Studi Numerik Pengaruh Diameter Bed Particle Terhadap Karakter Fluidisasi dan Tingkat Erosi pada CFB Boiler

Putra, Andika Mandala (2023) Studi Numerik Pengaruh Diameter Bed Particle Terhadap Karakter Fluidisasi dan Tingkat Erosi pada CFB Boiler. Other thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Pada penelitian ini, boiler yang menjadi objek penelitian yaitu boiler pada PLTU X berkapasitas 100 MW yang merupakan jenis circulating fluidized bed (CFB) boiler. CFB boiler merupakan salah satu sub-kategori boiler dari fluidized bed boiler. Boiler ini menggunakan media pasir yang disirkulasikan oleh umpan udara yang dimasukkan ke dalam furnace. Panas yang dihasilkan oleh pembakaran batubara di dalam furnace akan diserap oleh partikel pasir kemudian didistribusikan pada seluruh bagian furnace. Hal tersebut mengakibatkan CFB boiler memiliki kapasitas termal yang tinggi dan dapat menghasilkan tekanan steam yang tinggi. Fleksibilitas bahan bakar serta efisiensi pembakaran menjadi keunggulan jenis boiler ini. Terdapat sejumlah masalah pada boiler ini, yaitu terjadinya penurunan tekanan steam bahkan saat boiler bekerja hingga mendekati 100 MW. Penambahan komponen AAB mengakibatkan penurunan tingkat erosi sekaligus menurunkan kemampuan penyerapan panas oleh dinding furnace. Akan dilakukan investigasi untuk sejumlah varian ukuran diameter partikel pasir, yaitu 0.25 mm, 0.30 mm, 0.36 mm, dan 0.40 mm (Geldart group-type B). Investigasi ukuran partikel pasir dilakukan untuk melihat pengaruh terhadap tingkat erosi serta kemampuan dalam perpindahan panas pada dinding boiler. Penelitian dilakukan menggunakan metode CPFD MP-PIC pada skala geometri 1:1 untuk bagian furnace. Penelitian dilakukan dengan menganalisis sejumlah hasil simulasi yang berupa distribusi tekanan, laju erosi, fraksi volume partikel, kecepatan gas, dan temperatur. volume partikel, kecepatan vertikal udara, kecepatan vertikal partikel, laju sirkulasi eksternal, potensi erosi melalui parameter impact, temperatur udara, dan laju perpindahan panas. Dari hasil simulasi diperoleh bahwa diameter bed particle mempengaruhi distribusi tekanan pada ruang bakar. Peningkatan diameter bed particle akan menyebabkan peningkatan pressure drop lebih tinggi pada lower furnace. Konsentrasi partikel yang lebih tinggi pada bagian middle furnace untuk diameter bed particle berukuran lebih rendah akan menyebabkan peningkatan nilai tekanan di dalam ruang bakar. Pada kondisi fluidisasi minimum, bed particle berukuran lebih kecil akan memiliki kemampuan ekspansi yang rendah disebabkan interaksi antar partikel yang besar. Pada kondisi dimana partikel berada pada kondisi fluidisasi yang stabil, peningkatan diameter bed particle akan mengakibatkan peningkatan fraksi volume partikel pada lower furnace dan penurunan fraksi volume partikel pada upper furnace. Peningkatan diameter bed particle akan menyebabkan kecepatan partikel mengalami penurunan akibat gaya drag yang lebih kecil. Pada sisi kecepatan udara, peningkatan diameter bed particle akan menyebabkan kecepatan udara meningkat akibat penurunan gaya drag. Peningkatan diameter bed particle mengakibatkan zona sirkulasi internal pada lower furnace mengecil. Pada keseluruhan variasi, regime fluidisasi untuk seluruh variasi diameter bed particle berada pada regime turbulen. Peningkatan diameter bed particle mengakibatkan penurunan nilai impact secara keseluruhan akibat penurunan laju sirkulasi eksternal. Secara umum, fraksi volume partikel pada area dinding memiliki kontribusi paling besar terhadap nilai impact pada dinding furnace. Secara khusus pada dinding wingwall, kontribusi fraksi volume partikel dan kecepatan vertikal partikel pada area dinding memiliki kontribusi yang sama-sama besar terhadap nilai impact. Peningkatan diameter bed particle mengakibatkan penurunan temperatur udara di dalam ruang bakar. Hal ini diakibatkan pengurangan area sirkulasi internal sehingga proses mixing tidak terjadi dengan optimal. Penurunan diameter bed particle mengakibatkan penurunan laju perpindahan panas. Hal ini disebabkan area sirkulasi yang mengecil sehingga proses pembakaran tidak optimal. Nilai rasio luasan area terhadap volume partikel yang lebih tinggi pada diameter bed particle yang lebih kecil mengakibatkan area transfer panas meningkat.
