Ralph J. Tyler

Flash pyrolysis of coals. 1. Devolatilization of a Victorian brown coal in a small fluidized-bed reactor

The devolatilization behaviour of finely-ground (< 0.2 mm) Loy Yang brown coal was investigated under rapid heating conditions using a small-scale fluidized-bed pyrolyser. The pyrolyser operated continuously, coal being fed at rates of 1–3 g/h directly into a bed of sand fluidized by nitrogen. Particle heating rates probably exceeded 104 °C/s. The yields of tar, C1-C3 hydrocarbons and total volatile matter are reported for a pyrolyser-temperature range of 435 to 900 °C. A maximum tar yield of 23% w/w (dry ash-free coal), 60% more than the Fischer assay, was obtained at 580 °C. Yields of C1-C3 hydrocarbons increased with increasing temperature, reaching 8% at 900 °C. Elemental analyses showed that the composition of the tar and char products was strongly dependent on pyrolysis temperature. The effects on the devolatilization behaviour of the coal produced by the moisture associated with the coal, by hydrogen, and by the replacement of the sand by a fluidized bed of petroleum coke were investigated.

Flash pyrolysis of coals. Devolatilization of bituminous coals in a small fluidized-bed reactor

The devolatilization behaviour of ten bituminous coals was investigated under rapid heating conditions using a small-scale fluidized-bed pyrolyser. The pyrolyser operated continuously, coal particles being injected at a rate of 1–3 g h−1 directly into a heated bed of sand fluidized by nitrogen. Yields of tar, C1–C3 hydrocarbon gases, and total volatile-matter and an agglomeration index are reported for all coals. Maximum tar yields were obtained at about 600 °C and were always substantially higher than those from the Gray-King assay. Total volatile-matter yields were also substantially higher than the proximate analysis values. The maximum tar yields appear to be directly proportional to the coal atomic HC ratio. The elemental analysis of the tar is strongly dependent on pyrolysis temperature. The tar atomic HC ratio is proportional to that of the parent coal. The effect on the devolatilization behaviour of two coals produced by changes in the pyrolyser atmosphere and the nature of the fluidized-bed material were also investigated. Substituting an atmosphere of hydrogen, helium, carbon dioxide or steam for nitrogen, has no effect on tar yield and, with one exception, little effect on the hydrocarbon gas yields. In the presence of hydrogen the yield of methane was increased at temperatures above 600 °C. Tar yields were significantly reduced on substituting petroleum coke for sand as the fluid-bed material. A fluidized bed of active char virtually eliminated the tar yield.

Flash pyrolysis of coals: influence of cations on the devolatilization behaviour of brown coals

The influence of cations on the pyrolysis behaviour of brown coals under flash heating conditions was investigated by means of a small fluidized-bed pyrolyser. A stream of coal particles in nitrogen was injected at rates of 1–3 g coal/h directly into a heated bed of sand fluidized by nitrogen. Yields of tar, C1–C3 hydrocarbons and total volatile matter from four Gelliondale brown coals and a Montana lignite were determined as a function of pyrolysis temperature. With all coals the maximum tar yield was obtained at 600 °C. Removal of cations present in the coals markedly increased the yields of tar and total volatile matter, with little effect on the yields of hydrocarbon gases. The converse was also observed in that the addition of Ca2+ to a cation-free coal decreased the yields of tar and total volatile matter. The extent of the reduction in tar yield at 600 °C in the presence of cations was found to be similar for all coals. After acid washing, tar yields appear to correlate with the atomic HC ratios of the coals in a manner similar to that observed previously with bituminous coals.

1H n.m.r. study of tars from flash pyrolysis of three Australian coals

Abstract The structure and composition of tars from the flash pyrolysis of one brown and two bituminous Australian coals were investigated by 1 H n.m.r. spectroscopy. Reaction times in a fluidized bed were about 1 s. For each tar the aromatic hydrogen content increases slightly with pyrolysis temperature up to ≈650 °C and then rapidly up to 900 °C. The aromatic carbon content increases rectilinearly with temperature. The yield of aromatic carbon reaches a maximum at 600–700 °C, and then decreases; the yield of aromatic hydrogen is independent of temperature. The proportion of aromatic material with condensed ring structures increases with temperature. Three temperature zones of reactivity can be recognized. Polymethylene chains and aromatic groups are stable up to 600 °C. Between 600 and 700 °C aliphatic substituents, other than α groups, decompose; between 700 and 900 °C α-aliphatic and aromatic groups also decompose, resulting in lower yields of tar.

Products from rapid heating of a brown coal in the temperature range 400–2300 °C

The devolatilisation behaviour of Yallourn brown coal was investigated under rapid heating conditions using two different flash pyrolysers: a fluid-bed reactor giving coal particle heating rates of 104 °Cs−1 with a gas residence time of about 0.5 s and a shock tube which generated heating rates of the order of 107 °Cs−1 and a 1 ms reaction time. Yields of products are reported covering pyrolysis temperatures in the range 400–2300 °C. Hydrocarbon gas yields reached maximum values which were remarkably similar for both reactors although occurring at different temperatures. Carbon oxide production was also similar for both reactors with CO yields reaching 30% wt/wt daf coal. These high yields of CO are very different from those reported for slow heating conditions. It appears that on flash heating, coal decomposition pathways change in a manner which increases CO yields at the expense of H20 and to a lesser extent C02, resulting in the volatilisation of additional carbon from the coal.

