United States Patent Application: 0090261296
We have many times described and made reference to the Fischer-Tropsch process, wherein a synthesis gas, composed ideally and primarily of Carbon Monoxide and Hydrogen generated by the gasification of Coal, is catalytically condensed into a mixture of gaseous and liquid hydrocarbons.
Further, we have documented that Steam can be employed as one of the agents of the initial Coal gasification, with some sophistication having been developed in such use of Steam, which helps to maximize the generation of Carbon Monoxide, as opposed to less-desirable Carbon Dioxide; but, which also, more importantly, serves to provide an additional source of Hydrogen for the synthesis gas, which enables the conversion of more of the Coal's original Carbon content into a wider range of more valuable hydrocarbons.
However, such use of purpose-generated Steam does have drawbacks.
Some energy must be expended to produce it; and, since it doesn't support the partial oxidation of Coal in the gasification process nearly as well as Oxygen or Air, it's use as a medium of gasification is restricted.
Methods, as we will document in a coming report or two, have been developed to maximize the efficiency of using Steam directly in the Coal gasification process; but, those methods are somewhat complicated and could involve interruptions, or discontinuities, in production; and, some additional costs.
Herein, from the world's current major commercial, industrial operator of Coal-to-Liquid factories, South Africa Synthetic Oil Limited, we have a fairly sophisticated take on how to go about getting the necessary Hydrogen into the synthesis gas through the use, not of energy-demanding purpose-generated Steam; but, of Steam, Water Vapor and of plain Hot Water that are, or can be, all created as by-products of the Coal gasification and hydrocarbon synthesis processes themselves.
The Steam can be efficiently generated, for inclusion in the gasification medium, through the capture and use of heat evolved during the exothermic Fischer-Tropsch catalytic condensation of the Coal-derived synthesis gas into hydrocarbons, and transfer of that heat to a boiler.
Water can also be heated when the Syngas is, as it apparently must be, cooled down immediately after being formed from the Coal, and before being directed into the hydrocarbon synthesis catalyst.
And, Water Vapor and Hot Water are actually co-produced, along with various alcohols and, potentially, depending on choice of catalysts, some light hydrocarbon gases, such as Methane, when the syngas is converted into the primary product liquid hydrocarbons.
The Steam, Water Vapor and Hot Water herein can all, thus, be considered simply as useful by-products of the Coal conversion process.
It ain't really as complicated as we make it sound, as seen in our excerpts, with comment appended, from the link to:
"United States Patent Application 20090261296 - Method for the Production of Synthesis Gas
Date: October, 2009
Inventor: Werner Siegfried Ernst, South Africa
Assignee: Sasol Technology Limited, Johannesburg
Abstract: A method for the production of synthesis gas includes humidifying an oxygen-containing stream by contacting the oxygen-containing stream with a hot aqueous liquid to produce a humidified oxygen-containing stream, and feeding the humidified oxygen-containing stream into a gasifier in which a carbonaceous material is being gasified, thereby to produce synthesis gas.
Claims: A method for the production of synthesis gas, the method including producing an oxygen-containing stream in an air separation unit; humidifying the oxygen-containing stream by contacting the oxygen-containing stream with a hot aqueous liquid to produce a humidified oxygen-containing stream, humidifying the oxygen-containing stream including heating the oxygen-containing stream by directly contacting the oxygen-containing stream with the hot aqueous liquid; and feeding the humidified oxygen-containing stream into a low temperature non-slagging gasifier in which a carbonaceous material is being gasified, thereby to produce synthesis gas, the gasifier forming part of a complex for Fischer-Tropsch hydrocarbon synthesis and which produces reaction water, with the oxygen-containing stream being contacted with said reaction water, and in which the reaction water includes oxygenated hydrocarbons, with at least some of these oxygenated hydrocarbons being taken up by the oxygen-containing stream during humidification.
