Hydrocarbon Fuel Reformer for Fuel Cell Car

Fuel cell vehicles offer many advantages when compared to internal combustion or battery-powered electric vehicles. Advantages over the internal combustion engine (ICE) include the potential for higher fuel efficiency and lower emissions. The advantages over a battery- powered vehicle include an improved driving range and shorter refueling times.

The fuel efficiency of a fuel cell vehicle is expected to be about twice that for current internal combustion engines and the overall energy consumption (fuel chain and vehicle) is expected to be lower than that of battery-powered vehicles. Emission levels are expected to meet the Super Ultra Low Emission Vehicle Standard, much lower than those from current ICEs.

The ideal fuel for the low-temperature proton exchange membrane (PEM) fuel cells being considered for automotive applications is hydrogen. Currently, the infrastructure for hydrogen refueling is lacking, and hydrogen storage technologies available for onboard storage provide a decreased driving range compared to gasoline and ICE technology.

However, it is apparent that the commercial success of a fuel cell vehicle will be tied to the availability of a refueling infrastructure. In other words, it will be difficult to sell hydrogen-powered fuel cell vehicles without first investing in a hydrogen refueling infrastructure. However, it will be difficult to convince investors to build a hydrogen infrastructure if there are no commercial vehicles to use it.

A solution to this “chicken or the egg” dilemma is to provide an onboard reformer to convert a hydrocarbon fuel into a hydrogen-rich gas for utilization by the fuel cell. This strategy could help introduce fuel cell cars to the marketplace earlier and smooth the transition from internal combustion engine to fuel cell-powered vehicles. Hydrocarbon fuels can use the existing infrastructure for refueling and provide a higher hydrogen density than current hydrogen-storage technologies.

Currently, hydrogen is produced industrially from natural gas using a steam reforming process. A similar process can be used for onboard conversion of natural gas or higher hydrocarbons to hydrogen-rich product gases. However, onboard reforming presents several unique challenges, which include size and weight limitations and the need for rapid startup and the need to be responsive to demand. In addition, since the fuel to be used for onboard reforming is still to be determined, the reformer should be fuel-flexible.

There is some debate about which hydrocarbon fuel is optimal for fuel cell systems. Methanol and ethanol are available commodity chemicals and have numerous advantages as fuel (e.g., water soluble, renewable), and methanol is easy to reform. Gasoline and diesel have advantages over the alcohols, including existing refueling infrastructures and higher energy density. However, they are blends of different kinds of hydrocarbons and are more difficult to reform.

Wind Energy for Hydrogen Production

Wind energy is defined as the kinetic energy of the wind converted into mechanical work. This mechanical work can be used to drive an electrical generator for the production of electricity. A machine that performs this conversion is called a Wind Turbine Generator (WTG).

The stochastic nature of wind is responsible for the intermittent operation of the wind energy systems; an effect that unpredictable operating and high maintenance costs. To solve those problems, any appropriate energy storage technique associated with the unstable performance of wind energy systems was proposed.

Producing hydrogen as energy storage by the electrolysis of water, where the main power input is electrical power produces from the conversion of wind energy, is a very promising way. It is because (i) the existing experience regarding the handling of hydrogen is already high; and (ii) hydrogen is well adapted for seasonal energy storage without energy loss over time.

The water electrolysis process consists of electrochemically splitting water into its constitutents, namely hydrogen and oxygen. According to the electrolyte used for electricity conduction in the process, 4 types of water electrolysis may be found. There are (i) Acid electrolyte, (ii) Polymer electrolyte, (iii) Steam electrolysis, and (iv) Alkaline electrolyte.

There are no electrolyzers developed specifically for operation with wind turbines. However, the rapid response of electrochemical systems to power variations makes them suitable "loads" for wind turbines. For example: Advanced alkaline electrolyzers may be subject to input power variations in the range 15-120% of their nominal power within 1 s and this feature makes them attractive for coupling with the wind turbines.

