Numerical Analysis of Primary Air to Coal Ratio Variation on Water Wall Tube Temperature and Equivalent Stress

Callista, Vivi Bella (2023) Numerical Analysis of Primary Air to Coal Ratio Variation on Water Wall Tube Temperature and Equivalent Stress. Other thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Pada salah satu pembangkit listrik tenaga uap di Indonesia, terjadi kegagalan pada water tube di dinding boiler dengan bentuk retakan berupa fish mouth opening. Ini merupakan tanda dari kegagalan short-term overheating, yang terjadi ketika equivalent stress yang dialami oleh tube melebihi endurance limit dari material. Salah satu penyebab dari short-term overheating adalah flame impingement, yaitu kondisi Ketika api fireball menyentuh tube. Konfigurasi fireball dipengaruhi oleh rasio primary air terhadap coal (PA/coal). Oleh karena itu, analisis numerik variasi PA/coal terhadap temperatur dan equivalent stress pada water wall tube dilakukan. Rasio primary air terhadap coal terdiri atas 1, 2, 3, 4, dan 4,5. Variasi posisi water wall tube terdiri atas di tengah dinding dan di dekat burner. Data diambil pada ketinggian burner C. Perangkat lunak yang digunakan dalam penelitian ini adalah Ansys fluent, Ansys static structural, dan Ansys steady state thermal. Untuk PA/coal 2 hingga 4,5, semakin besar PA/coal, diameter fireball menjadi lebih besar. Panas radiasi dan konveksi lebih banyak diterima oleh water wall, menyebabkan peningkatan temperature water wall tube. Flame impingement terjadi pada PA/coal 4,5. Sementara itu, pada PA/coal 1, fireball hampir menyentuh water wall tube. Pada PA/coal 1, partikel batubara hampir tidak mendapatkan cukup oksigen dari primary air untuk pembakaran awal, menyebabkan pembakaran batubara yang buruk. Temperatur water wall maksimum terjadi pada PA/coal 4,5, dengan nilai 580,25oC di tengah dinding. Perbedaan tube temperatur maksimum terjadi pada PA/coal 4,5, dengan nilai 93,68oC untuk posisi tengah dinding. Perbedaan temperatur yang lebih besar pada tube menyebabkan peningkatan tegangan termal, yang sangat tergantung pada perbedaan temperatur maksimum dan minimum pada tube. Ketika tegangan termal meningkat, equivalent stress juga akan meningkat. Equivalent stress maksimum pada tube terjadi pada sisi api bagian dalam. Equivalent stress maksimum terjadi pada PA/coal 4,5, dengan nilai 186.45 Mpa untuk posisi tengah dinding. Perbedaan temperatur dan equivalent stress tube pada tengah dinding lebih tinggi daripada posisi dekat burner. Kondisi dengan equivalent stress di atas endurance limit adalah PA/coal 4,5 di tengah dinding dan dekat burner serta PA/coal 1 di tengah dinding
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At one of steam power plants in Indonesia, there was water tubes failure at furnace side wall with a fish mouth opening crack. This is a sign of short-term overheating, which happens when the equivalent stress experienced by the tube surpasses the endurance limit of the material. One of the causes of short-term overheating is flame impingement, which is the condition of the flame touching the tube. The fireball configuration is influenced by primary air to coal ratio (PA/coal). Therefore, a numerical analysis of PA/coal variation on water wall tube temperature and equivalent stress was explored. The primary air to coal ratio was 1, 2, 3, 4 and 4.5. The variation of water wall tube position was in the middle of the wall and near burner. The data was taken at burner C elevation. Software used in this study were Ansys fluent, Ansys static structural, and Ansys steady state thermal. For PA/coal 2 to 4.5, as PA/ coal increases, the diameter of fireball becomes bigger. More radiant and convective heat transfer is received by the water wall, causing a rise in water wall tube temperature. Flame impingement occurs at PA/coal 4.5. While PA/coal 1, the fireball almost impinges the water wall tube. For PA/coal 1, coal particles hardly obtain enough oxygen from primary air to support initial combust, causing deteriorated coal combustion. The maximum water wall temperature is at PA/coal 4.5, with values of 580.25oC at middle of the wall. The maximum tube temperature difference is at PA/coal 4.5, with values of 93.68oC for middle of the wall position. Bigger temperature difference on the tube causes an increase in thermal stress, as it depends heavily on temperature maximum and minimum on tube. As the thermal stress increases, the equivalent stress would increase too. The maximum equivalent stress on tube occurred at inner flame side. The maximum equivalent stress is at PA/coal 4.5, with values of 186.45Mpa for middle of the wall position. The tube temperature difference and equivalent stress at the middle of the wall is higher than near burner position. The conditions that have equivalent stress above endurance limit or in finite life are PA/coal 4.5 at middle of the wall and near burner and PA/coal 1 middle at the middle of the wall.

Item Type:	Thesis (Other)
Uncontrolled Keywords:	Overheating, Water Wall Tube, PA/coal, Flame Impingement, Equivalent Stress
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:	Vivi Bella Callista
Date Deposited:	18 Sep 2023 10:05
Last Modified:	18 Sep 2023 10:05
URI:	http://repository.its.ac.id/id/eprint/102472

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