Patent Application
20130008310
This disclosure relates to a method for stripping acid gases such as carbon dioxide from an absorption or adsorption medium. The disclosure further relates to processes, uses, and apparatus.
Large-scale combustion processes are commonly used for municipal and industrial energy production, in the manufacturing of refined products from raw ores and other crude materials, and for the disposal of municipal and industrial waste materials. Such combustion processes typically produce on a continuous basis, significant volumes of gaseous exhaust waste streams that contain one or more undesirable gaseous compounds. comprise one or more of the acid gases such as carbon dioxide (CO2), sulfur dioxide (SO2), and oxides of nitrogen (NOx), which can cause significant environmental pollution and health risks. In particular, increasing concentrations of atmospheric CO2 are thought to be the primary cause of global warming.
Gas absorption, separation and recovery processes have long been provided for both industrial and environmental purposes. Industrial applications typically involve the separation and removal of at least one gaseous component from a process gas stream in order to enhance the quality of gas products produced and/or to prevent undesirable downstream operational problems that might subsequently occur in downstream processes. Examples include the removal of CO2 and/or hydrogen sulfide (H2S) from natural gas and synthesis gas or the removal of volatile organic compounds (VOCs) or other gases (e.g. nitrogen (N2), oxygen (O2), hydrogen (H2)) from industrial process gas streams. Environmental applications typically involve the removal of at least one gaseous component such as SO2, CO2, NOx, or mercury (Hg) from combustion flue or exhaust gas streams in order to reduce emissions of pollutants.
Numerous systems for scrubbing undesirable gaseous compounds from combustion flue or exhaust gas streams exist and typically involve the use of a counterflow solvent, such as one comprising one or more alkanolamines, against a gas stream containing the undesirable components. Such systems are commonly referred to as countercurrent absorbers and strippers. Certain of the systems and their operation are described in Kohl and Neilson in Gas Purification, 5th Edition (1997, Elsivier B. V.); US 2003/0221555; US 2005/0169825; US 2007/0044658; US 2007/0077188; US 2009/0104098; US 2009/0151318; US 2009/0151564; US 2009/0151566; US 2009/0155889; U.S. Pat. No. 3,725,529; U.S. Pat. No. 5,220,782; U.S. Pat. No. 6,270,739; U.S. Pat. No. 6,436,174; U.S. Pat. No. 7,001,519; U.S. Pat. No. 7,388,120; WO 89/07979; WO 2004/089512; WO 2006/108532; WO 2009/003238; WO 2009/052313; and EP 544,515.
Most acid gas removal methods include a step for regenerating the absorption or adsorption medium. This step is variously known as desorption, regeneration, or stripping. One common method of performing the stripping step (for example, in CO2 removal process) is to contact the CO2-rich scrubbing medium with steam. The steam drives off the CO2 from the medium and the CO2-lean medium can be reused. The energy required to generate the steam is costly and reduces the overall efficiency of the system.
The present disclosure relates to a method for stripping acid gases, exemplified by carbon dioxide, from absorption media and/or adsorption media using an alcohol selected from those having a boiling point lower than the boiling point of the absorption medium and/or adsorption medium.
The disclosure further provides the use of gaseous alcohols and/or alcohol vapours, for stripping an acid gas from absorption media and/or adsorption media.
The disclosure further provides use of heat recovery apparatus and processes for regeneration and recirculation of an alcohol stripping component (or carrier). It is optional to employ exogenous low-grade heat inputs for regeneration and recirculation of an alcohol stripping component (or carrier).
The disclosure further provides the use of heat pumps for recovery and utilization of waste heat generated during the gas-stripping processes.
The disclosure further provides a process for stripping an acid gas from an absorption medium and/or adsorption medium, said process comprising:
(a) contacting an acid gas-enriched absorption medium and/or adsorption medium with a gaseous alcohol;
(b) recovering the lean i.e., acid gas-depleted, absorption medium and/or adsorption medium;
(c) preferably, cooling the acid gas-enriched alcohol by passage through a heat-exchange apparatus to separate the acid gas from the alcohol;
(d) preferably, regenerating the alcohol into a gaseous vapour stream; and
(e) optionally, recovering waste heat with one or more heat-pumps.
The disclosure further provides an apparatus for stripping an acid gas from absorption medium and/or adsorption medium.
As used herein, the term ‘rich absorption and/or adsorption media’ refers to media that has absorbed a relatively greater amount of acid gas compared to lean media.
As used herein, the term ‘lean absorption and/or adsorption media’ refers to media that comprises no or low amounts of acid gas.
As used herein, the term ‘acid gas’ refers to gases that form acidic solutions when mixed with water.
As used herein, the term ‘boiling point’ refers to the boiling point at standard temperature and pressure.
