Optical probes for process Raman spectroscopy and methods of use

Abstract

One aspect of the present disclosure discloses a probe comprising: a probe body having a central axis defining a proximal end and a distal end and including an orifice in the distal end; a window fixed in the orifice, wherein the window is substantially optically transparent; and a flange abutting the proximal end of the probe body, the flange comprising a sealing surface and a sealing edge, wherein the flange separates an in-process portion of the probe from a post-process portion of the probe, the in-process portion comprising at least the probe body, the sealing surface and the sealing edge, wherein at least the in-process portion of the probe consists substantially of an austenitic stainless steel material. A further aspect includes a computer product configured to perform a method employing a probe.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is related to and claims priority to U.S. Provisional Patent Application No. 62 / 807,022, filed on February 18, 2019, the entire disclosure of which is hereby incorporated by reference. Technical Field

[0003] The present disclosure relates generally to laser spectroscopy, and more particularly to an optical probe assembly for laser spectroscopy. Background Art

[0004] Raman spectroscopy is a type of laser spectroscopy based on an effect called Raman scattering. Raman scattering is an inelastic scattering of electromagnetic radiation, such as the excitation light from a laser, when traversing a medium. Its effect can be summarized as follows. Most of the incident photons of the excitation light undergo elastic scattering (called Rayleigh scattering), so that the scattered radiation has the same frequency as the incident radiation. However, a minority of the incident photons undergo inelastic scattering, so that the emitted photons have lower or higher energy, thus resulting in higher and / or lower frequencies than the incident radiation.

[0005] Inelastic scattering is caused by the selective interaction between the incident radiation and the molecules in the medium, which is specific to each form of chemical bonding. The frequency shift observed in the inelastically scattered radiation provides information about the composition of the medium, for example, the concentration of a specific molecule. By filtering the frequency of the incident radiation, the relatively weak inelastically scattered light can be separated from the relatively strong Rayleigh scattered light, and the inelastically scattered light is collected to generate information about the composition of the medium.

[0006] Raman spectroscopy has emerged as a powerful tool for use in conjunction with in situ process analysis. Precision fiber-coupled Raman probes are currently used for process sampling in a variety of industries, including polymer, chemical, petrochemical, food and beverage, pharmaceutical, biopharmaceutical, and other life science industries. However, certain processes involve extreme process conditions, including high temperatures, high pressures, and corrosive environmental conditions, which conventional spectroscopic probes cannot withstand for extended periods of time. Furthermore, because conventional optical probes cannot withstand certain process conditions, analytical methods for in situ Raman-based analysis of such processes have not previously been developed.

[0007] Thus, there remains a need for further contributions in this area of ​​technology. Summary of the invention

[0008] One aspect of the present disclosure includes a probe comprising: a probe body having a central axis defining a proximal end and a distal end and including an orifice in the distal end; a window fixed in the orifice, wherein the window is substantially optically transparent; a flange adjacent to the proximal end of the probe body, the flange including a sealing surface and a sealing edge, wherein the flange separates an in-process portion of the probe from a post-process portion of the probe, the in-process portion including at least the probe body, the sealing surface and the sealing edge; and a collar adjacent to the flange opposite the probe body in the post-process portion of the probe, wherein the probe body, the flange and the collar define an internal volume passing therethrough, the internal volume being configured to accommodate an optical cable so that the optical cable can pass through the probe body, the flange and the collar to be optically connected to the window, and wherein at least the in-process portion of the probe is substantially composed of an austenitic stainless steel material.

[0009] In an embodiment, the austenitic stainless steel material complies with ASTM UNS S31050 or AISI 310 MoLN. In a further embodiment, the austenitic stainless steel material complies with EN X1CrNiMoN25-22-2 or EN 1.4466. In an embodiment, the probe body, flange and collar are made of the same austenitic stainless steel material. In an embodiment, the probe body, flange and collar form an integral part. In a further embodiment, the post-process portion of the probe consists essentially of 316 steel material.

[0010] In certain embodiments, the probe further comprises: a main body having a distal end and a proximal end, the main body defining a passage therethrough, wherein the passage is configured to accommodate at least the proximal end of the probe body into the proximal end of the main body, the passage further configured to enable an optical cable to pass into the main body and connect to the probe body; and a process connection secured to the main body at or near the proximal end of the main body, the process connection configured to enable the probe to be attached to the process connection when assembled, wherein the flange of the probe seats against the process connection, and wherein the probe is reversibly attached at or near the proximal end of the main body such that the probe body extends from the main body. In further embodiments, the probe further comprises a fiber optic connection comprising an interlock connected to the distal end of the main body and configured to reversibly attach the optical cable to the probe.

[0011] In an embodiment, the sealing surface is adapted to seal against a complementary surface of a process vessel or a flow cell configured to receive the probe body.In certain embodiments, the window is comprised of sapphire.

[0012] A further aspect of the present disclosure includes a method for online quantitative analysis of at least one process stream of a urea synthesis process. The method uses a spectroscopic system comprising: a narrowband light source adapted to generate excitation light of a suitable wavelength; an optical probe comprising: a probe body having a central axis defining a proximal end and a distal end and comprising an orifice in the distal end; a window fixed in the orifice, wherein the window is substantially optically transparent; a flange adjacent to the proximal end of the probe body, the flange comprising a sealing surface and a sealing edge, wherein the flange separates the process portion of the probe from the process post portion of the probe, the process post portion comprising at least the probe body, the sealing surface and the sealing edge; and a collar adjacent to the flange opposite the probe body, wherein the probe body, the flange and the collar define an internal volume therethrough, the internal volume being configured to accommodate an optical cable so that the optical cable can pass through the probe body, the flange and the collar and be in optical communication with the window, and wherein at least the process portion of the probe is substantially composed of an austenitic stainless steel material. The spectroscopic system further includes: a spectrometer configured to generate a Raman spectrum from scattered light transmitted to the spectrometer via the probe, the spectrometer including a detector; an optical cable that performs optical communication between the probe and the spectrometer; and a processor configured to control the spectroscopic system and process and analyze the Raman spectrum.