Hydrogen production from electrolysis of water powered from a wind energy system is installed on some sites. A very important issues related to the performance of the whole wind-hydrogen system are:

- Reliability of the power electronics used for the AC/DC conversion

- The cooling system of the electrolyzer

- The compressor of the gaseous hydrogen

- The purification units of water and hydrogen

The combination of hydrogen and wind energy systems may contribute to the further growth of both technologies while one serves the other for different reasons. From the time that hydrogen becomes the primary energy carrier for transportation and other mobile applications, this method will be considered as one of the most competitive investments.

Pipelines for Hydrogen Transportation

Pipelines represent the primary option for the most efficient transportation mode in a hydrogen energy environment. There are some issues for gaseous hydrogen delivery via pipelines:

1. High initial capital investment costs.

Although pipeline transmission offers technical and economic advantages as compared to other transportation methods, new pipeline construction imply high initial capital costs. Transporting gaseous hydrogen via existing natural gas pipelines can be a possible option to solve the costs, however more substantial modifications may be required for delivering hydrogen-natural gas mixture.

2. Material challenge.

The pipelines has always been troubled by hydrogen attack in the form Hydrogen Embrittlement (HE), Hydrogen Induced Cracking (HIC), Sulfide Stress Cracking (SSC), and Stress Corrosion Cracking (SCC) issues. Gaseous hydrogen via pipeline also need very high pressure levels (up to 3000 psi). The use of composites, fiber-reinforced polymer (FRP), for pipelines may be an alternative to resolve that issues. But, the challenges for adapting FRP pipeline technology still appear, such as:

- Evaluating the pipeline materials for hydrogen compatibility

- Developing a method for manufacturing large-diameter pipelines

- Developing a plastic liner with accpetably low hydrogen permeability

3. Hydrogen leakage and integrity monitoring sensors

Hydrogen is odorless, colorless, and tasteless and therefore undetectable by human senses. Because of that, hydrogen pipelines requires sensors for detecting hydrogen leaks and monitoring pipeline integrity. There are several sensor technologies currently available for monitoring mechanical integrity of pipelines. To apply those sensor technologies for hydrogen pipelines, some issues need to resolved, such as: characteristics of leak signal from light atomic weight of hydrogen gas, special distance resolution along the pipeline, response time, and the accuracy of alert calls.

4. Hydrogen compression

Compression is an integral aspect of gaseous hydrogen delivery via pipelines. Utilizing natural gas compression technologies for hydrogen is unreliable because (a) the hydrogen molecule is much smaller and ligher than natural gas (b) gaseous hydrogen contains only one-third he energy of natural gas. For example: this requires up to 60 stages of centrifugal compression of hydrogen as compared with four to five stages for natural gas.

Solar-Hydrogen Production Efficiency

When determining how much electricity is needed to produce H2 by solar energy, the energy requirements of generation (electrolysis), compression, liquefaction, storage, and transportation all have to be considered and added up. The energy content of 1 kg of H2 is 39.3 kWh. In order to generate 1 kg of H2 by the electrolysis of water, about 50 kWh of electric energy is required. Therefore, the efficiency of H2 generation is about 66%.

Once a kilogram of H2 is produced, it is either compressed or liquefied before storage or distribution. If handled in the high-pressure gas form, about 3 kWh of energy is required for its compression and 2.5 kWh is required for its transportation over each 100 km distance. Therefore, a total of about 6 kWh is required to compress and transport the gas over a distance of 100 km.

This energy corresponds to about 15% of the higher heating value (HHV) of the gas. As the transportation distance increases, this percentage also rises. Therefore, when transportation over long distances is required, it is more economical to transport the H2 in liquid form by trucks, rails, or ships. If handled as a cryogenic liquid, about 12 kWh is required to liquefy each kilogram of H2 and about 1 kWh is needed to store and transport it, for a total of about 13 kWh, which is about 33% of the HHV of the liquid.