TWI569866B - Automatic controlling device and method for adsorbing carbon dioxide - Google Patents

Description

Automated carbon dioxide absorption device and method thereof

The present invention relates to an automated carbon dioxide absorption apparatus and method thereof, and more particularly to an apparatus and method for controlling the flow rate of an absorption liquid by detecting a pH value.

In the treatment of flue gas, the chemical absorption method captures carbon dioxide as the most commonly used carbon capture method. The process requires chemical absorption, carbon capture, regeneration, and emission of carbon dioxide in accordance with the standard concentration of emissions. At present, the optimal energy consumption value of carbon capture is known to be related to the carbon dioxide loading of the absorption liquid. However, the concentration of carbon dioxide in the flue gas is usually not fixed, and the manner of fixing the flow rate of the absorption liquid is conventionally used to capture carbon. It can only provide a fixed amount of carbon dioxide. When the concentration of carbon dioxide is high, the concentration of exhaust gas is higher than the standard and cannot meet the emission regulations. When the concentration of carbon dioxide is low, it is impossible to capture carbon at the lowest energy consumption. .

For example, in the Republic of China Patent Publication No. I421123, a method for capturing carbon dioxide is disclosed, which comprises: performing a front-end removal of certain specific components in the exhaust gas of the chimney; and providing chimney exhaust gas at a flow rate of 10 to 11 cubic meters per hour. Wherein the temperature of the chimney exhaust gas is 30 to 40 ° C; a primary amine solution containing water and a primary amine is supplied as an absorption liquid at a predetermined flow rate, and the carbon dioxide in the chimney exhaust gas is absorbed by the primary amine, wherein the predetermined flow rate is 60 to 70 kg per hour. a primary amine; and a primary amine regeneration step to remove the carbon dioxide absorbed by the primary amine from. However, this method of capturing carbon dioxide has the disadvantage of still lacking the function of automatically controlling the flow rate of the absorbing liquid, and cannot solve the current problem.

Therefore, it is necessary to provide an automatic carbon dioxide absorption device and method for automatically controlling the flow rate of the absorption liquid, reducing the processing energy and saving the cost in accordance with different carbon dioxide concentrations, and ensuring that the emission standards are met to solve the problems of the conventional technology.

The main object of the present invention is to provide an automatic carbon dioxide absorbing device and a method thereof, which utilizes a chemical absorption method to capture carbon dioxide in a mixed gas by using an alkaline solution as an absorbing liquid, and the carbon dioxide concentration directly affects the pH value of the absorbing liquid (pH value) ), and the detection of the pH value is simple and rapid. By the correlation curve between the carbon dioxide concentration and the pH value of the absorption liquid, the flow rate of the absorption liquid required for the adjustment can be automatically adjusted to form a feedback system, so that the fluctuation of the carbon dioxide concentration can be More efficient use of absorbents, saving on exhaust gas treatment costs while meeting CO2 emission standards.

A secondary object of the present invention is to provide an automatic carbon dioxide absorbing apparatus and method thereof, which can monitor the regeneration and decay of the absorbing liquid by measuring the pH value of the absorbing liquid after regeneration, and avoid the incomplete regeneration or the fading of the absorbing liquid. A mechanism that affects the automatic control of the flow of absorbed liquid.

In order to achieve the above object, an embodiment of the present invention provides an automatic carbon dioxide absorption apparatus, comprising: an absorption unit for accommodating an alkaline solution and a mixed gas, wherein the mixed gas contains at least carbon dioxide, wherein the alkaline The solution and the mixed gas react to form a carbon-containing mixed liquid, and the carbon-containing mixed liquid is led out through a lead-out line; a regeneration unit collects the derived carbon-containing mixed liquid, and heats the carbon-containing mixed liquid to generate a Recycled liquid as well a carbon dioxide gas; a pH detector disposed on the lead-out line between the absorption unit and the regeneration unit for measuring a pH value of the carbon-containing mixture to obtain a measured value; and a flow control Provided on a return line between the absorption unit and the regeneration unit; wherein the recovery liquid is returned to the absorption unit via the return line and mixed with the alkaline solution, and the flow controller adjusts the a flow rate of the recovered liquid to maintain the measured value at a first predetermined value, wherein the first predetermined value is measured by the pH detector when the carbon dioxide gas concentration is a standard value The pH of the carbon-containing mixture.

