Hydrogen Fuel Cell Electric Vehicles Individual Assignment
Name: C.M. Kallegoda 130262G
Department of Chemical & Process Engineering University of Moratuwa
1. How Hydrogen Fuel Cell Electrical Vehicle (HFCEV) Works?
The internal combustion engine runs on gasoline or diesel to rotate axially in conventional vehicles. But fuel cell vehicles are driven through an electric motor which is powered by hydrogen gas. Hydrogen fuel cell combines with H2 and O2 to generate electricity [1].
The same principle applied on HFCEV. Hydrogen and Oxygen combine and generate electricity needed to drive motor fuel cell vehicles. Although, this technology does not include charging a battery from external sources, HFCEV involves electricity. So that these vehicles considered as electrical vehicles.
Air flow to the vehicle used as the oxygen source and hydrogen filled to the high-pressure hydrogen cylinders mounted at the back. Air and hydrogen supplied to the fuel cell, as a result, electricity, water and heat generated in the cell. 2. Advantages over battery electric vehicles
Both batteries and fuel cell are based on electrochemical reactions which produce zero emissions virtually. The main difference between the two technologies is the method of storage of fuel. In a battery, there is a finite amount of chemical compound or substance which undergo reversible electrochemical reaction to generate electricity. When the substances are consumed battery needs to be recharged which drives the chemical reaction to the other side of the reaction. In a fuel cell, H2 which is the main compound in the electrochemical reaction, stored in a tank on-board the vehicle. HFCEV can obtain following advantages over battery electric vehicles due to above technology difference [2]. •
Long range (300-400 miles)
HFCEV have the feature that can last 300-400miles per fuel refill. But it depends on the size of the fuel(H2) tank. But, battery charged vehicles can be used in 100-200miles. When comparing battery electric vehicles and HFCEVs this is a huge advantage. •
Short refueling time
HFCEVs only want 10mins to refill the hydrogen tanks while the battery electric vehicles need around 1 hour of recharging. •
Idle-off driving
Idle off is a special feature in HFCEVs which shuts the fuel cell and driven by energy recovered by regenerative braking. This feature is more important in traffics or stop signs. Most battery charged EVs and hybrid vehicles have the same option.
3. Drawbacks of using hydrogen as a fuel
As an energy source hydrogen has many advantages and disadvantages. H2 can be produced by water electrolysis or steam reforming of naphtha or natural gas. •
Renewable and available in large quantities but expensive [3]
The H2 fuel cell gives H2O, electricity, and heat as outputs which are obviously renewable. H2 is largely available in nature and can be produced by electrolysis and steam reforming. Both methods are highly expensive and need large capital in producing hydrogen. •
Storage complication
Hydrogen is a low-density gas which must be compressed and liquify at lower temperatures to store. This is a complex process and far from feasible when comparing with fuel oil storage. •
Non-toxic energy but not safe
Produce H2O is harmless for the environment. So that it is a clean energy source. But in producing H2 through steam reforming or auto-thermal reforming processes environment pollution can happen. The flammability of hydrogen can’t be underestimated. Since hydrogen does not have an odor or color, leakages can’t be detected which may leads explosions [3]. •
Transportation complication
Hydrogen is a light gas (Low density). So that it need high pressure transportation method to carry reasonable amount of hydrogen. Unlike other fuel oils and solid fuels, it is not safe to transport by pipe line due to its explosiveness. Nowadays hydrogen is transported in small batches. •
Far from sustainability
Unlike hydrogen energy, fossil fuel is a well-established industry. It takes years to well establish such an industry as hydrogen energy which need high amount of capital. Although hydrogen energy established well enough, the cost of hydrogen will be much higher th an fossil fuel and also normal car user won’t be able to use hydrogen directly to vehicle.
4. Hydrogen production methods •
Electrolysis
Water electrolysis is a major method used in hydrogen production. Two electrodes split water into H2 and O2 by supplying an external electric source [4]. Power plants split the demineralized water to produce H2 which are needed in turbine cooling. Excess energy from renewable power plants (wind, solar) can be used as the electric source for electrolysis. •
Steam reforming of naphtha or natural gas
Generation of synthesis gas from naphtha or natural gas is an industrially used method for production of H2 [4]. Naphtha or natural gas reacts with steam supplied to produce H 2, CO, and CO2 (Syngas) mixture. Following reactions happen in natural gas steam refo rmer, 4 + 2 ↔ + 32 + 2 ↔ 2 + 2
Other than steam reforming partially oxidation method is also used in syngas generation which is called auto-thermal reforming. Steam reforming and auto-thermal reforming are cheapest, most efficient, and commonly used method in hydrogen production. •
Renewable liquid reforming
Renewable liquid reforming uses the same principle as the natural gas reforming. Renewable liquids like ethanol allowed to react with steam and generate H 2.
•
Coal gasification [4]
Synthesis gas can be generated by reacting coal or biomass with high temperature steam and oxygen in a pressurized gasifier. •
Fermentation
Biologically convert biomass to sugar rich feedstock which can produce H2 by fermentation. 5. Hydrogen delivery pathway to vehicle •
Gaseous hydrogen pathway
Compression, Storage, and transport by pipe lines is involved in gaseous h ydrogen pathway to fuel stations [5]. Multiple compression points are available in between end user and production facility. According to figure showed H2 produced compressed and transmitted to the storage through pipe lines. Geologic storages are connected to the same pipe line. Stored hydrogen can transport to the fuel stations by tube trailers or distribution pipe lines. Storage, transmission, and distribution pipe lines have a risk of leaking hydrogen and contamination of hydrogen flow by aging of construction material. Although, developed countries like United states already using H2 gas distribution lines to distribute produced H2 in hydrogen plants.
•
Liquid hydrogen pathway
Unlike gaseous pathway using pipe lines is impractical in liquify hydrogen pathway. Produced gaseous H2 from steam reforming, electrolysis or other method is liquified using liquefier and pumped into cryogenic storage in order to load into trucks. In Liquification process hydrogen gas cooled below -235oC using liquid nitrogen and series of compression and expansion stages [5]. Liquification is not only a high cost but also a low energy efficient process. Liquid hydrogen from liquefier stored and distributed to the fuel stations using liquid trucks. Fuel stations mainly have cryogenic storage and a vaporizer. So that both cryocompressed and gaseous outlets are present at the end of the liquid pathway. 6. Future of HFCEV
Engineers trying various methods to replace fossil fuel by different methods. As a result, electrical vehicles become a top global trend. Considering the electric many ex pertise predicts hydrogen fuel cell electric vehicle has high potential for sustainability on long run than battery electric vehicles. According to KPMG’s Global Automotive Executive survey 2017 78% believe that fuel cell electric vehicles would be the golden bullet of electric mobility [6]. Using electrical vehicles are relatively growing up, but the question is how much environmental friendly using electrical vehicles. It seems like battery electric vehicles are
environmentally friendly. But different types of fuels (coal, fuel oil) are used to generate electricity. So that hydrogen fuel cell vehicles are recommended over battery electric vehicles since hydrogen fuel cells are far less polluting [6]. Still hydrogen fuel cell energy is not well stablished when comparing to gasoline. But large amount of money behind the HFCEV technology since it seems like the replacement for fossil fuel. United state government also promote the fuel cell vehicles by funding 23$ million for boost hydrogen fuel cell car manufacturing [8]. Major car companies like Toyota, KIA, Ford, Honda etc. boosting the research and development on fuel cell vehicles.
References
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