Analysis combustion efficiency in a fluidized-bed combustor with a modified perforated plate for air distribution

- Combustion efficiency is one of the most important parameters, especially in the FBC combustion chamber. Investigations into the efficiency of combustion in FBC fuels using solid biomass waste fuels in recent years are increasingly in demand by researchers around the world. Specifically, this study aims to calculate the combustion efficiency in the FBC combustion chamber. Combustion efficiency is calculated based on combustion results from modification of hollow plates in the FBC combustion chamber. The modified hollow plate aims to control combustion so that the fuel incorporated can burn out and not saturate. The combustion experiments were tested using palm oil biomass solid waste fuels such as PKS, OPM, and EFB. The results of the measurements showed that the maximum combustion temperature for MCC fuel reached 863 o C for M1 and 887 o C on M2. The maximum combustion temperature measurements for M1 and M2 from OPM fuel testing reached 898 o C and 858 o C, respectively, while the maximum combustion temperature for EFB fuel was 667 o C andM2 847 o C, respectively. The rate of combustion efficiency with the modification of the hole plate in the FBC combustion chamber reached 96.2%. Thermal efficiency in FBC combustion chamber for OPM 72.62%, MCC 70.03%, and EFB 52.43%. The highest heat transfer rates for OPM fuel reached 7792.36 w/m, MCC 7167.38 w/m, and EFB 5127.83 w/m. Thus, modification of the holed plate in the FBC chamber showed better performance of the plate without modification.


Introduction
Investigations into the efficiency of combustion in FBC fuels using solid biomass waste fuels in recent years are increasingly in demand by researchers around the world. This is due to the existence of highly promising solid biomass waste that can be converted into energy.
Solid biomass waste is one of the renewable energy sources that can be converted to replace fossil energy that has been decreasing in recent years. The availability of renewable energy is currently abundant in Southeast Asia [1][2][3]. Abundant renewable energy sources today, one of which is a solid waste of palm oil biomass [4][5][6]. Meanwhile, an analysis of the availability of energy from palm oil biomass waste has also been conducted [7]. Where the results of the analysis with simulations conducted showed that biomass solid waste can produce energy of 106.15 MW from the results of a mixture of several types of biomass. While one type of biomass alone can produce energy of 61.05 MW. Thus, renewable energy sources from palm oil biomass solid waste are suitable for reducing dependence on fossil fuels, especially in remote areas/islands.
Combustion efficiency is one of the most important parameters especially in the combustion chamber such as Fluidized-Bed Combustor (FBC). Combustion efficiency, , can generally be defined as in Equation (1). Equation (1) shows the definition for combustion efficiency i.e., the ratio of chemical heat release rate (HRR), QCH, to heat of perfect combustion QT. This is as evidenced in the study [8].
An investigation into the efficiency of combustion in the combustion chamber with a case study in a 1:20 scale tunnel has recently been conducted [9]. Where the results obtained show that the length of the tunnel can affect the efficiency of combustion. The average value of propane fire recorded reaches 89% and for heptane, fire is lower which is 80%. The chemical HRR value decreased from normal fire, but the heptane combustion efficiency rate reached 94%. Research to predict combustion efficiency in methane and propane fires has also been conducted [10]. Where overall combustion efficiency was found to be close to one unit through various oxidizing dilutions, but at the beginning of testing, there was a sudden decrease. In different studies conducted with combustion experiments using porous and non-porous alumina base fuel in the FBC, fuel chamber has been investigated [11]. Where the results obtained that polypropylene can be used effectively to fuel on both materials FBC. Experiments conducted showed a combustion efficiency rate of 99.9% at 750°C. Detailed process development to evaluate the heat potential of biomass combustion results in CFB combustion chambers with Aspen Plus simulator and FORTRAN special subroutines have also been analyzed [12]. An investigation into the efficiency of combustion in FBC fuel using sawdust, rice husks, and cane pulp has been discussed [13]. The experiments tested in the study aimed to investigate temperature, CO, NO, and CO2 concentrations along with the height of the combustion chamber as well as exhaust gases (chimneys). Operating conditions and fuel properties can affect overload and air.
Research with the use of perforated plate quatrefoil (QPP) designed for the optimization of heat exchangers has recently been studied [14]. The main purpose of the study was to study the degree of influence on hole height and QPP plate distance on thermal-hydraulic performance. The results showed that the coefficient of heat transfer and pressure drop on the shell side of the heat exchanger increased with a decrease in hole height and plate distance from QPP. However, the level of heat transferred on the side of the shell becomes reduced.
Experiments to investigate hydrodynamic loads with two-dimensional perforated plates have been studied [15]. The test results between the two hollow plates with gaps of 0.14 and 0.29 overall showed an excellent association. Modification of hollow plates in the FBC fuel chamber with the use of biomass solid waste fuel is still very little found in the literature. Investigation of combustion efficiency in the FBC fuel chamber, especially with palm oil biomass fuel is also very rarely found in publications. Therefore, research to analyze the efficiency of combustion by making various modifications in the combustion chamber is very important. This is because the use of biomass solid waste as a very abundant source of renewable energy can be used as an alternative fuel to reduce dependence on fossil energy.
The investigation through experiments conducted in the study specifically aimed to calculate the efficiency of combustion in the FBC combustion chamber. Efficient combustion is calculated based on a modification of the hole plate contained in the FBC combustion chamber. The modified hollow plate aims to control combustion so that the fuel incorporated can burn out and not saturate. The combustion experiments were tested using palm oil biomass solid waste fuels such as palm kernel shell (PKS), oil palm midrib (OPM), and empty fruit bunches (EFB).

