Patent Application
20080021119
For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which:
This invention provides a combination of procedures, where in one embodiment of the invention, the feedstock for an SMR is a mixture of steam and methane rich product gas generated by means of hydro-gasification of a mixture of carbonaceous material and water in an SHR. The steam is present as a result of superheating the water in the feedstock and serves as an ideal feed stream for the SMR.
The other procedure requires a method of removing impurities from the product stream from the SHR, such as fine particles of ash & char, hydrogen sulfide (H2S) and other inorganic components. These impurities must be removed in order to prevent poisoning of the catalyst used in the SMR while maintaining the SMR feed stream at its high process temperatures. Accordingly, in another embodiment of the invention, a gas cleanup unit is provided that operates at process temperatures and pressures and is located in between the SHR and SMR.
Referring to
Operating the unit above the bubbling temperature of the water allows the water to be present as steam in the gaseous product stream from the SHR, thereby enabling the process to retain most of the sensible heat in the effluent stream. A mass balance process flow diagram is shown in
Any filter capable of operating at the process temperature can be used. One such commercially available filter is a candle filter, which is well known to the art. See, for example U.S. Pat. No. 5,474,586, the disclosure of which is incorporated herein by reference. An available gas cleanup unit that can be used in this invention is what is known as a candle filter in which a series of candle-shaped filters are carried in a filter vessel. The candle filters are made of stainless steel metal frit to remove fine particulate matter (ash, inorganic salts and un-reacted char) from the gas stream. The slurry is fed into the vessel at a bottom inlet and filtrate taken out at a top outlet. Particulate matter is taken from another outlet as cake. Sulfur impurities existing in the SHR product gas, mostly in the form of hydrogen sulfide, are removed by passing the product gas through a packed bed of metal oxide sorbents in the gas cleanup unit, particulate matter being taken from a cake outlet.
Active sorbents include, but are not limited to, Zn based oxides such as zinc oxide, sold by Süd-Chemie, Louisville, Ky. Porous metal filter elements are available from Bekaert in Marietta, Ga. in the appropriate forms and sizes, such as Bekpor® Porous Media-which is made from stainless steel sintered fiber matriox with a pore size of 1. These sorbents and filter elements allow the effects of pressure drop and gas-solid mass transfer limitations to be minimized. At a pressure of 28 atm., temperatures in the range of 300° C. to 500° C. and space velocities up to 2000/hr have been used in the desulphurization of SHR product gas. The hydrogen sulfide content of the gas is diminished by means of sulfidation of the sorbents to levels low enough to avoid the deactivation of the SMR catalyst. The used sorbents in the gas cleanup unit can either be replaced with fresh sorbents or regenerated in-situ with diluted air in parallel multiple sorbent beds.
Experimental data demonstrating the successful operation of the SMR with direct feeding of the SHR product stream is shown in
The resulting effluent is a synthesis of gases rich in hydrogen, carbon monoxide, and steam. Approximately one third of the hydrogen produced in the SMR is recycled back to the HGR. Consequently, no outside source of hydrogen is needed to maintain steady state operation. The HGR and SMR processes, therefore, may be considered to be chemically self-sustaining. The remaining synthesis gas is then available for the production of fuels and process heat.
In an embodiment of the invention, the synthesis gas is fed to a Fischer-Tropsch reactor in a process that can produce a zero-sulfur, ultrahigh cetane value diesel-like fuel and valuable paraffin wax products. The absence of sulfur enables low pollutant and particle emitting diesel fuels to be realized. Useful by-products can be produced, foe example, purified water, which can be re-cycled to create the slurry feed into the process. The Fischer-Tropsch reactions also produce tail gas that contains hydrogen, CO, CO2, and some light hydrocarbon gases. Hydrogen can be stripped out of the tail gas and recycled either to the HGR or the Fischer-Tropsch reactor. Any small amounts of other gases such as CO and CO may be flared off.
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process and apparatus described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes and apparatuses, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include such processes and use of such apparatuses within their scope.
