To Hydrogen or not to Hydrogen. Potential as a Ship Fuel. Dr. John Emmanuel Kokarakis. Emmanuel John Kokarakis University of Crete

Transcription

1 To Hydrogen or not to Hydrogen. Potential as a Ship Fuel Dr. John Emmanuel Kokarakis Emmanuel John Kokarakis University of Crete

2 THE VISION "I believe that water will one day be employed as fuel, that hydrogen and oxygen which constitute it, used singly or together, will furnish an inexhaustible source of heat and light, of an intensity of which coal is not capable. I believe then that when the deposits of coal are exhausted, we shall heat and warm ourselves with water. Water will be the coal of the future." 2

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4 Hydrogen The simplest and lightest fuel is hydrogen gas. Hydrogen may contain low levels of carbon monoxide and carbon dioxide, depending on the source. It is invisible, extremely flammable gas It can be produced using fossil fuels, such as natural gas and coal, nuclear, biomass and other renewable energy technologies (wind, solar, geothermal, hydro-electric power). It will a sustainable fuel of the future because it may be produced in virtually unlimited quantities using renewable resources. It is being explored for use in combustion engines and fuel cells. Its energy density is very low under ambient conditions which presents greater transportation and storage hurdles than for liquid fuels. Storage systems are being developed to address these problems. It is not an energy source, but rather an energy carrier from which a secondary form of energy must be created 50 million t / yr 4

5 Renewable Energy for Electrolysis Electrolysis at high temperatures uses less energy to split water. Process is cost competitive with steam reforming. HTE processes are generally only considered in combination with a nuclear heat source In HTE some of the energy needed to split the water is added as heat instead of electricity, thus reducing the overall energy required and improving process efficiency. Conversion efficiency of heat to electricity is low compared to using the heat directly, and energy efficiency can be achieved by providing the energy to the system in the form of heat rather than electricity. 5

6 Or use Biomimicry Nature has very simple methods to split water and transform H2 into its component protons and electrons. The catalyst that splits water during photosynthesis consist of clusters of manganese and oxygen (cubane). Bacteria use the iron based cluster to catalyze the transformation of two protons and two electrons into H2. The hope is to create synthetic versions of these natural catalysts 6

7 Hydrogen Usually chemically combined in water or fossil fuels (most of it is locked in water or hydrocarbon fuels and must be separated) Fossil fuel sources contribute to pollution and greenhouse gases to a greater extent than if those fossil fuels were to be used directly. CH 4 + H 2 O CO + 3 H 2 Electrolysis requires large amounts of energy Hydrogen mixed with natural gas can be used in internal combustion engine 7

8 What is a hydrogen fuel cell? Hydrogen fuel cell (HFC) is a type of electrochemical cell. It generates electricity by reactions within the cell. Three main components: Fuel, Oxidant, Electrolyte. HFCs use hydrogen as a Fuel, oxygen as an Oxidant, a proton exchange membrane as an Electrolyte. Water as waste. 2H 2 4H + + 4e - 4H + + O 2 + 4e - 2H 2 O 8

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10 Why fuel cells? Hydrogen fuel cells have significantly lower power density than medium and high speed diesels, however, they have the technical potential to perform significantly better. Hydrogen fuel cells are significantly more expensive than diesels Low density of hydrogen calls for frequent re-fuelling. Need on-board reformers or to run fuel cells on naval liquid fuels. 10

11 Pros and Cons of Hydrogen Advantages l Unlimited availability l Large chemical energy per unit mass (140 MJ/kg) l Non polluting, non toxic & non poisonous l Very light. Diffuses if it leaks l Burning only in close vicinity l Well known production, distribution, transport l Clean electricity in Fuel Cells Drawbacks l Low energy density per volume (1/3 of natural gas) l Very flammable l Low minimum ignition energy l High auto-ignition temperature l Colorless, odorless, not visible flame l Tendency to leak at joints l Reaction with metals (metal embrittlement) 11

12 Stumbling blocks for hydrogen economy Lack of hydrogen infrastructure (refueling stations & consumer distribution systems) Cost of hydrogen fuel cells ( $61/kw) Carbon cost of producing hydrogen Its volume energy density is very low under ambient conditions (1/3rd of natural gas). One gallon of hydrogen produces an amount of energy as 1/4 gallon of gasoline. It is difficult and costly to compress, store, and transport. It s flammable over a wide range of concentrations and is very easily ignited. One of the most leak prone gases. 12

13 The hydrogen storage problem H 2 can be compressed to reduce volume (compressor energy). It requires heavy, strong, type C tanks. Hydrogen gas has good energy density per weight, but poor energy density per volume versus hydrocarbons, hence it requires a larger tank to store. H 2 can be liquefied to reduce volume. It boils at -253 C (cryogenic). It requires heavily insulated, expensive tanks. Liquefaction imposes a large energy loss, used to cool H 2 down. Ice forming around the tank promotes corrosion if the insulation fails. Insulation for liquid hydrogen tanks is expensive and delicate. Even liquid hydrogen has worse energy density per volume than hydrocarbon fuels such as gasoline by approximately a factor of four. Both compression and liquefaction require a lot of energy 13

14 Alternative means of storage H 2 can be stored as ammonia (NH 3 ) at very high hydrogen densities. H 2 is released in a catalytic reformer Ammonia production is energy intensive and it is a toxic gas. Metal hydrides can carry hydrogen (boron, lithium). Hydrides can be coerced, in varying degrees of ease, into releasing and absorbing hydrogen. A hydride tank is about three times larger and four times heavier than a gasoline tank holding the same energy. 14

15 Hydrogen in ships Hydrogen can be used in a fuel cell to generate electricity for electric drive systems completely replacing existing internal combustion engines. Navies are interested in fuel cell powered boats for their stealth capabilities and efficient electrical generation efficiency. Local governments in harbor cities are interested b e c a u s e o f t h e i r b e t t e r e m i s s i o n s performance. Noise-vibration friendly. Hydrogen cannot be used in a conventional diesel engine, because its auto-ignition temperature is too high. This can be overcome by fitting spark plugs or by using a small amount of pilot diesel fuel. Hydrogen and diesel co-combustion 15

16 Safety and design code on a LH2 carrier Large bulk transportation is not covered by any existing codes Liquid hydrogen carriers can be considered, based on IGC code. Test of spilling Liquid hydrogen on ground or water Test of cloud dispersion from vent and its ignition Performance test of various thermal insulation Risk assessment of typical accidents. Experimental examinations on accident cases LH2 storage and transportation is not covered by any existing regulations, code, and standards EX Safety distance ( LH2 quantity- Distance relationship ) Reliable rules or standards for modeling or reducing the effect of hydrogen explosion 16

17 Viability of hydrogen fuel cells for marine propulsion 60% higher cost. Surplus cost mostly for fuel cells 17

18 In conclusion Hydrogen promises to lead better, faster, more efficient, environmentally clean transportation designs. Hydrogen Fuel Cells produce no harmful emissions just a trickle of water. The only emissions might be from the burning of natural gas used to produce the hydrogen. Burns twice as efficiently in a fuel cell as gasoline does in an engine Todays technologies need more maturity. Prototype testing is necessary. Regulatory framework yet to be established. Need for interdisciplinary synergistic efforts. 18

19 A Hydrogen Economy 19