Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - FUEL DEOX (Optimisation of an on-board adsorbent/catalyst unit for aviation fuel thermal stability improvement)

Teaser

This project experimentally investigates the application of an optimised on-board adsorbent/catalyst unit to reduce the tendency of jet fuel to generate solid carbonaceous deposit the moderate temperature regimes which occur in engine fuels systems. The presence of dissolved...

Summary

This project experimentally investigates the application of an optimised on-board adsorbent/catalyst unit to reduce the tendency of jet fuel to generate solid carbonaceous deposit the moderate temperature regimes which occur in engine fuels systems. The presence of dissolved oxygen is a key component in the production of these deposits and the proposed onboard conditioning system would seek to remove this dissolved gas from the fuel. Improved fuel thermal oxidative stability offers the potential for the fuel to serve as a better heat sink, absorbing more waste heat from VHBR engines, lowering the cooling load and using the heat to benefit in the engine performance cycle. This leads to a higher efficiency in comparison to adding extra cooling systems employing bleed air that is dumped overboard, and could yield around 2% SFC improvement in association with heat exchanger weight and volume savings.
Furthermore, the elimination of overboard bleed is a potential to reduce IR signature.

Several methods for dissolved oxygen removal from liquids are reported in the public literature. Some have already been applied for liquid hydrocarbons and at least two have been investigated specifically for the aviation fuel thermal stability improvement including “fuel sparging” and “membrane separation” techniques. The oxygen separation by adsorbent/catalysts shows promise as an alternative to the other deoxygenation methods being developed for aviation.
The application of adsorbents/catalysts requires a careful assessment of any changes in fuel chemical composition following fuel deoxygenation. This is primarily due to the fact that there is a trade-off between thermal stability enhancement via oxygen adsorptive separation and fuel lubricity decrease as a result of polar species separation.

The goal of the project is to demonstrate a TRL 5 deoxygenation unit on the Aviation Fuel Thermal Stability Test Unit at Sheffield University.

To achieve the programme goal, the following project objectives will be completed:
1) Optimise the size of the adsorbents/catalysts unit in small scale, bespoke experimental device with respect to flow regime and bulk fuel temperature.
2) Simultaneous thermal oxidative stability assessment of deoxygenated fuel using low medium scale test device namely, “High Reynold Thermal Stability (HiReTS)”.
3) Compositional analysis of deoxygenated fuels with particular focus on side reactions.
4) Fuel lubricity assessment.
5) Calculation of adsorbent longevity using available quantum chemistry methods.
6) Calculation of trade-off between thermal stability enhancement and lubricity decrease using
available quantum chemistry methods.
7) Project scale up and use of the optimised adsorbent/catalyst unit in a TRL5 scale engine representative jet fuel system simulator, namely the “Aviation Fuel Thermal Stability Test Unit (AFTSTU)”.

Work performed

WP1
A through literature review of the methods investigated for the removal of dissolved oxygen and on-board per-treatment of fuel was completed. Several studies were identified which utilized sparging or membrane separation techniques for the removal of oxygen on-board. No studies were identified showing the per-treatment of fuel on-board, however a limited number of studies investigated the use of sorbents as part of separation processed for the identification of trace components in fuels.

WP2 Experimental work
Significant delays have been encountered in the supply of suitable monolith catalyst and sorbent materials from the suppliers selected by the project. This has delayed the deliverable D3 as an optimisation of bed size was not possible without the material. This material was delivered to Sheffield on the 2nd August and testing work has commenced.
Whilst this work was delayed, the project, in conjunction with the topic manager, carried out work assessing the potential sorbent materials using a small scale thermal stability test methods.
This led onto the use of solid phase extraction techniques to investigate the interactions between adsorbent\'s active surface and specific polar species. Activated Carbon, Zeolite 3.7 Angstrom and Zeolite 4.5 Angstrom were used with a range of polar species of high purity.
Oxygen separation is delayed by the early absorbtion of Nitrogen containing species and only proceeds once this has reached a saturation absorbtion. This work was reported at the IASH (International Association for the Stability and Handling of Fuels) conference in Rome, September 2017.

WP 3 Modelling work
Computational Models have been developed to understand the interaction of specific Zeolite and Sorbant structures with dissolved oxygen and other hetroatomic species representative of those in Jet fuel. Specifically, these calculations were based on a discrete unit cell of a CHA zeolite. In the commercial software, Gaussian 09, atomic orbital basis sets are used to construct the wave function and calculate the electronic structure and properties of the discrete molecule.
The level of energy corresponding to the biding oxygen and zeolite as well as polar species and zeolites determine the dominant process (Chemisorption or Physisorption).
Three classes of zeolite including FER, MFI and CHA are under investigation numerically, but only CHA will be used experimentally. The modelling shows that the oyxgen is physiorbed on the surface and pores of CHA and other materials. I
The challenge remaining is to link the quantum chemistry results to the diffusion modelling in a macro scale which can be used for the design rules for a full scale device (this will be validated against the experimental work). A 1-D model has been developed in COMSOL and can predict the rate of oxygen and limited polar species removal from the fuel. A reaction rate term is used in the mass transport equation through a porous medium with a constant porosity to model the capture process.
A further investigation into the Si/Aluminia ratio in the zeolite is also underway using computational techniques as a result in the long lead times associated with experimental material becoming available.

WP 4 Design work
Based on the work in WP2, an design concept for the sorbant structure has been proposed using a monolith structure rather than a pellet based design, which was the previous best possible design. The monolith structure has a number of advantages for the application in aircraft - it has a lower pressure drop across it and a more benign failure mode compared to other methods for carrying the active material.
Results so far suggest that the developed design will be suitable for use in the TRL 5 rig. However, the full scale system may be prohibitively large for use onboard an aircraft and may require use as a ground handling process at the skin of the aircraft.

Final results

The project has demonstrated the potential advantages from a thermal stability perspective of the removal of polar species as well as oxygen using a novel technique and sorbent materials which have previously not been used within the fuels community.
The project has demonstrated the competitive absorption characteristics of this technology for the first time.
The project has used the Quantum Chemical tools to support the experimental work for the first time in the thermal stability community.