by Louis Lemos, Former Project Leader, Engineering Design Group, Navy Division, United States Defense Attach Office, Saigon, Vietnam
FUEL CELL DEVELOPMENT - Various scientific theories and subsequent discoveries have been identified as stepping stones in the evolution of what has become known as the Fuel Cell, for the purpose of generating electricity through heat. The concept of "Thermoelectric Generation" discovered by Seebeck around 1821, is based on the principle that current is produced in a closed circuit of two dissimilar metals, if the two junctions are maintained at different temperatures, such as in thermocouples for measuring temperature.
Potentials are produced by thermocouples, typically, in the order of 5o to 70 microvolts per degree Centigrade, and power at efficiencies of approximately 1 percent. Consequently, the criterion for evaluating material characteristics for thermoelectric generation is the "figure of merit", Z, also known as the "Seebeck coefficient". Whereas the Peltier effect discovered in 1834, is quite the inverse of the Seebeck effect. In this case it consists of the heating or cooling of the junction of two thermoelectric materials by passing a current through the junction. The effectiveness of thermo-junction as a cooling device has been greatly increased by the application of semiconductor thermoelectric materials. In 1915 the concept of "Thermionic Generation" was proposed by Schlicter, using a thermionic converter, which is basically a vacuum or gas-filled device with a hot electron emitter as the cathode, and a cold electron collector as the anode within a gas-tight enclosure. This included means of heating the cathode and of cooling the anode. By heating the cathode, it imparts enough energy to some of the electrons to enable them to escape from the work-function barrier at the surface of the cathode, into the interelectrode space. For this purpose the work function of the anode should be relatively small and the anode should be maintained at a lower temperature to prevent anode emission or "back-current".
Given that electrons are charged particles, those in the space between the cathode and the anode form a space-charge barrier that limits the electrodes emitted from the cathode. By close spacing of the cathode and anode surfaces, space-charge formation can be reduced. Alternatively, the space charge can be reduced by the introduction of a suitable gaseous atmosphere that can be ionized by heating, and thereby neutralize the space charge. Gas-filled converters can attain efficiencies as high as 17 percent but with an output voltage averaging 1 to 2 volts, several units are required to be connected in series to attain a reasonably useful voltage.
FUEL CELL FUELS - According to the Fuel Cell Technologies Program of the U.S. Department of Energy, of the various fuels available for use in Fuel Cell systems, hydrogen appears to be the most logical, given that (a), it is non-toxic, (b), yields a higher ratio of chemical energy per unit mass than that available from natural gas, and (c), it is abundant as an unlimited resource in atomic form. In addition to which, another important factor in favor of hydrogen is that it is non-polluting. The Director of Environmental Technology for the American Bureau of Shipping, (ABS), Yoshi Ozaki, states that fuel cells use hydrogen and oxygen (or air) as fuel to generate electricity, and that hydrogen can be generated from fossil fuels such as natural gas or bio-synthesized by a process called reformation. In the US for example, 95 percent of hydrogen is produced industrially from natural gas by steam methane reformation (SMR). However, he also points out that 1.0 tons of natural gas and 2.25 tons of water produce only 0.5 tons of hydrogen plus 2.75 tons of CO2 as a by-product In addition to creating CO2 emissions, SM1 requires a considerable amount of heat energy for it to work, creating further CO2 emissions if fossil fuels are the energy source. The US National Renewable Energy Laboratory reports that for every ton of hydrogen produced, 8.9 tons of CO2 are emitted from an SMR plant. Therefore to have merit from the point of view of CO2 emissions, the hydrogen would need to be generated from alternative energy sources such as wind, solar, wave or nuclear, essentially taking this approach out of the marine application sphere. Some high temperature fuel cells can internally reform fossil fuel into hydrogen without the need for an external heat energy source, thereby significantly improving efficiency and CO2 emission performance. These include the Solid Oxide Fuel Cell (SOFC) and the Molten Carbonate Fuel Cell (MCFC). However, among the many other types of fuel cells currently being researched, very few are considered suitable for marine propulsion purposes. Another disadvantage tending to limit progress in the adoption of Fuel Cell Prime Movers for maritime propulsion is the relatively high cost of production, compared to conventional I.C. engines.
