WO2025136185A1 - Method and system for monitoring a steam explosion process - Google Patents

Method and system for monitoring a steam explosion process Download PDF

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Publication number
WO2025136185A1
WO2025136185A1 PCT/SE2024/051059 SE2024051059W WO2025136185A1 WO 2025136185 A1 WO2025136185 A1 WO 2025136185A1 SE 2024051059 W SE2024051059 W SE 2024051059W WO 2025136185 A1 WO2025136185 A1 WO 2025136185A1
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steam
steam explosion
reactor
severity
blow
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French (fr)
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Andreas AVERHEIM
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Valmet Technologies Oy
Valmet AB
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Valmet Oy
Valmet AB
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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21B—FIBROUS RAW MATERIALS OR THEIR MECHANICAL TREATMENT
    • D21B1/00—Fibrous raw materials or their mechanical treatment
    • D21B1/04—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres
    • D21B1/12—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres by wet methods, by the use of steam
    • D21B1/30—Defibrating by other means
    • D21B1/36—Explosive disintegration by sudden pressure reduction
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/28—Investigating the spectrum
    • G01J3/44—Raman spectrometry; Scattering spectrometry ; Fluorescence spectrometry
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/02—Devices for withdrawing samples
    • G01N1/10—Devices for withdrawing samples in the liquid or fluent state
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/02—Devices for withdrawing samples
    • G01N1/10—Devices for withdrawing samples in the liquid or fluent state
    • G01N1/20—Devices for withdrawing samples in the liquid or fluent state for flowing or falling materials
    • G01N1/2035—Devices for withdrawing samples in the liquid or fluent state for flowing or falling materials by deviating part of a fluid stream, e.g. by drawing-off or tapping
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/02—Devices for withdrawing samples
    • G01N1/22—Devices for withdrawing samples in the gaseous state
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • G01N1/40—Concentrating samples
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/65—Raman scattering
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/02—Devices for withdrawing samples
    • G01N1/10—Devices for withdrawing samples in the liquid or fluent state
    • G01N2001/1031—Sampling from special places
    • G01N2001/105—Sampling from special places from high-pressure reactors or lines
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • G01N1/40—Concentrating samples
    • G01N1/4022—Concentrating samples by thermal techniques; Phase changes
    • G01N2001/4033—Concentrating samples by thermal techniques; Phase changes sample concentrated on a cold spot, e.g. condensation or distillation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N2021/8411—Application to online plant, process monitoring

Definitions

  • the invention relates to the field of treatment of biomass material by means of thermal treatment and steam explosion discharge of the biomass material. More specifically, the invention relates to monitoring and controlling such a process.
  • Thermal treatment of lignocellulose biomass material at elevated pressure and temperature is known in the art. Such thermal treatment is used for example to produce fiber board, fuel pellets /briquettes and ethanol and other chemicals.
  • One advantageous method for thermal treatment is the steam explosion process.
  • Steam explosion refers to a process step where the material undergoes a rapid/instantaneous pressure decrease. Hot and softened biomass from thermal treatment is released or blown from a pressurized reactor through a blow valve or orifice, while the pressure drops to an environment with substantially lower pressure, such as below 5 bar, or preferably to substantially atmospheric pressure.
  • the structure of the biomass breaks, partly due to the expanding steam, and partly by the shear forces and impact during the blow through the orifice or valve.
  • the steam explosion process chemically degrades biomass to a suitable level to facilitate downstream processing.
  • the biomass needs to be degraded to an appropriate level, otherwise yield losses or problems with downstream processing may occur.
  • a combination of temperature, residence time, and in some cases, pH (acid charge) is utilized.
  • These variables combined are typically referred to as the severity factor (or combined severity factor if acid is used).
  • This (theoretical) measure is usually based on a temperature or pressure measurement (usually at the mantle of the reactor), a residence time calculated for example from a speed of a feeding screw or surface height in a reactor, and optionally a pH measurement.
  • the biomass type, age, harvest season, and plant location may however all affect the actual /effective severity of the process. Some changes in material or other processing parameters may also affect the actual /effective severity, although not immediately evident Such examples could be particle size that affects temperature gradient in the reactor or impregnation efficiency. Furthermore, if a pre-steaming step is carried out, pre-steaming efficiency may affect impregnation. Furthermore, temperature and acidity may affect the compaction, thus the actual time in a vertical reactor. Consequently, the actual/effective severity may deviate from the severity factor calculated based on the measured temperature, residence time and pH. The severity factor may thus need to be controlled by varying residence time, temperature or acid charge to achieve a desired actual/effective severity.
  • An object of the invention is to provide improved methods for monitoring and controlling steam explosion processes. Another object is to provide corresponding systems.
  • a method for monitoring a steam explosion process comprising thermally treating the biomass material with steam (and optionally a catalyst such as an acid catalyst) at elevated pressure and temperature in at least one reactor and discharging the biomass material and blow steam from the at least one reactor by means of steam explosion discharge.
  • the method for monitoring comprises the following steps:
  • the predicting may be carried out by means of a processing unit.
  • Raman spectroscopy measurements are carried out on a blow steam condensate, and at least one parameter indicative of the (actual/effective) severity of the steam explosion process is predicted based on the obtained Raman spectra.
  • the method may comprise, prior to the collecting, separating blow steam from the biomass material using for example a cyclone or a steam separator with moving parts such as a Perivapor or Perisplitter.
  • the thermal treatment comprising treatment with steam may also be referred to as hydrothermal treatment.
  • hydrolysis or prehydrolysis reactions may take place. Pre-hydrolysis is carried out at milder conditions compared to a hydrolysis process and is used for hydrolyzing the hemicellulose content of the biomass.
  • the invention is based on the insight that it would be advantageous to be able to rapidly estimate the process window to avoid producing too much product that is off specifications.
  • the invention is furthermore based on the insight that a more rapid analysis/response can be obtained by analyzing the blow steam rather than the steam-exploded biomass (for example by measuring the physical or chemical properties of the biomass).
  • the invention is furthermore based on the insight that there is a close correlation between parameter(s) of the blow steam (for example a concentration of an organic compound, or more specifically a concentration of a furan derivative such as furfural and/or a concentration of an acid such as acetic acid and/or a concentration of an alcohol such as methanol) and the actual severity of the steam explosion process.
  • the invention is furthermore based on the insight that such parameter (s) correlated to/indicative of the actual severity of the steam explosion process can be determined using Raman spectroscopy measurements on a condensate of blow steam.
  • the invention is furthermore based on the insight that such parameter(s) indicate of the severity of the steam explosion process can be used, alone or combined with other parameters obtained from the process, to control the process to compensate for non-obvious changes which have affected impregnation (acidity) and/or compaction (residence time) and/or temperature gradient
  • An experimentally derived Raman spectra comprises a set of observed intensities at different wavenumbers I v i, I V 2, I V 3-- Ivn where I vx denotes the intensity at a specific wave number.
  • the inventors have realized that the parameter (s) correlated to/indicative of the actual/effective severity of the steam explosion process can be derived from the spectra, or more specifically from the set of observed intensities.