Coal flash pyrolysis: secondary cracking of tar vapours in the range 870–2000 K☆

Abstract Tar free from influences of the original coal or char was cracked in two reaction systems, one using tar vapour in tubular quartz reactors at 900–1400 K and reactor residence times of ≈ 0.2 and ≈ 1 s, the other using tar aerosol in a shock tube at 1100–2000 K and residence time ≈ 1 ms. In the latter system the aerosol evaporated rapidly after passage of the shock front and the tar behaved kinetically as a vapour. Yields of light hydrocarbons including C6H6 and CO from tar cracking were determined as a function of temperature. Maximum yields of individual species agreed well between the two reactors but the temperatures of maximum yield depended on residence time. Hydrocarbon yields on a daf coal basis were very similar to those obtained previously by direct flash pyrolysis of the same coal at 870–1270 K. Kinetic analyses of the formation of C2H4, C3H6 and C2H2 gave activation energies of 220–260 kJ mol−1, similar to those for formation of the same hydrocarbons from n-hexadecane. The precursors of the alkenes could be polymethylene groups in the tar. CH4, C6H6 and CO all had low activation energies of formation, reflecting the many different functional groups capable of eliminating these molecules.

Intrinsic reactivity of petroleum coke to oxygen

Abstract The kinetics of the reaction of petroleum coke with oxygen 2 were investigated using a continuous flow reaction system incorporating facilities for reactant modulation. An apparent order in O 2 of 0.6 and activation energies in the range 151–167 kJ mol −1 were observed. Measurement of the surface areas of partially combusted coke samples enabled intrinsic reaction rates (ρ i ) to be calculated. Regression analyses of all data after correction to a common O 2 pressure of 21.3 kPa gave the following relation for the intrinsic reactivity of petroleum coke in the region of 750 K: ρ = 133 × 10 6 exp exp (− 158.6/ RT ) g m −2 min −1 where: R = the gas constant and T = the temperature. As combustion proceeded, pores in the radius range 0.5–5 μm were enlarged. Present kinetic results were compared with earlier data obtained at high temperatures (1200–2300 K) for a similar petroleum coke. After correction for mass transfer limitations, intrinsic rates derived from the high-temperature data correlated well with the present low-temperature results.

Coal flash pyrolysis: 2. Polymethylene compounds in low temperature flash pyrolysis tars

Abstract Pyrolysis of coals at low temperatures ( 700 °C produce ethylene, propylene and other cracking products similar to those obtained on flash pyrolysis of coal.

Reactivity of petroleum coke to carbon dioxide between 1030 and 1180 K

Abstract Measurements were made of the reaction rate of three sizes (2.9, 0.9 and 0.22 mm) of petroleum-coke particles with carbon dioxide over the temperature range 1018–1178 K, and at carbon dioxide partial pressures between 26 and 118 kPa. A limited number of similar measurements were made on samples of a commercial aluminium-smelting anode, an experimental anode, and AGKSP graphite. The materials were all reacted under conditions of chemical rate control alone: there were no rate limitations due to transport processes without or within the carbon particles. The order of the rate with respect to carbon dioxide concentration was found to be close to 0.6 for the petroleum coke and anode carbons, and between 0.6 and 0.8 for the graphite. Activation energies in the range 203–237 kJ/mol were found for petroleum coke; 187–237 kJ/mol for electrode carbon; and 293 kJ/mol for the graphite. For the petroleum coke, the order was found to be constant up to 45% burn-off and the activation energy essentially constant between 21 and 45% burn-off. The reactivity ϱ s , based on unit pore surface area of the petroleum coke at a carbon dioxide pressure of 101 kPa, can be represented by: ϱ s = α exp [− E (RT) ] . For the 2.9 and 0.9 mm particles, α = 6.1 / sx 10 6 g/m 2 min and E = 215 kJ/mol; for the 0.22 mm particles the respective values are 1.8 / sx 10 7 and 222. The reactivity ϱ of the commercial electrode on a weight basis was within the range of those of the coke and experimental electrode. For AGKSP graphite, values of ϱ s were close to those found by Walker and Raats 14 .

Upgrading of flash pyrolysis tars to synthetic crude oil: 1. First stage hydrotreatment using a disposable catalyst

Abstract The hydrotreatment of tars produced by flash pyrolysis of Millmerran (subbituminous), Loy Yang and Yallourn (both brown) Australian coals was investigated in a continuous reactor containing a packed bed of sulphided steelwool. Reactor performance and product yields are reported for each tar. Overall mass balances of 96.7–100.3% and carbon balances of 96.0–100.2% were achieved. Recovered yields of product oil were 82.7–86.8%, 62.1% and 75.5% wt/wt dry, char-free tar for Millmerran, Loy Yang and Yallourn tars respectively. The steelwool reactor was found to decrease the coking propensity, specific gravity, viscosity and heteroatom levels and to increase the hydrogen content of the tars. It also acted as a filter to remove the char fines present in the tar. The operating life of the reactor was limited by the build up of carbonaceous deposits within the steelwool.