In an embodiment of the invention, the alkaline solution is selected from the group consisting of an alcohol amine, an aqueous ammonia solution, an aqueous sodium hydroxide solution, an organic amine, an organic base, or a mixed solution thereof.

In an embodiment of the present invention, a second pH detector is disposed on the return line between the absorption unit and the regeneration unit to measure the pH value of the recovered liquid. A second measurement is obtained.

In an embodiment of the invention, when the second measured value is lower than a second predetermined value, the absorption efficiency of the alkaline solution in the recovered liquid or the absorption unit is decreased, and the second predetermined value is The pH value of the recovered liquid measured by the second pH detector when the carbon dioxide gas concentration is the standard value.

In an embodiment of the present invention, when the measured value is less than the first predetermined value, the flow controller increases the flow rate of the recovered liquid to raise the measured value to the first predetermined value; when the measured value is greater than the first At a predetermined value, the flow controller reduces the flow of the recovered liquid to reduce the measured value to the first predetermined value.

Another embodiment of the present invention provides an automated carbon dioxide absorption method comprising the steps of: (S1) providing a mixed gas containing carbon dioxide; (S2) Passing the mixed gas into an alkaline solution, reacting the alkaline solution with the carbon dioxide in the mixed gas to form a carbon-containing mixed liquid; (S3) heating the carbon-containing mixed liquid to form a recovered liquid and a carbon dioxide (S4) introducing the recovered liquid back into the alkaline solution to form an absorption liquid cycle; (S5) detecting the pH value of the carbon-containing mixed solution in the step (S2) to obtain a measured value; S6) an adjustment step (S4) of the flow rate of the recovered liquid to maintain the measured value at a first predetermined value, wherein the first predetermined value is when the concentration of carbon dioxide contained in the carbon dioxide gas is a standard value The pH value of the carbon-containing mixture was measured.

In an embodiment of the invention, the step (S6) comprises: (S61) increasing the flow rate of the recovered liquid to increase the measured value to the first predetermined value; or (S62) decreasing the flow rate of the recovered liquid, so that The measured value is reduced to the first predetermined value.

In an embodiment of the present invention, after the step (S6) and before returning the recovered liquid to the alkaline solution, the method further comprises a step of: (S7) detecting the pH value of the recovered liquid to obtain a second Measurements.

In an embodiment of the present invention, when the second measured value is lower than a second predetermined value, the absorption efficiency of the recovered liquid or the alkaline solution is decreased, and the second predetermined value is that the concentration of the carbon dioxide gas is The pH value of the recovered liquid measured by the second pH detector when the standard value is used.

In an embodiment of the invention, the alkaline solution is selected from the group consisting of an alcohol amine, an aqueous ammonia solution, an aqueous sodium hydroxide solution, an organic amine, an organic base, or a mixed solution thereof.

10‧‧‧Absorption unit

20‧‧‧Renewal unit

30‧‧‧pH detector

40‧‧‧Flow controller

50‧‧‧Second pH detector

61‧‧‧Export pipeline

62‧‧‧Return pipeline

63‧‧‧Exhaust line

Fig. 1 is a schematic view showing the use of an automatic carbon dioxide absorption apparatus according to an embodiment of the present invention.

Fig. 2 is a graph showing the correlation between the concentration of carbon dioxide gas discharged and the pH value in an embodiment of the present invention.

The above and other objects, features and advantages of the present invention will become more <RTIgt; Furthermore, the directional terms mentioned in the present invention, such as upper, lower, top, bottom, front, rear, left, right, inner, outer, side, surrounding, central, horizontal, horizontal, vertical, longitudinal, axial, Radial, uppermost or lowermost, etc., only refer to the direction of the additional schema. In addition, the singular forms "a", "the" For example, the term "a compound" or "at least one compound" may include a plurality of compounds, including mixtures thereof; "%" as referred to in the present specification means "percent by weight (wt%)" unless otherwise specified; For example, 10%~11% of A) include upper and lower limits (ie 10% ≦A≦11%) unless otherwise specified; if the value range does not define a lower limit (such as B below 0.2%, or 0.2) B) below B) means that the lower limit may be 0 (ie 0% ≦ B ≦ 0.2%); the proportional relationship of the "weight percentage" of each component may also be replaced by the proportional relationship of "parts by weight". The above terms are used to illustrate and understand the present invention and are not intended to limit the invention.

