18-12-2012, 05:11 PM
Arizona Public Service – Alternative Fuel (Hydrogen) Pilot Plant Design Report
Arizona Public Service.pdf (Size: 2.14 MB / Downloads: 76)
INTRODCUTION
Hydrogen has promise to be the fuel of the future. Its use as a chemical reagent and as a rocket propellant has grown to over eight million metric tons per year in the United States. Although use of hydrogen is abundant, it has not been used extensively as a transportation fuel. To assess the viability of hydrogen as a transportation fuel and the viability of producing hydrogen using off-peak electric energy, Pinnacle West Capital Corporation (PNW) and its electric utility subsidiary, Arizona Public Service (APS) designed, constructed, and operates a hydrogen and compressed natural gas fueling station—the APS Alternative Fuel Pilot Plant. This report summarizes the design of the APS Alternative Fuel Pilot Plant and presents lessons learned from its design and construction. Electric Transportation Applications prepared this report under contract to the U.S. Department of Energy’s Advanced Vehicle Testing Activity. The Idaho National Engineering and Environmental Laboratory manages these activities for the Advanced Vehicle Testing Activity.
Objectives
The objectives of constructing and operating the Alternative Fuel Pilot Plant have been to:
1. Ascertain the safety issues for a hydrogen production operation in a commercial setting
2. Evaluate the adequacy of existing codes, standards, regulations, and recommended practices within a commercial setting
3. Establish models for future codes and standards for distributed hydrogen generation systems within a commercial setting
4. Determine performance limitations of existing technologies and components
5. Evaluate the practicality of the systems in a commercial facility
6. Evaluate hydrogen and blended CNG/hydrogen as a potential fuel for internal combustion engines
7. Develop a working model of a refueling system for fuel-cell electric vehicles and internal combustion engine vehicles.
Background
Several stored forms of hydrogen could be considered for use as a transportation fuel: gas, liquid, slush, and metal hydrides. Two common methods of producing hydrogen are reforming of hydrocarbons such as methane and methanol, and electrolysis of water. Reforming of hydrocarbons, although today the most common and economical way of hydrogen production, results in carbon dioxide (a greenhouse gas) as a byproduct. Electrolysis of water produces only hydrogen and oxygen and is of interest to an electric utility company as a means of improving its load factor and increasing energy sales. In contrast to centralized manufacturing of hydrogen and use of tube trailers for delivery (as in gasoline distribution), the electrolysis process can be used with the existing electric distribution system to produce relatively small quantities of hydrogen during off-peak periods at the point of use. This provides the advantage of leveling electric energy usage and eliminating the need for tube trailer transportation.
Due to the very small number of hydrogen refueling stations, there are limited standards for their construction. Five other commercial hydrogen vehicle-refueling stations have been built in the United States: Sun Line Transit in Palm Springs, California; Ford Proving Ground in Dearborn, Michigan; California Fuel Cell Partnership in Sacramento, California; Las Vegas Transit in Las Vegas, Nevada; and the Honda Proving Ground in Torrance, California. Commercial hydrogen refueling stations have also been built in Germany and Iceland.
Siting the Fueling Station
PNW and APS chose to construct the APS Alternative Fuel Pilot Plant in an urban setting to determine the full impact of existing codes and standards as well as building inspector requirements on station design and on the siting process. This approach is unique to fueling station design in the United States and provides unique insight into the requirements for hydrogen fueling stations to be constructed and operated in commercial, rather than industrial, areas.
Fueling Station Design
The APS Alternative Fuel Pilot Plant is a model alternative fuel refueling system, consisting of hydrogen, compressed natural gas (CNG), and CNG/hydrogen blends. Figure 1.2 shows the plant in plan view. The plant distinctly separates the hydrogen system from the natural gas system, but can blend the two fuels at the stationary filling system. Section 2 focuses on the hydrogen portion of the plant. Section 3 focuses on the natural gas portion of the plant, which is similar in various ways.
The plant’s hydrogen system consists of production, compression, storage, and dispensing. The hydrogen produced is suitable for use in fuel cell-powered electric vehicles, for which the minimum hydrogen purity goal is 99.999%, and the upper limit of purity is 99.99999%. To obtain these purity levels, the facility uses two methods of production. One method takes advantage of the centralized manufacturing of hydrogen. The other method uses an electrolysis process that separates water into hydrogen and oxygen. At present, the hydrogen is compressed and stored at a maximum operating