Use of NIR spectroscopy in a urea process, and related method and plant

Abstract

Use of Near Infrared (NIR) spectroscopy, preferably Fourier Transform NIR- spectroscopy, for obtaining a NIR spectrum or NIR spectra for determination of one or more chemical species in one or more process stream(s) of a urea process, said urea process comprising at least one from among a synthesis process, an evaporation process, a crystallisation process, a waste water treatment process, and / or a finishing process. In particular, the urea process comprises a urea synthesis process by reacting carbon dioxide and ammonia. The chemicals involved in the synthesis, such as ammonia, carbon dioxide, urea and biuret, can be quantitatively determined by NIR spectroscopy and the synthesis process can be adjusted based on the determination. The invention relates also to a urea synthesis plant involving NIR spectroscopy.

Description

[0001] Use of NIR spectroscopy in a urea process, and related method and plant

[0002] DESCRIPTION

[0003] Field of the invention

[0004] The present invention relates to analytical methods in urea synthesis process and plants. Particularly, the invention refers to a qualitative and quantitative determination of chemical species by means of Near Infrared (NIR) spectroscopy in one or more process stream(s) of a urea plant.

[0005] Prior art

[0006] Urea is synthesized by a reaction between ammonia (NH3) and carbon dioxide (CO2) in urea-forming conditions. The reaction between NH3 and CO2 produces ammonium carbamate, which is subsequently decomposed into urea and water. A detailed description of available urea synthesis processes can be found in Meessen, J.H. and Petersen, H. (2000), Urea, Ullmann's Encyclopedia of Industrial Chemistry.

[0007] Biuret is a known and undesired by-product in conventional urea production. Several efforts are invested for avoiding biuret formation, or at least for maintaining biuret content in urea below a certain threshold (e.g., < 1 .0% by weight). However, biuret may be a valuable component as a source of non-protein nitrogen (NPN) for cattle feed, or as a pre-planting fertilizer for crops.

[0008] Usually, process streams in urea synthesis are analysed with off-line procedures, in particular by sampling process streams that are subsequently analysed in a laboratory. More in detail, sampling is performed by collecting a process stream from a pressurized environment in a known amount of water to absorb those gases that are released by depressurization.

[0009] This off-line procedure has several drawbacks. Among others: - sampling from a pressurized environment must be performed by more than one experienced worker for safety reasons;

[0010] - the most volatile compounds go usually lost in spite of all due care during sampling, thereby affecting accuracy of the analysis;

[0011] - the samples must be correctly quenched to block reaction kinetics;

[0012] - besides the reaction having been correctly quenched, a time delay from sampling to analysis still has an influence on the amounts of the analysed substances;

[0013] - reaction conditions are different from analysis conditions (in terms of differing pressures and temperatures), and this is an additional circumstance reducing analytical precision because diverse conditions change chemical equilibrium;

[0014] - it is not possible to monitor transient conditions because the reactor must be always stopped at the condition of interest for the analysis. This leads to the need of multiple sampling to obtain a complete profile.

[0015] In-line analysis is difficult to be implemented because of the high corrosive nature of ammonium carbamate; pressure and temperature conditions during urea synthesis, due to a supercritical behaviour of the components in the synthesis section and to the presence of water that has a matrix effect causing a loss or an increase in response.

[0016] WO 2015 / 189075 A1 of the same Applicant discloses Raman spectroscopy applied to urea process streams.

[0017] The following documents also belong to the known prior art: CN101393120A, CN107703096A, KEN-ICHIRO SUEHARA "Rapid and Simple Determination of Oil and Urea Concentrations and Solids Content to Monitor Biodegradation Conditions of Wastewater Discharged from a Biodiesel Fuel Production Plant', JOURNAL OF NEAR INFRARED SPECTROSCOPY, vol. 15, no. 2, pages 89-96 (XP093154430), PETER B. SKOU: "Monitoring Process Water Quality Using Near Infrared Spectroscopy and Partial Least Squares Regression with Prediction Uncertainty Estimation", APPLIED SPECTROSCOPY, vol. 71 , no. 3, pages 410-421 (XP093155271), and JING LIU: "A diffuse reflectance portable near infrared spectroscopy system for the determination of biuret content in urea fertilizer1', JOURNAL OF NEAR INFRARED SPECTROSCOPY, vol. 31 , no. 1 , pages 33-40 (XP093155259).

