Patent Application
20160166976
This application relates to a CO2 recovery solvent and heat integrated process unit that can reduce the amount of energy used in regenerating a CO2 absorbent in a CO2 recovery process.
Carbon dioxide (CO2) is a major greenhouse gas responsible for global warming, and hence, much effort is being put on the development of technologies for its capture from process gas streams (e.g., flue gas, natural gas, coke oven gas, refinery off-gas, and bio-gas). Carbon dioxide is emitted in large quantities from large stationary sources. The largest single sources of carbon dioxide are conventional coal-fired power plants. Technology developed for such sources should also be applicable to CO2 capture from gas and oil fired boilers, combined cycle power plants, coal gasification, and hydrogen plants and bio-gas purification plants. Absorption/stripping is primarily a tail-end technology and is therefore suitable for both existing and new boiler flue gas emissions. The use of absorption and stripping processes for recovery of the carbon dioxide from the gaseous mixture is known in the art.
The conventional carbon capture process consists of an absorber column and a stripper column. Gaseous mixture enters the absorber where it comes in contact with the CO2 absorbing solvent. The rich stream leaving the absorber has carbon dioxide trapped in solvent composition. The captured CO2 is stripped in the stripper column with the help of thermal energy provided in the reboiler. The overhead stream from the stripper is condensed and the condensate is passed back to the stripper while the gaseous stream, rich in carbon dioxide is compressed and sent for the suitable applications. The major drawback of conventional carbon capture system is the energy needed to strip the carbon dioxide from the rich solvent.
In this system, CO2 can be removed in the stripper (103) by supplying steam and increasing the temperature of the rich solvent (102). The rich solvent temperature is increased by heating the rich solvent with the lean solvent in the lean/rich exchanger (107). The temperature of the rich solvent to the stripper is limited by the temperature of the lean solvent and the approach to be maintained in the lean rich exchanger. As the mass flow of rich solvent is high compared to lean, the rich solvent temperature is limited by the rich in and lean out temperatures.
In light of foregoing discussion, it is necessary to develop both the improved solvents and heat integrated CO2 capture processes and systems that can consume less energy for recovering the carbon dioxide from a gaseous mixture.
This disclosure includes a process, system or apparatus for recovering CO2 from a gas contain CO2 in which an absorption section has (i) an absorption tower having a top portion and a bottom portion and (ii) a liquid feed where the CO2 containing gas comes in contact with the liquid absorbent feed, a cooling section having where a CO2 semi rich solution is extracted from the second point downstream of the first point of the absorption cooled using a cooling medium and pumped back to the absorber at a point between the first and second points of the absorption tower; a first heating section; a second heating section where the second portion of CO2 rich solution gets heated with CO2 lean solution coming from the regenerator; a third heating section where steam heats the CO2-rich solution, and/or a fourth heating section where section portion of CO2-rich solution gets heated with steam condensate. After the first heating section, the CO2-rich solution slits into a first CO2 rich solution portion (5-90% of mass flow) that is conveyed to the first point of the regenerator and the second portion of CO2 rich solution is conveyed to the second heating section.
This disclosure also includes a solvent for recovery of carbon dioxide from gaseous mixture a tertiary amine, cyclic amine promoter or derivative of piperazine with three or more amino groups as a promoter, and a carbonate buffer.
The following specific embodiments of a method, system and apparatus for CO2 recovery are given as examples only without being limitative in any way, with reference to the accompanying drawings, in which:
Specific embodiments of a CO2 recovery system, method, and solvent will now be explained in detail with reference to the drawings. The specific embodiments disclosed herein are not intended to limit the scope of the application in any way.
A first specific embodiment shown in
A steam supplier or supplying means (B) or 200 (heating section) is provided for supplying the heat energy to the stripper (103) to strip the carbon dioxide from the rich solvent mixture received from the inlets (103a and 103b). The outlet of the solvent filter (110) is split into two (110a and 110b), and said outlet (110a) is configured to pass through a solvent reclaimer (108) for removing the unrecoverable degraded products from the solvent and recover part of the solvent for reuse in the system, and the outlet (110b) is configured to pass through a carbon bed (111) for removing hydrocarbons, corrosion products, and other solids from the lean solvent. A condenser (109) is provided at the outlet (103d) of the stripper (103) for removing the water present in the recovered carbon dioxide before supplying to the carbon dioxide flow line (104).
The temperature of the rich solvent (102) in the stripper can be increased by utilizing the heat in the lean solvent (103c) more efficiently. The rich solvent (102) is split and higher portion of the rich solvent (102b) is heated using lean solvent (103c) from stripper (103) achieving higher temperature for rich solvent. This rich stream is fed to the lower section of the stripper at the inlet point (103b). The remaining portion of the rich solvent (102a) is fed to the top of the stripper at the inlet point (103a). The embodiment helps in reducing the energy required in the stripper (103) by maintaining a high temperature at the bottom and a low temperature at the top rather than a flat temperature profile as in conventional and other cases.
