Viscosity reduction by direct oxidative heating

A method is disclosed for reducing the viscosity of a hydrocarbon feed. The feed is heated from an initial temperature to a second temperature and an oxidizing agent is introduced to oxidize components in the feed and provide heat to increase the temperature of the feed to a reaction temperature. The reaction temperature is maintained to produce a reaction product having a lower viscosity than the feed.

FIELD OF THE INVENTION 
This invention relates to a method for improving the transportability of 
heavy oils and other hydrocarbons by thermal viscosity reduction with 
reduced coke formation on reactor walls wherein an incremental portion of 
the heat is provided by direct oxidative heating of the hydrocarbon 
material. 
BACKGROUND OF THE INVENTION 
Vertical tube reactors which ordinarily involve the use of a subterranean 
U-tube configuration for providing a hydrostatic column of fluid 
sufficient to provide a selected pressure are well known. This type of 
reactor has been primarily used for the direct wet oxidation of materials 
in a waste stream and particularly for the direct wet oxidation of sewage 
sludge. Bower in U.S. Pat. No. 3,449,247 discloses a process in which 
combustible materials are disposed of by wet oxidation. A mixture of air, 
water and combustible material is directed into a shaft and air is 
injected into the mixture at the bottom of the hydrostatic column. 
Lawless in U.S. Pat. No. 3,606,999 discloses a similar process in which a 
water solution or suspension of combustible solids is contacted with an 
oxygen-containing gas. Excess heat is removed from the apparatus by either 
diluting the feed with the product stream or withdrawing vapor, such as 
stream, from the system. 
Land, et al. in U.S. Pat. No. 3,464,885 (issued Sept. 2, 1969) is directed 
to the use of a subterranean reactor for the digestion of wood chips. The 
method involves flowing the material through countercurrent coaxial flow 
paths within a well bore while flowing heated fluid coaxially of the 
material to be reacted. The reactants, such as sodium hydroxide and sodium 
sulfate, are combined with the wood chip stream prior to entry into the 
U-tube which is disposed within a well bore. 
Titmas in U.S. Pat. No. 3,853,759 (issued Dec. 10, 1974) discloses a 
process in which sewage is thermally treated by limiting combustion of the 
material by restricting the process to the oxygen which is present in the 
sewage, i.e. no additional oxygen is added. Therefore, it is necessary to 
provide a continuous supply of heat energy to affect the thermal 
reactions. 
McGrew in U.S. Pat. No. 4,272,383 (issued June 9, 1981) discloses the use 
of a vertical tube reactor to contact two reactants in a reaction zone. 
The method is primarily directed to the wet oxidation of sewage sludge in 
which substantially all of the organic material is oxidized. Heat exchange 
between the inflowing and product streams is contemplated. The temperature 
in the reaction zone is controlled by adding heat or cooling as necessary 
to maintain the selected temperature. It is disclosed that when gas is 
used in the reaction, it is preferred to use a series of enlarged bubbles 
known as "Taylor bubbles". These bubbles are formed in the influent stream 
and passed downward into the reaction zone. It is disclosed that 
preferably air is introduced into the influent stream at different points 
with the amount of air equalizing one volume of air per volume of liquid 
at each injection point. While such a large amount of oxygen can be needed 
to oxidize minor organic components dissolved or suspended in a primarily 
aqueous liquid, this process is not feasible when the liquid stream is 
primarily a mixture of hydrocarbons. The presence of such large volumes of 
oxygen could result in an uncontrollable exothermic reaction. 
The above-cited patents which disclose vertical tube reactor systems 
describe the use of such systems with primarily aqueous streams. None of 
these patents describe treatment of a primarily hydrocarbon stream. 
Specifically, there is no suggestion of the thermal treatment of a 
hydrocarbon stream in a vertical tube reactor system. 
The reduction in viscosity of heavy hydrocarbon material by thermal 
treatment are well known. The thermal cracking known as "visbreaking" 
involves the treatment of hydrocarbon materials at elevated temperatures 
and pressures. Such processes are exemplified by Biceroglu, et al. in U.S. 
Pat. No. 4,462,895 (1984), Beuther, et al. in U.S. Pat. No. 3,132,088 
(1964), Taff, et al. in U.S. Pat. No. 2,695,264 (1954), and Shu, et al. in 
U.S. Pat. No. 4,504,377 (1985). Such processes are commonly used in 
refineries where there are the necessary distillation units to provide 
selective fractions to the visbreaking unit and the necessary product 
treatment facilities to handle the gaseous and low boiling products from 
the visbreaking unit. Such capital intensive processes do not readily lend 
themselves to the treatment of heavy oils at the production site to 
improve their transportability. 
