Dissertation for the Degree of Doctor of Philosophy Plant-Based Biomass Pyrolysis and Reaction Kinetic Models in Different Types of Reactor Thanh-An Ngo Department of Chemical Engineering Graduate School Kyung Hee University Seoul, Korea August, 2010 Dissertation for the Degree of Doctor of Philosophy Plant-Based Biomass Pyrolysis and Reaction Kinetic Models in Different Types of Reactor Thanh-An Ngo Department of Chemical Engineering Graduate School Kyung Hee University Seoul, Korea August, 2010 Plant-Based Biomass Pyrolysis and Reaction Kinetic Models in Different Types of Reactor by Thanh-An Ngo Supervised by Prof. Jinsoo Kim Submitted to the Department of Chemical Engineering and the Faculty of the Graduate School of Kyung Hee University in partial fulfillment of the requirements for degree of Doctor of Philosophy Dissertation committee Chairman Prof. Sung Hun Ryu ………… Prof. Seung-soo Kim ……….
Chang Woo Lee ………. ABSTRACT Plant-Based Biomass Pyrolysis and Reaction Kinetic Models in Different Types of Reactor Thanh-An Ngo Department of Chemical Engineering Graduate School of Kyung Hee University Seoul, Korea Biomass, a plant-derived material, is currently considered as a renewable resource for producing energy owing to its low cost as well as its abundance. It largely contains hemicellulose, cellulose (for wood-based biomass) or cellulose- like compound (for seed-based biomass), and lignin of which the content could change depending on type of biomass. Recently, much attempt has been focused on pyrolysis, a thermochemical technology, as a promising approach for biomass conversion into bio-fuel.
Although paid much more attention, pyrolysis, especially its reaction pathways, is ambiguously understood because of its complexity. In addition, it should be noted that the most important factor to lower technology and operation cost is to reduce the number of controlling variables. If the operating parameter is more systematically investigated through which the insignificant ones could be realized, i the controlling process would be more simplified and easily operated, resulting in improving technology’s economical feasibility. As a consequence of all previous reasons, in this research, the plant-derived biomass was used as an object for pyrolysis in both closed and open reactor.
The statistical design of experiment (DOE) was applied to set up for some experiments and then all the model equations would be employed to optimize the process. More importantly, the kinetic mechanisms were also explored carefully by using different lumped kinetic models. Subsequently, experimental data would be applied for verifying the accordance with proposed models. All the detail contents of this research were briefly shown as follows: For the pyrolysis in closed reactor (micro-tubing reactor), a statistical design of experiment (DOE) was applied to set up for experiment run and then all the model equations would be employed to optimize the process.
The palm kernel cake was utilized as the feedstock for all experiment using this type of reactor. In order to understand more about pyrolysis mechanism in the micro-tubing reactor, through which all the affecting parameters could be clarified, leading to the ability to upgrade the performance of pyrolysis, the kinetic model was also proposed, and the rate constants were subsequently drawn. The results showed that all the primary reactions were much more dominant than the secondary ones and the pyrolysis in closed condition seem to be preferable to generating solid product rather than other products. ii As for the fast pyrolysis in tubular reactor, first of all, a comparative study of pyrolysis was carried out using both types of biomass: palm kernel cake (major non-cellulosic material) and pine wood chip (cellulosic material).
The effect of biomass feedstock on the distribution and properties of product were also investigated. In addition, the kinetic model of fast pyrolysis was also presented and verified. From regression calculation, the rate constants were obtained. From these constants, it can be found that the fast pyrolysis in tubular reactor was more favorable to occur via the reaction forming tar following by the decomposition of tar to produce gas, rather than reaction forming the mixture product of char and gas.
