1-D Coupled Chemical Reaction and Heat Transfer Models for Biomass Fast Pyrolysis

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1 1-D Coupled Chemical Reaction and Heat Transfer Models for Biomass Fast Pyrolysis Presenter: Jianqiu Huang (Tim) Mentor: Shankar Subramaniam Department of Mechanical Engineering

2 Motivation To understand the gas-solid heat transfer and chemical reaction in fast pyrolysis of biomass particles To develop a realistic or predictive model for gassolid flow in biomass fast pyrolysis based on literature of Xue et al. (2011) To improve the existing models to predict biofuel yield accurately

3 Introduction sustainable energy generation from renewable sources that minimizes environmental impact such as the potential of biofuels biomass fast pyrolysis is one of the most promising technologies to produce bio-fuel Experiments of biomass fast pyrolysis is time-consuming and expensive Multiphase computational fluid dynamics (CFD) with chemical reactions is increasingly being used Improvement of the CFD models to predict the biofuel yield precisely A flow diagram of the fluidized-bed pyrolysis reactor system (from Xue et al.)

4 Biomass Fast Pyrolysis Kinetic schemes for cellulose, hemicellulose, and lignin. As indicated, the material components, the active intermediates, and the char are solid phase species, while tar and gas are vapor products. Reaction constant,

5 Deterministic Model

6 Deterministic Model Reaction constant k1 (1/s) Reaction rate of raw materials VS. Temperature (k1) Cellulose Hemicellulos Lignin Reaction constants highly depend on temperature Temperature (K) Reaction constant vs Temperature for 1 st phase

7 1 1.2 Mass decay vs. time for pure cellulose Reaction rate of cellulose is very fast mass in percentage (%) Non-dimensional Time cellulose active cellulose Tar(g) gas(g) Char(s+g) Mass decay plot for pure cellulose for T=790K

8 Chemical Reaction and Heat Transfer Model Two-way coupling system Gas mass balance: 1, Gas species mass balance: 1, Solid mass balance: 1, Solid species mass balance:,,,, Heat transfer model: ε ε R is the reaction rate. S2 stands for solid mass, and g stands for gas mass. All simulations are using the same gas phase velocity since we assume that this is a homogeneous case

9 Results Changes of temperature for all phases Solid temperature Gas temperature Temperature (K) Non-dimensional time (t*k1c) Temperature Changes of Solid and gas species applied heat transfer model

10 Results Reaction Rate 6 x 104 Changes of Reaction Rate for all phases Non-dimensional time (t*k1c) Reaction rate plot for pure cellulose Cellulose(s) Rs21 Semicellulose(s) Rs22 Lignin(s) Rs23 Active Cellulose(s) Rs24 Active Semicellulose(s) Rs25 Active Lignin(s) Rs26 Tar(g) Rg7 Gas(g) Rg8 Char(g) Rg9 Char(s) Rs

11 Results Changes of mass fraction for all phases Cellulose(s) Xs21 Active Cellulose(s) Xs24 Tar(g) Xg7 Total gas: Xg8+Xg9 Char(s) Xs mass fraction (%) Non-dimensional time (t*k1c) Mass fraction plot for pure cellulose in 1

12 Results mass fraction (%) Changes of mass fraction for all phases Cellulose(s) Xs21 Semicellulose(s) Xs22 Lignin(s) Xs23 Active Cellulose(s) Xs24 Active Semicellulose(s) Xs25 Active Lignin(s) Xs26 Tar(g) Xg7 Total gas: Xg8+Xg9 Char(s) Xs Non-dimensional time (t*k1c) x 10 4 Mass fraction plot the reaction is reaching stable

13 Summary and Future work Implementation of first-order chemical kinetics model 1. Reaction constant changed by 6 orders of magnitude with gas temperature from 400K to 800K 2. Limitation of this first order chemical model due to the one-way coupling system Development of the coupled chemical reaction and heat transfer model 1. Two-way coupling system with variation of density, temperature, and reaction rate 2. This model can build a more realistic and predictive model for biofuel yields during fast pyrolysis of biomass Future work: Incorporation of probability distribution function (PDF) of temperature with the model to obtain uncertainty for final biofuel yields

14 Questions?

15 mass fraction (%) Changes of mass fraction for all phases Cellulose(s) Xs21 Semicellulose(s) Xs22 Lignin(s) Xs23 Active Cellulose(s) Xs24 Active Semicellulose(s) Xs25 Active Lignin(s) Xs26 Tar(g) Xg7 Total gas: Xg8+Xg9 Char(s) Xs Non-dimensional time (t*k1c) Mass fraction plot for Bagasse in 1

16 Mass change Mass decay vs. time cellulose Hemicellulose Lignin Active cellulose Active Semicellulose Active Lignin Tar(g) Gas(g) Char(s+g) Non-dimensional Time (t*k1c) Mass decay plot for Bagasse in 1

17 Applied Heat Transfer Model Gas energy: ε Solid energy: ε Gas energy balance: Solid energy balance: ε ε

18 Testament and Evaluation Mass conservation Energy conservation Summation of specific mass (g+s),, Summation of specific energy

19 sum of specific mass 4 x 108 Sum of Specific enthalpy Sum of gaseous mass and solid mass (kg/m 3 ) Specific enthalpy (kj/m 3 ) Time(s) Summation of specific mass Time(s) Summation of specific enthalpy

20 Introduction Major alternative resource of energy supply Using bio-wasted to generate bioenergy (recycle) Less pollution to the environment Economics Less dangerous and easier to control Raw material for the reaction is common and easy to obtain Fig. 1. A flow diagram of the fluidized-bed pyrolysis reactor system.