In an earlier report, made some years ago:
Exxon Co-Gasifies Coal and Carbon-Recycling Biomass | Research & Development | News; concerning: "United States Patent Application 20100083575 - Co-gasification Process for Hydrocarbon Solids and Biomass; April, 2010; Inventors: Ramesh Varadaraj, et. al., NJ; Assignee: ExxonMobil Research and Engineering Company, NJ; Abstract: A process for the co-gasification of carbonaceous solids (coal) and biomass in which the biomass material is pyrolyzed to provide a biomass pyrolysis oil and biomass char or coke which are then mixed with the carbonaceous solid to form a slurry. This slurry is then heated if necessary to achieve a viscosity which can be processed conveniently in the gasifier. The heat required for pyrolyzing the biomass can conveniently be obtained from the heat exchanger used to cool the hot synthesis gas product emerging from the gasifier. Claims: A process for forming a slurry feed for the gasification to synthesis gas of solid carbonaceous particles and solid biomass ... wherein the solid carbonaceous particles comprise coal (or) a coke derived from coal (and) wherein the biomass comprises biological matter selected from wood, plant matter, municipal waste, green waste, byproducts of farming or food processing waste, sewage sludge, black liquor from wood pulp, and algae";
we saw that such a formidable supplier of the world's liquid hydrocarbon fuels as ExxonMobil had been at work improving processes wherein our abundant USA Coal and all sorts of renewable organic materials, most of them outright wastes or otherwise of little value, could be transformed together into a hydrocarbon synthesis gas blend of Carbon Monoxide and Hydrogen suitable for chemical, catalytic condensation, as via for example the now somewhat generic Fischer-Tropsch synthesis, into liquid hydrocarbon fuels.
ExxonMobil themselves say, as excerpted from deep within the Disclosure of "Application 20100083575":
"One established route to the production of hydrocarbon liquids is the gasification of carbonaceous materials followed by the conversion of the produced synthesis gas to form liquids by processes such as Fischer-Tropsch and its variants. In this way, solid fuels such as coal ...may be converted to liquids. Gasification can proceed from just about any organic material, including biomass, paper, plastic and rubber waste (and) may be one of the best ways to produce clean liquid fuels ... from coal".
In fact, there are other implications imbedded within that Disclosure that have more lately been built upon by other major "players" in the petroleum industry. And, before addressing those further developments, we wanted to document that the United States Government recently confirmed the validity of ExxonMobil's advanced synthesis gas generation technology, wherein Coal and renewable organic wastes, together, are transformed into a reactive blend of Carbon Monoxide and Hydrogen suitable for further processing to manufacture liquid hydrocarbon fuels and other chemicals.
Comment is inserted within and follows rather brief excerpts from the initial link in this dispatch to the recent:
"United States Patent 9,057,031 - Co-Gasification Process for Hydrocarbon Solids and Biomass
Date: June 16, 2015
Inventors: Ramesh Varadaraj, et. al., NJ;
Assignee: ExxonMobil Research and Engineering Company, NJ;
Abstract: A process for the co-gasification of carbonaceous solids (coal) and biomass in which the biomass material is pyrolyzed to provide a biomass pyrolysis oil and biomass char or coke which are then mixed with the carbonaceous solid to form a slurry. This slurry is then heated if necessary to achieve a viscosity which can be processed conveniently in the gasifier. The heat required for pyrolyzing the biomass can conveniently be obtained from the heat exchanger used to cool the hot synthesis gas product emerging from the gasifier.
(We've previously documented that heat energy can be recovered from "hot synthesis gas", as above; and, that is one of the implications being built upon by other developers of Coal conversion technology, as indicated in our introductory comments and as will be further addressed in additional reports to follow.)
Claims: A process for forming a slurry feed for the gasification to synthesis gas of solid carbonaceous particles and solid biomass ... wherein the solid carbonaceous particles comprise coal (or) a coke derived from coal (and) wherein the biomass comprises biological matter selected from wood, plant matter, municipal waste, green waste, byproducts of farming or food processing waste, sewage sludge, black liquor from wood pulp, and algae.
Background and Field: The present invention relates to the production of synthesis gas by gasification of solid carbonaceous fuel sources such as coal ... and, more particularly, to the co-gasification of such fuels sources with biomass.
