Cavern Gasification
I've filed a provisional patent application today on cavern gasification. Below is the description:
Abstract of the invention
Cavern gasification uses an underground gasifier in which the gasification pressure is less than the local lithostatic pressure. The gasification chambers of prior art gasifiers are usually a major portion of the cost of any prior art gasifier. Normally the gasifier is quite expensive because it operates at high- temperature and high-pressure simultaneously. The key observation of this invention is that it is possible to use mining methods to create an enormous gasification chamber at relatively low cost compared to the types of metal and ceramic gasifiers that are used in most modern gasification equipment at present.
Such an underground gasification chamber can either be designed for continuous use or for one-time use. In the case that the chamber is designed for one-time use, at the end of the useful life of the chamber, when it becomes clogged by ash, it will have a potential second Life as a natural gas reformer. At the end of its life as a gasifier, such an underground gasification chamber will be at a temperature between about 600 and 1000 Celsius and will be full of a porous bed of Ash. Note that cool Ash coal ash is a known catalyst for the reactions of methane with steam. The large underground chamber could have a second life as a high-pressure reformer for natural gas to create syngas which would likely be used m8 Fischer-Tropsch synthesis to make liquid fuels, or else as a way to make hydrogen sequestering the carbon dioxide.
Background of the invention
Gasification of coal was a widely used technology in the 19th century. At that stage gasifiers operated at modest pressures. Typically, gasifiers would be fed coke. In some cases, the coal was devolatized in the same reactor that would later be used to generate the gas. Coal tar was a byproduct of this and also coal oil. These were very common in commerce in that era. After natural gas started to dominate over synthesis gas (syngas) from coal, gasifiers pretty much disappeared from commerce.
During world war II, the Germans resorted to gasification coupled with Fischer-Tropsch synthesis to make liquid fuels for their war machine. This was a dramatic modernization of the technology, and those gasifiers operated at a higher temperature and pressure than the prior art gasifiers.
If one is using a gasifier to feed a Fischer-Tropsch synthesis unit it is highly desirable to operate the gasifier at an appropriate pressure for the Fischer-Tropsch synthesis. This is typically 10 to 30 atmospheres.
After world war II the gasification technology was pretty much on hold until the embargo of South Africa at which stage South Africa developed a liquid fuel industry based upon coal gasification. The key company in this is Sasol, and there was a breakthrough on the gasifier design, the Lurgi gasifier. The Lurgi gasifier is essentially a countercurrent heat exchanger coupled with devolatilization and
Cavern gasification uses an underground gasifier in which the gasification pressure is less than the local lithostatic pressure. The gasification chambers of prior art gasifiers are usually a major portion of the cost of any prior art gasifier. Normally the gasifier is quite expensive because it operates at high- temperature and high-pressure simultaneously. The key observation of this invention is that it is possible to use mining methods to create an enormous gasification chamber at relatively low cost compared to the types of metal and ceramic gasifiers that are used in most modern gasification equipment at present.
Such an underground gasification chamber can either be designed for continuous use or for one-time use. In the case that the chamber is designed for one-time use, at the end of the useful life of the chamber, when it becomes clogged by ash, it will have a potential second Life as a natural gas reformer. At the end of its life as a gasifier, such an underground gasification chamber will be at a temperature between about 600 and 1000 Celsius and will be full of a porous bed of Ash. Note that cool Ash coal ash is a known catalyst for the reactions of methane with steam. The large underground chamber could have a second life as a high-pressure reformer for natural gas to create syngas which would likely be used m8 Fischer-Tropsch synthesis to make liquid fuels, or else as a way to make hydrogen sequestering the carbon dioxide.
Background of the invention
Gasification of coal was a widely used technology in the 19th century. At that stage gasifiers operated at modest pressures. Typically, gasifiers would be fed coke. In some cases, the coal was devolatized in the same reactor that would later be used to generate the gas. Coal tar was a byproduct of this and also coal oil. These were very common in commerce in that era. After natural gas started to dominate over synthesis gas (syngas) from coal, gasifiers pretty much disappeared from commerce.
During world war II, the Germans resorted to gasification coupled with Fischer-Tropsch synthesis to make liquid fuels for their war machine. This was a dramatic modernization of the technology, and those gasifiers operated at a higher temperature and pressure than the prior art gasifiers.
If one is using a gasifier to feed a Fischer-Tropsch synthesis unit it is highly desirable to operate the gasifier at an appropriate pressure for the Fischer-Tropsch synthesis. This is typically 10 to 30 atmospheres.
After world war II the gasification technology was pretty much on hold until the embargo of South Africa at which stage South Africa developed a liquid fuel industry based upon coal gasification. The key company in this is Sasol, and there was a breakthrough on the gasifier design, the Lurgi gasifier. The Lurgi gasifier is essentially a countercurrent heat exchanger coupled with devolatilization and
gasification of coal. The outgoing hot syngas from the gasifier preheats the incoming coal, and the coal is devolatized as it enters the gasification chamber.
Since then, there are various other designs for rapid gasifiers that operate at significantly higher temperatures, and which are fed coal dust. The faster the reaction, the less of the liquid content of the coal comes out of the gasifier as recoverable liquid. Insofar as the liquid part is worth more per unit of combustion energy, this is a major deficiency of current gasifiers, especially the most modern units. The way that gasification was done in the 19th century recovered far more of the coal tar and coal oil than present units. However, in that case, the liquid was not the major desired product, so none of the city gasifiers would have been feeding their process with low rank coal such as lignite.
