Claims:I/We claim:
1. A system of utilizing ultrasound to regenerate carbon-rich solvent regeneration at ultra low temperature comprises of;
a) A tank-type (bath-type) sonication to strip CO2 from aqueous carbon rich 30 wt% MEA solvent is loaded into the glass reactor, and it was placed in a water circulation chamber;
b) A chiller inlet and outlet are connected to the water circulation chamber to maintain the desired regeneration temperature and placed in a sonication bath;
c) The temperature of the reaction mixture, water circulation chamber and the ultrasonic tank water bath were measured using a k-type thermocouple;
d) During regular intervals of 5, 15, 30,45, and 60 minutes of sonication, the carbon-lean solvent was collected then subjected to the carbon loading measurement using a Chittick apparatus and the reaction mixture temperature, carbon loading is used to calculate the solvent regeneration energy;
e) In low frequency ultrasound, a cavitation mechanism is predominant, the bubble forms, grow by coalescing with the neighbouring bubbles and finally collapses;
f) During bubble collapse, fragments of smaller bubbles are generated as like a micro-jet and the majority of micro-jets that are containing CO2are reabsorbed by the surrounding solvents;
g) The lowest carbon loading and higher efficiency is achieved at 60th minute (5.825 mol CO2/kg solution, 29%) in the tested range and the initial five minutes of sonication shows drastic reduction in carbon loading as 6.6 mol CO2/kg solution and then a gradual drop in carbon loading is observed.
2. The system of utilizing ultrasound to regenerate carbon-rich solvent regeneration at ultra low temperature according to claim (1), the stripping rate of CO2 is found to be higher at the initial 5 minutes then a gradual drop is observed for the total one hour of sonication.
3. The system of utilizing ultrasound to regenerate carbon-rich solvent regeneration at ultra low temperature according to claim (1), maximum attained reaction mixture temperature in this sono-assisted process is 17.5°C.
4. The system of utilizing ultrasound to regenerate carbon-rich solvent regeneration at ultra low temperature according to claim (1), the regeneration energy (KJ/mol. CO2) for the temperature-controlled CO2 stripping for low temperature ultrasonics is 6.3 KJ/mol. CO2.
, Description:The present invention generally pertains to Post-Combustion CO2 Capture Process. More particularly, the invention describes about utilization of high frequency ultrasound efficiently for carbon capture solvent regeneration with minimal energy consumption.
BACKGROUND OF THE INVENTION
Conventional carbon-rich solvent regeneration/CO2 stripping process in solvent-based post-combustion CO2 capture (PCCC) process uses thermal methods to regenerate the solvent or to strip the CO2.
The thermal degradation of the amine-based solvents usually occurs at high temperature locations, such as reboilers, stripper columns or lean/rich heat exchangers. This process usually forms higher molecular weight undesired products through a condensation mechanism. In addition, degradation products can cause environmental damage as well.
Thermal degradation not only consumes amines, resulting in a higher solvent make-up rate, but also causes operational difficulties such as increasing foaming tendency and the corrosion/erosion of CCS unit construction materials. The thermal degradation of the MEA in-stripper conditions shows that the rate of MEA degradation varies from 2.5 to 6 % per week at 135°C. However, it is a slow phenomenon, and it takes for a week to months in an industrial capture plant and has a drastic impact on reducing absorption capacity thereby increasing the overall CCS process energy demand.
The alternate techniques such as microwave solvent regeneration (T=80-90°C), electrochemical regeneration of solvents (T=~60°C), Megasonics assisted solvent regeneration (T=~45°C) and ultrasonics are developed for carbon-rich solvent regeneration with the use of minimal temperature compared to conventional method.
Inventions that describe the use of high frequency ultrasonics and thermal method for regeneration of Carbon-di-oxide have been described in varied capabilities in the past.
A scientific literature titled “Intensification of CO2 Stripping from Amine Solutions by Ultrasonic”, [Jiru Ying, et al., 2014] describes the effects of ultrasound on desorption of CO2 from loaded amine solutions (MEA (Monoethanolamine) and MDEA (Methyldiethanolamine)) at various values of parameters (temperature, amine concentration, CO2 loading, energy input) were investigated at ambient pressure.
Another scientific literature titled “Desorption of CO2 from low concentration monoethanolamine solutions using calcium chloride and ultrasound irradiation”, [Kosuke Tanaka, et al., Jul 2015] describes a method for desorbing CO2 from low-concentration (0.2 mol/l) monoethanolamine (MEA) solutions using calcium chloride (CaCl2) and ultrasound irradiation at 25 °C. The proportion of CO2 desorbed from the MEA solution was calculated from the amount of CaCO3 generated and the amount of CO2 emitted.
