Incoloy reactor

Vycor Glass Type of Reactor Incoloy 800 304 Stainless Steel... 

The initial surface composition of boiler tubing, prior to its installation will have an important impact on the amount and type of activated corrosion products in an aqueous reactor coolant. Consequently, the type of thermal pre-treatment the tubing undergoes, for example, for mechanical stress release,will affect the surface oxide film, and ultimately, the corrosion behavior. This particular work has been directed toward characterization of surface oxide films which form on Inconel 600 (nominal composition 77% Ni, 16% Cr, 7% Fe, — a tradename of Inco Metals Ltd., Toronto Canada) and Incoloy 800 (nominal composition 31% Ni, 19% Cr, 48% Fe 2% other, — a tradename of Inco Metals Ltd., Toronto, Canada) heated to temperatures of 500-600°C for periods of up to 1 minute in flowing argon. These are conditions equivalent to those experi enced by CANDU(CANadian Deuterium Uranium)ractor boiler hairpins during in situ stress relief. 

Figure 13. Corrosion behavior of reduction reactor materials samples in anhydrous environment (O), Hastelloy C276 Cartech CB3 (V), Incoloy 825 (A), Inconel 625 (O), SS 310 and (0), SS 18-18-2. Furnace temperature, 482°C (900°F) anhydrous S03 12 cc/min argon 128 cc/min. Erratic erosion rate behavior of SS 310 and Cartech 20CB3 is caused by the spalling of the corrosion product. Negative values indicate weight gain per unit area.

Ethane was pyrolyzed in several tubular reactors having internal diameters of about 0.47 cm and a heated length of 107 cm. The reactors used were constructed of Incoloy 800, stainless steel 304 (SS 304), stainless steel 410 (SS 410), Hastelloy X, and Vycor glass. Each reactor was maintained at almost isothermal conditions by suspending it in a fluidized sand bath. More details on the reactors are described by Dunkleman and Albright (12) and Herriott, Eckert, and Albright (13). After suitable pyrolysis, the reactor was cut to expose the coke on the inner surfaces. 

Metal coupons were inserted at various positions in the horizontal tubular reactor. The coupons had two types of surfaces an Incoloy 800 surface and an aluminized Incoloy 800 surface. To prepare these coupons, flat pieces of Incoloy 800 were aluminized (or alonized) by the Alon Processing, Inc. of Tarentum, PA. In this process, gaseous aluminum was contacted with the Incoloy 800, and aluminum diffused into the surface. The alonized samples as received from Alon Processing were cut in small coupons so as to expose an Incoloy 800 surface which was cleaned and polished before use. 

Variables Affecting Type of Coke. The material of construction of the solid on which the coke formed, the temperature, and the space time all affected the type of coke formed. Cokes formed on Incoloy 800, SS 304, SS 410, and Hastelloy X were sometimes magnetic. Cokes formed in an alonized surface were always nonmagnetic, and no metals were detected by EDAX except for a trace of aluminum. Cokes formed in Vycor glass reactors were also nonmagnetic. 

Figures 4 and 5 indicate that the types of coke formed on Incoloy 800 as ethylene and propylene, respectively, were contacted with an Incoloy 800 surface at various temperatures and at slightly different conversion levels. In these experiments, the Incoloy 800 coupons were positioned at different positions in the horizontal tubular reactor. The residence time of gases in the reactor was about 7, 10, 15, and 25 sec by the time the gases reached the coupon. The temperature of each location was about 460°, 560°, 600°, and 565°C, respectively. The cokes...

Thermal reactions of acetylene, butadiene, and benzene result in the production of coke, liquid products, and various gaseous products at temperatures varying from 4500 to 800°C. The relative ratios of these products and the conversions of the feed hydrocarbon were significantly affected in many cases by the materials of construction and by the past history of the tubular reactor used. Higher conversions of acetylene and benzene occurred in the Incoloy 800 reactor than in either the aluminized Incoloy 800 or the Vycor glass reactor. Butadiene conversions were similar in all reactors. The coke that formed on Incoloy 800 from acetylene catalyzed additional coke formation. Methods are suggested for decreasing the rates of coke production in commercial pyrolysis furnaces. 

The pyrolysis reactors were similar to those used earlier (1,2) they were 1.1 to 1.26-cm i.d. tubes that were heated in an electrical resistance furnace over a length of about 48 cm. The materials of construction in the four reactors used in this investigation were as follows Incoloy 800, stainless steel 304, Vycor glass, and alonized Incoloy 800. The latter reactor was prepared by Alon Processing, Inc. of Tarentum, Pennsylvania. 

Figure 1 indicates an example of how pretreatment of the Incoloy 800 reactor had a very large effect on the acetylene conversion (or on the kinetics of acetylene decomposition). The coke-coated Incoloy 800 reactor (the coke had been deposited on this reactor when butadiene reacted at 500°-700°C.) used in Run 14 resulted in much lower acetylene conversions in the range of 450° to 550°C compared with the same Incoloy 800 reactor after the coke had been burned off with oxygen and after the reactor had been contacted with hydrogen until nearly all surface oxides were eliminated. Most conversion results for the 11 gas samples collected during Run 15 are shown in Figure 1. Gas Samples 1 through 3 at 350°, 400°, and 450°C, respectively, indicated almost no acetylene conversions. A small amount of carbon dioxide was produced at 450°C, indicating some metal oxides had still been present on the surface after the hydrogen pretreatment. The temperature was then increased to 500°C, and the conversions then increased from 66% to 99% during the first 23 min (Samples 4 and 5). Some carbon oxide production was noted in Sample 4 but none in Sample 5 or in any later samples of the run presumably...

