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Development of a Hydrogen Refueling Station Design Tool
international journal of hydrogen energy xxx (xxxx) xxx
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Development of a hydrogen refueling station design tool Sean M. Riedl University of Hawaii at Manoa, Department of Mechanical Engineering, Honolulu, HI, USA
highlights
graphical abstract
The model of a hydrogen refueling station can run indefinitely. The design tool can accurately predict
the
performance
and
operating cost. The model can determine how much to charge to make a profit. As the design tool continues to be developed,
it
has
shown
improvement.
article info
abstract
Article history:
In the last couple of decades, there has been a growing concern in what effects fossil fuels
Received 17 June 2019
are having on the environment, resulting in governments and governing organizations
Received in revised form
issuing stringent emission standards in an effort to curve their environmental damage. To
28 September 2019
meet these new standards, the transportation industry has been conducting research into
Accepted 30 September 2019
alternative fuels, such as hydrogen, but one critical problem utilizing hydrogen is that
Available online xxx
there is almost no infrastructure. A network of hydrogen refueling stations similar to modern gasoline stations will be required to be constructed to meet future demand. The
Keywords:
hydrogen refueling station model was created to aid in designing hydrogen facilities, thus
Hydrogen
accelerating their development while reducing design cost. A model was created using
Refueling station
Simulink consisting of an electrolyzer that generates hydrogen, a compressor, numerous
Distribution system
storage tanks, a dispensing unit that transfers hydrogen, and a vehicle component that
Service station
consumes hydrogen fuel. The model was validated using data from existing hydrogen
Alternative fuels
refueling stations, and the data obtained from testing the previous version of the hydrogen
Modeling
refueling station model to determine model accuracy and if the model has improved. The model has demonstrated that it can produce reasonable results for a station's performance and has improved compared to the previous version. © 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
E-mail address: [email protected]. https://doi.org/10.1016/j.ijhydene.2019.09.234 0360-3199/© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Riedl SM, Development of a hydrogen refueling station design tool, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.234
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Introduction For over a century, fossil fuels have powered society's transportation needs, due to their abundance and low cost to produce. However, in the last thirty years fossil fuels are becoming more expensive to extract, refine, and distribute, due to dwindling global supply, which has forced companies to look for fossil fuels in more remote locations. As the cost in utilizing fossil fuels keeps increasing, another growing concern is the potential damage fossil fuels are having on the environment. As a result, governments and governing organizations from around the world have implemented strict air pollution regulations in an effort to reduce the effects of burning fossil fuels. For example, the European Union, California, and the International Maritime Organization (IMO) have all introduced standards that reduce vehicle emissions to zero or close to it [1,2]. For example, in 2017, the California Air Resources Board (CARB) approved the 2030 Climate Change Scoping Plan, which targets a 40% reduction of emissions from 2020 levels [3]. These new standards have forced the transportation industry to look into alternative fuels to reduce our dependence on fossil fuels in an effort to comply with these new emission requirements [1]. Hydrogen as an alternative fuel has the potential to meet or exceed these new standards and improve our daily lives by creating a more sustainable energy economy. The obvious reasoning for this assertion is that hydrogen is the most abundant element; is considered to be more environmentally friendly than other fuel sources, and is the most renewable of all the alternative fuel options [2]. Hydrogen can be produced from a variety of sources, such as water. When hydrogen is consumed in the combustion process the main by-product is water, and produces very little harmful emissions. This in turn has a beneficial effect of increasing the life expectancy of the system components used in consuming hydrogen. Another way hydrogen can be consumed to produce energy is utilizing fuel cells. In using fuel cells to power a vehicle, where the only byproduct is water, from which hydrogen was originally produced. Refueling a hydrogen-powered vehicle takes the same amount time as refueling a gasoline powered vehicle: about 5 min for a car and 10 min for a transit bus [3]. Even with hydrogen having all of its potential benefits it has little to no infrastructure outside of universities or certain parts of California or Europe. Currently, no one has built a network of thousands of hydrogen refueling stations that would make owning a hydrogen power vehicle practical [4]. The hydrogen refueling stations built thus far have been built to service one of two purposes: as a stand-alone power system or as a hydrogen refueling station to test and demonstrate the technology to the public [5]. This means there are very few hydrogen refueling stations used commercially, even with most of the technology required to implement the hydrogen economy has already been in operation for the last couple of decades [6]. However, in the last couple of years, hydrogen refueling stations and hydrogen powered vehicles is just beginning to become commercially available to the public. Hydrogen Fuel first went on sale in California in January 2015, more than three years ago, though it had been dispensed free at a dozen or so prototype
locations before that [7]. Royal Dutch Shell has begun to install hydrogen-refueling infrastructure in the UK, California, and Germany. Also, Shell has several hydrogen fueling projects under consideration in the US, China, and a number of other European countries. Other major companies are also investing in hydrogen distribution include the Line Group and Trillium, while others like NEL Hydrogen and ITM Power are developing hydrogen production from renewable sources [3]. As of 2018, there was a total of 369 hydrogen refueling stations in operation worldwide, with 152 in operation in Europe, 136 in Asia, 78 in North America, one in South America and one in Australia [8,9]. However, there is still not enough hydrogen service stations to subvert fossil fuels as the main transportation fuel source. More investment and development will be need if hydrogen is to become the fuel that drives the world's economies, and thus break our dependency on fossil fuels. For example, five years ago, the state of California set a goal of 100 hydrogen fueling stations throughout the state by 2020, a deadline that now appears unlikely to be met [7]. The main obstacles facing the reliance on alternative fuels, such as hydrogen, are: availability, cost, reliability, safety and the compliance with regulations [1]. The Hydrogen Refueling Station Design Tool was developed in an effort to reduce research and development time and cost. Thus, allowing a hydrogen service stations to be designed quicker before construction can begin. This results in lowering the overall expense of the hydrogen facility research and development in an attempt to eliminate some of the obstacles facing hydrogen. As society adopts and develops the hydrogen economy, this will generate a demand for this tool to aid in designing individual service stations.
Refueling station model A hydrogen refueling station software design tool was developed using Matlab/Simulink® [10]. Originally, the hydrogen refueling station model was very basic in its design, as described in “Development of a Design Tool for Modeling Hydrogen Refueling Stations” [11], and only consisted of an electrolyzer, a compressor, main storage tanks consisting of one or more banks, a buffer tank and a very basic dispensing unit. The only information the model could provide was the total amount of time to refill the storage tanks, and the associated cost in producing hydrogen. The design tool has evolved into a more complex tool that includes a more sophisticated dispensing unit and a vehicle component, which will allow the model to run indifferently by dispensing fuel and refilling the storage tanks as required. The electrolyzer produces the hydrogen from water by consuming electricity to separate the hydrogen from the oxygen atoms through a process called electrolysis. The reason for selecting the electrolyzer over other forms of hydrogen production methods, like a gas reformer, is because it would reduce society's dependency on fossil fuels and is a nonrenewable energy source to produce hydrogen. It should be noted that the software design tool of hydrogen refueling station was designed to be as general as possible so it could accommodate a wide variety of hydrogen refueling station configurations. If each component was modeled to match a specific electrolyzer or compressor, for
Please cite this article as: Riedl SM, Development of a hydrogen refueling station design tool, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.234
international journal of hydrogen energy xxx (xxxx) xxx
example, then if that same numerical model was used to represent a different electrolyzer or compressor a significant amount of error would be introduced. This is due to each specific manufactured electrolyzer and compressor models have their own unique operating profile and characteristics. As a result of this design philosophy, and to simplify the calculations and design of the model, temperature was held constant while the software design tool is running. As an input parameter, temperature can be changed for each individual operating component and allows the temperature to be set at different values to match the average temperature for a specific region or location. Surprisingly, changing the temperature for any of the individual components will affects the model's accuracy.
Electrolyzer The model could accommodate any type or size of electrolyzer regardless if it is an alkaline or a Polymer Electrolyte Membrane (PEM) Electrolyzer, and was created from a design or consumer standpoint. The only inputs and outputs important in modeling the electrolyzer is how much hydrogen the electrolyzer can produce in a given amount of time and how much is it going to cost. Manufacturers’ electrolyzer model specifications do not include the oxygen production rate, or the amount of water consumed, thus the two parameters were neglected. In most cases, the oxygen is vented to the atmosphere, or captured for industrial or commercial applications, but the cost of water and the production of oxygen can be incorporated at a later time if there is a demand to do so. What information electrolyzer manufacturers are willing to provide about the performance characteristics of their individual units is the hydrogen production rate and the corresponding conversion efficiency. Based on this information, the amount of electricity a particular electrolyzer consumes in a particular timeframe can be determined. Equations (1) and (2) govern the electrical operating cost predicted by the model for a given electrolyzer [12], Zt Pel ¼
·
· m RT h ifm > 0 PM el
(1)
to ·
Pel ¼ Pidle if m ¼ 0
(2) ·
where,”Pel ” is the total electrical power consumed (kW); “m ”is the hydrogen flow rate (kg/h); “R” is the ideal gas constant (8.314 J/(mol K)); “T” is the assumed constant temperature (293.15 K); “P” is the atmospheric pressure under standard conditions (101,325 Pa); “M” is the molar mass of hydrogen (0.002016 kg/mol); “hel” is the electricity consumed divided by the volume of hydrogen gas produced, also known as the conversion efficiency (kWh/Nm3); “N” (in the conversion efficiency units) stands for normal conditions; “Pidle” ¼ Power consumed while idling (kW); and to ¼ initial time.
