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Biomass; Fuel Pellet; Rice Husk; Wood Chips; Physical properties

Introduction

The heat and power energy sector are one of the most dynamic sectors. There are several renewable options including wind, solar, geothermal, hydro thermal and bioenergy for energy production. Installation of equipment and needed infrastructure make these renewable energies economically unbearable. Nevertheless, solid biofuels can be used as substitute for coal in traditional power plant with the same infrastructure [1]. Aside being the alternative renewable energy, biomass contributed to climate change mitigation, energy security, maintaining carbon neutral value [2].

Forestry, agriculture, livestock and greenery sectors are the major sources of biomass production [3]. Since agricultural waste has been used for various heating process, higher moisture content and lower density make them technically unrealistic for direct combustion and handling problems [2]. In addition, non woody type Agro-industrial wastes have low density, low calorific value and high ash content [4]. These problems could be reduced by biomass pellets [5]. Through that, volumetric calorific value is increased, thus reduces the transportation, collection and storage cost [2]. Biomass pellet is a plant derivate matter, directly used as fuel or converted into the form of fuel by physical process [1]. It is tradable product popular in Europe and East Asian countries [4]. Based on the final objective, numerous strategies are used to standardize: for example, ask content from woody plant removed by bark removal [6], the biomass for energy, energy density increased by thermal conversion [7], bulk density increased by the densification process [8]. Through the application of densification process, briquettes, logs, bales, chips and pellets can be produced and they have the significant role among rural people [2]. Durability is the most important characteristic of pellets which depend on feedstock characters, moisture content, pre-processing size reduction, pelletization physical conditions such as die pressure, temperature and feedstock mixers [1].

Wood chips and rise husk are one of the most readily available easily collectable biomass in Sri Lanka which uses commonly as a fuel in rice mills parboiling process, furnace and brick kilns. In addition, it is used as a raw material for sodium silicate, briquettes and molecular sieves. There are several studies have been reported on rice husk fuel pellet as a lignocellulosic biomass [9,10]. However, there are many reasons behind with wood chips for not being utilized effectively, which mainly includes, lack awareness, insufficient data, lack environmental concern and lack of technology [2]. This present work is aimed to produce the fuel pellets from wood chips and rice husk with various ratio for household purpose and evaluate the Physical properties and combustion characteristics.

Material and Methods

Raw material collection

The wood chips were collected from wood workshop at Trincomalee and rice husks were collected from paddy field cultivation area. It was further grinded into a powdered form and sieved and obtained 1000 micrometer particle density.

Fuel pellet Densification

Wood chips fuel pellet and rice husk fuel pellets were produced by compaction in a mold with the dimension of 10mm diameter and 20mm length at 20MPa pressure. Water is used as a binder and lubricant for densification process. The wood chip and rice husk powder were mixed with little water before loading in the mold. Wood chips and rice husk were mixed using different proportions (Rise husk: Wood chips, 100:0, 50:50, 25:75, 75:25 and 0:100)

Determination of Ash Content

Ash content was determined by following equation. Pellet samples were placed in a pre-weighted crucible. The samples were incinerated in a furnace at 760-degree Celsius. The crucibles were allowed to cool and weighed.

Ash Content= (W5-W3)/(W4-W3)×100

Where:

W3= Weight of the crucible

W4= Weight of the crucible + sample before heating

W5= Weight of the crucible + sample after incineration

Determination of Moisture Content

The moisture content was analyzed by the oven drying method [2]. This was conducted at temperature of 105 degree Celsius for 1 hour.

Ash Content= (W7-W6)-(W8-W6)/(W5-W3)×100

Where:

W6= weight of empty container

W7= weight of container + sample before drying

W8= weight of container + sample after drying

Determination of Porosity Index

The porosity was determined based on the amount of water sample was able to absorb [2]. Pellet sample was immersed in water at room temperature for 1 min. The porosity index was calculated as the ratio of the mass of water absorbed to the mass of the sample immersed in the water.

Porosity Index= (W10-W9)/W9×100

Where:

W9= mass of sample

W10= mass of sample immersed in water

(W10 – W9)= mass of water absorbed

Determination of Calorific Value

The net calorific values (NCV) was determined by using below equation [2].

NCV= 18.7 (1.0-AC-MC)-(2.5 MC)

Where:

NCV= net (lower) calorific value

AC= ash content

MC= moisture content

Determination of Burning Rate

Burning rate is the ratio of the mass of the fuel burnt to the total time taken. The combustion was initiated by the addition of a little kerosene and igniting with matches. The temperature of the burning samples was taken by means of thermocouple at every two minute intervals using a stop watch until it was completely burnt [2].

Burning rate= Mass of fuel burnt/Time taken

Elemental analysis

Total organic carbon was calculated by following equation using a factor of 1.724 [1]. Sample was calcinated at 400 degree Celsius for 14 hours.

TOC= (((W1-W2)×100)/W1)/1.724

Where:

TOC= Total organic carbon

W1= Mass of dry materials

W2= Mass of incinerated material

Water Boiling Test

Cooking efficiency was compared by measures the time taken for each pellet to boil equal volume of water under similar condition.

Results and Discussion

Fuel pellets prepared from rice husk and wood particles with different weight ration were uniform in structure (shape and diameter). All the pellets have a moisture content less than 3%and total organic carbon fall between (15-17.5%) (Table 1), which synchronize with the results reported in the literature [11]. The solid fuel with high carbon content has a good potential for thermal energy conversion process. The moisture content is increased when the wood portion is increased. Ash level is comparatively high when the pellet has high rice husk portion. High ash content generally a constrain for the thermal conversion application because of the need of ash removal, slagging equipment corrosion and deposit formation in furnace [11]. Therefore, using ash mitigating additives with rice husk pellet is an alternative way to overcome this issue [12].

