Geometry Effect Investigation on a Conical Chamber with Porous Media Boundary Condition Using Computational Fluid Dynamic (CFD) Technique

The present study is an attempt to introduce a method for optimizing the geometry of a unit process. The comprehensive unit process performances are generated by a CFD engine. The CFD engine can simulate the unit process performances at whatever conditions. Both design geometry and operating variables were used on the CFD simulation. The burden on a simplified process was taken out from CFD simulation. A complex geometry of a unit process is represented by a secondary reformer. A secondary reformer has a conical chamber as a space to undergo a combustion reaction before entering a catalyst bed. This complexity is added by the boundary on a porous solid surface as the top surface of the catalyst bed. The conical angle affects the flow pattern inside the conical chamber having a porous solid surface as its base. The conical angle above 65° results the disappearing of the recirculation flow. The inlet distance from the porous solid surface also can exhibit different characteristics of recirculation flow. The closer the distance to the porous solid surface, the stronger the recirculation is. The inlet velocity values have no significant effect on the flow pattern. The introduction of a solid volume inside the geometry creates distortion in the flow pattern. In the application, the inserted solid volume is equivalent to a burner. It means that the use of the burner inherently produces some problems of the flow distribution

New Correlations for Coal and Biomass Pyrolysis Performances with Coal-Biomass Type Number and Temperature

The pyrolysis of coal and biomass is generally reported as the mass yield of released chemicals at various temperatures, pressures, heating rates and coal or biomass type. In this work, a new coal-biomass type number, NCT, is introduced. This number is constructed from the mass fractions of carbon, hydrogen, and oxygen in the ultimate analysis. This number is unique for each coal or biomass type. For 179 different species of coal and biomass from the literature, the volatile matter mass yield can be expressed by the second order polynomial function ln(NCT). This unique correlation allows the effects of the temperature and heating rate on the volatile yield YVY for coal and biomass to be empirically correlated as well. The correlation for the mass fraction of each chemical component in the released volatile matter correlation is obtained from the YVY correlation. The weight factor for some of the components is constant for the variation of NCT, but not for others. The resulted volatile matter and yield correlations are limited to atmospheric pressure, very small particles (less than 0.212 mm) and interpreted for wire-mesh pyrolysis reactor conditions and a nitrogen gas environment

Geometry Effect Investigation on a Conical Chamber with Porous Media Boundary Condition Using Computational Fluid Dynamic (CFD) Technique

The present study is an attempt to introduce  a  method for optimizing the  geometry  of  a  unit  process.  The  comprehensive  unit  process  performances are generated by a  CFD engine. The CFD engine can simulate the unit process performances  at  whatever  conditions.  Both  design  geometry  and  operating variables were used on the CFD simulation. The burden on a simplified process was taken out from CFD simulation. A complex geometry of a unit process is represented  by  a  secondary  reformer.  A  secondary  reformer  has  a  conical chamber  as a space to undergo  a  combustion reaction before entering  a  catalyst bed. This complexity is added by the boundary  on a  porous solid surface as the top surface of  the catalyst bed. The  conical  angle affects the flow pattern inside the  conical chamber  having a porous solid surface as its  base. The  conical  angle above  65° results  the  disappearing  of  the recirculation  flow.  The  inlet  distance from  the  porous  solid  surface  also  can  exhibit  different  characteristics  of recirculation  flow.  The  closer  the  distance  to  the  porous  solid  surface,  the stronger the recirculation is. The inlet velocity values have no significant effect on  the  flow  pattern.  The  introduction  of  a  solid  volume  inside  the  geometry creates distortion in the flow pattern. In the application, the inserted solid volume is equivalent to a burner. It means that the use of the burner inherently produces some problems of the flow distribution

EFISIENSI PEMBAKARAN NYALA TURBULEN TAK-PRACAMPUR YANG DIPENGARUHI ANGIN SILANG DAN PENAMBAHAN STEAM

Artikel ini memaparkan hasil yang diperoleh dari dinamika fluida komputasi (DFK) untuk mensimulasi nyala turbulen tak pra-campur. Konfigurasi, diskretisasi dan kondisi batas nyala digambarkan menggunakan perangkat lunak pra-prosessor Gambit dan kalkulasi turbulensi dan pembakaran menggunakan perangkat lunak Fluent. Penelitian ini memfokuskan pada kajian pengaruh berbagai kecepatan angin silang dan penambahan steam terhadap karakteristik nyala hidrokarbon dan pengaruhnya terhadap efisiensi pembakaran yang dihasilkan. Model turbulensi yang digunakan pada penelitian ini adalah model k-ε standard dan model pembakaran Eddy Dissipasi.  Kajian dilakukan pada berbagai kecepatan angin silang yaitu 3,77 m/s, 7,5 m/s dan 10 m/s dan ratio steam terhadap bahan bakar 0,14, 0,25, dan 2,35 serta dilakukan pada kecepatan bahan bakar tetap 20 m/s. Hasil yang diperoleh ditampilkan dalam bentuk kontur temperatur dari berbagai kecepatan angin silang dan penambahan steam. Dari kontur tersebut terlihat bahwa besarnya nilai S yang diberikan pada berbagai kecepatan angin sangat mempengaruhi terhadap temperatur pembakaran yang dihasilkan, dimana dari hasil kontur tersebut dapat diketahui bahwa temperatur nyala menurun seiring peningkatan jumlah steam yang diberikan di dalam aliran bahan bakar, dan hal tersebut secara nyata terlihat pada nilai S yang besar (2,35). Efisiensi pembakaran pada berbagai kecepatan angin silang semakin menurun seiring bertambahnya ratio steam terhadap bahan bakar