Compressor The next major component in the model of a hydrogen refueling station is the compressor. Usually, diaphragm
3
compressors, which is a form of reciprocating compressors, are used in hydrogen refueling stations due to their reduce potential of igniting the hydrogen gas. Modeling the compression process determines the amount of work the unit has to perform to store the hydrogen produced. Once the amount of work is known, the amount of electrical power consumed can be determined dependent on the assumptions discussed below. Making precise calculations that describe the work performed by a compressor is not widely known. To overcome this obstacle and to simplify the calculations, one of three assumptions can be made in determining the quantity of work performed. The first simplification is to assume the process is isentropic. This process assumes entropy is conserved throughout the compression process. The second assumption is to assume the whole process is isothermal, where the temperature of the hydrogen gas does not change during the compression process. These two theoretical assumptions represent the upper and lower range of the work performed during the compression process, respectively. However, for practical applications the compression of hydrogen is neither isothermal nor isentropic, which leads to the actual work of the compressor being somewhere in between the two aforementioned extremes. Using a thermodynamic approach, the actual work of the compressor can be determined by assuming the process is a reversible polytropic process [13]. Equation (3) below is used to calculate the work of a compressor assuming the process is polytropic [13]. 3 2 n1 n 7 6 P2 n RT1 4 15 Wpolytropic ¼ n1 P1
(3)
Where, Wpolytropic ¼ Polytropic work performed by the compressor (J/mol); n ¼ Polytropic Index; P1 ¼ suction pressure (Pa), P2 ¼ discharge pressure (Pa); R ¼ Ideal gas constant (8.314 (J/(K$mol)); T1 ¼ Temperature of hydrogen (K). In addition, equation (4) is used to calculate the work of a compressor assuming the process is isothermal [14]. P2 WIsothermal ¼ RTln P1
(4)
Where, Wisothermal ¼ Isothermal work (J/mol); R ¼ Ideal gas constant (8.314 (J/(K$mol)); T ¼ Temperature of hydrogen (K); P2 ¼ discharge pressure (bar); and P1 ¼ suction pressure (bar). Lastly, equation (5) is used to calculate the work of a compressor assuming the process it isentropic [13] given by 2 3 g g1 g P 2 RT4 15 WIsentropic ¼ g1 P1
(5)
where, WIsentropic ¼ isentropic work (J/mol); P1 ¼ suction pressure (bar); P2 ¼ discharge pressure (bar); g ¼ specific heat ratio for hydrogen at 20 C ¼ 1.41; R ¼ Ideal gas constant (8.314 (J/(K$mol)). In determining which thermodynamic assumption to use, either isothermal, isentropic, or polytropic, is dependent on what information can be obtained from the individual compressor companies about a particular compressor model used in a hydrogen refueling station's design. All three
Please cite this article as: Riedl SM, Development of a hydrogen refueling station design tool, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.234
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processes have been modeled, but at this point in time only the isentropic process using equation (5), has been incorporated into the model. If the compressor has two-stages, the work for each stage is added per either Equation (3) and (4), or (5) depending how the work is being calculated to determine the total amount of work performed. Also, the pressure between the two stages or intermediate pressure is determined by using Equation (6), which maintains the pressure ratio going from one stage to the next [13] as, P3 ¼
pffiffiffiffiffiffiffiffiffiffi P1 P2
(6)
where, P1 ¼ suction pressure (Pa); P2 ¼ discharge pressure (Pa); and P3 ¼ optimal intermediate pressure (Pa). Once the work done by the compressor is known either for a single or a two-stage compressor, the power for the compressor can be determined from Equation (7) [12,15], ·
Pcomp ¼
Wcomp m acomp
(7)
where, Pcomp ¼ compressor power (W); Wcomp ¼ compressor · work (J/mol);m ¼ compressor flow rate (mol/s); and acomp¼ compressor efficiency. It should be noted only a single stage and a two-stage isentropic compressor have been modeled and are incorporated into the design tool. The user has the option of selecting which of the two compressor options they wish to use in designing their hydrogen refueling station.
Storage tanks The compressor's main function is to take the hydrogen gas produced and compress it into an assortment of storage tanks. A hydrogen refueling station's storage tank design can be comprised of one or more storage tanks with each being able to be pressurized to a different maximum pressure or all can be pressurized to a similar pressure. These multiple storage tank designs are referred to as banks with each bank being able to operate independently from each other. Modeling the pressure within the storage tanks can be derived from either Van der Waals equation of state for a real gas or using the ideal gas law [15,16]. However, for ease of modeling the ideal gas law was used [12,15], and [16]. The pressure within the storage tank banks is based on the ideal gas law given by equations (8) and (9), PT ¼ Po þ PðtÞ
PT ¼ Po þ
RT VM
(8) Zt
·
m dt
(9)
to
where, V ¼ volume of the gas tank (m3); PT ¼ total pressure in tank (Pa); and Po ¼ initial pressure (Pa). Based on information provided by the compressor manufacturers [17], the compressibility factor “Z” has been omitted from the ideal gas equation due to the actual value being so close to unity that its effect would be negligible. It also should
be noted that the initial pressure of the storage tanks can be adjusted. In the model there are two different main storage tank configuration that have been incorporated and can be selected. The station's storage tanks setup can be comprising of two or three independent banks and can have the same or have different volumes. A third option, comprising of four independent banks was going to included, but was decided against incorporating it because it was not required for validation purposes. Again, this option can be added at a later time if there is a desire to design a hydrogen refueling stations with four banks to meet demand.
Buffer tank The buffer tank is located between the electrolyzer and the compressor to regulates the flow of hydrogen between the electrolyzer and the compressor. In most cases the electrolyzer is going to have a different flow rate than the compressor. This may result in a buildup of pressure within the connecting pipe potentially resulting in rupturing the pipe, or if the compressor has a higher flow rate than the electrolyzer, a vacuum could result. Another reason for the buffer tank is to consider the effects of discontinuity of the refueling process [18] and to ensure a constant flow of hydrogen to the compressor. When full, the buffer tank sends a signal to the compressor to engage, draining the buffer tank to a preset pressure where the compressor automatically shuts down until the buffer tank is refilled to its preset maximum pressure. The maximum and minimum pressures for the buffer tank are determined by a particular compressor model's maximum and minimum inlet operating pressure range. The pressure within the buffer tank is governed by equations (8) and (9).
Dispensing unit Once the storage tanks have been filled, the station is ready to dispense hydrogen. Dispensing hydrogen is achieved by emptying the storage tanks by the corresponding amount required to fill the vehicle's fuel tank until the two tank pressures have reached equilibrium or the desired maximum pressure for the vehicle has been achieved. In a multiple storage bank setup when the pressure in the first storage bank equals the pressure in the vehicle's fuel tank, the modeled station will automatically switch to the next storage tank or bank until the vehicle's fuel tank is full by reaching the desired maximum pressure. At present, a second compressor has not been incorporated into the model to draw the remaining hydrogen out of the storage tanks once the pressure has dropped below the vehicle's tank pressure. Besides transferring hydrogen, the only other outputs from the dispensing unit within the model is the amount of electricity consumed while dispensing hydrogen, and the amount of hydrogen dispensed to the vehicle. The amount of time to completely refill a vehicle, the amount of electricity the dispensing unit consumes while operating, and the amount of hydrogen to dispense to the vehicle are the only inputs for the
Please cite this article as: Riedl SM, Development of a hydrogen refueling station design tool, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.234
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dispensing unit model. Refueling a hydrogen-powered vehicle takes the same time as refueling a gasoline tank, about 5 min, but can be changed within the model. When the dispensing unit is not dispensing hydrogen, it does not consume any electricity [19]. The amount of electrical power the dispensing unit consumes is given by Equation (10), 0:001ðelÞðrateÞ ¼W 60
(10)
where, el ¼ electrical consumption rate (W/h); rate ¼ time frame to transfer hydrogen (min); and W ¼ amount of electricity consumed within a certain time frame (kW).
Vehicle The vehicle component consumes the hydrogen dispensed to it by the hydrogen refueling station at a given rate. The vehicle's fuel tank operates along the same principle as the main storage tanks and the buffer tank using equations (8) and (9). At present, the amount of hydrogen dispensed to the vehicle is based on the tank's volume, and is pressurized until the fuel tank reaches a predetermined pressure, indicating the vehicle's fuel tank is full. Then over a certain amount of time the vehicle consumes the hydrogen at a predetermine rate until it requires to be refilled again. Hopefully, by the time the vehicle has consumed all of its hydrogen fuel and needs to be refilled, the station has already refilled the storage tanks and is ready to resupply the vehicle. Thus, repeating the process of refilling the vehicle's fuel tank, which then prompting the station to start producing more hydrogen to refill the station's storage tanks. With the vehicle component integrated into the model, this process will repeat itself automatically depending on how long the model is set to run.