Referring to FIG. 1 , an embodiment of the present invention provides an automatic carbon dioxide adsorption device, which mainly includes an absorption unit 10 , a regeneration unit 20 , a pH detector 30 , and a flow controller 40 . The inter-systems can be interconnected by lines or channels to form a circulating fluid system.

Referring to FIG. 1 , the absorption unit 10 is configured to accommodate an alkaline solution and a mixed gas, and may have a plurality of inlets (not shown) for injecting the alkaline solution or the mixture. Combined with gas. The alkaline solution may be selected from the group consisting of an alcohol amine, an aqueous ammonia solution, an aqueous sodium hydroxide solution, an organic amine, an organic base or a mixed solution thereof, but is not limited thereto, as long as it can react with carbon dioxide, and the solution after the reaction has a change in pH value. Features can be. The mixed gas may be, for example, a flue gas or a factory-derived exhaust gas containing at least carbon dioxide. By using a chemical absorption method, the alkaline solution can react with carbon dioxide in the mixed gas to form a carbon-containing mixed liquid, and then the carbon-containing mixed liquid carries carbon dioxide in the mixed gas from the absorption unit 10, and is disposed at the A derivation line 61 between the absorption unit 10 and the regeneration unit 20 is led out and transported to the regeneration unit 20.

The regeneration unit 20 is configured to collect and heat the carbon-containing mixed liquid derived from the outlet line 61 to generate a recovery liquid and a carbon dioxide gas. The main component of the recovered liquid is still the alkaline solution, but may contain other impurities. The recovered liquid is then output from the regeneration unit 20, transported by a return line 62 disposed between the absorption unit 10 and the regeneration unit 20, and returned to the absorption unit 10 for reuse. The carbon dioxide gas is discharged from an exhaust line 63, and its concentration is required to comply with the gas discharge standard, and may be, for example, 1.5%, 3% or 4%, but is not limited thereto.

Furthermore, the pH detector 30 can be disposed between the absorption unit 10 and the regeneration unit 20, for example, at any position of the outlet line 61 for measuring the pH value of the carbon-containing mixture. To obtain a measured value. Preferably, the pH detector 30 is preferably disposed near the inlet of the regeneration unit 20 to instantly obtain the pH value of the carbon-containing mixture. The flow controller 40 can then be disposed between the absorption unit 10 and the regeneration unit 20, for example, at any position of the return line 62, and can control the flow rate of the recovered liquid into the absorption unit 10. Preferably, the flow controller 40 is preferably disposed adjacent the inlet of the absorption unit 10. Due to the amount of carbon dioxide supported, the pH of the carbon-containing mixture can be maintained at a first predetermined value by adjusting the flow rate of the recovered liquid, the first predetermined value being concentrated in the carbon dioxide gas The pH value of the carbon-containing mixture measured by the pH detector 30 when the degree is a standard value.

In addition, in an embodiment, a second pH detector 50 is further disposed on the return line 62 between the absorption unit 10 and the regeneration unit 20, and preferably disposed in the regeneration unit 20 Near the entrance. The second pH detector 50 is configured to measure the pH value of the recovered liquid in the return line 62 to obtain a second measurement value, which can be used to observe the recovery liquid after being processed by the regeneration unit 20 Whether it has normal absorption capacity. When the second measured value is lower than a second predetermined value, the absorption efficiency of the recovered liquid or the alkaline solution is lowered, which may be because the recovery of the recovered liquid is incomplete, and the setting of the regeneration unit 20 should be checked at this time. Or whether the operating conditions are suitable; or because the recovered liquid or the alkaline solution has deteriorated, a new alkaline solution should be replaced. The second predetermined value is a pH value of the recovered liquid measured by the second pH detector 50 when the carbon dioxide gas concentration is the standard value.