Pengaruh Kadar Karbon pada Proses Gasifikasi

Investigasi proses gasifikasi dilakukan dengan pemodelan termodinamik. Kuantifikasi unjuk kerja proses gasifikasi dinyatakan dengan kadar H2 dan kadar CO dalam gas produser, temperatur dan efisiensi termal. Investigasi pengaruh kadar karbon terhadap unjuk kerja proses gasifikasi dilakukan dengan simulasi menggunakan batubara: lignit, bituminus dan antrasit. Ketiga jenis batubara diharapkan mewakili tingkatan kadar karbon. Kajian termodinamika digunakan sebagai piranti prediksi kinerja gasifikasi dan dapat melihat efek berbagai faktor secara cepat. Penyimpangan kinerja gasifier aktual terhadap hasil prediksi termodinamika sering ditemui dan biasanya dianggap sebagai akibat faktor-faktor teknis yang berhubungan dengan laju proses, misalnya pengontakan partikel dengan medium gasifikasi. Pada makalah ini, kajian termodinamika disempurnakan dengan melibatkan pemodelan dekomposisi batubara yang sangat tergantung pada jenis batubara dalam hal ini mewakili kadar karbon. Harapannya, pengabungan model dekomposisi batubara yang diusulkan dalam penelitian ini dan model kesetimbangan reaksi konvensional menghasilkan kajian termodinamika yang lebih rasional. Hasil dari kajian termodinamika digunakan sebagai piranti prediksi kinerja gasifikasi dengan mempertimbangkan kadar karbon batubara. Fraksi mol gas hidrogen maksimum yang dihasilkan lignit lebih tinggi daripada antrasit dan bituminus, berturut-turut 0,43 dan 0,25. Fraksi mol maksimum gas hidrogen dari lignit berada pada laju udara/batubara sekitar 1,2 kg/kg sedangkan antrasit dan bituminus berada pada sekitar 3 kg/kg. Temperatur proses gasifikasi, seperti diduga sangat dipengaruhi oleh jenis batubara. Sesuai dengan kadar H2, temperatur gasifikasi sebaiknya dijaga sekitar 1000 oC (Ru = 2,4 dan 4 berturut-turut untuk batubara lignit, antrasit dan bituminus). Keuntungan pada temperatur sekitar 1000 oC, tar secara praktis sudah terdekomposisi lebih lanjut, sehingga gas produser hanya sedikit mengandung tar

Development of Instant Microbial Starter for Production of Fermented Cassava Flour: Effect of Vacuum Drying Temperature, Carrier Media, and Storage Temperature

Cassava is an important crop for tropical countries such as Nigeria, Brazil, Thailand, and Indonesia. The potential utilization of cassava in the food industry can be enhanced by processing cassava into fermented cassava flour (fercaf), which has been shown to have a neutral color and aroma as well as low cyanogenic content. The use of specific microbial starter in the cassava chip fermentation for fercaf production will direct the fermentation process, maintaining a high quality of the produced flour. Thereby, the availability of an easy-to-use microbial starter is important for the production of fermented cassava flour. The aim of this study was to evaluate vacuum drying methods in the preparation of microbial starter for fermented cassava flour production. In particular, the effects of carrier media, drying and storage temperature on cell viability in dry starter were tested. The results showed that different methods should be applied to different microbial species. Bacillus subtilis and Aspergillus Oryza should be prepared using fercaf as the carrier media at a drying temperature of 55 °C, whereas Lactobacillus plantarum starter should be prepared using skim milk as the carrier media at a drying temperatur of 40°C. Apart from B. subtilis, the starters should be stored in a refrigerator

