INNOVATION OF SUSPENDED FURNACE CYCLONE BURNER FOR COMBUSTION OF LIGHT BIOMASS PARTICLES

• Main Author: Pasymi
• Format: Dissertations
• Language: Indonesia
• Subjects: Teknik kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/40528
• Institution: Institut Teknologi Bandung

Miscanthus x giganteus is one of the potential energy biomass, with an average energy productivity of 517 GJ/hectare/year. This biomass is very easily cultivated; does not require irrigation, fertilization, and pesticides, intensively. It is even reported can grow in clay, and dry and dusty soils. Thus, this biomass can be relied upon as primary energy in power plants in Indonesia, especially on small islands and remote areas. From the various ways of using Miscanthus x giganteus as fuel in power plants, direct combustion grooves are the most widely used because they are simpler and have higher heat efficiency. The ideal furnace technology for biomass in a power plant is the suspended furnace. The combustion process in this kind of furnace has high efficiency and is easily controlled. The design of suspended furnace is usually unique and is largely determined by the fuel characteristics. The uniqueness of the suspended furnace lies on the design of its burner. Different fuel characteristics require different burner designs. This dissertation study aimed to formulate burner design of a furnace so that the furnace is able to combust the Miscanthus x giganteus particles in a suspended state. To realize this goal, 4 research objectives were established, namely: (1) preparing dry Miscanthus particles, (2) determining the physical and chemical characteristics of dry Miscanthus particles, (3) innovating burner designs for Miscanthus, and (4) determining the combustion characteristics of Miscanthus particles. The method used to undertake this dissertation research was a combination method, which is a combination of modeling and experimental methods. The combination of these two methods had been claimed by previous researchers able to produce the reliable research results with relatively fast time and relatively low costs. The preparing process of Miscanthus x giganteus particles was done by chopping fresh Miscanthus plants using CM-01 machine. The physical characteristics of dried Miscanthus particles obtained from chopping process were as follows: average diameter 1.384 ?m, bulk density 101.23 kg/m3, individual density 240 kg/m3, and shape factor of 0.45. Meanwhile, the proximate and ultimate analysis results were as follows (adb): water content 12.35%, volatile matters 56.93%, fixed carbon 18.87%, ash 11.85%, carbon 37.41%, hydrogen 5, 99%, oxygen 43.48%, nitrogen 1.09%, sulfur 0.18%, and calorific value of 3,472 kcal / kg (14.53 MJ/kg). Determination of combustion characteristics of Miscanthus particles was carried out in two types of furnace, namely fixed bed and suspended furnaces. The suspended combustion process in a furnace was carried out using the help of a cyclone burner. The burner was attached to one side of the furnace wall in a horizontal position. In addition to deliver fuel to the furnace, the burner also functions to initiate combustion process and to maintain the particles burning in suspended conditions. The burner design used for the suspended furnace consisted of the head and body sections of burner. The head section was a cylindrical pipe embedded by an extended axial inlet and 4 tangential injections. The cylindrical axial inlet was mounted concentrically to the burner head, with a diameter ratio of axial inlet to the burner head is 0.33. Meanwhile, the rectangular tangential inlet was mounted symmetrically around the burner head, with a slope of 20 degrees to the abscissa. While the burner body was a horizontal cylinder where the interaction between axial and tangential flow occurs. In this study, the burner cylinder length was varied by 1.5 and 2.5 times of the burner diameter. The particles combustion test results in the form of fixed beds indicated that there are two models of particle combustion that occur in this type of furnaces, namely: (i) simultaneous combustion model, where the combustion process of volatile substances and charcoal takes place simultaneously and (ii) sequential combustion model, where the charcoal combustion process occurs after the combustion of volatile substances is complete. The simultaneous combustion model was found to occur at temperatures of ? 400oC. There was no flame seen in the simultaneous combustion model, while the sequential combustion process was characterized by the presence of flames. The sequential combustion models took place at temperatures of ? 450oC. The higher the furnace temperature, the faster the Miscanthus particles to ignite. Even at temperatures of ? 550oC, Miscanthus particles could ignite spontaneously shortly after being dropped in the furnace. The combustion study in suspended furnace revealed that the combustion process of Miscanthus particles in the furnace was influenced by the swirl flow intensity and the burner cylinder length. The higher the swirl flow intensity, the longer the particles flow time in the furnace and the greater the potential of particles to be burned in a suspended state. However, the value of the swirl flow intensity was limited by the particle loading ratio. The optimal particle loading ratio obtained in this experiment was 23.35%, so the initial swirl flow intensity was only 7.52. The combustion process of Miscanthus particles in a furnace with a long burner cylinder (l = 2.5d) could take place in a suspended form. Meanwhile, the combustion process of Miscanthus particles in a furnace with a short burner cylinder (l = 1.5d) was similar to the combustion process in a fixed bed furnace, where the particle combustion process takes place at the base of the furnace. Other findings obtained from the combustion study in suspended furnaces were: (1) the particles flow time of Miscanthus in the furnace was not always directly proportional to the particle size and (2) the combustion residues (charcoals) still contained a little fixed carbon and volatile matters (combustible substances). From the results mention above, it could be concluded that the cyclone burner designed, with a burner cylinder length 2.5 times of the burner diameter, could burn -5600 ?m sized particles of dry Miscanthus in suspended state. The combustion efficiency of the proposed suspended furnace was ± 96%.