[0013] The method includes generating excitation light using a light source and emitting the excitation light to a process sample of at least one process stream of a urea synthesis process via a probe; detecting scattered light with a detector of a spectrometer via the probe, processing the scattered light to generate a Raman spectrum; modeling the Raman spectrum using a chemometric model, the model including a transition of spectral bands corresponding to excitation of carbonyl diamide bonds and spectral bands corresponding to excitation of atomic bonds in the form of carboxyl groups, the modeling being performed using a processor; and determining the concentration of urea in the at least one process stream based on the modeled excitation of the carbonyl diamide bonds using Raman spectroscopy, wherein the concentration in the at least one process stream of carbon-containing molecules other than urea and having carboxyl groups is determined by Raman spectroscopy as an equivalent concentration of carbon dioxide corresponding to excitation of atomic bonds in the form of carboxyl groups, the determination being performed using a processor, wherein urea is synthesized from ammonia and carbon dioxide using the urea synthesis process in a pressure range of 100 to 300 bars and a temperature range of 50 to 250° C.

[0014] In an embodiment, from 900 to 1050 cm -1 The method detects the excitation of the carbonyl diamide bond of the urea molecule by a Raman shift of the excitation light in the frequency range of 1000 to 1150 cm -1 In an embodiment, the processor is further configured to detect Raman shifts in the frequency range from 1350 to 1750 cm -1 The Raman shift of the excitation light within the frequency range determines the ammonia concentration.

[0015] A further aspect of the present disclosure includes a computer program product including a non-transitory computer readable medium having stored thereon instructions which, when executed by at least one programmable processor, cause the at least one programmable processor to perform Raman spectroscopy analysis by performing operations of the method. In an embodiment, the stored instructions include instructions for performing operations including: -1 The Raman shift of the excitation light within the frequency range determines the ammonia concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The embodiments and other features, advantages and disclosures contained herein and the manner in which they are obtained will become apparent and the present disclosure will be better understood by referring to the following description of various embodiments of the present disclosure in conjunction with the accompanying drawings, in which:

[0017] Figure 1 is a schematic diagram of an embodiment of a system for performing the method of the present disclosure;

[0018] Figure 2 is a schematic diagram of a further embodiment of a system for performing the method of the present disclosure;

[0019] Figure 3 are spectra of two process streams with different urea and carbon dioxide concentrations;

[0020] Figure 4 shows a perspective view of an optical probe according to the present disclosure;

[0021] Figure 5A shows a cross-sectional view of the optical probe assembly of FIG. 5 taken at line AA;

[0022] Figure 5B Shows Figure 5A Detail of the optical probe at D;

[0023] Figure 6 shows a side view of a probe assembly of the present disclosure;

[0024] Figure 7 shows a perspective view of a probe assembly according to the present disclosure;

[0025] Fig. 8A shows a cross section taken at line AA Figure 6 a cross-sectional view of a portion of a probe assembly;

[0026] Figure 8B Shows Fig. 8A Detail of the probe assembly at detail C;

[0027] Fig.9Aa plan view showing a process connection flange; and

[0028] Fig. 9B The line BB is shown Fig.9A Cross-sectional view of the process connection flange;

[0029] Fig.10 A method of determining urea concentration according to the present disclosure is shown; and

[0030] Fig.11 It shows that according to the present disclosure Figure 1 Schematic diagram of the control unit of the system. DETAILED DESCRIPTION

[0031] The present disclosure discloses various embodiments of an optical probe and methods of use and construction thereof. The present disclosure further discloses various embodiments of methods and models related to online quantitative analysis of a process stream for synthesizing urea in a production plant starting with ammonia and carbon dioxide at high pressure and high temperature. According to one aspect of the present disclosure, an optical probe configured for Raman spectroscopy and adapted for high pressure, high temperature and corrosive process conditions of a urea synthesis process is disclosed.

[0032] For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will be understood, however, that no limitation of the scope of the disclosure is thereby intended.

[0033] Urea can be synthesized from ammonia and carbon dioxide. An overview of the relevant process can be found in Ullmann's Encyclopedia of Industrial Chemistry , 5th edition, vol. A27, paragraph 3.3. Several process streams may be involved in the urea synthesis process, which are highly sensitive to their components, especially to the concentrations of reactants such as ammonia and carbon dioxide, and to the concentration of water which is detrimental to the equilibrium yield. Parameters that strongly influence the process include, for example, the molar ratio of ammonia to carbon, the molar ratio of water to carbon, and the conversion of carbon to urea. Therefore, ideally, the reactant concentrations should be controlled within a narrow range to obtain optimal performance and maximum yield.

[0034] A urea synthesis process for industrial production of urea is a known full cycle technology. Alternatively, urea synthesis can be performed according to known stripping techniques. The main components of a stripping plant include a high-pressure synthesis reactor, a stripping column, a carbamate condenser and a possible scrubber, which together form a high-pressure loop, and one or more recovery sections operating at a lower pressure. Process streams include, for example, effluents of a reactor, a carbamate condenser or a scrubber, a concentrated solution leaving a stripping column, and a low-pressure carbamate solution from a low-pressure recovery section.

[0035] Efficient synthesis processes require monitoring the composition of process streams in order to better understand and optimize the process and ensure proper control of the plant. Traditional monitoring techniques involve off-line analysis of samples of one or more selected process streams. For example, a sample of a pressurized process stream is extracted in a known amount of water to dissolve the gases produced by decompression from the reaction environment, and the sample is then analyzed in a separate laboratory. However, this technique has several disadvantages. Sampling of process streams must be performed by trained personnel for safety reasons and is inherently subject to errors due to the easy loss of volatile compounds. Off-line analysis introduces a time delay between sampling and analysis and is not suitable for timely control of evolving processes. Another disadvantage is that the extraction of samples can lead to sudden changes in thermodynamic parameters and affect the equilibrium and concentration of the evolving medium. As a result, the composition of the sample and the analytical results may be affected.

[0036] Thus, there is a motivation to perform online analysis to obtain real-time data of the relevant process streams. However, online analysis is challenging due to the corrosive nature of ammonium carbamate and the transient products involved in urea synthesis and due to the elevated temperatures and pressures, especially in the high-pressure loop. For example, the solution leaving the reactor is often under supercritical conditions.

[0037] Previous attempts to perform on-line analysis have involved monitoring the gas phase from the reactor using gas chromatography techniques. However, chromatography techniques are only applicable if the reactor has an independent outlet gas line. Furthermore, it has been found that information on the composition of the gas phase is not applicable to on-line control of the production plant, since the ammonium carbamate formed by subsequent dehydration of the carbamate and the urea formed evolve in the liquid phase. Another disadvantage is that gas chromatography techniques require expensive maintenance.

