Partial oxidation steam reforming

Separation, combustion, pyrolysis, hydrogena-tion, anaerobic fermen-tation, aerobic fermen-tation, biophotolysis, partial oxidation, steam reforming, chemical hy-drolysis, enzyme hydrol-ysis, other chemical conversions, natural processes... 

Compared vdth partial oxidation, steam reforming has received more attention due to its relatively higher conversion efficiency [155]. 

Total oxidation Partial oxidation Steam reforming... 

This model accounts for fuel atomization and vaporization, partial oxidation, steam reforming, and anode exhaust combustion. It is asumed that the partial oxidation reaction is very fast and occurs at the top of the catalyst bed along with fuel atomization and vaporization. It is also assumed that the steam reforming initiates after all O2 is consumed in the partial oxidation reaction. Therefore, the reactor will initially be considered as two plug-flow reactors in series. Figure 2 and 3 depict the inlet conditions for the ATR model and results from the model, respectively. 

Carbon formation has been observed to occur both in the partial oxidation/steam reforming catalyst and in the reformate after it exits the catalyst. Analysis of carbon formed in the steam reformer catalyst found that the carbon was mostly carbonaceous carbon with an approximate H/C ratio of 0.2 - thus about 97% carbon. Carbon that formed in the reformate after it exited the catalyst (probably from unconverted hydrocarbons) has been analyzed to contain 30% by weight solidified hydrocarbons. 

Various fuel components and fuels have been tested with various 0/C and S/C ratios in partial oxidation/steam reforming reactors. The addition of aromatics slows the overall reaction rate for catalytic oxidation. Real fuels have similar oxidation rates at high 0/C compared with iso-octane, but lower oxidation rates at 0/C < 1.0. 

Precombustion capture. This solution is developed in two phases (1) the conversion of the fuel in a mixture of H2 and CO (syngas mixture) through, for example, partial oxidation, steam reforming, or autothermal reforming of hydrocarbons, followed by water-gas shift (WGS), and (2) the separation of CO2 (at 30%-35%) from the H2 that is then fed as clean fuel to turbines. In these cases, the CO2 separation could happen at very high pressures (up to 80 bar of pressure difference) and high temperatures (300°C-700°C).42... 

Pre-combustion capture this solution is developed in two phases (i) the conversion of the fuel to a mixture of H2 and CO (syngas mixture) through, e.g. partial oxidation, steam reforming or auto-thermal reforming of hydrocarbons, followed by water-gas... 

There are several methods for reforming hydrocarbons to produce H2, including partial oxidation, steam reforming, and autothermal reforming. We can use CH4 as an example to illustrate the processes. 

Exxon (now ExxonMobil) has developed a two-step process for conversion of natural gas to liquid hydrocarbons. The process, referred to as AGC-21, utilizes a fluidized bed for catalytic partial oxidation/steam reforming of natural gas to syn gas, and a slurry bed reactor for conversion of the syn gas to hydrocarbons. The hydrocarbons are processed further to produce liquid products that are used as refinery or chemical plant feedstock. 

Schematically, CO2 capture can be achieved following three main strategies (Figure 39.1) [12] (1) oxy-combustion (or oxy-fuel combustion) where the fuel combustion is performed with pure or enriched O2 instead of air, so that a CO2/ H2O mixture is produced (2) pre-combustion, where the carbon from the fuel is removed prior to combustion (decarbonization) either as CO2, as coke, or in other forms, and whereby the primary fuel heating value is transformed into H2 through partial oxidation, steam reforming, or autothermal reforming with subsequent water-gas shift (WGS) reaction and (3) post-combustion, where CO2 recovery is performed at the end of pipe from a wet exhaust flue gas, usually at 10-30% (v/v) CO2 concentration. The target separations to achieve in these processes to make them feasible are O2/N2 for oxy-combustion, CO2/H2 for precombustion, and CO2/N2 for post-combustion CO2 capture.

H2 production from ethanol (as well as methanol) employs these methodologies either as such or after slight modifications, especially in the ATR process, wherein a separate combustion zone is usually not present (Scheme 3). A mixture of ethanol, steam and 02 with an appropriate ethanol steam 02 ratio directly enters on the catalyst bed to produce syngas at higher temperature, around 700 °C.18,22 The authors of this review believe that under the experimental conditions employed, both steam reforming and partial oxidation could occur on the same catalyst surface exchanging heats between them to produce H2 and carbon oxides. The amount of 02 may be different from what is required to achieve the thermally neutral operation. Consequently the reaction has been referred to as an oxidative steam reforming... 

This review analyzed the chemistry involved, thermodynamics, catalysts used, reaction pathways and mechanisms of various reforming techniques reported for the conversion of ethanol into H2-rich gas. The known reforming processes are broadly classified into three categories, namely steam reforming of ethanol (SRE), partial oxidation of ethanol (POE) and oxidative steam reforming (OSR)/autothermal reforming of ethanol. All these reactions are thermodynamically favorable even at lower temperatures, above 200 °C. 

The gas feed stream is split, recycle CO2 is added to each stream and the combined streams are fed to each of the two gasification trains. Oxygen from the Air Separation Unit (ASU) is preheated by steam, split and fed to the two gasification trains. Partial oxidation and reforming reactions take place in the Gasifiers. 

As discussed above in the reforming of hydrocarbon fuels, H2 can be produced from alcohol fuels by at least three major catalytic processes, namely steam reforming, partial oxidation and ATR or oxidative steam reforming. The chemistry, thermodynamics, and recent developments in catalysis of methanol and ethanol reforming with steam for H2 production will be discussed in this section. 

Similar to the methanol reforming methods discussed in Section 2.4.1, hydrogen can also be produced from ethanol by steam reforming (Eq. 2.79), partial oxidation (Eq. 2.80), and oxidative steam reforming or ATR (Eqs. 2.81 and 2.82). Among them, the SRE has been studied extensively. 

The 6 scenarios differ by whether the hydrogen is produced off-site and transported by truck or pipeline, or whether the hydrogen is produced on-site by steam methane reformer (SMR), partial oxidation POx) reforming, or grid electrolysis. The scenarios are depicted in Figure 1. 

Developed a prototype CFD model including all the key elements of auto-thermal reforming (ATR) Developed a model that accounts for fuel atomization and vaporization, partial oxidation, steam gasification, and anode exhaust gas combustion... 

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