  • the at least one parameter indicative of the severity comprises at least one concentration of one or more organic compounds, for example furan derivatives such as furfural, 5 -MF, 5-HMF, acids such as acetic acid, formic acid, and levulinic acid, alcohols such as methanol.
  • the at least one parameter indicative of the severity may comprise at least one of furfural concentration, acetic acid concentration, methanol concentration, and 5 -MF concentration.
  • furfural concentration has proven particularly relevant to determine since it has a strong Raman signature and is closely correlated with the severity of the process since it is a secondary or tertiary degradation product from hemicellulose.
  • any organic compound being a precursor or intermediate in forming furfural could be suitably used.
  • the at least one parameter indicative of the severity comprises a parameter S predicted based on said Raman spectra, the blow steam flow and the biomass material feed rate to the at least one reactor, wherein:
  • the at least one parameter indicative of the severity is predicted/modeled as a linear combination of at least two of the observed intensities.
  • furfural concentration may be predicted/modeled using the following expression:
  • Furfural concentration Co + Cixl vl + C2xl v2 + Csxlvs + •••• C n x Ivn
  • I vx denotes the Raman spectra intensity at a specific wavenumber
  • Co- n are constants.
  • the constants, Co-n may be obtained via a multivariate calibration through Partial Least Squares (PLS), or orthogonal partial least squares (OPLS).
  • the furfural concentration may be weighted based on the blow steam flow in relation to the feed rate to the steam explosion process to define a severity parameter, Sutural, indicative of the (actual /effective) severity as follows:
  • Sfurfurai Furfural concentration x Blow steam flow /Biomass feed rate.
  • the at least one parameter indicative of the severity comprises a parameter Sfurfurai predicted based on said Raman spectra, the blow steam flow and the biomass material feed rate to the at least one reactor.
  • concentration of other substances can be modeled in a corresponding manner, and severity parameters can be calculated in a corresponding manner as Sfurfurai
  • a spectra containing for example the wavenumbers in the 300-3200 cm 1 range can be used for the models, but limited spectra containing sections of wavenumbers or individual wavenumbers in said range may alternatively be used.
  • the at least one parameter indicative of the severity is a linear combination of at least two of the observed intensities, optionally multiplied by the ratio of blow steam flow to biomass feed rate.
  • the at least one parameter indicative of the severity may comprise a parameter defined as follows:
  • a spectra containing the wavenumbers in the 300-3200 cm 1 range can be used for the models, but limited spectra containing sections of wavenumbers or individual wavenumbers in said range may alternatively be used.
  • S spe ctra can be used instead of, or in addition to, furfural concentration and/or Sf Ur furai to estimate the severity experienced by the material.
  • the collecting comprises collecting at least part of the blow steam in the form of at least one sample, and wherein said condensing comprises condensing one or more of the at least one sample.
  • the steps of the method are carried out repeatedly.
  • the predicted parameter(s) can be obtained in 2-3 minutes, which allows the method steps to be repeated once eveiy 2-3 minutes.
  • the predicting comprises using a predictive model based on a at least one, or a plurality of, previously obtained Raman spectra of the predominant compounds (such as furfural, acetic acid, formic acid, methanol, 5 -methylfurfural, 5 -hydroxymethylfurfural and levulinic acid) found in the blow steam condensates from said steam explosion process.
  • the presently obtained one or more Raman spectra is/are compared with previously obtained Raman spectra of said predominant compounds found in the blow steam condensates to determine the at least one parameter.
  • the predictive model is based on peak-picking, i.e. the model predicts the at least one parameter indicative of the severity (such as furfural concentration) based on the intensity of a selected point/peak in the Raman spectra, where the selected point/peak is such that furfural has a unique peak which does not interfere with other chemicals.
  • the predictive model may be based on Multivariate Curve Resolution (MCR-ALS), i.e. a model where the at least one parameter indicative of the severity is based not only on a single peak but on a greater portion of the Raman spectra (i.e. two or more observed intensities).
  • MCR-ALS Multivariate Curve Resolution
  • the above-described embodiments wherein the predicting comprises using a predictive model based on a plurality of previously obtained Raman spectra of the predominant compounds may be based on for example peak-picking or MCR-ALS.
  • the data set D is a data table comprising the obtained Raman spectra of the blow steam
  • ST is the matrix of Raman spectra of one or more predominant compounds (such as furfural, acetic acid, formic acid, methanol, 5 -methylfurfural, 5 -hydroxymethylfurfural and levulinic acid) found in the blow steam condensates from said steam explosion process
  • C is a matrix comprising concentration profiles for each of the compounds.
  • the MCR-ALS algorithm which solves this problem (to obtain C) is well-known for the person skilled in the art and will not be described in further detail here.
  • the predictive model may be based on multivariate calibration using for example Partial Least Squares (PLS), or orthogonal partial least squares (OPLS).
  • PLS Partial Least Squares
  • OPLS orthogonal partial least squares
  • the furfural concentration is also based not only on a single peak but on a greater portion of the Raman spectra (i.e. two or more observed intensities).
  • a method for controlling a steam explosion process comprising thermally treating the biomass material with steam (and optionally a catalyst such as an acid catalyst) at elevated pressure and temperature in at least one reactor, and discharging the biomass material and blow steam from the at least one reactor by means of a steam explosion discharge.
  • the method for controlling comprising the following steps:
  • the controlling may be carried out using a control system.
  • controlling the steam explosion process based at least in part on said at least one parameter indicative of the severity of the steam explosion process means that the process may be controlled also based on other parameters such as the flow of blow steam, the production (output flow of steam-exploded biomass) and/or the feed rate (flow of biomass to the process/reactor).
  • the at least one operating parameter may comprise temperature in the at least one reactor, which is controlled by the steam charge /flow to the at least one reactor.
  • the at least one operating parameter may alternatively or additionally comprise acid catalyst charge or concentration (which may be controlled by controlling at least one flow of acid catalyst to the at least one reactor and/or to an impregnator arranged upstream of the at least one reactor).
  • the catalyst concentration may be measured using pH measurements and/or conductivity measurements.
  • the at least one operating parameter may alternatively or additionally comprise residence time in the at least one reactor, which may be controlled by adjusting a speed of one or more feeding screws providing biomass material to the at least one reactor.
  • the residence time typically correlates with the speed of the feedings screw(s).
  • the residence time correlates closely with a level in the reactor vessel.
  • the controlling comprises determining if the at least one parameter indicative of the actual severity indicates a severity which is too high or is above a threshold value, and if so, the controlling may comprise reducing the temperature and/or acid catalyst charge and/or the residence time. On the contrary, if the at least one parameter indicative of the (actual) severity indicates a severity which is too low or below a threshold value, the controlling may comprise increasing the temperature and/or acid catalyst charge and/or the residence time.