[0018] In view of the above, there is an increasing need to perform more accurate analysis in order to obtain an improved picture of urea plant streams.

[0019] Summary of the invention

[0020] The scope of the present invention is to overcome the above drawbacks. The invention concerns a method, a plant and a use according to the attached independent claims. Preferred embodiments are described in the dependent claims.

[0021] An object of the present invention is a method comprising the following steps:

[0022] (I) reacting ammonia and carbon dioxide in a urea synthesis section to obtain urea or biuret-containing urea, e.g., high-biuret urea;

[0023] (II) subjecting one or more process stream(s) of said urea synthesis section to Near Infrared (NIR) spectroscopy to obtain a NIR spectrum or NIR spectra and thereby a qualitative determination of one or more chemical species in said one or more process stream(s);

[0024] (III) processing said NIR spectrum or NIR spectra to obtain a quantitative determination of said one or more chemical species.

[0025] Another object of the present invention is a plant comprising:

[0026] (A) a urea synthesis section wherein ammonia and carbon dioxide are reacted to obtain urea or biuret-containing urea, e.g., high biuret urea;

[0027] (B) one or more Near Infrared (NIR) spectroscopic probes positioned at one or more process stream(s) of said urea synthesis section;

[0028] (C) at least one NIR spectroscopic apparatus functionally connected with said NIR spectroscopic probes to obtain a NIR spectrum or NIR spectra;

[0029] (D) at least a processing unit of said NIR spectrum or NIR spectra configured to obtain a quantitative determination of said one or more chemical species.

[0030] Still another object of the present invention is a use of Near Infrared (NIR) spectroscopy for obtaining a NIR spectrum or NIR spectra and thereby a determination of one or more chemical species in one or more process stream(s) of a urea process, said urea process comprising at least one from among a synthesis process, an evaporation process, a crystallisation process, a waste water treatment process, and / or a finishing process.

[0031] In practice, the present invention allows to achieve a determination of one or more chemical species in said process stream (s) of a urea process, preferably urea synthesis, making use of a NIR spectrum or NIR spectra. Such NIR spectrum or NIR spectra provide(s) direct qualitative information of said chemical species, and also quantitative information of said chemical species after appropriate processing.

[0032] Description of the preferred embodiments of the present invention

[0033] According to possible embodiments, urea obtained in step (I) may be a urea aqueous solution or a urea melt (i.e., a highly concentrated urea). A urea melt typically has a concentration of equal to or higher than 98% by weight, preferably equal to or higher than 99% by weight, more preferably equal to or higher than 99.5% by weight, even more preferably equal to or higher than 99.7% by weight, wherein the balance is water and / or unavoidable impurities. Preferably, said urea melt is free of formaldehyde.

[0034] Preferably, said biuret-containing urea is a h igh-biuret urea containing of at least 45% by weight, more preferably from 45% to 80% by weight, even more preferably from 50% to 75% by weight, still more preferably from 55% to 70% by weight, of biuret with respect to the overall weight of said biuret-containing urea.

[0035] A biuret-containing urea may be obtained according to the process disclosed in WO 2022 / 106083 A1 defining the biuret-containing urea as high-biuret urea. Specific reference is made to page 11 , line 11 to page 12, line 9 of WO 2022 / 106083 A1.

[0036] According to an embodiment, said biuret-containing urea may contain an amount of triuret comprised from 2% to 30% by weight, preferably from 5% to 25% by weight, more preferably from 10% to 20% by weight, with respect to the overall weight of said biuret-containing urea.

[0037] Preferably, said urea synthesis section or process is a high-pressure synthesis section or process.

