【S015】 淨零碳排新興能源科技論壇

Thursday, 18 November, 16:30 ~ 18:00, Conference Room ROOM 7
Organizer: Shu-San Shiau, Shou-Yin Yang
Chair: 楊授印

16:30 ~ 16:45 (15')
0069  Numerical Simulation of Biomass Particle Behavior and Conversion in a Fluidized Bed Pyrolysis Condition
Thoharudin Thoharudin, Shu-San Hsiau, Yi-Shun Chen and Shouyin Yang
Fast pyrolysis is one of attractive solid thermochemical conversion producing valuable chemical feedstocks and fuels. In recent years, numerical simulations of fast pyrolysis in a fluidized bed reactor have been developed using a variety of reaction mechanisms including simple mechanisms (single-step mechanism, semi-global mechanism, and global mechanism) and advanced multistep comprehensive mechanism; however, most simulation models were constructed by ignoring the particle evolution (shrink in density and size). Thus, the biomass particles tended to rest in the dense zone mixing with the fluidizing medium (sand) and required more fluidizing gas to push the biomass particle out from the reactor. This study implemented the biomass particle shrinkage widely used in the gasification model integrated with an improved multistep comprehensive mechanism. A Fluidized bed reactor with a height and diameter of 650 mm and 72 mm was used and modeled in a 2D domain for the reason of less computational cost. The multi-fluid model (MFM) integrated with heterogeneous chemical reactions was developed to simulate the gas-particle flows and chemical reactions in the fluidized bed reactor. The reaction constants, heats of reactions, and particle size evolution were calculated by developing user-defined functions (UDFs) written in C/C++ code and integrated using DEFINE_HET_RXN_RATE, DEFINE_SOURCE, and DEFINE_PROPERTY macros, respectively. Biomass with a particle size of 850 µm was injected into the reactor at 27 oC and the pyrolysis was conducted at a temperature of 400‒600 oC. Silica sand with a particle size of 300 um was initially packed at a height of 100 mm and a volume fraction of 0.55. Preheated nitrogen was used as the fluidized gas and flown at 0.25 m/s from the bottom of the reactor. The simulation resulted in a good agreement with the experiment counterpart with the relative errors of 4.4%, ‒14.8%, and 9.6% predicting bio-oil, NCG, and char yields. In addition, by implementing the particle size shrinkage, the biomixture particles distributed more homogeneous and the fluidizing gas enabled the biomixture particles conveyed in the freeboard zone. Biomixture particles pyrolyzed at low temperature (<500 oC) tended to accumulate in the dense zone and the vertical velocity of biomixture particles was enhanced by the increase in temperature. This is attributed to the biomixture particle weight and drag forces where the raise of temperature released more volatile matter and left the biomixture particle with lower weight and smaller particle size. Therefore, the low particle weight with a particular particle size enabled fluidizing gas to drag the particle to move to the freeboard. In summary, this simulation was capable to predict the pyrolysis product yields; moreover, implementing the particle shrinkage could illustrate the particle behavior more realistic in the reactor.

16:45 ~ 17:00 (15')
0051  The Energy Saving Technique Development-The Metal Foam Multichannel Heat Exchanger
Heng Yu Chen and David TW Lin
The purpose of this study is to develop the model of the multi-channel metal foam heat exchanger (Hx) based on the porous TH model. The free and porous flow model and porous heat transfer model are used. The validation is agreed with the experiment. In this study, the effects of porosity of metal foam are discussed. The heat extraction of waste heat increases as the porosity decreases. Therefore, the enhanced heat transfer is observed apparently. This study can be used to design the optimal operating conditions of waste heat recycling.

The model of the multi-channel heat exchanger is shown in Figure 1. The porous heat transfer model and free and porous flow model are used. The boundary conditions of this model are assumed as the inlet air velocity Va, in of channel (22.85m/s), the inlet air temperature Ta, in is 343.15K, the inlet temperature and velocity of water Tw, in, Vw, in is set as 293.15K and 0.00004167m3/s, the upper surface and the left and right sides are as adiabatic conditions. The difference of inlet air velocity and temperature are discussed.

Figure 2 shows the heat extraction with the porosity. The heat extraction increases as the porosity decreases. This phenomena due to the increase in the Hx between the working fluid and the metal foam. Therefore, the efficiency of heat extraction also increases. These results are validated with experiment. The related results are shown in the report of MOST-108-3116-F-024-001-CC2.