  • a system for monitoring a steam explosion arrangement comprising at least one reactor configured to thermally treat the biomass material with steam at elevated pressure and temperature, and a steam explosion discharge device configured to discharge the biomass material and blow steam from the at least one reactor by means of steam explosion discharge, said system for monitoring comprising:
  • a condenser arranged to condense the blow steam collected by the collecting means
  • a Raman spectroscopy measurement arrangement connected to the condenser to receive a condensate therefrom and being configured to conduct Raman spectroscopy measurements on said at least one condensate, and
  • a processing unit arranged to receive data from said Raman spectroscopy measurement arrangement, said data comprising at least one Raman spectra resulting from said Raman spectroscopy measurements, said processing unit being configured to, based on said at least one Raman spectra, predict at least one parameter indicative of the severity of the steam explosion process.
  • the at least one parameter indicative of the severity comprises at least one concentration of one or more organic compounds, for example furan derivatives such as furfural, 5-MF, 5-HMF, acids such as acetic acid, formic acid, and levulinic acid, alcohols such as methanol.
  • the at least one parameter indicative of the severity comprises at least one of furfural concentration, acetic acid concentration, methanol concentration, and 5-MF concentration.
  • the collecting means may be configured to collect at least part of the blow steam in the form of at least one sample and said condenser may be configured to condense one or more of the at least one sample.
  • the collecting means, the condenser, the Raman spectroscopy measurement arrangement, and the processing unit are configured to operate continuously or repeatedly such as once eveiy 2-3 minutes.
  • the processing unit (or a separate control unit) may be configured to control the collecting means and the Raman spectroscopy measurement arrangement to achieve the continuous or repeated operation.
  • the processing unit may be configured to predict the at least one parameter using a predictive model based on a plurality of previously obtained Raman spectra of blow steam condensates from said steam explosion process.
  • the predictive model may be based on peak-picking, Multivariate Curve Resolution (MCR-ALS), Partial Least Squares (PLS), or orthogonal partial least squares (OPLS).
  • a steam explosion arrangement comprising:
  • At least one reactor configured to thermally treat biomass material with steam at elevated pressure and temperature
  • a steam explosion discharge device configured to discharge the biomass material and blow steam from the at least one reactor by means of a steam explosion discharge
  • the collecting means is connected to the steam explosion discharge device, and - a control system connected to said processing unit to receive a signal corresponding/correlating to the at least one parameter indicative of the severity of the steam explosion process, said control system being configured to control at least one operating parameter of the at least one reactor based at least in part on said at least one parameter indicative of the severity of the steam explosion process.
  • the at least one operating parameter may comprise temperature in the at least one reactor, which is controlled by the steam charge /flow to the at least one reactor.
  • the at least one operating parameter may alternatively or additionally comprise acid catalyst charge or concentration (which may be controlled by controlling at least one flow of acid catalyst to the at least one reactor and/or to an impregnator arranged upstream of the at least one reactor).
  • the catalyst concentration may be measured using pH measurements and/or conductivity measurements.
  • the at least one operating parameter may alternatively or additionally comprise residence time in the at least one reactor, which may be controlled by adjusting a speed of one or more feeding screws providing biomass material to the at least one reactor.
  • the control system is configured to determine if the at least one parameter indicative of the actual severity indicates a severity which is too high or is above a threshold value, and if so, the control system may be configured to reduce the temperature and/or acid catalyst charge and/or the residence time. On the contrary, if the at least one parameter indicative of the (actual) severity indicates a severity which is too low or below a threshold value, the control system may be configured to increase the temperature and/or acid catalyst charge and/or the residence time.
  • fig. 1 shows a flowchart illustrating an embodiment of the method according to the second aspect of the invention
  • fig. 2 shows a schematic illustration of an embodiment of the steam explosion arrangement according to the fourth aspect of the invention
  • fig. 3 shows experimental data comprising Raman spectra of two blow steam condensates compared with Raman spectra of acetic acid and furfural
  • fig. 4a shows furfural concentration of a blow steam condensate predicted using an embodiment of the method according to the first aspect of the invention in relation to furfural concentration obtained using HPLC
  • Steps 1-5 also illustrate an embodiment of the method for monitoring according to first aspect of the invention.
  • Fig. 2 shows a schematic illustration of an embodiment of the steam explosion arrangement according to the fourth aspect of the invention.
  • the steam explosion arrangement comprises a substantially vertically arranged reactor 105 configured to thermally treat biomass material with steam at elevated pressure and temperature.
  • the steam S is provided via steam injection orifice 105a.
  • Biomass material B and an acid catalyst A is provided to an impregnation unit 108.
  • Acid impregnated biomass material from 108 is fed to the reactor 105 using a feed screw 105b.
  • the (optional) part of the blow steam D not collected for condensing is discharged form further processing.
  • the cyclone is atmospheric which means that a vacuum need to be applied to obtain the blow steam sample.
  • a condenser 102 is connected to the cyclone to receive blow steam therefrom and to condense the blow steam to form a condensate.
  • a Raman spectroscopy measurement arrangement 103 is connected to the condenser 102 to receive condensate therefrom and being configured to conduct Raman spectroscopy measurements on said at least one condensate.
  • Parts 101-104 also illustrate an embodiment of the system for monitoring according to third aspect of the invention.
  • Figures 3 and 4 show experimental data from a continuous pilot-scale steam explosion process where blow steam was collected from the cyclone steam outlet, whereafter the samples were condensed. Data was collected during different conditions: autohydrolysis (without acid) and dilute acid hydrolysis with sulphuric acid of different concentrations, and different residence times, temperatures, and raw materials (bark, softwood, nonwood). Condensate samples were filtered and measured with Raman spectroscopy and HPLC (high- pressure liquid chromatography).
  • HPLC measurements were conducted using a Dionex Ultimate 3000 with Biorad Aminec HPX-87H columns with a refractive index detector. Measurements were conducted to obtain concentrations of furfural, acetic acid, formic acid, levulinic acid, methanol, 5- hydroxymethylfurfural (5-HMF) and 5 -methylfurfural (5-MF). HPLC is considered the reference standard that provides the "true” value of the concentrations.
  • Fig. 3 shows experimental data comprising Raman spectra of two blow steam condensates and Raman spectra of acetic acid and furfural.
  • Raman spectra of the two blow steam samples correlate well with the Raman spectra of Furfural. It is particularly noted that the peaks correlate well.
  • Raman spectra of the two blow steam samples which correlate with the Raman spectra of acetic acid. This hints that prediction of acetic acid is also feasible.
  • Fig. 4b shows predicted furfural concentration in relation to (actual) acid dosage to the reactor.
  • the Furfural concentration was estimated using the predictive model based on MCR-ALS.
  • the operating conditions were temperature 200 °C and residence time 10 min.
  • the predicted furfural concentration is indicative of the acid dosage and thus of the severity of the process.
  • Fig. 4c shows predicted furfural concentration in relation to residence time.
  • the operating conditions were temperature 200 °C and autohydrolysis (no acid dosage).
  • the predicted furfural concentration is indicative of the residence time and thus of the severity of the process.
