Catalytic reactor shutdown

Dust explosions (ASTM E789) that can occur during catalytic reactor shutdown and cleaning are due to the production of finely divided solids through attrition. Many catalyst dusts can bum explosively in air. Thus, control of dust generated by catalyst attrition is essential (Mody and Jakhete, 1988). 

Preventing masking of active surface of catalysts in a fixed-bed reactor by filtering the incoming gas streams containing dust particles. This also minimizes pressure drop in catalyst beds and frequent shutdown of the catalytic reactor for screening of the bed is not required. 

The practical advantages gained from the use of steady-state models in design, optimization, and operation of catalytic reactors are tremendous. It is estimated that about 80—85% of the success of the process depends on the steady-state design and the remaining 15—20% depends on the successful dynamic control of the optimum steady state. These estimates are, of course, made for a process operating smoothly with conventional control which is not model based. However, in certain cases, inefficient dynamic control may cause temperature runaway or a complete shutdown of the process. 

In industrial catalytic reactors with their heterogeneous and distributed nature (variation of the state variables with respect to the space coordinates), dynamic temperature runaways may occur, especially for highly exothermic reactions. A reliable dynamic model is one of the best ways to discover and monitor these temperature runaways, which may cause explosions or, at the least, emergency shutdowns, which are quite expensive, especially with today s large-capacity production lines. 

A number of refinery processes require the use of a fixed-bed catalyst These processes include catalytic reforming, hydrodesulfurization, hydrotreating, hydro-cracking, and others. These catalysts become inactive in six months to three years and are eventually replaced in the reactors with fresh catalyst during a unit shutdown. Many of these catalysts contain valuable metals which can be recovered economically. Some of these metals, such as platinum and palladium, represent the active catalytic component other metals such as nickel and vanadium are contaminants in the feed which are deposited on the catalyst during use. After valuable metals are recovered (a service usually performed by the outside companies), the residuals are expected to be disposed of as solid waste. 

Gas-catalytic reactions. Temperature and pressure drop across bed are usually key variables. When a hot spot develops, it usually develops at the front end of the bed and gradually moves through the bed. It may take three to four weeks to travel through the full bed. If the hot spot is 100-200 °C above normal, then usually carbon is deposited and the catalyst is irrevocably damaged. Temperature control is critical for exothermic reactions. Ap rapidly increases emergency shutdown . Pressure surge possible shutdown /[runaway reactor]. ... 

The H-Coal process was an adaptation of the H-Oil process used in the petroleum industry to convert heavy oil residues to lighter fractions using a catalytic ebullated bed reactor.Research on the H-Coal process began in 1964 at Hydrocarbon Research, Inc. (HRI) on a bench-scale unit, and by 1973 the design of a 200- to 600-ton/day pilot plant was under way. Construction of the plant was completed in early 1980. Located adjacent to the Ashland Oil refinery in Cattletsburg, Kentucky, it operated succesfully from startup in May 1980 until shutdown in November 1982. 

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