ha of vegetable greenhouses belonging to the agricultural complex mentioned. The boiler house was built in the immediate vicinity of the greenhouse complex.

Technologies enabling biomass use for energy generation are mainly dependant on biomass characteristics. Different biomass conversion technologies available on the market include: fixed-bed combustion, combustion on the grate, combustion in dust burners, fluidized bed combustion and gasification [12]. Utilization of agricultural biomass faces a lot of challenges. One of the main disadvantages associated with combustion of agricultural biomass is a ten‐ dency of biomass ash to melt [13]. Two technologies are currently used for the combustion of biomass bales. The first is based on whole-bale combustion in the combustion chamber, while the second considers combustion of biomass bales in so called "cigar" burners. Cigar burner technology was found to be very suitable for straw combustion and was deemed not to be associated with any process limitations. The research investigation described herein was focused on developing a cigar burner combustion system suitable for the combustion of

The experimental boiler burning small soya, corn, rape seed or wheat straw bales, with 0.8x0.5x0.4 m in size, has been designed and built [10, 14-16]. The combustion has been or‐ ganized on the principles of cigarette burning [17]. Thermal power of the boiler is around 75 kW. In Figure 1, the scheme of the experimental boiler is shown. Baled straw is introduced through the inlet (3) into the combustion zone (7). The inlet is supplied by devices for con‐ tinuous bale feedings and provides stable combustion conditions (Figures 2 and 3). Furnace walls (4) have been made of refractory material – chamotte, with thermal insulation (5).

Under the original solution fresh air is injected through two channels, the primary air through channel (8), and secondary air through channel (9), and they are divided using compartment (11). The tertiary air is supplied through the inlet (12), and is previously heat‐ ed by flowing inside the walls (13). In the zone (14) is carried out the process of final com‐

After the first examination of the boiler some changes were carried out in the distribution of air so that after this change the air for combustion is inserted into the space through the dis‐ tributor (26) which is connected to a fan of fresh air (27). By changing the position of the air distributor can be regulated the part of the bale involved in combustion and thus indirectly

The heat produced by combustion of biomass is transferred by the gas-to-water heat ex‐ changer (15). After passing through the channels (16) to the flue gases collector (17), the flue gases leave the boiler through the smokestack (18), equipped with the valve (19) and flue gas fan (28), and through the cyclone-type particle precipitator (29). Ash is collected in ash

bales of various sizes and shapes and their utilization for energy production.

**3.1. An efficient boiler burning small straw bales**

**3. Materials and methods**

58 Sustainable Energy - Recent Studies

bustion of the bale.

is regulated the heat output of the boiler.

**Figure 2.** Heat accumulator and bale storage and feeding system

ed, b) Hot water from the boiler goes into heat only tank, c) Hot water from the boiler going at the same time in the building and heat reservoir, d) Hot water tank from the heat goes into the building. Also, the boiler is equipped with appropriate management and control

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

http://dx.doi.org/10.5772/51095

61

The thermal power of the boiler has been regulated with: the amount of straw engaged in the combustion process, the air excess and the fuel feeding rate. This experimental boiler could be scaled, since it satisfies the similarity requirements in: geometry, flow patterns, thermal load,

In order to assess the combustion quality and to obtain data for the design of a soya strawfired hot water boiler, a demo furnace with thermal power of 1 MW has been designed and built [10, 18, 19]. The appearance of the furnace, with the thermocouple probes, the primary air fan and channel, and the fuel feeding channel is shown in Figure 6. This furnace has been adopted for cylindrical bales, with 1.2-1.5 m in diameter which were available at that time. The cross is clearly visible on Figure 7 where the scheme of the experimental demonstration unit for burning large rolled soy straw bales was presented. There can be also clearly distin‐ guish three characteristics combustion zones in the cigar burner: drying zone (6), zone of de‐

The proximate analysis of soya straw used in testing is given in Table 1. The sum of five tests was done. A summary of main test parameters is given in Table 2. During all tests, three gas temperatures in the combustion zone were measured, with shielded type K thermocouple

thermal flux, adiabatic temperature, average temperature and flue gases content.

**3.2. The demo furnace burning soya straw bales**

volatilization (5) and zone of char burning (13).

**Figure 5.** The boiler control system and cyclone-type particle precipitator

system (Figure 5).

**Figure 3.** Bale storage and feeding system with push piston

**Figure 4.** Thermal scheme of distribution facilities

In order to obtain to plant work at nominal power, heat accumulator (thermal reservoir, with volume of 5 m3 ) has been installed (Figure 2). In this way it is ensured that no matter what the current needs for heating buildings are, boiler always works with the nominal power. The transitional periods (spring, autumn), for example, the need for heating usually amount to 20-40% rated power boiler, which would mean a much lower level of utility plant. Thermal scheme of distribution facilities is shown in Figure 4. From it can be seen fol‐ lowing thermal circles: a) Hot water from the boiler goes directly into a building that is heat‐ ed, b) Hot water from the boiler goes into heat only tank, c) Hot water from the boiler going at the same time in the building and heat reservoir, d) Hot water tank from the heat goes into the building. Also, the boiler is equipped with appropriate management and control system (Figure 5).

The thermal power of the boiler has been regulated with: the amount of straw engaged in the combustion process, the air excess and the fuel feeding rate. This experimental boiler could be scaled, since it satisfies the similarity requirements in: geometry, flow patterns, thermal load, thermal flux, adiabatic temperature, average temperature and flue gases content.
