Fundamentals of bitumen coking processes analogous to granulations: A critical review

Abstract

estern Canada has enormous resources of bitumen in oilsands deposits, estimated at 4.6 x 10" m3 (NEB, 2000), of which W 12% is recoverable using current technology of either openpit mining or in situ production by steam assisted gravity drainage. This bitumen requires extensive processing in order to produce transportation fuels and petrochemicals. The bitumen contains 50-60 weight % of vacuum residue, i.e., components that cannot be distilled, which must be converted to distillable fractions. The main commercial technologies to accomplish this production are coking the vacuum residue to produce a carbon rich coke solid, distillable liquids and light ends, and hydroconversion with catalyst or additives at high pressure with hydrogen gas (Gray, 1994). Due to a variety of economic and historical factors, coking processes account for the large majority of installed and announced capacity in Canadian upgrading operations. The importance of coking makes further improvements to a process vital to the Canadian oilsands industry.A number of process variables are significant in coking processes, but the two most important are the method used to heat the oil and the residence time of the cracked products in the reactors. The most common process worldwide is delayed coking, where the feed oil is heated in a furnace then introduced into a coke drum. The liquid feed cracks in the coke drum to produce vapour products, light ends and coke. The process operates at low pressure (0-300 kPa) and temperatures of 450-51 0°C (Nelson, 1958). The alternative established commercial coking process is based on a fluid-bed reactor. In fluid coking, the feed is sprayed into a fluidized bed of coke particles (Figure 1; Gray, 1994).The liquid reacts on the surface of the hot particles, again cracking to give distillate products, light gases and coke. The higher reaction temperature (500-540°C) and short residence time of the cracked vapour in the reactor give a higher yield of distillate products relative to coke plus light ends (Nelson, 1958). For example, the yield of coke from fluid coking is approximately 68% of the yield of coke from delayed coking for a range of feed oils. The higher yield of liquid product from fluid coking, for a given feed, is usually attributed to the higher operating temperature and the lower gas-phase residence time of the cracked vapours than in delayed coking.Recent development of thermal cracking processes has sought to enhance the yield of liquid products by reducing the residence time of the cracked vapours still further, and by enhancing the heat transfer 'Author to whom correspondence may be addressed. E-mail address: murray.gray@ualbena.caA number of coking processes use hot particles to heat liquid bitumen or petroleum residue to cause cracking reactions. These particles may be mineral or coke solids. Interactions of these particles, in fluid beds, moving beds and other types of contactors, are governed by the liquid films on the particle surfaces. This paper explores the analogy between granulation and co...

Measurement of Efficiency of Distribution of Liquid Feed in a Gas-Solid Fluidized Bed Reactor

“…This observation was consistent with the analysis of the coking process at a microscopic level by analogy to granulation, where liquid droplets contact a limited number of particles (Gray, 2002). This result means that 61% of the particles should have been contacted by feed after a duration of 1 solids residence time for nozzle A as compared to 36% for nozzle B.…”

A novel coalescence model for binary collision of identical wet particles

“…However, in some cases, when there are jets penetrating into the bed (leading to large inter-particle velocities) or when binder viscosity increases significantly due to chemical reactions, the capillary number becomes close to unity or larger. Both of these cases are commonly encountered in fluid coking processes, in which liquid viscosity gradually increases from an initial value of 1 mPa s (Gray, 2002) to 10 4 mPa s (Aminu et al, 2004) while surface tension remains within the range of 6-21 mN/m throughout the process (Aminu et al, 2004). Assuming the same characteristic impact velocity as above, i.e.…”

Role of Pressure in Coking of Thin Films of Bitumen

“…Syncrude Canada Ltd.,Edmonton,AB,Canada T6N 1H4 coke particles. Other processes under development propose the use of fluidized sand or other reactor geometries (Gray, 2002). All of these hot-particle processes operate at temperatures in excess of 500ºC, which gives some vaporization of the vacuum residue components (524ºC+), in addition to the gas oil and lighter fractions (< 524ºC).…”

“…E-mail address: murray.gray@ualberta.ca (1998) found that components with boiling points up to approximately 650ºC were subject to a combination of volatilization and cracking. The reactors operating in this high-temperature regime usually involve thin liquid films reacting on the surfaces of solid particles that serve as a heat medium (Gray, 2002), therefore, the geometry of the reacting liquid phase promotes the transport of high-boiling components to the liquid phase. During the cracking reactions, light components and gases form in the liquid phase.…”

“…This combination of transport and reaction is fundamentally different from processes such as evaporation or boiling in thin films. The formation of bubbles by reaction changes the transport processes in the liquid phase, and may have mechanical implications when the feed liquid is aggregated with fine solid particles, as would normally occur when spraying liquid in to a fluidized bed (Gray, 2002). Some prior reports considered reaction and product evolution from softening coal (Attar, 1978;Oh et al, 1989), a system that offers some analogies, but the physical properties were dramatically different from bitumen fractions and the temperature arrange of interest was much higher, up to 1000ºC.…”