[0038] Another conventional technique is to implement process control that relies primarily on indirect measurement of the ammonia to carbon molar ratio (N / C) as a function of density. Density can be measured in a conventional, relatively simple manner, and the N / C ratio is linearly related to density over a very narrow temperature and pressure range. Therefore, as long as the temperature and pressure are within a certain range, the N / C ratio can be estimated with acceptable accuracy and the technique is considered reliable.

[0039] However, the molar ratio of ammonia to carbon in the reaction mixture is only one of the parameters that actually controls the process. For example, the above techniques do not provide information about the water-to-carbon ratio or the conversion of carbon to urea. In addition, the N / C ratio is measured only by a model based on density readings. The model is adjusted for a narrow density range, so the accuracy may be affected when the actual density (which depends on temperature and pressure) is outside the narrow range or close to the boundary values.

[0040] Another problem encountered in controlling the cyclic urea process is the cascade effect that may be caused by changes in the composition of the process streams. For example, the performance of the reactor is affected by the composition of the carbamate recycle stream from the low-pressure recovery section, while the composition of the recycle stream also depends on the composition of the urea solution at the outlet of the high-pressure stripper that feeds the recovery unit. However, the conventional control system described cannot take this behavior into account. Therefore, there is still a need for a method for online detection of detailed information about the composition of the media involved in urea synthesis to solve the above problems.

[0041] The present disclosure addresses these problems and provides a method, model, probe and system for improved quantitative analysis and improved control and optimization of an industrial urea synthesis process in a plant. The present disclosure includes the application of Raman spectroscopy for on-line quantitative analysis of streams of a urea synthesis process, and an optical probe adapted to withstand the harsh conditions of a urea synthesis process.

[0042] One aspect of the present disclosure is a method for online quantitative analysis of at least one process stream of a urea synthesis process, wherein urea is synthesized from ammonia and carbon dioxide, characterized in that online quantitative analysis is performed using Raman spectroscopy, including a computational model that has been verified to convert Raman spectroscopy data into process components (e.g., ammonia, carbon dioxide, urea) and key performance indicators (e.g., conversion percentage, N / C ratio, hydrogen / carbon molar ratio). The method, probe and model can be applied to high pressure and high temperature synthesis processes. In addition, the method, probe and model can be applied to urea processes in which the synthesis pressure is 100 to 300 bar and the temperature is 50 to 250° C. Therefore, at least one process stream can have a pressure and temperature within the above range.

[0043] Raman spectroscopy of a stream of a urea process according to the present disclosure can be performed with a narrowband light source such as a laser diode or a light emitting diode. The excitation light emitted by the light source is focused in the process stream region to be analyzed. In certain embodiments, the light source can be in the visible light or near-visible light range. In certain embodiments, the light source is monochromatic. The visible light range should generally be understood as a wavelength of 390 to 700 nanometers (nm). The near-visible light range should generally be understood as a wavelength of 300nm to 1.4 micrometers (μm). In at least one embodiment, the method is performed with a monochromatic light source with a wavelength between 300 and 1400nm or further between 400 and 1000nm. For example, an embodiment of the system of the present disclosure includes a 785nm laser source.

[0044] Applicants have discovered that molecules involved in urea synthesis, including urea, ammonium carbamate, carbonates and bicarbonates, and ammonia, provide selective and distinguishable Raman scattering. The disclosed systems and methods use Raman spectroscopy to collect quantitative information about the concentration of target molecules by weight (e.g., wt%). The disclosed methods can be used to determine the concentration of at least one of urea, carbon dioxide, and / or ammonia contained in a process stream.

[0045] Another aspect of the present disclosure is the modeling of solution chemistry (e.g., chemometrics), which is advantageous for the application of Raman spectroscopy. Thus, the chemistry is modeled with reference to the following components: 1) A first component represents the form of carbon converted in the carbonyl diamide formula; a second pseudo-component represents all forms of unconverted carbon, such as carbamate, carbonate, and bicarbonate, etc., assumed to be equivalent single components; a third pseudo-component represents all forms of nitrogen that are not part of the urea molecule, either free in the form of ammonia or bound in the form of ammonium hydroxide, or in the form of salts, such as ammonium carbonate, bicarbonate, and carbamate.

[0046] In the following description, the first component is referred to as urea, the second component is referred to as carbon dioxide and the third component is referred to as ammonia. The above-described stoichiometric model can be applied to any process stream, for example to the solution effluent from a reactor or from a stripper.

[0047] Applicants have discovered that urea concentration can be associated with a characteristic Raman band corresponding to the excitation of a carbonyl diamide bond. The carbonyl diamide bond is present in the urea molecule, and the goal in the present disclosure is to distinguish urea from other forms of unconverted carbon (such as carbon dioxide). The behavior of other forms of unconverted carbon is different from Raman scattering, which is atomic bonds within molecules (carbonates, bicarbonates, and carbamates) that are primarily in the carboxyl form. The method of the present disclosure includes detecting the urea concentration in the process stream using the detection of a spectral band corresponding to the excitation of a carbonyl diamide bond. The concentration of carbon-containing molecules other than urea (unconverted carbon) can be determined as an equivalent concentration of carbon dioxide corresponding to the excitation of atomic bonds in the carboxyl form.

[0048] According to one aspect of the present disclosure, these components can be detected as follows: The first component (e.g., "urea") can be detected by excitation of the carbonyl diamide bond using a frequency range from 900 to 1050 cm -1 The second component (e.g., "carbon dioxide") comprises carbon in an unconverted form, more particularly from 1000 to 1150 cm -1 found to be Raman reactive; the third component (e.g., "ammonia"), including other forms of nitrogen (except urea), can be detected by the 1350 to 1750 cm -1The frequency range of the Raman excitation is measured in cm. -1 The incident excitation light may have a wavelength of about 785 nm.

[0049] In a complex mixture where urea and ammonium carbamate are mixed together, the above frequency range identifies all nitrogen forms in the sample, including those belonging to urea molecules. Once the concentration of the first component is known by its specific frequency, the third pseudo-component ("ammonia") can be detected by subtracting the contribution of the first component ("urea") to the signal intensity.

[0050] The method can be applied to any industrial process for synthesizing urea at high pressure and high temperature, including but not limited to full cycle process and stripping process, such as CO2 stripping and self-stripping. In an embodiment, the method is applied to a process in which urea synthesis occurs at a pressure in the range of 100-300 bar and a temperature in the range of 50-250°C.