Dynamic Behavior of Reverse Flow Reactor for Lean Methane Combustion

The stability of reactor operation for catalytic oxidation of lean CH4 has been investigated through modeling and simulation, particularly the influence of switching time and heat extraction on reverse flow reactor (RFR) performance. A mathematical model of the RFR was developed, based on one-dimensional pseudo-homogeneous model for mass and heat balances, incorporating heat loss through the reactor wall. The configuration of the RFR consisted of inert-catalyst-inert, with or without heat extraction that makes it possible to store the energy released by the exothermic reaction of CH4 oxidation. The objective of this study was to investigate the dynamic behavior of the RFR for lean methane oxidation and to find the optimum condition by exploring a stability analysis of the simple reactor. The optimum criteria were defined in terms of CH4 conversion, CH4 slip, and heat accumulation in the RFR. At a switching time of 100 s, the CH4 conversion reached the maximum value, while the CH4 slip attained its minimum value. The RFR could operate autothermally with positive heat accumulation, i.e. 0.02 J/s. The stability of the RFR in terms of heat accumulation was achieved at a switching time of 100 s

ANALISIS EFISIENSI DAN PENURUNAN TEKANAN PADA SIKLON PERSEGI MENGGUNAKAN CFD

Artikel ini memaparkan hasil penelitian yang diperoleh melalui aplikasi komputasi dinamika fluida (Computational Fluida Dynamic,CFD) untuk mensimulasi medan alir di dalam siklon persegi. Perangkat lunak Gambit digunakan sebagai pre-processor untuk menggambar konfigurasi, diskritisasi, dan pendefinisian kondisi batas siklon. Geometri siklon silinder Lapple dan persegi ditinjau dari volume yang sama. Diameter siklon yang digunakan 0,2 m menyesuaikan dengan diameter siklon silinder Lapple yang digunakan Wang pada eksperimennya, dengan kondisi operasi  ditentukan pada laju alir gas sebesar 0,1m3/s sementara beban partikel dalam  laju alir gas sebesar 0,01kg/m3. Perangkat lunak CFD FLUENT 6.2.16 digunakan untuk simulasi medan alir dan dinamika partikel dalam siklon. Penelitian ini bertujuan untuk mengetahui pengaruh geometri siklon persegi terhadap medan alir, efisiensi dan penurunan tekanan. Prediksi yang dihasilkan memberikan informasi mengenai medan alir berupa kecepatan axial dan tangensial di dalam siklon serta informasi efisiensi dan penurunan tekanan. Hasil kajian menunjukkan bahwa kecepatan tangensial mendominasi medan alir di luar garis tengah siklon, sementara kecepatan aksial mendominasi medan alir di daerah garis tengah siklon. Penurunan tekanan yang terjadi pada siklon persegi lebih tinggi dari siklon silinder, namun efisiensi untuk siklon persegi lebih tinggi dibandingkan siklon Lapple

Utilizing Shear Factor Model and Adding Viscosity Term in Improving a Two-Dimensional Model of Fluid Flow in Non Uniform Porous Media

In a packed bed catalytic reactor, the fluid flow phenomena are very complicated because the fluid and solid particle interactions dissipate the energy. The governing equations were developed in the forms of specific models. The shear factor model was introduced in the momentum equation for covering the effect of flow and solid interactions in porous media. A two dimensional numerical solution for this kind of flow has been constructed using the finite volume method. The porous media porosity was treated as non-uniform distribution in the radial direction. Experimentally, the axial velocity profiles produce the trend of having global maximum and minimum peaks at distance very close to the wall. This trend is also accurately picked up by the numerical result. A more comprehensive shear factor formulation results a better velocity prediction than other correlations do. Our derivation on the presence of porous media leads to an additional viscosity term. The effect of this additional viscosity term was investigated numerically. It is found that the additional viscosity term improves the velocity prediction for the case of higher ratio between tube and particle diameter

Comparative Performance Study of Two Simple Soot Models for the Prediction of Soot Level in Atmospheric Turbulent Non-premixed Flames

The increase of current fossil fuel consumption has led to an increase of soot emission into atmosphere. Accurate prediction of soot production and destruction in a combustion system is not only important for the purpose of the design of the system, but also vital for the operation of the combustor. Numerous soot models have been proposed to predict the soot production and destruction in a flame, categorized as empirical, semi-empirical and detailed soot models. Although the detailed model represents the highest level of soot modelling, its use has been impaired by substantial requirement of resources of computer and time. Therefore, empirical and semi-empirical approaches still have their position in soot modelling of practical combustors. In this study, two soot models, single-step and two-step models are examined in the simulation of atmospheric turbulent non-premixed sooting flames. The soot models are compared and evaluated for their performance in predicting soot level in methane and ethylene non-premixed flames. The commercial software Fluent 6.3 was used to perform the calculations of flow and mixing fields, combustion and soot. Standard k-ε and eddy dissipation models were selected as solvers for the representation of the turbulence and combustion, respectively. The two soot models used in the study are available directly from the code for evaluation. The results show that the two-step model clearly performed far better than the single-step model in predicting the soot level in both methane and ethylene non-premixed flames. With a slight modification in the constant a of the soot formation equation, the two-step model was capable of producing prediction of soot level closer to experimental data. In contrast, the single-soot model produced very poor results, leading to a significant under-prediction of soot levels in both flames