  • the at least one parameter indicative of the severity comprises (instead of, or in addition to, furfural concentration), a parameter defined as follows:
  • Fig. 5 shows a score plot from a principal component analysis of the Raman spectra of a blow steam condensate at five combined severity factors with 5-20 min residence time, 0-4% acid dosage and 200 °C temperature.
  • the first principal component explained almost 70% of the variation in the spectra and sorted the data from left to right with increasing combined severity. This indicates that combined severity experienced by the material can be modelled directly from the Raman spectra.
  • blow steam can be separated and collected by other means than a cyclone such as a Perivapor.
  • the collection may alternatively be carried out by feeding the whole blow steam flow to a system for separating/recycling furfural from the blow steam, wherein a sample is collected from a suitable point in said system.

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Abstract

Method for monitoring a steam explosion process, the steam explosion process comprising thermally treating the biomass material with steam (and optionally a catalyst such as an acid catalyst) at elevated pressure and temperature in at least one reactor and discharging the biomass material and blow steam from the at least one reactor by means of steam explosion discharge. The method for monitoring comprises the following steps: collecting (2) at least part of the blow steam; condensing (3) the collected blow steam to provide a condensate; carrying out Raman spectroscopy measurements (4) on the condensate to obtain at least one Raman spectra and predicting (5) at least one parameter indicative of the severity of the steam explosion process based on said Raman spectra. A method for controlling a steam explosion process is also provided as well as corresponding systems.

Description

METHOD AND SYSTEM FOR MONITORING A STEAM EXPLOSION PROCESS
TECHNICAL FIELD
The invention relates to the field of treatment of biomass material by means of thermal treatment and steam explosion discharge of the biomass material. More specifically, the invention relates to monitoring and controlling such a process.
BACKGROUND
Thermal treatment of lignocellulose biomass material at elevated pressure and temperature is known in the art. Such thermal treatment is used for example to produce fiber board, fuel pellets /briquettes and ethanol and other chemicals. One advantageous method for thermal treatment is the steam explosion process. Steam explosion refers to a process step where the material undergoes a rapid/instantaneous pressure decrease. Hot and softened biomass from thermal treatment is released or blown from a pressurized reactor through a blow valve or orifice, while the pressure drops to an environment with substantially lower pressure, such as below 5 bar, or preferably to substantially atmospheric pressure. The structure of the biomass breaks, partly due to the expanding steam, and partly by the shear forces and impact during the blow through the orifice or valve. In other words, the steam explosion process chemically degrades biomass to a suitable level to facilitate downstream processing. The biomass needs to be degraded to an appropriate level, otherwise yield losses or problems with downstream processing may occur.
To control the degradation of the material in the process a combination of temperature, residence time, and in some cases, pH (acid charge) is utilized. These variables combined are typically referred to as the severity factor (or combined severity factor if acid is used). This (theoretical) measure is usually based on a temperature or pressure measurement (usually at the mantle of the reactor), a residence time calculated for example from a speed of a feeding screw or surface height in a reactor, and optionally a pH measurement.
The biomass type, age, harvest season, and plant location may however all affect the actual /effective severity of the process. Some changes in material or other processing parameters may also affect the actual /effective severity, although not immediately evident Such examples could be particle size that affects temperature gradient in the reactor or impregnation efficiency. Furthermore, if a pre-steaming step is carried out, pre-steaming efficiency may affect impregnation. Furthermore, temperature and acidity may affect the compaction, thus the actual time in a vertical reactor. Consequently, the actual/effective severity may deviate from the severity factor calculated based on the measured temperature, residence time and pH. The severity factor may thus need to be controlled by varying residence time, temperature or acid charge to achieve a desired actual/effective severity.
To date, the feedback from the steam explosion process is slow. Response from downstream processing take hours to days, and actual quality or yield measures (calorific values or ethanol for example) take even longer. Controlling the process is consequently difficult, and there is a need for improved methods for controlling the steam explosion process.
SUMMARY
An object of the invention is to provide improved methods for monitoring and controlling steam explosion processes. Another object is to provide corresponding systems.
These and other objects are achieved by the present invention by means of a method and a system according to the independent claims.
According to a first aspect of the invention, there is provided a method for monitoring a steam explosion process, the steam explosion process comprising thermally treating the biomass material with steam (and optionally a catalyst such as an acid catalyst) at elevated pressure and temperature in at least one reactor and discharging the biomass material and blow steam from the at least one reactor by means of steam explosion discharge. The method for monitoring comprises the following steps:
- Collecting at least part of the blow steam;
- Condensing the collected blow steam to provide a condensate;
- Carrying out Raman spectroscopy measurements on the condensate to obtain at least one Raman spectra, and
- Predicting at least one parameter indicative of the severity of the steam explosion process based on said Raman spectra. The predicting may be carried out by means of a processing unit.
In other words, Raman spectroscopy measurements are carried out on a blow steam condensate, and at least one parameter indicative of the (actual/effective) severity of the steam explosion process is predicted based on the obtained Raman spectra. Thus, an indication of the actual severity of the steam explosion process, which can differ from the severity factor expected from the temperature, residence time and optional acid charge, is obtained. The method may comprise, prior to the collecting, separating blow steam from the biomass material using for example a cyclone or a steam separator with moving parts such as a Perivapor or Perisplitter. The thermal treatment comprising treatment with steam may also be referred to as hydrothermal treatment. Depending on the conditions during the treatment, hydrolysis or prehydrolysis reactions may take place. Pre-hydrolysis is carried out at milder conditions compared to a hydrolysis process and is used for hydrolyzing the hemicellulose content of the biomass.
The invention is based on the insight that it would be advantageous to be able to rapidly estimate the process window to avoid producing too much product that is off specifications. The invention is furthermore based on the insight that a more rapid analysis/response can be obtained by analyzing the blow steam rather than the steam-exploded biomass (for example by measuring the physical or chemical properties of the biomass). The invention is furthermore based on the insight that there is a close correlation between parameter(s) of the blow steam (for example a concentration of an organic compound, or more specifically a concentration of a furan derivative such as furfural and/or a concentration of an acid such as acetic acid and/or a concentration of an alcohol such as methanol) and the actual severity of the steam explosion process. The invention is furthermore based on the insight that such parameter (s) correlated to/indicative of the actual severity of the steam explosion process can be determined using Raman spectroscopy measurements on a condensate of blow steam. The invention is furthermore based on the insight that such parameter(s) indicate of the severity of the steam explosion process can be used, alone or combined with other parameters obtained from the process, to control the process to compensate for non-obvious changes which have affected impregnation (acidity) and/or compaction (residence time) and/or temperature gradient
An experimentally derived Raman spectra comprises a set of observed intensities at different wavenumbers Ivi, IV2, IV3-- Ivn where Ivx denotes the intensity at a specific wave number. The inventors have realized that the parameter (s) correlated to/indicative of the actual/effective severity of the steam explosion process can be derived from the spectra, or more specifically from the set of observed intensities.