One more literature titled “Ultrasound Enhanced CO2 Stripping from Lean MEA Solution at Pressures from 1 to 2.5 bar(a)”, [Jiru Ying, et al., Jul 2017] describes an ultrasonic assisted CO2 stripping from lean 30 wt% MEA aqueous solutions in a reboiler. The effect of ultrasound on CO2 stripping was investigated at 2.5 bar(a) under two pressure control methods, solenoid operated on/off valve (OOV) and manual needle valve (NV) method. The results show that the CO2 stripping rate can be improved significantly when ultrasound is introduced.
However, the challenges associated with these methods may include consumption of high energy to carry out the solvent regeneration, which takes place at high-temperature conditions to regenerate the CO2 from solvent, degrading the nature of the solvent due to high-temperature reaction mechanisms and formation of undesired and harmful by-products leads to an increase in the overall energy consumption of the carbon capture and sequestration (CCS) process.
Therefore there exists a need to design and develop an advanced system which utilizes low temperature to regenerate solvent inorder to capture carbon dioxide with minimal solvent degradation.
SUMMARY OF THE INVENTION:
The following summary is provided to facilitate a clear understanding of the new features in the disclosed embodiment and it is not intended to be a full, detailed description. A detailed description of all the aspects of the disclosed invention can be understood by reviewing the full specification, the drawing and the claims and the abstract, as a whole.
The objective of the present invention is to design and develop a system to regenerate the carbon-rich solvent using high frequency ultra sound with minimal energy consumption, negligible solvent degradation and scalable continuous process.
The aforementioned aspects along with the objectives and the advantages can be achieved as described herein.
According to the embodiment of the present invention, the use of tank-type (bath-type) sonication to strip CO2 from aqueous carbon rich 30 wt% MEA solvent in a controlled temperature environment at 12°C using 470 kHz (streaming dominant frequency).
In an aspect of the present invention, the tank-type sonication provides uniform distribution of the sonication effect hence energy is distributed throughout the system which leads to the better performance also attribute to the scalable potential.
In another aspect of the present invention, acoustic cavitation and streaming effects are responsible for all the effects and these effects are more pronounced at low temperature.
In yet another aspect of the present invention, high frequency ultrasound favours the CO2 stripping/ solvent regeneration compared to the low-frequency ultrasound (re-dissolution of CO2).
Further in accordance with the present invention, low-temperature sono-assisted solvent regeneration facilitates negligible thermal degradation, less solvent loss, less undesired/harmful contaminants formation and low corrosion issues.
BRIEF DESCRIPTION OF FIGURES
Other features and advantages of the present invention will become apparent from the detailed description of the invention which follows, when considered in light of the accompanying drawings in which:
Fig. 1 illustrates the schematic diagram of temperature controlled sono-assisted CO2 stripping/ solvent regeneration;
Fig. 2 illustrates the effect of temperature controlled sono-stripping on carbon loading and CO2 stripping efficiency;
Fig. 3 illustrates the schematic of cavitation and streaming mechanisms in sono-assisted CO2 stripping;
Fig. 4 illustrates the effect of 470 kHz ultrasonic frequency on CO2stripping rate;
Fig. 5 illustrates the reaction mixture temperature profile during CO2 stripping for conventional and 470 kHz frequency;
DETAILED DESCRIPTION
The principles of operation, design configurations and evaluation values in these non-limiting examples can be varied and are merely cited to illustrate at least one embodiment of the invention, without limiting the scope thereof.
The embodiments will be described in detail with corresponding marked references to the drawings, in which the illustrative components of the invention are outlined. The embodiments disclosed herein can be expressed in different forms and should not be considered as limited to the listed embodiments in the disclosed invention. The various embodiments outlined in the subsequent sections are construed such that it provides a complete and a thorough understanding of the disclosed invention, by clearly describing the scope of the invention, for those skilled in the art.
It must also be noted that as used herein and in the appended claims, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Although any systems and methods similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present invention, the preferred, systems and methods are now described.
The present invention involves use of tank-type (bath-type) sonication to strip CO2 from aqueous carbon rich 30 wt% MEA solvent in a controlled temperature environment at 12°C using 470 kHz (streaming dominant frequency). Tank-type sonication provides uniform distribution of the sonication effect hence energy is distributed throughout the system which leads to the better performance and also attribute to the scalable potential. Acoustic cavitation and streaming effects are responsible for all the effects and these effects are more pronounced at low temperature. High frequency ultrasound favours the CO2 stripping/ solvent regeneration compared to the low-frequency ultrasound (re-dissolution of CO2).
