移動床式生質物焙燒爐之初步研究

Abstract

植物做為生質燃料，因為可以藉由增加栽種來大規模取得原料，是十分具有發展潛力的石化替代能源之一；木材經過熱裂解後，在不同的反應條件而產生不同狀態的燃料，相較於氣、液燃料，固態燃料更便於運輸及貯藏，因此本研究中使用產生固態產物的焙燒反應進行研究。在本研究中使用COMSOL Multiphysics 4.2a軟體模擬20 mm立方體柳杉木質原料在焙燒時的熱、質傳遞現象，並且經由實驗加以驗證。從在焙燒過程因受熱傳遞阻力影響，由模擬得知半纖維素、纖維素、木質素濃度中心向表面遞減，同時生質炭以相反的趨勢產生。實驗的結果驗證，半纖維素、纖維素與模擬同樣的趨勢存在，但木質素因為分離過程中摻雜著類似木質素不為強酸溶解的焙燒產物，不容易單獨量測，但合計木質素與焙燒產物之總重與實驗模擬的數據趨勢相合。在重量的模擬及驗證中，以250℃、270℃、290℃焙燒30分鐘，重量模擬值與實驗值依序相差相差9.0%、9.1%、4.1%。而生質炭收率依序為39.1 %、36.3%、34.5%。以此基礎數據，設計一具焙燒爐來生產生質炭，此焙燒爐藉燃燒木材本身來供應反應所需熱源，不需經由外界加熱以達到節能環保的目的。使用電阻溫度計(RTD)測量焙燒時爐體的溫度分布，得知焙燒區可達到溫度200℃以上，並可控制焙燒反應溫度，但此焙燒爐原料的運動與排氣的處理仍待進一步的改進。

Wood is a high potential alternative to petrochemical fuels due to the mass production by growing plants. The pyrolysis of wood, which involves various conditions produces corresponding rich carbon content residues, char or gas and liquid products. Different from gas and liquid fuels, biochar, a stable solid created by pyrolysis of biomass, is easier for storage and transportation. In our study, therefore, we focused on the torrefaction process that leads to a final dry solid product. We used COMSOL Multiphysics 4.2a to simulate the heat and mass transfer of a cubed biomass, Cryptomeria japonica, with 20 mm edge length during torrefaction process. Then, we validated the simulation results by comparing to torrefaction experiments. Simulation result showed that the concentration of hemicellulose, cellulose, and lignin were decreased from the center towards the surface of biomass, meanwhile, the concentration of biochar was increased. Experimental data also indicated the same tendency of the concentration of hemicellulose, cellulose. It is hard to measure the concentration of lignin since some lignin-like products are undissolved during the separation of lignin by using strong acid solvents. However, we measured the total weight of products from torrefaction and lignin, and the measured data were agreed with the simulated results. During 30 min torrefaction process at 250°C, 270°C, and 290°C, the average error between simulation and experiment were 9.0%, 9.0, and 4..1%, respectively. Also, the yield of biochar are 39.19%, 36.13%, and 34.15%, respectively. According to previous results, we designed a torrefaction reactor for biochar production, and this reactor can obtain the energy from combustion of the wood itself for energy conservation and environmental protection. Besides, the performance of the reactor can be well operated in the temperature range for torrefaction, which is validated by using RTD (Resistance Temperature Detectors). However, improvements are needed for solid material flow and exhaustion in operation of this reactor.