Another second aspect of this embodiment is to utilize the heat going out of the stripper in the form of high temperature water and CO2 to the overhead condenser. Hence, line (102a) which is at a low temperature compared to the stripper top temperature is allowed to pass at the top of the stripper and line (102b) is allowed to be heated by lean solvent line (103c) via heat exchanger (105). At the top section, the rich solvent (103a) gets the latent and sensible heats available in the vapor (CO2+water) going to the top and releases some more CO2 (104). As per the energy balance around the stripper the heat going out of the stripper in the conventional process is utilized within the stripper. In this manner, a smaller amount of energy is required in the regenerating heater or third heating section (Section B). As a result the amount of steam consumed in the regeneration tower compared with conventional process is reduced by about 20%.
In a second specific embodiment shown in
In third specific embodiment shown in
Lean solvent composition line (106) can be configured to pass solvent through a heat exchanger (105, 107) provided in rich solvent mixture flow line (102) for preheating the rich solvent mixture.
The amount of steam used in the regenerating heater is further reduced compared to second embodiment, improving the heat efficiency of the entire system further. As a result the amount of steam consumed in the regeneration tower compared with conventional process is reduced by about 25%.
As can be seen, thiole solvent invention addresses the low CO2 loading capacity and high energy requirement of the existing carbon dioxide capture solvents. Conventional solvent has several disadvantages with regards to chemical degradation, thermal degradation and corrosivity. These increase the solvent cost and CO2 recovery cost. The present invention relates generally to solutions for absorbing CO2 for extraction and purification of gases. More particularly, it relates to a CO2 absorption solution containing a tertiary amine or primary amino hindered alcohol, a cyclic amine promoter as an activator and carbonate buffer salt to increase CO2 absorption rate.
Various process steps are described as follow:
An aqueous solution of solvent reacts reversibly with CO2. Therefore, in chemical industries, for the purpose of removing and recovering general acidic gases, the solvent solution is widely used as the solvent solutions can be regenerated by supplying heat. With respect to the aqueous solution containing a single type of a certain solvent, the absorption capacity performance is not improved proportionally even when the amine concentration is increased. Accordingly, with respect to a certain type of amine, even when the amine concentration of the absorbent liquid is increased, there cannot be obtained an expected effect such that the amount of the absorbent liquid circulated is reduced. Therefore, for reducing the energy for CO2 recovery, the development of an absorbent liquid, which has an absorption capacity performance and an absorption reaction heat performance dramatically improved, is desired. State of art alkanolamines which are primary and secondary solvent react rapidly with CO2 to form carbamates. However, the heat of absorption associated with carbamate formation is high. Consequently, this results in high solvent regeneration costs. Further, the CO2 loading capacity of such alkanolamines solvent is limited to 0.5 mol of CO2/mol of amine. In particular tertiary amine or hindered amine solvent, which have a low reactivity with respect to CO2, as in case of MEA and DEA, and thus the carbamation reaction cannot take place. Instead, tertiary amine or primary amino hindered alcohol promote the CO2 hydrolysis reaction forming bicarbonates. The reaction heat released in bicarbonate formation is lower than that of carbamate formation, thus resulting in lower solvent regeneration costs. Moreover, tertiary primary amino hindered alcohol have a high CO2 loading capacity of 1 mol of CO2/mol of amine. In recovering a great amount of CO2 in a large-scale plant, an apparatus which can recover CO2 with energy as small as possible is desired. For achieving such an apparatus, an amount of the absorbent liquid circulated and an amount of heat required for desorption of the absorbed CO2 must be reduced. For reducing the amount of the absorbent liquid circulated, it is necessary to increase the absorption capacity of the absorbent liquid per unit amount of the absorbent liquid, and hence the absorbent liquid frequently has an increased amine compound concentration.
An absorbent that absorbs CO2 contained in gas, the absorbent comprising two or more amine and carbonate buffer salt compounds selected from tertiary amine or primary amino hindered alcohol and cyclic amine compounds. For improving the CO2 capture solvent in an absorption performance, the use of a cyclic amine, such as amino ethyl piperazine which enhances the CO2 absorption rate has been proposed. For reducing the overall vapor pressure of the solvent system and increasing the active amine in the CO2 capture system carbonate buffer act as a specific role.
An apparatus for removing CO2 according to the present invention includes an absorption tower that allows gas containing CO2 and an absorbent liquid to be in contact with each other to remove CO2 from the gas; and a regeneration tower that regenerates a solution which has absorbed the CO2, the absorption tower reusing the solution regenerated at the regeneration tower by removing the CO2 from the solution. The absorbent liquid includes a first component, including tertiary amine which comprises two alkyl replacing the hydrogen atoms of the amino or primary amino hindered alcohol which comprises of hindered group attached with the amine group. Since there is a hydrogen atom attached to the nitrogen atom but due to the hindrance effect around amine group the carbamation reaction cannot take place due to the bulky group. A second component which acts as an activator in an aqueous hindered amine solution enhances the rate of CO2 absorption. A piperazine derivative with three or more amino groups was selected as an activator.