Model outputs Once the model has run for a period of time several graphical and numerical outputs are generated to aid in the analysis of a particular station design. The model produces 8 different graphical outputs, which include: the electrolyzer's hydrogen flow rate, buffer tank's pressure, compressor's hydrogen flow rate, each individual storage bank pressure, the storage tank bank pressure being refilled or emptied as the model switch from one storage tank bank to another, and lastly the vehicle fueling tank pressure. The model also produces 8 numerical output values. The first three are the electolyzer's, compressor's, dispensing units electrical power consumption cost, follow by the total electrical cost during the station's operation. The next numerical output is based on the cost per kg of hydrogen dispensed to the vehicle. Basically, the amount a consumer is charged for the amount of hydrogen dispensed to their vehicle. In the previous version of the hydrogen refueling station model could not immediate determine the net income from dispensing hydrogen, but had to extrapolate this information. The next two numerical outputs are the amount of hydrogen dispensed, and secondly the pressure in the vehicle's fuel tank when the model stops running. The last numerical output is amount of time the model has taken to refill the storage tanks after supplying hydrogen to a paying consumer.
5
Results/discussion The hydrogen refueling station design tool was validated using existing hydrogen refueling stations by comparing the model's output results to actual real-world data. The model was also compared with the results of the previous version of the hydrogen refueling station design tool as described in “Development of a Software Design Tool for Modeling Hydrogen Distribution Systems” [20]. As before the Simlink [10] time interval was set at 0.001 h for the best possible accuracy and for the model to function properly. This was done to see if the design tool had improved or reduced in accuracy compared to the previous version. The hydrogen refueling stations used to validate the model were the Humboldt State University (HSU) Hydrogen Refueling Station, the BP e Praxair Hydrogen Refueling Station at Los Angeles International Airport (LAX), and the hydrogen refueling station at the Windto-Hydrogen Demonstration Project in Minot, North Dakota (ND). These three stations where chosen largely at random, and were selected by how available the required data was for each hydrogen refueling stations. This was especially true for the compressor's companies who were very reluctant to provide a certain compressor model's efficiency out of fear it could give a competitor a competitive advantage. The model of a hydrogen refueling station was tested similar to how the previous version of the model was test in Development of a Software Design Tool for Modeling Hydrogen Distribution Systems [20], and in Development of a Design Tool for Modeling Hydrogen Refueling Stations [11]. The station's performance and its associated operating cost were used to validate the model so the two versions can be accurately compared. This was accomplished by comparing the amount of time the model takes to refill the storage tanks after refueling a single vehicle, and the associated electrical or operational cost to dispensing hydrogen and refilling the storage tanks. The performance and operational data for the actual hydrogen refueling stations that the model is being validated against is show in the following tables, list as “actual”. The results of the validation testing are shown in Tables 1e3 alongside results of the previous version from “Development of a Software Design Tool for Modeling Hydrogen Distribution Systems” [20]. It should be noted, that the variability for the mean data provided could not be obtained for the individual components. In addition, to a hydrogen refueling station's performance and operating cost, the model can also provide the amount of money ($) an operator/owner can charge a paying consumer in order to generate a profit. This information would allow a designer to see if any additional design changes would be required to reduce the station's operating expenses. In order, to make a profit is largely dependent on the station's intended location, where the local utility charges a certain amount per KWh of electricity. Unfortunately, the amount charged was not able to be obtained for the stations used to validate the design tool, because the hydrogen refueling stations used were prototypes designed to show proof of concept or were only for research purposes. As before in Development of a Software Design Tool for Modeling Hydrogen Distribution Systems [20], the validation
Please cite this article as: Riedl SM, Development of a hydrogen refueling station design tool, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.234
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international journal of hydrogen energy xxx (xxxx) xxx
testing was performed by setting the buffer tank's initial pressure at opposite ends of the compressor suction pressure operating range. For Case 1, the buffer tank was set at the maximum inlet pressure of the compressor, and in Case 2, the buffer tank was set at the minimum inlet pressure of the compressor. However, this time the main storage tanks were left full compare to the previous version where they were manually emptied to simulate the station had just refueled a vehicle. The station would dispense fuel and then refill the station's storage tanks. The model of hydrogen refueling station was ran twice for the Humboldt State University (HSU) Hydrogen Refueling Station, and BP/Praxair Hydrogen Refueling Station at LAX, but was ran four separate times for the Hydrogen Refueling Station in Minot, ND, due to the station servicing two different types of vehicles. The results for Humboldt State University (HSU) Hydrogen Refueling Station are shown in Table 1, BP/Praxair Hydrogen Refueling Station at LAX in Table 2, and the Hydrogen Refueling Station in Minot, ND, in Table 3. In Table 2 below, only one case is shown for the validation results in comparing the model's results with the BP/Praxair Hydrogen Refueling Station at LAX. This is because there was virtually no difference in the two cases regardless if the buffer tank's initial pressure was set at the compressor's maximum or minimum suction pressure operating ranges. The BP-Praxair Hydrogen Refueling Station at Los Angeles International Airport was originally designed to service a large volume of vehicles, including a couple of city transit buses, various airport vehicles, as well as public vehicles [21]. However, the station only serviced four DaimlerChrysler Fuel Cell vehicles with each vehicle having a compacity to hold 1.8 kg of hydrogen [21]. Previously, in Development of a Software Design Tool for Modeling Hydrogen Distribution Systems [20] the model was tested by reducing each of the four banks of the main storage tank by 1.8 kg of hydrogen and seeing how long it took the station to refill each bank. However, upon further review of the station specifications, it was determined that the station only had three cascading banks [22], but had four stainless steel pressure vessels that made up the storage capacity [21,22]. Subsequently, the station model was reconfigured to have the main storage tank comprised of only three banks. The model was tested by only dispensing hydrogen to a single DaimlerChrysler Fuel Cell vehicle and then multiplying the results by a factor of four. Then the model was tested, by dispensing hydrogen to all four vehicles for a total 7.2 kg hydrogen the amount of time to refill the storage tanks to see if there was any difference, but the results were the same. In the previous version of the hydrogen refueling station design tool the cost of operating the station was omitted due to the huge error when compared to the actual station's operation expenses. It costed the operators $46.88 to refuel the four DaimlerChrysler Fuel Cell vehicles, which resulted in an error of 46.8% [11]. This was considered to be an anomaly when compared to the accuracy of the model to the other two real world hydrogen refueling stations: Humboldt State University Hydrogen Refueling Station and the Hydrogen Refueling Station in Minot, ND. With the current version of the model the amount of error has not improved and was determined to be 46%. Originally, as mentioned in the Development of a Design Tool for Modeling Hydrogen Refueling Stations [11] it was believed this error was the result of the manufactures not
including all the electricity the electroylzer or other components were consuming. For example, the electrolyzer was connected to a chiller to keep it cool during the day. This electrical draw was not included in the information provided by the operators. Another reason for this excessive error has to do with how the electrical costs are calculated within the model. All the electrical costs were calculated using the U.S. national average of 6.2 cents in 2008 [23]. The cost of electricity in California apparently is much higher than the U.S national average. Using the model, the electrical cost would need to be around 11.4 cents per kilowatt hour, to yielded a more realistic operating error of 0.77%. As a result, the operating expenses for the Hydrogen Refueling Station at LAX was not included in Table 2. In the following three tables are the results of the validation testing in comparing the design tool to actual hydrogen refueling station data for all three stations as well as the
Table 1 e Humboldt state university hydrogen refueling station validation results. Previous Version
Current Version
Performance Case Case Case Case 1 2 1 2 Model's Time to Refill Storage Tanks 23.3 h 23.8 h 23.5 h 24 h (A) Actual Station's Performance (B) 24 h % Error ¼ [(B-A)/B*100] 2.90% 0.83% 2.1% 0% Operational Costs Electolyzer Compressor Dispensing Unit Model Cost Predictions (A) Actual Station's Operating Cost (B) % Error ¼ [(B-A)/B*100] Cost per kg of Hydrogen to equal Expenses
$11.21 $0.29 $0.01 $11.51
$11.45 $11.45 $0.29 $0.29 $0.01 $0.01 $11.75 $11.74 $12.40 7.18% 5.20% 5.32% NA NA $4.67
$11.69 $0.29 $0.01 $11.98 3.31% $4.76
Table 2 e BP e praxair hydrogen refueling station at LAX validation results. Previous Version
Current Version
Performance Model Time Predictions to Refill Storage Tanks (A) Actual Station's Performance (B) % Error ¼ [(B-A)/A*100]
7.1 h
1.40%
1.796 h (7.18 h) 7.2 h 0.28%
Operational Costs Electolyzer Compressor Dispensing Unit Model Cost Predictions (A) Actual Station's Operating Cost (B) % Error ¼ [(B-A)/A*100] Cost per kg of Hydrogen to equal Expenses
NA NA NA NA NA NA NA
NA NA NA NA NA NA NA
Please cite this article as: Riedl SM, Development of a hydrogen refueling station design tool, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.234
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previous version of the model. The first part or upper half of the tables is the performance data in how long it took the model to refill their storage tanks after dispensing hydrogen. This is followed by the actual hydrogen refueling station time. A comparison than was made between the model's performance result and the actual hydrogen refueling station that the model was configured to represent to determine the amount of error in the results. The second half of the tables is the data concerning the how much it cost to operate or the electrical cost of the station during refueling a vehicle and the refilling processes of the hydrogen refueling stations. The first three rows represent how much it would cost to operate the station's individual components, followed by the sum total.
