Patent Application
20080040975
Before proceeding with the detailed description of the invention by making use of the drawings, it is to be noted that for the sake of clarity reference will be made to the numerals and to the words to represent the various components and process streams.
Referring to
Before describing the operation of the instant invention, it is to be noted that the various streams incorporated in the method would include pressure boosting and pressure let-down equipment, such as compressors, expanders, and miscellaneous valves as required, depending upon the prevailing conditions to enable the navigation of the flow of each stream. Since the use of such equipment is common practice in the field of chemical engineering and is known in the art to which this invention pertains, the Applicant has obviated the inclusion of such equipment in the drawings, even though such equipment will be used in the application of the instant invention.
Assuming that the process is already at steady state and referring to both
Hot char stream 31, the second part of the char from stream 24, is directed to the activator denoted by numeral 63 for converting the hot char into activated carbon by means of steam-stream 33; stream 66 denotes the off-gas from activator 63; stream 55 represents the activated carbon discharged from activator 63. During the activation of the hot char with steam, it loses temperature by virtue of the water-gas reaction that takes place.
Activated carbon stream 55 is, in turn, further divided into sub-stream 58 and sub-steam 61, with sub-stream 58 being fed into reheater 64 where the temperature of the activated carbon is raised by making use of the elevated temperature of the hot, raw lean gas-stream 67, by directly contacting the activated carbon contained in reheater 64. The partially cooled raw lean gas leaves reheater 64 as stream 25 and is directed to lean gas cleanup 18. In both cleanup systems 12 and cleanup 18, the sulfur in the gases is removed, and it leaves cleanup 12 via stream 28 and cleanup 18 via stream 29; these two sulfur streams join to form stream 44.
The cleaned rich gas which essentially is CO+2H2 leaves cleanup 12 via stream 46 and is directed to methanol plant 13 where the rich gas is converted to methanol which, in turn, is directed as stream 47, to gasoline plant 14 where the methanol is converted to gasoline via Exxon Mobil's process known as “MTG” for short. The clean lean gas which essentially is N2+CO leaves cleanup 18 via stream 30 to which CO—stream 48, is added to form stream 32 which fuels gas turbine 15; air to combust stream 32 is furnished by stream 52 which is compressed prior to entering the combustion chamber (not shown) of gas turbine 15. The flue gas exhausting from the gas turbine is passed through heat recovery steam generator 16 to raise steam which is directed to steam turbine 17 via stream 50. Both gas turbine 15 and steam turbine 17 are each followed by a generator (not shown) to generate electric power most efficiently via the combined cycle mode which power leaves as streams 37 and 38, respectively, to form stream 39. The flue gas leaving heat-recovery steam generator 16, which is made up of nitrogen and carbon dioxide (N2+CO2) is denoted by stream 34. A portion of the steam generated in heat-recovery steam generator 16 is withdrawn as a side stream which is denoted by numeral 36; this side stream of steam together with H2 stream 49 form stream 53 which is directed to high-temperature electrolysis system 19 in order to increase the efficiency of H2 generation. It is to be noted that side stream 36 may also be withdrawn from steam turbine 17.
An alternating electric current stream denoted by numeral 40 is directed to rectifier 21 where it is converted to direct electric current to form streams 42 and 43 which are introduced into electrolysis system 19 in order to electrolyze the steam contained in stream 53 to yield a larger output of H2-stream 56 and also producing O2 as stream 22; this larger output of H2 is directed to synthesis system 20, while the O2, after being compressed (not shown), is directed to pyrolysis chamber 10 as stream 22.
Referring now to the flue gas, stream 34 (N2+CO2) is split to create a bleed of flue gas to maintain system balance denoted by numeral 35, to result in stream 57 which joins H2 stream 45 (the net H2 produced in electrolysis system 19) to form stream 65. The activated carbon (C)—stream 68 and the flue gas (N2+CO2) together with the H2—stream 65 are respectively introduced into urea plant 20 to produce urea (CONH2)2)+CO as stream 69. The CO, as stream 48, is separated from stream 69 to result in the formation of urea as stream 59 whence this stream joins activated carbon sub-stream 61 to form a super-fertilizer for export denoted by stream 62.
