Rohmah, Aisyah Alifatul Zahidah (2026) Studi Efisiensi Penggunaan Bahan Baku Biomassa Dalam Bentuk Pellet Dan Serbuk Dalam Proses Co-Firing Batubara Serta Kajian Efektifitas Penggunaan CaCO3 Dalam Pengendalian Slagging-Fouling Pada Proses Pembakaran Di Boiler. Doctoral thesis, Institut Teknologi Sepuluh Nopember.
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Abstract
Penggunaan batu bara dalam pembangkit listrik masih menjadi penyumbang utama emisi gas rumah kaca serta menyebabkan berbagai permasalahan operasional, seperti slagging dan fouling pada sistem boiler. Salah satu pendekatan yang banyak dikembangkan untuk menekan dampak lingkungan tersebut adalah melalui teknologi co firing, yaitu pembakaran bersama antara batu bara dan biomassa. Dalam penelitian ini, biomassa digunakan dalam dua bentuk fisik berbeda, yaitu serbuk dan pelet, untuk dievaluasi kinerjanya terhadap efisiensi pembakaran, emisi gas buang (SO₂, CO, NOx), serta potensi pembentukan slagging dan fouling. Selain itu, penelitian ini juga mengkaji efektivitas penambahan kalsium karbonat (CaCO₃) sebagai aditif dalam menekan risiko slagging dan fouling, serta mekanisme reaksinya dalam mengurangi emisi gas buang. Metode penelitian meliputi uji karakterisasi bahan bakar (nilai kalor, kadar abu, indeks alkali, dan Ash Fusion temperature/AFT), pengukuran efisiensi termal boiler, analisis emisi gas buang, serta analisis slagging dan fouling berdasarkan indeks prediktif. Variasi bahan bakar diuji dalam bentuk campuran antara batu bara dan biomassa dengan rasio tertentu, baik pada biomassa serbuk maupun pelet, dengan dan tanpa penambahan CaCO₃ sebagai bahan aditif. Hasil karakterisasi menunjukkan bahwa biomassa serbuk memiliki nilai kalor tertinggi pada sawdust (4.492 kkal/kg) dan terendah pada sekam padi (3.633 kkal/kg). Nilai Alkali Indeks (Alk) tertinggi dimiliki oleh cocopeat (0,346), menandakan potensi fouling yang tinggi, sedangkan sawdust memiliki nilai terendah (0,0369). Ash Fusion Temperature (AFT) pada cocopeat serbuk mencapai 957°C, mengindikasikan kecenderungan pembentukan slagging yang lebih tinggi dibandingkan jenis biomassa lainnya. Dari aspek emisi gas buang, hasil menunjukkan bahwa biomassa dalam bentuk pelet menghasilkan emisi yang lebih rendah dibandingkan biomassa serbuk. Campuran serbuk biomassa (50% sekam padi, 40% sawdust, dan 10% cocopeat) menghasilkan emisi CO tertinggi sebesar 885 mg/Nm³, sedangkan pelet 100% sawdust menghasilkan emisi CO jauh lebih rendah, yaitu 418 mg/Nm³. Pada pembakaran batu bara murni, emisi SO₂ mencapai 7,82 mg/Nm³, namun setelah dilakukan pencampuran dengan biomassa dan penambahan ekses udara, nilai emisi SO₂ turun drastis hingga 0,1 mg/Nm³. Emisi NOx pada pelet biomassa sebesar 209 mg/Nm³, lebih rendah dibandingkan serbuk biomassa (312 mg/Nm³). Dari sisi efisiensi termal, performa terbaik dicapai oleh campuran 95% batu bara dan 5% sawdust, baik dalam bentuk serbuk maupun pelet, dengan efisiensi tertinggi 74,40%. Namun demikian, biomassa dalam bentuk pelet menunjukkan kestabilan pembakaran yang lebih baik, laju pembakaran yang lebih merata, dan kadar kehilangan panas lebih rendah dibandingkan serbuk. Sebaliknya, biomassa serbuk lebih mudah mengalami fluktuasi suhu dan incomplete combustion, terutama pada jenis sekam padi yang memiliki kadar abu tinggi. Dari aspek potensi slagging dan fouling, serbuk sawdust dan cocopeat memiliki indeks slagging yang tinggi masing-masing 957 dan 999, yang menunjukkan potensi pembentukan kerak signifikan pada dinding boiler. Sementara itu, bentuk pelet menunjukkan kecenderungan slagging-fouling yang lebih rendah karena proses peletisasi menghasilkan bahan bakar yang lebih homogen dan densitas tinggi, sehingga pembakaran berlangsung lebih sempurna dan stabil. Karakterisasi fisik dan kimia pelet biomassa dibandingkan dengan SNI 8675:2018 menunjukkan bahwa sebagian besar parameter telah memenuhi standar. Nilai durability