[0051] According to embodiments, the Raman analysis may be performed directly on the main process stream. In such embodiments, a suitable probe is mounted directly on the relevant main process pipeline. According to other embodiments, the analysis may also be performed on a side stream taken from the main process pipeline. Such embodiments may provide for safer and easier inspection and maintenance of the system. In such embodiments, the analysis system may include a sampling chamber.

[0052] Another aspect of the invention is a method for controlling a plant for the synthesis of urea according to the appended claims. The method for controlling a urea synthesis process utilizes Raman spectroscopy to analyze in real time the components of at least one, and in some embodiments more, streams of the process. The process may be any known urea process used for industrial production, including stripping and non-stripping processes.

[0053] A further aspect of the present disclosure is an apparatus for controlling and optimizing a urea synthesis plant according to the appended claims.The information provided by Raman spectroscopy analysis can be used for automatic control and optimization of the plant.

[0054] The apparatus of the present disclosure may comprise one or more probes, wherein the or each probe is arranged to focus excitation light from a light source to a focal region, the focal region comprising at least one of the process streams, and to capture and return Raman scattered light.

[0055] At least one probe may be a high pressure optical probe adapted to focus excitation light into the outlet stream from the synthesis reactor, the outlet urea solution stream from the high pressure stripper and the carbamate recycle stream from the recovery section to the synthesis unit. Each probe may be connected to a spectrum analyzer via a fiber optic cable connection.

[0056] A significant advantage of the present disclosure is the online quantitative detection of the components of the streams involved in urea synthesis and the collection of real-time information on process performance, not only in terms of ammonia to carbon molar ratio, but also in terms of water to carbon ratio and carbon conversion to urea.

[0057] Compared to prior art systems, the present disclosure further enables improved optimization of the plant by continuously monitoring the composition of convenient process streams, which are combined with each other through a cascade effect, allowing real-time control of the plant to predict the effects of predictable deterioration due to changes in the composition and parameters of the basic streams. Related benefits include improved overall stability of the process, minimized downtime risks, increased conversion, reduced energy consumption and reduced pollutants.

[0058] Figure 1 A spectroscopic system 100 according to an embodiment of the present disclosure is shown, comprising a control unit 1 and a plurality of probes 3 with suitable corresponding optical cables 2. The probes 3 may be installed on selected process pipes 4 of a urea plant, each process pipe 4 carrying a corresponding process stream 5. The process pipe 4 may be, for example, a pipe or pipeline leading to a high pressure synthesis loop or to a recovery section of a urea plant. In such an embodiment, the process stream 5 may include urea, water, ammonia, ammonium carbamate, carbon dioxide, and other chemical compounds that may be involved in the synthesis process.

[0059] For example, process conduit 4 may include one or more of the following: an outflow conduit from a reactor (e.g., an aqueous solution carrying urea, unconverted carbamate, and free ammonia), an outflow conduit from a high-pressure stripper, or a conduit for recovering carbamate when delivered by a high-pressure pump. Process stream 5 may have an elevated temperature and pressure. For example, process stream 5 may have a pressure of up to 300 bar and a temperature of up to 250°C.

[0060] In at least one embodiment of the present disclosure, Fig.11 As shown in , the control unit 1 may include a spectrometer 110 optically connected to the optical probe 3 via an optical cable 2. The spectrometer 110 may include an optical component 112 and a detector 114, and the detector 114 is configured to receive and detect light scattered from the optical probe 3 via the optical cable 2. The optical component 112 may include one or more lenses, filters, beam splitters and / or diffraction gratings, which are configured and arranged to guide only Raman scattered light to the detector 114. In some embodiments, the control unit 1 may include conventional spectrometers suitable for performing Raman spectroscopy. In at least one embodiment, the control unit 1 may include a suitable Raman spectrometer.

[0061] The control unit 1 may further include an excitation light source 120, such as a laser emitter, which is in optical communication with the probe 3 via the optical cable 2, as further described herein. In some embodiments, the control unit 1 may include an internal optical cable 122 in optical communication with the optical cable 2. Alternatively, in some embodiments, the internal optical cable 122 may be the proximal end of the optical cable 2.

[0062] The control unit 1 may further include a controller 130 configured to process and analyze the scattered light received by the detector 114 from the probe 3. The controller 130 may further be configured to control the system 100 and the spectrometer 110 to perform the method of the present disclosure and analyze the data (e.g., spectrum) generated by the system 100 according to the model of the present disclosure, thereby performing the method. The controller 130 may communicate with a control system of a urea plant (not shown).

[0063] The controller 130 may be configured to perform certain operations as further described herein, and may be part of a processing subsystem including one or more computing devices with memory, processing and / or communication hardware. The controller 130 may be a single device or a distributed device, and the functions of the controller 130 may be performed by hardware and / or software. The controller 130 may include one or more arithmetic logic units (ALUs), central processing units (CPUs), memories, limiters, regulators, filters, format converters, etc., which are not shown for clarity. In an embodiment, the controller 130 may be programmable to execute algorithms and process data according to an operational logic defined by programming instructions such as software or firmware. Alternatively or in addition, the operational logic of the controller 130 may be at least partially defined by hardwired logic or other hardware, for example, defined using any suitable type of application specific integrated circuit (ASIC). Those skilled in the art and those who benefit from the present disclosure should understand that the controller 130 may be specifically used to perform the operations of the disclosed method, or may be further used for the regulation, control and activation of one or more other subsystems or aspects of the system 100.

[0064] for Figure 1For each process stream 5 shown in FIG. 5 , an excitation light 6 emitted by a control unit 1 is transmitted via an optical fiber cable 2 to a focal region (e.g., a focus) of a probe 3 in the process stream 5. The focal region is formed by the probe 3 so that the excitation light 6 is incident on the medium (e.g., a fluid or a gas) of the corresponding process stream 5. Then, according to the Raman effect, most of the incident excitation light 6 undergoes elastic scattering (e.g., Rayleigh scattering), and therefore, these scattered lights will have the same wavelength as the incident light. A small portion of the excitation light 6 undergoes Raman scattering and therefore will exhibit a wavelength / frequency shift. The extent of the shift depends on the composition of the stream 5. A portion of the scattered light is transmitted as a signal from the probe 3 back to the main control unit 1 via the optical fiber cable 2. The spectrometer of the control unit 1 separates the inelastic scattered light that defines the Raman signal from the elastic light and detects the Raman signal. The intensity and wavelength of the detected Raman signal are processed by the spectrometer, which can be integrated in the control unit 1 to measure the concentration of target compounds (e.g., urea, carbon dioxide, and ammonia).