Significant Calorific value was observed and it was high when the wood particles take full portion in the pellet. As the moisture content value increases, calorific value also increases. Japhet at al. [2] reported the contrast result of rice husk fuel pellet production, where heating value increases with decreasing moisture content (Table 1).

Table 1: Physical properties of fuel pellet.

Porosity index determine the quality of fuel in terms of water penetration resistance. Porosity and water penetration resistance have negative relationship. In this study, fuel pellet only made by rice husk showed the higher porosity index, indicated lower water penetration resistance resulting low combustion efficiency. Sengar et al. reported the higher water resistance percentage and concluded the good potential for handling and transportation. On other hand, porosity index would have shown widely disparate value if the compaction pressure would have been varied [2].

Water boiling test explains the suitability of pellets for domestic usage [13]. 100 g of each fuel pellet was used to boil 750 ml of water and recorded the time duration taken to reach 100 degree Celsius. Pellet only has wood portion took less time recorded as 6 minutes to reach 100 degree Celsius (Figure 1).

Figure 1: Water boiling test, (R: W), a- 100:0, b- 75:25, c- 50:50, d- 25:75, e- 0:100.

From the burning test data (figure 2), wood portion pellet reaches 100ºC in 6 minutes and peak temperature in 15 minutes and keeps the temperature above 100ºC till first 40 minutes. This means, the useful heat energy could be sustained for 40 minutes. In contrast, rice fuel pellet reaches 100ºC in 15 minutes and drops in 40 minutes and sustains only 15 minutes. Therefore, wood pellet has a high heating potential than rice husk pellet and rice husk pellet potential could be improved by the addition of wood chips portion (Figure 2).

Figure 2: Temperature and time on burning 100g of fuel pellet (R: W), a- 100:0, b- 75:25, c- 50:50, d- 25:75, e- 0:100.

Conclusion

The study was motivated by the large quantity of rice husk and wood chips waste seen in the paddy field and timber workshop. Solid fuel pellet was formed by different weight ration of rice husk and wood chips. Physical and combustion characters were investigated. The heating value is increased with the increasement of wood portion in the pellet. The calorific value of wood pellet was observed as 17.89 MJ/kg. Based on the water boiling test, wood pellets are the effective domestic solid fuel. Moreover, wood pellet has a high heating potential than rice husk pellet and rice husk pellet potential could be improved by the addition of wood chips.

1. Ríos-Badrán IM, Luzardo-Ocampo I, García-Trejo JF, Santos-Cruz J, Gutiérrez-Antonio C (2020) Production and characterization of fuel pellets from rice husk and wheat straw. Renewable Energy 500-507.

Google Scholar, Crossref

2. Japhet JA, Tokan A, Muhammad MH (2015) Production and characterization of rice husk pellet. American J Eng Res 4: 112-119.

Indexed at, Google Scholar

3. Ilari A, Pedretti EF, De Francesco C, Duca D (2021) Pellet production from residual biomass of greenery maintenance in a small-scale company to improve sustainability. Resources 10: 122.

Google Scholar, Crossref

4. Widjaya ER, Triwahyudi S, Rosmeika, Harsono (2019) Rice Husk Fuel Pellet: Characterization on Physical and Thermogravimetric (TGA) Combustion Properties. IOP Conference Series: Earth and Environ Sci 355: 1-10.

Google Scholar, Crossref

5. Sokhansanj S, Mani S, Bi X, Zaini P, Tabil L (2013) Binderless Pelletization of Biomass.

Google Scholar, Crossref

6. Radacovska L, Holubcík M, Nosek R, Jandačka J (2017) Influence of Bark Content on Ash Melting Temperature. Procedia Eng192: 759-764.

Google Scholar, Crossref

7. Simonic M, Goricanec D, Urbancl D (2020) Impact of torrefaction on biomass properties depending on temperature and operation time. Sci Total Environ 740: 140086.

Google Scholar, Crossref

8. Muazu RI, Stegemann, JA (2015) Effects of operating variables on durability of fuel briquettes from rice husks and corn cobs. Fuel Processing Tech 133: 137-145.

Google Scholar, Crossref

9. Pliego-Arreaga R, Regalado C, Amaro-Reyes A, García-Almendárez BE (2013) Valorisation of rice husks and bean straws through fuel pellets production: an experimental and modelling approach. Revista Mexicana de Ingeniería Química 12: 505-511.

Google Scholar, Crossref

10. Djomdi, Fadimatou H, Hamadou B, Nguela LJM, Christophe G, et al. (2021) Improvement of thermophysical quality of biomass pellets produced from rice husks. Energy Conversion and Management: X 12: 100132.

Google Scholar, Crossref

11. Bajo PO, Acda MN (2017) Fuel pellets from a mixture of rice husk and wood particles. Bio Resources 12: 6618-6628.

Indexed at, Google Scholar, Crossref

12. James AK, Thring RW, Helle S, Ghuman HS (2012) Ash management review-applications of biomass bottom ash. Energies 5: 3856-3873.

Google Scholar, Crossref

13. Tokan A, Muhammad MH, Japhet JA, Kyauta EE (2016) Comparative Analysis of the Effectiveness of Rice Husk Pellets and Charcoal AsFuel For Domestic Purpose. IOSR J Mech Civil Eng 13: 21-27.

Google Scholar, Crossref