Then, the recovered liquid is mixed with the alkaline solution to continue to absorb the mixed gas that is continuously supplied. In an embodiment of the present invention, when the measured value is less than the first predetermined value, the flow controller 40 may automatically increase the flow rate of the recovered liquid, for example, by increasing the valve opening to raise the measured value to the a first predetermined value; when the measured value is greater than the first predetermined value, the flow controller 40 reduces the flow rate of the recovered liquid, such as reducing the valve opening to reduce the measured value to the first predetermined value. The flow controller 40 can additionally include a computer or a control circuit to control the flow rate in response to changes in the measured values. Therefore, by comparing the difference between the measured value and the first predetermined value, the flow rate of the recovered liquid can be programmed or automatically controlled to achieve rapid and effective carbon dioxide absorption, and the exhaust gas treatment cost can be saved under the premise of meeting the carbon dioxide emission standard.

Furthermore, another embodiment of the present invention provides an automated carbon dioxide absorption method, which mainly comprises the steps of: (S1) providing a mixed gas; (S2) introducing the mixed gas In an alkaline solution, forming a carbon-containing mixed solution; (S3) heating the carbon-containing mixed liquid to form a recovered liquid and carbon dioxide gas; (S4) conducting the recovered liquid back to the alkaline solution; (S5) detecting The pH value of the carbon-containing mixed solution of the step (S2) to obtain a measured value; and (S6) the adjusting flow (S4) the flow rate of the recovered liquid to be returned to maintain the measured value at a first predetermined value. The details of the implementation of the above-described steps of the embodiment and the principles thereof will be described in detail below.

The automated carbon dioxide absorption method of the above embodiment of the present invention is first of all: (S1) providing a mixed gas. In this step, the mixed gas contains carbon dioxide, which may be, for example, a flue gas or a factory-discharged exhaust gas, and the subsequent step is to remove carbon dioxide from the mixed gas (exhaust gas).

The automated carbon dioxide absorption process of the above embodiment of the present invention is followed by: (S2) passing the mixed gas into an alkaline solution to form a carbon-containing mixed liquid. In this step, the alkaline solution may be selected from the group consisting of an alcohol amine, an aqueous ammonia solution, an aqueous sodium hydroxide solution, an organic amine, an organic base, or a mixed solution thereof, but is not limited thereto, as long as it can react with carbon dioxide, and the solution after the reaction has The characteristic of the change in pH value is sufficient. By the chemical absorption method, the alkaline solution can react with the carbon dioxide in the mixed gas to form the carbon-containing mixed liquid, and the carbon dioxide is carried by the carbon-containing mixed solution and partially removed from the mixed gas.

The automated carbon dioxide absorption process of the above embodiment of the present invention is followed by: (S3) heating the carbon-containing mixed liquid to form a recovered liquid and carbon dioxide gas. In this step, the main component of the recovered liquid is still the alkaline solution, but may contain other impurities such as carbon dioxide which is not completely removed after heating. The carbon dioxide gas can be discharged at a concentration that meets the gas emission standards.

The automated carbon dioxide absorption method of the above embodiment of the present invention is followed by: (S4) The recovered liquid is returned to the alkaline solution. In this step, the recovered liquid can be mixed with the alkaline solution through a line and then used as an absorption liquid of carbon dioxide, thereby forming an absorption liquid circulation.

The automated carbon dioxide absorption method of the above embodiment of the present invention is followed by: (S5) detecting the pH value of the carbon-containing mixed solution of the step (S2) to obtain a measured value. In actual operation, the measured value is continuously varied, and a correlation curve can be formed against the concentration of the carbon dioxide gas. This is because the pH value of the carbon-containing mixed liquid is affected by the carried two quantized carbon gas, and it shows that the higher the concentration of the carbon dioxide gas, the lower the measured value. Conversely, the lower the concentration of carbon dioxide gas, the higher the measurement.

The automatic carbon dioxide absorption method of the above embodiment of the present invention is finally: (S6) adjusting step (S4) the flow rate of the recovered liquid is returned to maintain the measured value at a first predetermined value. Wherein, the first predetermined value is a measured value of the pH of the carbon-containing mixed liquid when the concentration of carbon dioxide contained in the carbon dioxide gas is a standard value. In this step, in order to make the concentration of the discharged carbon dioxide gas fixed within a standard value range, and when the concentration of the carbon dioxide gas is low, the use of the absorption liquid is not excessively wasted, so the measurement value needs to be controlled in a specific The range interval is preferably a measurement value corresponding to the time when the carbon dioxide gas concentration is a standard value, that is, the first predetermined value. Further, the step (S6) of adjusting the flow rate of the recovered liquid may include: (S61) increasing the flow rate of the recovered liquid to increase the measured value to the first predetermined value; or (S62) decreasing the flow rate of the recovered liquid, so that The measured value is reduced to the first predetermined value.