Material and Experimental Setup
This research was conducted to analyze the level of combustion efficiency through modification of perforated plates as well as different fuels. This test was conducted twice for each of the different fuels. For the type of fuel and experiment setup designed in the research as described in the stages below.

Fuel Material
The fuel materials used in the study were a solid waste of palm oil biomass such as palm kernel shell (PKS), oil palm midrib (OPM), and empty fruit bunches (EFB). Each type of fuel used in this experiment weighed 2.5 kg as shown in Fig. 1.

Experimental Setup
The testing tools used in this experiment include combustion chambers (FBC) and

Fig. 2. Eksperimentan Setup
The modification of perforated plates made in this study aims to analyze the level of breeding efficiency using different fuels. Modifications made include making a hole as many as 32 by adding a spoonful of four pieces and the main hole placed in the middle of the plate.
This is made to provide a windway that enters the combustion chamber so that the fuel inside is not saturated. Plate modifications were made in this test as shown in Fig. 3.

Fig. 3. Modification of Hollow Plate with Four Spoons
Furthermore, the steaming of combustion temperature in this study uses Digital Thermometer HT-306 as shown in Fig. 3. While the specifications of the Digital Thermometer HT-306 are presented in Table 1.   The combustion temperature of OPM fuel began to increase at seconds 12-18 and so on continued to decrease until the end of testing. The desperation temperature produced in this study is mainly for OPM fuel slightly lower than the results of the study [16]. However, the amount of fuel in this experiment was less so the resulting temperature was lower due to the shorter combustion time. Fig. 4 Fig. 5.a. The combustion fire state of the three types of biomass used is shown in While the heat temperature phenomenon of the three types of fuel used shows better results as shown in Fig. 8.b. a. Combustion temperature on M4 b. 3D temperature display on M4 At 20 seconds the temperature shows a drastic decrease in OPM fuel. This decrease is affected by malfunctioning dredging tools (errors) as shown in Fig. 9.a. This result is reinforced from the results of the 3D analysis in Fig. 9.b. a. Combustion temperature on the outer wall b. Temperature 3D display on the outer wall Fig. 9. FBC Wall Temperature of Different Fuels

