Gas: heating and illuminating – Processes – Fuel mixtures
Reexamination Certificate
1999-05-18
2002-02-26
Tran, Hien (Department: 1764)
Gas: heating and illuminating
Processes
Fuel mixtures
C048S092000, C048S198200
Reexamination Certificate
active
06350289
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
This invention relates to a process of conversion of hydrocarbons via gasification into two high pressure gas streams: a hydrogen-rich stream and a carbon-monoxide-rich stream. More specifically, this invention relates to the use of a two-zone predominantly molten iron or molten iron alloy system in conjunction with the above gasification conversion.
II. Discussion of the Prior Art
Two-zone molten iron gasifiers are disclosed by:
U.S. Pat. No. 1,803,221 (1931) to Tyrer describes hydrogen-rich gas production by feeding methane or a methane-steam mixture into one molten iron zone below the surface of the metal, thereby assuring complete reaction of the gaseous feed. The carbon which dissolves in the molten iron in the first zone is burned out of the molten iron in the second zone with an oxygen containing gas. Additional oxygen containing gas may be added to the combustion products leaving the second zone to completely oxidize to carbon dioxide any carbon monoxide remaining.
The disadvantages of the process described in this patent include:
The feedstocks are limited to hydrocarbon gases such as methane and do not include lower value hydrocarbon liquids or solids.
Operating pressure is nominally atmospheric pressure which is less economical to operate than equipment producing hydrogen at elevated pressures; two atmospheres and above.
The importance of controlling the carbon level in the molten iron is not considered and thus production of only lower purity hydrogen-rich gas is possible. If a minimum carbon level of at least 0.3% is not maintained, excess iron oxide will form in the molten iron during oxidation and will be converted to carbon monoxide and dilute the hydrogen-rich gas when hydrocarbon feeds are introduced to the hydrogen-rich gas producing first zone.
U.S. Pat. Nos. 4,187,672 (1980) and 4,244,180 (1981) to Rasor describe a hydrocarbon gasification process in which solid hydrocarbons such as coal are introduced on the surface of one molten iron bath zone in which high temperature cracking of the hydrocarbons into lighter molecular weight materials takes place with residual carbon being dissolved in the molten iron. The cracked hydrocarbon products are removed via outlets in the shaft through which the feed hydrocarbon solids enter the molten iron. The molten iron containing the carbon is transferred to the second molten iron zone in which an oxygen containing gas is introduced to convert the carbon into carbon monoxide and raise the temperature of the iron for transfer back to the carbonization section. The carbon monoxide is further oxidized above the molten iron bath and the heat recovered via a boiler or similar system. Sulfur, if present in the feed, is removed via slag formation on top of the molten iron. The disadvantages of the process described in this patent include.
The feedstocks are limited to solid hydrocarbons such as coal and do not include lower value hydrocarbon liquids or gases.
Since the solid hydrocarbon feeds are introduced above the surface of the molten iron, cracking of the feeds occurs such that a very impure hydrogen gas stream is produced because of the presence of cracked hydrocarbon gases.
Since the product gas from the oxidation zone is further oxidized for energy recovery in, for example, a steam boiler, no attempt is made to produce a carbon monoxide-rich gas.
Sulfur removal from the solid feed via reaction with and removal of slag from the equipment is complicated and expensive.
Operating pressure is nominally atmospheric pressure, which is less economical to operate that equipment producing hydrogen at elevated pressures, two atmospheres and above.
The importance of controlling tile carbon level above 0.30% in the molten iron is not considered and thus production of only lower purity hydrogen-rich gas is possible.
U.S. Pat. No. 5,435,814 (1995) to Miller and Malone (Ashland) describes the general concept of a two-zone molten iron system process operating at high pressures, up to 100 atmospheres, with solid and liquid feed introduction below the surface of the molten iron and production of a hydrogen-rich and carbon monoxide rich gas streams. The disadvantages of the process described in this patent include:
There is no method described for handling the feedstock sulfur.
The importance of controlling the carbon level in the molten iron is not considered and thus production of only lower purity hydrogen-rich gas may be possible. The process is restricted to a particular method of circulating molten iron.
In summary, all of the above patents operate at atmospheric pressure and do not control carbon at a minimum of 0.3% in molten iron. Furthermore, the Rasor patents do not inject feed below the surface of the molten iron and are restricted to solids feeds. Furthermore, all the patents ignore sulfur in the feed or use slag to remove it.
One-zone molten metal gasifiers are disclosed by:
U.S. Pat. No. 4,496,369 (1985) to Torneman and U,S. Pat No. 4,511,372 (1985) to Axelsson in which coal or other liquid hydrocarbons are injected advantageously below the surface of the molten iron along with oxygen and water vapor to form a mixed hydrogen and carbon monoxide gas. Iron oxides are also added to the molten iron to act as a coolant for the melt. The primary objective of the invention is to produce gasified hydrocarbons and it is disclosed that production can be increased by operating at high pressures. The high pressures are not only economic because of the reduced size of equipment but it is also disclosed that high pressure decreases the degree of refractory wear in the reactor and the amount of dust carry-over in the gas from the reactor. In addition, it is disclosed that a higher sulfur level in the molten bath will also reduce the amount of dust carry-over from the reactor. The process disclosed cites the advantage of maintaining the carbon content of the bath below 0.8% carbon to reduce the amount of dust carry-over from the reactor.
The primary disadvantage of the process described in this patent include the lack of separate molten iron zones for gasification and thereby does not permit production of individual hydrogen-rich and carbon monoxide-rich gas streams.
U.S. Pat. Nos. 4,574,714 and 4,602,574 (1986) to Bach and Nagel in which solid or liquid toxic and/or lower value hydrocarbons are injected advantageously below the surface of the molten iron alloy, along with oxygen specifically to destroy the toxic compounds. With appropriate feeds a mixed hydrogen and carbon monoxide gas can be formed and C1 chemistry may be utilized to advantage at times to produce useful products. It is further disclosed that maintaining a carbon level of 0.5-6% carbon, preferably 2-3% carbon in tile molten metal is desired to prevent refractory degradation and facilitate reaction kinetics by providing a high concentration gradient for toxics destruction. Sulfur, when present in the feed, is removed via absorption in the slag. The disadvantages of the process described in this patent include.
The feedstocks are introduced to the molten iron single zone system for destruction as hazardous materials and not to produce hydrogen-rich or carbon monoxide-rich gases and thereby misses the advantages of feeding non-hazardous feedstocks.
Sulfur removal from the solid feed via reaction with and removal of slag from the equipment is complicated and expensive.
Operating pressure is nominally atmospheric, which is less economical to operate than equipment producing gases at elevated pressures; two atmospheres and above. Also, rotating gasification vessels on trunnions for slag removal makes operating at higher pressures impractical.
The importance of controlling the carbon level in the molten iron at more than 0.3% is not considered and thus production of only lower purity hydrogen-rich gas is possible.
The primary disadvantage of the process described in this patent include the lack of separate molten iron zones for gasification and thereby does not permit production of individual hydrogen-rich and carbon monoxide
Holcombe Thomas C.
Malone Donald P.
Marathon Ashland Petroleum LLC
Stone Richard D.
Tran Hien
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