Then the operational cost of the actual hydrogen refueling station the model was configured to represent. Once again, a comparison was made between the model's results and the data of the actual hydrogen refueling station to determine the amount of error in the model's results. The bottom row of the tables shows how much the owner or operator of the station would have to charge just to cover their operating expenses. As mention previously the model can also produce various graphical information in the form of plots of 6e8 different aspects depending on the model's configuration. For example, Fig. 1, below, represents the pressure within the hydrogen refueling station's storage tanks while the model is configured to represent the hydrogen refueling station in Minot, North
Table 3 e Hydrogen refueling station in Minot, ND, validation results. Previous Version
Current Version
Performance Vehicle 1
Model Time Predictions to Refill Storage Tanks (A) Actual Station's Performance (B) % Error ¼ [(B-A)/B*100]
Vehicle 2
Vehicle 1
Vehicle 2
Case 1
Case 2
Case 1
Case 2
Case 1
Case 2
Case 1
Case 2
2.44 h 2.44 h 0.00%
2.43 h 2.44 h 0.40%
0.82 h 0.82 h 0.00%
0.83 h 0.82 h 1.20%
2.44 h 2.44 h 0.00%
2.44 h 2.44 h 0.00%
0.82 h 0.82 h 0.00%
0.82 h 0.82 h 0.00%
$21.70 $0.88 $0.05 $22.64 $26.60 14.90% NA
$21.70 $0.88 $0.05 $22.63 $26.60 14.90% NA
$7.25 $0.30 $0.05 $7.60 $8.89 14.50% NA
$7.24 $0.30 $0.05 $7.60 $8.89 14.60% NA
$21.8 $0.89 $0.01 $22.71 $26.60 14.62% $3.45
$21.81 $0.88 $0.01 $22.71 $26.60 14.62% $3.45
$7.28 $0.30 $0.01 $7.59 $8.89 14.62% $3.45
$7.28 $0.30 $0.01 $7.59 $8.89 14.62% $3.45
Operational Costs Electolyzer Compressor Dispensing Unit Model Cost Predictions (A) Actual Station's Operating Cost (B) % Error ¼ [(B-A)/B*100] Cost per kg of Hydrogen to equal Expenses
Hyrogen Refueling Station Model of Minot North Dakota Servicing the Chevrolet Silverado Pickup Truck
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320
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Fig. 1 e Hydrogen refueling station model's storage tank pressure during a 14 h run while servicing a Chevrolet Silverado pickup truck with a 6.6 kg fuel tank. Please cite this article as: Riedl SM, Development of a hydrogen refueling station design tool, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.234
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Dakota, while servicing a Chevrolet Silverado pickup truck with a 6.6 kg storage capacity [24]. In the first 30 min the model is first dispensing fuel followed by the refilling process. The 30-min refueling time was chosen solely to more easily see the pressure plot on the graph. Normally, refueling time would only take around 5 min [19]. After the dispensing and refilling the storage tanks process is complete the model station waits until the vehicle has completely emptied its fuel tank before repeating the process. The vehicle was arbitrary set to consume its hydrogen fuel at 0.7 kg/h. The vertical lines in Fig. 1, is the station switching from one storage tank bank to the next, once the vehicle's fuel tank has reached equilibrium with a particular station's storage bank or has finished being refilled.
Conclusion The current version of the design tool has improved compared to the previous version and has increased the model's accuracy in contrast with all three existing hydrogen refueling stations. In determining the model performance accuracy, the design tool demonstrated a total average error of 0.44%, which resulted in a decrease from the previous performance average error of 1.22%. As for estimating the electrical cost for a particular hydrogen refueling station design the model had an average error of 8.38%, which is an improvement over the previous version that had an average error for electrical cost of 10.5%. With all the improvements to the hydrogen refueling station software design tool, like an addition of a vehicle component that simulates demand, to integrating all the different model variants into a single model with a centralized user interface, has shown to improve the model's overall performance. These results illustrate, as the model continues to be developed to accurately reflect real world conditions, it becomes more successfully in predicting the performance and cost of operating of any hydrogen refueling station design. The differences between the two versions of the hydrogen refueling stations design tool can be associated with the current model being more accurately resembling how a station would actually operate. The model can now operate indefinitely, compared to the model's original design, which required the main storage tanks to be manually set to a pressure right after they would have dispensed hydrogen. In doing so, some mathematical error in terms of rounding was introduced into the design tool's results. The current version removes this possible error because the model can automatically switch from dispensing fuel to refilling the main storage tanks. During validation testing of the current version of the hydrogen refueling station model there were some unexpected results. It was illustrating a couple flaws in the previous version's design and some of the past assumptions were incorrect. For example, during the third station's validation testing of the model, the hydrogen refueling station in Minot, North Dakota, using the Chevrolet Silverado Pickup Truck with a 6.6 kg hydrogen storage capacity the station actually required a second bank to finish refueling the vehicle, and showed the first bank's pressure actually dropped below 350 bars during the refueling process before switch the next
bank to complete the vehicle fueling. Previously, it was assumed the storage tank's first bank was the only bank required to service the pickup truck. Although, the net improvement in the model might seem small, one most remember the model's percent error was already low in the previous version as shown in Tables 1e3. Even with substantial development that went into the model of a hydrogen refueling station from the previous version the potential for reducing the amount of error may only be in small amounts. This could be done by improving the signal processing elements in how the model functions, which makes up a large portion of the model, to refining the equations that describe certain aspects of the model. However, the design tool will never will be perfect in comparison to real world systems. Assumptions must be made to be able to mathematically describe observed phenomena. Substantial development has gone into Hydrogen Refueling Station Design Tool, since Development of a Design Tool for Modeling Hydrogen Refueling Stations [11], and Development of a Software Design Tool for Modeling Hydrogen Distribution Systems [20] has reached a point where it could be marketed to institutions or companies within the field of hydrogen refueling facility development. From the feedback obtained from the model's use will determined what possible further development of the hydrogen refueling station design tool is required. However, other components that could possibly be added to the model are different types of hydrogen storage options, like metal hydrides. From a safety standpoint it would be beneficial to use metal hydrides as a hydrogen storage option especially on vehicles. Metal hydrides can store hydrogen at a fraction of the pressure than storing hydrogen gas in pressurized cylinders at very high pressures.
Acknowledgements The author would like to thank Hawaii Natural Energy Institute for their initial support in the development of the software model. Appreciation is extended also to Cugnet Mikael, Project Manager at the French Institute for Solar Energy, for his help with the Hydrogen Refueling Station Design Tool. The author would like to thank Dr. Ronald Knapp, (Retired) Former Chairman of the Mechanical Engineering and professor at University of Hawaii at Manoa for his advice and help in developing the model and in reviewing this paper. The author would like to thank the following people for providing valuable data on HSU Hydrogen Refueling Station, BP e Praxair Hydrogen Refueling Station at LAX, and the Wind-to-Hydrogen Demonstration Project in Minot, ND: Chapman, Greg P.E., Senior Research Engineer, Schatz Energy Research Center. Busch, Tim, Onsite Business Manager e West Region, Praxair Inc. Beeson, Jerry, Standard Plant Tech, Praxair Inc. Vale, Michael, Product Development Specialist, Hydrogenics Corporation. Bush, Randy, Distributed Resource Coordinator, Basin Electric Power Cooperative.
Please cite this article as: Riedl SM, Development of a hydrogen refueling station design tool, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.234
international journal of hydrogen energy xxx (xxxx) xxx
Filosa, Bob, Power Pressure Industries. Gallow, Grey, Engineer, Pdc Machines. Heartken, Jim, Hydro-Pac.
references
[1] Seddiek IS, Elgohary MM, Ammar NR. The hydrogen-fuelled internal combustion engines for marine applications with a case study. Brodogradnja/Shipbilding 2015;66(1). [2] Brert Lv, Godjevac M, Visser K, Aravind P. A review of fuel cell systems for Maritime applications. J Power Sources 2016;327:345e64. [3] Pocard N. Why hydrogen fueling stations are gaining global momentum. Hydrogen Solutions July 2018;19. [4] Fagone J. Solar powered electrolyzers [Online]. Available, http://theatlantic.com/magazine/archive/2010/11/tomsullivan/8264; November 2010. [5] Uleberg O. Modeling of advanced alkaline electrolyzers: a system simulation approach. Int J Hydrogen Energy 2003;28:21e33. [6] International Partnership for the Hydrogen Economy. Hydrogen safety codes & standards. 2007 [Online]. Available, http://www.iphe.net/docs/Fact_Sheets/Hydrogen_Safety_ Codes_and_Standards.pdf. [Accessed 23 October 2009]. [7] Voelcker J. California now has 33 hydrogen fueling stations for 4,200 fuel-cell cars so far. Green Car Reports 2 Apirl 2018 [Online]. Available, https://www.greencarreports.com/news/ 1116044_california-now-has-33-hydrogen-fueling-stationsfor-4200-fuel-cell-cars-so-far. € lkow-Systemtechnik GmbH. Hydrogen refueling [8] Ludwig-Bo stations worldwide [Online]. Available, https://www. netinform.net/h2/h2stations/h2stations.aspx; 2019. [9] TUV SUD America Inc. Highest increase of hydrogen refuelling stations in Germany worldwide in 2018 again. Presse Med February 2019;15 [Online]. Available, https:// www.globenewswire.com/news-release/2019/02/15/1726095/ 0/en/Highest-increase-of-hydrogen-refuelling-stations-inGermany-worldwide-in-2018-again.html. [10] Mathworks. Matlab/simulink. Mathworks; 2018. [11] Riedl S. Development of a design tool for modeling hydrogen refueling stations. 2010.
