利用蓄熱式焚化法(regenerative oxidation)處理揮發性有機物(volatile organic compounds, VOC)，在國內外已有許多成功的應用實例，尤其是針對VOC濃度超過1,200 mg/m3的廢氣排放，蓄熱式焚化法亦被證實為一種有效且經濟的處理方法。蓄熱式焚化法的原理是將VOC焚化後的熱排氣以適當的蓄熱填充料(例如：石質或陶瓷材料)加以吸收，其優點為有效地降低排氣溫度，而回收的熱能藉由進氣與排氣控制閥之切換使氣體流向逆轉，又可作為下一序次進流氣體預熱的能量來源。該方法的應用分成「蓄熱式觸媒焚化爐」(regenerative catalytic oxidizers, RCO)與「蓄熱式熱焚化爐」(regenerative thermal oxidizers, RTO)等兩大類，而觸媒床的安裝與否，是兩者最主要的差別。

雖然蓄熱式焚化法在工業界已被廣泛採用，然而針對其處理VOC之設計參數與最佳操作條件，則少有文獻發表與探討。特別是蓄熱填充床的相關性質，例如：填充材質之種類與其填充密度、壓差及填充高度等，通常被視為商業機密而難以取得。本研究為探討蓄熱填充床的相關熱傳性質與最適操作條件，故建立一個「一維移動-延散熱傳模式」(one dimensional convection-dispersion model)加以模擬床內之固體溫度分布，並以模場RCO系統驗證其適用性。該模式係以填充床之軸向「有效熱擴散係數」(effective axial diffusivity,αe)來描述氣固相間的相關熱傳性質，包括：床體填充密度(bulk density)、固體比熱(solid specific heat)及有效熱導係數(effective thermal conductivity)等。模場RCO主體為一組雙床式不?袗?蓄熱床(20 cm(ID)×200 cm(H))，以礫石(gravel)作為填充蓄熱材料，其基本物化性質為平均粒徑1.25 cm、比表面積(specific area) 205 m2/m3及比熱840 J/kg.oC等。在不同深度之床位則設置K型熱感器，分別量測固體與氣體溫度，並隨操作時間加以記錄。觸媒床則加裝電熱器以控制反應溫度。

分別以氣體空塔流速(superficial velocity, Ug)為0.080、0.212及0.382 Nm/s進行測試。實驗結果顯示，當Ug控制在上述流速值，並以2.0×10-6、3.5×10-6及3.8×10-6 m2/s等數值對應代入模式中之αe項，則模擬之固體溫度與試驗數據均得以充分吻合。實驗結果亦可證實，氣固相間之溫差小於10oC，遠小於床體內平均操作溫度217oC，此與氣固相間之溫差極小，使其可以忽略不計之初始假設條件亦屬一致。由本階段所得之試驗成果，可以獲知軸向熱傳導作用(axial conductivity)為床體內之主要熱傳機制，而氣固相間的熱對流作用(convection)為次要機制。同時礫石因其具有迅速蓄熱與釋熱之性質，亦被證實為一種有效的蓄熱材料。

為了解VOC通過填充礫石層時，是否將對蓄熱床內之溫度分布造成影響，同時針對RCO對VOC的去除率加以測試，故分別以丁酮與甲苯作為進料成份進行試驗。進料實驗亦利用前述之模場RCO作為反應器，除了在熱感應器安裝處加裝氣體採樣孔進行氣樣採集，以分析兩種VOCs在床內之濃度變化情形，其餘規格均與前述RCO相同。以曝氣(purge)方式產生氣態形式VOCs後，該含VOCs氣體隨系統負壓流入RCO系統，Ug均為0.234 Nm/s，而觸媒床溫度則控制在400oC。實驗結果顯示甲苯在進流濃度約400 ppm(以甲烷計)，處理效率可達95%；丁酮895 ppm(以甲烷計)，處理效率可達98%。本階段試驗發現，丁酮在高於300oC之床位處，即使尚未通過觸媒床，則丁酮有部份分解現象發生，此作用可由氣流中伴隨含有非進料成份之產物得以證實。同時VOCs分解產生的高熱，使得上述高溫床位之氣固相溫差達到40oC以上，此差異與無VOC進料時氣固相溫差極小之現象完全不同。再由能量平衡計算與排氣溫度觀察亦可知，蓄熱床需維持足夠深度，且控制閥切換時間(shift time)亦應適當減短，則填充礫石所蓄留之熱量方可維持在蓄熱床內，不致隨排氣大量流失。