[0065] Figure 2 A further embodiment of the present disclosure is shown, in which Raman signal analysis is performed on a side stream 5a of the measured medium. In such an embodiment, the system 100 includes a sampling chamber 10 connected to the process pipe 4 via an inlet valve 11. The probe 3 is mounted on the sampling chamber 10. The side stream 5a is taken from the process pipe 4 and transferred to the sampling chamber 10 via the valve 11. Figure 1 The same method described performs analysis (e.g., Raman analysis) on the medium contained in the sampling chamber 10. Subsequently or continuously, the medium can be discharged from the sampling chamber 10 via the discharge valve 12 to a low pressure section of the plant, a waste outlet, or any suitable location. Such an embodiment of the system 100 can be less intrusive to the process and / or process piping 4. The sampling chamber 10 enables safe access to the system 100 via the valve 11 without affecting the operation of the process piping 4 (broadly a urea plant).

[0066] Figure 3 Figures showing an exemplary Raman analysis include: a first spectrum I, which relates to a sample containing more than 70% urea and less than 1% of the pseudo component CO2 (as defined herein); and a second spectrum II, which relates to a sample containing less than 5% urea and more than 10% of the pseudo component CO2. The figures show a peak at about 1000 cm -1 The urea band at about 1050cm -1 CO2 band at 1400 to 1650 cm-1 (sample II). -1 The nearby band is also clearly visible.

[0067] In at least one embodiment according to the present disclosure, logic algorithms implemented in the control unit 1 may generate signals to plant actuators to control the flow 5 to optimize the operation of the urea plant and the efficiency of the urea synthesis process based on Raman analysis.

[0068] Due to deviations in operating parameters, disturbances in the composition of the urea solution at the outlet of the high-pressure stripper may dynamically affect the composition of the carbamate recycle stream and, after a certain dynamic, again affect the performance of the reactor and its outlet composition. For example, if a deviation in the composition at the outlet of the stripper is detected, a logic algorithm can act to prevent the carbamate composition from changing and ultimately affecting the reactor performance.

[0069] Example

[0070] An experimental study was conducted on a process stream in an industrial plant for the production of urea. The process stream was selected to contain different concentrations of urea, carbon dioxide and ammonia, and the same analysis process was performed as follows. An optical probe 3 (described further herein) and a 785nm laser source were used. Although a 785nm laser was selected in this experimental example, the method of the present invention can also be extended to other monochromatic lasers mentioned above. The optical probe 3 is connected to the spectrum analyzer of the control unit 1 via an approximately 5-meter-long optical fiber cable 2.

[0071] The samples were placed in a glass container with a volume of 10 ml. A light shielding system was used to isolate the samples from ambient light pollution. Each sample was exposed for one minute using the detector of the spectrum analyzer, and the measurement of each sample was repeated at least 5 times. The above process was used to obtain spectra such as Figure 3 The acquired spectra clearly show peaks corresponding to urea and CO2 pseudo-components, as shown in FIG.

[0072] Figure 4 An optical probe 200 according to at least one embodiment of the present disclosure is shown. In at least one embodiment, the optical probe 200 is suitable for Raman spectroscopy and can be used in Figure 1 and Figure 2 The probe 3 of the system 100. Figure 4 As shown in FIG, optical probe 200 includes a post-process (i.e., out-of-process) portion 204 and an in-process portion 202 separated by a flange 212 having a probe sealing surface 220. Post-process portion 204 may include wrench flats 218 in collar 214, which are configured as complementary tools, thereby facilitating installation of probe 200 in a probe assembly.

[0073] The process portion 202 includes an elongated probe body 210 terminating in a probe tip 206 at a distal end of the probe body 210. The optical probe 200 may include internal optics and an optical interface (not shown) adapted to aim an excitation light (e.g., a light source) transmitted by an optical cable 340 at a focal region in a process or process sample under test. Figure 5A ), and transmits the light scattered from the focal area back to the control unit 1 through the optical probe 200 and the optical cable 2.

[0074] The optical probe 200 includes a window 216 mounted in an aperture in the probe tip 206. The window 216 is adapted to transmit excitation light emitted by the light source of the control unit 1 and transmitted to the optical probe 200 via the optical cable 2. The window 216 is further adapted to transmit scattered light to be analyzed from the process via the optical probe 200 to the control unit 1 of the system 100 via the optical cable 2 for processing and analysis. The window 216 can be press-fitted to the probe tip 206 without the need for brazing, solder, solder filler, or other sealant compounds that would compromise the corrosion resistance of the optical probe 200.

[0075] Window 216 is substantially optically transparent to at least the excitation light and the Raman scattered light. For example, window 216 may be transparent to visible light, near infrared light, and / or infrared light of the light source. In an embodiment, window 216 may be a sapphire window. In certain embodiments, window 216 may be made of glass (i.e., amorphous glass), glass ceramic (i.e., at least partially crystallized glass), diamond, crystalline quartz, silicon, germanium, gallium nitride (GaN) crystal, AlN crystal, optical metamaterial, transparent ceramic, such as sapphire (i.e., single crystal aluminum oxide), magnesium aluminate spinel (MgAl2O4), aluminum oxynitride spinel (AlN2O4), or amorphous silicon. 23 O 27 N5, commonly referred to as AlON) or other suitable transparent materials, as well as combinations of two or more of these materials.

[0076] The window 216 may be adapted for operating conditions of at least 160 bar and at least 185° C. In further embodiments, the window 216 may be adapted for operating conditions of pressures in the range of 100-300 bar and temperatures in the range of 50-250° C. The window 216 may include a coating or treatment thereon including an anti-reflective, hydrophobic, oleophobic, and / or repellent coating or treatment. For example, in an embodiment, the window 216 may include a glass repellent treatment manufactured by Aculon Corporation.

[0077] Figure 5A 2 shows a cross-sectional view along the central axis 224 of the optical probe 200. Figure 5AAs shown in , in some embodiments, the probe body 210, flange 212 and collar 214 can be manufactured to form an integral component. In alternative embodiments, the probe body 210, flange 212 and collar 214 can be composed of one or more separate components and assembled together.