Liquefied Natural Gas (LNG), which is now widely used in many Dual-Fuel marine Diesel engines, is also a strong contender for Fuel Cell use. Currently, there is an on-going initiative in Holland known as the Green Tug project, piloted by the "Offshore Ship Designer" Group, including participation by Bureau Veritas, featuring a hydrogen-powered Fuel Cell tugboat designed for near-zero exhaust emissions level, and estimated to increase propulsion efficiency by almost seventy percent compared to that of a conventional Dieseldirect-drive. There is also a Methanol-base Auxiliary Power System Fuel Cell known as METHAPU, sponsored by the European Union with the cooperation of Lloyd's Register, Wartsila and the University of Genoa, among others. This project involves a Methanol-fuelled Auxiliary Power System of the Solid Oxide Fuel Cell (SOFC) type, rated at 2okW that has recently been installed aboard a Swedish Car Carrier. In addition thereto is the MTU Onsite Energy Fuel Cell developed by the Fellow-SHIP Project, consisting of Det Norske Veritas, the Ship-owner Eidesvik, the System Integrator Wartsila and MTU Onsite Energy, who supplied the 320 kW Fuel Cell powered by LNG that was installed aboard the Norwegian Offshore-Support ship "VIKING LADY" in the latter part of 2009. Funding for the Fellow-SHIP project is provided by the Norwegian Research Council and Innovation Norway. The essential factors governing the selection of the most appropriate fuel for use in Fuel Cells are those of availability and cost.
Hydrogen, for instance, can be obtained from natural gas and coal, involving a process of carbon sequestration. Given that the submerged endurance of ninety days by nuclear submarines is attributable to the ability of replenishing their internal atmosphere with fresh oxygen extracted from seawater, it is conceivable that this capability may eventually be extended to surface ships powered by Marine Propulsion Fuel Cells.
Depending upon the practical feasibility and economic viability, the procedure would involve the extraction of hydrogen from seawater, (using a modified form of hydrolysis), for the purpose of fueling the Marine Propulsion Fuel Cell Engines. Given the inevitable trend toward Hydrogen as a preferred fuel for Fuel Cells, those -interested in the development of Fuel Cell Systems for Marine Prime Movers, will need to learn all they can about "SAFE HANDLING, TRANSPORTATION & STORAGE OF HYDROGEN", since this will undoubtedly become a primary choice of fuel for Marine Fuel Cell Systems.A logical starting point for such information is to be found within the growing application of "Dual-Fuel Engines", and associated support systems for main propulsion of recently-built European-flagged LNG carriers. Much of the current "Dual-Fuel" program consists of High-Grade conventional Marine Diesel fuel (MDO) and Liquefied Natural Gas (LNG), of which the latter already involves practice and procedures that are applicable to hydrogen. In due course, we may expect to see publication and indeed enforcement, of a formal Safety Code, on a worldwide basis, somewhat similar to the Guidelines recently published by Bureau Veritas. Hence it would be wise to monitor the pertinent publications from the American Bureau of Shipping (ABS), and their foreign counterparts; the U.S. Coast Guard; the International Maritime Organization; and major Fuel Refiners, for the benefit of those ultimately responsible for distribution and use of such fuel. Yet another authority on the subject, Edward Fort, a Fuel Cell proponent and the Engineering Rules Coordinator for Research and Development, with Lloyd's Register, is of the opinion that fuel compatibility may be a primary challenge as it relates to the marine application of Fuel Cells. Among other related concerns, he lists the storage and handling of fuels and waste; ventilation of equipment compartments; operational interface with existing shipboard systems; fuel specifications; and maintenance programs. From a "Classification" viewpoint, he summarizes his concern with the following statement: "With the introduction of fuel cell systems operating on fuels not traditionally associated with marine power generation, indeed not currently recognized by marine legislation, comes a variety of considerations, many of which will need to be addressed before their approval for installation onboard". Accordingly, Lloyd's Register has compiled a set of Process-Based Requirements pertinent to established and internationally recognized systems engineering principles to evaluate both the safety and dependability of Fuel Cell installations for Marine purposes. A practical application of these requirements is evident in the afore-mentioned METHAPU Methanol-base Auxiliary Power Fuel Cell project, described as "Validation of a renewable methanol-based auxiliary power system for commercial vessels", in which Lloyd's Register is involved.
FUEL CELL BASIC TECHNOLOGY - When provided with fuel and air, a Fuel Cell converts chemical energy directly into electricity and heat, but unlike batteries, will not run down. It is an electrochemical device that converts the chemical energy of the fuel directly into electricity and heat, and does so more efficiently than conventional combustion-based technologies. The common types of Fuel Cells are phosphoric acid (PAFC); molten carbonate (MCFC); proton exchange membrane (PEM); and solid oxide (SOFC); all named after their respective electrolytes. Given that they rely on electrochemical reactions instead of combustion, Fuel Cells need an easily oxidized substance, such as hydrogen. Some Fuel Cells, such as solid oxide Fuel Cells (SOFC), can also utilize carbon monoxide (CO), making them more fuel-flexible and generally more efficient with available fuels. Hydrogen and CO can be produced from natural gas and other fuels by steam reforming. Fuel Cells like the SOFC type, that
can reform natural gas internally have significant advantages in efficiency and simplicity when using natural gas because they do not need an external reformer.
