Numerical modeling of a high temperature carbon particle generator

Dokhale, Mugdha Shrikant

Miller, Fletcher J
Bhattacharjee, Subrata
Alves, Thais da C. L.

2012-10-24

Thesis

xii, 61 p. : ill.

In recent history, the world has depended on non-renewable, polluting and fast depleting fuels as a source of energy. As the consciousness for clean energy resources gains momentum, the most extensive source of energy comes from the sun. The best method to commercially use solar energy for power generation is by using a concentrated solar power plants. The project under Prof. Fletcher Miller on the CSP Plant is working towards increasing efficiency and get more heating power from concentrated solar rays. The idea is to circulate carbon nanoparticles mixed with air, through the high temperature solar receiver instead of any other circulation fluid. These carbon particles act as the heat exchanger to heat up the air directly and run the gas turbine. The small carbon particles are generated in a Small Carbon Particle Generator (CPG) currently built lab-scale. It enables experiments to be conducted with different flow rates of natural gas and nitrogen and to study the carbon particles generated. The work here deals with thermal analysis of the CPG, in order to have an idea about the reactions and the temperatures achieved by the reacting gases. This work is necessary to determine the rate and the size of the carbon particles generated to get good control of the mass flow rates of the reactants and the maximum wall and flow temperatures achieved when the CPG will be scaled up to a bigger size to provide carbon particles for the actual receiver. To begin with, a basic 3-D model of the inlet tube was built, and the analysis was conducted using air as a fluid with and without the effect of gravity, because the CPG can be turned to keep inlet at the top or at the bottom. It was shown that flow against gravity yields better results. Result from Fluent CFD was also validated by manual temperature calculations. After establishing the ideal orientation of the reaction tube to be used for further analysis, the initial design was modified to include two concentric tubes as inlet for the hydrocarbon gas and nitrogen. The soot model in Fluent was used to analyze the thermal and flow behavior of the gases to predict the quantity of soot formation. Different flow rates were used for hydrocarbon gas and nitrogen because eventually a much larger flow rate will be used to produce large amount of solid carbon particles i.e. soot. A study was done to get an idea about the ideal flow rate ratios, effect of wall temperature on pyrolysis and to confirm the findings about flow with respect to gravity

Includes bibliographical references (p. 57-58).

en_US

Mechanical Engineering

Mechanical Engineering

Engineering

Master of Science (M.S.) San Diego State University, 2012

TA350.2

microfiche