berada pada rentang 0,627 – 5,783 N/mm² (standar minimal 1,733 N/mm²), densitas berada pada rentang 1,042 – 1,464 g/cm³ (memenuhi standar minimal 0,8 g/cm³), ukuran pelet berada pada diameter 9,4 – 11 mm dan panjang 7,66 – 27,1 mm, sesuai dengan standar SNI (6 – 12 mm dan 3,15 – 40 mm). Namun, kadar klor (Cl) dan sulfur (S) pada beberapa sampel masih melampaui batas standar, sehingga berpotensi meningkatkan emisi gas SO₂ jika tidak dikendalikan dengan bahan aditif. Penambahan CaCO₃ terbukti efektif dalam menekan slagging, fouling, dan menurunkan emisi gas buang. Mekanisme reduksi slagging dan fouling terjadi melalui reaksi antara CaCO₃ dan SiO₂ membentuk CaSiO₃, senyawa dengan titik leleh tinggi yang mencegah pembentukan kerak. Selain itu, CaCO₃ juga bereaksi dengan SO₃ membentuk CaSO₄, yang lebih stabil dan mudah mengendap sebagai bottom ash, bukan sebagai fly ash. Dalam pengendalian emisi, CaCO₃ terdekomposisi menjadi CaO yang mengikat SO₂ membentuk CaSO₄, sehingga menurunkan pelepasan gas sulfur ke atmosfer. Selain itu, reaksi pembentukan Ca(NO₃)₂ dari interaksi CaCO₃ dengan NOx turut membantu menekan emisi NOx di udara. Secara keseluruhan, hasil penelitian ini menunjukkan bahwa penggunaan biomassa dalam bentuk pelet lebih unggul dibandingkan serbuk dalam aspek efisiensi pembakaran, kestabilan termal, serta pengurangan emisi gas buang. Sementara itu, penambahan CaCO₃ sebagai aditif terbukti menjadi pendekatan efektif untuk mengurangi potensi slagging dan fouling, sekaligus meningkatkan efisiensi perpindahan panas dan kinerja boiler. Dengan demikian, kombinasi co-firing pelet biomassa dan aditif CaCO₃ dapat diterapkan pada skala industri untuk mendukung transisi energi bersih dan pengurangan emisi karbon di sektor pembangkit listrik.==================================================================================================================================
The use of coal in power generation remains a major contributor to greenhouse gas emissions and causes various operational problems, such as slagging and fouling in boiler systems. One widely developed approach to mitigate these environmental impacts is co-firing technology, which involves the simultaneous combustion of coal and biomass. In this study, biomass was utilized in two different physical forms, namely powder and pellets, to evaluate their performance in terms of combustion efficiency, flue gas emissions (SO₂, CO, and NOx), and the potential formation of slagging and fouling. In addition, this research investigated the effectiveness of calcium carbonate (CaCO₃) as an additive in reducing slagging and fouling risks, as well as its reaction mechanisms in lowering gaseous emissions. The research methodology included fuel characterization tests (calorific value, ash content, alkali index, and ash fusion temperature/AFT), measurement of boiler thermal efficiency, analysis of flue gas emissions, and evaluation of slagging and fouling based on predictive indices. Fuel variations were tested in the form of coal–biomass mixtures at specific ratios, using both powdered and pelletized biomass, with and without the addition of CaCO₃ as an additive. The characterization results showed that powdered biomass exhibited the highest calorific value for sawdust (4,492 kcal/kg) and the lowest for rice husk (3,633 kcal/kg). The highest Alkali Index (Alk) was observed in cocopeat (0.346), indicating a high fouling potential, while sawdust had the lowest value (0.0369). The ash fusion temperature (AFT) of powdered cocopeat reached 957°C, indicating a higher tendency for slagging formation compared to other biomass types. In terms of flue gas emissions, the results demonstrated that pelletized biomass produced lower emissions than powdered biomass. A powdered biomass mixture (50% rice husk, 40% sawdust, and 10% cocopeat) generated the highest CO emission at 885 mg/Nm³, whereas 100% sawdust pellets resulted in a significantly