It is to be noted that the hot activated carbon may be reacted with the flue gas by itself in a reactor to form CO and cyanogen (C2N2), and the H2 may then be added in a subsequent reaction to form the urea. Further, the formation of urea may also occur via the ammonia (NH3) route by reacting N2 with 3H2 to make 2NH3 and subsequently reacting the 2NH3 with CO2 to form CO(NH2)2+H2O, the conventional method of making urea.
The step of making urea may be obviated by making use of the method to make activated carbon from a portion of the char, activating such portion, and sequestering it in the soil to enhance it by introducing cellular structure to store plant nutrients and to provide time release of such nutrients to result in causing the vigorous growth of plant life.
In summation, it is submitted that the method described herein for maximizing the benefits derived from a carbonaceous material such as coal which contains sulfur in an environmentally acceptable manner while co-producing liquid fuel, electric power and urea is comprised of pyrolyzing the coal with oxygen to produce a raw hydrogen (H2) rich gas and a hot char which is cellular in structure and substantially composed of carbon (C). The hot char so produced is divided into two streams, with the first stream being directed to a gasifier that is air blown to make a raw lean gas which is made up of nitrogen and carbon monoxide (N2+CO) and a second stream being activated with steam to produce activated carbon that is further divided into a “first” sub-stream of activated carbon and a “second” sub-stream of activated carbon whose use will be described hereinafter.
Subsequent to the cleaning of the H2 rich gas and the lean gas, including the removal of mercury from these gases, the cleaned H2 rich gas (syngas) may be converted to one or more chemicals, but preferably to methanol which, in turn, is converted to a transportation fuel such as gasoline, a most valuable liquid fuel. The cleaned lean gas fuels a gas turbine that is part of a combined-cycle system to generate electric power most efficiently by virtue of its large N2 content which contributes a large mass flow of gases through the gas turbine while exhausting an off-gas (flue gas) made up of N2+CO2. This flue gas which is reacted with activated carbon and H2, is synthesized with 2H2 to produce urea which is characterized chemically as NH2.NH2.CO or CO(NH2)2 plus CO. Alternatively, the formation of the urea may be the conventional route of making urea by first forming ammonia (NH3) and, in turn, reacting two molecules of NH3 with CO2 to form CO(NH2)2, and H2O as by-product; in this case, the N2 in the flue gas is separated from the CO2 prior to reacting with the NH3.
Preferably during off-peak periods, the excess of the electric power that can be generated for which there is no demand, such power is utilized to electrolyze steam in a high-temperature electrolysis system to generate H2 and O2, with the H2 produced being the source for the H2 needed in synthesizing the N2+CO2 (with the aid of hot activated carbon) into urea. Preferably, some of the H2 produced via electrolysis is recycled with the steam fed to the electrolysis system to enhance the production of H2. The O2 which is co-produced via electrolysis is used in the pyrolysis of the coal mentioned above.
The “first” sub-stream of activated carbon serves to activate N2 in the flue gas (N2+CO2) to make possible the formation of urea according to the following chemical reaction: (N2+CO2)+C+2H2→CO+CO(NH2)2, wherein the CO is separated from the urea and is added to the lean gas to become part of the fuel for the gas turbine mentioned above.
The urea so formed is mixed with the “second” sub-stream of activated carbon, mentioned above, to produce a super-fertilizer which is put into the soil, not only for the sequestration of carbon (C) directly and carbon dioxide (CO2) indirectly via the urea, but also to provide storage for plant nutrients in the abundant cellular structure of the activated carbon, thus:
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11506939 | Aug 2006 | US |
| Child | 11605695 | US |