[0038] According to a first preferred embodiment, said one or more process stream(s) is / are liquid process stream(s). Preferably, said one or more liquid process stream(s) is / are aqueous process stream(s).

[0039] According to a second preferred embodiment, said one or more process stream(s) is / are gaseous process stream(s).

[0040] According to different embodiments, said process stream(s) is / are contained in a high- pressure urea reactor, a high-pressure stripper, a high-pressure condenser, and / or a high-pressure scrubber, and / or is / are a feed stream and / or an effluent stream of a high- pressure urea reactor, a high-pressure stripper, a high-pressure condenser, and / or a high-pressure scrubber, and / or a low-pressure section (e.g., a low-pressure recovery section), used in or of said urea high-pressure synthesis section or process. Preferably, said process stream(s) is / are one or more effluent stream(s).

[0041] Possible examples of a process stream are a stream contained within the high- pressure urea reactor, an effluent stream of the high-pressure urea reactor, a stream contained within a high-pressure carbamate condenser, an effluent stream of a high- pressure carbamate condenser, a stream contained within a high-pressure scrubber, an effluent stream of a high-pressure scrubber, a stream contained within a high- pressure stripper, an effluent concentrated stream of the high-pressure stripper, a stream contained within a low-pressure recovery section of a carbamate-containing solution, or an effluent stream of a low-pressure recovery section of a carbamate- containing solution.

[0042] Further examples of a process stream are an effluent stream of the synthesis section or process (such as a urea-containing effluent stream, a water-containing effluent stream, and / or an ammonium carbamate-containing effluent stream), a urea- and water-containing effluent stream of a recovery section, an effluent urea melt containing stream of an evaporator, or a biuret-containing effluent of a urea reactor.

[0043] According to an embodiment, said NIR spectroscopy is Fourier Transform-Near Infrared (FT-NIR) spectroscopy. Preferably, a single NIR spectrum is the result of a plurality of spectroscopic acquisitions, e.g., at least five, or at least ten, or at least fifteen, or at least twenty different spectroscopic acquisitions.

[0044] As an example, a NIR Fourier Transform Spectrometer MATRIX-F II (according to ATEX) by Broker may be used. As another example, each spectrum may be acquired with an OPUS / QUANT2 software by Broker. Such software (or analogous program) may be used to evaluate main parameters for every characteristic peak, such as area, height, and / or position / shift (wavenumber).

[0045] According to another embodiment, said NIR spectroscopy covers a region of the electromagnetic spectrum comprised from 12500 cm-1to 4000 cm-1. The preferred region of the electromagnetic spectrum for the purpose of the present invention is comprised from 12000 cm-1to 7500 cm-1or comprised from 11995 cm-1to 7355 cm-1. Consequently, said one or more NIR spectroscopic probes and said at least one NIR spectroscopic apparatus are preferably configured for covering that same region of the electromagnetic spectrum.

[0046] According to a possible embodiment, an optical path length of said NIR spectroscopy is comprised from 2 mm to 20 mm, preferably comprised from 4 mm to 15 mm, more preferably comprised from 5 mm to 10 mm. Consequently, said one or more NIR spectroscopic probes and said at least one NIR spectroscopic apparatus are preferably configured for covering that same optical path length. Preferably, said determination (step (II)) comprises or consists of a real-time and in situ determination of said chemical species in said process stream(s).

[0047] According to a preferred embodiment, said obtaining the NIR spectrum or NIR spectra is performed without sampling of said one or more process stream(s). Expressed in other terms, said obtaining or subjecting of step (II) is not preceded by sampling of said one or more process stream(s).

[0048] In the present description “sampling” means collecting or taking a part of a process stream from its environment, said part being selected as a sample for inspection or analysis, in particular for obtaining the NIR spectrum or NIR spectra.

[0049] Said chemical species are preferably selected from among ammonia, carbon dioxide, ammonium carbamate, water, urea, biuret, triuret, cyanuric acid, and combinations thereof.