In embodiments, the at least one parameter indicative of the severity comprises at least one concentration of one or more organic compounds, for example furan derivatives such as furfural, 5 -MF, 5-HMF, acids such as acetic acid, formic acid, and levulinic acid, alcohols such as methanol. For example, the at least one parameter indicative of the severity may comprise at least one of furfural concentration, acetic acid concentration, methanol concentration, and 5 -MF concentration. Of these parameters, furfural concentration has proven particularly relevant to determine since it has a strong Raman signature and is closely correlated with the severity of the process since it is a secondary or tertiary degradation product from hemicellulose. However, the skilled person in the art understands that other organic compounds may be used to indicate the severity of the steam explosion process. In particular, any organic compound being a precursor or intermediate in forming furfural could be suitably used.
In embodiments, the at least one parameter indicative of the severity comprises a parameter S predicted based on said Raman spectra, the blow steam flow and the biomass material feed rate to the at least one reactor, wherein:
S = organic compound concentration x blow steam flow / biomass material feed rate.
In embodiments, the at least one parameter indicative of the severity (such as furfural concentration) is predicted/modeled as a linear combination of at least two of the observed intensities. For example, furfural concentration may be predicted/modeled using the following expression:
Furfural concentration = Co + Cixlvl + C2xlv2 + Csxlvs + •••• Cn xIvn where Ivx denotes the Raman spectra intensity at a specific wavenumber and Co-n are constants. By analyzing the components in the condensates with a technique such as high-performance liquid chromatography (HPLC), the constants, Co-n, may be obtained via a multivariate calibration through Partial Least Squares (PLS), or orthogonal partial least squares (OPLS)..
The furfural concentration may be weighted based on the blow steam flow in relation to the feed rate to the steam explosion process to define a severity parameter, Sutural, indicative of the (actual /effective) severity as follows:
Sfurfurai = Furfural concentration x Blow steam flow /Biomass feed rate.
In other words, the at least one parameter indicative of the severity comprises a parameter Sfurfurai predicted based on said Raman spectra, the blow steam flow and the biomass material feed rate to the at least one reactor.
The concentration of other substances (acetic acid, formic acid, levulinic acid, methanol, 5 -MF, 5- HMF etc.) can be modeled in a corresponding manner, and severity parameters can be calculated in a corresponding manner as Sfurfurai A spectra containing for example the wavenumbers in the 300-3200 cm 1 range can be used for the models, but limited spectra containing sections of wavenumbers or individual wavenumbers in said range may alternatively be used.
In embodiments, which are based on the inventive insight that there is a direct link between the severity experienced by the material and the Raman spectra itself (the Raman spectra of the blow steam condensate), the at least one parameter indicative of the severity is a linear combination of at least two of the observed intensities, optionally multiplied by the ratio of blow steam flow to biomass feed rate. For example, the at least one parameter indicative of the severity may comprise a parameter defined as follows:
Sspectra = (Ko + Kixlvl + K2X Iv2 + K3XIV3 + .... Knxlvn) x Blow steam flow /Biomass feed rate where Ivx denotes the Raman spectra intensity at a specific wavenumber and where Ko-n are constants (which may be derived from modeling using multivariate calibration such as PLS or OPLS). Sspectra may be described as providing a more generalized quantification of the severity experienced by the material (actual/effective severity) since it also accounts for degradation products other than furfural found in the blow steam condensate. A spectra containing the wavenumbers in the 300-3200 cm 1 range can be used for the models, but limited spectra containing sections of wavenumbers or individual wavenumbers in said range may alternatively be used. Sspectra can be used instead of, or in addition to, furfural concentration and/or SfUrfurai to estimate the severity experienced by the material.
In embodiments, the collecting comprises collecting at least part of the blow steam in the form of at least one sample, and wherein said condensing comprises condensing one or more of the at least one sample.
In embodiments, the steps of the method are carried out repeatedly. Using commercially available Raman spectroscopy techniques, the predicted parameter(s) can be obtained in 2-3 minutes, which allows the method steps to be repeated once eveiy 2-3 minutes.
In embodiments, the predicting comprises using a predictive model based on a at least one, or a plurality of, previously obtained Raman spectra of the predominant compounds (such as furfural, acetic acid, formic acid, methanol, 5 -methylfurfural, 5 -hydroxymethylfurfural and levulinic acid) found in the blow steam condensates from said steam explosion process. In other words, the presently obtained one or more Raman spectra is/are compared with previously obtained Raman spectra of said predominant compounds found in the blow steam condensates to determine the at least one parameter.
In embodiments, the predictive model is based on peak-picking, i.e. the model predicts the at least one parameter indicative of the severity (such as furfural concentration) based on the intensity of a selected point/peak in the Raman spectra, where the selected point/peak is such that furfural has a unique peak which does not interfere with other chemicals. Alternatively, or additionally, the predictive model may be based on Multivariate Curve Resolution (MCR-ALS), i.e. a model where the at least one parameter indicative of the severity is based not only on a single peak but on a greater portion of the Raman spectra (i.e. two or more observed intensities). The above-described embodiments wherein the predicting comprises using a predictive model based on a plurality of previously obtained Raman spectra of the predominant compounds may be based on for example peak-picking or MCR-ALS.
The MCR bilinear model may be described as: D = CST. In this application, the data set D is a data table comprising the obtained Raman spectra of the blow steam, ST is the matrix of Raman spectra of one or more predominant compounds (such as furfural, acetic acid, formic acid, methanol, 5 -methylfurfural, 5 -hydroxymethylfurfural and levulinic acid) found in the blow steam condensates from said steam explosion process, and C is a matrix comprising concentration profiles for each of the compounds. The MCR-ALS algorithm which solves this problem (to obtain C) is well-known for the person skilled in the art and will not be described in further detail here.
Alternatively, the predictive model may be based on multivariate calibration using for example Partial Least Squares (PLS), or orthogonal partial least squares (OPLS). In such models, the furfural concentration is also based not only on a single peak but on a greater portion of the Raman spectra (i.e. two or more observed intensities).
According to a second aspect of the invention, there is provided a method for controlling a steam explosion process, the steam explosion process comprising thermally treating the biomass material with steam (and optionally a catalyst such as an acid catalyst) at elevated pressure and temperature in at least one reactor, and discharging the biomass material and blow steam from the at least one reactor by means of a steam explosion discharge. The method for controlling comprising the following steps:
- Monitoring the steam explosion process using the method according to first aspect of the invention (or embodiments thereof) to obtain said at least one parameter indicative of the (actual) severity of the steam explosion process, and
- Controlling at least one operating parameter of the steam explosion process based at least in part on said at least one parameter indicative of the severity of the steam explosion process. The controlling may be carried out using a control system.