[0078] The probe body 210 defines an internal volume 208 within the probe body 210, and the internal volume 208 is configured to accommodate the optical cable 340. In some embodiments, the internal volume 208 is further defined through the flange 212 and the collar 214, such as Figure 5A , thereby enabling optical cable 340 to pass through optical probe 200 and be in optical communication with window 216. In at least one embodiment, optical cable 340 is a section of optical fiber separate from optical cable 2, having an interface connection configured to ensure optical communication between optical cable 340 and optical cable 2. In further embodiments, optical cable 340 is a distal portion of optical cable 2.

[0079] Figure 5B is the flange 212 of the optical probe 200 Figure 5A FIG. 2 is a detailed cross-sectional view of detail D of FIG. 2 , wherein the probe sealing surface 220 and the sealing edge 222 of the flange 212 are shown in detail. Figure 5B As shown in , in embodiments, the sealing surface 220 can be angled relative to the flange 212 and the probe body 210. In further embodiments, the sealing surface 220 can have any suitable profile to mate with and seat against a complementary sealing surface, as further described herein.

[0080] Figure 6 2 shows a probe assembly 300 according to at least one embodiment of the present disclosure. Figure 6 As shown in FIG. 1 , the probe assembly 300 includes the optical probe 200. The probe assembly 300 may include a main body 310 connected to a process connection flange 314 at a proximal end of the main body 310 and a fiber optic connector 320 at a distal end. The process connection flange 314 may be configured to facilitate connecting the probe assembly 300 to a process vessel, such as a process pipe 4, as shown in FIG. Figure 1 In the embodiments of the present disclosure, the process vessel may be a process pipe 4, a reactor vessel, a reactor chamber, a measurement chamber or any relevant subsystem of an industrial process plant, such as a urea plant.

[0081] The main body 310 defines an internal passage (not shown) in which at least the post-process portion 204 of the optical probe 200 can be disposed, and the optical cable 340 can pass through the internal passage from the fiber optic connector 320 to the optical probe 200, thereby enabling the optical cable 340 to be connected to the optical probe 200 within the internal passage. The probe assembly 300 and the optical probe 200 can each be formed as a separate, seamless, integral body to minimize or eliminate welds.

[0082] Fiber optic connector 320 may include a fiber interlock 322 configured to secure optical cable 2 of system 100 so as to be in optical communication with optical probe 200. Fiber optic connector 320 may further include an interlock indicator 324 configured to indicate to an operator when fiber interlock 322 has properly secured optical cable 2 in fiber optic connector 320, thereby signaling when the light source is in optical communication with optical probe 200. In at least one embodiment, optical cable 340 is a section of optical fiber separate from optical cable 2, which has an interface in fiber optic connector 320, the interface being configured to ensure optical communication between optical cable 340 and optical cable 2. In further embodiments, optical cable 340 is a distal portion of optical cable 2, and fiber optic connector 320 is configured to route optical cable 2 to optical probe 200.

[0083] At or near the proximal end, the main body 310 may include a flange stop 312 and an area adapted to facilitate assembly of the optical probe 200 into the probe assembly 300. For example, the area may include wrench flats 316, such as Figure 6 as shown in .

[0084] like Figure 6 As shown in , the probe body 210 of the optical probe 200 can extend from the post-process portion of the main body 310 of the probe assembly 300 into the process to be analyzed. In such an embodiment, the probe body 210 extends into the process so that the excitation light 6 is emitted into the process at the focal region, and the scattered light from the process is guided from the focal region through the window 216 to the control unit 1 via the optical cable 2 or the optical cable 2, 340.

[0085] In some embodiments, the probe body 210 having the window 216 can extend into a measurement chamber 332 of an in-process flow cell 330 that is configured to interface with the probe assembly 300, such as Figure 7 The flow cell may include an inlet 334 to the measurement chamber 332 and an outlet 336 from the measurement chamber 332 .

[0086] Fig. 8AA cross-sectional view of line AA along a section of probe assembly 300 is shown, which includes a flow cell 330 with a measuring chamber 332, an optical probe 200, and a section of body 310. Flow cell 330 can be arranged in a process (e.g., in a process) and communicated with the process so that process components (e.g., process reactants and / or products) can flow into and out of measuring chamber 332 via inlet 334 and outlet 336, respectively. Outlet 336 can be communicated with a process or with an alternative process stream. In certain embodiments, outlet 336 can be communicated with a waste liquid line so that a sample from measuring chamber 332 is not guided back into the process. In certain embodiments, measuring chamber 332 can at least be communicated with a process fluid so that a sample from a process is transported to measuring chamber 332 so that the sample represents the temperature, pressure, and composition of the process. In a further embodiment, measuring chamber 332 can be integrated with the process portion of probe assembly 300 and be defined therein.

[0087] The flow cell 330 can further include a process connection 338. In at least one embodiment, the process connection 338 can be configured to facilitate attachment of the flow cell 330 to a process vessel (not shown). In such an embodiment, the process connection 338 can be configured to engage with the process connection 314 of the probe assembly 300 with the wall of the process vessel therebetween, such as Fig. 8A For example, the wall of the process container can be sandwiched between the process connection 338 of the flow cell 330 and the process connection 314 of the probe assembly 300, so that the main body 210 of the optical probe 200 passes through the orifice in the wall. In such an embodiment, the process connection 338 and the process connection 314 are sufficiently sealed to the process container to prevent the process medium (which may be at high temperature and pressure) from the process container from leaking around the flow cell 330 to the back side of the process and the environment.

[0088] Figure 8B A detailed cross-sectional view of an exemplary interface between the main body 310 of the probe assembly 300, the post-process portion 204 of the probe 200, and the flow cell 330 is shown at detail C. In an embodiment, as shown in FIG. Figure 8B As shown in , the optical probe 200 at or near the proximal end of the probe body 210 and the main body 310 at its proximal end may include complementary and mating threads 344, so that the optical probe 200 can be attached to the main body 310 by engaging the complementary and mating threads of each. The optical probe 200 may further include a seal 346, which is configured to isolate the post-process portion and the in-process portion of the probe assembly 300. The seal 346 is configured to prevent the medium from the process container (which may be at high temperature and pressure) from leaking through the probe assembly 300 to the post-process side and the environment.

