“Green” path from fossil-based to hydrogen economy: An overview of carbon-neutral technologies

A surrogate for emulating the physical and chemical properties of conventional jet fuel

Carbon sources, such as coal, natural gas, biomass and waste, can be converted into transportation fuels by combining appropriate gasification, Fischer–Tropsch and refining technologies. Efficient refining of the Fischer–Tropsch synthesis derived syncrude requires a different approach to refinery design than commonly applied to crude oil refinery design. The design of refineries to optimise the production of on-specification motor-gasoline, jet fuel and diesel fuel respectively from both high temperature Fischer–Tropsch (HTFT) syncrude and low temperature Fischer–Tropsch (LTFT) are considered. Refinery designs are presented for the production of motor-gasoline and jet fuel with better than 50% yield (better than 70% selectivity on transportation fuel), without resorting to very complex designs. Only diesel fuel refining presented a problem, since the production of on-specification EN590:2004 diesel fuel is limited by a Fischer–Tropsch specific cetane-density-yield trade-off. The compound classes that are required to produce diesel fuel in high yield that meet both minimum cetane number and minimum density requirements are not abundant in Fischer–Tropsch syncrude. Refinery designs for diesel fuel production was limited to a yield of less than 25% EN 590:2004 compliant diesel fuel. This yield restriction does not apply when diesel fuel specifications do not have a minimum density requirement.

Fischer–Tropsch fuels refinery design

Fischer–Tropsch refining: technology selection to match molecules

Aviation has few near-term alternative-energy options to petroleum-based fuels. Of alternatives that may be available in commercial quantities in the next decade, Fischer-Tropsch and hydroprocessed renewable jet fuels may reduce aviation's impact on climate but are likely to be available only in limited quantities. All alternatives benefit aviation as well as nonaviation sectors and improve air quality.

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Near-Term Feasibility of Alternative Jet Fuels

As the U.S. Military considers fuel sources around the world and into the future, fuels produced via nonconventional means are anticipated to become increasingly available and of growing importance. One such type of fuel, a synthetic fuel, can be produced from conversion processes employing Fischer-Tropsch (F-T) synthesis and starting with natural gas, coal or biomass feed stocks. The Single Fuel Forward (SFF or single fuel in the battlefield) policy requires the use of JP-8, JP-5 or Jet A-1. Evaluations of F-T fuels, such as synthetic JP-8, in military ground vehicles, aircraft, associated equipment, and fuel storage and distribution systems is needed to assess ability to meet desired and/or required operational performance and to identify potential issues, as well as potential benefits, with the introduction and use of these fuels. Testing of a synthetic JP-5 aviation turbine fuel, produced by Syntroleum Corporation under DOD contract, in a 6.5L diesel engine used to power the High-Mobility Multipurpose Wheeled Vehicle (HMMWV), demonstrated reduced exhaust emissions when compared to a reference low sulfur D-2 fuel. Reductions of regulated pollutants were found to be 62-72% for unburned hydrocarbons (HC), 46-60% for carbon monoxide (CO), 13-15% for oxides of nitrogen (NO x ), and 52-55% for particulate matter (PM). Pump stand wear tests, conducted using the Stanadyne Artic Rotary Injection Pumps from the HMMWV, indicated poor performance without the addition of corrosion inhibitor/lubricity improver additive per MIL-PRF-25017. However, acceptable rotary pump performance was observed with the addition of MIL-PFR-25017 lubricity improver additive.

Alternative Fuels: Assessment of Fischer-Tropsch Fuel for Military Use in 6.5L Diesel Engine

: Clean, very low sulfur fuels produced from domestic resources are of interest to the U.S. Military to enhance supply security and reliability versus continuing to rely on the supply of fuels that are either manufactured from an increasing percentage of imported oil or imported in increasing amounts as finished products. Synthetic Fischer-Tropsch (FT) fuel is one type of fuel that can be produced from domestic resources. FT fuels can be produced from a variety of non-petroleum feed stocks, such as natural gas, coal, petroleum coke, or even biomass and various wastes. Starting with reforming or gasification processes, the FT technology first produces synthesis gas (syngas) which is subsequently processed to high-boiling hydrocarbons. These hydrocarbons are then hydrocracked, hydroisomerized, and/or hydroprocessed to produce the desired liquid fuels. The military has a Single Battlefield Fuel Policy which mandates use of the JP-8/JP-5/Jet A-1 aviation turbine fuels. These are currently derived from conventional resources such as petroleum (crude oil). FT aviation turbine fuels have been produced and are being evaluated for use in military equipment by a Joint Agency Department of Defense (DoD) and Department of Energy (DoE) Team. The military will most likely utilize blends of FT fuels with petroleum JP-8/JP-5/Jet A-1 as a first step in evolving towards the use of cleaner fuels that can be produced from domestic resources. Properties of these "FT/petroleum fuel blends" are shown to be similar to those of petroleum JP-8/JP-5/Jet A-1.

Properties of Fischer-Tropsch (FT) Blends for Use in Military Equipment

: The US Military uses JP-8/JP-5/Jet A-1 fuel. JP-8 is identical to Jet A-1 except that it contains additives required by the military. JP-8 differs from JP-8 only in that it has a slightly higher flash point. A synthetic JP-5 fuel products by Syntroleum Corporation, S-5, differers from petroleum-derived jet fuels in that it has much lower normal paraffin concentration and it does not contain any detectable S, N, or O compounds or aromatics. Despite these compositional differences, S-5 conforms to all JP-5 specification requirements for the chemical and key physical properties evaluated, except the density; S-5 density was slightly lower than the minimum density required. One other key requirement for JP-5 states that, The feed stock from which the fuel is refined shall be crude oils derived from petroleum, tar sands, oil shale, or mixtures thereof. Fuels such as S-5. synthesized from feed stocks other than those allowed, do not conform to the JP-5 specification in this regard.

Composition of Syntroleum S-5 and Conformance to JP-5 Specification

: The U.S. Military has initiated a project to evaluate jet fuel, produced from natural gas by processes developed by Syntroleum Corporation, for use in all military equipment capable of using either diesel fuel or jet fuel. A synthetic Single Battlefield Fuel would need to meet a wide range of specifications and in-use requirements before it would be accepted as a fuel by the military. The Syntroleum process for fuel production includes unique Autothermal Reforming of methane, reaction of the produced synthesis gas over cobalt catalyst to produce linear hydrocarbons of various chain lengths, and conversion of this feedstock into isoparaffinic fuel to meet the physical and chemical requirements per MIL-DTL-5624T for JP-5 Aviation Turbine Fuel. Syntroleum synthetic jet fuel produced for evaluation by DOD has an average carbon number of 13.2 and contains relatively little normal paraffins with proportionally lower normal paraffins at higher carbon numbers.

Patsy A. Muzzell

Papers

Alternative Fuels: Assessment of Fischer-Tropsch Fuel for Military Use in 6.5L Diesel Engine

Properties of Fischer-Tropsch (FT) Blends for Use in Military Equipment

Composition of Syntroleum S-5 and Conformance to JP-5 Specification

Production and characterization of synthetic jet fuel produced from Fischer-Tropsch hydrocarbons

Fischer-Tropsch Fuels: Why Are They of Interest to the United States Military?