The application of sono-assisted solvent regeneration shows significant reductions in regeneration temperature, thereby reducing CCS process energy consumption, which may result in negligible solvent degradation compared to conventional method. The positive attribute of this technology contributes to the aspects of improved mass transfer, reduced cost, compact design, reduction of solvents quantity, low temperature operation, and suitable for high viscosity operation compared to conventional solvent regeneration, making it a potential alternative.
The complete experimental setup used for this experimental investigation and the requirements to carry out the experiments such as chemicals, instruments, experimental procedure, lab-scale setup schematic for sono-assisted solvent regeneration/ CO2 stripping are detailed below.
The chemical specifications used in this experimental investigation is Monoethanolamine (MEA) 99.99% assay, Hydrochloric acid (35%), Bromo-cresol green indicator, Sulphuric acid (EMPLURA-98%), Indicators: Methyl orange and Phenolphthalein.
Ultrasonic DS generator 470 kHz 400W and Tank, Magnetic Stirrer, Chittick apparatus, Weighing balance, Low temperature circulating water bath, Thermo, Digital Temperature meter with K-Type thermocouple range: -50 to 1300°C, precision 0.5°C, resolution 0.1°C.
The schematic diagram of the temperature controlled sono-stripping experimental set up is shown in Figure 1. It consists of a reactor, an ultrasonic tank and a generator with high frequency of 470 kHz at 400 Watts. The experiment was carried out in the reactor for about 60 minutes. The known quantity of carbon-rich 30wt% aqueous MEA was loaded into the glass reactor, and it was placed in a water circulation chamber.
The chiller inlet and outlet are connected to the water circulation chamber to maintain the desired regeneration temperature. And the whole arrangements were placed in a sonication bath. The sono-assisted CO2 stripping was carried out at 12°C and these conditions were regulated by the chiller.
During the experiment, the temperature of the reaction mixture, water circulation chamber and the ultrasonic tank water bath were measured using k-type thermocouple. During regular intervals of 5, 15, 30,45, and 60 minutes of sonication, the carbon-lean solvent was collected and subjected to the carbon loading measurement using Chittick apparatus. Finally, the reaction mixture temperature, carbon loading was used to calculate the solvent regeneration energy.
Effect of CO2 stripping: The initial carbon loading value of the carbon-rich sample is estimated to be 8.228 ± 0.051 mol CO2/ kg solution. Table 1 presents the consolidated data on carbon loading and reaction mixture temperature for 470 kHz over the time interval of 5, 15, 30, 45 and 60 minutes.
Table 1 Consolidated data on carbon loading and reaction mixture temperature
Time
(mins) Reaction mixture temperature (°C) Carbon loading
(mol/kg) (mol/mol)
0
(Carbon-rich) 12.1 8.228 ± 0.051 0.503 ± 0.0031
5 12.8 6.600 ± 0.049 0.403 ± 0.0030
15 14.6 6.364 ± 0.05 0.389 ± 0.0031
30 13.6 6.282 ± 0.051 0.384 ± 0.0031
45 12.8 6.021 ± 0.05 0.368 ± 0.0030
60 17.5 5.825 ± 0.049 0.356 ± 0.0030

The lowest carbon loading and higher efficiency was achieved at 60th minute (5.825 mol CO2/kg solution, 29%) in the tested range and the initial five minutes of sonication shows drastic reduction in carbon loading as 6.6 mol CO2/kg solution and then a gradual drop in carbon loading was observed. Carbon loading and stripping efficiency in 470 kHz is found to be promising at the controlled lowest temperature of 12°C due to the streaming effects produced by 470 kHz, a high frequency ultrasonic phenomenon which significantly remove CO2 from carbon-rich solution.
Figure 2 shows the effect of sonication time on carbon loading and regeneration efficiency under temperature controlled sono-assisted CO2 stripping. First 5 minutes of sonication renders regeneration efficiency of 20% and 29% for 60 minutes indicates majority of the CO2 was stripped within a short span of time. Ultrasound propagation in a liquid enables cavitation, acoustic streaming, vibration, heating, sponge, and synergistic effects in chemical operations which depends on the range of ultrasonic frequency.
