Industrial hydrogenation reactor

In adiabatically operated industrial hydrogenation reactors temperature hot spots have been observed under steady-state conditions. They are attributed to the formation of areas with different fluid residence time due to obstructions in the packed bed. It is shown that in addition to these steady-state effects dynamic instabilities may arise which lead to the temporary formation of excess temperatures well above the steady-state limit if a sudden local reduction of the flow rate occurs. An example of such a runaway in an industrial hydrogenation reactor is presented together with model calculations which reveal details of the onset and course of the reaction runaway. 

Eigenberger, G. and V. Wegerle. Runaway in an Industrial Hydrogenation Reactor. (7th International Symposium of Chemical Reaction Engineering, Boston, 1982) A.C.S. Symp. Series No. 196, 133-143. 

Ross (R2) measured liquid-phase holdup and residence-time distribution by a tracer-pulse technique. Experiments were carried out for cocurrent flow in model columns of 2- and 4-in. diameter with air and water as fluid media, as well as in pilot-scale and industrial-scale reactors of 2-in. and 6.5-ft diameters used for the catalytic hydrogenation of petroleum fractions. The columns were packed with commercial cylindrical catalyst pellets of -in. diameter and length. The liquid holdup was from 40 to 50% of total bed volume for nominal liquid velocities from 8 to 200 ft/hr in the model reactors, from 26 to 32% of volume for nominal liquid velocities from 6 to 10.5 ft/hr in the pilot unit, and from 20 to 27 % for nominal liquid velocities from 27.9 to 68.6 ft/hr in the industrial unit. In that work, a few sets of results of residence-time distribution experiments are reported in graphical form, as tracer-response curves. 

Most industrial hydrogen is manufactured by the following hydrocarbon-based oxidative processes steam reforming of light hydrocarbons (e.g., NG and naphtha), POx of heavy oil fractions, and ATR. Each of these technological approaches has numerous modifications depending on the type of feedstock, reactor design, heat input options, by-product treatment,... 

Mitenkov, F.M., N.G. Kodochigov, A.V. Vasyaev, et al. (2004), High-temperature Gas-cooled Reactor as Energy Source for Industrial Hydrogen Production , Nuclear Power, Vol. 97, Issue 6, pp. 43-446. 

Rase [5] has presented several case studies of different scale-up methods involving industrially important reactions. Murthy [11] has provided a general guideline for the scale-up of slurry hydrogenation reactors, and other scale-up processes are illustrated elsewhere [12],... 

Purely adiabatic fixed-bed reactors are used mainly for reactions with a small heat of reaction. Such reactions are primarily involved in gas purification, in which small amounts of noxious components are converted. The chambers used to remove NO, from power station flue gases, with a catalyst volume of more than 1000 m3, are the largest industrial adiabatic reactors, and the exhaust catalyst for internal combustion engines, with a catalyst volume of ca. 1 L, the smallest. Typical applications in the chemical industry include the methanation of traces of CO and CO2 in NH3 synthesis gas, as well as the hydrogenation of small amounts of unsaturated compounds in hydrocarbon streams. The latter case requires accurate monitoring and regulation when hydrogen is in excess, in order to prevent complete methanation due to an uncontrolled temperature runaway. 

Catalytic hydrogenation reactors for the fine chemicals industries. Their design and operation... 

Presently, the ongoing research is focused on monoliths and monolithic catalysts especially with respect to hydrogenation reactions. Industrial hydrogenation is often performed by using slurry catalysts in stirred-tank reactors. These reaction systems are inherently problematic in chemical process safety, operability and productivity, Finely divided powder catalysts are often pyrophoric and require extensive operator handling during reactor charging and filtration. By the nature of their heat cycles for start-up and shut-down, slurry systems promote coproduct formation which can shorten catalysts life and lower yield. There are alternatives to slurry reactors. These include packed-bed and monolith reactors. 

A WGS reactor for the conversion of carbon monoxide and water to hydrogen and carbon dioxide is widely used in chemical and petroleum industries. The reactor is also critically needed for the conversion of fuels, including gasoline, diesel, methanol, ethanol, natural gas, and coal, to hydrogen for fuel cells. Since the WGS reaction is reversible, the reaction is not efficient, resulting in a high concentration of unconverted CO (about 1%) in the H2 product and a bulky, heavy reactor. 

The hydrogen produced at the reaction device exit is recovered in a separation unit downstream (Fig. 9.15). In the study performed, the two reactors plus the separator were compared in terms of capital and operating costs, with a Pd-based membrane reactor in which the pure hydrogen is recovered at the permeate side (Fig. 9.16). Table 9.8 shows the main operating conditions of the industrial plant considered. The membrane reactor unit was designed in order to operate with industrial quantities and to achieve the same industrial hydrogen recovery. An integrated membrane system in which the feed stream is first fed to a Pd-based... 

The model can be used to simulate reactors as big as industrial scale reactors. For example, the membrane area required for a given eonversion or a given hydrogen production can be evaluated. 

Defalco, M., Dipaola, L., Marrelli, L. (2007). Heat transfer and hydrogen permeabihty in modeUing industrial membrane reactors for methane steam reforming. International Journal of Hydrogen Energy, 32, 2902—2913. 

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