[0050] According to a first embodiment, said chemical species may be ammonia and carbon dioxide, and / or water and carbon dioxide, and / or ammonia and urea, and / or urea and carbon dioxide, and / or ammonium carbamate.

[0051] According to a second embodiment, said chemical species are urea, biuret, and water.

[0052] According to a third embodiment, said chemical species are urea, biuret, triuret, cyanuric acid, and water.

[0053] According to a fourth embodiment, said chemical species are at least ammonia, carbon dioxide, water, urea, and biuret, and optionally ammonium carbamate.

[0054] Preferably, said qualitative determination of step (II) comprises an identification of characteristic peak(s) of said one or more chemical species in said NIR spectra at a specific temperature (T) and at a specific pressure (P).

[0055] In general terms, these specific temperature and specific pressure correspond to temperature and pressure values of the process stream in a specific location of the urea plant. As an example, said specific temperature and specific pressure may correspond to urea-forming conditions.

[0056] According to an embodiment, the specific temperature is comprised from room temperature to 300 °C, preferably from 40 °C to 280 °C, more preferably from 50 °C to 250 °C.

[0057] According to another embodiment, the specific pressure is comprised from 80 bar to 350 bar, preferably from 90 bar to 325 bar, more preferably from 100 bar to 300 bar.

[0058] According to a preferred embodiment, said quantitative determination of step (III) comprises applying a chemometric method to data of said NIR spectra. Preferably said data of the NIR spectra comprise characteristic peak areas / intensities. As an example, a software (such as an OPUS software by Broker, such as an OPUS / QUANT2 software) may be used to apply said chemometric method. Preferably, said chemometric method is or comprises a partial least squares (PLS) regression method, and / or a principal component regression (PCR) method, and / or a multiple linear regression (MLR) method. A PLS regression method is preferred.

[0059] Preferably, said chemometric method involves a multivariate calibration.

[0060] The chemometric method makes use of a number of NIR spectra obtained in view of a series of calibration experiments with different known reference values such as: specific temperatures, specific pressures, amounts of each chemical species, amounts and weight ratios of chemical species in combination with each other, etc.

[0061] The method preferably comprises:

[0062] (IV) adjusting at least one from among an ammonia to carbon dioxide (N / C) equivalent molar ratio, a water to carbon dioxide (H / C) equivalent molar ratio, and a urea to carbon dioxide (U / C) equivalent molar ratio in said urea synthesis section based on said quantitative determination of step (III).

[0063] According to possible embodiments, said N / C ratio and / or H / C ratio is / are adjusted based on the quantitative determination of step (III) performed on the following process stream(s): urea reactor liquid stream effluent, and / or high-pressure carbamate condenser liquid stream effluent, and / or high-pressure stripper stream effluent.

[0064] Considering for example a urea reactor liquid stream effluent, if a measured H / C ratio is too high, i.e., higher than a reference value, a purge of water may be increased to lower such H / C ratio up to or below such reference value.

[0065] According to another example, a N / C ratio may be adjusted by modifying either an inlet reactor composition or operative conditions of upstream and / or downstream of the reactor.

[0066] Preferably, said plant is devoid of sampling means (e.g., sampling devices or sampling apparatuses) of the one or more process stream(s).

[0067] More preferably, the plant further comprises:

[0068] (E) adjustment means of at least one from among an ammonia to carbon dioxide (N / C) equivalent molar ratio, a water to carbon dioxide (H / C) equivalent molar ratio, and a urea to carbon dioxide (U / C) equivalent molar ratio in said urea synthesis section, said adjustment means being functionally connected with said processing unit so that adjustment of said adjustment means is based on said quantitative determination;

[0069] Even more preferably, the said one or more NIR spectroscopic probes are positioned within a high-pressure urea reactor, a high-pressure stripper, a high-pressure condenser, and / or a high-pressure scrubber, and / or at a feed stream and / or at an effluent stream (preferably at an effluent stream) of a high-pressure urea reactor, a high-pressure stripper, a high-pressure condenser, and / or a high-pressure scrubber, and / or low-pressure recovery section, of said urea synthesis section.

