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Romi Djafar
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Pemanfaatan Abu Terbang Circulating Fluidized Bed (CFBFA) sebagai Pengikat Rendah Karbon: Sintesis, Mekanisme Hidrasi–Geopolimerisasi, Stabilitas Volume, Durabilitas, dan Aplikasi Konstruksi (Literature Review) Romi Djafar; Yunita Djamalu
Journal of Energy and Mechanical Engineering Vol. 2 No. 2 (2025): Journal of Energy and Mechanical Engineering (Juni)
Publisher : Fakultas Sains dan Teknologi - Universitas Nahdlatul Ulama Gorontalo

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.62299/jeme.v2i2.29

Abstract

Abu terbang dari boiler circulating fluidized bed (CFBFA) semakin menonjol sebagai sumber bahan baku pengikat rendah karbon, seiring meningkatnya kebutuhan dekarbonisasi industri semen dan penanganan limbah padat pembangkit. Namun, pemanfaatan CFBFA berskala besar masih dibatasi oleh komposisi tidak stabil (mis. f-CaO dan SO₃), heterogenitas fase mineral, serta risiko ekspansi dan degradasi durabilitas bila desain sistem tidak mengendalikan pembentukan gypsum/ettringite dan evolusi pori. Review ini membangun sintesis komprehensif atas literatur terkini 2022–2026 dari korpus yang diekstrak (file DATA dan REF RS), memetakan: (i) karakteristik CFBFA (fasa, reaktivitas, morfologi, dan implikasinya pada kebutuhan air serta kompatibilitas admixture); (ii) rute pemanfaatan utama—semen campuran/low-clinker, binder multi-limbah (red mud–carbide slag–slag–gypsum), geopolimer (low-Ca vs high-Ca), aerated/autoclaved aerated concrete (AAC), serta produk bernilai tambah seperti ceramsite sinter/non-fired, filler berbusa, dan grout; (iii) mekanisme kinerja—transisi produk hidrasi (AFt, C-(A)-S-H, N-A-S-H), pemadatan mikrostruktur, serta kontrol porositas; (iv) durabilitas (sulfat, freeze–thaw, karbonasi) dan isu lingkungan (pelindian logam berat dan jejak lingkungan/LCA). Temuan kunci menunjukkan bahwa keberhasilan sistem CFBFA bergantung pada rekayasa kimia-kalsium-sulfat dan rekayasa pori (mis. foam/void management), serta sinergi ko-binder yang menyeimbangkan reaktivitas awal dan stabilitas jangka panjang. Review ini menutup dengan agenda riset untuk standardisasi, desain berbasis rasio unsur/gel, dan validasi jangka panjang di kondisi lapangan.
Perencanaan Orientasi Pahat dan Toolpath pada Pemesinan Lima-Sumbu dan Roboti: Integrasi Kendala Geometri–Kinematika, Singularity Avoidance, Feedrate Scheduling, Stabilitas, dan Kompensasi Error untuk Manufaktur Presisi Romi Djafar; Yunita Djamalu
Journal of Energy and Mechanical Engineering Vol. 2 No. 1 (2024): Journal of Energy and Mechanical Engineering (Desember)
Publisher : Fakultas Sains dan Teknologi - Universitas Nahdlatul Ulama Gorontalo

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.62299/jeme.v2i1.30

Abstract

Five-axis machining and robotic machining play a critical role in manufacturing complex-geometry components such as blades/bladisks, impellers, free-form surfaces, and thin-walled parts. Research developments from 2020–2026 reveal a shift from predominantly geometry-based toolpath planning toward integrated frameworks that incorporate machine/robot kinematic constraints, drive limits, singularity avoidance, process stability (e.g., chatter), and feedback-based error compensation. This review synthesizes the literature from multiple sources to construct a taxonomy of contributions, assess methodological trends, and identify top-tier research agendas. The synthesis focuses on: (i) tool orientation and tool center point (TCP) calibration in robotic milling; (ii) smooth and collision-safe tool orientation planning while maintaining favorable performance of rotary axes/joints; (iii) toolpath planning on NURBS/mesh surfaces, including iso-scallop strategies and geodesic mapping; (iv) time-optimal feedrate scheduling under geometry–drive constraints; (v) Jacobian-condition-based singularity avoidance with bounded orientation variation; (vi) control of surface texture/topography quality based on posture ranges; (vii) prediction and optimization of process stability to suppress chatter; and (viii) iterative contour error compensation and vision–CNC integration for real-time adaptation. The review shows that the best performance is achieved when tool orientation, toolpath, and feedrate are optimized coherently (co-optimization), and when surface quality is treated as an explicit constraint rather than merely an output. The review identifies key research gaps, including the need for integrated differentiable/real-time models, operational surface texture quality measurement for industrial systems, and the integration of stability, drive limits, and singularity avoidance in end-to-end planning for practical CNC and robotic machining systems.
Pengembangan Sistem Aerasi Hemat Energi pada Tambak Pesisir untuk Menurunkan Beban Nutrien dan Mencegah Eutrofikasi Perairan Laut: Kajian Literatur Naratif Terintegrasi Teknik Mesin dan Teknik Lingkungan pada Konteks Pesisir–Mangrove Romi Djafar; Yunita Djamalu
Journal of Energy and Mechanical Engineering Vol. 2 No. 1 (2024): Journal of Energy and Mechanical Engineering (Desember)
Publisher : Fakultas Sains dan Teknologi - Universitas Nahdlatul Ulama Gorontalo

