Hydrogen Generation From Residuum
Refineries in the U.S. are processing increasingly heavy sour crudes that contain metals, sulfur, and high molecular weight aromatic hydrocarbons. Many sour crude oils originate in the Western Hemisphere, including heavy crudes from Venezuela, southern California, and the oil sands in Canada. Processing and upgrading these heavy feedstocks requires considerable hydrogen, but unfortunately revamping or installing new hydrogen capacity with conventional technologies such as steam methane reforming or petroleum coke gasification can be prohibitively expensive.
TDA Research Inc. is developing a new technology that will allow hydrogen to be produced in refineries at a cost that is considerably lower than hydrogen produced from conventional technologies or purchasing hydrogen from a third party. This technology converts “bottom of the barrel” residuum into hydrogen. In TDA’s process, residuum is steam reformed over nickel based catalysts to produce hydrogen without catalyst deactivation and without the need for an oxygen plant; this greatly expands the range of feedstocks that can be used to generate hydrogen. We can steam reform residuum over nickel based catalysts without catalyst deactivation because the system uses a fluidized bed with periodic catalyst regeneration with air. The process is essentially chemical looping steam reforming. Residuum and steam are fed into a fluidized bed reactor containing Ni steam reforming catalyst at 870°C to generate syngas (CO + H2). Because the process uses contact times on the order of minutes, not enough carbon builds up on the catalyst to cause irreversible deactivation. The catalyst is then regenerated by burning the coke with air. In the laboratory, this is done using a single reactor with a nitrogen purge between reforming and regeneration steps; however, in an industrial setting, a circulating fluidized bed system would be used that would be somewhat similar to the early ESSO catalytic cracking reactors. Burning off the coke in the regenerator reheats the catalyst to about 900°C for the next reforming step (a small amount of residuum, heavy oil or other fuel can be added to the regenerator to increase the temperature if there is not enough coke on the catalyst). The hot nickel catalyst returning to the reforming reactor is present as NiO but is quickly reduced to active nickel metal by the hydrocarbons in the feed.
TDA has conducted an extensive series of tests with atmospheric tower bottoms (ATB) and two types of vacuum tower bottoms (VTB). Both VTB samples were solids at room temperature and were heated to be able to feed them into the laboratory reactor. With ATB, it was possible to operate with steam to carbon (s/c) ratios as low as 5. VTB required somewhat higher steam/carbon ratios (6-8). No catalyst deactivation has been observed with ATB or the lighter of the two VTB samples in that no change in product selectivity or yield was observed over 100+ cycles. We are currently investigating other catalysts and a very heavy VTB as well as conducting long term testing (hundreds of cycles).
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