The use of liquid hydrocarbon fuels on an enormous scale for transportation has led to the depletion of readily accessible petroleum reserves in politically stable regions and this, in turn, has focused attention, economically, technically and politically on the development of alternative sources of liquid fuels.
One established route to the production of hydrocarbon liquids is the gasification of carbonaceous materials followed by the conversion of the produced synthesis gas to form liquids by processes such as Fischer-Tropsch and its variants.
In this way, solid fuels such as coal ... may be converted to liquids.
(With regards to the above, and for some exposition of the Fischer-Tropsch process, see, for one example:
"United States Patent 9,011,788 - Advanced Fischer Tropsch System; 2015; Inventors: Joseph Hartvigsen, et. al., Utah and Idaho; Assignee: Ceramatec, Inc., Salt Lake City";
and which report contains links to additional information concerning the Fischer-Tropsch process, such as:
"United States Patent 8,557,880 - Multi-stage Adiabatic Method for Performing the Fischer-Tropsch Synthesis; 2013; Inventors: Ralph Schellen, et. al., Germany and Texas; Assignee: Bayer Intellectual Property GmbH, Germany".)
Coal gasification is well-established, being used in many electric power plants. Gasification can proceed from just about any organic material, including biomass, paper, plastic and rubber waste. Most importantly, in a time of unpredictable variations in the prices of electricity and fuels, gasification systems can provide a capability to operate on low-cost, widely-available coal reserves.
Gasification may be one of the best ways to produce clean liquid fuels and chemical intermediates from coal ... .
Four basic types of gasifiers are currently available for commercial use: counter-current bed, co-current bed, fluidized bed and entrained flow. In the counter-current fixed bed ("up draft") gasifier the gasification agent (steam, oxygen and/or air) flows in counter-current configuration through a descending bed of the carbon-containing fuel with the ash removed dry or as a slag. The co-current bed gasifier is similar to the counter-current type, but the gasification agent gas flows downwards in the same direction as the fuel. In the fluidized bed reactor, the fuel is fluidized in the gasification agent. In the entrained flow gasifier a dry pulverized solid, an atomized liquid fuel or a fuel slurry is gasified with oxygen or air in co-current flow and the gasification reactions take place in a dense cloud of very fine particles. Most coals are suitable for this type of gasifier because of the high operating temperatures and because the good contact achieved between the coal particles and the gasifying agent. Entrained flow gasifiers have been demonstrated as highly effective units for the gasification of coal and other carbonaceous fuels ... .
Biomass gasification is expected to play a significant role in a renewable energy economy, because biomass production removes CO2 from the atmosphere and the net effect of processing the biomass has a net lower CO2 generation as compared to fossil fuels. While other biofuel technologies such as biogas and biodiesel are also beneficial fuel sources for reducing carbon emissions, gasification runs on a wider variety of input materials, can be used to produce a wider variety of output fuels, and is an extremely efficient method of extracting energy from biomass. Biomass gasification is therefore one of the most technically and economically viable energy possibilities for a carbon emission constrained economy.
The integration of biomass gasification in existing large coal-fired power stations is being investigated in different countries. Integration is currently more practical than stand-alone biomass gasification due to the greater flexibility in response to annual and seasonal fluctuations in biomass availability and the lower investment costs for the biomass gasification unit.
Co-gasification or co-firing of coal and biomass can be carried out via a number of processes: Co-feeding biomass and coal to the gasifier as a mixture. Co-feeding biomass and coal to the gasifier using separate gasifier feed systems. Pyrolizing the biomass followed by co-feeding pyrolysis char and coal to the gasifier. Gasifying the biomass and coal in separate gasifiers followed by a combined fuel gas clean-up.
