Types of Non-catalytic Fuel Reforming
- Partial oxidation or fuel-rich reforming: The simplest way to convert fuels to hydrogen-rich syngas is by using air as an oxidizer. The products of this process can then be directly utilized by Solid Oxide Fuel Cells (SOFC), used in chemical processes, or mixed with other fuels. Hydrogen (H2) and carbon monoxide (CO) are the major equilibrium state products in an oxygen-deficient (fuel-rich) environment. However, the energy released from the exothermic partial oxidation reaction itself is typically insufficient to adequately raise the temperature necessary to drive the reforming reactions within the available residence time. Therefore, catalysts are usually needed to accelerate the reaction rate and enable sustained reactions. The use of catalyst allows the reformate to reach its chemical equilibrium state, where the optimal H2 and CO concentrations are achieved. However, common fuels, such as JP-8 used in military logistics, contain sulfur, a notorious catalyst poison. In addition, coking and degradation of catalysts are also technical challenges for catalytic-based fuel reformers.
- The non-catalytic partial oxidation (Thermal Partial Oxidation or TPOX) reforming: This method can avoid the catalyst issues stated above and efficiently generate the desired reformate composition. One strategy to keep temperatures sufficiently high in TPOX systems is to use pure oxygen as an oxidizer to avoid the additional thermal mass of inert nitrogen in the air. While such a strategy has been incorporated in other industries for large-scale reformate production, air/oxygen separation is hardly practical at the portable scale. It is possible to use air as an oxidizer by utilizing external energy sources, such as plasma, which promote the reforming reactions. However, the electricity needs for such a system are subject to efficiency loss during the conversion process, and the need for an additional power source increases the size, weight, and system complexity.
- Swiss-roll heat recirculating combustor: The technology enabling air-breathing TPOX reformers without an expensive catalyst or external power source is the Swiss-Roll heat recirculating combustor developed at Advanced Cooling Technologies, Inc. The combustor effectively recuperates the heat released from the exothermic partial oxidation to the reactants and significantly increases the reaction temperature. This enables the reformates to reach their chemical equilibrium state without the need for catalysts or external energy sources. Expensive catalysts and complicated subsystems are avoided in Swiss-Roll combustors. The long spiral inlet and outlet channels provide additional benefits for the reforming reaction, including enhanced mixing of reactants and increased residence time of the reaction.
Figure 1. The flare of reformate from liquid fuel (n-heptane). The blue color indicates no visible soot formation in the reformate.
Figure 2. Tests with a rich propane-air mixture. Left: Without reforming reaction in the center, the downstream flare is yellow due to the soot formation of non-premixed combustion of propane. Right: With reforming reaction in the center, the downstream flare is blue due to the absence of soot formation in an H2 and CO flame.
Figure 3. The Swiss-roll fuel reformer prototype under ultra-rich JP-8/air operation.
Fuel Compatability of Swiss-Roll Combustor Technology
The Swiss-Roll combustor is compatible with a wide range of fuels and is insensitive to the majority of contaminants. Furthermore, the compactness and robustness of the design allow for excellent system integration options, where reformed products can be used to improve other characteristics. The high conversion efficiency enables complex fuels to serve as hydrogen transport media. This allows to use of energy-dense fuels such as JP-8 (34.5MJ/L) or carbon-free Ammonia (11.5 MJ/L) to power hydrogen-burning systems without the need for high pressure or cryogenic H2 tanks (<10 MJ/L).
Figure 4. Comparison of H2 mole fraction between CFD (FLUENT) and 1D reactor (CHEMKIN) modeling. Left: CFD mole fraction contour. Right: CHEMKIN PFR mole fraction profile of the outlet channel.
Swiss-Roll Technology Innovation
The Swiss-roll reformer concept has been experimentally and numerically demonstrated at ACT (Figure 2 and Figure 3). Reforming liquid fuels such as n-heptane (Figure 1) and JP-8 (Figure 3) has also been demonstrated. The work on JP-8 fuel is concluded in Patent No. 9595726 for hydrocarbon fuel reforming under fuel-rich conditions. Notably, the reformer used in that project was entirely 3D printed in stainless steel, which enabled high internal complexity, leading to even higher efficiency compared to the non-3D printed reformer. Current work on Swiss-roll combustors studies innovative new applications for this technology in unique environments and complex systems, such as undersea energy harvesting.
United States Patent US 9,595,726 B2
LEARN MORE:
- A Non-Catalytic Fuel-Flexible Reformer presented at 8th U.S. National Combustion Meeting (2013)
- A Fuel Flexible Reforming System for Portable Scale SOFC presented at 2013 NDIA Ground Vehicle Systems Engineering and Technology Symposium (2013)
- A Novel TPOX-Based “Swiss-Roll” Fuel Reformer presented at 2014 AIChE Annual Meeting (2014)
- A “ Swiss-Roll ” Fuel Reformer: Experiments and Modeling presented at 9th U.S. National Combustion Meeting (2015)
- Progress on the Development of a “Swiss-Roll” Fuel Reformer for Syngas Production presented at ASME 2016 Heat Transfer Summer Conference (2016) (2016)
- A Swiss-Roll Style Combustion Reactor for Non-Catalytic Reforming of JP-8 presented at 10th U. S. National Combustion Meeting (2017)
- US Patent 9,595,726 B2 Fuel Reforming System and Process (2017)
- Swiss-roll JP-8 Fuel Reformer with Direct Center Fuel Injection and Mixing Chamber Design presented at 2018 ESSCI Spring Technical Meeting (2018)
- Development of a Non-Catalytic JP-8 Reformer presented at the 2018 NDIA Ground Vehicle Systems Engineering and Technology Symposium (2018)