In addition to the above steps, after the step (S6) and before returning the recovered liquid to the alkaline solution, a step (S7) may be further included: detecting the pH value of the recovered liquid to obtain a second measured value. . In this step, the second measured value can utilize a second pH detector obtain. When the second measured value is lower than a second predetermined value, the absorption efficiency of the recovered liquid or the alkaline solution is lowered. The second predetermined value is a pH value of the recovered liquid measured by the second pH value detector when the carbon dioxide gas concentration is the standard value.

In order to make the automated carbon dioxide absorption apparatus and method of the present invention clearer and easier to understand, please refer to the following experimental data and instructions.

First, 30% by weight of an alcohol amine is placed in the absorption unit 10 as an alkaline solution, and the smoke is discharged at a flow rate of 11.2 cubic meters per hour (m ³ ) at room temperature and at a pressure of 1 kg/cm ² G. The gas passes into the absorption unit 10 to perform carbon dioxide absorption and discharge treatment. Next, the data obtained by detecting the carbon-containing mixed liquid outputted from the absorption unit 10 into the outlet line 61 and detecting the pH value of the recovered liquid outputted from the regeneration unit 20 into the return line 62 are obtained. Table 1 below. Then, the carbon dioxide gas emission concentration (%) at the outlet of the regeneration unit 20 is taken as the vertical axis on the X-axis and the pH value (pH value), and a correlation curve between the emission concentration and the pH value is prepared, as shown in Fig. 2. It can be seen from Fig. 2 that the higher the pH of the carbon-containing mixture, the lower the corresponding carbon dioxide gas emission concentration. Therefore, if the standard value of the concentration of the emitted carbon dioxide is 3%, the pH of the carbon-containing mixture needs to be about 9.14. If the pH value of the carbon-containing mixture is continuously detected, it is found that the pH value becomes 9.01, which is 9.14 lower than the standard value of 3%, indicating the concentration that should be carried when the carbon dioxide concentration is higher than 3%. In order to make the emission comply with the standard, the flow controller 40 increases the flow rate of the recovered liquid at this time. For example, when the concentration of the carbon dioxide gas is 3%, the flow rate used is 100 kg/hr (Kg/hr). Adjusted to 105 ~ 110 kg / hour, the pH of the carbon-containing mixture gradually returned to about 9.14. Conversely, if the pH value of the carbon-containing mixture is continuously detected, the pH value becomes 9.34, which is 9.14 higher than the discharge standard value, which means that the carbon dioxide emission concentration is less than 3%. In order to avoid wasting excess absorption liquid, The flow controller then reduces the flow rate of the recovered liquid, for example, by 90 to 95 kg/hr until the pH returns to about 9.14. That is to say, by using the correlation curve between the concentration of the exhaust gas and the pH of the carbon-containing mixed liquid, the amount of the absorbed liquid can be adjusted in time according to the change in the pH value, thereby achieving the purpose of saving the processing cost.

Furthermore, please continue to refer to Figure 2, the pH of the recovered liquid can be used to evaluate the absorption of the recovered liquid. For example, taking the emission standard value of 3% as an example, when the pH value of the recovered liquid is continuously detected and found to be lower than 10.26, it means that the regeneration of the recovered liquid is incomplete, and it is necessary to check whether the operating conditions of the regeneration unit 20 are biased. Or the recovery effect of the recovery liquid itself has declined, and a new alkaline solution needs to be replaced. Furthermore, by monitoring the pH of the recovered liquid, it helps to ensure that the flow controller 40 is not affected by the degradation of the absorption effect, and consumes excess energy to provide a larger amount of recovered liquid flow.

Compared with the prior art, the automatic carbon dioxide absorption device and the method thereof according to the embodiments of the present invention can easily and quickly learn the state of carbon dioxide absorption, and adjust the flow rate of the required absorption liquid according to the concentration of carbon dioxide contained in the mixed gas. To achieve the goal of reducing energy consumption and saving costs.

Although the present invention has been disclosed in its preferred embodiments, it is not intended to limit the invention, and any person skilled in the art can make it without departing from the spirit and scope of the invention. Various changes and modifications are intended to be included within the scope of the appended claims.