17:00 ~ 17:15 (15')
0062  Optimal HTLC catalyst on tar model steam reforming by Taguchi method
Yueh-Heng (約亨) Li (李), Ming-Wei (明偉) Dai (戴), Chih-Hsin (志鑫) Hsieh (謝), Po-Chou (柏州) Chen (陳) and Chao-Wei (朝偉) Huang (黃)
Coal combustion produces carbon dioxide and suspended particles that harm the environment and human health. This issue has become controversial in recent years. Clean and renewable energy has become an essential topic in the energy field, replacing coal as the primary energy source. Gasification is a heat treatment process that converts biomass into synthetic gas at high temperatures. Synthetic gas can be used for (1) direct combustion to produce energy, (2) supplement for fuel cells, and (3) raw materials for the synthesis of methanol or other chemicals. However, tar is an unfavorable byproduct during the gasification process. It is a highly viscous mixture of aromatic hydrocarbons. When temperatures drop, tar's acidity causes pipe corrosion and blockage. Therefore, adding a catalyst reaction section at the back of the gasifier helps to reduce the tar content in the synthesis gas and to increase the output of the synthesis gas. In this study, the support of the catalyst was prepared by co-precipitation. It comprises calcium oxides and aluminum oxides to form hydrotalcite-like compounds (HTLC). The calcium/aluminum molar ratio was set by 1.5, 2.0, 2.5, and the calcination temperature was 1037K, 1137K, 1237K. Then, a wet dipping method was used to load nickel and iron onto the support. The nickel or iron loading was 3, 5, and 7 wt.%. The synthesis conditions of the catalyst were optimized by the Taguchi method to achieve the purpose of reducing the content of heavy tar substances and increasing the amount of hydrogen generation.

17:15 ~ 17:30 (15')
0038  加熱爐低碳混氫燃燒特性與展望
明勳 吳, 煒東 謝 and 瀚陽 胡
未來的熱能需求因應碳中和目標將朝電力化、低碳化演進。低溫(<400 oC)的加熱系統有對應的商用電力化技術可進行電熱轉換,但需要翻新改造已有加熱系統;高溫(>1000 oC)的電熱系統尚無大型商業化技術,因此使用燃料燃燒供熱仍將為主流。但為滿足熱能供應低碳化,預期朝向使用氫氣、bio syngas或含氫燃料混燒方向演進。在燃氣轉型的過程,燃燒區間、熱區分佈與燃料變化的關聯性,以及現有燃燒系統該如何因應、是否還能符合現用的加熱工藝,值得探討。其中,在現有加熱爐與設施基礎上,於燃料中混入氫氣取代部分碳氫燃料,是短期達成減碳之最有效技術。
欲轉換加熱爐燃料為混氫燃料,預見會衍生出在1) 安全性與經濟性,2)燃燒與排放特性,3)熱傳特性,4)模擬預測及5)儀控工程設計等個面向的問題與挑戰。安全與經濟性方面包含了混氫燃料與現有設施之材料相容性,可燃與爆炸極限的改變以及各式成等工程經濟的議題。在燃燒與排放特性方面,則須了解火焰型態、穩定性、可燃區間、汙染物與二氧化碳排放、煙氣溫度與組成上的改變。在熱傳特性上則跟燃燒與排放特性息息相關,需以煙氣之熱力跟傳輸性質評估轉換後之加熱性能。在模擬預測上,除基本之流程外,最重要的是找到可完整及準確預測混氫燃料燃燒的化學反應動力模型。而混氫燃燒可能造成燃料、空氣甚至煙氣流率的改變,甚至需用不同之燃燒方式以解決在上述面向衍生的問題,出現在儀控與工程設計上的新議題。
原有管閥與控制系統之適用性為混氫燃料應用於加熱爐首先面臨的挑戰。Wobbe index(Wo)是評估燃料互換性的重要指標。當兩種燃料有相近的Wo,代表在上游壓力設定及管閥不需調整即可有相近的熱釋率。天然氣為加熱爐最常見的氣態燃料,其中有90%甲烷(CH4),因此天然氣與甲烷之Wo非常接近,但氫氣就跟兩者差異較大。如要使用天然氣燃燒器與供氣管路直接置代氫氣可能會有流率與壓力匹配問題。值得注意的是Coke Oven Gas (COG) COG中除含達約60%左右的氫氣外,也含有CO,而CO之Wo甚至比氫氣小。故若以COG設施來進行混氫燃燒,很有機會在不更動管閥與壓力設定下進行混氫燃燒。
本文將利用開源熱化學反應模擬軟體搭配詳細反應模型,將加熱爐近似完全混合反應器(Perfectly Stirred Reactor, PSR)建模預測包括溫度與排放等參數隨混氫比之變化,解析混氫燃燒對於加熱爐燃燒、熱傳與排放之影響。初步模擬發現隨混氫比提高,溫度、水氣及氮氧化物在煙氣中的佔比皆增加,但二氧化碳及一氧化碳之比例會降低。我們將在此一維模擬工具基礎上篩選化學反應動力模型,接續以此模型探討包含甲烷、氫氣、一氧化碳、二氧化碳、氮氣及氨氣之混氫燃料燃燒,預測在不同組成比例、燃料流率、空燃比以及空氣預熱溫度下,煙氣之溫度、排放組成及吹熄極限(blow out limit),以掌握混氫燃燒特性。藉由煙氣溫度與組成之數據,將可進一步估算汙染排放、碳排量以及熱傳性能。