[0089] like Figure 8BAs shown in , when assembled, the sealing surface 220 of the optical probe 200 can be seated and sealed against the complementary sealing surface 342 of the flow cell 330. In such an embodiment, the sealing surface 220 and the sealing surface 342 can be pressed against each other by a compressive force. For example, the compressive force can be generated by a fastener attached by the process connection 314 and the process connection 338. Figure 8B The sealing surface 220 may be perpendicular to the central axis 224 of the optical probe 200, as shown by the angled surface in FIG. 2 , or any suitable form factor that is complementary to the mating sealing surface 342 as required for an operational sealing interface.

[0090] Fig.9A A plan view of the process connection 314 of the probe assembly 300 is shown. Fig.9A As shown in , the process connection 314 may include a plurality of fastener holes 348 configured for bolts, screws, or other suitable fasteners to facilitate attaching the probe assembly 300 to the process vessel. The process connection 314 may further include a central through hole 349 adapted to enable the optical probe 200 to pass through the process connection 314 and into the process or flow cell 330. In an embodiment, the through hole 349 may further be adapted to enable the optical probe 200 to be seated and sealed against the process connection 314. Fig. 9B Shown in Fig.9A 8 is a cross-sectional view of process connection 314 at line BB.

[0091] In at least one embodiment of the present disclosure, at least some of the optical probe 200, the probe assembly 300, and the flow cell 330 can be made of materials that can withstand the high temperature, high pressure, and / or corrosive process conditions that may exist in the process container and / or the measurement chamber 332. For example, as further described herein, the urea synthesis process includes such conditions. In at least one embodiment of the present disclosure, at least some of the optical probe 200 and the flow cell 330, for example, the parts that are in direct contact with the process and the process medium (e.g., wetted parts) can be made of austenitic stainless steel, including but not limited to materials that meet ASTMUNS S31050 or AISI 310 MoLN grade stainless steel, with EN designation X1CrNiMoN25-22-2 or 1.4466. Such an embodiment enables the optical probe 200, in particular the wetted parts of the optical probe 200, to withstand the harsh temperature, pressure, and corrosive conditions of the urea synthesis process. In an embodiment, the process connection 314, which may not be a wetted part, can be 316 type stainless steel (e.g., 316L type), titanium, or other suitable materials. Further embodiments may include materials capable of withstanding a corrosive environment at a pressure of at least between 100 and 300 bar and at a temperature in the range of at least 50 to 250°C.

[0092] In another aspect of the present disclosure, the spectroscopic system 100 may be adapted to perform the method 400 of the present disclosure for online quantitative analysis of at least one process stream of a urea synthesis process, wherein urea is synthesized from ammonia and carbon dioxide at a pressure in the range of 100 to 300 bar and a temperature in the range of 50 to 250° C. Fig.10 In an embodiment, method 400 includes using Raman spectroscopy to perform such online quantitative analysis. System 100 may include: a spectrometer 110; a probe assembly 300, which includes an optical probe 200; and computer hardware, which is configured such as a controller 130, such as Fig.11 , to perform the operations of method 400, including step 410, generating excitation light and emitting the excitation light to a process sample of a process flow at a focal region of optical probe 200. Method 400 may include step 420, receiving Raman scattered light at a Raman spectrometer via probe assembly 300 and optical cable 2, and processing the Raman scattered light to generate a Raman spectrum.

[0093] Method 400 may further include step 430 of modeling the Raman spectrum using a chemometric model of the present disclosure, the model including a conversion of spectral bands corresponding to the excitation of carbonyl diamide bonds and spectral bands corresponding to the excitation of atomic bonds in the form of carboxyl groups, wherein the concentration of carbon-containing molecules other than urea and having carboxyl groups in the process stream is determined by Raman spectroscopy as an equivalent concentration of carbon dioxide corresponding to the excitation of atomic bonds in the form of carboxyl groups. The chemometric model includes one or more algorithms that use a specific set of data in the form of Raman spectra to predict specific quantities and / or characteristics of underlying processes and / or materials. Such algorithms include principal component analysis, multiple regression, multiple linear regression, partial least squares regression, indirect hard modeling, and other suitable statistical methods. In at least one embodiment, the excitation of the carbonyl diamide bonds of the urea molecules is determined by the excitation light in the range of 900 to 1050 cm -1 The Raman shifts in the frequency range of 1000 to 1150 cm-1 are detected for molecules other than urea. -1 In an embodiment, the concentration of ammonia is detected by the Raman shift in the frequency range of 1350 to 1750 cm -1 The Raman shift in the frequency range is determined.

[0094] In at least one embodiment, method 400 may include step 440 of determining the concentration of urea in the process stream using Raman spectroscopy and by detecting spectral bands corresponding to excitations of carbonyl diamide bonds, wherein the concentration of carbon-containing molecules other than urea and having carboxyl groups in the process stream is determined by Raman spectroscopy as an equivalent concentration of carbon dioxide corresponding to excitations of atomic bonds in the form of carboxyl groups. In further embodiments, method 400 may include providing a spectroscopic system as described herein with respect to spectroscopic system 100 by way of non-limiting example.

[0095] In a further aspect of the present disclosure, a computer program product includes a non-transitory computer-readable medium storing instructions (e.g., software) thereon, configured such that when executed by at least one programmable processor, the at least one programmable processor is caused to perform the operations of method 400. The term "non-transitory" as used herein is a limitation on the medium itself (i.e., tangible, not a signal), not a limitation on data storage persistence (e.g., RAM vs. ROM).

[0096] In at least one embodiment, the computer program product may include instructions to: generate excitation light and transmit the excitation light to a process sample of the process stream at a focal region of the optical probe 200; receive and detect Raman scattered light at a Raman spectrometer via the probe assembly 300 and the optical cable 2, and process the Raman scattered light to generate a Raman spectrum; model the Raman spectrum using the chemometric model of the present disclosure, the model including a conversion of a spectral band corresponding to the excitation of carbonyl diamide bonds and a spectral band corresponding to the excitation of atomic bonds in the form of carboxyl groups; and determine the concentration of urea in the process stream using Raman spectroscopy and by detecting the spectral band corresponding to the excitation of carbonyl diamide bonds, wherein the concentration of carbon-containing molecules other than urea and having carboxyl groups in the process stream is determined by Raman spectroscopy as an equivalent concentration of carbon dioxide corresponding to the excitation of atomic bonds in the form of carboxyl groups. In at least one implementation, urea is synthesized from ammonia and carbon dioxide using a urea synthesis process at a pressure in the range of 100 to 300 bar and a temperature in the range of 50 to 250° C.

