1. Field of the Invention
The invention relates to detecting chemical composition and controlling chemical processes using Raman spectroscopy.
2. Description of the Related Art
There are a number of useful chemical processes that require carbonate, bicarbonate and total carbonate measurements. One such process is a carbon dioxide scrubbing process in which carbonate and bicarbonate are the main components. Another example is producing carbon dioxide from an alkali carbonate/bicarbonate solution.
The conventional method of determining carbonate, bicarbonate, and total carbonate measurements uses acid/base titration. This is a batch system, which necessarily introduces a finite time lag in concentration measurements. The acid/base titration method is also plagued by interferences from various chemical compounds.
What is needed, therefore, is a continuous, online apparatus and method of detecting and controlling carbonate and bicarbonate concentrations in a chemical process that is not subject to interference from other chemical compounds.
The invention is an apparatus and method that satisfies the need for a continuous, online way of detecting and controlling carbonate and bicarbonate concentrations in a chemical process that is not subject to interference from other chemical compounds. One aspect of the invention is a method for controlling a chemical process comprising the steps of flowing a carbonate/bicarbonate mixture through a measurement cell, exposing it with laser light of suitable wavelength and power; measuring the intensity of the scattered light using Raman spectroscopy; calculating the concentration of carbonate and bicarbonate from the intensity of the scattered light, and using the measurement to adjust process control parameters to control the ratio and concentration of bicarbonate and carbonate in the process fluid. These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claim, and accompanying drawings.
Turning to
Raman spectroscopy depends upon the inelastic scattering of monochromatic light. The incident light usually comes from a laser in the visible or ultraviolet range. When carbonate and/and bicarbonate are irradiated with the laser light, they shift the frequency of the light. This shift can be measured for both carbonate and bicarbonate and occurs at different frequencies. Turning to
By measuring the intensity of the scattered light either by peak height or peak area, the concentrations of each component can be determined. These two concentrations can then be used to calculate total carbonate.
The invention involves using Raman spectroscopy to identify and quantify carbonate and bicarbonate real time in a process that relies on the ratio of carbonate, and bicarbonate present as well as the total carbonate concentration. To our knowledge, there are presently no alternatives to performing this online.
One embodiment is a carbon dioxide scrubbing process where carbonate and bicarbonate are the main components as shown in
A “carbonate lean” solution 106 is introduced to a CO2 absorption process/CO2 absorber 108. A carbonate lean solution contains a ratio of HCO3−/CO32− greater than 1. Its composition is measured by a first Raman spectrometer 118. As CO2 is absorbed into the carbonate solution, the following general reaction will take place:
CO3−2+H2O+CO2→2HCO3− (1)
As this occurs, the total carbonate and carbonate/bicarbonate ratio will change. A “carbonate rich” solution with HCO3−/CO3−2 ratio less than 1 will exit the absorption process 114. Its composition is measured by a second Raman spectrometer 120. The carbonate/bicarbonate solution can be but is not limited to Na2CO3/NaHCO3, (NH4)2CO3/NH4HCO3, and K2CO3/KHCO3. The important factor for controlling the ratio of carbonate and bicarbonate in the solution is that the carbonate be soluble in the solution being measured.
This method would be used to control the total carbonate concentration and to control the ratio carbonate concentration to bicarbonate concentration. The concentration values would be sent to a PLC 116 as feedback to the process control loops to the process/absorber 108. These factors are important because if the carbonate to bicarbonate ratio is not controlled it would lead to poor absorption efficiency. If the total carbonate concentration is not controlled, it would lead to “salting out” or precipitation of the carbonate solution fouling mass and heat transfer surfaces. The method provides feedback to the PLC for adjusting parameters such as, but not limited to liquid flow rates, reagent addition rates, and temperatures.
Turning to
In such a process, feedback will be necessary to determine if the solution has been regenerated 126 to the degree required to by the process. A method of doing this is to measure the carbonate and bicarbonate concentrations along different points of the process.
A rich HCO3−/CO3−2 solution 124 is introduced to a regeneration process 126. Its composition is measured by a first Raman spectrometer 130. CO2 gas 134 is produced as a result of the regeneration process 126. A lean HCO3−/CO3−2 solution 122 exits the regeneration process. Its composition is measured by a second Raman spectrometer 128.
Information from the first and second Raman spectrometers 130, 128 would be fed to a PLC 132, which would then control an energy input to the regeneration process 126. The Raman spectrometers would provide real time data input to a PLC or other automated controller that could then be used for either regeneration 126 or absorber 108 control.
One embodiment of a measurement system could include, but not be limited to, the following:
Although the preferred embodiments of the present invention have been described herein, the above description is merely illustrative. Further modification of the invention herein disclosed will occur to those skilled in the respective arts and all such modifications are deemed to be within the scope of the invention as defined by the appended claim.
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/US09/51924 | 7/28/2009 | WO | 00 | 1/24/2011 |
Number | Date | Country | |
---|---|---|---|
61084524 | Jul 2008 | US |