Combustion Efficiency
The combustion process in the combustion chamber to produce heating, cooling and electrical energy need to be calculated efficiently so that the energy produced can be predicted.
The efficiency of the furnace or better known as the FBC combustion chamber can be done by equation (2).
Where Eff = efficiency The results of the calculation of furnace efficiency were obtained that OPM fuels showed better results compared to PKS and EFB fuels. The furnace efficiency levels recorded were recorded for OPM 11.23%, PKS 10.78%, and EFB 9.36% respectively. The results of the search in various publications showed that investigations of the efficiency of fuel furnaces are still very rarely found. Studies comparing thermal efficiency between AFC and OFC in axialfueled heating furnaces have been studied [17]. Measurement of furnace efficiency tested with five different cases can increase efficiency by 50%. However, previous tests have shown that in general efficiency measurements are not within the FBC space. Also, the fuel used in previous studies uses liquid fuel in general.

Thermal Efficiency
The calculation of thermal efficiency in a combustion test is a very important variable. It aims to know the efficient combustion resulting from the fuel used. Calculation of thermal efficiency can be done using equations (3) [18]. was lower than that of the [19]. Where the final thermal efficiency produced through the design of the solar receiver reaches 84.20%. Meanwhile, different studies predicting the thermal efficiency of LPG energy-efficient burners (EB) using CFD data showed lower yields than thermal efficiency in the FBC space in this study. The results of the calculation of the experiments conducted from both burners were carried out at 9.02% and 7.87% respectively.
While in different studies tested in combustion engines using mixed fuels between flaxseed oil and diesel showed lower thermal efficiency [20]. Fig. 11. Effect of thermal efficiency for different fuel

Measurement Heat Transfer Coefficient
Calculation of heat transfer in combustion needs to be done so that the necessary energy needs can be known. Besides, the calculation of heat transfer also aims to find out how much efficiency of combustion furnaces produced in this study. The calculation of heat transfer in this test was done using Equation (4)  Based on the results of the calculations showed that the rate of heat transfer in combustion furnaces conducted with oil palm biomass fuel is higher than the results of experiments in the study [21]. The heat transfer rate of OPM fuel reached 7792.36 w/m at 21 minutes compared to the PKS shown in Figure 12. While the heat transfer rate for EFB fuels showed lower yields of 5127.83 w/m and PKS of 7167.38 w/m. However, the overall fuel used in this study was higher than [22]. In the study they used component main heat transfer from fuel combustion is primary air as much as 33%, charcoal does not burn as much as 25%, pots 23%, others by 14%, and fuel space by 6%. The resulting efficiency rate is 24% with a time of 17 minutes. While the experiments conducted in this study used palm oil biomass fuel with a test time of 28 minutes. Overall, the fuel used is not as important as shown in Fig. 7. The results of the study on the calculation of heat transfer rates conducted earlier are lower than the experiments in this study [23].

Conclusion
The tests conducted in the study aimed to analyze the temperature and efficiency of combustion using three different types of biomass fuels. 2. Overall, the phenomenon of combustion temperature obtained shows excellent and perfect results. This is as shown in Fig. 7.
3. Modification of the perforated plate by providing four air conditioners supplied from the blower into the combustion chamber is quite perfect.
4. Furnace efficiency levels using PKS, OPM, and EFB fuels were 10.78%, 11.23%, and 9.36%, respectively. The outer radius of the cylinder Eff efficiency ri1 Radius in cylinder Pin power input ro2 The outer radius of insulation Pout power output ri2 The outer radius in isolation w/m Watt/meter ri3 Radius in cylinder M1 Measurement 1 k1 Thermal conductivity of the plate M2 Measurement 2 k2 Insulating conductivity M3 Measurement 3 ho Convection heat transfer coefficient M4 Measurement 4 hi The coefficient in the wall M5 Measurement 5 Ao Outer cross-sectional area Ai Inner cross-sectional area