The sono-assisted CO2 stripping/solvent regeneration mechanisms for low and high frequency ultrasound is shown schematically in Figure 3. In low frequency ultrasound, the cavitation mechanism is predominant, the bubble forms, grow by coalescing with the neighboring bubbles and finally collapses because it cannot retain the pressure within the bubble. During bubble collapse fragments of smaller bubbles are generated as like a micro-jet. And majority of micro-jets that are containing CO2 are reabsorbed by the surrounding solvents. However, this is not the case in high frequency ultrasonics.
In a high-frequencies, streaming phenomena is predominant, and it helps to release CO2 molecules and contribute to the solvent regeneration in a better way. The results observed from 470 kHz is mainly due to the acoustic streaming phenomenon. By reducing the bubble size and cavitation cycle time renders microstreaming and facilitates degassing.
The most promising CO2 stripping/solvent regeneration is achieved when the sono-assisted solvent regeneration was carried out at 12°C. Streaming effect in low temperature helps to create a sponge effect thereby effectively strip the CO2 molecules from the solvent.
Effect of CO2 Stripping rate: Figure 4 shows the stripping rate of CO2 for streaming dominant frequency 470 kHz. The stripping rate of CO₂ is defined in the equation (3.1) as,
Stripping rate of 〖CO〗_2 m ̇_(〖CO〗_2 )= n ̇_A (α_0-α)M_(〖CO〗_2 ) (3.1)
Where n ̇_A is the molar rate of the solvent, Mco₂ is the molecular weight of carbon dioxide, α₀ is mol-CO₂/mol-solvent of the rich loading and α is mol-CO₂/mol-solvent of the lean loading. The stripping rate depends on the parameters such as temperature, and the nominal power input of the sonication system. The stripping rate of CO2 is found to be higher at the initial 5 minutes then a gradual drop was observed for the total one hour of sonication.
Temperature profile: The temperature profile for conventional and sono-assisted CO2 stripping/solvent regeneration is shown in Figure 5. Maximum attained reaction mixture temperature in conventional heating is 102.2°C whereas in sono-assisted process the temperature attained is only 17.5°C. The corresponding lean loading values are 0.208 and 0.356 mol CO2/mol solution.
Energy consumption calculation: The regeneration energy (KJ/mol.CO2) for the temperature-controlled CO2 stripping was calculated according to the following equation (3.2).
Q=Mass of solution*Heat capacity*(((T_lean-T_rich ))/((Rich carbon loading-Lean carbon loading) )) (3.2)
The heat capacity of the solvent was analyzed using Differential Scanning Calorimetry as a function of temperature. Using the data obtained from DSC, the heat capacity equation (3.3) for the carbon-rich 30 wt % aqueous MEA solution was derived and which was used to calculate heat capacity values (KJ/kg.K) with respect to the lean temperature of the solvent.
Heat capcity=0.00002〖*T〗_lean^3-0.0035*T_lean^2+0.1912〖*T〗_lean+1.0508 (3.3)
After regeneration, the sample was subjected to carbon loading analysis and are tabulated. Table 2 shows the comparison of the sensible heat calculation for both the conventional and high-frequency ultrasonics solvent regeneration techniques. From the table 2, it has been observed that the regeneration energy for conventional heating was 68.71 KJ/mol.CO2 whereas for low temperature ultrasonics its 6.3 KJ/mol.CO2, which is 10.9 times lesser than the conventional method.
Table 2. solvent regeneration energy calculation
Nominal Power Input Conventional High-frequency Ultrasonics
Mass of Solvent, kg 0.05 0.05
Regeneration Time, s 3600 3600
Heat Capacity, kJ/kg.K 5.43 3.43
Rich Initial Temp., oC 26.9 12.1
Lean Final Temp. oC 102.2 17.5
Rich Carbon Loading, mol CO2/mol Solvent 0.503 0.503
Lean Carbon Loading, mol CO2/mol Solvent 0.208 0.356
Regeneration Energy, KJ/mol CO2 68.71 6.30

It is emphasized that the Abstract of the Disclosure is provided to allow a reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein,” respectively. Moreover, the terms “first”, “second,” “third,” and so forth, are used merely as labels, and are not intended to impose numerical requirements on their objects.
What has been described above includes examples of the disclosed architecture. It is, of course, not possible to describe every conceivable combination of components and/or methodology, but one of ordinary skill in the art may recognize that many further combinations and permutations are possible. Accordingly, the novel architecture is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims.
Without further description, it is believed that one of ordinary skill in the art can, using the preceding description and the illustrative examples, make and utilize the present invention and practice the claimed methods. It should be understood that the foregoing discussion and examples merely present a detailed description of certain preferred embodiments. It will be apparent to those of ordinary skill in the art that various modifications and equivalents can be made without departing from the spirit and scope of the invention.