[0070] According to an embodiment, said NIR spectroscopic probe(s) is / are connected with said processing unit by optical fiber(s). According to another embodiment, said processing unit comprises or consists of a programmable logic controller (PLC).

[0071] Advantages of the present invention

[0072] Advantageously, NIR spectroscopy can work at high pressures and temperatures and can resist to high corrosive environments, e.g., in presence of ammonium carbamate solutions, due to a preferred implementation of corrosion-resistant NIR spectroscopic probes (e.g., a probe made of a VDM® Alloy 59 or another corrosion-resistant alloy).

[0073] Advantageously, NIR spectroscopy allows to obtain rapid and non-destructive NIR spectra on bulk materials. NIR spectra cover also chemical species positioned at a certain depth from the surface due to a longer optical pathlength. For illustrative purposes, an absorption coefficient in the NIR spectral range is relatively low requiring a rather long optical path length (typically comprised from 2 mm to 20 mm, preferably comprised from 4 mm to 15 mm, more preferably comprised from 5 mm to 10 mm).

[0074] Advantageously, the method of the present invention allows to achieve a real-time and in situ assessment of the chemical species of interest, and hence to obtain an actual picture of a reaction progress and of eventual by-product formation.

[0075] Advantageously, the present invention avoids sampling of a specimen of the process stream(s), and is hence capable of determining the chemical species in their environment, so that reaction conditions and analysis conditions are the same.

[0076] Advantageously, in comparison with the current analytical methods available for urea synthesis, the method of the present invention provides a better control, improvement, or optimization of the process parameters.

[0077] Advantageously, an analysis performed with NIR spectroscopy requires de facto no sample preparation.

[0078] Advantageously, the present method allows to obtain NIR spectra almost simultaneously at different locations with a single NIR spectroscopic apparatus connected with a plurality of NIR spectroscopic probes. This simultaneous monitoring of a plurality of different process streams enables to establish how adjustment of one or more parameter(s) at a certain location affects other downstream process streams.

[0079] Advantageously, the present method is adapted for determining chemical species in gas phase and in liquid phase.

[0080] Advantageously, the sampling rate of the method of the present invention is not particularly limited, and can range from a detection per minute to a detection per hour or a certain number of hours.

[0081] Advantageously, the present invention allows to avoid the drawback of saturation of the signal by water in the region between 4000 cm-1and 7300 cm-1.

[0082] Advantageously, the optical pathlength is selected short enough to avoid saturation of absorption bands of water, while at the same time long enough to allow to measure other species. The one selected is a compromise between the two requirements that works well.

[0083] The invention is now further elucidated with reference to preferred embodiments and with the help of the figures.

[0084] Description of the figure

[0085] Fig. 1 : Diagram of urea concentration (expressed as percentage by weight) as a function of reaction time for two reactions at fixed temperature. In the lower curve - related to urea decomposition to give ammonia and carbon dioxide - urea concentration is decreasing over time after 40 minutes. In the upper curve - related to ammonia carbamate decomposition to give urea and water - urea concentration increases progressively after 30 minutes, i.e. , after solid urea is completely molten and the reaction has reached the equilibrium condition. Detailed description of a preferred embodiment of the present invention

[0086] In step (I) of the present method ammonia and carbon dioxide are reacted in a urea synthesis section to obtain urea or biuret-containing urea.

[0087] In step (II) one or more process stream(s) of said urea synthesis section are subjected to Near Infrared (NIR) spectroscopy to obtain a NIR spectrum or NIR spectra. The NIR spectrum or NIR spectra contain data (in particular characteristic peaks) that allow to obtain a qualitative determination of one or more chemical species in said one or more process stream(s).

[0088] In a subsequent step (III) said NIR spectrum or NIR spectra is / are processed to obtain a quantitative determination of said one or more chemical species.