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.62299/jeme.v2i1.31

Abstract

Mechanical aeration is essential in intensive coastal aquaculture (particularly shrimp ponds) to maintain dissolved oxygen (DO) and sustain high stocking densities, yet it frequently dominates farm electricity consumption. Concurrently, feed-derived nitrogen (N) and phosphorus (P) accumulate in pond water and sediments and may be exported through water exchange and harvesting effluents, potentially intensifying coastal eutrophication, harmful algal blooms, and hypoxia. This narrative literature review integrates mechanical engineering viewpoints (aerator typologies, oxygen transfer performance metrics such as SOTR/SAE, mixing/circulation behavior, and energy demand) with environmental engineering outcomes (nutrient transformations, water-quality variables, and effluent nutrient loads) and extends the discussion to receiving ecosystems at the coast–mangrove interface. Energy-focused assessments highlight large variability in aeration energy intensity and identify avoidable over-aeration as a major inefficiency source. Beyond demand reduction, renewable/off-grid supply becomes relevant in remote coastal settings; techno-economic optimization of floating PV/battery systems indicates feasible and reliable aeration power under day- and night-aeration scenarios. Environmental evidence links pond effluents to elevated nutrients and chlorophyll-a in adjacent coastal waters, motivating designs that evaluate effluent loads alongside DO control. Mangrove studies further indicate complex ecological consequences of nutrient enrichment and redox-driven nitrogen fate (denitrification vs DNRA) that determines whether nitrogen is removed as N₂ or retained as bioavailable NH₄⁺. The review proposes an integrated “mechanical performance–water quality–effluent load–receiving ecosystem” framework and recommends a practical minimum set of reporting metrics to align aeration innovations with energy efficiency and eutrophication risk reduction.
Produksi Syngas Bersih dari Gasifikasi Biomassa dan Limbah (2023–2026): Intensifikasi Reaktor, Pengendalian Tar/Partikulat, Kondisioning Impuritas, dan Integrasi ke Hidrogen serta Sustainable Aviation Fuel Romi Djafar; Yunita Djamalu
Journal of Energy and Mechanical Engineering Vol. 1 No. 2 (2024): Journal of Energy and Mechanical Engineering (Juni)
Publisher : Fakultas Sains dan Teknologi - Universitas Nahdlatul Ulama Gorontalo

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.62299/jeme.v1i2.32

Abstract

Biomass and waste gasification is positioned as a pillar of the energy transition because it can convert renewable carbonaceous materials into syngas that can be directed toward electricity and heat generation, hydrogen production, synthetic fuels, and high-value chemicals. The main challenge of industrialization is no longer merely producing syngas, but producing clean syngas that meets downstream catalyst thresholds: tar, particulates, alkali species, Cl/S/N compounds (e.g., NH₃), and variability in the H₂/CO composition often become bottlenecks in terms of cost and reliability. This review synthesizes literature from the Plain Text and RIS corpus up to 2026 to construct an updated taxonomy: (i) reactor intensification through in-situ cleaning concepts (SiC membranes combined with biochar or structured catalysts), (ii) in-situ versus ex-situ catalytic strategies for tar conversion, (iii) conditioning of trace impurities (e.g., NH₃) and their implications for downstream catalysts, (iv) sorption-enhanced gasification (SEG) and integrated carbon capture concepts, (v) system modeling, techno-economic assessment, and scale-up strategies for fuel pathways (SAF, drop-in diesel, e-fuels), and (vi) the role of digital technologies (AI/ML/IoT/digital twins) in value-chain optimization. The synthesis reveals a strong 2024–2026 trend toward integrated intensification, namely reactors that combine particulate separation and tar cracking at high temperatures (≈800 °C) to avoid cooling stages that trigger tar condensation and corrosion, accompanied by strategies to mitigate catalyst deactivation. Downstream, the gasification–FTS pathway remains dominant for aviation fuel production; however, alternative configurations are emerging (gasification → olefins → oligomerization) along with partial electrification to improve carbon efficienc.   The proposed top-tier research agenda includes the design of coking-resistant reactor–catalyst systems, syngas quality metrics based on catalyst thresholds, and hybrid physics–ML optimization frameworks that can be applied operationally.
PEMANFAATAN ABU TERBANG CIRCULATING FLUIDIZED BED (CFBFA) SEBAGAI PENGIKAT RENDAH KARBON: SINTESIS, MEKANISME HIDRASI–GEOPOLIMERISASI, STABILITAS VOLUME, DURABILITAS, DAN APLIKASI KONSTRUKSI (LITERATURE REVIEW) Romi Djafar; Yunita Djamalu
Journal of Energy and Mechanical Engineering Vol. 1 No. 2 (2024): Journal of Energy and Mechanical Engineering (Juni)
Publisher : Fakultas Sains dan Teknologi - Universitas Nahdlatul Ulama Gorontalo