根據先前累積之經驗，先後設計一系列之低溫蓄熱式熱焚化爐(low temperature RTO, LTRTO)，推廣於工業界使用。LTRTO仍以相同規格之礫石為蓄熱填充材料，惟以僅安裝電熱器之燃燒床取代觸媒床，分別用來處理金屬表面處理、IC封裝及石化廠等含VOCs廢排氣。比起傳統的RTO，LTRTO具有反應溫度較低(300-440oC)可節省操作費用，氮氧化物排放量較少，及排氣溫度較低等優點。根據測試結果，LTRTO的重要設計參數與最佳操作條件為：氣流在爐床內氣體溫度高於300oC主要氧化區(main oxidation zone)之實際停留時間(actual residence time)約為1秒，而控制閥切換時間則可少於5分鐘，此切換時間與傳統RTO所採用的極為接近。在此操作情況下，不論VOCs濃度低於100 ppm(以甲烷計)之單一成份(如：丙酮)，或高達3,000 ppm(以甲烷計)之混合成份(如：甲醇、異丁醇、1-4丁二醇、異壬醇、二甲基丙二醇、甲苯、環氧氯丙烷、甲醛及二甲基胺等)，均可被有效處理，其去除效率均可超過98%。本階段試驗結果與其他VOC處理方法相比較，可以充分證實LTRTO之操作費用相對較低，且其處理效率亦高，值得在工業界大量推廣使用。

Regenerative oxidation is an economic and effective means of controlling volatile organic compounds (VOCs) with concentrations exceeding 1,200 mg/m3 in gas streams. Regenerative catalytic oxidizers (RCO) and regenerative thermal oxidizers are two main applications for the regenerative oxidation. However, factors influencing the performance of regenerative oxidation when treating VOCs in gas streams have seldom been addressed. Therefore, this study presents a convection-dispersion model with an effective thermal diffusivity (αe ) as a parameter to simulate the performance of regenerative beds. To verify the effectiveness of the proposed model, a pilot-scale RCO was constructed with two 20-cm x 200-cm (ID x H) regenerative beds. Gravel was used as the thermal regenerative solid material. Experimental results indicated that the model with an αe of 2.0-3.8 x 10-6 m2/s can be used to describe the time variation of solid temperatures with the packing height at superficial gas velocities (Ug ) of 0.080-0.382 Nm/s . Values ofαe for the bed are closer to those for the gravel solids (αs = 1.0 x 10-6 m2/s) than for air (αg = 54 x 10-6 m2/s). Those results demonstrate that the conductive heat transfer in the solid material in the axial direction of the bed is a major controlling factor for the performance of the RCO and the convective one is a minor factor in the present case.

The above pilot RCO was then used to treat methyl ethyl ketone (MEK) and toluene, respectively, in air streams. The catalyst bed temperature was kept around 400oC and the Ug was operated at 0.234 Nm/s. This investigation measured and analyzed distributions of solid and gas temperatures with operating time and variations of VOC concentrations in the regenerative beds. The overall VOCs removal efficiency exceeded 98% for MEK of around 800 ppm as methane and 95% for toluene of around 400 ppm as methane. Degradation of MEK was believed to occur on the surface of solid material (gravel) in the temperature range of 330-400oC, which is much lower than its autoignition point, and toluene did not exhibit this phenomenon. The calculated energy conservation presents that RCO is an economic approach to treat VOCs, and it should be much further applied to industrial fields.