The present disclosure will be described in conjunction with reference to the following drawings in which:
In an embodiment of the present disclosure there is provided a method of stripping acid gas from absorption media and/or adsorption media using alcohols. Any suitable alcohol may be used herein. For example, short chain alcohols such as C1-C6 or C1-C4 alcohols may be used herein. Exemplary alcohols include methanol, ethanol, iso-propanol, n-propanol, and combinations thereof.
While not wishing to be bound by theory, it is believed that, because the stripping solvent vaporises at a lower temperature, the present disclosure allows the stripping to be performed at lower temperatures compared to the conventional stripping operation using steam. This can save energy and improve the efficiency of regeneration of media (absorbent and/or adsorbent). Furthermore, due to the lower operating temperatures, the present disclosure allows for different materials to be used in the construction of the apparatus used for the stripping process. Such materials may, for example, be lighter and/or cheaper than those currently used. In addition, it may be possible to use low-quality heat sources such as geothermal energy for the stripping process.
The present method may be used to strip any suitable gas from an absorption medium and/or adsorption medium. For example, gases that may be stripped are exemplified by CO2, NON, SO2, and the like.
The present disclosure provides for stripping acid gas from an absorption medium and/or adsorption medium. Typically absorption media are liquids and adsorption media are solids. Any suitable type of absorption media may be stripped using the present method. Examples of absorption media include, but are not limited to, monoethanolamine (MEA), diglycolamine (DGA), diethanolamine (DEA), methyldiethanolamine (MDEA), 2-amino-2-methyl-1-propanol (AMP), piperazine (PZ), ammonia, amines, alkanolamines, derivatives and/or combinations thereof These amines should be used as aqueous solutions.
The alcohol stripper preferably has a lower boiling point than the absorption media and/or adsorption media so that the alcohol is a vapour, i.e., gaseous form when it contacts the media.
In an embodiment of the present disclosure rich absorption media is delivered to a stripping vessel. The rich media may conveniently be delivered to, or near, the top of the stripping vessel. For embodiments using adsorption media, the rich media may be packed in an adsorption vessel where its operation is switched to the stripping mode. An alcohol, such as methanol, ethanol, iso-propanol, and/or n-propanol, is delivered to the stripping vessel. The alcohol may conveniently be delivered at, or near, the bottom of the stripping vessel or at various points in the vessel. The alcohol may be delivered as a gas or a vapour. Alternatively, the alcohol may be converted to a gas or a vapour in situ.
The gaseous alcohol rises through the vessel and contacts the descending absorption media and/or adsorption media. This contact allows the alcohol to strip at least a portion of the acid gas from the media. The lean media can be collected and, if desired, recycled. The acid gas-alcohol vapour rises through the vessel, leaves the vessel and may be cooled, preferably via a heat-recovery and exchange mechanism, and condensed to separate the alcohol and acid gas. The alcohol may be reused for further stripping. The acid gas may be collected for storage, and then used for other industrial purposes or disposed of in another suitable manner. The heat recovered in the heat-recovery and exchange mechanism may, for example, be transmitted to an alcohol vapour generator (reboiler) via a heat-pump thus improving the efficiency of the system.
The vessel may be of any suitable type. For example, suitable gas-liquid or gas-solid contactors. For example, packed, membrane, module, spray, tray vessels may be used. Or a suitable combination thereof The vessel may be a column.
Because of a lower temperature of reboiler (126) used for alcohol vaporization, the heat-pump concept can be readily integrated into the proposed stripping operation. From
Because the boiling point of the present alcohol (64.7° C. for methanol) is lower than that of the amine solution, CO2 stripping by alcohol vapour can be achieved at a lower temperature compared to the conventional stripping operations. The lower stripping temperature may provide an opportunity to use low-quality energy drawn from power plants or low-cost heat sources, such as hot water from geothermal fields. This can lead to a significant reduction in the cost of CO2 capture. In addition, the lower stripping temperature also allows for the difference in operating temperature between absorber and stripper to be reduced, offering a potential reduction in heat-duty and size of the cross heat-exchanger used.
A preliminary assessment of a supercritical coal-fired power plant (Table 1) suggests that the proposed CO2 stripping process using alcohol vapour carrier can be expected to offer an energy saving of approximately 29-37% contributing to a reduction in the energy penalty by 2.6-3.2% point drop.
aCengel, Y. A. and Boles, M. A., Thermodynamics: An Engineering Approach, 6th Ed., McGraw Hill Higher Education, Boston, 2008.
bKohl, A. L. and Nielsen, R. B., Gas Purification, 5th Ed., Gulf Publishing Company, Houston, 1997.
cA heat pump is designed to operate at 10° C. (condenser cooling medium) and 90° C. (reboiler heating medium).
dTemperature of reboiler in the conventional process (110-120° C.) is too high for heat pump application.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/CA10/01970 | 12/8/2010 | WO | 00 | 9/24/2012 |
| Number | Date | Country | |
|---|---|---|---|
| 61267922 | Dec 2009 | US |
