STUDI PERBANDINGAN SIMULASI PROSES PEMBAKARAN BATUBARA DAN VINASSE METODE NON-PREMIX COMBUSTION MODEL

Abstrak-Vinasse merupakan limbah dari industri gula dengan debit yang sangat besar sehingga harus diolah dengan berbagai metode. Salah satu alternatif metode yang dapat digunakan adalah pembakaran. Pembakaran merupakan reaksi kimia yang memproduksi panas dan dapat digunakan sebagai suplai energi untuk proses selanjutnya. Berdasarkan analisis proksimat dan ultimat, vinasse memiliki karakteristik yang hampir sama dengan batubara setelah mengalami proses evaporasi. Penelitian ini mempelajari perbandingan dari karakteristik pembakaran antara batubara dan vinasse sebagai bahan bakar yang dilihat dari aspek distribusi temperatur, distribusi spesies, dan vektor kecepatan. Proses pembakaran dijalankan dengan metode computational fluid dynamics (CFD) khususnya model pembakaran non-premix. Geometri dari ruang bakar yang digunakan adalah 84 x 5,2 m dengan kualitas ortogonal mesh yang digunakan mendekati 1 dan bentuk cell segiempat 100 persen. Simulasi pembakaran dijalankan dengan geometri 2D (dua dimensi) dengan udara sebagai oksidator. Hasil dari simulasi menunjukkan bahwa vinasse memiliki potensi untuk digunakan sebagai bahan bakar alternatif karena lebih cepat terbakar dibandingkan dengan batubara serta karakteristik lain yang sedikit berbeda. Kata kunci : pembakaran, vinasse, batubara, CFD, non-premix Abstract-Vinasse as a sugarcane waste has large amount of debit that must be treated through various methods. One of the methods is combustion. Combustion is a chemical reaction that produced heat which is can be used as energy supply for further process. Vinasse according to proxymate and ultimate analysis has characteristic similar to coal after being evaporated. This paper is studied about the comparassion of combustion characteristic between vinasse and coal as a fuel in terms of temperature distribution, species distribution, and velocity vector. Combustion process conducted with computational fluid dynamics method especially non-premix combustion model. The geometry of furnace is 84 m x 5.2 m with the orthogonal quality of mesh is close to 1 and 100 percent of quad cells. The simulation of combustion process conducted in 2D (two dimensions) with air as oxydizer. The results of the simulation shows that vinasse were very potential to use as a fuel with quicker combustion compared to coal but with slightly different characteristic. Keywords : Combustion, vinasse, coal, CFD, non-premix

Behavior of Flame Propagation in Biogas Spark Ignited Premix Combustion with Carbon Dioxide Inhibitor

Biogas is a mixture of gases which commonly consists of methane (up to 50%) and other inhibitor gases which are dominated by carbon dioxide (up to 50%). Biogas is produced naturally by the decomposition of organic materials such as vegetation or animal manure in the absence of oxygen and it also contributes less greenhouse gases which may lead to global warming or climate change. The presence of carbon dioxide (CO2) in biogas is presumed to have some effects on biogas flame propagation characteristics. This study focuses on the effect of carbon dioxide (CO2) as the biggest inhibitor composition in biogas on flame propagation speed as the important flame propagation characteristic in spark ignited premix combustion. Propagating flames are employed to measure the flame propagation speed as a function of the mixture composition. This parameter was measured using a transparent tube fuel chamber with dimensions of 60 mm inner diameter and 300 mm height based on DIN 51649 standards and recorded by high speed digital photographic technique. The characteristic of biogas-oxygen flames were studied at stoichiometric, room temperature and atmospheric condition from 0% to 50% CO2 biogas inhibitor composition increased by 10% for each experiment. The results showed that the carbon dioxide decreases flame propagation speed of biogas. These indicated that carbon dioxide reduced reaction rate of biogas premixed combustion.

Modelling the Formation of Oxides of Nitrogen in Premix Combustion by Extending Tabulated Chemistry With Algebraic Relations

Models of finite rate combustion chemistry based on tabulation have been found to be efficient and accurate for a broad range of fuel and flame configurations. However, the modelling of formation of oxides of nitrogen remains a challenging issue. Even recent developments that take into account heat losses do not provide accurate prediction of NOx species despite a very good match for major species and temperature. The present paper introduces a model based on a chemical lookup-table for the NO formation rate in the preheat, initiation and fuel consumption region of a premix flame combined with algebraic relations in the post-flame area, thus reducing advantageously the tabulated information. This model is applied to a premixed laminar burner and compared to previous models based on tabulated chemistry.

Laminar Burning Velocity and Flammability Characteristics of Biogas in Spark Ignited Premix Combustion at Reduced Pressure

Biogas as a “Powergas” is an alternative fuel produced in digestion facilities, that is sustainable and renewable. Based on chemical analysis, the composition of the biogas produced in East Java is 66.4% methane, 30.6% carbon dioxide and 3% nitrogen. Methane is a flammable gas, whereas, nitrogen and carbon dioxide are inhibitors. Given it has a different composition to traditional fuels, a fundamental study of biogas flame propagation characteristics is desirable to quantify this important fuel property. Spherically expanding flames propagating at constant pressure are employed to measure the laminar burning velocity and flammability characteristics as mixture function of the mixture composition. These important parameters were measured using a photographic technique in a high pressure fan-stirred bomb. The characteristics of biogas-air flames were initially studied at reduced pressure and at various equivalence ratios from the lower flammable limit to the upper flammable limit. The results were compared with those from biogas-air flames at atmospheric pressure. Based on this experimental investigation, the laminar burning velocities of biogas-air mixtures at reduced pressure were 0.218 m/s for ϕ=0.75, 0.246 m/s for ϕ=0.80 and 0.269 m/s for ϕ=0.85 respectively and only for these biogas mixtures propagated at reduced pressure. At the same equivalence ratio (ϕ), the laminar burning velocities of the biogas-air mixtures at reduced pressure are higher than those at atmospheric pressure. The flammable region of biogas became narrower by reducing initial pressure. The dilution effect is stronger at reduced pressure. Therefore, the flammable composition mixture areas of biogas-air mixtures are more limited at reduced pressure than those at atmospheric pressure.