Coke gasification rate

Effect of Impregnated Metals on Coke Gasification Rate. 

Effect of Substrate on Coke Gasification Rate. The effect of substrate variations on the steam-carbon reaction rate at 1500°F is shown in Table II and in Figure 3. The substrates can be classified into two categories according to their effect on coke gasification reaction rates ... 

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. 

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. 

Ni Acceleration of the initial gasification rate (for coke conversions up to 30%). 

In marked contrast to the effects observed with iron, vanadium and copper oxides, prior impregnation of silica-alumina with nickel oxide led to a considerable increase in the initial rate of subsequent coke gasification, up to a coke conversion level of a>30% (Figure 2). 

At 1500°F, the steam-coke reaction on alumina occurs approximately three to six times faster than on silica-alumina type substrates. Comparison of results from Runs 56 and 58 indicates the extent of reproducibility of the experiments. In comparison with this reproducibility and in consideration of the observed consistency, the increased gasification rates on the alumina substrates are significant. All alumina-based materials tested, viz., y-alumina, calcined Catapal, and bauxite, showed equally high activities. 

Particle Size. The effect of particle size of bituminous coke on the gasification rate was studied. Testing conditions were the same as for previous studies 1740°F., 3 atm. absolute pressure, 1 ft./sec. superficial gas velocity, 2% bituminous coal ash in a melt of 4-in. height and 4% carbon charged initially. The results of the tests on three particles sizes are given in Table IV. 

This comparison shows that there is a potential to form carbon from the methane-cracking reaction in the inside of the reformer wall at this location in the reformer tube. Detailed, proprietary kinetic expressions for the reactions 8-10 indicate that while reaction 9 will form carbon, the coke will be gasified by steam and CO2 (reactions 8 and 10), so there is no net accumulation of carbon in this example. However, as the steam-to-hydrocarbon feed ratio is reduced further there will be a point where there is an accumulation of carbon because the coking rate of reaction 9 will be greater than the combined gasification rates of reactions 8 and 10. 

Tabie 6.5.2 Parameters used to calculate the effective reaction rate of coke gasification with carbon dioxide. Partly taken from Hedden (1976) and Heynert and Hedden (1961). 

In 1984, the Ube Ammonia Industry Co. began operating the largest Texaco coal gasification complex to date. This faciUty is located in Ube City, Japan, and has a rated gasification capacity of 1500 t/day of coal, and production capacity of 1000 t/day of ammonia. The plant has successfully gasified coals from Canada, AustraUa, South Africa, and China. At the present time the plant uses a mixture of petroleum coke and coal (43). 

In the present investigation, ethane was pyrolyzed at conditions of commercial interest in several tubular reactors. Information has been obtained that provides further insights on the coke precursors, on the rate of formation of coke, on the rate of gasification as the coke reacts with steam, and on photographs of the coke and resulting metal surfaces as obtained by a scanning electron microscope. 

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. 

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