|Overview of the Chattanooga Process. Click to enlarge.|
Chattanooga Corp has successfully tested its upgrading process (the Chattanooga Dry Process) to convert oil shale and oil sand to high-grade, low-sulfur, synthetic crude oil on Colorado oil shale. A major focus of the company earlier had been oil sands production in Canada.
Upgrading is a key step in the converting the bitumen in oil sands or the kerogen in oil shale (as well as in the processing of very heavy crude oils) into useful, lighter-grade synthetic oil. The Chattanooga process is designed with a number of benefits in mind: greater process efficiency, the emission of fewer greenhouse gases, elimination of water pollution and greatly reduced water usage, among others.
Essentially, the process treats dry oil sand or shale without prior enhancement in a specially designed reactor that is heated and pressurized by recycled hot hydrogen, which is in turn partly replenished as reactions take place.
The approach thus avoids the use of the physical and chemical pre-processing units used to upgrade wet tar sand and produces less stack gas and substantially no coke.
The Chattanooga Process, in brief, performs the following:
Crushed tar sand or oil shale (less than one-inch in size) is mixed with cooled hydrogen and fed into a reactor which operates at a pressure of about 600 psi.
Once in the reactor, the sand or shale mixture is met by a second stream of hydrogen, emerging from a heater at about 1,500º F. The flow rate and velocity of the hydrogen are sufficient to fluidize the sand or shale, and to take it to the desired reaction temperature of between 900º F and 1,000º F.
The sand or shale reacts with the hydrogen mixture in the fluidized bed by endothermic hydrocracking and exothermic hydrogenating reactions.
Reaction products include the spent sand or shale and an overhead product stream that contains hydrogen, hydrogen sulfide, sulfur gases, hydrocarbons, ammonia, fines (sand particles and clay) and vaporous products. Solids are trapped by cyclone separators, where they are again put to the fluidized bed. A heat exchanger transfers product stream heat back to heat the second hydrogen stream.
A condenser further lowers the heat of the product stream. The stream now contains liquid and gas fractions, and moves to a separator where the gas fraction is removed, sent to an amine scrubber, after which the scrubbed and recycled hydrogen is sent back to the reactor. The volume of recycled hydrogen to fresh, replenishing hydrogen is about 21:1, but can vary from about 15:1 to 26:1.
The liquid fraction is removed as low-sulfur, synthetic oil—good for refining into transportation fuels.
Although currently still not yet in pilot plant stage, the Chattanooga process (which is one of several more technologically radical approaches to upgrading) offers benefits compared to the more conventional processes for treatment and upgrading.
Dry processing of resource material eliminates water pollution and greatly reduces water usage.
Greenhouse gas production is substantially reduced—by 50% in early tests of the technology by Canada’s National Center for Upgrading Technology (NCUT). (Less than 150 pounds of CO2 per barrel in the current design compared to close to 300 pounds per barrel with conventional upgrading technologies.)
The plant footprint is smaller than facilities using current technologies.
Proven commercial processes are used to remove 99.8% of all sulfur as elemental sulfur.
The process produces the plant’s steam requirements for motive and electric power. Waste heat is also recovered throughout the process using commercially proven systems.
Chattanooga will next test its capability with Kentucky oil shale.