生質燃料氣化熱電共生系統之燃燒控制研究

Abstract

本熱電共生系統利用燃燒機將向下氣流式生質氣化爐與史特靈引擎作結合。氣化爐上利用封閉式的儲料桶的代替電子進料系統，避免額外的能量輸入。史特靈引擎為分置式(γ–type)，工作流體為空氣，並以水冷方式來冷卻。橋接氣化爐以及史特靈引擎的燃燒機，則透過回熱的設計，將高溫的廢氣用來加熱來自氣化爐的產氣及空氣以提昇效率。本研究主要是在探討氣化爐以及熱電共生系統的操作參數，如：進氣高度、點火高度、進氣風量、燃料消耗率、產氣熱值、燃燒室溫度、引擎的輸出功及力矩。氣化爐反應所用的的燃料尺寸與種類分別是邊長15mm與邊長10mm以及紅柳安木與白柳安木。 經由實驗結果發現，本氣化爐需將爐床位置降低來增加氣化長度以延長燃料在氣化區停留的時間。而點火高度位於進氣口位置時，可以降低氣化爐操作所需的穩定時間以及燃料消耗。本氣化爐最高產氣熱值為5081kJ/Nm3，其操作風量為14Nm3，並使用小尺寸燃料顆粒(邊長10mm)。在熱電共生實驗中可以發現氣化爐的產氣可以順利驅動史特靈引擎，並持續的運轉。引擎所能達到的最高轉速為463rpm，最高輸出軸功為3.12W。

A fixed-bed air-blown stratified downdraft biomass gasifier was built in this study. The gasifier was coupled to a Stirling engine via a burner to construct a combined heat and power system. An air-sealed hopper was used for fuel storage and feeding, rather than an electric feeding system, to reduce the energy consumption. A water-cooled gamma-type Stirling engine filled with air as working fluid was built in this study. A burner was designed to combine the gasifier with Stirling engine, and preheating the intake air with flue gas exhausted from the burner can improve the system efficiency. The main purpose of this study is to investigate the influences of operation parameters including the height of air inlet, height of fuel ignition, airflow rate, air-fuel ratio, and the fuel feeding rate, on the producer gas heating value, the temperature of gas inside the burner, and the torque and power of Stirling engine. Tests have been performed by using wooden cubes (10×10×10 and 15×15×15 mm) of Red Lauan and White Lauan as gasification feedstock. Experimental results of the gasifier indicate that reducing the height of grate to increase the length of gasification zone is required for prolonging the retention time of fuel in gasification region. Ignition of fuel at the height of air intake can shorten the time required for start-up and consequently reduce the consumption of fuel and energy during the start-up period. An optimum mean producer gas HHV of 5081 kJ/Nm3 was obtained as the gasifier was operated with small-sized fuels (10×10×10 mm ) at an airflow rate of 14 Nm3/h. Test results of the combined heat and power system indicate that the Stirling engine can run smoothly and be continuously driven by the combustion heat of the syngas produced by the gasifier. A maximum engine speed of 463 rpm and a maximum shaft power of 3.12 W were reached in the tests performed.