There are, however, some drawbacks of co-firing/co-gasification of biomass and coal. Biomass has a high moisture content that results in low calorific value of the fuel, low bulk density compared to coal, low ash melting point, chemical composition with potentially high chlorine content, as well as hydrophilic and non-friable characteristics. Additionally, co-firing/co-gasification faces the possibility of decreases in overall efficiency, deposit formation (slagging and fouling), agglomeration, corrosion and/or erosion, and ash utilization. The importance of the problems depends upon the biomass/coal ratios and the quality of the biomass used as a feedstock; especially in direct co-firing systems without dedicated biomass infrastructure. During co-gasification, ash-forming species from biomass may either leave the process as bottom ash, or become released as fly ashes and flue dust. The fate of these species is dependent on their physical characteristics, the chemistry, the equipment design and the combustion conditions. These problems are further complicated by the presence of alkali metals (K, Na), alkaline earth metals (Ca, Mg), silicon, chlorine and sulphur in the ashes and can lead to reduced efficiency, capacity and availability of the facilities and therefore increased power cost.
Reburning, a combustion modification technology originally introduced by the John Zink.TM. Company, provides one way to integrate biomass and coal power generation minimizing the problems described above. In the reburning process, the biomass is pre-gasified and the resulting gas is used as reburn fuel in a coal-fired boiler that uses the fuel as a reducing agent to remove NOx from the combustion products. This process has the advantage of keeping undesired components, such as alkaline, chlorine, and heavy metal compounds commonly associated with biomass, away from the coal-fired boiler and, in addition, the environmental aspects of air pollution, as well as operational and economical problems, such as slagging, fouling, corrosion, and contamination of ash, are avoided. During the gasification of biomass, the solid feedstock is separated into fuel gas and a solid residue. The aim of the separate gasification of biomass is to bond the problem-causing components into the solid pyrolysis residue in order to avoid operational problems within coal-fired boilers.
With entrained flow gasifiers operating with coal-biomass mixture fuels, one problem is the delivery of the feedstock mixture of carbonaceous solids and biomass to the gasifier. Different types of entrained flow gasifiers feeding solid coal or coal-water slurries with wood chips have been reported to encounter feedstock delivery as one of the hurdles to continuous running. Failure of slurry pumps and the clogging of lock hoppers have been observed. It is therefore desirable to develop a way of feeding biomass to entrained flow gasifiers which does not suffer from these disadvantages.
Summary: We have now developed a process for the co-gasification of carbonaceous solids (such as coal and coke) and biomass which enables the biomass to be fed into the gasifier using existing types of feed transfer and feed injection equipment without encountering the delivery problems commonly associated with handling the solid bio-materials.
According to the present invention, the biomass material is pyrolyzed to provide a biomass pyrolysis oil and biomass char which are then mixed with the hydrocarbon solid to form a slurry. This slurry is then heated if necessary to achieve a viscosity which can be processed conveniently in the gasifier.
In a specific embodiment, the present invention comprehends a process for the co-gasification of solid carbonaceous particles (such as coal and coke) and biomass which comprises the steps of:
a) pyrolyzing a biomass to provide a biomass pyrolysis oil and biomass char;
b) mixing the biomass pyrolysis oil, biomass char and solid carbonaceous particles to form a complex plastic slurry of pumpable viscosity ... ;
c) pumping the slurry into the mixing zone of a gasifier where it is mixed with an oxygen containing gas;
d) passing the mixture of the slurry and oxygen containing gas through a feed injector into a gasifier reactor; and:
e) gasifying the mixture.
In a preferred embodiment, the heat required for pyrolyzing the biomass can conveniently be obtained from the heat exchanger used to cool the hot synthesis gas product emerging from the gasifier.
The present invention provides a route for converting carbonaceous solids, usually hydrocarbon solids, to synthesis gas which can then be used to make liquid transportation fuels such as gasoline, road diesel, aviation turbine fuels as well as lubricants.
The carbonaceous solid fuel source is used in combination with biomass to secure the advantages of biomass conversion. The carbonaceous solid is preferably coal (and) coke derived from coal may also be used in the process in lieu of or in conjunction with coal.
Most commonly, biomass refers to plant matter but also includes animal matter. Most typically, biomass will be comprised of plant matter grown for use as biofuel, but it also includes discarded plant or animal matter which has been primarily used for other purposes such as production of food, production of fibers, chemical manufacturing or heat production.
Biomass may also include biodegradable wastes that can be burnt as fuel including municipal wastes, green waste (the biodegradable waste comprised of garden or park waste such as grass or flower cuttings and hedge trimmings), byproducts of farming including animal manures, food processing wastes, sewage sludge, black liquor from wood pulp or algae.