Figure 1. Acetylene conversions in coke-coated Incoloy 800 and clean Incoloy 800 reactors. Acetylene feed (A) Run 14y coke-coated Incoloy 800 (D) Run 15, clean Incoloy 800.

The results for Run 19 (Vycor glass reactor), Run 21 (alonized Incoloy 800 reactor), and Run 14 (coke-covered Incoloy 800 reactor) were similar to both the kinetics and type of products obtained. Although neither oxygen or hydrogen pretreatments were tried in Vycor glass or alonized Incoloy 800 reactors prior to acetylene pyrolyses, it is thought that such pretreatments would have little or no effect on acetylene reactions. This conclusion is based on such pretreatments prior to pyrolysis with other hydrocarbons in these two reactors. It has been concluded that all increases in acetylene conversions above those of Runs 14, 19, and 21 were in some way caused by surface reactions. Based on this assumption, surface reactions were of major importance in Runs 15, 18, and 23. 

Butadiene reacted in Incoloy 800, alonized Incoloy 800, and Vycor glass reactors to give quite similar results. Butadiene conversions increased from about 60%-80% at 500°C to about 94%-97% at 700°C. The main products formed were liquids (i.e., products that condensed... 

Figure 2. Hydrogen concentration in product gas stream during benzene pyrolysis in various reactors. 12% benzene feed ( J) Vycor, (Q) Incoloy...

Methane was formed in significant amounts in such cases it is thought that hydrogen reacts with the surface coke or metal carbides on the surface, such as has been shown earlier to occur (1). At the same temperatures (600°-700°C), little or no reactions occurred in the Vycor glass or in the alonized Incoloy 800 reactors. Clearly the Incoloy 800 surfaces were promoting significant coking reactions at these temperatures. 

A series of runs was made in the alonized Incoloy 800 reactor by using ethylene, ethane, propylene, and propane. These runs were com-... 

Although more information is needed to determine details concerning factors that favor inactive coke formation, relatively high levels of surface sulfides probably promote formation of such coke. On the other hand, metal oxides on the surface likely favor production of active coke. Sulfiding the reactor tube immediately upon completion of the decoking step would form metal sulfides. An aluminized surface, such as provided by the alonized Incoloy 800 reactor, also has been found to be an effective way to prevent the production of active coke. Quite possibly, the initial type of coke formed on the just-cleaned tube would have an important effect on the length of time a reactor tube could be used in a commercial plant before decoking would be required. 

Considerable information was obtained for ethane pyrolysis relative to coke deposition on and to decoking from the inner walls of a tubular reactor. Both phenomena are affected significantly by the materials of construction (Incoloy 800, stainless steel 304, stainless steel 410, Hastelloy X, or Vycor glass) of the pyrolysis tube and often by their past history. Based on results with a scanning electron microscope, several types of coke were formed. Cokes that formed on metal tubes contained metal particles. The energy of activation for coke formation is about 65 kcal/g mol. 

Figure 7. Surfaces formed on tubular reactors during or after pyrolysis of ethane at 800°C. (Top left,) stainless steel 304—Surface A (top right,) Incoloy 800—Surface A, (magnification 20% of other pictures) (middle left) stainless steel 304—Surface B (middle right) Incoloy 800—Surface B (bottom left) stainless steel 304—Surface C (bottom right) Incoloy 800...

Surfaces B and C for the Incoloy 800 reactor were quite different from the platelets and crystallites formed in the stainless steel 304 and 410 reactors. The metal concentrations for Surfaces A, B, and C varied rather erratically compared with the bulk metal (see Table III). Clearly, further investigations are needed to learn about coke deposits formed during ethane pyrolysis in Incoloy 800 reactors. 

G D ratios greater than 1.0 sometimes occurred with Incoloy 800, and stainless steel 410 and 304 reactors. Initially, dry ethane was pyro-lyzed in a new reactor and then wet ethane was used, resulting in high G D ratios. In such cases, 90% or more steam reacted, but the deposition rate did not appear to change markedly. After a short period of time, the gasification rate dropped to produce G D ratios less than 1.0. As this occurred, the deposition rates increased to large values. 

The tubing containing the coupon samples were placed inside a Vycor glass tube (2.2 cm. I. D. and 85 cm.long) that was positioned horizontally in an electrical furnace controlled at either 700 or 900°C. For inorganic gas treatments Incoloy 800 and polished Incoloy 800 coupons were positioned side by side 4. 5 cm. upstream of the reactor midpoint polished and unpolished aluminized Incoloy 800 coupons were likewise positioned side by side except 2.0 cm. upstream... 

The above indicates that low alloy steel, e.g. IViCr ViMo, can be used for most loop equipment including the converter pressure shell. Critical parts are the reactor internals (the basket ), which are most often made fi om stainless steel (SS 321), and the inlet part of the waste heat boiler which must either be made from or cladded by corrosion-resistant material, like Incoloy or similar. 

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