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In this study, the object of research is the boiler at Power Plant-X with a capacity of 100 MW, which is a type of circulating fluidized bed (CFB) boiler. CFB boiler is one of the sub-categories of fluidized bed boilers. This boiler uses sand as the circulating medium, which is fed with air into the furnace. The heat generated by coal combustion in the furnace is absorbed by the sand particles and then distributed throughout the furnace. This results in the CFB boiler having a high thermal capacity and can produce high steam pressure. The flexibility of fuel and combustion efficiency are advantages of this type of boiler. However, there are several issues with this boiler, including a decrease in steam pressure even when operating close to 100 MW. The addition of component AAB causes a reduction in erosion rates while also decreasing the heat absorption capability by the furnace walls. An investigation will be conducted on several variants of sand particle diameter sizes, namely 0.25 mm, 0.30 mm, 0.36 mm, and 0.40 mm (Geldart group-type B). The investigation of sand particle sizes aims to observe their effects on erosion rates and heat transfer capabilities on the boiler walls. The research will be conducted using the CPFD MP-PIC method at a 1:1 geometric scale for the furnace section. The study will analyze several simulation results, including pressure distribution, erosion rate, particle volume fraction, gas velocity, and temperature. The simulation results were analyzed based on several parameters, including pressure in the furnace, particle volume fraction, vertical air velocity, vertical particle velocity, external circulation rate, erosion potential through impact parameter, air temperature, and heat transfer rate. From the simulation results, it was found that the diameter of the bed particles affects the pressure distribution in the combustion chamber. An increase in the diameter of the bed particles leads to a higher pressure drop in the lower furnace. Higher particle concentration in the middle furnace for smaller bed particle diameters results in increased pressure values inside the combustion chamber. At minimum fluidization conditions, smaller bed particles exhibit low expansion capability due to significant particle interactions. Under stable fluidization conditions, an increase in bed particle diameter leads to a higher particle volume fraction in the lower furnace and a decrease in the upper furnace. The larger bed particle diameter causes a reduction in particle velocity due to a smaller drag force. As for the air velocity, an increase in bed particle diameter leads to an increase in air velocity due to reduced drag force. The larger bed particle diameter causes the internal circulation zone in the lower furnace to become smaller. Throughout the variations, the fluidization regime for all bed particle diameter variations is in the turbulent regime. An increase in bed particle diameter results in an overall decrease in impact value due to a reduction in the external circulation rate. In general, the particle volume fraction on the wall area has the most significant contribution to the impact value on the furnace walls. Specifically, on the wingwall, both the particle volume fraction and the vertical particle velocity on the wall area contribute significantly to the impact value. Increasing the bed particle diameter results in a decrease in air temperature inside the combustion chamber. This is due to the reduction in internal circulation area, leading to suboptimal mixing processes. Decreasing the bed particle diameter leads to a reduction in the heat transfer rate. This is caused by a smaller circulation area, which hinders the combustion process from being optimal. A higher value of the area-to-volume ratio for smaller bed particle diameters leads to increased heat transfer areas..

Item Type:	Thesis (Other)
Uncontrolled Keywords:	CFB boiler, Diameter bed particle, Erosi dinding furnace; CFB boiler, Bed particle diameter, Furnace wall erosion
Subjects:	T Technology > T Technology (General) > T57.62 Simulation T Technology > TJ Mechanical engineering and machinery > TJ254.7 Combustion chambers 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:	Andika Mandala Putra
Date Deposited:	10 Oct 2023 04:15
Last Modified:	10 Oct 2023 04:15
URI:	http://repository.its.ac.id/id/eprint/102937

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