Pyrolysis is slightly endothermic and various methods have been proposed to provide heat to the reacting biomass particles, but the preferred method is circulating fluidized beds: biomass particles are introduced into a circulating fluidized bed of hot sand, coke or other solid particles. Gas, solid particles and biomass particles move together, with the transport gas usually being a recirculated product gas, although it may also be a combustion gas. High heat transfer rates from the solid particles ensure rapid heating of biomass particles and ablation is stronger than with regular fluidized beds. A fast separator separates the product gases and vapors from the solid particles and char particles. The solid particles are reheated in a fluidized burner vessel and recycled to the reactor.
The coal may be of any rank suitable for gasification and this may be lignite, sub-bituminous, bituminous or even anthracite. To form a slurry in the selected oil, the coal/coke will preferably be reduced to an average particle size (by weight) from about 0.01 millimeters (mm) to about 10 mm, and even more preferably in most cases, and average particle size from about 0.05 to about 5 mm. Conventional slurrying techniques and equipment may be utilized. The ratio of solids (coal/coke plus char) and oil is selected to provide a complex plastic slurry of the pyrolysis biomass oil, the biomass char and the carbonaceous material which can be handled readily and fed into the gasifier. In preferred embodiments of the present invention, the ratio (wt/wt) of coal/coke to bio-oil will be from about 80:20 to about 20:80, and even more preferably from about 60:40 to about 40:60.
Additional fuel sources may be added to the slurry if desired, for example, waste polymer materials such as the polyolefins, mainly polyethylene or polypropylene, polyesters, polyamides or even such waste materials as rubber tires and dried sewage sludge. In all such cases, the amount of the additional fuel source should be controlled so as to maintain the viscosity of the slurry at a suitable value for pumping. Normally, the amount of added fuel material will not exceed 10 wt. percent of the total slurry.
EXAMPLE: Experiments using biomass oil and coal were conducted. Pocahontas (bituminous) coal and pyrolysis bio-oil derived from pyrolysis of wood chips (from Biomass Technology Group.TM., Netherlands) were used".
The above final passage seems a good place to close, so that we can point out the "Pocahontas (bituminous) coal" used by ExxonMobil in the development of this Coal and biomass gasification technology, which generates a "synthesis gas which can then be used to make liquid transportation fuels such as gasoline, road diesel, aviation turbine fuels as well as lubricants", as seen in:
(e-WV | Pocahontas No. 3 Coal Seam; "Covering some 900 square miles in Mercer, Wyoming, and McDowell counties in West Virginia, and neighboring Tazewell County, Virginia, the rich Pocahontas No. 3 coal seam was first mined by Jordan Nelson, whose backyard coalbank eventually attracted serious interest from the Philadelphia founders of the Norfolk & Western Railway. The N&W completed its line to the Pocahontas, Virginia, location of Nelson’s coalbank in March 1883 and began the rapid industrialization of the region. (The) Pocahontas Coalfield has been one of the most productive in the nation ... and was the chosen fuel of the U.S. Navy during the age of steam. ... The exploitation of the Pocahontas No. 3 seam transformed southern West Virginia, creating the cities of Bluefield, Bramwell, Keystone, Northfork, Kimball, Welch, and Gary, and numerous coal company towns. The huge demand for miners in the labor-intensive early years created great racial and ethnic diversity. The U.S. Coal Commission’s 1923 survey showed that 20,000 of West Virginia’s 92,000 miners worked in the Pocahontas region. Twenty percent were foreign-born immigrants, 33 percent African-American, and the remainder native-born whites";
is, indeed, pretty much a West Virginia Coal, as per the title of this dispatch. And, that West Virginia Coal can be gasified in combination with, for instance, European "pyrolysis bio-oil derived from pyrolysis of wood chips (from Biomass Technology Group.TM., Netherlands", as well as with "waste polymer materials ... or even such waste materials as rubber tires and dried sewage sludge", and be made thereby to form a "synthesis gas", which syngas can then be used "to form liquids by processes such as Fischer-Tropsch and its variants", and thus represents "one of the best ways to produce clean liquid fuels""such as (non-OPEC, all-USA) gasoline".