氣泡式流體化床應用於農業廢棄物之焚化特性研究

Study on the Incineration Characteristics Using Agricultural Wastes in Bubbling Fluidized Bed Incinerator

王豊政(Feng-Jehng Wang)

指導教授 ： 陳世銘

國立臺灣大學/生物資源暨農學院/生物產業機電工程學研究所/博士(2007年)

https://doi.org/10.6342/NTU.2007.10639

摘要

本研究係根據農業廢棄物如農業廢棄塑膠布及病死豬等之理、化特性分析結果，以及農業廢棄物的燃燒與質能平衡理論，加上焚化爐設計與操作之主要參數等，設計並製造一實驗室用中型氣泡式流體化床焚化爐（Bubbling Fluidized Bed Incinerator；BFBI），並透過流體化理論、數值模擬分析及實驗量測等方法以了解流體化床焚化爐內部流體化氣體流速與壓力降之關係，藉以驗證及確認自行研製之氣泡式流體化床焚化爐之床質（矽砂）流體化調控特性。最後進行農業廢棄物之焚化試驗，透過焚化後所排放之廢氣與灰燼採樣分析結果，來建立本焚化爐之最佳操控體系。
本研究針對農業廢棄物之理、化特性分析，採用美國材料試驗協會（ASTM）之標準測定方法進行三成份、高熱值及組成元素等分析，結果顯示：L.Y.D.3品種病死公豬整隻豬體之低熱值（LHV）平均為5763.65kcal/kg，平均含水率為65.86%w.b.，平均含碳量為55.27%，平均含氧量為23.53%，可知豬體係為一高熱含量、高含水率及高含碳、氧量之有機燃料；又農業廢棄PP、PE、PVC及PS等塑膠布皆係含有高達95%以上之碳、氫可燃成份，且低熱值含量皆達10000 kcal/kg，為具有極高熱含量之化合物，且含水率及灰份皆極低（平均在1%以下）。根據這些農業廢棄物之理、化特性分析結果，可判定利用焚化法來處理該等農業廢棄物係為最適當可行的方法。
本研究並利用L.Y.D.3品種病死公豬化學組成元素之重量百分比與高熱值之實測值，經SAS迴歸分析而得到能準確估算豬隻高熱值（HHV）之相關公式（其相關係數皆達R2 = 0.65），為生質燃料之熱值估算公式建立一套標準研究方法。
本研究並透過流體化理論、數值模擬分析及實驗量測等方法來驗證該氣泡式流體化床焚化爐之流體化特性與床壓降之關係，以了解焚化爐內部流場變化情況，並建立一省時、有效之氣泡式流體化床焚化爐之數值模擬方法。利用計算流體力學軟體來模擬氣泡式流體化床焚化爐空床氣速（最小流體化速度）與流體化床壓力降的關係，根據數值模擬的結果顯示空床氣速和流體化床壓力降間具有顯著的線性關係（R2 = 0.9977），當空床氣速為0.188m/s時，床壓降等於4562.499Pa，與試驗計算值（4573.33Pa）的結果甚為接近，故本研究採用空床氣速為0.188m/s作為焚化實驗之最小流體化速度。本研究同時以3種不同之床砂拖曳係數與雷諾數之假設公式，求得流體化床床砂的終端速度為3.684m/s。進而確認本研究氣泡式流體化床操作時之空床氣速需限制在最小流體化速度與終端速度之間。
本研究利用BFBI焚化爐進行農業廢棄PP塑膠布之焚化試驗，在固定進料率與供氧率下，燃燒溫度自500℃至1000℃之間，其排放廢氣經採樣分析結果顯示：SO2之排放濃度隨著溫度之升高稍有遞減之趨勢；NO之排放濃度隨著溫度之升高有遞增之趨勢；CO之排放濃度隨著溫度之升高有遞減之趨勢；CO2之排放濃度隨著溫度之升高有遞增之趨勢；PM10之排放濃度隨著溫度之升高有遞減之趨勢。且根據農業廢棄PP塑膠布之焚化試驗結果顯示，焚化效率隨著溫度之升高有遞增之趨勢，且爐床溫度在700℃（含）以上時之焚化效率達94%（含）以上，顯示本焚化爐之焚化效率極佳。
本研究利用BFBI焚化爐進行農業廢棄PE、PP及PVC等塑膠布之焚化試驗，廢氣採樣分析結果顯示，在500、600、700、800、900及1000℃等不同焚化溫度下，16種PAHs之總排放濃度以700℃時為最少量或並無PAHs污染物生成；又自焚化後灰燼之組成份採樣分析結果顯示，飛灰及底灰中所含之碳、氫可燃成份，以焚化溫度為700℃時最低。故可判定700℃為本焚化爐之最佳操作溫度。

