Partial oxidation processor

A 50 kW multi-fuel partial oxidation processor coupled to an SPFC stack has been presented in October 1997 by Arthur D. Little Inc., USA, and test-operated in the meantime for more than 3000 h. The fuels that can be applied are gasoline, methanol, and ethanol in a later stage, also diesel, oil, methane and propane processing will be possible [27]. In the UK, a bench-scale steam reformer system processing gasoline and diesel was successfully demonstrated for over 50 hours each. The H2 concentration in the reformate was typically... 

This system includes several mixing and heat exchange units. A concept for an integrated, microtechnology-based fuel processor was proposed by PNNF [8]. As examples for unit operations which may be included in future integrated systems the same publication mentions reactors for steam reforming and/or partial oxidation, water-gas shift reactors and preferential oxidation reactors for carbon monoxide conversions, heat exchangers, membranes or other separation components. 

Gardner et al. reported that H2S catalytic partial oxidation technology with an AC catalyst is a promising method for the removal of H2S from fuel cell hydrocarbon feedstocks.206 Three different fuel cell feedstocks were considered for analysis sour natural gas, sour effluent from a liquid middle distillate fuel processor, and a Texaco 02-blown coal-derived synthesis gas. Their experimental results indicate that H2S concentration can be removed down to the part per million level in these plants. Additionally, a power-law rate expression was developed and reaction kinetics compared with prior literature. The activation energy for this reaction was determined to be 34.4 kJ/g mol with the reaction being first order in H2S and 0.3 order in 02. 

Gardner, T.H., Berry, D.A., Lyons, K.D., Beer, S.K., and Freed, A.D. Fuel processor integrated H2S catalytic partial oxidation technology for sulfur removal in fuel cell power plants. Fuel, 2002, 81, 2157. 

Measure the emissions from a partial oxidation/autothermal fuel processor for a proton exchange membrane (PEM) fuel cell system under both cold-start and normal operating conditions. 

Fuel reformer operation is generally divided into two operating modes start-up and normal partial oxidation. During start-up, the fuel processor bums fuel at near stoichiometric conditions until critical system temperatures and pressures stabilize to target values. Once the target conditions are reached, the reformer operates in normal mode in which the fuel processor bums fuel at very rich conditions. Since these modes are comprised of considerably different operating conditions, it follows that the emissions associated with each of these modes are also considerably different. 

Systems Analysis Figure 1 shows a concept identified by NETL for a integrated fuel processor/ fuel cell system targeted for diesel APUs. There are several favorable attributes of this system. For example, startup occurs by firing an internal combustor in the dual reactor reformer. This provides heat to the ATR reformer (via conduction) as well as supplying heat to the fuel cell cathode via direct exhaust from the combustor or preheated air from the heat exchanger (optional). If necessary, the ATR is fired in a partial oxidation mode to aid in heatup and to provide heat to the anode side of the... 

K. D., Monahan, M. J. "Fuel Processor Integrated H2S Catalytic Partial Oxidation Technology for Sulfur Removal in Fuel Cell Power Plants". FUEL, Vol. 81, issue 17, September 2002. 

The fuel processor subsystem was operated with pure iso-octane to verify its performance. Figure 3 shows 800 hours of the fuel processor operation on iso-octane, showing the temperatures in the different stages, and the CO outlet concentration. The temperature in the partial oxidation stage is about 800 - 825°C, and the outlet temperature of the steam reforming section is 775°C. The average residence time for the ATR section is about 0.5 sec (GHSV ... 

Flow rate of fuel processor output Flow rate range 30-300 standard L/min Temperature 80°C Gas environment high-humidity reformer/partial oxidation gas H2 30-75%, CO2, N2, H2O, CO at 1-3 atm total pressure... 

