Deposition rate, gasification

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. 

Figure 8. Gasification rate vs. deposition rate at surface steady state (Kpseudo constant). 800°C 1 atm 50 mol % steam.

The results of this investigation have indicated the importance of several variables relative to rates of coke deposition and of coke gasification. Both deposition and gasification depend, in some complex manner, on the surface composition. The present investigation indicates that important information can be obtained with the scanning electron microscope. 

Deposits were collected from the disengagment section and from the horizontal pass. A summary of properties for deposits removed from both locations appears in Table 3. Surface temperatures were controlled to about 500°C for probes in the disengagement zone. Specific deposition rates in the disengagment section are higher for the combustion tests than the gasification tests due to the higher fuel feed rate for gasification with the same total deposit mass. 

The solvent elimination problem became less of a problem with the commercialization of microbore columns. Hayes et al. (54) studied gradient HPLC-MS using microbore columns and a moving-belt interface. The heart of the system was the spray deposition device designed to be compatible with microbore-column flow rates. Nebulization of the eluent was found to be applicable to a variety of mobile-phase compositions and thus was readily compatible with gradient elution. Figure 13 shows a comparison of UV detection with that obtained with the HPLC-MS system. Applications of this system were demonstrated on water from coal gasification processes. 

Rhodium and iridium behave quite difterently from platinum. For similar metal surface areas, Rh and Ir give coking rates much lower than those obtained on Pt (compare Pt4A, Rh2A and Ir4A). The moat conspicuous diCTerences concern the gasification by steam of the carbon deposits, faster on Ir, and still faster on Rh, than on Pt. For example, 3 kPa of steam at 460 C can eliminate 67% of the carbon deposited on Rh, 42% on Ir and 17% on Pt. 

The experimental results (Fig. 4) indicate (a) there are two kinds of coke deposited on A-01 and B. (b) The rate of gasification on A-01 Is higher than that on B. 

C. Conversions increased with alkali content indicating that the potassium cation was involved in the active sites for the reaction. Carbon was deposited on the catalyst and the conversion increased in proportion to the amount of carbon deposited. The carbon was steamed off subsequently and the rate of gasification with steam increased with K content, confirming the promoting effect of K on the steam-carbon reaction (see Figure 10). A linear relationship... 

Gasification of a carbonaceous deposit formed on a radiantly heated ethylene steam cracker pyrolysis tube, in water vapour, at 721-1056°C was chemically controlled. Oxidation rates were linear between 10-85% burn off and increased proportionally with water vapour partial pressure (38-362 mm Hg). The activation energy and pre-exponential factor were 57 Real mole-l and 3.6 x 10 mg cm min" respectively. Gasification was catalysed by inorganic impurities entrained in the deposit and was promoted by hydrogen and butane. 

For the experimental conditions of temperature, water vapour partial pressure and gas flow rate examined the kinetics of gasification of the ESC deposit were consistent with previous observations for the carbon-water vapour reaction (7,8). The reaction was chemically controlled and the oxidation rate was linearly dependent upon water vapour partial pressure. The measured activation energy (57 Real mole-1) was in the middle of the previously reported values (13.5 (JO-83 (9) Real mole-1) for this reaction. 

The ESC deposit contained appreciable levels of potential catalytic elements. These appeared to have promoted gasification, as the oxidation of the ESC coke was nearly five orders of magnitude greater than that of effectively pure graphite (SP-1), with an ash content of 1 ppm (Table 3). Such a wide discrepancy would be less likely to be attributable to structural or textural differences. Also, metallic nickel dispersed in the SP-1 graphite at concentrations of 303 ppm and 1.4 wt.% increased its gasification rate by factors of 10 and 4 x 10 respectively. 

During TPSR, the rate of gasification of the carbon deposit (as determined by continuous measurement of the effluent gas composition) was recorded as a function If time. The data are represented by the calculated gas production rate versus bed temperature as In conventional thermal analysis. TPSR analysis was performed for various conditions of exposure temperature, exposure duration, and exposure gas (CO, or C2H2) for both 1-... 

Gasification Kinetics of Coke Deposited on Silica-Alumina. Within the temperature range 1400 to 1600°F and in the presence of excess steam, the gasification reaction of coke deposited on the silica-alumina cracking catalyst closely followed first-order kinetics with respect to unreacted carbon (Figure 1). First-order rate constants were calculated from the slopes of these plots (Table III), and yielded an activation energy of 55.5 Kcal/mole. 

The steam-carbon reaction is known to be catalyzed by metals, particularly transition metals (3,4.). In an effort to improve the rate of gasification, separate samples of the silica-alumina (Durabead) catalyst were impregnated with one of various metals prior to coke deposition, and the results for the subsequent steam-carbon reaction at 1500°F over these materials are shown in Figure 2 and Table IV. The effects of the deposited metal oxides can be summarized as follows ... 

The addition of potassium to a nickel/ -alumina steam reforming catalyst provides resistance to the accumulation of carbonaceous deposits in two ways. First, the alkali reduces the rate of hydrocarbon cracking on the nickel component of the catalyst. Second, the promoter enhances the rate of the steam gasification of carbon on the catalyst. This is accomplished by increasing the surface coverage of water on the catalyst and hence supplementing the pre-exponential component of the gasification rate equation. 

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