關鍵字

流體化 ； 氣泡式流體化床 ； 焚化爐 ； 農業廢棄物 ； 數值模擬

並列摘要

This study was based on the analysis results of the physical and chemical characteristics of the agricultural wastes: For example the used plastic sheets from agricultural production and sick-and-dead pigs (L.Y.D.3 male pig), etc., as well as the combustion and mass-energy balances theories of the agricultural wastes, together with the main parameters of the incinerator design and operation, etc. In order to design and manufacture a middle Laboratory-scale Bubbling Fluidized Bed Incinerator (BFBI). Moreover, through the fluidized theory, numerical simulation analysis and experimental measurements etc., to determine the relationship between the fluidized gas flow velocity and pressure drop within the fluidized bed incinerator. In order to prove and confirm the fluidized characteristics of the bed sand (silica sand) of the BFBI developed by oneself. Finally, the incinerations of the agricultural wastes were being tested. The sample analysis from the emission pollutants and ash discharged through incinerating, in order to set up the optimum operation and control system of this incinerator.
This research based on the analysis of the physical and chemical characteristics of agricultural wastes. The standard methods of American Society for Testing Materials (ASTM ) were being used for proximate analysis, higher heating value（HHV）and ultimate analysis. The experimental results indicated that for the entire L.Y.D.3 male pig, the average lower heating value (LHV) and the average rate for the moisture content were 5763.65kcal/kg and 65.86%wb, respectively; carbon content was 55.27%, and oxygen content was 23.53% on average. These showed that L.Y.D.3 male pig's body had high heat and moisture contents, as well as high carbon and oxygen content organic fuel. Moreover, the agriculture discarded plastic films, such as PP, PE, PVC and PS, etc., contained up to more than 95% carbons and hydrogen combustible compositions, as well as the LHV all reached 10000 kcal/kg, had extremely higher chemical heat compound, together with the moisture content and ash were all extremely low (under 1% on average). According to the analysis result of the physical and chemical characteristics of the agricultural wastes can be concluded that the method of incinerating to deal with these agricultural wastes was considered as the optimal and feasible method.
The research also based on the L.Y.D.3 male pig's chemical compositions weight percentage and actual measurement value of HHV, through the regression analysis by SAS software, can develop the correlation models accurately in order to determine the HHV of pigs (their correlation coefficients all reached to R2 =0.65), as well as to build up a set of standard research approach formulae for the prediction of the HHV of bio-fuel.
This research through the methods of fluidized theory, the numerical simulation analysis, and the experimental measurement to prove that relationship between the fluidized characteristics and pressure drops of the BFBI. To determine that change flows within the incinerator, as well as to set up a saving time and effective method for bubbling fluidized bed incinerator numerical simulation. This study used the computational fluid dynamics (CFD) to determine relationship between the superficial velocity and pressure drop in BFBI. According to results of the numerical simulation showed that the linear equation had a significant relationship between the superficial velocity and pressure drop. When the superficial velocity of bed is 0.188m/s, the pressure drop equaled to 4562.499Pa was close to the result of the experimental calculating value (4573.33Pa) extremely. So this research adopted the superficial velocity 0.188m/s to be regarded as the minimum fluidization velocity when incinerated experiments. This research utilized 3 kinds of different assumption formulae with drag coefficient and Reynolds numbers to obtain the terminal velocity of bed particle was 3.684m/s. And then, confirmed that the superficial velocity must be limited between minimum fluidization velocity and terminal velocity in the BFBI.
This research utilized the BFBI to incinerate the agriculture discarded plastic film of PP. Under the regular feed rate and oxygen support, combustion temperature from 500 to 1000℃, the sampled emission gas and the analysis results showed that: the emission trend of SO2 slightly decreased progressively with the increase of temperature; the emission trend of NO was increased progressively as the increase of temperature; the emission trend of CO decreasing progressively as the increase of temperature; the emission trend of CO2 increasing progressively as the rising of temperature; the emission trend of PM10 decreasing progressively as the rising of temperature, respectively. The results showed based on the result of the incineration experiments of agriculture discard plastic film of PP, there was an increasing progressively trend with the increase of the temperature to incineration efficiency, and the incineration efficiency at the above of 700℃ (include) of bed temperature was up to 94% (include) above, showed that the incineration efficiency of the BFBI is extremely well.
This research utilized the BFBI to incinerate the agriculture discards plastic films, such as PE, PP and PVC, etc. The analysis results of the emission gas sample showed that incineration under difference temperatures 500, 600 , 700 , 800 , 900 and 1000℃, etc., the total emission of 16 kinds of PAHs was less or there was no PAHs emission at 700℃. Ashes composition was sampled and analyzed after incinerating; the results indicated that combustible carbon and hydrogen which included in fly ash and bottom ash were lowest with incinerating temperature at 700℃. Therefore, the results proved that 700℃ was the optimal operation temperature for the BFBI.

並列關鍵字

fluidized ； bubbling fluidized bed ； incinerator ； agricultural waste ； numerical

參考文獻

1. 王岱淇、馮丁樹。1993。農業品廢棄物焚化物性之研究。農業機械學刊。2(4)：1-12。

2. 王岱淇、馮丁樹、1994。高濕穗軸在燃燒爐之燃燒分析及其顯熱輸出模式之探討。農業機械學刊。3(1)：31-46。

8. 吳中興。1994。玉米穗軸焚化爐三維流場模擬。農業機械學刊。3(3)：1-14。

23. 台灣農業年報。2005。行政院農業委員會。

24. 行政院環境保護署九十四年統計年報。