Gas separation: processes – Liquid contacting – And degasification of a liquid
Reexamination Certificate
2000-01-21
2002-01-29
Smith, Duane S. (Department: 1724)
Gas separation: processes
Liquid contacting
And degasification of a liquid
C095S173000, C095S181000, C095S183000, C095S184000, C095S193000, C095S235000, C095S236000, C095S237000
Reexamination Certificate
active
06342091
ABSTRACT:
FIELD OF THE INVENTION
Our present invention relates to a process for the removal of carbon dioxide, sulphur compounds, water and aromatic and higher aliphatic hydrocarbons from industrial gases. Industrial gases in this context are, in particular, natural gas and/or raw synthesis gas. Sulphur compounds according to the present invention are, in particular, hydrogen sulphide and organic sulphur compounds present in natural gas and raw synthesis gas.
BACKGROUND OF THE INVENTION
Carbon dioxide and hydrogen sulphide are, among others, so-called sour gas components present in natural gas and raw synthesis gas. Apart from sour gas components, such as hydrogen sulphide and carbon dioxide, water vapor must also be removed from natural gas. If the natural gas also contains aromatic hydrocarbons and higher aliphatic hydrocarbons, these can be recovered as a useful substance by absorption using an absorbent. In such case, care must be taken when regenerating the absorbent to ensure that none or only minute quantities of these hydrocarbon components are released or emitted into the environment.
It is known, in principle, that hydrogen sulphide and carbon dioxide can be removed from industrial gases, such as natural gas and synthesis gas, with the aid of chemical absorbents, e.g. ethanolamines, alkaline salt solutions and the like. When using chemical scrubbing agents, the absorbent is present in the form of an aqueous solution. It is, therefore, necessary to dry the industrial gas downstream of the absorption step which removes hydrogen sulphide and carbon dioxide. This is effected preferably by glycol scrubbing or by molecular sieve adsorption. When glycol is used for drying, for instance, aromatic hydrocarbons and higher aliphatic hydrocarbons are partly removed from the natural gas in addition to water. In regenerating the scrubbing solution, these hydrocarbons are emitted disadvantageously to the environment. Statutory requirements allow only limited toleration of such emissions.
U.S. Pat. No. 3,773,896 describes the use of morpholine derivatives as absorbents for hydrogen sulphide and carbon dioxide. By employing thermal regeneration of the absorbent at a temperature of 80° C., 70% to 80% of the absorbed sulphur compounds and 55% to 65% of the absorbed carbon dioxide can be removed from the absorbent. This limited desorption of the dissolved gases from the laden absorbent is disadvantageous, because the gas portions remaining in solution impede the absorption of carbon dioxide, sulphur compounds and water from the raw gas and prevent the achievement of low residual concentrations of these substances in the treated gas.
It is also known from DE 1 568 940 A1 that morpholine derivatives have a high affinity for aromatic hydrocarbons and can, therefore, be used for the removal of these aromatic hydrocarbons from natural gas.
In addition, it is known that physical absorbents, such as polyethylene glycol dimethyl ether, propylene carbonate or methanol, can be used for the removal of hydrogen sulphide and carbon dioxide from industrial gases. In order to remove the major portion of the dissolved sour gas components from the physical scrubbing fluids, the use of inert stripping gases, such as nitrogen, is also known for stripping the dissolved gas components. In these cases, the inert stripping gas flows counter-current to the absorbent laden with sour gas components. The dissolved gas components are entrained by the inert gas and withdrawn from the head of the desorption column.
It is further known that water can be added to the absorbent, the water being vaporized by indirect heating in the bottom of the desorption column. In this way, a quantity of stripping steam is generated as is required for expelling the dissolved gas components from the absorbent. This process is used especially when it is necessary to keep the evaporation temperatures in the column bottom low in order to prevent thermal decomposition of the absorbent. Because of the total miscibility of morpholine derivatives with water, this process can also be used for the removal of sour gas components from the morpholine derivatives. However, the last-mentioned process has a considerable disadvantage, in that the water portion in the absorbent does not contribute towards the sour gas absorption and has to be transported as ballast in the absorbent cycle. Moreover, due to the absorbent being pre-laden with water, an effective removal of the water portion from the industrial gas is not possible.
OBJECTS OF THE INVENTION
It is the object of the present invention to provide a process that permits, on the one hand, the complete removal of various substances, especially sour gas components, water and aromatic and higher aliphatic hydrocarbons with the aid of an adsorbent, and, on the other hand, the complete regeneration of the absorbent or, in other words, virtually total removal of the above-named components from the absorbent.
SUMMARY OF THE INVENTION
To meet this requirement , the present invention describes a process for the removal of carbon dioxide, sulphur compounds, water and hydrocarbons from industrial gases, in which
sour gas components, water and aromatic and higher aliphatic hydrocarbons are removed at an elevated operating pressure from the gas to be treated,
at least a morpholine derivative is used as the absorbent,
the absorbent laden with the absorbed components is regenerated with the aid of a stripping gas, and
the stripping gas is generated by partial evaporation of the laden absorbent.
It is an integral part of the invention that the absorbed components are partly removed from the absorbent by pressure relief of thermal regeneration. It is also an integral part of the invention that the stripping gas is generated by partial evaporation of the laden absorbent at negative pressure.
Within the scope of the invention, absorption at an elevated operating pressure means that the absorption takes place at a pressure above standard pressure or above 1 bar. In other words, an absorption column is used operating at a pressure above 1 bar. In a preferred embodiment of the invention, the absorption is performed at an operating pressure of 10 to 150 bar.
A preferred embodiment of the invention provides for the use of at least one morpholine derivative from the group of N-formylmorpholine, N-acetylmorpholine, and N-propionylmorpholine as the absorbent. It is within the scope of the invention that only N-formylmorpholine (NFM) or only N-acetylmorpholine (NAM) is used. A very preferred embodiment of the invention provides for the use of a mixture of two morpholine derivatives. According to a preferred embodiment, which has a special significance within the scope of the invention, a mixture of N-formylmorpholine (NFM) and N-acetylmorpholine (NAM) is used as the absorbent. The mixing ratio can be in the range of 10 to 90 parts (mass) of NFM to 90 to 10 parts (mass) NAM, referred to 100 parts (mass). A preferred embodiment of the invention provides for the use of 30 to 70 parts (mass) NFM and 70 to 30 parts (mass) NAM, such that the total is 100 parts (mass). The absorbent can also contain 0.1 to 5 parts (mass) of water.
A very preferred embodiment of the invention provides for at least one absorber and an absorbent temperature of −20° C. to +40° C. One embodiment of the invention provides for at least one absorber and an absorbent temperature of −15° C. to +10° C. Another preferred embodiment of the invention provides for an absorbent temperature of −20° C. to 0° C.
According to a very preferred embodiment of the invention, water and hydrocarbons are absorbed in a separate absorption stage. Such a separate absorption stage would appropriately be an upstream absorption column. It would, however, also be within the scope of the invention for the separate absorption stage to be the lower part of an absorption column, the sour gas components being absorbed in the upper part of the column. The preferred operating pressure of the separate absorption stage for the absorption of water and hydrocarbons is 10
Menzel Johannes
Tondorf Oliver
Dubno Herbert
Krupp Uhde GmbH
Myers Jonathan
Smith Duane S.
LandOfFree
Method of removing carbon dioxide, sulphur compounds, water... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of removing carbon dioxide, sulphur compounds, water..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of removing carbon dioxide, sulphur compounds, water... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2832735