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[12] Jallouli R, Krichen L, Francois B, Ouali A. Modelling and control of an optimized PV array with hydrogen system comprising a PEMFC and an electrolyzer. International Journal of Electrical and Power Engineering 2007;1(3):264e73. [13] Tzimas E, Filiou C, Peteves S, Veyret J-B. Hydrogen storage: state-of-the-art and future perspective. Petten, The Netherlands: European Commission; 2003. [14] University of Dayton. Energy efficient compressed air systems [Online]. Available, http://academic.udayton.edu/ kissock/http/eem/lecturesandhomework/10-compressedair/ energyefficientcompressedair.docx. [15] Zhou T, Francois B. Modeling and control design of hydrogen production process for an active hydrogen/wind hybrid power system. Int J Hydrogen Energy 2009;34:21e30. [16] Boccaletti C, Di Grazia G, Fabbri G, Nistico E. Energy models for stand alone power systems. 2004. Rome, Italy. [17] Machines PDC. Diaphragm compressors: designed and constructed for high reliability and low maintenance [Online]. Available, http://www-eng.lbl.gov/~shuman/NEXT/ GAS_SYS/PDC_Compressor.pdf. [18] Marcuello P, Correas L, Aso I, Romero L, Pena JA. Zaragoza EXPO 2008 hydrogen fuelling station: simulation and optimization of process variables and strategies in different scenarios. Spain: University of Zaragoza; 2008. [19] Hydrogen dispensers -safe hydrogen refueling. FTI International Group Inc; 2007 [Online]. Available, http:// www.fuelingtech.com/index990e.html?id¼806. [20] Riedl SM, Knapp RH. Development of a software design tool for modeling hydrogen distribution systems. International Society of Offshore and Polar Engineers (ISOPE) 2011;1:39e45. [21] Busch T. Interviewee, onsite business manager - West Region: Praxair. Interview 2009. [22] Weinert J. The LAX hydrogen fueling station development: a historical, technical, and economic overview with a discussion of the obstacles encountered and lessons learned. March, 2004. [23] HSU Hydrogen Fueling Station and Hydrogen Vehicle Frequently Asked Questions. Schatz energy research center. Humboldt State University; 2008 [Online]. Available, http:// www.schatzlab.org/docs/FAQsBrochure_sm.pdf. [24] Rebenitsch R, Bush R, Boushee A, Woeste J. Wind-toHydrogen energy pilot project: Basin Electric power cooperative. Basin Electric Power Cooperative; 2009.
Please cite this article as: Riedl SM, Development of a hydrogen refueling station design tool, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.234
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Development of a hydrogen refueling station design tool Sean M. Riedl University of Hawaii at Manoa, Department of Mechanical Engineering, Honolulu, HI, USA
highlights
graphical abstract
The model of a hydrogen refueling station can run indefinitely. The design tool can accurately predict
the
performance
and
operating cost. The model can determine how much to charge to make a profit. As the design tool continues to be developed,
it
has
shown
improvement.
article info
abstract
Article history:
In the last couple of decades, there has been a growing concern in what effects fossil fuels
Received 17 June 2019
are having on the environment, resulting in governments and governing organizations
Received in revised form
issuing stringent emission standards in an effort to curve their environmental damage. To
28 September 2019
meet these new standards, the transportation industry has been conducting research into
Accepted 30 September 2019
alternative fuels, such as hydrogen, but one critical problem utilizing hydrogen is that
Available online xxx
there is almost no infrastructure. A network of hydrogen refueling stations similar to modern gasoline stations will be required to be constructed to meet future demand. The
Keywords:
hydrogen refueling station model was created to aid in designing hydrogen facilities, thus
Hydrogen
accelerating their development while reducing design cost. A model was created using
Refueling station
Simulink consisting of an electrolyzer that generates hydrogen, a compressor, numerous
Distribution system
storage tanks, a dispensing unit that transfers hydrogen, and a vehicle component that
Service station
consumes hydrogen fuel. The model was validated using data from existing hydrogen
Alternative fuels
refueling stations, and the data obtained from testing the previous version of the hydrogen
Modeling
refueling station model to determine model accuracy and if the model has improved. The model has demonstrated that it can produce reasonable results for a station's performance and has improved compared to the previous version. © 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
E-mail address: [email protected]. https://doi.org/10.1016/j.ijhydene.2019.09.234 0360-3199/© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Riedl SM, Development of a hydrogen refueling station design tool, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.234
2
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Introduction For over a century, fossil fuels have powered society's transportation needs, due to their abundance and low cost to produce. However, in the last thirty years fossil fuels are becoming more expensive to extract, refine, and distribute, due to dwindling global supply, which has forced companies to look for fossil fuels in more remote locations. As the cost in utilizing fossil fuels keeps increasing, another growing concern is the potential damage fossil fuels are having on the environment. As a result, governments and governing organizations from around the world have implemented strict air pollution regulations in an effort to reduce the effects of burning fossil fuels. For example, the European Union, California, and the International Maritime Organization (IMO) have all introduced standards that reduce vehicle emissions to zero or close to it [1,2]. For example, in 2017, the California Air Resources Board (CARB) approved the 2030 Climate Change Scoping Plan, which targets a 40% reduction of emissions from 2020 levels [3]. These new standards have forced the transportation industry to look into alternative fuels to reduce our dependence on fossil fuels in an effort to comply with these new emission requirements [1]. Hydrogen as an alternative fuel has the potential to meet or exceed these new standards and improve our daily lives by creating a more sustainable energy economy. The obvious reasoning for this assertion is that hydrogen is the most abundant element; is considered to be more environmentally friendly than other fuel sources, and is the most renewable of all the alternative fuel options [2]. Hydrogen can be produced from a variety of sources, such as water. When hydrogen is consumed in the combustion process the main by-product is water, and produces very little harmful emissions. This in turn has a beneficial effect of increasing the life expectancy of the system components used in consuming hydrogen. Another way hydrogen can be consumed to produce energy is utilizing fuel cells. In using fuel cells to power a vehicle, where the only byproduct is water, from which hydrogen was originally produced. Refueling a hydrogen-powered vehicle takes the same amount time as refueling a gasoline powered vehicle: about 5 min for a car and 10 min for a transit bus [3]. Even with hydrogen having all of its potential benefits it has little to no infrastructure outside of universities or certain parts of California or Europe. Currently, no one has built a network of thousands of hydrogen refueling stations that would make owning a hydrogen power vehicle practical [4]. The hydrogen refueling stations built thus far have been built to service one of two purposes: as a stand-alone power system or as a hydrogen refueling station to test and demonstrate the technology to the public [5]. This means there are very few hydrogen refueling stations used commercially, even with most of the technology required to implement the hydrogen economy has already been in operation for the last couple of decades [6]. However, in the last couple of years, hydrogen refueling stations and hydrogen powered vehicles is just beginning to become commercially available to the public. Hydrogen Fuel first went on sale in California in January 2015, more than three years ago, though it had been dispensed free at a dozen or so prototype
locations before that [7]. Royal Dutch Shell has begun to install hydrogen-refueling infrastructure in the UK, California, and Germany. Also, Shell has several hydrogen fueling projects under consideration in the US, China, and a number of other European countries. Other major companies are also investing in hydrogen distribution include the Line Group and Trillium, while others like NEL Hydrogen and ITM Power are developing hydrogen production from renewable sources [3]. As of 2018, there was a total of 369 hydrogen refueling stations in operation worldwide, with 152 in operation in Europe, 136 in Asia, 78 in North America, one in South America and one in Australia [8,9]. However, there is still not enough hydrogen service stations to subvert fossil fuels as the main transportation fuel source. More investment and development will be need if hydrogen is to become the fuel that drives the world's economies, and thus break our dependency on fossil fuels. For example, five years ago, the state of California set a goal of 100 hydrogen fueling stations throughout the state by 2020, a deadline that now appears unlikely to be met [7]. The main obstacles facing the reliance on alternative fuels, such as hydrogen, are: availability, cost, reliability, safety and the compliance with regulations [1]. The Hydrogen Refueling Station Design Tool was developed in an effort to reduce research and development time and cost. Thus, allowing a hydrogen service stations to be designed quicker before construction can begin. This results in lowering the overall expense of the hydrogen facility research and development in an attempt to eliminate some of the obstacles facing hydrogen. As society adopts and develops the hydrogen economy, this will generate a demand for this tool to aid in designing individual service stations.
Refueling station model A hydrogen refueling station software design tool was developed using Matlab/Simulink® [10]. Originally, the hydrogen refueling station model was very basic in its design, as described in “Development of a Design Tool for Modeling Hydrogen Refueling Stations” [11], and only consisted of an electrolyzer, a compressor, main storage tanks consisting of one or more banks, a buffer tank and a very basic dispensing unit. The only information the model could provide was the total amount of time to refill the storage tanks, and the associated cost in producing hydrogen. The design tool has evolved into a more complex tool that includes a more sophisticated dispensing unit and a vehicle component, which will allow the model to run indifferently by dispensing fuel and refilling the storage tanks as required. The electrolyzer produces the hydrogen from water by consuming electricity to separate the hydrogen from the oxygen atoms through a process called electrolysis. The reason for selecting the electrolyzer over other forms of hydrogen production methods, like a gas reformer, is because it would reduce society's dependency on fossil fuels and is a nonrenewable energy source to produce hydrogen. It should be noted that the software design tool of hydrogen refueling station was designed to be as general as possible so it could accommodate a wide variety of hydrogen refueling station configurations. If each component was modeled to match a specific electrolyzer or compressor, for
Please cite this article as: Riedl SM, Development of a hydrogen refueling station design tool, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.234
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example, then if that same numerical model was used to represent a different electrolyzer or compressor a significant amount of error would be introduced. This is due to each specific manufactured electrolyzer and compressor models have their own unique operating profile and characteristics. As a result of this design philosophy, and to simplify the calculations and design of the model, temperature was held constant while the software design tool is running. As an input parameter, temperature can be changed for each individual operating component and allows the temperature to be set at different values to match the average temperature for a specific region or location. Surprisingly, changing the temperature for any of the individual components will affects the model's accuracy.