10‧‧‧Absorption unit

20‧‧‧Renewal unit

30‧‧‧pH detector

40‧‧‧Flow controller

50‧‧‧Second pH detector

61‧‧‧Export pipeline

62‧‧‧Return pipeline

63‧‧‧Exhaust line

Claims (10)

An automatic carbon dioxide absorption device comprising: an absorption unit for accommodating an alkaline solution and a mixed gas, wherein the mixed gas contains at least carbon dioxide, wherein the alkaline solution reacts with the mixed gas to form a carbon-containing mixture, The carbon-containing mixed liquid is led out through a lead-out line; a regeneration unit is configured to collect the derived carbon-containing mixed liquid and heat the carbon-containing mixed liquid to generate a recovered liquid and carbon dioxide gas; a pH detector Provided on the lead-out line between the absorption unit and the regeneration unit for measuring the pH value of the carbon-containing mixed liquid to obtain a measured value; and a flow controller disposed at the absorption unit and the Returning one of the regeneration units to the pipeline; wherein the recovery liquid is led back to the absorption unit via the return line and mixed with the alkaline solution, and the flow controller is used to adjust the flow rate of the recovered liquid. And maintaining the measured value at a first predetermined value, wherein the first predetermined value is measured by the pH detector when the carbon dioxide gas concentration is a standard value The pH of the mixture containing carbon. The automatic carbon dioxide absorption device according to claim 1, wherein the alkaline solution is selected from the group consisting of an alcohol amine, an aqueous ammonia solution, an aqueous sodium hydroxide solution, an organic amine, an organic base, or a mixed solution thereof. The automatic carbon dioxide absorption device of claim 1, further comprising a second pH detector disposed on the return line between the absorption unit and the regeneration unit for measuring the The pH of the recovered liquid is recovered to obtain a second measurement. The automatic carbon dioxide absorption device according to claim 3, wherein when the second measurement value is lower than a second predetermined value, the absorption efficiency of the alkaline solution in the recovery liquid or the absorption unit is decreased. The second predetermined value is a pH value of the recovered liquid measured by the second pH detector when the carbon dioxide gas concentration is the standard value. The automatic carbon dioxide absorption device of claim 1, wherein when the measured value is less than the first predetermined value, the flow controller increases the flow rate of the recovered liquid to raise the measured value to the first predetermined value. And when the measured value is greater than the first predetermined value, the flow controller reduces the flow rate of the recovered liquid to reduce the measured value to the first predetermined value. An automatic carbon dioxide absorption method comprising the steps of: (S1) providing a mixed gas containing carbon dioxide; (S2) passing the mixed gas into an alkaline solution to make the alkaline solution and the mixed gas The carbon dioxide reaction forms a carbon-containing mixed liquid; (S3) heating the carbon-containing mixed liquid to form a recovered liquid and a carbon dioxide gas; (S4) guiding the recovered liquid back to the alkaline solution to form an absorption liquid circulation (S5) detecting the pH value of the carbon-containing mixture in the step (S2) to obtain a measured value; and (S6) adjusting (S4) the flow rate of the recovered liquid to be returned to maintain the measured value a first predetermined value, wherein the first predetermined value is a pH value of the carbon-containing mixture measured when the carbon dioxide gas concentration is a standard value. The automatic carbon dioxide absorption method according to claim 6, wherein the step (S6) comprises: (S61) increasing a flow rate of the recovered liquid to increase the measured value to the first predetermined A value is set; or (S62) reducing the flow rate of the recovered liquid to lower the measured value to the first predetermined value. The automatic carbon dioxide absorption method according to claim 6, wherein after the step (S6) and before returning the recovered liquid to the alkaline solution, the method further comprises a step of: (S7) detecting the acid of the recovered liquid. The base value is obtained as a second measurement. The method of claim 6, wherein the second measured value is lower than a second predetermined value, and the absorption efficiency of the recovered liquid or the alkaline solution is decreased, and the second predetermined value is The pH value of the recovered liquid measured by the second pH detector when the carbon dioxide gas concentration is the standard value. The automatic carbon dioxide absorption method according to claim 6, wherein the alkaline solution is selected from the group consisting of an alcohol amine, an aqueous ammonia solution, an aqueous sodium hydroxide solution, an organic amine, an organic base, or a mixed solution thereof.