Autothermal process

The transformation of straw and agrofood residues with high sulfur and ash content requires the development of materials for sulfur abatement at high temperature, tar cracking and as monolith for syngas production by exothermic or autothermal processes thanks to catalysts supported on materials with a high thermal conductivity. 

Shinnar, R., Doyle, F. J., Budman. H. M., and Morari, M. Design Considerations for Tubular Reactors with Highly Exothermic Reactions, AIChE J., 38,1729-1743 (1992). van Heerden, C. Autothermic Processes—Properties and Reactor Design, Ind. Eng. Chem., 45, 1242-1247 (1953). 

The carbon deficit observed in methane steam nsforming does not occur if naphtha feedstock is converted. In autothermal processes using fuel oil as a feedstock, sufficient quantities of excess carbon dioxicte are available within the instailation itself. This gas is recycled from a scrubbing unit... 

The submerged-flame technique developed by BASF represents the latest de> cIopment in autothermal processes. Within a liquid hydrocarbon, a flame creates a suf ciently high temperature in its vicinity to cause the formation of light products, tnduding acetylene. The gases are quendied in the cold zones of the liquid, and the carbon black formed is sent with the hydrocarbon to the burner. The reactor can operate undo pressure with any hydrocarbon oomponnd, without the substandal producdon of carbon black. The weak point of the device is the control of the burner, which is difficult to achieve due to the bi gas flow velocity (Fig. 5.13). 

Gasoline and other higher hydrocarbons may be converted to hydrogen on board cars by the autothermal processes, using suitable catalysts (Ghen-ciu, 2002 Ayabe et ah, 2003 Semelsberger et ah, 2004). Partial oxidation may also be combined with the palladium-catalyst membrane reactors mentioned in section 2.1.1 (Basile et ah, 2001). 

Semelsberger, T., Brown, L., Borup, R., Inbody, M. (2004). Equilibrium products from autothermal processes for generating hydrogen-rich fuel-cell feeds. Int.. Hydrogen Energy 29,1047-1064. 

After desulfurization, steam is added and the mixture heated to 480 to 550°C before it is fed into the primary reformer. The gas leaving the primary reformer contains between 7 and 10% methane. This is removed in so-called secondary reformers in which the gas leaving the primary reformer is partially burnt with air in nickel catalyst-filled shaft furnaces (autothermal process), whereupon the temperature increases to ca. 1000°C. Under these conditions the methane reacts with the steam reducing the methane content in the synthesis gas to ca. 0.5 mole %. The quantity of air is adjusted to give the nitrogen to hydrogen ratio required for the stoichiometry of the ammonia synthesis. 

C. van Heerden, Autothermic Processes. Properties and Reactor Design/ Ind. Eng. Chem., 1242 (1953). 

The fraction of CH4 feed is fed through the bottom section in such a way that the permeating O2 is able to generate CPO (catalytic partial oxidation) equilibrium conditions in the bottom section, the temperature of which is in turn favorable for the permselective O2 transport. The steam is also added to avoid coke formation in the bottom section. The top section is then fed with the remaining CH 4 and steam feed so that overall autothermal process is achieved when both sections are considered together. The endothermic heat demand of the top section is thus catered by the equilibrium mixture corning from the bottom section and the side feed of additional CH4 and steam. 

ACETYLENE MANUFACTURE FROM hydrocarbons AUTOTHERMAL PROCESSES... 

Table 5.3 lists the main characteristics of the best known autothermal processes. 

Calculate the steady-state conversion for the synthesis of ammorila using the autothermal process shown in Figure 6.37 [25]. A rate expression for the reaction... 

The autothermal process, described in Chap. 6, is competitive with tubular fired reforming only for large applications as GTL plants or if oxygen or enriched air are available at low cost since the use of natural air for methane combustion would not allow the high temperature required by reactions to be reached. 

Synthesis gas can be produced by the steam reforming process or by the autothermal process. Hydrocarbons are catalytically cracked in the presence of steam and applied heat in the steam reforming process. Hydrocarbons from methane up to the C4-C7 fractions of light petroleum can be used as raw materials. In contrast, the energy required for cracking is obtained by the partial combustion of the hydrocarbons themselves in the autothermal process. This latter process works without catalysts using steam-oxygen mixtures and hydrocarbons from methane to heavy fuel oils. 

Steam reforming and dry reforming are endothermic, bnt partial oxidation of methane and water gas shift reactions are exothermic. The autothermal process becomes exothermic and is thermodynamically favorable. 

All commercial grades of phosphate rock are acceptable Large size rock particles are acceptable CAN granulation is an autothermal process... 

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