17:30 ~ 17:45 (15')
0087  乳化燃料液滴的不穩定燃燒
Atul Kumar and Shouyin Yang
本研究通過對液滴燃料燃燒中的微粒消光係數、燃燒速率、擴散特性和自然對流的分析,研究了乳化/非乳化燃料的煙塵特性以及微爆炸對微粒產生的影響。同步紋影法成像和雷射消光成像方法進行實驗。實驗進行是在大氣條件下進行的,燃料液滴是玻璃纖維所支撐。結果顯示,熱邊界距離,即從液滴表面到紋影成像獲取的最外層高濃度區域的距離,隨著粘性的減小而增加。此外,雷射消光結果顯示,微粒的產生受到粘性和燃料擴散的影響。粘性由 Grashof (Gr) 數分析,它是浮力和粘性的函數,伴隨著微爆,燃料的粘性降低。微粒消光是一種用於計算微粒厚度 (KL) 或微粒消光係數 (K) 的成像機制,結果顯示,自然對流受到微爆炸的影響,Ri的結果顯示熱對流由自然對流轉變為混合對流,在乳化燃料中所會發生連續的微爆炸和膨脹循環,但在非乳化燃料中大多數情況下會發生直接爆炸,因為在非乳化燃料中,宏觀液滴的運動不存在,因為它很常見在乳化燃料中。因此,由於這種乳化燃料表現出與純燃料非常不同的行為,但非乳化燃料表現出與純燃料相似的行為,直到發生直接爆炸。

17:45 ~ 18:00 (15')
0231  使用Ni1-xCox-BCZY合金陽極提升以甲烷為燃料之質子傳導型固態氧化物燃料電池壽命
博駿 鄭, 家銘 林, 侃融 李, 重仁 曾 and 嘉恩 吳

然而,碳氫化合物進料 SOFC的問題之一是陽極觸媒上的碳沉積。在長期運行中,陽極積碳會降低SOFC的性能。已有部分文獻指出,在傳統氧離子傳導SOFC之陽極(Ni/SDC)中摻雜少量過渡金屬可以有效減少積碳,但卻導致SOFC性能下降。本研究提出使用合金觸媒Ni1-xCox (x = 0.1, 0.2, 0.3)取代金屬鎳作為陽極之觸媒材料並將其運用於質子傳輸型SOFC(P-SOFC),期望改善陽極材料在長時間操作時,因使用碳氫燃料所造成陽極之積碳問題。並希望透過合金觸媒優異之材料特性,開發出具高電子/質子導性、高穩定性與具良好氣體擴散通路之陽極材料。

本研究透過固態反應法製備Ni1-xCox-BCZY作為P-SOFC之陽極。研究結果顯示,Ni0.8Co0.2-BCZY的NiCo陽極電池在工作溫度800 °C下,最高功率密度達到316 mW/cm2。儘管Ni0.8Co0.2-BCZY的電池性能略低於Ni陽極電池(361 mW/cm2),但可大幅降低碳沉積並延長使用壽命5.5倍(Ni:5.5小時;Ni0.8Co0.2:30小時)。本研究結果證明使用Ni、Co合金可有效抑制陽極的碳沉積,大幅延長使用壽命。