[0089] Steps (II) and (III) are preferably performed in real-time mode, preferably without sampling the one or more process stream(s).

[0090] The qualitative determination of step (II) comprises an identification of characteristic peaks of said one or more chemical species in said NIR spectrum or NIR spectra at a specific temperature and at a specific pressure. Temperature and pressure are dictated by the conditions of the specific process stream.

[0091] The quantitative determination of step (III) comprises applying a chemometric method to data of said NIR spectra. These data comprise characteristic peak areas / intensities, that can be related to absolute amounts of the chemical species in the process stream through said chemometric method.

[0092] The chemometric method involves a multivariate calibration. A univariate calibration is not suitable for such calibration due to an interference between more than two different molecules in a multi-component system.

[0093] In an optional step (IV), at least one from among an ammonia to carbon dioxide (N / C) equivalent molar ratio, a water to carbon dioxide (H / C) equivalent molar ratio, and a urea to carbon dioxide (U / C) equivalent molar ratio is adjusted in said urea synthesis section based on said quantitative determination of step (III).

[0094] Process parameters can thus be controlled, improved, or optimized.

[0095] The present invention will be further disclosed based on the following non-limiting example.

[0096] Example

[0097] For the present tests, a NIR Fourier Transform Spectrometer MATRIX-F II (according to ATEX) by Broker was used. The spectra were acquired with OPUS / QUANT2 software, and an initial spectra elaboration was performed with the OPUS software, in order to evaluate parameters for every absorption peak, such as area, height, and position / shift (wavenumber). An automatic integration tool of each peak was used.

[0098] Spectra were acquired in two different ways: with a single sample acquisition every 5 °C (degrees Celsius) or with spectra acquired repeatedly every 30 seconds until the desired condition was reached. In both cases the spectral resolution was of 8 cm’1. A single spectrum was acquired as an average of 16 different acquisitions.

[0099] Initially, single elements were analyzed with NIR to identify the characteristic peaks of each compound. Exemplary characteristic peak wavenumbers of some chemical species - tested individually and not as a mixture - are listed in the following Table 1 together with temperature (T) and pressure (P) values for which such wavenumbers have been obtained.

[0100] Table 1

[0101] NIR spectra of binary mixtures (ammonia and water; urea and water; etc.) were also obtained to study the presence of overlapping peaks. A shifting of all characteristic peaks was observed in all mixtures with respect to NIR spectra performed on the single chemical species.

[0102] A univariate calibration model was used for the binary mixtures for quantification purposes, with the aid of other analytical techniques (e.g., HPLC for urea and acidbase titration for ammonia). Other NIR spectra were obtained for binary mixtures where the chemical species were in different ratios, and in presence of different temperatures.

[0103] NIR spectra of ternary mixtures (e.g., urea, water and ammonia; ammonium carbamate, urea and water; urea, biuret and triuret; etc.) were also obtained.

[0104] A PLS regression method (a specific chemometric method) involving a multivariate calibration was used for the ternary mixtures for quantification purposes.

[0105] For each calibration experiment, a reference solution was prepared with weighted amounts of water and urea and loaded in a reactor. A first reference NIR spectrum was hence acquired. Ammonia was dosed and added to the same solution. A second NIR reference spectrum was then acquired after the system had reached an equilibrium to establish interactions with ammonia. Then, when the set temperature (i.e. 185°C) has been reached, a third spectrum was acquired at equilibrium conditions. Then, the reaction was quenched and an amount of solution at high temperature and pressure was sampled; urea was quantified through HPLC and ammonia via titration. In this way, the reference values were obtained at the end of the experiment, in order to consider also spectral changes due to increase of temperature and pressure. For every different composition of the calibration solution, different final temperatures were tested, e.g., comprised from 80°C to 185°C.

[0106] After the calibration of the compounds, urea decomposition to give ammonia and carbon dioxide and ammonia carbamate decomposition to give urea and water were observed. The percentage by weight of urea was monitored as a function of time along all the experiment.