FUEL CELL GUIDELINES - Guidelines for the safe operation of Fuel Cells for marine propulsion have been recently proposed by Bureau Veritas (BV), one of the world's largest Classification Societies, according to BV Product Manager Gijsbert de Jong. The intent being to establish a regulatory framework within which, building and testing of prototype Fuel Cell Systems can be safely conducted while ensuring that the technology is developed and applied in accordance with safe performance-criteria. In his comments Mr. de Jong stated that "BV's guidelines for the safe application of fuel cells on ships take into account all relevant existing IMO conventions and guidelines together with a wide range of international non-marine standards. They reflect BV's in-house knowledge and expertise, and could have important commercial - as well as environmental - implications for ship-
FUEL CELL GUIDELINES - (continued) - The intent being to establish a regulatory framework within which, building and testing of prototype Fuel Cell Systems can be safely conducted while ensuring that the technology is developed and applied in accordance with safe performance-criteria. In his comments Mr. de Jong stated that "BV's guidelines for the safe application of fuel cells on ships take into account all relevant existing IMO conventions and guidelines together with a wide range of international non-marine standards. They reflect BV's in-house knowledge and expertise, and could have important commercial - as well as environmental - implications for ship-owners and operators". He further explained The object of the BV guidelines is to provide criteria for the arrangement and installation of machinery for propulsion and auxiliary purposes, using fuel cell installations, which have an equivalent level of integrity in terms of safety, reliability and dependability as that which can be achieved with new and comparable conventional oil-fuelled main and auxiliary machinery. The guidelines currently have a preliminary status and are subject to internal and external revue. After taking into account all relevant feed-back, they will be published as a Bureau Veritas Guidance Note entitled Guidelines for Fuel Cell Systems on board commercial ships.
FUEL CELL SAFETY CODES AND STANDARDS - As Fuel Cells become successfully adopted by the U.S. Maritime Industry, for purposes of main propulsion and auxiliary power generation, we should expect to see the promulgation and enforcement of U.S. Coast Guard Rules and Regulations applicable thereto, as well as comparable Rules and Standards issued by the American Bureau of Shipping, for Fuel Cell-powered American flag vessels. In addition to the afore-mentioned Guidelines for Fuel Cell systems on board commercial ships, proposed by Bureau Veritas, there are various Codes and Standards (non-marine) that may be applicable to basic Fuel Cells with particular emphasis on the safe handling, transportation, storage and usage of hydrogen and related fuels. The U.S. Department of Energy is currently developing and testing complete system solutions that address all elements of infrastructure and vehicle technology, validating integrated hydrogen and Fuel Cell technologies transportation, infrastructure and electric generation in a systems context under real-world operating conditions. Data will be collected under realistic operating conditions to provide feedback on progress and to efficiently manage the research elements of the program while providing re-direction as needed. Meanwhile, it may be useful to compare the respective properties of conventional fuels frequently used within the U.S.A.
COMPARATIVE PROPERTIES - For purposes of comparison the average common factors of relative calorific value and safety concern are listed in the table below.
Comparative Properties of Gasoline, Diesel, Natural Gas and Hydrogen
The above factors are based on data provided by the Alternative Fuels Data Center of the U.S. Department of Energy.
FUEL CELL OPERATION - Basic requirements for a Hydrogen Fuel Cell are 1) fuel; 2) oxidant; and 3) an electrolyte; plus a negative anode and a positive anode. In a typical Polymer Electrolyte Membrane Fuel Cell (PEMFC), such as that developed for Space Missions of the 1960's, the system works as follows:
a) Hydrogen is fed into the anode, which is the electrically negative post of the Fuel Cell.
b) In the center of the Fuel Cell the electrolyte absorbs an electron from the hydrogen atom using it to make electricity.
C) The cathode, as the electrically positive post of the Fuel Cell, is where the electrons recombine with the hydrogen and oxygen to make water, which is the exhaust effluent.
This transition of protons and electrons is referred to as ionic conduction wherein there is a transmission of electrons (electrically-charged atoms) or protons, produced by dissolution of electrolytes, a characteristic of Fuel Cells. A good example of marine fuel cells actually in operation is to be found in the U-212A class submarines of the German Navy. These units, from the Thyssen-Krupp Marikne Systems Group, are of the PEM (polymer electrolyte membrane) tyoe of Fuel Cells, fuelled by hydrogen and oxygen. They are silent, non-magnetic, exhaust-free and reportedly, have very low heat emissions.
FUEL CELL TRANSPLANT - Given the eventual phase-out of fossil fuels and the conventional marine propulsion plants (of existing vessels) the latter could be replaced by Fuel Cell power plants with electric drive motors. Feasibility of such transplant would of course be contingent upon successful reduction of current Fuel Cell systems to a size compatible with that of existing I.C. engines, but of comparable power range. The original Diesel fuel tanks would have to be replaced with specifically designed high-pressure vessels for storage of hydrogen, with matching high-pressure piping,...