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.62299/jeme.v1i2.33

Abstract

Fly ash from circulating fluidized bed boilers (CFBFA) is increasingly emerging as a potential low-carbon binder feedstock in response to the growing need for decarbonization in the cement industry and improved management of solid waste from power plants. However, the large-scale utilization of CFBFA is still constrained by its unstable composition (e.g., free CaO and SO₃), heterogeneity of mineral phases, and the risk of expansion and durability degradation when system design fails to control gypsum/ettringite formation and pore evolution. This review develops a comprehensive synthesis of recent literature from 2022–2026 derived from the extracted corpus (DATA and REF RS files), mapping: (i) the characteristics of CFBFA (phases, reactivity, morphology, and their implications for water demand and admixture compatibility); (ii) the main utilization pathways—blended/low-clinker cement, multi-waste binders (red mud–carbide slag–slag–gypsum), geopolymers (low-Ca vs. high-Ca), aerated/autoclaved aerated concrete (AAC), and value-added products such as sintered/non-fired ceramsite, foamed fillers, and grouts; (iii) performance mechanisms—hydration product transitions (AFt, C-(A)-S-H, N-A-S-H), microstructural densification, and porosity control; and (iv) durability (sulfate resistance, freeze–thaw, carbonation) and environmental issues (heavy-metal leaching and environmental footprint/LCA).    Key findings indicate that the success of CFBFA-based systems depends strongly on calcium–sulfate chemical engineering and pore engineering (e.g., foam/void management), as well as co-binder synergy that balances early reactivity with long-term stability. The review concludes with a research agenda focused on standardization, element/gel-ratio-based design, and long-term validation under field conditions.
Digitalisasi dan Intensifikasi Proses Termokimia Biomassa dan Limbah menuju Syngas Bersih, Hidrogen, dan Bahan Bakar Cair Rendah Karbon: Tentang Pemodelan Multiskala, Pengendalian Emisi, Katalis, Membran, dan Optimasi Sistem (Literature Review): Digitalisasi dan Intensifikasi Proses Termokimia Biomassa dan Limbah menuju Syngas Bersih, Hidrogen, dan Bahan Bakar Cair Rendah Karbon: Tentang Pemodelan Multiskala, Pengendalian Emisi, Katalis, Membran, dan Optimasi Sistem (Literature Review) Romi Djafar; Yunita Djamalu
Journal of Energy and Mechanical Engineering Vol. 1 No. 2 (2024): Journal of Energy and Mechanical Engineering (Juni)
Publisher : Fakultas Sains dan Teknologi - Universitas Nahdlatul Ulama Gorontalo

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.62299/jeme.v1i2.34

Abstract

Energy transition and the strengthening of the circular economy are accelerating the utilization of biomass and waste as energy sources and feedstocks for low-carbon liquid fuels. However, the implementation of thermochemical conversion processes (combustion, pyrolysis, gasification) remains constrained by feedstock heterogeneity, the complexity of bed and freeboard phenomena, tar and particulate formation in syngas, ash–slagging–corrosion issues, and uncertainties in catalyst performance during downstream processes. This review presents a critical synthesis of literature from 2020–2026 provided in two data packages (a collection of recent abstracts and a structured reference database), focusing on the integration of multiscale modeling, process intensification, and digitalization to produce clean syngas, hydrogen, and liquid fuels (including SAF and e-fuels). First, we map advances in devolatilization/pyrolysis modeling, fixed-bed/grate CFD, DEM–CFD approaches, and data-driven operational optimization to reduce NOx emissions and improve efficiency in boilers, furnaces, and MSW incinerators. Second, we discuss syngas cleaning technologies and tar upgrading (in-situ, ex-situ, plasma-catalysis), membrane-reactor-based intensification strategies (SiC/ceramic) that integrate tar reforming and particulate retention, as well as the development of Fe–K biochar catalysts for tar and NH₃ reduction. Third, we review syngas conversion pathways to liquid fuels (Fischer–Tropsch, olefin-to-oligomerization, bio-aromatics) and e-fuels (SOEC, Power-to-X), including gas purity requirements, catalyst deactivation mechanisms (water, NH₃, phosphorus), and techno-economic implications. Finally, we propose a research agenda toward end-to-end digital twin systems and fouling-/poisoning-resistant process intensification, accompanied by recommendations for performance metrics that link feedstock quality, reactor operation, gas conditioning, product output, cost, and environmental impacts.
Co-Authors Yunita Djamalu