Fuel Processing to Power a Fuel Cell

Emily Walsh

Summary:

Internal combustion engines are the current method of obtaining the power needed to operate automotives. One consequence is the amount of pollution being emitted as a result of burning the fuel required. Currently, a hydrocarbon fuel will be used as the source of hydrogen with the knowledge that this will only be a short-term solution. In the future, other sources of power will replace the combustion engine, and will eventually use a different fuel source as well. Fuel cells are one of the possible alternatives being investigated. Fuel cells are currently used in space craft and work well for the desired effect and environment. Eventually, the fuel cell may be able to replace the combustion engine. In order for this to become the new primary power source, the fuel entering a series of reactors must be converted into the desired product, hydrogen. This process must be modeled in order to determine the best conditions for operation.
To model this process, four reactors must be considered in series. The difficulty with working with chemical reactions is that the large majority of them do not proceed to completion. Instead, it becomes a balancing act with the conditions in each reactor. This process must be accurately modeled and the parameters varied to determine the best overall conditions to satisfy the objectives. The main objectives of the model were to produce hydrogen gas from a hydrocarbon fuel source to power the fuel cell, keep the amount of carbon monoxide released as a byproduct within environmental regulations, prevent combustible mixtures from forming in the process, have a fuel source of either gasoline or methanol, have no corrosion of the parts, use catalysts with a long lifetime, and have standard issue parts.
Unlike a mechanical design, a best scenario for the project cannot be determined ahead of time. An overall design can be determined, as seen in Figure 1. From this design, the flows, temperatures, and pressures can be varied to find the best operating conditions. In Figure 1, all the bold statements are those that were to be determined as the best operating conditions. Some of the variables, such as the temperature outlet of the water gas shift reactors (WGS) were required to be within a range of 120°C. When the best conditions were being determined, the entire problem was solved using one set of conditions first for methanol, then for gasoline, one atmosphere pressure and the highest allowable operating temperatures, regardless of the overall output. Once the model was complete, the temperatures and pressures could be varied to determine the best conditions to maximize the hydrogen and minimize the carbon monoxide output.
In the end, with the use of methanol, the best operating conditions were when the entire pressure of the system remained at one atmosphere, the water gas shift (WGS) high temperature reactor operated at an inlet temperature of 320°C which corresponded to an outlet temperature of 300°C, the WGS low temperature reactor operated at an inlet temperature of 165°C which corresponded to an outlet temperature of 160°C, and the PROX reactor had 29 kg of catalyst. With the use of gasoline, the best operating conditions were when the entire pressure of the system remained at one atmosphere, the water gas shift (WGS) high temperature reactor operated at an inlet temperature of 320°C which corresponded to an outlet temperature of 300°C, the WGS low temperature reactor operated at an inlet temperature of 165°C which corresponded to an outlet temperature of 162°C, and the PROX reactor had 202 kg of catalyst.
Both of these situations provide the maximum amount of hydrogen output while keeping the amount of carbon monoxide released within environmental regulations. One thing not evaluated was the heat transfer and the fluid flow that would be involved with this problem. This would be future work that would have to be done to complete this problem.