Finally, for the pyrolysis in open reactor (fluidized bed reactor), the central composite rotatable design (CCRD) was employed for investigating the effect of feed rate of feedstock, biomass particle size, pyrolysis temperature and residence time on fast pyrolysis of biomass (palm kernel cake). The activation energy of pyrolysis in the open condition was also determined using thermogravimetric analysis (TGA). Moreover, from TGA data the surveyed temperature range was withdrawn. From the data, the mathematical model for liquid product yield was hence obtained and used to reach the optimum of 49.5 wt%, corresponding to the condition of feed rate 225 g/hr, particle size 600µm, pyrolysis temperature 500°C, and residence time 0.
iii Table of Contents Abstract. i List of Figures. ix List of Tables. xii CHAPTER 1 – General Introduction 1.12 CHAPTER 2 – Literature Review 2.
Concept of biomass. Biomass definition and classification. Approaches for biomass conversion into energy. Concept of pyrolysis.
Pyrolysis mechanisms and pathways. Theory of central composite rotatable design (CCRD). Set up experiment using matrix design. Calculating the regression coefficients.
Verifying the statistical significance of each regression coefficient. Verifying the lack of fit of regression equation .38 CHAPTER 3 – Effect of Operating Parameters and Kinetics of Pyrolysis in a Tubing Reactor 3. Characterization of biomass. Pyrolysis of palm kernel cake.
Characterization of pyrolysis product. Results and discussion. Characteristics of biomass. Thermal decomposition analysis of biomass.
Optimization of pyrolysis conditions by CCRD. Characterization of pyrolysis products .71 CHAPTER 4 – Comparative Study of Pyrolysis of Palm Kernel Cake and Pine Wood Chip Using an Open Tubular Reactor 4. Results and discussion. Thermogravimetric analysis of biomass.
Effect of fast pyrolysis conditions on product yield.93 vi CHAPTER 5 – Kinetic Model of Fast Pyrolysis using Palm Kernel Cake in a Closed Tubular Reactor 5. Calculating product yield. Results and discussion. Composition of gas product .112 CHAPTER 6 – Pyrolysis kinetics and parametric effects on fast pyrolysis of palm kernel cake using thermogravimetric analyzer and fluidized bed reactor 6.
Fluidized bed reactor. Results and discussion. Kinetic parameters of pyrolysis using TGA. Fast pyrolysis using fluidized bed reactor.
Characteristic of pyrolyzing liquid product.141 CHAPTER 7 – Conclusions and further researches 7.147 viii List of Figures Page Figure 2.1 Structure of hemicellulose 17 Figure 2.2 Structure of cellulose 17 Figure 2.3 Structure of lignin 18 Figure 2.4 Structure of mannan 18 Figure 2.5 Some typical applications of biomass 23 Figure 2.6 Energy products and classification 25 Figure 2.7 Pyrolysis definition 27 Figure 2.8 Pure cellulose pyrolysis pathway: (1): primary pyrolysis; (2) secondary pyrolysis 33 Figure 2.9 Global kinetic model 33 Figure 2.10 Reaction scheme used by Liden, and Diebold 33 Figure 2.11 Reaction scheme of Knight.1 Schematic diagram of experimental apparatus 45 Figure 3.2 TGA and DTG curve for pyrolysis of palm kernel cake using TG method 50 Figure 3.3 Gas yield in the variation of experiment 54 Figure 3.4 Liquid yield in the variation of experiment 54 Figure 3.5 Solid yield in the variation of experiment 55 Figure 3.6 The chromatogram of GC – FID for gas product 57 ix Figure 3.7 Proposed pyrolysis model 63 Figure 3.8 Effect of residence time on product distribution at 400°C 68 Figure 3.9 Effect of residence time on product distribution at 430°C 68 Figure 3.10 Effect of residence time on product distribution at 460°C 69 Figure 4.1 Schematic diagram of experimental apparatus 76 Figure 4.2 DTG data of TG analysis for PKC and PWC at heating rate of 20oC/min 79 Figure 4.3 Product yield of fast pyrolysis of palm kernel cake 82 Figure 4.4 Product yield of fast pyrolysis of pine wood chip 82 Figure 4.5 Yield of hydrocarbon and mixture of CO and CO2 in gas products obtaining from fast pyrolysis at different conditions: (1) - 550oC, 20 mL/min; (2) - 550oC, 500 mL/min; (3) - 750oC, 20 mL/min; (4) - 750oC, 