An alternative method of approaching the poisoning effect of carbon monoxide is to clean up the reformed fuel stream prior to admission to the fuel cell. For instance, methanol is fed to a reforming processor which produces a gas stream containing approximately 55% H2, the required fuel mixed with 22% CO2, 21% N2 and 2% CO. The overall process is achieved by combining the exothermic partial oxidation reaction with an endothermic steam reforming reaction over the same catalyst particles. This achieves a very high rate of internal heat transfer and a very easily controlled reactor. In the last step the reformer output can then fed to a clean-up reactor where the fuel is reacted further with air to reduce the CO content from 2% to 10 ppm, a far more viable concentration for the electrocatalysts used in the low temperature fuel cell. 

Partial oxidation of methane is another way to produce water gas (Equation 1.3). This process is mainly used when we need lesser H2/CO ratio and if there are difficulties in external heat supply, internal heat generation is needed as in the case of fuel processors for fuel cell applications. Partial oxidation of methane produces H2/CO in a ratio of 2. If we need H2/CO in a ratio of 1, dry reforming of methane can be done (Equation 1.4). 

A certain portion of the hydrogen produced by the fuel processor is frequently fed back to it, because it is not completely consumed by the fuel cell (see Section 2.3). The curious situation may then arise where the fuel processor efficiency exceeds 100%. In particular, this is the situation for steam reforming, where substantially more heat is required to run the process compared with partial oxidation and autothermal reforming (see Section 3). A fuel processor running on steam reforming may reach up to 120% efficiency according to the Eqs. (2.2) and (2.3). 

An obvious advantage of partial oxidation is that only an air feed is required, apart from the fuel. This makes the system simpler because evaporation processes, as required for steam reforming, are avoided. On the other hand, the amount of carbon monoxide formed is considerably higher compared with steam reforming. This puts an additional load onto the subsequent clean-up equipment, but only where CO-sensitive fuel cells are cormected to the fuel processor. When fuels are converted by partial oxidation, some total oxidation usually takes place as an undesired side reaction [46]. In practical applications, an excess of air is fed to the system and consequently even more fuel is subject to total oxidation. The water formed by the combustion process in turn gives rise to some water-gas shift. Another typical byproduct of partial oxidation is methane, which is formed according to reaction (3.5). Coke formation is a critical issue (see Sections 4.1.1 and 4.2.11). Coke may be formed by reaction of carbon monoxide with hydrogen ... 

Running a fuel processor at an O/C ratio of 1.0 or higher in the presence of steam feed should be termed steam supported partial oxidation. 

Running a fuel processor under conditions of partial oxidation is most favourable with methane, because it has the highest atomic hydrogen content of all hydrocarbons. While the theoretical hydrogen concentration of the reformate still reaches... 

Fuel processor concepts based upon autothermal reforming or partial oxidation usually generate a surplus of heat, which has to be removed from the system at the low temperature level, as discussed below. 

The addition point of gaseous fuels requires careful consideration to avoid homogeneous reactions upstream of the reformer vith autothermal reforming and partial oxidation. Commercial flame arresters are normally not capable of operating under the elevated temperatures of the fuel processor. Microchannels are known to act as flame arresters (see Section 6.3.2) and may be inserted into the tubing system to avoid uncontrolled reaction of the fuel/air mixture. For liquid fuels, which are usually injected into the pre-heated steam feed or even into the air/steam feed mixture, either cooled injection nozzles [567] or the application of steam jackets may be used to ensure stable operation of the nozzle. 

MitdieD et cd., at the company Arthur D. little, described early projections for an ethanol fuel processor based upon partial oxidation [475]. The efficiency of the fuel processor was calculated to be 80% and power densities of 1.44 LkW and 1.74kg kW were achieved. 

A breadboard gasoline fuel processor was assembled by Moon et d. [67]. Fixed bed reactors served for reforming by steam supported partial oxidation (see Section 7.1.1), followed by high and low temperature water-gas shift Commercial iron oxide/ chromium oxide catalyst was applied for high temperature shift at a 4200 h gas hourly space velocity and 450 °C reaction temperature, while the copper/zinc oxide low temperature water-gas shift catalyst was operated at 250 °C and 5600 h gas hourly space velocity. 

Specchia, S., Negro, G., Saracco, G. and Specchia, V. (2007) Fuel processor based on syngas production via short contact time catalytic partial oxidation reactors. Appl. Catal. B, 70, 523-531. 

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