Renewable Energy and Fuels from Waste: Thermochemical Pathways

Focus of this work is on energy conversion to generate clean, renewable fuel or electricity from a wide variety of feedstocks often considered as "waste" (e.g., petroleum coke, industrial waste, and biomass). One example of thermochemical technology is gasification, and through this research we will examine this technology to convert the chemical energy stored in a wide variety of feedstocks, including municipal and industrial waste and refinery by-products to generate heat, steam, and fuels including: hydrogen and chemicals, as well as other products. Our goal in thermochemical conversion is to achieve a radical improvement in the technology through analysis and advanced simulation, with parallel efforts in design and optimization using simulation codes. Concurrent laboratory work and experimental diagnostics in Abu-Dhabi will be used for validation particularly when unconventional and previously untested feedstocks are used.

The approach is to simulate the reactive flow occurring within the gasifier to capture the intrinsic and extrinsic flow dynamics, transport and chemistry, and their coupling. It is a progressive approach: first, equilibrium zero-dimension reacting species are considered and the mixture fractions are computed while the effects of pressure and temperature are studied. Second, detailed two and three dimensional CFD cold (nonreacting) flow analysis are conducted. Third, the effect of the discrete particle on the mass, momentum and energy on the continuous fluid medium and on its trajectory, as part pf a two-way coupled system, is integrated. Fourth, reactive flow dynamics on the two phase flow with chemical kinetics coupling will be carried out.

While the first task implements only the 1st and 2nd thermodynamic laws, it provides a good prediction of the mean species mass/molar fractions. Particle residence times and trajectories along with flow field variables will be studied in the 2nd and 3rd tasks. The detailed CFD chemical coupling, studied in the 4th task, provides us with the local distribution of the species, their mixing, heating and accurate syngas yield and composition. A pilot laboratory scale gasifer plant is planned in Abu Dhabi to obtain experimental data and simulation validation. It will be instrumented with gas optical diagnostics for gas emissions, pressure transducers, thermocouples as well as a digital data acquisition system. Other experimental equipment, including mass spectroscopy and gas chromatography, are planned for non-conventional feedstocks and ultimate and proximate analyses. Issues related to minimizing the Combined Cycle capital cost by integration or elimination of heat recovery units or bottoming cycles will be addressed.

Thorough literature searches are being conducted on zero-dimensional-modeling, the basis of gasification, and the governing conservation laws for detailed CFD/chemical kinetic coupling. So far we have achieved the following:

(1) Zero -dimension modeling of two examples of feedstocks: baseline (coal) and industrial waste (tire);
(2) Reactor geometry identification with CFD cold-flow analysis for the axisymmetrical and three-dimentional geometries;
(3) Introduction of discrete phase into the cold-flow and CFD analyses for the axisymmetrical and three-dimensional geometries;
(4) Testing the integration of coupled CFD/Chemical kinetics (work in progress).