It is understood that controlling the steam explosion process based at least in part on said at least one parameter indicative of the severity of the steam explosion process means that the process may be controlled also based on other parameters such as the flow of blow steam, the production (output flow of steam-exploded biomass) and/or the feed rate (flow of biomass to the process/reactor). In embodiments of the method according to the second aspect of the invention, the at least one operating parameter may comprise temperature in the at least one reactor, which is controlled by the steam charge /flow to the at least one reactor. The at least one operating parameter may alternatively or additionally comprise acid catalyst charge or concentration (which may be controlled by controlling at least one flow of acid catalyst to the at least one reactor and/or to an impregnator arranged upstream of the at least one reactor). The catalyst concentration may be measured using pH measurements and/or conductivity measurements. The at least one operating parameter may alternatively or additionally comprise residence time in the at least one reactor, which may be controlled by adjusting a speed of one or more feeding screws providing biomass material to the at least one reactor. In a horizontal reactor, the residence time typically correlates with the speed of the feedings screw(s). In a vertical reactor, the residence time correlates closely with a level in the reactor vessel.
In embodiments of the method according to the second aspect of the invention, the controlling comprises determining if the at least one parameter indicative of the actual severity indicates a severity which is too high or is above a threshold value, and if so, the controlling may comprise reducing the temperature and/or acid catalyst charge and/or the residence time. On the contrary, if the at least one parameter indicative of the (actual) severity indicates a severity which is too low or below a threshold value, the controlling may comprise increasing the temperature and/or acid catalyst charge and/or the residence time. The specific details of the control algorithm need not to be provided here since control methods per se are known in the art.
According to a third aspect of the invention, there is provided a system for monitoring a steam explosion arrangement, said steam explosion arrangement comprising at least one reactor configured to thermally treat the biomass material with steam at elevated pressure and temperature, and a steam explosion discharge device configured to discharge the biomass material and blow steam from the at least one reactor by means of steam explosion discharge, said system for monitoring comprising:
- Collecting means arranged to collect at least part of the blow steam;
- A condenser arranged to condense the blow steam collected by the collecting means;
- A Raman spectroscopy measurement arrangement connected to the condenser to receive a condensate therefrom and being configured to conduct Raman spectroscopy measurements on said at least one condensate, and
- A processing unit arranged to receive data from said Raman spectroscopy measurement arrangement, said data comprising at least one Raman spectra resulting from said Raman spectroscopy measurements, said processing unit being configured to, based on said at least one Raman spectra, predict at least one parameter indicative of the severity of the steam explosion process.
In embodiments of the system, the at least one parameter indicative of the severity comprises at least one concentration of one or more organic compounds, for example furan derivatives such as furfural, 5-MF, 5-HMF, acids such as acetic acid, formic acid, and levulinic acid, alcohols such as methanol. For example, the at least one parameter indicative of the severity comprises at least one of furfural concentration, acetic acid concentration, methanol concentration, and 5-MF concentration.
In embodiments of the system, the collecting means may be configured to collect at least part of the blow steam in the form of at least one sample and said condenser may be configured to condense one or more of the at least one sample.
In embodiments of the system, the collecting means, the condenser, the Raman spectroscopy measurement arrangement, and the processing unit are configured to operate continuously or repeatedly such as once eveiy 2-3 minutes. The processing unit (or a separate control unit) may be configured to control the collecting means and the Raman spectroscopy measurement arrangement to achieve the continuous or repeated operation.
In embodiments of the system, the processing unit may be configured to predict the at least one parameter using a predictive model based on a plurality of previously obtained Raman spectra of blow steam condensates from said steam explosion process. The predictive model may be based on peak-picking, Multivariate Curve Resolution (MCR-ALS), Partial Least Squares (PLS), or orthogonal partial least squares (OPLS).
According to a fourth aspect of the invention, there is provided a steam explosion arrangement comprising:
- at least one reactor configured to thermally treat biomass material with steam at elevated pressure and temperature;
- a steam explosion discharge device configured to discharge the biomass material and blow steam from the at least one reactor by means of a steam explosion discharge,
- a system for monitoring according to the third aspect of the invention (or embodiments thereof), wherein the collecting means is connected to the steam explosion discharge device, and - a control system connected to said processing unit to receive a signal corresponding/correlating to the at least one parameter indicative of the severity of the steam explosion process, said control system being configured to control at least one operating parameter of the at least one reactor based at least in part on said at least one parameter indicative of the severity of the steam explosion process.
In embodiments of the steam explosion arrangement, the at least one operating parameter may comprise temperature in the at least one reactor, which is controlled by the steam charge /flow to the at least one reactor. The at least one operating parameter may alternatively or additionally comprise acid catalyst charge or concentration (which may be controlled by controlling at least one flow of acid catalyst to the at least one reactor and/or to an impregnator arranged upstream of the at least one reactor). The catalyst concentration may be measured using pH measurements and/or conductivity measurements. The at least one operating parameter may alternatively or additionally comprise residence time in the at least one reactor, which may be controlled by adjusting a speed of one or more feeding screws providing biomass material to the at least one reactor.
In embodiments of the steam explosion arrangement, the control system is configured to determine if the at least one parameter indicative of the actual severity indicates a severity which is too high or is above a threshold value, and if so, the control system may be configured to reduce the temperature and/or acid catalyst charge and/or the residence time. On the contrary, if the at least one parameter indicative of the (actual) severity indicates a severity which is too low or below a threshold value, the control system may be configured to increase the temperature and/or acid catalyst charge and/or the residence time.
The features of the embodiments described above are combinable in any practically realizable way to form embodiments having combinations of these features. Further, all features and advantages of embodiments described above with reference to the first and second aspects of the invention may be applied in corresponding embodiments of the third and fourth aspects of the invention and vice versa.
BRIEF DESCRIPTION OF THE DRAWINGS
Above discussed and other aspects of the present invention will now be described in more detail using the appended drawings, which show presently preferred embodiments of the invention, wherein: fig. 1 shows a flowchart illustrating an embodiment of the method according to the second aspect of the invention; fig. 2 shows a schematic illustration of an embodiment of the steam explosion arrangement according to the fourth aspect of the invention; fig. 3 shows experimental data comprising Raman spectra of two blow steam condensates compared with Raman spectra of acetic acid and furfural; fig. 4a shows furfural concentration of a blow steam condensate predicted using an embodiment of the method according to the first aspect of the invention in relation to furfural concentration obtained using HPLC; fig. 4b shows predicted furfural concentration in relation to acid dosage; fig. 4c shows predicted furfural concentration in relation to residence time, and fig. 5 shows a score plot from a principal component analysis of the Raman spectra of a blow steam condensate.
DETAILED DESCRIPTION
Fig. 1 shows a flowchart illustrating an embodiment of the method according to the second aspect of the invention. The method concerns controlling a steam explosion process comprising thermally treating the biomass material with steam (and optionally a catalyst such as an acid catalyst) at elevated pressure and temperature in at least one reactor and discharging the biomass material and blow steam from the at least one reactor by means of steam explosion discharge. The method comprises the following steps:
1. Separating blow steam from the biomass material using a cyclone;
2. Collecting a sample of the blow steam;
3. Condensing the collected blow steam sample to provide a condensate;
4. Raman spectroscopy measurements on the condensate to obtain at least one Raman spectra;
5. Predicting at least one parameter indicative of the severity of the steam explosion process based on said Raman spectra, wherein the at least one parameter comprises furfural concentration, and wherein the predictive model is based on Multivariate Curve Resolution (MCR-ALS), and
6. Controlling at least one operating parameter of the steam explosion process based at least in part on said at least one parameter indicative of the severity of the steam explosion process, wherein said at least one parameter is reactor temperature and/or acid charge and/or residence time. The steps of the method are carried out repeatedly. In lab testing, samples were measured for 10-12 minutes in the instrument In a commercial process, condensates are more concentrated and testing time can be reduced to 2-3 minutes, which allows the method steps to be repeated once every 2-3 minutes.