Electrolyzer The model could accommodate any type or size of electrolyzer regardless if it is an alkaline or a Polymer Electrolyte Membrane (PEM) Electrolyzer, and was created from a design or consumer standpoint. The only inputs and outputs important in modeling the electrolyzer is how much hydrogen the electrolyzer can produce in a given amount of time and how much is it going to cost. Manufacturers’ electrolyzer model specifications do not include the oxygen production rate, or the amount of water consumed, thus the two parameters were neglected. In most cases, the oxygen is vented to the atmosphere, or captured for industrial or commercial applications, but the cost of water and the production of oxygen can be incorporated at a later time if there is a demand to do so. What information electrolyzer manufacturers are willing to provide about the performance characteristics of their individual units is the hydrogen production rate and the corresponding conversion efficiency. Based on this information, the amount of electricity a particular electrolyzer consumes in a particular timeframe can be determined. Equations (1) and (2) govern the electrical operating cost predicted by the model for a given electrolyzer [12], Zt Pel ¼
·
· m RT h ifm > 0 PM el
(1)
to ·
Pel ¼ Pidle if m ¼ 0
(2) ·
where,”Pel ” is the total electrical power consumed (kW); “m ”is the hydrogen flow rate (kg/h); “R” is the ideal gas constant (8.314 J/(mol K)); “T” is the assumed constant temperature (293.15 K); “P” is the atmospheric pressure under standard conditions (101,325 Pa); “M” is the molar mass of hydrogen (0.002016 kg/mol); “hel” is the electricity consumed divided by the volume of hydrogen gas produced, also known as the conversion efficiency (kWh/Nm3); “N” (in the conversion efficiency units) stands for normal conditions; “Pidle” ¼ Power consumed while idling (kW); and to ¼ initial time.
Compressor The next major component in the model of a hydrogen refueling station is the compressor. Usually, diaphragm
3
compressors, which is a form of reciprocating compressors, are used in hydrogen refueling stations due to their reduce potential of igniting the hydrogen gas. Modeling the compression process determines the amount of work the unit has to perform to store the hydrogen produced. Once the amount of work is known, the amount of electrical power consumed can be determined dependent on the assumptions discussed below. Making precise calculations that describe the work performed by a compressor is not widely known. To overcome this obstacle and to simplify the calculations, one of three assumptions can be made in determining the quantity of work performed. The first simplification is to assume the process is isentropic. This process assumes entropy is conserved throughout the compression process. The second assumption is to assume the whole process is isothermal, where the temperature of the hydrogen gas does not change during the compression process. These two theoretical assumptions represent the upper and lower range of the work performed during the compression process, respectively. However, for practical applications the compression of hydrogen is neither isothermal nor isentropic, which leads to the actual work of the compressor being somewhere in between the two aforementioned extremes. Using a thermodynamic approach, the actual work of the compressor can be determined by assuming the process is a reversible polytropic process [13]. Equation (3) below is used to calculate the work of a compressor assuming the process is polytropic [13]. 3 2 n1 n 7 6 P2 n RT1 4 15 Wpolytropic ¼ n1 P1
(3)
Where, Wpolytropic ¼ Polytropic work performed by the compressor (J/mol); n ¼ Polytropic Index; P1 ¼ suction pressure (Pa), P2 ¼ discharge pressure (Pa); R ¼ Ideal gas constant (8.314 (J/(K$mol)); T1 ¼ Temperature of hydrogen (K). In addition, equation (4) is used to calculate the work of a compressor assuming the process is isothermal [14]. P2 WIsothermal ¼ RTln P1
(4)
Where, Wisothermal ¼ Isothermal work (J/mol); R ¼ Ideal gas constant (8.314 (J/(K$mol)); T ¼ Temperature of hydrogen (K); P2 ¼ discharge pressure (bar); and P1 ¼ suction pressure (bar). Lastly, equation (5) is used to calculate the work of a compressor assuming the process it isentropic [13] given by 2 3 g g1 g P 2 RT4 15 WIsentropic ¼ g1 P1
(5)
where, WIsentropic ¼ isentropic work (J/mol); P1 ¼ suction pressure (bar); P2 ¼ discharge pressure (bar); g ¼ specific heat ratio for hydrogen at 20 C ¼ 1.41; R ¼ Ideal gas constant (8.314 (J/(K$mol)). In determining which thermodynamic assumption to use, either isothermal, isentropic, or polytropic, is dependent on what information can be obtained from the individual compressor companies about a particular compressor model used in a hydrogen refueling station's design. All three
Please cite this article as: Riedl SM, Development of a hydrogen refueling station design tool, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.234
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processes have been modeled, but at this point in time only the isentropic process using equation (5), has been incorporated into the model. If the compressor has two-stages, the work for each stage is added per either Equation (3) and (4), or (5) depending how the work is being calculated to determine the total amount of work performed. Also, the pressure between the two stages or intermediate pressure is determined by using Equation (6), which maintains the pressure ratio going from one stage to the next [13] as, P3 ¼
pffiffiffiffiffiffiffiffiffiffi P1 P2
(6)
where, P1 ¼ suction pressure (Pa); P2 ¼ discharge pressure (Pa); and P3 ¼ optimal intermediate pressure (Pa). Once the work done by the compressor is known either for a single or a two-stage compressor, the power for the compressor can be determined from Equation (7) [12,15], ·
Pcomp ¼
Wcomp m acomp
(7)
where, Pcomp ¼ compressor power (W); Wcomp ¼ compressor · work (J/mol);m ¼ compressor flow rate (mol/s); and acomp¼ compressor efficiency. It should be noted only a single stage and a two-stage isentropic compressor have been modeled and are incorporated into the design tool. The user has the option of selecting which of the two compressor options they wish to use in designing their hydrogen refueling station.
Storage tanks The compressor's main function is to take the hydrogen gas produced and compress it into an assortment of storage tanks. A hydrogen refueling station's storage tank design can be comprised of one or more storage tanks with each being able to be pressurized to a different maximum pressure or all can be pressurized to a similar pressure. These multiple storage tank designs are referred to as banks with each bank being able to operate independently from each other. Modeling the pressure within the storage tanks can be derived from either Van der Waals equation of state for a real gas or using the ideal gas law [15,16]. However, for ease of modeling the ideal gas law was used [12,15], and [16]. The pressure within the storage tank banks is based on the ideal gas law given by equations (8) and (9), PT ¼ Po þ PðtÞ
PT ¼ Po þ
RT VM
(8) Zt
·
m dt
(9)
to
where, V ¼ volume of the gas tank (m3); PT ¼ total pressure in tank (Pa); and Po ¼ initial pressure (Pa). Based on information provided by the compressor manufacturers [17], the compressibility factor “Z” has been omitted from the ideal gas equation due to the actual value being so close to unity that its effect would be negligible. It also should
be noted that the initial pressure of the storage tanks can be adjusted. In the model there are two different main storage tank configuration that have been incorporated and can be selected. The station's storage tanks setup can be comprising of two or three independent banks and can have the same or have different volumes. A third option, comprising of four independent banks was going to included, but was decided against incorporating it because it was not required for validation purposes. Again, this option can be added at a later time if there is a desire to design a hydrogen refueling stations with four banks to meet demand.
Buffer tank The buffer tank is located between the electrolyzer and the compressor to regulates the flow of hydrogen between the electrolyzer and the compressor. In most cases the electrolyzer is going to have a different flow rate than the compressor. This may result in a buildup of pressure within the connecting pipe potentially resulting in rupturing the pipe, or if the compressor has a higher flow rate than the electrolyzer, a vacuum could result. Another reason for the buffer tank is to consider the effects of discontinuity of the refueling process [18] and to ensure a constant flow of hydrogen to the compressor. When full, the buffer tank sends a signal to the compressor to engage, draining the buffer tank to a preset pressure where the compressor automatically shuts down until the buffer tank is refilled to its preset maximum pressure. The maximum and minimum pressures for the buffer tank are determined by a particular compressor model's maximum and minimum inlet operating pressure range. The pressure within the buffer tank is governed by equations (8) and (9).
