Non-catalytic Fuel Reforming
Syngas, a mixture of hydrogen, carbon monoxide (CO) and carbon dioxide, is an important as a fuel and a feedstock for other chemical processes. Most syngas is produced through catalytic steam reforming of methane (CH4). This process is effective but catalysts often limit the feedstock in terms of purity to avoid catalyst contamination or deactivation. The Ellzey Combustion Group is researching non-catalytic fuel reforming known as filtration combustion (see Figure 1). In this process, a fuel-rich mixture of air and fuel is reacted in an inert porous matrix to produce syngas. Some of the fuel and air mixtures under study lie outside the conventional rich flammability limits, meaning that at standard temperature and pressure these mixtures will not ignite. These mixtures react because high local temperatures are created as the reaction front propagates into a region where the solid matrix has been heated by exhaust gases. These high temperatures effectively broaden the flammability limits, allowing the mixture to react and break down the fuel into syngas.
Figure 1. Filtration Combustion
The overall goal of this project is to test the use of filtration combustion with many different, from corn ethanol to heavier hydrocarbons. Although hydrogen yields and efficiency are the main concern, the exhaust composition as a whole is also of interest. In order to maximize hydrogen production and confirm computational models of the experiment, various parameters like inlet velocity and equivalence ratio (fuel to air ratio) are altered and the results are investigated.
Application of Filtration Combustion to Conversion of Wet Ethanol
Though there are many biofuels, ethanol (C2H5OH) is a popular choice for replacing fossil fuels. However, many have questioned its value as a renewable fuel since it requires a significant amount of energy to produce, especially from corn. Producing pure ethanol requires substantial energy for distillation and dehydration to yield an appropriate "dry" fuel for traditional combustion engines. Wet ethanol, or ethanol that has not been fully distilled and dehydrated, requires significantly less energy to create than pure ethanol. This research demonstrated successful conversion of wet ethanol to syngas in a filtration reactor.
Counterflow Reactor Design and Manufacture
Current advances in mobile devices are bringing about power demands that are quickly outpacing available battery technologies. Portable power systems based on fuel cells promise higher power densities, but face challenges with respect to the storage of suitable fuels. Hydrocarbon fuels offer high power densities and can be reformed into a hydrogen-rich syngas, which, once purified, can be used to power hydrogen-operated fuel cells. In order to reform these hydrocarbon fuels, the Ellzey group has developed a novel non-catalytic mesoscale fuel reformer concept, which is based on heat recirculation between parallel channels with opposing flow directions (see Figure 2). This heat recirculation allows for the creation of stationary combustion zones that react fuel and air mixtures beyond the conventional rich flammability limit. This means that fuel-rich mixtures that will not ignite at standard temperature and pressure are able to react in the high temperature environment created by the counterflow design. These fuel-rich conditions are favorable for syngas production. Over the past several years, Dr. Ingmar Schoegl developed a working prototype of the proposed reactor and confirmed that the groups members' theoretical and computational predictions were correct.
Figure 2. Counterflow configuration
Current Work with SLS Manufacturing
Although a working reactor design has now been developed, commercial viability of such a device necessitates that it is rugged and easily produced. To that end, group members are investigating the use of Selective Laser Sintering (SLS), which was developed here at the University of Texas, as a method of producing the reactor from a single block of material. Due to tolerances of the sintering process, further design of the reactor and experimentation are necessary, alongside further investigations into streamlining the manufacturing process as a whole and maximizing the reforming characteristics if the reactor for real-world use. In 2019, a counterflow reactor was manufactured using SLS and successfully ignited; current work involves manufacturing a second reactor for further testing and investigating operational hazards such as coking.