[0107] The reaction was performed increasing the temperature from 25 °C to 185 °C; the temperature was kept constant for 120 minutes to verify that equilibrium had been reached. The amount of urea and NH3 was then quantified (HPLC and titration) and compared with the NIR spectra and the areas of the relative characteristic peaks. Additionally, the reverse reaction that starts from urea and water was also observed as a function of time to validate the results and be sure that equilibrium conditions were reached.

[0108] Fig. 1 shows the quantification of urea as a function of time both reactions from urea to ammonia and carbon dioxide and from ammonium carbamate to urea and water. As soon as the carbamate is decomposed and urea has melted above 130 °C, the concentration of urea is more stable (approx, after 30 minutes) and a production or decomposition trend is clearly visible.

Claims

CLAIMS1 ) Use of Near Infrared (NIR) spectroscopy, preferably Fourier Transform-Near Infrared (FT-NIR) spectroscopy, for obtaining a NIR spectrum or NIR spectra and thereby a determination of one or more chemical species in one or more process stream (s) of a urea process, said urea process comprising at least one from among a synthesis process, an evaporation process, a crystallisation process, a waste water treatment process, and / or a finishing process.2) Use according to the previous claim, wherein said determination comprises or consists of a real-time and in situ determination of said chemical species in said process stream(s).3) Use according to any of the previous claims, wherein said obtaining the NIR spectrum or NIR spectra is performed without sampling of said one or more process stream(s).4) Use according to any of the previous claims, wherein said one or more process stream(s) is / are liquid process stream(s), and wherein said NIR spectroscopy covers a region of the electromagnetic spectrum comprised from 12000 cm-1to 7500 cm-1or comprised from 11995 cm-1to 7355 cm-1.5) Use according to the previous claim, wherein said one or more liquid process stream(s) is / are aqueous process stream(s).6) Use according to any of the previous claims, wherein said chemical species are selected from among ammonia, carbon dioxide, ammonium carbamate, water, urea, biuret, triuret, cyanuric acid, and combinations thereof; preferably ammonia and carbon dioxide, and / or water and carbon dioxide, and / or urea and carbon dioxide, and / or ammonium carbamate; more preferably at least ammonia, carbon dioxide, water, urea, and biuret, and optionally ammonium carbamate.7) Use according to any of the previous claims, wherein said process stream(s) is / are contained in a high-pressure urea reactor, a high-pressure stripper, a high-pressure condenser, and / or a high-pressure scrubber, and / or is / are a feed stream and / or an effluent stream of a high-pressure urea reactor, a high-pressure stripper, a high-pressure condenser, and / or a high-pressure scrubber, and / or a low-pressure section (e.g., a low-pressure recovery section), used in said urea synthesis process.8) A method comprising the following steps:(I) reacting ammonia and carbon dioxide in a urea synthesis section to obtain urea or biuret-containing urea, e.g., high-biuret urea;(II) subjecting one or more process stream(s) of said urea synthesis section to Near Infrared (NIR) spectroscopy to obtain a NIR spectrum or NIR spectra and thereby a qualitative determination of one or more chemical species in said one or more process stream(s);(III) processing said NIR spectrum or NIR spectra to obtain a quantitative determination of said one or more chemical species.9) The method according to claim 8, wherein said step (II) comprises or consists of a real-time and in situ determination of said chemical species in said process stream(s).10) The method according to any of claims 8-9, wherein said subjecting of step (II) is not preceded by sampling of said one or more process stream(s).11 ) The method according to any of claims 8-10, wherein said one or more process stream(s) is / are liquid process stream(s), and wherein said NIR spectroscopy covers a region of the electromagnetic spectrum comprised from 12000 cm-1to 7500 cm-1or comprised from 11995 cm-1to 7355 cm-1.12) The method according to the previous claim, wherein said one or more liquid process stream(s) is / are aqueous process stream(s).13) The method according to any of claims 8-12, wherein said chemical species are selected from among ammonia, carbon dioxide, ammonium