Dispensing unit Once the storage tanks have been filled, the station is ready to dispense hydrogen. Dispensing hydrogen is achieved by emptying the storage tanks by the corresponding amount required to fill the vehicle's fuel tank until the two tank pressures have reached equilibrium or the desired maximum pressure for the vehicle has been achieved. In a multiple storage bank setup when the pressure in the first storage bank equals the pressure in the vehicle's fuel tank, the modeled station will automatically switch to the next storage tank or bank until the vehicle's fuel tank is full by reaching the desired maximum pressure. At present, a second compressor has not been incorporated into the model to draw the remaining hydrogen out of the storage tanks once the pressure has dropped below the vehicle's tank pressure. Besides transferring hydrogen, the only other outputs from the dispensing unit within the model is the amount of electricity consumed while dispensing hydrogen, and the amount of hydrogen dispensed to the vehicle. The amount of time to completely refill a vehicle, the amount of electricity the dispensing unit consumes while operating, and the amount of hydrogen to dispense to the vehicle are the only inputs for the
Please cite this article as: Riedl SM, Development of a hydrogen refueling station design tool, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.234
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dispensing unit model. Refueling a hydrogen-powered vehicle takes the same time as refueling a gasoline tank, about 5 min, but can be changed within the model. When the dispensing unit is not dispensing hydrogen, it does not consume any electricity [19]. The amount of electrical power the dispensing unit consumes is given by Equation (10), 0:001ðelÞðrateÞ ¼W 60
(10)
where, el ¼ electrical consumption rate (W/h); rate ¼ time frame to transfer hydrogen (min); and W ¼ amount of electricity consumed within a certain time frame (kW).
Vehicle The vehicle component consumes the hydrogen dispensed to it by the hydrogen refueling station at a given rate. The vehicle's fuel tank operates along the same principle as the main storage tanks and the buffer tank using equations (8) and (9). At present, the amount of hydrogen dispensed to the vehicle is based on the tank's volume, and is pressurized until the fuel tank reaches a predetermined pressure, indicating the vehicle's fuel tank is full. Then over a certain amount of time the vehicle consumes the hydrogen at a predetermine rate until it requires to be refilled again. Hopefully, by the time the vehicle has consumed all of its hydrogen fuel and needs to be refilled, the station has already refilled the storage tanks and is ready to resupply the vehicle. Thus, repeating the process of refilling the vehicle's fuel tank, which then prompting the station to start producing more hydrogen to refill the station's storage tanks. With the vehicle component integrated into the model, this process will repeat itself automatically depending on how long the model is set to run.
Model outputs Once the model has run for a period of time several graphical and numerical outputs are generated to aid in the analysis of a particular station design. The model produces 8 different graphical outputs, which include: the electrolyzer's hydrogen flow rate, buffer tank's pressure, compressor's hydrogen flow rate, each individual storage bank pressure, the storage tank bank pressure being refilled or emptied as the model switch from one storage tank bank to another, and lastly the vehicle fueling tank pressure. The model also produces 8 numerical output values. The first three are the electolyzer's, compressor's, dispensing units electrical power consumption cost, follow by the total electrical cost during the station's operation. The next numerical output is based on the cost per kg of hydrogen dispensed to the vehicle. Basically, the amount a consumer is charged for the amount of hydrogen dispensed to their vehicle. In the previous version of the hydrogen refueling station model could not immediate determine the net income from dispensing hydrogen, but had to extrapolate this information. The next two numerical outputs are the amount of hydrogen dispensed, and secondly the pressure in the vehicle's fuel tank when the model stops running. The last numerical output is amount of time the model has taken to refill the storage tanks after supplying hydrogen to a paying consumer.
5
Results/discussion The hydrogen refueling station design tool was validated using existing hydrogen refueling stations by comparing the model's output results to actual real-world data. The model was also compared with the results of the previous version of the hydrogen refueling station design tool as described in “Development of a Software Design Tool for Modeling Hydrogen Distribution Systems” [20]. As before the Simlink [10] time interval was set at 0.001 h for the best possible accuracy and for the model to function properly. This was done to see if the design tool had improved or reduced in accuracy compared to the previous version. The hydrogen refueling stations used to validate the model were the Humboldt State University (HSU) Hydrogen Refueling Station, the BP e Praxair Hydrogen Refueling Station at Los Angeles International Airport (LAX), and the hydrogen refueling station at the Windto-Hydrogen Demonstration Project in Minot, North Dakota (ND). These three stations where chosen largely at random, and were selected by how available the required data was for each hydrogen refueling stations. This was especially true for the compressor's companies who were very reluctant to provide a certain compressor model's efficiency out of fear it could give a competitor a competitive advantage. The model of a hydrogen refueling station was tested similar to how the previous version of the model was test in Development of a Software Design Tool for Modeling Hydrogen Distribution Systems [20], and in Development of a Design Tool for Modeling Hydrogen Refueling Stations [11]. The station's performance and its associated operating cost were used to validate the model so the two versions can be accurately compared. This was accomplished by comparing the amount of time the model takes to refill the storage tanks after refueling a single vehicle, and the associated electrical or operational cost to dispensing hydrogen and refilling the storage tanks. The performance and operational data for the actual hydrogen refueling stations that the model is being validated against is show in the following tables, list as “actual”. The results of the validation testing are shown in Tables 1e3 alongside results of the previous version from “Development of a Software Design Tool for Modeling Hydrogen Distribution Systems” [20]. It should be noted, that the variability for the mean data provided could not be obtained for the individual components. In addition, to a hydrogen refueling station's performance and operating cost, the model can also provide the amount of money ($) an operator/owner can charge a paying consumer in order to generate a profit. This information would allow a designer to see if any additional design changes would be required to reduce the station's operating expenses. In order, to make a profit is largely dependent on the station's intended location, where the local utility charges a certain amount per KWh of electricity. Unfortunately, the amount charged was not able to be obtained for the stations used to validate the design tool, because the hydrogen refueling stations used were prototypes designed to show proof of concept or were only for research purposes. As before in Development of a Software Design Tool for Modeling Hydrogen Distribution Systems [20], the validation
Please cite this article as: Riedl SM, Development of a hydrogen refueling station design tool, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.234
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testing was performed by setting the buffer tank's initial pressure at opposite ends of the compressor suction pressure operating range. For Case 1, the buffer tank was set at the maximum inlet pressure of the compressor, and in Case 2, the buffer tank was set at the minimum inlet pressure of the compressor. However, this time the main storage tanks were left full compare to the previous version where they were manually emptied to simulate the station had just refueled a vehicle. The station would dispense fuel and then refill the station's storage tanks. The model of hydrogen refueling station was ran twice for the Humboldt State University (HSU) Hydrogen Refueling Station, and BP/Praxair Hydrogen Refueling Station at LAX, but was ran four separate times for the Hydrogen Refueling Station in Minot, ND, due to the station servicing two different types of vehicles. The results for Humboldt State University (HSU) Hydrogen Refueling Station are shown in Table 1, BP/Praxair Hydrogen Refueling Station at LAX in Table 2, and the Hydrogen Refueling Station in Minot, ND, in Table 3. In Table 2 below, only one case is shown for the validation results in comparing the model's results with the BP/Praxair Hydrogen Refueling Station at LAX. This is because there was virtually no difference in the two cases regardless if the buffer tank's initial pressure was set at the compressor's maximum or minimum suction pressure operating ranges. The BP-Praxair Hydrogen Refueling Station at Los Angeles International Airport was originally designed to service a large volume of vehicles, including a couple of city transit buses, various airport vehicles, as well as public vehicles [21]. However, the station only serviced four DaimlerChrysler Fuel Cell vehicles with each vehicle having a compacity to hold 1.8 kg of hydrogen [21]. Previously, in Development of a Software Design Tool for Modeling Hydrogen Distribution Systems [20] the model was tested by reducing each of the four banks of the main storage tank by 1.8 kg of hydrogen and seeing how long it took the station to refill each bank. However, upon further review of the station specifications, it was determined that the station only had three cascading banks [22], but had four stainless steel pressure vessels that made up the storage capacity [21,22]. Subsequently, the station model was reconfigured to have the main storage tank comprised of only three banks. The model was tested by only dispensing hydrogen to a single DaimlerChrysler Fuel Cell vehicle and then multiplying the results by a factor of four. Then the model was tested, by dispensing hydrogen to all four vehicles for a total 7.2 kg hydrogen the amount of time to refill the storage tanks to see if there was any difference, but the results were the same. In the previous version of the hydrogen refueling station design tool the cost of operating the station was omitted due to the huge error when compared to the actual station's operation expenses. It costed the operators $46.88 to refuel the four DaimlerChrysler Fuel Cell vehicles, which resulted in an error of 46.8% [11]. This was considered to be an anomaly when compared to the accuracy of the model to the other two real world hydrogen refueling stations: Humboldt State University Hydrogen Refueling Station and the Hydrogen Refueling Station in Minot, ND. With the current version of the model the amount of error has not improved and was determined to be 46%. Originally, as mentioned in the Development of a Design Tool for Modeling Hydrogen Refueling Stations [11] it was believed this error was the result of the manufactures not
including all the electricity the electroylzer or other components were consuming. For example, the electrolyzer was connected to a chiller to keep it cool during the day. This electrical draw was not included in the information provided by the operators. Another reason for this excessive error has to do with how the electrical costs are calculated within the model. All the electrical costs were calculated using the U.S. national average of 6.2 cents in 2008 [23]. The cost of electricity in California apparently is much higher than the U.S national average. Using the model, the electrical cost would need to be around 11.4 cents per kilowatt hour, to yielded a more realistic operating error of 0.77%. As a result, the operating expenses for the Hydrogen Refueling Station at LAX was not included in Table 2. In the following three tables are the results of the validation testing in comparing the design tool to actual hydrogen refueling station data for all three stations as well as the
Table 1 e Humboldt state university hydrogen refueling station validation results. Previous Version
Current Version
Performance Case Case Case Case 1 2 1 2 Model's Time to Refill Storage Tanks 23.3 h 23.8 h 23.5 h 24 h (A) Actual Station's Performance (B) 24 h % Error ¼ [(B-A)/B*100] 2.90% 0.83% 2.1% 0% Operational Costs Electolyzer Compressor Dispensing Unit Model Cost Predictions (A) Actual Station's Operating Cost (B) % Error ¼ [(B-A)/B*100] Cost per kg of Hydrogen to equal Expenses
$11.21 $0.29 $0.01 $11.51
$11.45 $11.45 $0.29 $0.29 $0.01 $0.01 $11.75 $11.74 $12.40 7.18% 5.20% 5.32% NA NA $4.67
$11.69 $0.29 $0.01 $11.98 3.31% $4.76
Table 2 e BP e praxair hydrogen refueling station at LAX validation results. Previous Version
Current Version
Performance Model Time Predictions to Refill Storage Tanks (A) Actual Station's Performance (B) % Error ¼ [(B-A)/A*100]
7.1 h
1.40%
1.796 h (7.18 h) 7.2 h 0.28%
Operational Costs Electolyzer Compressor Dispensing Unit Model Cost Predictions (A) Actual Station's Operating Cost (B) % Error ¼ [(B-A)/A*100] Cost per kg of Hydrogen to equal Expenses
NA NA NA NA NA NA NA
NA NA NA NA NA NA NA
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previous version of the model. The first part or upper half of the tables is the performance data in how long it took the model to refill their storage tanks after dispensing hydrogen. This is followed by the actual hydrogen refueling station time. A comparison than was made between the model's performance result and the actual hydrogen refueling station that the model was configured to represent to determine the amount of error in the results. The second half of the tables is the data concerning the how much it cost to operate or the electrical cost of the station during refueling a vehicle and the refilling processes of the hydrogen refueling stations. The first three rows represent how much it would cost to operate the station's individual components, followed by the sum total.