Hindered amine compounds used as the first component in the present invention include N,N-diethyl ethanolamine (DEEA) or primary amino hindered alcohol as 2-amino-2-methylpropanol (AMP), Wherein the cyclic amine is selected from group comprising N-aminoethylpiperazine (AEP), and potassium carbonate buffer to catalyze the reaction of CO2 with the solvent.
Specific embodiments also include a solvent for recovery of carbon dioxide from gaseous mixture having a primary amino hindered alcohol, a derivative of piperazine with three or more amino groups as promoter, a buffer (e.g., a carbonate buffer). The primary amino hindered alcohol can be 2-amino-2-methylpropanol (AMP) and the carbonate buffer is a potassium carbonate buffer and the promoter can be N aminoethylpiperazine (AEP). A solvent for recovery of carbon dioxide from gaseous mixture also may have a tertiary amine, a derivative of piperazine with three or more amino groups as promoter, and buffer (e.g., a carbonate or potassium carbonate buffer). The solvent can contain less than about 75% by weight of water and has a single liquid phase. In one example, the carbonate buffer is a potassium carbonate buffer and the tertiary amine is N,N-diethyl ethanolamine (DEEA). In another example, the solvent the promoter is N-aminoethylpiperazine (AEP) and the carbonate buffer is potassium carbonate buffer.
The following examples are not intended to limit or depart from the scope and spirit of the disclosure.
The energy supplied in the reboiler is mainly contributed towards the heat of desorption (kcal/kg of CO2 stripped), latent heat of vaporization water (kcal/kg of CO2 stripper) and sensible heat (entire heat of lean solvent can't be transferred to rich solvent going to stripper) supplied to rich solvent to attain the required temperature of stripper. In the conventional configuration the rich solvent is heated using the lean solvent heat and fed at the top of the stripper. The temperature profile in the stripper is almost flat. The vapor leaving at the top of the stripper is at high temperature (80-100 Deg C) and contains lot of water vapor. This stream cooled in the condenser to remove water and get high concentration of CO2. And as the temperature of the rich solvent coming to the stripper is also at high temperature there would be further evaporation of water.
As shown herein, the utilization of evaporation energy in the stripper itself in
As shown in
The optimum rich solvent split depends on characteristics of the solvent. The quantity of rich solvent that shall be sent to top of the stripper depends on the amount of water evaporated in the reboiler. For absorbent solutions with high concentration of water, high heat of absorption and low CO2 loading capacity (requires high temperature) need higher portion of rich solvent to be routed to top of the stripper.
A study was performed to understand the optimum split of rich solvent for APBS solvent. Because of high CO2 loading capacity the optimum split required is 15-20% of the rich solvent to the top section of the regenerator as the evaporation of water in the case of APBS is less. For the case MEA solvent the split required is more than 40% because of its low CO2 loading capacity. Hence, this also significantly reduces the condenser duty as shown in the Table 1.
Along with the rich solvent split if we consider withdrawal of stream from the middle of the stripper and heat it in the lean rich exchanger the temperature can be further increased as explained in the second embodiment section which can reduce the energy requirement further.
The heat from the steam condensate to heat the rich solvent further increases the temperature in the stripper to further reducing the steam requirement.
The energy savings for all the three embodiments for MEA and APBS solvents are as shown in Table 2 and Table 3 respectively.
The first component is 2-amino-2-methylpropanol (AMP) which is a primary amino alcohol. In the absorbent liquid according to the present invention, the primary amino alcohol may be contained in an amount in a range from equal to or larger than 1M-4 M.
The second compound component is 2-Piperazine-1-ethylamine (AEP) which act as the activator to enhance the CO2 absorption rate with a unique characteristic of low vapor pressure, high boiling point and special molecule with primary, secondary and tertiary amine promoter in the same compound associated with different pKa in an amount in a range from equal to or larger than 0.5 M-3.5 M. The third compound is carbonate buffer salt in a range from equal to or larger than 0.01 M to 0.8 M.
The first component is N, N-diethyl ethanolamine (DEEA) that is a tertiary amine. In the absorbent liquid according to the present invention, the tertiary amine may be contained in an amount in a range from equal to or larger than 1M-4 M.
The second compound component is 2-Piperazine-1-ethylamine (AEP) which act as the activator to enhance the CO2 absorption rate with a unique characteristic of low vapor pressure, high boiling point and special molecule with primary, secondary and tertiary amine promoter in the same compound associated with different pKa in an amount in a range from equal to or larger than 0.5 M-3.5 M. The third compound is carbonate buffer salt in a range from equal to or larger than 0.01 M to 0.8 M.
The vapor liquid equilibrium data for few combinations of the first component, activator and buffer salt are shown in
The above detailed description, the drawings, and the examples, are for illustrative purposes only and are not intended to limit the scope and spirit of the invention, and its equivalents, as defined by the appended claims. One skilled in the art will recognize that many variations can be made to the invention disclosed in this specification without departing from the scope and spirit of the invention.
This application claims the benefit of U.S. Provisional Application No. 61/857,288, filed Jul. 23, 2013, the entire contents of which are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2014/002368 | 7/23/2014 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61857288 | Jul 2013 | US |