carbamate, water, urea, biuret, triuret, cyanuric acid, and combinations thereof; preferably ammonia and carbon dioxide, and / or water and carbon dioxide, and / or ammonia and urea, and / or urea and carbon dioxide, and / or ammonium carbamate; preferably wherein said chemical species are at least ammonia, carbon dioxide, water, urea, and biuret, and optionally ammonium carbamate.14) The method according to any of claims 8-13, wherein said urea synthesis section of step (I) is a urea high-pressure synthesis section, and wherein said process stream(s) is / are contained in a high-pressure urea reactor, a high-pressure stripper, a high-pressure condenser, and / or a high-pressure scrubber, and / or is / are a feed stream and / or an effluent stream of a high-pressure urea reactor, a high-pressure stripper, a high-pressure condenser, and / or a high-pressure scrubber, and / or a low-pressure section (e.g., a low-pressure recovery section), of said urea high-pressure synthesis section.15) The method according to any of claims 8-14, wherein said qualitative determination of step (II) comprises an identification of characteristic peak(s) of said one or more chemical species in said NIR spectra at a specific temperature and at a specific pressure, and wherein said quantitative determination of step (III) comprises applying a chemometric method to data of said NIR spectra; preferably said data comprising characteristic peak areas / intensities; more preferably wherein said chemometric method involves a multivariate calibration; even more preferably said chemometric method being or comprising a partial least squares (PLS) regression method, and / or a principal component regression (PCR) method, and / or a multiple linear regression (MLR) method.16) The method according to any of claims 8-15, wherein said specific temperature is comprised from room temperature to 300 °C, preferably from 40 °C to 280 °C, more preferably from 50 °C to 250 °C, and wherein said specific pressure is comprised from 80 bar to 350 bar, preferably from 90 bar to 325 bar, morepreferably from 100 bar to 300 bar.17) The method according to any of claims 8-16, further comprising:(IV) adjusting at least one from among an ammonia to carbon dioxide (N / C) equivalent molar ratio, a water to carbon dioxide (H / C) equivalent molar ratio, and a urea to carbon dioxide (U / C) equivalent molar ratio in said urea synthesis section based on said quantitative determination of step (III).18) A plant comprising:(A) a urea synthesis section wherein ammonia and carbon dioxide are reacted to obtain urea or biuret-containing urea, e.g., high biuret urea;(B) one or more Near Infrared (NIR) spectroscopic probes positioned at one or more process stream(s) of said urea synthesis section;(C) at least one NIR spectroscopic apparatus functionally connected with said NIR spectroscopic probes to obtain a NIR spectrum or NIR spectra;(D) at least a processing unit of said NIR spectrum or NIR spectra configured to obtain a quantitative determination of said one or more chemical species.19) The plant according to the previous claim, wherein said plant is devoid of sampling means of the one or more process stream(s).20) The plant according to any of claims 18-19, wherein said one or more NIR spectroscopic probes and said at least one NIR spectroscopic apparatus are configured for covering a region of the electromagnetic spectrum comprised from 12000 cm-1to 7500 cm-1or comprised from 11995 cm-1to 7355 cm-1.21 ) The plant according to any of claims 18-20, further comprising:(E) adjustment means of at least one from among an ammonia to carbon dioxide (N / C) equivalent molar ratio, a water to carbon dioxide (H / C)equivalent molar ratio, and a urea to carbon dioxide (U / C) equivalent molar ratio in said urea synthesis section, said adjustment means being functionally connected with said processing unit so that adjustment of said adjustment means is based on said quantitative determination; preferably said one or more NIR spectroscopic probes being positioned at least partially within a high-pressure urea reactor, a high-pressure stripper, a high- pressure condenser, and / or a high-pressure scrubber, and / or at a feed stream and / or at an effluent stream of a high-pressure urea reactor, a high-pressure stripper, a high-pressure condenser, and / or a high-pressure scrubber, and / or a low-pressure section (e.g., a low-pressure recovery section), of said urea synthesis section.

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