500 mL/min 85 Figure 4.6 GC-FID analysis of pyrolyzing gas product of pine wood chip at 750oC, 20 mL/min 85 Figure 5.1 Pyrolysis reaction mechanisms proposed by Liden [1] 96 Figure 5.2 Schematic diagram of experimental apparatus 96 Figure 5.3 Relationship between biomass yield and reaction time described by equation (10) 106 Figure 5.4 Product yields of fast pyrolysis obtained from experimental data and calculations at various conditions 110 Figure 6.1 Schematic diagram of experimental apparatus 119 x Figure 6.2 DTG data from thermogravimetric analysis of palm kernel cake 123 Figure 6.3 The relationship between ln(dX/dt) and 1/T at different iso-conversion points 124 Figure 6.4 Calculated activation energy of pyrolysis as a function of conversion 124 Figure 6.5 Relationship between actual and predicted value of liquid product yield 134 Figure 6.6 Liquid yield at the condition of feed rate = 160g/hr, particle size = 300µm 134 Figure 6.7 Liquid yield at the condition of pyrolysis temperature = 400oC, residence time = 0.8 Liquid yield at the condition of residence time = 0.9 sec, particle size = 600µm 135 xi List of Tables Page Table 3.1 - Sample characteristic of palm kernel cake 47 Table 3.2 Central composite rotatable design 22 + 2x2 + 5 53 Table 3.3 Composition of solid product by Elemental analysis 60 Table 3.4 GC – MS analysis of bio-oil from pyrolysis of palm kernel cake at 460oC 61in 12 min 61 Table 3.5 Reaction rate constants (min-1) of pyrolysis 67 Table 4.1 Bio-oil and water content in liquid product at 550oC 86 Table 4.2 Major bio-oil product analyzed by GC-MS for fast pyrolysis of Palm kernel cake at 550oC, 500 mL/min 89 Table 4.3 Major bio-oil product analyzed by GC-MS for fast pyrolysis of Pine wood chip at 550oC, 500 mL/min 90 Table 5.1 Reaction rate constants (s-1) 109 Table 6.1 Factor variation intervals 126 Table 6.2 Experimental design matrix and response value 127 Table 6.3 Statistical significance of regression coefficients 130 Table 6.4 GC-MS analysis of bio-oil from pyrolysis of palm kernel cake at 400 and 500°C 139 xii CHAPTER 1 General Introduction 1. Biomass source As commonly known, fossil fuels, namely oil and coal, are limited. Oil is estimated to be run out within 40 years and coal within 250 years from now [1]. From this issue, many researchers have focused on finding a new source for energy.
Biomass is one of the most interesting alternative sources, which has been paid much more attention to in recent years, owing to its low cost as well as its abundance [2]. The term biomass is used to describe all biologically produced substances. World production of biomass is estimated at 146 billion metric tons a year. Some farm crops and trees can produce up to 20 metric tons of biomass per acre a year.
Only algae and grasses may produce 50 metric tons per year [3]. The source of biomass is infinite and can be replenished through natural processes, hence it is also considered as a renewable source for producing energy. For instance in the United States, biomass contributes 1.5% of the total electricity supply compared to 0.1% for wind and solar combined. More than 7800 MW of power is produced in biomass power plants installed at more than 350 locations in the U., which represent about 1% of the total electricity generation capacity.
1 According to the International Energy Agency, approximately 11% of the energy is derived from biomass throughout the world [4]. Biomass can stem from timber industry, agricultural crops, forestry residues, household wastes and wood [5]. Of all these types of biomass, woody biomass makes up the most major amount. Therefore, most researches have now focused on this one.
This material largely contains hemicellulose, cellulose (for wood-based biomass) or cellulose-like compound (for seed-based biomass), and lignin of which the content could change depending on type of biomass. Hemicellulose, a branched biopolymer with a random and amorphous structure, is most favorably decomposed. In contrast, lignin is the most difficult one to be degraded due to its cross-linked three-dimensional structure.