The controlling 6 comprises determining if the at least one parameter indicative of the actual severity indicates a severity which is too high or is above a threshold value, and if so, the controlling 6 comprises reducing the temperature and/or acid catalyst charge and/or the residence time. On the contrary, if the at least one parameter indicative of the actual severity indicates a severity which is too low or below a threshold value, the controlling 6 comprises increasing the temperature and/or acid catalyst charge and/or the residence time. The specific details of the control algorithm need not to be provided here since control methods per se are known in the art.
Steps 1-5 also illustrate an embodiment of the method for monitoring according to first aspect of the invention.
Fig. 2 shows a schematic illustration of an embodiment of the steam explosion arrangement according to the fourth aspect of the invention. The steam explosion arrangement comprises a substantially vertically arranged reactor 105 configured to thermally treat biomass material with steam at elevated pressure and temperature. The steam S is provided via steam injection orifice 105a. Biomass material B and an acid catalyst A is provided to an impregnation unit 108. Acid impregnated biomass material from 108 is fed to the reactor 105 using a feed screw 105b.
In a bottom portion of the reactor 105, a discharge screw is provided which feeds the thermally treated biomass material towards a steam explosion discharge device (blow valve) 106 configured to discharge the biomass material and blow steam from the reactor 105 by means of steam explosion discharge. A cyclone 101 is connected to the blow valve 106 to receive discharged biomass material and blow steam. The cyclone separates blow steam from the biomass material (which is discharged for further processing as steam exploded biomass C). The blow steam may be collected from an upper portion of the cyclone. In this embodiment, the cyclone is pressurized, which means that the blow steam (sample) can be collected (withdrawn) by means of overpressure. Thus, the cyclone acts as collecting means for the blow steam. The (optional) part of the blow steam D not collected for condensing is discharged form further processing. In other embodiments, the cyclone is atmospheric which means that a vacuum need to be applied to obtain the blow steam sample. A condenser 102 is connected to the cyclone to receive blow steam therefrom and to condense the blow steam to form a condensate. A Raman spectroscopy measurement arrangement 103 is connected to the condenser 102 to receive condensate therefrom and being configured to conduct Raman spectroscopy measurements on said at least one condensate. A processing unit 104 arranged to receive data from the Raman spectroscopy measurement arrangement, the data comprising at least one Raman spectra resulting from said Raman spectroscopy measurements, the processing unit being configured to, based on the at least one Raman spectra, predict at least one parameter indicative of the severity of the steam explosion process. The at least one parameter comprises furfural concentration, and the predictive model is based on Multivariate Curve Resolution (MCR-ALS). In other embodiments, the predictive model may be based on peak-picking or PLS/OPLS.
A control system 107 is configured to receive a signal from the processing unit 104 corresponding to the at least one parameter indicative of the severity of the steam explosion process. In the figure, the processing unit is illustrated as part of the control system 107, but the processing unit may in other embodiments be a separate part.
As can be seen in fig. 2, the control system is connected to the steam injection orifice 105a to control the steam flow to the reactor 105 (and consequently the temperature in the reactor), and to a motor of feeding screw 105b to control the flow of biomass to the reactor (and consequently the residence time), and to an acid catalyst injection orifice 108a connected to the impregnation unit 108 to control the acid flow (and consequently the acid charge in the reactor). The steam flow, biomass flow and acid flow are controlled by the control system on the at least one parameter indicative of the severity of the steam explosion process.
Parts 101-104 also illustrate an embodiment of the system for monitoring according to third aspect of the invention.
Figures 3 and 4 show experimental data from a continuous pilot-scale steam explosion process where blow steam was collected from the cyclone steam outlet, whereafter the samples were condensed. Data was collected during different conditions: autohydrolysis (without acid) and dilute acid hydrolysis with sulphuric acid of different concentrations, and different residence times, temperatures, and raw materials (bark, softwood, nonwood). Condensate samples were filtered and measured with Raman spectroscopy and HPLC (high- pressure liquid chromatography).
The samples were measured in the Raman spectroscopy instrument for 10-12 min. The instrument was a Bruker BRAVO handheld unit with vial accessory operate as follows: scanning from 300-3200 cm-1. Class 1 laser 800-900 nm 40 scans 2000 ms exposure time.
The spectra were trimmed to 300-3000 cm-1 and smoothened via Savitzy-Golay filtering.
The HPLC measurements were conducted using a Dionex Ultimate 3000 with Biorad Aminec HPX-87H columns with a refractive index detector. Measurements were conducted to obtain concentrations of furfural, acetic acid, formic acid, levulinic acid, methanol, 5- hydroxymethylfurfural (5-HMF) and 5 -methylfurfural (5-MF). HPLC is considered the reference standard that provides the "true” value of the concentrations.
In the embodiments described above with reference to figures 1 and 2, the predictive model is based on Multivariate Curve Resolution (MCR-ALS). The spectra containing the wavenumbers in the 300-3200 cm 1 range is used, but limited spectra containing sections of wavenumbers or individual wavenumbers in said range may alternatively be used.
In other embodiments, the predictive model may be based on peak-picking. In yet other embodiments, the model may be based on multivariate calibration (for example PLS, OPLS) to accurately quantify furfural from the Raman spectra derived from a blow steam condensate. OPLS can also be used to derive models that quantify some of the other components (acetic acid, methanol, 5-MF). Acetic acid concentration may be especially useful in addition to furfural concentration. However, furfural is the most important parameter. Yet other components such as 5-HMF and levulinic acid are low in concentration which make them hard to detect using this set up. However, if another set up is used it is foreseeable that these components, or other components mentioned herein may be used. In addition, formic acid also has a weak Raman signature and is thus hard to detect
Fig. 3 shows experimental data comprising Raman spectra of two blow steam condensates and Raman spectra of acetic acid and furfural. As can be seen, several significative features of the Raman spectra of the two blow steam samples correlate well with the Raman spectra of Furfural. It is particularly noted that the peaks correlate well. There are also some significative features of the Raman spectra of the two blow steam samples which correlate with the Raman spectra of acetic acid. This hints that prediction of acetic acid is also feasible.
Fig. 4a shows furfural concentration of a blow steam condensate predicted using the predictive model based on MCR-ALS in relation to furfural concentration obtained using HPLC. The correlation is very good with a R2 value of 0.9978.