(Note: The co-produced "oxygenated hydrocarbons", as above, would include various alcohols, such as Methanol and Ethanol, which can, as we've earlier documented, and as herein, be recycled back into the synthesis gas generation process, where they provide a beneficial effect, especially as conveyors of Hydrogen back into the system. They could also, of course, be recovered as valuable and versatile products, with many uses, in and of themselves.)
The method ... in which the humidified oxygen-containing stream being fed into the gasifier has a water concentration of at least 3% by volume (and, up to) 90% by volume.
(Depending, we suppose, on the final desired mix of alcohol and hydrocarbon products.)
The method ... in which the oxygen-containing stream is contacted with water used as cooling water.
The method ... in which the oxygen-containing stream is contacted with water used to cool reaction product from a hydrocarbon synthesis stage.
The method ... in which the water is reaction water.
The method ... which includes feeding steam to the gasifier as a gasification agent, the steam and the humidified oxygen-containing streams being combined before being fed to the gasifier.
The method ... in which the gasifier is a fixed bed dry bottom gasifier, with the humidified oxygen-containing stream, steam and solid carbonaceous material being fed into said gasifier so that the carbonaceous material is gasified in the presence of oxygen and steam to produce synthesis gas ... .
Description: This invention relates to a method for the production of synthesis gas, and to a method of operating a fixed bed dry bottom gasifier.
There are various gasification technologies available to gasify a carbonaceous material, such as coal, to produce synthesis gas. With suitable coal used for fixed bed dry bottom gasification technology, less oxygen and coal are required for the production of a particular effective amount of synthesis gas than with high temperature gasification technologies, especially for coal containing a lot of inorganic matter and inherent moisture. (Effective synthesis gas is defined as that part of a synthesis gas that can potentially be converted into hydrocarbon product given the chosen product slate and conversion technology). However, the use of steam as gasification or moderating agent is higher when fixed bed dry bottom gasification technology is employed compared to other gasification technologies. If the coal required for steam production is included, the benefit provided by fixed bed dry bottom gasification technology of using less coal, compared to alternative high temperature gasification technologies, to produce an effective amount of syngas, is reduced or nullified.
According to one aspect of the invention, there is provided a method for the production of synthesis gas, the method including: humidifying an oxygen-containing stream by contacting the oxygen-containing stream with a hot aqueous liquid to produce a humidified oxygen-containing stream; and feeding the humidified oxygen-containing stream into a gasifier in which a carbonaceous material is being gasified, thereby to produce synthesis gas.
The term "gasifier" in this specification is used in the conventional sense, i.e. an apparatus for converting a hydrocarbonaceous feedstock that is predominantly solid (e.g. coal) ... into synthesis gas (and, wherein) steam may ... be used ... to adjust the H2/CO ratio of synthesis gas produced by a gasifier.
The invention makes it possible to increase the amount of steam obtained from current coal-based hydrocarbon synthesis plants (e.g. coal to liquids or CTL plants) without the addition of boilers to generate steam from low level heat. For new plants, the capacity of coal-fired boilers can be decreased, resulting in less CO2 production and thus a more competitive gasification footprint. The advantages will be lower capital cost and a reduced environmental footprint for coal-based hydrocarbon synthesis plants ... ."
------------
The full Disclosure is much more detailed and lengthy than our already over-long excerpts.
But, the concept is simple enough:
Heat energy generated in the Coal conversion process, both in the gasification and catalytic condensation stages, is used to collect and heat Water, some of which is, as well, a by-product of the hydrocarbon synthesis reaction process appearing in the form of Steam and Water Vapor; and, to combine that heated H2O with the medium, Air or concentrated Oxygen, with which the Coal is first gasified.
The gasification medium is, simply, as Sasol puts it, "humidified"; with the end result being an increase in the Hydrogen content of the synthesis gas, and, we are led to conclude, a fuller and more efficient conversion of the Carbon content of the Coal into more desirable, and more valuable, hydrocarbons in such "coal-based hydrocarbon synthesis plants" that, subsequently, have a "lower capital cost and a reduced environmental footprint".