Craig Picach’s US patent 9,982,205 is the closest prior art technology to our knowledge compared to the invention disclosed herein. In US patent 9,982,205, carbonaceous fuel is formed into a slurry in water and is injected into a depleted fossil fuel reservoir in combination with oxygen to create an underground gasifier of sorts. There are numerous problems with this method which are described in the email from professor Brian Towler, a co-inventor of this matter below.
Description of the invention
There are multiple known ways to create large underground caverns including mining technology, solution-mined cavities such as salt domes that have been mined with water, and various solution mined cavities that have been mined with acid. Hard and soft rock mining methods may be used to create underground cavities suitable for the gasification chambers of this invention, including particularly tunnel boring machines. In general, salt domes are appealing if they can be stable, but many salt domes are too large to be stable mechanically, and salt itself becomes quite thermoplastic and will flow at the temperatures corresponding to devolatilization, pyrolysis, and gasification of coal for example. Because of these and other complications, salt domes will only be used for this technology in special cases.
In general, I favor placing the gasification chambers directly below an area that has already been decimated by strip mining. In particular, there are many strip mines in Wyoming where the coal seam is more than 50 ft thick, and these mines are currently the source of much of the coal used in coal-burning power plants in the US. This Powder River Basin coal is fairly low sulfur and has been widely used for coal-burning power plants that are more than a thousand miles away from the coal mine. Normally this coal is sent to power plants via by means of a unit train, in which the entire train carries only coal. By gasifying the coal below the coal mine, it would then be feasible to transport the gas by pipeline to distant power plants. This is part of the motivation for this invention but there are other important pieces.
Powder River Basin coal is a favored fuel for coal-burning power plants in part because it has low sulfur content. It is a low-rank coal which means it has a large volatile content. The volatiles that come out of low-rank coal are partially liquids which are in the molecular weight range where they can go into a conventional oil refinery and be converted to liquid fuels, lubricants, etc. It turns out that the yield of these liquids is much higher if the pyrolysis of the coal is quite slow. Normally in prior art gasifiers, one tries for rapid conversion of coal to gas because the chamber itself is so expensive that you can't afford to hold something as cheap as coal in an expensive chamber for hours at a time.
Since then, there are various other designs for rapid gasifiers that operate at significantly higher temperatures, and which are fed coal dust. The faster the reaction, the less of the liquid content of the coal comes out of the gasifier as recoverable liquid. Insofar as the liquid part is worth more per unit of combustion energy, this is a major deficiency of current gasifiers, especially the most modern units. The way that gasification was done in the 19th century recovered far more of the coal tar and coal oil than present units. However, in that case, the liquid was not the major desired product, so none of the city gasifiers would have been feeding their process with low rank coal such as lignite.
Craig Picach’s US patent 9,982,205 is the closest prior art technology to our knowledge compared to the invention disclosed herein. In US patent 9,982,205, carbonaceous fuel is formed into a slurry in water and is injected into a depleted fossil fuel reservoir in combination with oxygen to create an underground gasifier of sorts. There are numerous problems with this method which are described in the email from professor Brian Towler, a co-inventor of this matter below.
Description of the invention
There are multiple known ways to create large underground caverns including mining technology, solution-mined cavities such as salt domes that have been mined with water, and various solution mined cavities that have been mined with acid. Hard and soft rock mining methods may be used to create underground cavities suitable for the gasification chambers of this invention, including particularly tunnel boring machines. In general, salt domes are appealing if they can be stable, but many salt domes are too large to be stable mechanically, and salt itself becomes quite thermoplastic and will flow at the temperatures corresponding to devolatilization, pyrolysis, and gasification of coal for example. Because of these and other complications, salt domes will only be used for this technology in special cases.
In general, I favor placing the gasification chambers directly below an area that has already been decimated by strip mining. In particular, there are many strip mines in Wyoming where the coal seam is more than 50 ft thick, and these mines are currently the source of much of the coal used in coal-burning power plants in the US. This Powder River Basin coal is fairly low sulfur and has been widely used for coal-burning power plants that are more than a thousand miles away from the coal mine. Normally this coal is sent to power plants via by means of a unit train, in which the entire train carries only coal. By gasifying the coal below the coal mine, it would then be feasible to transport the gas by pipeline to distant power plants. This is part of the motivation for this invention but there are other important pieces.
Powder River Basin coal is a favored fuel for coal-burning power plants in part because it has low sulfur content. It is a low-rank coal which means it has a large volatile content. The volatiles that come out of low-rank coal are partially liquids which are in the molecular weight range where they can go into a conventional oil refinery and be converted to liquid fuels, lubricants, etc. It turns out that the yield of these liquids is much higher if the pyrolysis of the coal is quite slow. Normally in prior art gasifiers, one tries for rapid conversion of coal to gas because the chamber itself is so expensive that you can't afford to hold something as cheap as coal in an expensive chamber for hours at a time.
My invention turns this on its head. I believe the cost per unit volume in a cavern gasifier could be less than $10 per cubic meter. By having a gasification reactor with a very low cost / cubic meter it becomes economically feasible to have the coal stay in the gasifier for quite a long time. This, in turn, enables efficient removal of liquids, mercury, and also efficient water gas shift towards carbon dioxide and hydrogen as the primary outputs. By shifting the reaction towards carbon dioxide rather than carbon monoxide in terms of the total carbon that was present in the initial fuel, it becomes more feasible to sequester carbon dioxide and therefore to minimize the climate impact of burning the coal. In this case most of the combustion energy would be produced by combustion of the hydrogen. Distance gas turbine facilities could be adapted to use this high hydrogen fuel and would not need to have exhaust scrubbers of any kind. This has enormous implications for the economics of sequestration of carbon.
Comments
Post a Comment