Endothermic catalytic steam

With the right mixture of input fuel, air, and steam, the POX reaction supplies all the heat needed to drive the endothermic catalytic steam reforming reaction. Unlike the steam methane reformer, the autothermal reformer requires no external heat source and no indirect heat exchangers. These features make autothermal reformers simpler and more compact than steam reformers and thus can be built for a relatively low capital cost. 

PURE HYDROGEN FOR FUEL CELLS A NOVEL DESIGN OF COMPACT ENDOTHERMIC CATALYTIC STEAM REFORMER... 

Hydrocarbons react with steam in an endothermic reaction to form carbon monoxide and hydrogen. The most important feedstock for the catalytic steam reforming process is natural gas. Other feedstocks are associated gas, propane, butane, liquefied petroleum gas, and some naphtha fractions (q.v.). The choice is usually made on the availability and the price of the raw material. 

Steam reforming refers to the endothermic, catalytic conversion of light hydrocarbons (methane to gasoline) in the presence of steam [see Eq. (5.1)]. The reforming reaction takes place across a nickel catalyst that is packed in tubes in an externally-fired, tubular furnace (the Primary Reformer). The lined chamber reactor is called the secondary reformer , and this is where hot process air is added to introduce nitrogen into the process. Typical reaction conditions in the Primary Reformer are 700°C to 830°C and 15 to 40 bar46. 

The most important reactions taking place in catalytic steam reforming are the endothermic methane steam reforming reaction and the parallel exothermic water gas shift reaction, respectively [4] ... 

Catalytic steam reforming is an extremely endothermic reaction. The heat necessary is supplied by the burning of natural gas or petroleum distillates. 

Reactions of a light gas with a liquid are almost always exothermic. Though very important in industry, endothermic reactions are exclusively gas phase reactions. It seems more economical to produce, in large scale endothermic processes (steam cracking, catalytic reforming and steam reforming), reactive intermediates from which, by exothermic reactions the wide variety of chemicals are synthetized. So, enthalpy of reaction cannot be used as a cri-terium to classify three phase industrial processes and, in the design of such plants, heat removal and temperature control are always important problems, sometimes critical ones. 

The shell/tube configuration of tubular PBRs depends on the nature of the catalytic reaction. For highly endothermic reactions such as catalytic steam reforming, the reactor geometry is similar to that of a fired furnace in which the catalyst-packed tubes are heated by the energy released by the combustion of a fuel on the shell side. Catalytic steam reforming involves the conversion of a hydrocarbon to a hydrogen-rich mixture in the presence of steam ... 

In the Monsanto/Lummus Crest process (Figure 10-3), fresh ethylbenzene with recycled unconverted ethylbenzene are mixed with superheated steam. The steam acts as a heating medium and as a diluent. The endothermic reaction is carried out in multiple radial bed reactors filled with proprietary catalysts. Radial beds minimize pressure drops across the reactor. A simulation and optimization of styrene plant based on the Lummus Monsanto process has been done by Sundaram et al. Yields could be predicted, and with the help of an optimizer, the best operating conditions can be found. Figure 10-4 shows the effect of steam-to-EB ratio, temperature, and pressure on the equilibrium conversion of ethylbenzene. Alternative routes for producing styrene have been sought. One approach is to dimerize butadiene to 4-vinyl-1-cyclohexene, followed by catalytic dehydrogenation to styrene ... 

The catalytic combustor provides heat for the endothermic reforming reaction and the vaporization of liquid fuel. The endothermic reforming reaction is carried out in a parallel flow-type micro-channel of the reformer unit. It is well known that the methanol steam reforming reaction for hydrogen production over the Cu/ZnO/AbOs catalyst involves the following reactions [10]. Eq. (1) is the algebraic summation of Eqs. (2) and (3). 

SMR (reaction 2.4) and shift (reaction 2.6) reactions. Reactions between N2 and hydrocarbon radicals leading to the formation of such by-products as NH3 and HCN can also take place in the thermal zone. By proper adjustment of 02/CH4 and H20/CH4 ratios, the partial combustion in the thermal zone provides the heat for the subsequent endothermic steam reforming reaction taking place in the catalytic zone [40]. Thus, simplistically, ATR of methane at temperature T can be represented as follows ... 

Feed to the FCC unit is mixed with hot catalyst and steam in a reactor line called a riser. The ratio of catalyst oil feed can typically range from 4 1 to 9 1 by weight. Overall, FCC is an endothermic process. Heat provided by the hot, circulating catalyst is the prime source of energy driving the FCC process. In the riser, vaporized oil is cracked catalytically in less than two seconds. The vapors and catalyst flow out of the riser and into the reactor. At this point, most cracking reactions have occurred. 

---