Fuel and Oxidant Utilization

The coefficients in these equations were correlated from performance data for cells (45) operating at 120 psia (8.2 atm), 405°F (207°C) (16) with fuel and oxidant utilizations of 85% and 70%, respectively, an air fed cathode, and an anode inlet composition of 75% H2, and 0.5% CO. Similarly, at atmospheric conditions, the magnitude of this loss can be approximated by... 

The hot clean fuel gas and the compressed ambient air are electrochemically combined within the high-pressure fuel cell with fuel and oxidant utilizations of 90% and 24.5%, respectively. 

A PAFC, operating on reformed natural gas (900 Ib/hr) and air, has a fuel and oxidant utilization of 86% and 70% respectively. With the fuel and oxidant composition and molecular weights listed below, (a) How much hydrogen will be consumed in lb mol/hr (b) How much oxygen is consumed in lb mol/hr (c) What is the required air flow rate in lb mol/hr and Ib/hr (d) How much water is generated (e) What is the composition of the effluent (spent) fuel and air streams in mol % ... 

The hot clean fuel gas and the compressed ambient air are electrochemically combined within the high-pressure fuel cell with fuel and oxidant utilizations of 90 percent and 24.5 percent, respectively. The SOFC module is set (sized) to operate at 0.69 volts per cell. The spent fuel and air effluents of the SOFC are combusted within the module to supply heat for oxidant preheating. Unlike the natural gas case, the fuel does not require a pre-reformer with only 0.3 percent methane along with 36 percent hydrogen and 43 percent carbon monoxide. The carbon monoxide will be either water gas shifted to hydrogen or utilized directly within the fuel cell. A... 

Reactant Utilization and Gas Composition Reactant utilization and gas composition have major impacts on fuel cell efficiency. It is apparent from the Nemst equations in Table 2-2 that fuel and oxidant gases containing higher partial pressures of electrochemical reactants produce a higher cell voltage. 

Cell performance for any fuel cell is a function of pressure, temperature, reactant gas composition and fuel utilization. In addition, performance can be adversely affected by impurities in both the fuel and oxidant gases. 

Low utilizations, particularly oxygen utilization, yield high performance. Low utilizations, however, result in poor fuel use. Optimization of this parameter is required. State-of-the-art utilizations are on the order of 85% and 50% for the fuel and oxidant, respectively. 

The combusted air and fuel stream (stream 12) from the high-pressure fuel cell are expanded (stream 13) in a turbine expander. The work of this turbine is used to drive the low- and high-pressure air compressors. The reduced pressure exhaust stream (stream 13) is utilized as the low-pressure fuel cell oxidant stream. Although vitiated, it still has 15% oxygen. The low-pressure TSOFC operates at 0.62 volts per cell, and fuel and air utilizations of 78 and 21.9%, respectively. The spent air and fuel effluents are combusted and sent (stream 14) to the low-pressure power turbine. The turbine generator produces approximately 1.4 MW AC. The low-pressure exhaust (stream 15) still has a temperature of 649°C (1200°F) and is utilized to... 

The hot processed fuel and the compressed ambient air are electrochemically combined within the fuel cell module. The fuel hydrocarbons still remaining after the mild reformer are reformed within the fuel cell. The heat required for the endothermic steam reforming reactions is supplied by the exothermic fuel cell reactions. The overall reactions are exothermic, and the fuel and oxidant temperatures rise to 999°C (1830°F) (streams 8 and 12). The fuel cell is capable of utilizing both H2 and CO as fuel and has an overall fuel utilization of 94%. 

When designing an MCFC power system, several requirements must be met. An MCFC system must properly condition both the fuel and oxidant gas streams. Methane must be reformed into the more reactive hydrogen and carbon monoxide. Carbon deposition, which can plug gas passages in the anode gas chamber, must be prevented. To supply the flow of carbonate ions, the air oxidant must be enriched with carbon dioxide. Both oxidant and fuel feed streams must be heated to their proper inlet temperatures. Each MCFC stack must be operated within an acceptable temperature range. Excess heat generated by the MCFC stacks must be recovered and efficiently utilized. 

Fuel cells incorporating lithographic methods and masking/deposition/etching protocols have been fabricated on Si wafers and thereby satisfy two critical needs in a standard fuel cell collection of electrons (current collectors) and controlling the flow field of fuel and oxidant. Kelley et al. produced a miniature direct methanol fuel cell (DMFC) with a current— voltage and fuel utilization performance that matched standard-sized DMFCs prepared in-lab.A working volume for the miniature DMFC of 12 mm was reported, with an operational performance of 822 W h kg at 70 °C. ... 

Before anything else can be said about IEs, some rudimentary chemistry is needed. From a cookbook perspective, all explosives (be they military, commercial, or improvised) require the same chemical building blocks, which consist of a fuel and an oxidizer. Some explosives have the fuel and oxidizer as part of the same molecule, such as trinitrotoluene (TNT), and some explosives are comprised of mixtures of separate fuels and oxidizers, such as ammonium nitrate-fuel oil (ANFO). The oxidizer employed by the vast majority of explosives tends to be the NO2 (nitro) group. It is so predominant as an explosive ingredient that the primary focus of detection methods traditionally has been to look for nitro-derived properties. IEs tend to utilize a more diverse range of oxidizers. Table 3.1 gives a list of the numerous oxidizer possibilities. 

Rocket Engine. A non-airbreathing reaction propulsion device that consists essentially of an injector, thrust chambers) and exhaust nozzle(s), and utilizes liquid fuels and oxidizers at controlled rates from which hot gases are generated by combustion and expanded thru a nozzle(s) (Ref 40a, p 125)... 

Abstract Single-chamber solid oxide fuel cells (SC-SOFCs) immerse the entire cell in a mixture of fuel and oxidizer gases within a single chamber, which eliminates the need for high temperature sealant, simplifies construction, and increases reliability over traditional double-chamber cells. However, there are challenges, such as low fuel utilization and electrode catalytic selectivity, that need to be overcome. This brief review paper looks at recent improvements in materials, processing, and operation of SC-SOFCs, which are rapidly approaching the performances of the double-chamber fuel cells and may become attractive for specific fuel cell applications. 

In volume limited applications, high density propellant combinations are favored and some appropriate trade-off between performance and density is established. In a truly volume limited system as shown in section IV. A. 1., the appropriate performance parameter is the product of the specific impulse and the propellant bulk density, a quantity usually labeled the density impulse. Conceivably, mixture ratio may be determined by yet other vehicle system considerations. If a new propellant combination is to be utilized in an existing vehicle, the optimum mixture ratio may be influenced by such considerations as existing pump flow rate capacities, tank volumes, and structure load carrying capacities. Even other system considerations, such as the desirability of operating at equal fuel and oxidizer volume flow rates to allow interchange of fuel and oxidizer flow hardware, may determine the propellant mixture ratio. 

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