[0097] Although various embodiments of Raman optical probes, probe assemblies, Raman spectroscopy systems, and methods of using and constructing them have been described in considerable detail herein, these embodiments are provided only as non-limiting examples of the disclosure described herein. It should therefore be understood that various changes and modifications may be made, and elements thereof may be substituted with equivalents, without departing from the scope of the present disclosure. The present disclosure is not intended to be exhaustive or limit the scope of the subject matter of the present disclosure.

[0098] In addition, when describing representative embodiments, the present disclosure may have presented the method and / or process as a specific sequence of steps. However, insofar as the method or process does not rely on the specific sequence of steps set forth herein, the method or process should not be limited to the specific sequence of steps described. Other sequences of steps are also possible and thus still within the scope of the present disclosure.

Claims

1. A probe (200) for online quantitative analysis of at least one process stream of a urea synthesis process, comprising: a probe body (210) having a central axis defining a proximal end and a distal end and including an aperture in the distal end with a probe tip (206); a window (216) secured in the aperture, wherein the window (216) is optically transparent, wherein the window (216) is comprised of sapphire, wherein the window (216) is press-fit to the probe tip (206) without the need for brazing, solder, solder filler, or other sealant compounds; a flange (212) adjacent to the proximal end of the probe body (210), the flange (212) comprising a sealing surface (220) and a sealing edge (222), wherein the flange (212) separates an in-process portion (202) of the probe (200) from a post-process portion (204) of the probe (200), the in-process portion (202) comprising at least the probe body (210), the sealing surface (220) and the sealing edge (222); and a collar (214) abutting against a flange (212) opposite the probe body (210) in a post-process portion (204) of the probe (200), wherein the probe body (210), the flange (212) and the collar (214) define an internal volume (208) therethrough, the internal volume (208) being configured to accommodate an optical cable (340) such that the optical cable (340) can pass through the probe body (210), the flange (212) and the collar (214) and be in optical communication with the window (216), wherein the probe body (210), the flange (212) and the collar (214) form an integral part, and Wherein, at least the in-process portion (202) of the probe (200) is composed of an austenitic stainless steel material, wherein the austenitic stainless steel material complies with ASTM UNS S31050 or AISI 310MoLN.

2. The probe (200) according to claim 1, wherein: The austenitic stainless steel material complies with EN X1CrNiMoN25-22-2 or EN 1.4466.

3. The probe (200) according to claim 1, wherein: The probe body (210), the flange (212) and the collar (214) are made of the same austenitic stainless steel material.

4. The probe (200) according to claim 1, wherein: The post-process portion (204) of the probe (200) is composed of 316 steel material.

5. The probe (200) according to claim 1, further comprising: a main body (310) having a distal end and a proximal end, the main body (310) defining a passage therethrough, wherein the passage is configured to accommodate at least the proximal end of the probe body (210) into the proximal end of the main body (310), the passage being further configured to enable an optical cable (2) to pass through the main body (310) and be connected to the probe body (200); and a process connection secured to the main body (310) at or near a proximal end of the main body (310), the process connection being configured to enable the probe (200) to be attached to a process when assembled, wherein a flange (212) of the probe (200) seats against the process connection, and The probe (200) is reversibly attached at or near the proximal end of the main body (310) such that the probe body (210) extends from the main body (310).

6. The probe (200) according to claim 5, further comprising: A fiber optic connector (320) includes an interlock connected to a distal end of the main body (310) and configured to reversibly attach an optical cable (2) to the probe (200).

7. The probe (200) according to claim 1, wherein: The sealing surface (220) is adapted to seal against a complementary surface (342) of a process vessel or a flow cell (330) configured to receive the probe body (210).

8. A spectroscopic system (100) for online quantitative analysis of at least one process stream of a urea synthesis process, the spectroscopic system comprising: A narrowband light source (120), wherein the narrowband light source (120) is suitable for generating excitation light of a suitable wavelength; The probe (200) according to any one of claims 1 to 7; a spectrometer (110) configured to generate a Raman spectrum from scattered light transmitted to the spectrometer via the probe (200), the spectrometer comprising a detector (114); as well as A processor is configured to control the spectroscopic system (100) and process and analyze the Raman spectrum.

9. A method for online quantitative analysis of at least one process stream of a urea synthesis process, the method comprising: Providing a spectroscopic system (100) according to claim 8; generating the excitation light using the light source (120) and emitting the excitation light via the probe to a process sample of at least one process stream of a urea synthesis process; detecting the scattered light via the probe (200) with a detector (114) of the spectrometer (110), and processing the scattered light to generate a Raman spectrum; Providing a stoichiometric model of reactants and products in a urea synthesis process, the stoichiometric model including a shift in a spectral band corresponding to excitations of carbonyl diamide bonds and a spectral band corresponding to excitations of atomic bonds of carboxyl forms; determining a concentration of urea in the at least one process stream using the Raman spectrum and a chemometric model based on excitations of carbonyl diamide bonds in the Raman spectrum, wherein the determining is performed using the processor; and A concentration of carbon-containing molecules other than urea and having carboxyl groups in the at least one process stream is determined using the Raman spectrum and a chemometric model based on excitations of atomic bonds of carboxyl forms in the Raman spectrum, wherein the determining is performed using the processor.

10. The method according to claim 9, wherein: From 900 to 1050cm -1 detecting the excitation of the carbonyl diamide bond of the urea molecule by a Raman shift of the excitation light in a frequency range of Among them, molecules other than urea are from 1000 to 1150 cm -1 The Raman shift of the excitation light within the frequency range is detected.

11. The method according to claim 10, wherein: The processor is further configured to transmit from 1350 to 1750 cm -1 The Raman shift of the excitation light within the frequency range determines the ammonia concentration.

12. A computer program product comprising a non-transitory computer readable medium having stored thereon instructions which, when executed by the spectroscopic system (100) according to claim 8 using at least one programmable processor, cause the at least one programmable processor to perform an on-line Raman spectroscopic analysis of at least one process stream of a urea synthesis process by performing the steps of the method according to any one of claims 9 to 11, in, The computer program product includes a stoichiometric model of reactants and products in a urea synthesis process, the stoichiometric model including a shift in spectral bands corresponding to excitations of carbonyl diamide bonds and spectral bands corresponding to excitations of atomic bonds of carboxyl forms.

13. The computer program product of claim 12, wherein: The stored instructions include instructions for performing operations including: -1 The Raman shift of the excitation light within the frequency range determines the ammonia concentration.

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