Fuel stack

A fuel stack is a series connection of fuel cells. Strictly speaking, it is fuel cell battery (cf. footnote 1). The composition and design of the fuel cell stack differ for the implementation of each type of cell. 

An example of a system transient is shown in Figure 9.3. The figure shows a 20 amp load increase on a nominal 3 kW SOFC system using a stream-reformed methane fuel. Stack load current, stack voltage, and input fuel flow rate are shown. Here, the system is pre-warmed to the conditions shown (ca. 20 amps), following which the controller permits exporting more power to a load at the ramp rate shown. As the transition occurs, numerous other system variables also adjust, some in direct response to the increase in load, and others imposed by the control system in order to keep all system components within their design limits. 

The only really serious problem with an unknown system is if the fuel stack is pretty well spent. Contact the manufacturer before purchasing a unit to find out if replacement MEAs and other stack components are available, and what the costs are. 

This chapter introduces the reader to the automated dispensing equipment commonly used in electronics packaging, printed circuit board assembly, and other electronics manufacturing. Automated dispensers excel in the areas of manufacturing that can be most helpful in the construction of fuel stacks. 

Fuel cells, together with their ancillary equipment, are very compUcated systems. Therefore, fuel ceU service technicians wUl be expected to perform a variety of tasks in areas such as electrical, thermal, water, ventilation, fuel, magnetic, fuel stack, and process air systems. People who have an acceptable level of skill in aU of the listed areas wiU be in high demand. Therefore, colleges might want to consider programs that include training in aU of these technical areas. 

In the test KAKADU 30 an overenriched fuel pellet within a normal fuel stack (power peaking factor 2.25) was irradiated for a few days the overpower of about 900 W/cm in the "hot spot" fuel pellet did not cause overheating. 

In Fig. 6.27, the flue gas is cooled to pinch temperature before being released to the atmosphere. The heat releaised from the flue gas between pinch and ambient temperature is the stack loss. Thus, in Fig. 6.27, for a given grand composite curve and theoretical flcune temperature, the heat from fuel amd stack loss can be determined. 

Figure 6.30 shows the grand composite curve plotted from the problem table cascade in Fig. 6.186. The starting point for the flue gas is an actual temperature of 1800 C, which corresponds to a shifl ed temperature of (1800 — 25) = mS C on the grand composite curve. The flue gas profile is not restricted above the pinch and can be cooled to pinch temperature corresponding to a shifted temperature of 145 C before venting to the atmosphere. The actual stack temperature is thus 145 + 25= 170°C. This is just above the acid dew point of 160 C. Now calculate the fuel consumption ...

Environmental Protection Processes that treat the refinery gases (fuel and tail gas), stack gas, and water effluents. 

Selection of pollution control methods is generally based on the need to control ambient air quaUty in order to achieve compliance with standards for critetia pollutants, or, in the case of nonregulated contaminants, to protect human health and vegetation. There are three elements to a pollution problem a source, a receptor affected by the pollutants, and the transport of pollutants from source to receptor. Modification or elimination of any one of these elements can change the nature of a pollution problem. For instance, tall stacks which disperse effluent modify the transport of pollutants and can thus reduce nearby SO2 deposition from sulfur-containing fossil fuel combustion. Although better dispersion aloft can solve a local problem, if done from numerous sources it can unfortunately cause a regional one, such as the acid rain now evident in the northeastern United States and Canada (see Atmospheric models). References 3—15 discuss atmospheric dilution as a control measure. The better approach, however, is to control emissions at the source. 

Fig. 3. Schematics of gas manifolds for MCFC stacks (a) internally manifolded fuel cell stack (b) externally manifolded fuel cell stack.

A subsidiary of lEC and Toshiba Corp. called ONSI Corp. was formed for the commercial development, production, and marketing of packaged PAEC power plants of up to 1-MW capacities. ONSI is commercially manufacturing 200-kW PAEC systems for use in a PC25 power plant. The power plants are manufactured in a highly automated faciHty, using robotic techniques to assemble the repeating electrode, bipolar separator, etc, units into the fuel cell stack. 

BaUard Power Systems, the leader in the manufacture of PEEC stacks, has sold at least fifty 3- to 5-kW units worldwide. BaUard is involved in a program in Canada to demonstrate a 120-kW PEEC stack to power a transit 20-passenger, 9752-kg bus. Eor this demonstration, on-board compressed hydrogen, sufficient for 150-km range, is the fuel. 

Energy Partners, Inc. (West Palm Beach, Florida), acquired fuel ceU technology from TreadweU Corp. (Thomaston, Coimecticut), which suppHed electrochemical equipment to the U.S. Navy. Energy Partners, Inc. are involved in developing PEECs for propulsion appHcations in transportation and submersible vehicles. A 20-kW PEEC stack was designed for demonstration tests. 

From the standpoint of commercialization of fuel ceU technologies, there are two challenges initial cost and reHable life. The initial selling price of the 200-kW PAFC power plant from IFC was about 3500/kW. A competitive price is projected to be about 1500/kW orless for the utiHty and commercial on-site markets. For transportation appHcations, cost is also a critical issue. The fuel ceU must compete with conventional mass-produced propulsion systems. Furthermore, it is not clear if the manufacturing cost per kilowatt of small fuel ceU systems can be lower than the cost of much larger units. The life of a fuel ceU stack must be five years minimum for utiHty appHcations, and reHable, maintenance-free operation must be achieved over this time period. The projection for the PAFC stack is a five year life, but reHable operation has yet to be demonstrated for this period. 

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