Evaluasi Indeks Slagging dan Fouling pada Boiler Batubara Jenis Lignit dan Bituminus

<p>Batubara saat ini merupakan salah satu jenis bahan bakar yang banyak digunakan padaPLTU. Pada proses pembakaran batubara selain menghasilkan panas juga menghasilkan partikulat abu yang terbawa bersama gas panas. Partikulat abu batubara memiliki kemampuan untuk menempel pada dinding boiler dan kemampuan menempelnya abu ini terutama dipengaruhi oleh suhu melebur abu (ash fusion temperature, AFT) dan unsur – unsur dalam abu.Ada 2 jenis fenomena menepelnya abu batubara pada dinding boiler, yaitu <em>slagging</em> dan <em>fouling</em>. Hal ini akan berdampak pada penggunaan batubara menjadi lebih banyak dan meningkatkan pekerjaan pemeliharaan boiler. Metode evaluasi indeks <em>slagging</em> dan <em>fouling</em> mengunakan analisa karakteristik batubara melalui perhitungan indeks <em>slagging</em> dan <em>fouling</em>. Analisa karakteristik batubara dengan menggunakan analisis komposisi abu (SiO2, Al2O3, Fe2O­3, CaO, MgO, K2O, Na2O, TiO2, MnO2), ash fusion temperature, analisis proksimat (Kadar air, abu, zar terbang, dan karbon padat), analisis ultimat(C, H, S, N), dan penentuan nilai kalor batubara. Penelitian ini menggunakan metode perhitungan dengan menggunakan data analisa dari batubara,yaitu analisa proksimate, ultimate dan ash fusion temperature. Berdasarkan evaluasi dan analisa yang diperoleh bahwa abu jenis bituminous dengan kandungan unsur Fe2O3 memiliki pengaruh pada indeks pembentukan <em>slagging</em> dengan hasil indeks <em>slagging</em> lebih rendah, dan abu jenis lignit dengan unsure kandungan CaO dan MgO sangat mempengaruhi besar nilai indeks pembentukan <em>slagging</em> dengan hasil indeks <em>slagging</em> lebih tinggi jika dibandingkan dengan batubara jenis bituminus. Begitujuga halnya dengan kandungan Na2O pada abu bituminous dan lignit menjadi unsur yang berpengaruh ini selain indeks pembentukan <em>fouling</em>.</p>

Effect of dual-rotation on MHD natural convection of NEPCM in a hexagonal-shaped cavity based on time-fractional ISPH method

The time-fractional derivative based on the Grunwald–Letnikove derivative of the 2D-ISPH method is applying to emulate the dual rotation on MHD natural convection in a hexagonal-shaped cavity suspended by nano-encapsulated phase change material (NEPCM). The dual rotation is performed between the inner fin and outer hexagonal-shaped cavity. The impacts of a fractional time derivative $$\alpha$$ α $$\left( {0.92 \le \alpha \le 1} \right)$$ 0.92 ≤ α ≤ 1 , Hartmann number Ha $$\left( {0 \le Ha \le 80} \right)$$ 0 ≤ H a ≤ 80 , fin length $$\left( {0.2 \le L_{Fin} \le 1} \right)$$ 0.2 ≤ L Fin ≤ 1 , Darcy parameter Da $$\left( {10^{ - 2} \le Da \le 10^{ - 4} } \right)$$ 10 - 2 ≤ D a ≤ 10 - 4 , Rayleigh number Ra $$\left( {10^{3} \le Ra \le 10^{6} } \right)$$ 10 3 ≤ R a ≤ 10 6 , fusion temperature $$\theta_{f}$$ θ f $$\left( {0.05 \le \theta_{f} \le 0.8} \right)$$ 0.05 ≤ θ f ≤ 0.8 , and solid volume fraction $$\varphi$$ φ $$\left( {0 \le \varphi \le 0.06} \right)$$ 0 ≤ φ ≤ 0.06 on the velocity field, isotherms, and mean Nusselt number $$\overline{Nu}$$ Nu ¯ are discussed. The outcomes signaled that a dual rotation of the inner fin and outer domain is affected by a time-fractional derivative. The inserted cool fin is functioning efficiently in the cooling process and adjusting the phase change zone within a hexagonal-shaped cavity. An increment in fin length augments the cooling process and changes the location of a phase change zone. A fusion temperature $$\theta_{f}$$ θ f adjusts the strength and position of a phase change zone. The highest values of $$\overline{Nu}$$ Nu ¯ are obtained when $$\alpha = 1$$ α = 1 . An expansion in Hartmann number $$Ha $$ Ha reduces the values of $$\overline{Nu}$$ Nu ¯ . Adding more concentration of nanoparticles is improving the values of $$\overline{Nu}$$ Nu ¯ .