Furthermore, based on the earlier empirical results of RCO, a series of plant scale low temperature regenerative oxidizers (LTRTOs) equipped with heating wires were constructed to treat VOC-laden gas streams. The regenerative beds were still packed with the same gravel which was applied to the above pilot RCO. Gas streams for performance tests were exhausted from manufacturing sections of varnishing, semiconductor packing, and petrochemical plants, respectively. Components of tested VOCs were comprised of several commercial solvents (e.g. ketone, toluene, iso-propanol, methanol, ethanol, formaldehyde, dimethylamine, and others). Results indicate that exceeding 98% of single or multiple VOCs with concentrations of less than 100 and increasingly to 7,000 ppm as methane would be effectively destroyed. Gas temperature variations with time at various bed depths were analyzed, and results confirm that the degradation of VOCs exists in the gravel beds at the temperatures ranging from 300 to 440oC, which are much lower than auto-ignition points of tested compounds. Moreover, the residence time for a gas stream passing through the main oxidation zone (Tg >300oC) in the regenerative beds is an essential criteria for LTRTO design and 1.0 s is recommended. These findings demonstrate that LTRTO is an effective approach to treat VOCs.

CHAPTER I INTRODUCTION

1.1 Problems Considered……………….............…………………
1.2 Literature Survey………………..............……………………..
1.2.1 Outline of Regenerative Oxidation Systems...........................
1.2.2 Study of Regenerative Beds....................................................
1.2.3 Industrial Applications of Regenerative Oxidation.....….......
1.3 Objects of Research………….............………………………..
1.4 Organization of Dissertation…………...............………………..
CHAPTER II HEAT TRANSFER MODEL FOR REGENERATIVE BEDS

2.1 Introduction……...............…………………………………….
2.2 Model Development……...........………….………………….
2.3 Materials and Methods………………..............……………….
2.3.1 Experimental Setup…..............………………………….
2.3.2 Operation…….....………...………............…………………
2.4 Results and Discussion………………….................…………….
2.4.1 Bed Temperature Profiles and Model Verification...............
2.4.2 Heat-Transfer Zone……..................…….……………..........
2.4.3 Gas and Solid Temperature Difference…….................…......
2.4.4 Significance and Limits of the Proposed Model.................…
2.5 Summary….....……………....................………………………….
CHAPTER III PERFORMANCE CHARACTERISTICS OF OXIDATION OF VOCs IN REGENERATIVE BEDS

3.1 Introduction…………...............……………………………….
3.2 Materials and Methods……………..…................…………….
3.2.1 Experimental Setup………........…..............………………
3.2.2 Operation………………........…................…………………
3.3 Results and Discussion…………..................……………………
3.3.1 VOC Concentration and Solid Temperature Variations in Regenerative Beds……….…...................................……

3.3.2 Comparison of Temperatures of Solid Particles and Air Streams….………………….................................….......…..

3.3.3 Overall VOC Removal Efficiency……….................……..
3.3.4 Energy Conservation……..................……………….…..
3.4 Summary….......……..............……………………….…...……..
CHAPTER IV APPLICATIONS OF LOW TEMPERATURE
REGENERATIVE THERMAL OXIDIZERS TO
TREAT VOCs

4.1 Introduction………………..............…………….…………….
4.2 Materials and Methods…………….................………..………
4.2.1 Experimental Setup……………..……………..…................
4.2.2 Operation………………...............……………………….…
4.3 Results and Discussion……………...................……………….…
4.3.1 Performance Characteristics of RTO1....................................
4.3.2 Performance Characteristics of RTO2....................................
4.3.3 Performance Characteristics of RTO3....................................
4.3.4 Comparison of Residence Time in Regenerative Beds of LTRTO............................................................................................

4.4 Summary….................................………………………………….

CHAPTER V CONCLUSION REMARKS

5.1 Conclusions.................................………………………………….
5.2 Recommendations for Future Work.…………………………….

Boussant-roux, Y., Zanoli, A., and Leahy Jr., W. D., 1995, “Latest
Development in Measurement of Regenerative Thermal Performance,”
Ceram. Eng. Sci. Proc., Vol. 16, No. 2, pp. 74-83.

Brooks, J., 1994, “Help in Controlling VOCs in the Painting-finishing
Industry,” Plating and Surface Finishing, Vol. 81, Nov..

Chen, J., 1996, “Lower Operating Temperatures Oxidizing VOCs,” Pollution
Engineering, Dec., pp. 42-44.

Cheremisinoff, P. N., 1992 , “Industrial Odour Control,” Butterworth-
Heinemann Ltd., Oxford, Great Britain.

Church, F. L., 1989, “Deodorant for a Container Firm: Regenerative
Oxidation,” Modern Metals, Sep., pp. 76-80.