lower CO emission of 418 mg/Nm³. For pure coal combustion, SO₂ emissions reached 7.82 mg/Nm³; however, after co-firing with biomass and increasing excess air, SO₂ emissions decreased drastically to 0.1 mg/Nm³. NOx emissions from biomass pellets were recorded at 209 mg/Nm³, lower than those from powdered biomass (312 mg/Nm³). From the thermal efficiency perspective, the best performance was achieved by a fuel mixture of 95% coal and 5% sawdust, in both powdered and pelletized forms, with a maximum efficiency of 74.40%. Nevertheless, pelletized biomass demonstrated better combustion stability, more uniform burning rates, and lower heat losses compared to powdered biomass. In contrast, powdered biomass was more prone to temperature fluctuations and incomplete combustion, particularly rice husk, which has a high ash content. Regarding slagging and fouling potential, powdered sawdust and cocopeat exhibited high slagging indices of 957 and 999, respectively, indicating a significant risk of deposit formation on boiler walls. Meanwhile, pelletized biomass showed a lower tendency toward slagging and fouling due to the pelletization process, which produces a more homogeneous fuel with higher density, resulting in more stable and complete combustion. The physical and chemical characteristics of biomass pellets were compared with the Indonesian National Standard SNI 8675:2018, revealing that most parameters met the required standards. Durability values ranged from 0.627 to 5.783 N/mm² (minimum standard: 1.733 N/mm²), density ranged from 1.042 to 1.464 g/cm³ (meeting the minimum standard of 0.8 g/cm³), and pellet dimensions ranged from 9.4 to 11 mm in diameter and 7.66 to 27.1 mm in length, complying with the SNI requirements (6–12 mm diameter and 3.15–40 mm length). However, chlorine (Cl) and sulfur (S) contents in several samples exceeded the standard limits, potentially increasing SO₂ emissions if not controlled using additives. The addition of CaCO₃ proved effective in suppressing slagging and fouling and in reducing gaseous emissions. The mechanism of slagging and fouling reduction occurs through the reaction between CaCO₃ and SiO₂ to form CaSiO₃, a compound with a high melting point that prevents deposit formation. In addition, CaCO₃ reacts with SO₃ to form CaSO₄, which is more stable and preferentially settles as bottom ash rather than fly ash. For emission control, CaCO₃ decomposes into CaO, which captures SO₂ to form CaSO₄, thereby reducing sulfur gas release into the atmosphere. Furthermore, the formation of Ca(NO₃)₂ from the interaction between CaCO₃ and NOx contributes to the reduction of NOx emissions. Overall, the results of this study indicate that biomass in pelletized form is superior to powdered biomass in terms of combustion efficiency, thermal stability, and flue gas emission reduction. Meanwhile, the addition of CaCO₃ as an additive is demonstrated to be an effective approach to reducing slagging and fouling potential, while simultaneously enhancing heat transfer efficiency and overall boiler performance. Therefore, the combination of pelletized biomass co-firing and CaCO₃ additives can be applied at an industrial scale to support the transition toward cleaner energy and carbon emission reduction in the power generation sector.
| Item Type: | Thesis (Doctoral) |
|---|---|
| Uncontrolled Keywords: | boiler, CaCO3, cofiring biomassa, fouling, slagging, boiler, CaCO3, biomass cofiring, fouling, slagging |
| Subjects: | T Technology > TP Chemical technology > TP155.7 Chemical processes. |
| Divisions: | Faculty of Industrial Technology and Systems Engineering (INDSYS) > Chemical Engineering > 24001-(S3) PhD Thesis |
| Depositing User: | Aisyah Alifatul Zahidah Rohmah |
| Date Deposited: | 04 Feb 2026 08:04 |
| Last Modified: | 04 Feb 2026 08:04 |
| URI: | http://repository.its.ac.id/id/eprint/132132 |
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