Studi Numerik Pengaruh Rasio Primary Air dan Secondary Air (PA/SA) terhadap Aliran Multifasa pada Furnace CFB Boiler dengan Metode Computational Particle Fluid Dynamics (CPFD)

Alfaruqy, Hilmi (2023) Studi Numerik Pengaruh Rasio Primary Air dan Secondary Air (PA/SA) terhadap Aliran Multifasa pada Furnace CFB Boiler dengan Metode Computational Particle Fluid Dynamics (CPFD). Other thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Circulating Fluidized Bed (CFB) Boiler merupakan ketel uap yang beroperasi dengan kondisi hidrodinamik khusus, yaitu adanya sirkulasi partikel padat pada rangkaian furnace dan siklon. Disamping kelebihannya dalam hal fleksibilitas bahan bakar dan emisi yang lebih rendah, kekurangan CFB boiler adalah potensi erosi yang tinggi pada dinding furnace dan siklon akibat tumbukan partikel pasir sepanjang kondisi operasi. Sirkulasi partikel padat di dalam sistem CFB menyebabkan kondisi hidrodinamiknya berbeda dan unik dibanding jenis boiler lainnya, sedangkan salah satu faktor yang memengaruhinya adalah rasio udara primer/sekunder berdasarkan dua penelitian terdahulu. Metode CPFD dengan keunggulannya dalam memodelkan partikel sebagai fasa diskret masih jarang digunakan untuk mempelajari hidrodinamik pada CFB boiler dan belum terdapat literatur mengenai rasio udara pirmer/sekunder dengan menggunakan metode ini. Berdasarkan hal tersebut perlu dilakukan studi terkait pengaruh rasio PA/SA terhadap aliran multifasa furnace CFB boiler. Penelitian ini dilakukan menggunakan simulasi numerik CPFD. Simulasi dilakukan dengan empat variasi rasio PA/SA yaitu: 80/20, 70/30, 65/35, 60/40. Pemodelan aliran gas-padat pada metode ini merupakan pendekatan Eulerian-Lagrangian dengan model turbulen Large Eddy Simulation, model drag WenYu-Ergun, kondisi transien, reaksi pembakaran on, serta rasio 1:1 untuk model geometri furnace CFB boiler. Penelitian dilakukan dengan menganalisis hasil simulasi yang berupa distribusi fraksi volume partikel, kecepatan sumbu-z gas, kecepatan sumbu-z partikel, tekanan, temperatur, penyerapan panas, serta indeks erosi. Hasil simulasi menunjukkan rasio PA/SA berpengaruh terhadap aliran multifasa di dalam furnace CFB boiler. Fraksi volume partikel secara aksial lebih besar di ketinggian sebelum SA pada rasio 60/40 dan rasio 80/20 mengakibatkan lebih sedikit partikel di bagian bawah furnace. Fraksi volume partikel secara lateral berbentuk struktur core-annulus. Partikel bergerak naik di tengah dan turun di pinggir furnace menyebabkan sirkulasi internal dimana rasio PA/SA dengan proporsi udara primer lebih banyak menyebabkan partikel bergerak naik di tengah dan turun di pinggir furnace secara lebih cepat sehingga terjadi sirkulasi internal yang lebih tinggi. Temperatur furnace yang lebih tinggi disebabkan partikel baik pasir maupun batu bara terfluidisasi lebih baik pada rasio dengan proporsi udara primer yang lebih banyak. Kenaikan proporsi udara primer dapat meningkatkan perpindahan panas dari bed ke dinding. Pada ketinggian 9 m erosi lebih tinggi pada rasio dengan proporsi udara primer yang lebih sedikit sedangkan di ketinggian 12 m, 15 m, dan 18 m erosi lebih tinggi terjadi pada rasio dengan proporsi udara primer yang lebih banyak. Secara rata-rata rasio 60/40 mengalami peningkatan erosi sebesar 34% terhadap rasio eksisting sedangkan pada ketinggian 12 m, 15 m, dan 18 m rasio 80/20 mengalami peningkatan erosi sebesar 3.4%, 10.2%, dan 8.9% secara berturut-turut
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Circulating Fluidized Bed (CFB) Boiler is a steam boiler that operates under specific hydrodynamic conditions, namely, the presence of solid particle circulation within the furnace and cyclone. Despite its advantages in fuel flexibility and lower emissions, one of the drawbacks of CFB boilers is the potential for high erosion on the furnace and cyclone walls due to the collision of sand particles during operation. The solid particle circulation in the CFB system results in unique and distinct hydrodynamic conditions compared to other types of boilers, where one influencing factor is the primary/secondary air ratio based on two previous studies. The Computational Particle Fluid Dynamics (CPFD) method, which excels in modeling particles as discrete phases, has been rarely employed to investigate the hydrodynamics of CFB boilers, and there is currently no literature on the application of this method to study the primary/secondary air ratio. Given these circumstances, there is a need for a study concerning the influence of the PA/SA ratio on the multiphase flow in the CFB boiler furnace. This research was conducted using Computational Particle Fluid Dynamics (CPFD) numerical simulations. The simulations were performed with four cases of the PA/SA ratio: 80/20, 70/30, 65/35, and 60/40. The gas-solid flow modeling in this method employed an Eulerian-Lagrangian approach with Large Eddy Simulation for turbulent modeling, the WenYu-Ergun drag model, transient conditions, combustion reactions enabled, and a 1:1 ratio for the CFB boiler furnace geometry model. The study involved analyzing the simulation results, which included the distribution of particle volume fractions, gas axial velocity, particle axial velocity, pressure, temperature, heat absorption, and erosion indices. The simulation results demonstrate that the PA/SA ratio significantly influences the multiphase flow within the CFB boiler furnace. The axial volume fraction of particles is higher at the height before SA in the 60/40 and 80/20 ratios, resulting in fewer particles at the bottom of the furnace. Laterally, the particle volume fraction forms a core-annulus structure. The particles move upwards in the central region and downwards at the furnace edges, leading to internal circulation, where a higher PA/SA ratio with a larger proportion of primary air causes faster upward movement in the central region and quicker downward movement at the furnace edges, resulting in increased internal circulation. The higher furnace temperature is attributed to better fluidization of both sand and coal particles in ratios with a higher proportion of primary air. An increase in the proportion of primary air enhances heat transfer from the bed to the walls. At a height of 9 m, erosion is higher in ratios with a smaller proportion of primary air, while at heights of 12 m, 15 m, and 18 m, higher erosion occurs in ratios with a larger proportion of primary air. On average, the 60/40 ratio experiences a 34% increase in erosion compared to the existing ratio, while at heights of 12 m, 15 m, and 18 m, the 80/20 ratio experiences an increase in erosion of 3.4%, 10.2%, and 8.9% respectively."

Item Type:	Thesis (Other)
Uncontrolled Keywords:	CPFD, furnace CFB boiler, multifasa, rasio PA/SA; CFB boiler furnace, multiphase, PA/SA ratio
Subjects:	T Technology > TJ Mechanical engineering and machinery > TJ263.5 Boilers (general)
Divisions:	Faculty of Industrial Technology and Systems Engineering (INDSYS) > Mechanical Engineering > 21201-(S1) Undergraduate Thesis
Depositing User:	Hilmi Alfaruqy
Date Deposited:	18 Sep 2023 11:18
Last Modified:	18 Sep 2023 11:18
URI:	http://repository.its.ac.id/id/eprint/100834

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