Fig. 4b shows predicted furfural concentration in relation to (actual) acid dosage to the reactor. The Furfural concentration was estimated using the predictive model based on MCR-ALS. The operating conditions were temperature 200 °C and residence time 10 min. As can be seen, there is a close correlation between the predicted furfural concentration and the acid dosage. Thus, the predicted furfural concentration is indicative of the acid dosage and thus of the severity of the process.
Fig. 4c shows predicted furfural concentration in relation to residence time. The operating conditions were temperature 200 °C and autohydrolysis (no acid dosage). As can be seen, there is a close correlation between the predicted furfural concentration and the residence time. Thus, the predicted furfural concentration is indicative of the residence time and thus of the severity of the process.
In other embodiments, the at least one parameter indicative of the severity comprises (instead of, or in addition to, furfural concentration), a parameter defined as follows:
Sspectra = (Ko + Kixlvl + K2X Iv2 + K3XIV3 + .... Knxlvn) x Blow steam flow /Biomass feed rate where Ivx denotes the Raman spectra intensity at a specific wavenumber and where Ko-n are constants. The constants Ko-n may be determined using multivariate calibration (for example using PLS or OPLS) based on modelled combined severity.
Fig. 5 shows a score plot from a principal component analysis of the Raman spectra of a blow steam condensate at five combined severity factors with 5-20 min residence time, 0-4% acid dosage and 200 °C temperature. The first principal component explained almost 70% of the variation in the spectra and sorted the data from left to right with increasing combined severity. This indicates that combined severity experienced by the material can be modelled directly from the Raman spectra.
The description above and the appended drawings are to be considered as non-limiting examples of the invention. The person skilled in the art realizes that several changes and modifications may be made within the scope of the invention. For example, other parameters than furfural (such as the above-mentioned Sspectra) may be predicted. Furthermore, predictive models other than MCR-ALS may be used. Furthermore, the blow steam can be separated and collected by other means than a cyclone such as a Perivapor. Furthermore, the collection may alternatively be carried out by feeding the whole blow steam flow to a system for separating/recycling furfural from the blow steam, wherein a sample is collected from a suitable point in said system.

Claims

1. Method for monitoring a steam explosion process, said steam explosion process comprising thermally treating the biomass material with steam at elevated pressure and temperature in at least one reactor, and discharging the biomass material and blow steam from the at least one reactor by means of steam explosion discharge, said method for monitoring comprising the following steps:
- Collecting (2) at least part of the blow steam;
- Condensing (3) the collected blow steam to provide a condensate;
- Carrying out Raman spectroscopy measurements (4) on the condensate to obtain at least one Raman spectra, and
- Predicting (5) at least one parameter indicative of the severity of the steam explosion process based on said Raman spectra.
2. Method according to claim 1, wherein the at least one parameter comprises furfural concentration.
3. Method according to any of claim 1 or 2, wherein said at least one parameter comprises a parameter SfUrfurai predicted based on said Raman spectra, the blow steam flow and the biomass material feed rate to the at least one reactor, wherein:
Sfurfurai = furfural concentration x blow steam flow / biomass material feed rate.
4. Method according to any of claims 1-3, wherein the at least one parameter comprises at least one of acetic acid concentration, methanol concentration, 5-MF concentration, 5- HMF concentration, formic acid concentration and levulinic acid concentration.
5. Method according to any of the preceding claims, wherein said obtained at least one Raman spectra comprises a plurality of observed intensities, wherein said at least one parameter comprises a severity parameter being a linear combination of at least two of the observed intensities times the ratio of blow steam flow to biomass feed rate.
6. Method according to any of the preceding claims, wherein said collecting (2) comprises collecting at least part of the blow steam in the form of at least one sample, and wherein said condensing (3) comprises condensing one or more of the at least one sample.
7. Method according to claim 6, wherein the steps of the method are carried out repeatedly.
8. Method according to any of the preceding claims wherein said predicting (5) comprises using a predictive model based on a plurality of previously obtained Raman spectra of predominant compounds, such as furfural, found in blow steam condensates from said steam explosion process.
9. Method according to claim 8, wherein said predictive model is based on peak-picking or Multivariate Curve Resolution (MCR-ALS),
10. Method according to any of claims 1-7, wherein said predicting (5) comprises using a predictive model based on multivariate calibration using Partial Least Squares (PLS) or orthogonal partial least squares (OPLS).
11. Method according to any of the preceding claims, further comprising, prior to said collecting, separating (1) blow steam from the biomass material.
12. Method for controlling a steam explosion process, said steam explosion process comprising thermally treating the biomass material with steam at elevated pressure and temperature in at least one reactor, and discharging the biomass material and blow steam from the at least one reactor by means of a steam explosion discharge, said method for controlling comprising the following steps:
Monitoring the steam explosion process using the method according to any of the preceding claims to obtain said at least one parameter indicative of the severity of the steam explosion process, and
Controlling (6) at least one operating parameter of the steam explosion process based at least in part on said at least one parameter indicative of the severity of the steam explosion process.
13. Method according to claim 12, wherein said at least one operating parameter comprises at least one of a steam charge to said at least one reactor, an acid catalyst charge to said at least one reactor and a residence time in said at least one reactor.
14. Method according to claim 13, wherein said controlling (6) comprises, if said at least one parameter indicative of the severity of the steam explosion process is equal to or higher than a threshold value indicative of the severity being higher than a target severity, reducing the steam charge and/or the catalyst charge and/or the residence time.
15. System for monitoring a steam explosion arrangement, said steam explosion arrangement comprising at least one reactor (105) configured to thermally treat the biomass material with steam at elevated pressure and temperature, and a steam explosion discharge device configured to discharge the biomass material and blow steam from the at least one reactor by means of a steam explosion discharge, said system for monitoring comprising:
Collecting means (101) arranged to collect at least part of the blow steam;
A condenser (102) arranged to condense the blow steam collected by the collecting means;
A Raman spectroscopy measurement arrangement (103) connected to the condenser (102) to receive a condensate therefrom and being configured to conduct Raman spectroscopy measurements on said at least one condensate, and A processing unit (104) arranged to receive data from said Raman spectroscopy measurement arrangement, said data comprising at least one Raman spectra resulting from said Raman spectroscopy measurements, said processing unit being configured to, based on said at least one Raman spectra, predict at least one parameter indicative of the severity of the steam explosion process.
16. Steam explosion arrangement comprising: at least one reactor (105) configured to thermally treat biomass material with steam at elevated pressure and temperature; a steam explosion discharge device (106) configured to discharge the biomass material and blow steam from the at least one reactor (105) by means of a steam explosion discharge, a system for monitoring according to claim 15, wherein the collecting means is connected to the steam explosion discharge device, and a control system (107) connected to or comprising said processing unit (104) to receive a signal corresponding to the at least one parameter indicative of the severity of the steam explosion process, said control system being configured to control at least one operating parameter of the at least one reactor based at least in part on said at least one parameter indicative of the severity of the steam explosion process.
PCT/SE2024/051059 2023-12-19 2024-12-11 Method and system for monitoring a steam explosion process Pending WO2025136185A1 (en)

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