Co-pending and commonly assigned application U.S. Ser. No. 771,205 filed 
Aug. 30, 1985 now abandoned, discloses a method for viscosity reduction of 
a hydrocarbon feed in the field. In this process a vertical tube reactor 
is used to create a hydrostatic pressure on the crude oil feed and the 
feed is heated by an external heat source to provide the viscosity 
reduction necessary to improve transportability of the feed from the 
production area. The temperature differential between the heat source and 
the feed is maintained small to minimize the formation of coke. 
Commonly assigned U.S. Pat. No. 4,648,964 of Leto et al. (1987) discloses 
the use of a vertical tube reactor to separate hydrocarbons from tar sands 
froth. The formation of coke deposits on the walls of the reaction vessels 
or heating surfaces has been a continuing problem. It has been disclosed 
that at higher severities there is an increased tendency to form coke 
deposits in the heating zone or furnace. Black in U.S. Pat. No. 1,720,070 
teaches that operating at lower temperatures for increased lengths of time 
provides "a much smaller amount of carbon is deposited than is deposited 
at higher temperatures." Akbar et al., "Visbreaking Uses Soaker Drum", 
Hydrocarbon Processing, May 1981, p. 81 discloses that, when there is a 
high temperature differential between the tube wall in a furnace cracker 
and the bulk temperature of the oil, the material in the boundary layer 
adjacent to the tube wall gets overcracked and excessive coke formation 
occurs. In furnace cracking this boundary layer is commonly about 
30.degree. C. to 40.degree. C. higher than the bulk temperature. 
The problem associated with excessive coke formation in the boundary layer 
stems from the fact that the coke adheres to vessel walls. This coating of 
material acts to insulate the reaction vessel which necessitates 
additional heating for sufficient viscosity reduction. The added heat 
compounds the problem by further increasing coke formation. 
In refinery operations, coke formation in viscosity reduction processes can 
be tolerated because frequent shutdowns of the process for coke removal 
are possible since storage space for the feedstock is usually available. 
However, this limitation is unacceptable in a field operation where crude 
is continually produced and must be rapidly transported. Such periodic 
shutdowns are also unacceptable with a vertical tube reactor system. In 
the co-pending application Ser. No. 771,205, the temperature difference 
between the heat source and the feed is kept small to minimize formation 
of coke. However, this process still has the limitation that the 
temperature of the wall of the reaction vessel is necessarily higher than 
the temperature of the bulk of the hydrocarbon stream. Consequently, over 
a period of time coke formation can occur which requires either a decoking 
operation or shutdown of the unit. 
Accordingly, there is a need for an improved method for reducing the 
viscosity of recovered heavy hydrocarbon material in which coking of 
reactor vessels can be substantially reduced. 
The present invention provides a method for reducing the viscosity of a 
hydrocarbon feed in which a final incremental amount of heat necessary for 
increased thermaly degradation of heavy components is provided by the 
exothermic oxidation of components in the feed. This process avoids 
undesirable coking in the reactor vessel by maintaining the temperature in 
the boundary layer of the stream near the vessel walls below coking 
temperatures. 
SUMMARY OF THE INVENTION 
The present invention comprises a process for reducing the viscosity of a 
hydrocarbon composition in which a feed stream of the composition having a 
core portion and a boundary layer is introduced into a vessel. The bulk 
temperature of the stream is increased from a first bulk temperature to a 
second bulk temperature. An oxidizing agent is introduced into the core 
portion of the stream to oxidize components in the stream and provide heat 
to the core portion of the stream to provide a bulk reaction temperature 
greater than the second temperature. The amount of the oxidizing agent is 
controlled to maintain the reaction temperature below the coking 
temperature of the feed. The reaction bulk temperature is maintained to 
produce a reaction product having a lower viscosity than the feed. 
In another embodiment, the instant invention comprises a method for 
reducing viscosity of a hydrocarbon composition using a vertical tube 
reactor. An influent stream of the hydrocarbon feed is increased from a 
first temperature to a second temperature by heat exchange between the 
influent stream and effluent product stream. At least one of the streams 
is in turbulent flow during the heat exchange. The pressure on the 
hydrocarbon feed is increased from a first pressure to a second pressure 
by a hydrostatic head. An incremental amount of heat necessary to increase 
the bulk temperature of the feed from the second temperature to a reaction 
temperature is provided by introducing an oxidizing agent into the core 
portion of the feed stream to oxidize components in the feed. 
In another embodiment, the instant invention comprises a method for 
reducing the viscosity of a hydrocarbon feed by thermal degradation of 
heavy molecular weight components of the feed at a reaction temperature. 
The feed is heated with a heat source to below a reaction temperature. The 
incremental amount of heat necessary to heat the feed to the reaction 
temperature is provided by internal combustion of a portion of the feed.