Devinny, J. S., Deshusses, M. A., and Webster, T. S., 1999, “Biofiltration for
Air Pollution Control,” Lewis Publishers, U.S.A..

Don, J. A., and Feenstra, L., 1984, “Odour abatement through biofiltration,”
Proc., Symp.on Characterization and Control of Odoriferous Pollutants in
Process Industries, Belgium.

Environmental Shorts, 1994, “Adhensive Tape Manufacturer Sticks it to VOC
Emissions With Energy Efficiency Regenerative Technology,”
Environmental Progress, Vol. 13, No. 4, pp. N5.

Flagan, R. C., and Seinfeld, J. H.,1988, “Fundamentals of Air Pollution
Engineering,” Prentice-Hall, Inc., U.S.A..

Geankoplis, C. J.,1995, “Transport Processes and Unit Operations,” 3rd. Ed.,
Prentice-Hall International, Inc., Singapore.

Haggin, J., 1994, “Catalytic Oxidizing Processing Cleans Volatile Organic
Compounds from Exhaust,” Chemical and Engineering, Vol. 72, pp. 42-43.

Incropera, F. P., and DeWitt, D. P., 1996, “Fundamentals of Heat and Mass
Transfer,” Fourth Edition, John Wiley and sons, Inc., U.S.A..

Klobucar, J. M., 1997, “Development and Testing of an RTO System for
Control of Plywood Veneer Dryer Air Emissions,” 90th Annual Meeting and
Exhibition of Air and Waste Management Association, Toronto, Canada.

Kunii, D., and Levenspiel, O., 1969, “Fluidization Engineering,” Wiley, New
York, U.S.A..

Levenspiel, O., and Smith, W. K., 1957, Chemical Engg. Sci., Vol. 6, pp. 227.

Lewandowski, D. A., 1999, “Design of Thermal Oxidation System for Volatile
Organic Compounds,” Lewis Publishers Co., U.S.A..
Lippmann, M., 1992, “Environmental Toxicants,” Van Nostrand Reinhold,
New York, U.S.A..

Long, K.; and Parr, G. L.,1980, “Resin Plant Uses Fluidized Bed, Catalytic
Incineration System to Remove 98.1% Pollutants,” Chemical Processing,
Vol. 43, pp. 30-32.

McCabe, W. L.; Smith, J. C.; and Harriott, P., 1985, “Unit Operations of
Chemical Engineering,” McGraw- Hill Book Companies, Inc., Forth Edition,
U.S.A..

Nester, J. L., and Uphues, R., 1997, “Regenerative Thermal Oxidizer Upgrades
Allow Coil Coater to Increase Production and Maintain Regulatory
Compliance,” Metal Finishing, Jan., pp. 46-48.

Nevers, N. D., 2000, “Air Pollution Control Engineering,” McGraw-Hill Co.,
Inc., U.S.A..

Pennington, R. L., 1990, “Regenerative Thermal Oxidation Destroys VOCs and
Saves Energy,” Industrial Finishing, No. 3.

Perry, R. H., and Green, D. W., 1997, “Perry’s Chemical Engineers’
Handbook,” Seventh Edition, McGraw Hill, U.S.A..

R.O.C. EPA, 1988, “Handbook of Odour Control Technology,” Vol. 1-4.

R.O.C. EPA, 1997, “Regulations and Emission Standards of Volatile Organic
Compounds.”

Suzukawa, Y., Sugiyama, S., and Mori, I., 1996, “Heat Transfer Improvement
and NOx Reduction in an Industrial Furnace by Regenerative Combustion
System,” Proceeding of the Intersociety Energy Conversion Engineering
Conference, pp. 804-809.

Tamme, R., Grözinger, U., Kanwischer, A., and Neitzel, U., 1995, “Advanced
Regenerative Media for Industrial and Solar Thermal Applications,”
Proceeding of the Intersociety Energy Conversion Engineering Conference,
pp. 218-221.

U.S. EPA, 1991, “Handbook: Control Technologies for Hazardous Air
Pollutants,” EPA/625/6-91/014, Jun..

Yi, J., and Choi, B. -S., 2000, “Simulation and Optimization on the
Regenerative Thermal Oxidation of Volatile Organic Compounds,” Chemical
Engineering Journal, Vol. 76, pp. 103-114.