Gas separation: processes – Liquid contacting – And degasification of a liquid
Reexamination Certificate
2001-12-26
2004-04-27
Smith, Duane S. (Department: 1724)
Gas separation: processes
Liquid contacting
And degasification of a liquid
C095S177000, C095S228000, C095S230000, C096S242000, C423S246000
Reexamination Certificate
active
06726747
ABSTRACT:
TECHNICAL FIELD
The present invention relates to methods and apparatuses for treating syngas.
BACKGROUND ART
For purposes of this patent, the following terms are defined. As used herein, the term “air separating unit” or “air separation unit” means and refers to a facility, plant, location or process for separating the components of a feed gas and may include both cryogenic and non-cryogenic facilities. The term “contaminant” means and refers to components of a gas that are undesired in the final product. The terms “remove” and/or “withdraw” means and refers to removing, withdrawing, extracting, and/or the like.
The term “feed gas” means and refers to a gas fed to a process or distillation apparatus. The term “cold box process” means and refers to processes to purify carbon monoxide (“CO”) and/or hydrogen (“H2”). The term “methane wash” means and refers to a type of cold box process. The term “syngas” means and refers to synthetic and/or synthesis gas containing at least H2 and CO. Syngas is commonly produced by catalytic conversion or partial oxidation of a hydrocarbon.
The use of a particular structure, structures, or embodiments in this disclosure is not meant to be limiting. For instance, the term apparatus or apparatuses means and includes production facilities, plants, and/or the like. Further, the term process or processes means and includes methods, plans, production plans, and/or the like. The term led out means and refers to allowing out, passing out, discharging, releasing, and/or the like. The term fed or feed means and refers to directing, introducing, adding, channeling or sending a substance and/or substances to a process and/or apparatus. The term substance means and refers to and includes a liquid, a gas and/or a solid.
There are various prior art patents and/or patent applications that disclose producing CO from syngas, including, but not limited to, U.S. Pat. No. 5,133,793, GB-A-1579553, U.S. Pat. No. 5,295,356 and U.S. Pat. No. 5,592,831. The disclosures of which are incorporated herein by reference.
The '793 patent discloses the separation of a synthesis gas or other gaseous mixture of hydrogen and carbon monoxide by a process in which feed gas condensate is separated from the feed prior to the methane wash column. Only the vapor portion of the separation is fed to the wash column. The condensate is vaporized and fed to the stripping column at a location below that of the sump liquid from the wash column. The hydrogen stripped CO loaded methane liquid is subcooled and split into three substreams. One substream is introduced, at its bulb temperature, at the upper location of the separation column. Another substream is vaporized and introduced, at about it dew point, at a lower location of the separation column. The third substream is vaporized and introduced, at an intermediate temperature of the other streams, at an intermediate location to the other streams.
The '553 patent discloses a process in which CO loaded methane is countercurrently contacted with hydrogen rich vapor.
The '356 patent discloses a separation process whereby the columns are cooled with a closed loop refrigeration cycle of nitrogen.
The '831 patent discloses a process in which the methane wash is conducted with methane containing at least 2 to 15 mol % CO. The methane scrubbing column and the flash column are combined into a single column and the hydrogen stripped CO loaded methane is fed to the CO/methane separation column as a subcooled liquid with the remainder after vaporization.
Generally, cold box efficiencies are measured by several factors. In a classical cold box utilizing a methane wash, the performance of a methane wash cold box is most often measured by, but not limited to:
CO recovery (this parameter has a direct impact on the quantity of feedstock required to generate the syngas)
Power consumption required to produce refrigeration and separation/purification of the products usually through a CO (or N2) refrigeration cycle including a compressor and a cryogenic expander.
Often, a desired end product H2/CO ratio does not match the H2/CO ratio of the syngas feed gas. Quite commonly, an excess of H2 is produced. This excess H2 is then required to be disposed of through burning, such as a fuel in reformer and/or the like or disposed of elsewhere. The prior art has arrived at various solutions to this problem.
For example, one prior art solution is to use a membrane-based permeation unit. Commonly, membrane-based permeation units are installed upstream of the cold box in a methane wash treatment. H2 is extracted from the syngas and produced impure and at low pressure from the membrane. The cold box then treats the required quantity of H2. However, such methods are limited by equipment sizing and power consumption. Prior art solutions related to this method are economical only when the excess of H2 is large enough so that the savings on cold box can justify the additional cost of the membrane and retrofitting of the facility. As well, prior art solutions of this type remove an H2 stream that contains a CO concentration of about 1-2%, thereby decreasing the CO production.
Another prior art solution is to treat all the syngas in a cold box. The entire H2 flow is washed in the methane wash column so that most of the CO is extracted from the H2. The H2 is extracted and a first portion of the H2 product is produced under pressure and a second portion is expanded in a cryogenic expander to produce refrigeration. However, prior art methods of this type do not produce adequate refrigeration when the volume of the second portion is relatively small, consequently increasing power consumption is required when there are only small amounts of H2 in the syngas.
Other prior art examples of improving CO recovery are illustrated in U.S. Pat. No. 4,888,035 to Bauer and European Patent No. EP 0 895 961 to McNeil. These patents illustrate processes for increasing CO recovery from a stripper column by an additional injection of CH4 as a wash liquid in the stripper column. The '035 patent teaches and discloses the use of a regenerated CH4 stream that is removed from a flash column and injected into the stripper column above the feed from the wash column to increase CO recovery from the syngas. However, these patents do not teach or suggest the use of an intermediate withdraw of a portion of the H2 from a point intermediate on a methane wash column to reduce an amount of liquid methane required to wash a hydrogen product. As well, the '035 patent does not teach or suggest procedures and or structures for the reduction of power consumption and capital expenditure reduction. Moreover, the '035 patent does not appreciate that increasing the amount of methane wash requires decreasing the operating pressure of the flash column, thereby not producing CO at a maximum rate.
The '961 patent discloses the use of a feed of a H2/Ch4 liquid from the wash column to wash the CO in the stripper column. The '961 patent is directed at CO loss and power conservation by removing an intermediate stream from the bottom stage of the methane wash column to provide impure methane reflux to the top of the hydrogen stripping column. The '961 patent states that it is an improvement over the '035 patent because the '961 patent discloses using an impure methane reflux from the wash column that is rich in CO, thereby allowing for savings in methane. The '961 patent recognizes that the procedure requires a greater amount of methane for washing the CO, but the amount of methane used would be less than the amount required for the '035 patent which would result in power savings of between 2 to 4 percent as compared to equivalent CO content in the reject hydrogen stream of the '035 patent. However, the '961 patent still requires extra capital expenditure for a large pump and costs associated with the operation of the pump. Accordingly, the art field is in search of a method of enhancing CO recovery from syngas without excessively increasing energy consumpti
American Air Liquide
Russell Linda K.
Smith Duane S.
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