Then the operational cost of the actual hydrogen refueling station the model was configured to represent. Once again, a comparison was made between the model's results and the data of the actual hydrogen refueling station to determine the amount of error in the model's results. The bottom row of the tables shows how much the owner or operator of the station would have to charge just to cover their operating expenses. As mention previously the model can also produce various graphical information in the form of plots of 6e8 different aspects depending on the model's configuration. For example, Fig. 1, below, represents the pressure within the hydrogen refueling station's storage tanks while the model is configured to represent the hydrogen refueling station in Minot, North
Table 3 e Hydrogen refueling station in Minot, ND, validation results. Previous Version
Current Version
Performance Vehicle 1
Model Time Predictions to Refill Storage Tanks (A) Actual Station's Performance (B) % Error ¼ [(B-A)/B*100]
Vehicle 2
Vehicle 1
Vehicle 2
Case 1
Case 2
Case 1
Case 2
Case 1
Case 2
Case 1
Case 2
2.44 h 2.44 h 0.00%
2.43 h 2.44 h 0.40%
0.82 h 0.82 h 0.00%
0.83 h 0.82 h 1.20%
2.44 h 2.44 h 0.00%
2.44 h 2.44 h 0.00%
0.82 h 0.82 h 0.00%
0.82 h 0.82 h 0.00%
$21.70 $0.88 $0.05 $22.64 $26.60 14.90% NA
$21.70 $0.88 $0.05 $22.63 $26.60 14.90% NA
$7.25 $0.30 $0.05 $7.60 $8.89 14.50% NA
$7.24 $0.30 $0.05 $7.60 $8.89 14.60% NA
$21.8 $0.89 $0.01 $22.71 $26.60 14.62% $3.45
$21.81 $0.88 $0.01 $22.71 $26.60 14.62% $3.45
$7.28 $0.30 $0.01 $7.59 $8.89 14.62% $3.45
$7.28 $0.30 $0.01 $7.59 $8.89 14.62% $3.45
Operational Costs Electolyzer Compressor Dispensing Unit Model Cost Predictions (A) Actual Station's Operating Cost (B) % Error ¼ [(B-A)/B*100] Cost per kg of Hydrogen to equal Expenses
Hyrogen Refueling Station Model of Minot North Dakota Servicing the Chevrolet Silverado Pickup Truck
420
410
400
Pressure (bars)
390
380
370
360
350
340
330
320
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Time (Hours)
Fig. 1 e Hydrogen refueling station model's storage tank pressure during a 14 h run while servicing a Chevrolet Silverado pickup truck with a 6.6 kg fuel tank. Please cite this article as: Riedl SM, Development of a hydrogen refueling station design tool, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.234
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Dakota, while servicing a Chevrolet Silverado pickup truck with a 6.6 kg storage capacity [24]. In the first 30 min the model is first dispensing fuel followed by the refilling process. The 30-min refueling time was chosen solely to more easily see the pressure plot on the graph. Normally, refueling time would only take around 5 min [19]. After the dispensing and refilling the storage tanks process is complete the model station waits until the vehicle has completely emptied its fuel tank before repeating the process. The vehicle was arbitrary set to consume its hydrogen fuel at 0.7 kg/h. The vertical lines in Fig. 1, is the station switching from one storage tank bank to the next, once the vehicle's fuel tank has reached equilibrium with a particular station's storage bank or has finished being refilled.
Conclusion The current version of the design tool has improved compared to the previous version and has increased the model's accuracy in contrast with all three existing hydrogen refueling stations. In determining the model performance accuracy, the design tool demonstrated a total average error of 0.44%, which resulted in a decrease from the previous performance average error of 1.22%. As for estimating the electrical cost for a particular hydrogen refueling station design the model had an average error of 8.38%, which is an improvement over the previous version that had an average error for electrical cost of 10.5%. With all the improvements to the hydrogen refueling station software design tool, like an addition of a vehicle component that simulates demand, to integrating all the different model variants into a single model with a centralized user interface, has shown to improve the model's overall performance. These results illustrate, as the model continues to be developed to accurately reflect real world conditions, it becomes more successfully in predicting the performance and cost of operating of any hydrogen refueling station design. The differences between the two versions of the hydrogen refueling stations design tool can be associated with the current model being more accurately resembling how a station would actually operate. The model can now operate indefinitely, compared to the model's original design, which required the main storage tanks to be manually set to a pressure right after they would have dispensed hydrogen. In doing so, some mathematical error in terms of rounding was introduced into the design tool's results. The current version removes this possible error because the model can automatically switch from dispensing fuel to refilling the main storage tanks. During validation testing of the current version of the hydrogen refueling station model there were some unexpected results. It was illustrating a couple flaws in the previous version's design and some of the past assumptions were incorrect. For example, during the third station's validation testing of the model, the hydrogen refueling station in Minot, North Dakota, using the Chevrolet Silverado Pickup Truck with a 6.6 kg hydrogen storage capacity the station actually required a second bank to finish refueling the vehicle, and showed the first bank's pressure actually dropped below 350 bars during the refueling process before switch the next
bank to complete the vehicle fueling. Previously, it was assumed the storage tank's first bank was the only bank required to service the pickup truck. Although, the net improvement in the model might seem small, one most remember the model's percent error was already low in the previous version as shown in Tables 1e3. Even with substantial development that went into the model of a hydrogen refueling station from the previous version the potential for reducing the amount of error may only be in small amounts. This could be done by improving the signal processing elements in how the model functions, which makes up a large portion of the model, to refining the equations that describe certain aspects of the model. However, the design tool will never will be perfect in comparison to real world systems. Assumptions must be made to be able to mathematically describe observed phenomena. Substantial development has gone into Hydrogen Refueling Station Design Tool, since Development of a Design Tool for Modeling Hydrogen Refueling Stations [11], and Development of a Software Design Tool for Modeling Hydrogen Distribution Systems [20] has reached a point where it could be marketed to institutions or companies within the field of hydrogen refueling facility development. From the feedback obtained from the model's use will determined what possible further development of the hydrogen refueling station design tool is required. However, other components that could possibly be added to the model are different types of hydrogen storage options, like metal hydrides. From a safety standpoint it would be beneficial to use metal hydrides as a hydrogen storage option especially on vehicles. Metal hydrides can store hydrogen at a fraction of the pressure than storing hydrogen gas in pressurized cylinders at very high pressures.
Acknowledgements The author would like to thank Hawaii Natural Energy Institute for their initial support in the development of the software model. Appreciation is extended also to Cugnet Mikael, Project Manager at the French Institute for Solar Energy, for his help with the Hydrogen Refueling Station Design Tool. The author would like to thank Dr. Ronald Knapp, (Retired) Former Chairman of the Mechanical Engineering and professor at University of Hawaii at Manoa for his advice and help in developing the model and in reviewing this paper. The author would like to thank the following people for providing valuable data on HSU Hydrogen Refueling Station, BP e Praxair Hydrogen Refueling Station at LAX, and the Wind-to-Hydrogen Demonstration Project in Minot, ND: Chapman, Greg P.E., Senior Research Engineer, Schatz Energy Research Center. Busch, Tim, Onsite Business Manager e West Region, Praxair Inc. Beeson, Jerry, Standard Plant Tech, Praxair Inc. Vale, Michael, Product Development Specialist, Hydrogenics Corporation. Bush, Randy, Distributed Resource Coordinator, Basin Electric Power Cooperative.
Please cite this article as: Riedl SM, Development of a hydrogen refueling station design tool, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.234
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Filosa, Bob, Power Pressure Industries. Gallow, Grey, Engineer, Pdc Machines. Heartken, Jim, Hydro-Pac.
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Please cite this article as: Riedl SM, Development of a hydrogen refueling station design tool, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.234