Kurniawan, Rizky Ryan (2022) Analisa Numerik Pengaruh Ketebalan & Konduktivitas Slag Terhadap Terhadap Performa Plant & Tegangan Termal Pada Tube Superheater. Other thesis, Institut Teknologi Sepuluh Nopember.
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Abstract
Belakangan ini berbagai pembangkit listrik tenaga uap (PLTU) di Indonesia berusaha untuk menurunkan biaya pokok produksi (BPP) guna meningkatkan profit perusahaan. Salah satu cara yang dilakukan adalah dengan melakukan coal switch pada boiler menjadi low-rank coal. Salah satu karakteristik low-rank coal adalah rendahnya ash fusion temperature (AFT), sehingga hal ini menyebabkan semakin mudahnya terjadi fenomena slagging pada tube boiler. Slag deposit pada boiler bertindak sebagai insulator pada tube, sehingga menurunkan nilai perpindahan panas dari flue gas ke steam. Selain itu, dengan adanya slagging yang hanya menutupi bagian bawah dari tube menyebabkan tingginya temperature gradient pada metal pipa pada bagian yang tidak tertutupi slagging sehingga berpotensi menimbulkan tegangan termal. Hal ini melatarbelakangi dilakukannya analisis terhadap pengaruh ketebalan slagging terhadap perpindahan panas pada boiler, performa plant, dan thermal stress secara khusus pada bagian superheater divisional panelet (SHDP).
Tugas akhir ini menggunakan perangkat lunak ANSYS FLUENT dan Cycle Tempo untuk melakukan simulasi pada SHDP. Pemodelan simulasi pada penelitian ini yaitu SHDP dimodelkan sebagai tube, dimana tube akan dilewati flue-gas dengan geometri boiler diatas nose. Simulasi aliran dilakukan dengan memodelkan boiler dengan skala dan bentuk sebenarnya pada bagian atas nose. Variasi yang dilakukan pada penelitian ini meliputi ketebalan slag yaitu 0, 2 mm, 4 mm pada ketebalan slagging yang tipis, dan 3 cm pada kasus slagging yang tebal. Nilai konduktivitas pada slagging yaitu 0.4 W/m.K dan 0.7 W/m.K. Output dari simulasi adalah karakteristik perpindahan panas akibat perbedaan ketebalan slagging, nilai laju perpindahan panas yang nantinya digunakan untuk menghitung perbedaan temperatur superheated steam dan penurunan daya pembangkit akibat adanya slagging, dan distribusi temperature metal pipa yang kemudian dihitung menjadi tegangan termal.
Peningkatan ketebalan slagging menyebabkan penurunan koefisien konveksi eksternal dan laju perpindahan panas. Akibat berkurangnya laju perpindahan panas, temperature superheat dan daya turbin juga mengalami penurunan yang semula bernilai 598.5 MW menjadi 587.3 MW pada variasi slag tebal dan konduktivitas rendah. Penurunan konduktivitas lapisan slagging juga menyebabkan penurunan laju perpindahan panas dan daya turbin. Penurunan konduktivitas slagging menyebabkan meningkatnya temperatur luar slagging dengan ketebalan yang sama, akibatnya slagging akan semakin mudah menempel di permukaan tube dikarenakan abu batu bara menjadi lebih mudah mencair. Pada kasus ketebalan slagging 3 cm dan konduktivitas 0.4 W/m.K, terjadi tegangan termal sebesar 1.3 MPa. Besarnya tegangan termal masih dalam batas aman dikarenakan jauh lebih rendah dibandingkan yield strength dari material. Pada kasus yang sama terjadi penambahan penggunaan batu bara sebesar 0.3 kg/s guna mempertahankan daya turbin seperti semula, akibatnya terjadi potensi peningkatan temperature outlet flue gas pada SHDP sebesar 13-69°C, dimana hal ini berpotensi menyebabkan overheating pada heating part berikutnya.
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Recently, various steam power plants (PLTU) in Indonesia are trying to reduce the cost of production in order to increase company profits. One way to do this is to switch the coal on the boiler to low-rank coal. One of the characteristics of low-rank coal is the low ash fusion temperature (AFT), so this makes it easier for the slagging phenomenon to occur in tube boilers. Slag deposits in the boiler act as an insulator in the tubes, thereby reducing the value of heat transfer from flue gas to steam. In addition, the presence of slagging that only covers the bottom of the tube causes a high-temperature gradient in the metal pipe on the part that is not covered by slagging, so it has the potential to cause thermal stress. Based on that background, this research will analyze the effect of slagging thickness on heat transfer in the boiler, plant performance, and thermal stress in particular on the superheater divisional panel (SHDP) section.
This final project uses ANSYS FLUENT and Cycle Tempo software to perform simulation on SHDP. The simulation modeling in this study is SHDP is modeled as a tube, where the tube will be passed by flue-gas with the boiler geometry above the nose. Flow simulation is done by modeling the boiler with the actual scale and shape at the top of the nose. The variations carried out in this study include the slag thickness of 0.2 mm, 4 mm in the thin slagging thickness, and 3 cm in the thick slagging case. The conductivity values for slagging are 0.4 W/m.K and 0.7 W/m.K. The output of the simulation is the characteristics of heat transfer due to the difference in slagging thickness, the value of the heat transfer rate which will be used to calculate the difference in temperature of superheated steam and the decrease in generating power due to slagging, and the distribution of pipe metal temperature which is then calculated as thermal stress.
The increase in slagging thickness causes a decrease in the coefficient of external convection and the rate of heat transfer. Due to the reduced heat transfer rate, superheat temperature and turbine power also decreased from 598.5 MW to 587.3 MW in thick slag variations and low conductivity. The decrease in the conductivity of the slagging layer also causes a decrease in the heat transfer rate and turbine power. The decrease in slagging conductivity causes an increase in the outer temperature of the slagging with the same thickness, as a result, the slagging will be easier to stick to the tube surface because the coal ash becomes easier to melt. In the case of a slagging thickness of 3 cm and a conductivity of 0.4 W/m.K, the thermal stress of 1.3 MPa occurs. The amount of thermal stress is still within safe limits because it is much lower than the yield strength of the material. In the same case, there was an increase in the use of coal of 0.3 kg/s in order to maintain the turbine power as before, as a result, there was a potential increase in the flue gas outlet temperature at SHDP by 13-69°C, where this has the potential to cause overheating in the next heating part.
| Item Type: | Thesis (Other) |
|---|---|
| Uncontrolled Keywords: | Boiler, CFD, Daya, Panas, Slag |
| Subjects: | Q Science > QC Physics > QC320 Heat transfer T Technology > TJ Mechanical engineering and machinery T Technology > TJ Mechanical engineering and machinery > TJ164 Power plants--Design and construction T Technology > TJ Mechanical engineering and machinery > TJ263 Heat exchangers T Technology > TJ Mechanical engineering and machinery > TJ263.5 Boilers (general) T Technology > TJ Mechanical engineering and machinery > TJ265.E23 Thermodynamics. |
| Divisions: | Faculty of Industrial Technology and Systems Engineering (INDSYS) > Mechanical Engineering > 21201-(S1) Undergraduate Thesis |
| Depositing User: | Rizky Ryan Kurniawan |
| Date Deposited: | 08 Feb 2022 04:14 |
| Last Modified: | 17 Oct 2024 05:01 |
| URI: | http://repository.its.ac.id/id/eprint/93012 |
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