Experimental Study of Polyethylene Fusion by Scheffler Solar Concentrator

Aims: The present work is the use of Scheffler technology to melt plastic waste to produce composite materials using an oven type receiver. The composite material in this study contains polyethylene as a matrix and sand as reinforcement. Study Design: The fusion temperature of polyethylene is about 200°C and is obtained by solar concentration. The experimental plastic melting unit in Saaba (latitude 12.38° N; longitude -1.43° E), Burkina Faso, uses two 8 m² Scheffler concentrators sharing a cubic receiver. Three types of mirrors with a reflectivity of at least 90% are used as reflecting facets to equip the Scheffler dishes at the site. Methodology: The thermal behavior of the receiver is analyzed experimentally. Temperatures are measured on the inner and outer walls as well as the internal air temperature with 5 K-type thermocouples. When the fusion temperature is reached on the inside, we introduce the plastic waste which has been previously washed, crushed, dried and weighed. Results: The installed model obtained an average energy of 1.80 kW at the receiver and an average internal temperature of 251.15°C for an average irradiance of 623 W/m² during the no-load test. During the load test, an average energy of 1.34 kW and an internal temperature of 206.4°C were reached for an average irradiance of 473 W/m² and an optical efficiency of 56%. This test led to the production of two pavers of the composite material matrix with 2.2 kg of plastic waste. Conclusion: These results show that the profiles of the primary reflector, tracking system, and tilt axis are accurate and the maximum concentrated solar flux converges on the absorbing surfaces of the receiver. The tempered panes of the absorbing surfaces is more transparent and less emissive. Thus our device contributes to the valorization of plastic waste by using a non-polluting energy source.

Research on Purification Technology of Ultra-Large Flake Graphite Based on Alkali-Acid Method

Graphite is a strategically scarce resource, and the preparation of high-purity graphite is the prerequisite and basis for the application of graphite. In order to determine the optimal purification technology parameters of an ultra-large flake graphite mine pneumatic separation ore with a fixed carbon content of 77.69%, a particle size of mainly 10 to 40 mesh, and main impurities of calcium carbonate, iron oxide and silica , two additional experiments of acid method and alkali method were added on the basis of alkali-acid method, to investigate the purification effect of different technological processes and acid leaching times on graphite raw materials, as well as to analyze the retention extent of different methods and alkali fusion temperature on graphite ultra-large flake structure. The results show that all three methods can increase the fixed carbon content of graphite to above 99%. However, compared with the acid method and the alkali method, the alkali-acid method can obtain high-purity graphite while also better protecting the graphite's ultra-large flake structure. The optimal fusion temperature is 400 °C, the optimal acid leaching time is 30% sulfuric acid thrice and 5% hydrofluoric acid once. After purification, the fixed carbon content of the product exceeds 99.97%.

Determination of crystallization enthalpies of some organic peroxides by a differential isothermal calorimeter

We developed a method for determination of the crystallization enthalpy of organic substances in a heat-conducting calorimeter at a temperature close to 298 K. Crystallization was conducted in the MID-200 calorimeter using an ampoule technique. The volume of ampoules, which contain the supercooled liquids, was approximately 0.2 cm3. The residual pressure was 650 Pa to lessen the heat loss. A few crystals of the material under investigation were employed as the crystallization centers. Based on the results of the experiment, the crystallization enthalpies of dicumyl peroxide, peroxyoctanoic acid and di-tert-butylperoxy isophthalate were determined. The vaporization and sublimation enthalpies of peroxyoctanoic acid were assessed using an ampoule method in the calorimeter. It was established that dicumyl peroxide which was supercooled 14 K below the fusion temperature exhibited a 20% increase in crystallization enthalpy as compared with that calculated from the difference between vaporization and sublimation enthalpy. At the same time, the crystallization enthalpy of peroxyoctanoic acid supercooled by 5 K was equal to that calculated from the difference between vaporization and sublimation enthalpy within the limiting experimental error. The received data show that the proposed method is promising for determining the heat of crystallization of liquids that are able to exist in a supercooled state during some time.

A Model for Predicting Arsenic Volatilization during Coal Combustion Based on the Ash Fusion Temperature and Coal Characteristic

Arsenic emission from coal combustion power plants has attracted increasing attention due to its high toxicity. In this study, it was found that there was a close relationship between the ash fusion temperature (AFT) and arsenic distribution based on the thermodynamic equilibrium calculation. In addition to the AFT, coal characteristics and combustion temperature also considerably affected the distribution and morphology of arsenic during coal combustion. Thus, an arsenic volatilization model based on the AFT, coal type, and combustion temperature during coal combustion was developed. To test the accuracy of the model, blending coal combustion experiments were carried out. The experimental results and published data proved that the developed arsenic volatilization model can accurately predict arsenic emission during co-combustion, and the errors of the predicted value for bituminous and lignite were 2.3–9.8%, with the exception of JingLong (JL) coal when combusted at 1500 °C.