FI20235647A1

FI20235647A1 - Method and arrangement for controlling pretreatment by measuring condensate color

Info

Publication number: FI20235647A1
Application number: FI20235647A
Authority: FI
Inventors: Juha Tamper; Mika Laitila; Vilho Nissinen; Sami Turunen
Original assignee: Upm Kymmene Corp
Priority date: 2023-06-09
Filing date: 2023-06-09
Publication date: 2024-12-10
Also published as: WO2024252064A1

Abstract

For controlling a pretreatment part (121, 122, 123) in a manufacturing process of chemical bioproducts, there is separated steam (501) from an output flow of a hemi-hydrolysis reactor (401) that forms a part of said pretreatment part. A portion of said separated steam is condensed into a condensate, and an optical measurement (301) of at least one optical characteristic of said condensate is performed. The value of at least one process parameter of said pretreatment part is controlled (302) based on results obtained from said optical measurement (301). Said results indicate content of one or more impurities in said condensate.

Description

METHODS AND ARRANGEMENTS FOR CONTROLLING PRETREATMENT

BY MEASURING COLOUR OF CONDENSATE

TECHNICAL FIELD

The disclosure relates in general to control- ling an industrial-scale manufacturing process of chem- ical bioproducts. In particular, the disclosure relates to the application of specific measurement methods at various parts of the process and to the control deci- sions that can be made on the basis of such measurements.

BACKGROUND OF THE INVENTION

The production of biomass-based chemicals may use for example wood particles as the main raw material.

In a biomass-to-sugar process the wood particles or other biomass may be subjected to various kinds of pre- treatment such as washing and impregnating with water and/or other liquids, and subjected to elevated temper- ature and pressure, in order to prepare the material for later stages of the process. The later stages may in- volve for example enzymatic hydrolysis, from which the purified sugars may go further to a so-called sugar-to- chemical process. Such a latter part of the process may produce for example glycols such as monoethylene glycol and monopropylene glycol. The enzymatic hydrolysis stage & may also produce lignin as one of its outputs.

N In its known form, controlling the pretreatment

S involves a number of uncertainties. The pretreatment 2 30 process may be designed and optimized for certain nom-

T inal characteristics of the raw material, but inherent * variations in what actually enters the process cause 3 continuous fluctuation in how successful the pretreat- 2 ment is in achieving its objectives. Effects of such

S 35 fluctuation are seen for example in the material flow coming out of a hemihydrolysis reactor where the impregnated wood particles are subjected to elevated temperature and pressure and subsequent steam explosion at the output of the reactor. If the reaction is too severe, the product coming out of the reactor is too finely grained; in other words, the particle size dis- tribution of the product shows too large proportions in the smallest size bins, which makes the product more difficult to handle. Also, too severe a reaction may produce excessive amounts of unwanted chemical constit- uents like acetic acid and/or furfural, which have dis- advantageous effects in the later stages of the process, while the yield of desired chemical constituents like

C5 carbohydrates becomes low. Towards the other extreme, if the reaction in the hemihydrolysis and steam explo- sion stage is not severe enough, the product coming out of the reactor is too coarsely grained for effective use in the later stages of the process, and the yield of desired chemical constituents like C5 carbohydrates is again lower than would be possible.

It would be advantageous to have a possibility to react in real time (or at least as quickly as possi- ble) to detected deviations from the expected proceeding of the process. However, it is difficult to obtain ac- curate knowledge of the current status of each step in the process fast enough. Any measurement method that is to be applied must be applicable for prolonged operation in the harsh conditions of an industrial environment,

N which typically makes it difficult or impossible to uti-

N lize instruments built for use in laboratory conditions.

S 30 2 SUMMARY

E According to a first aspect there is provided

K a method for controlling a pretreatment part in a man- 3 ufacturing process of chemical bioproducts. The method & 35 comprises separating steam from an output flow of a

N hemihydrolysis reactor that forms a part of said pre- treatment part; condensing a portion of said separated steam into a condensate; performing an optical measure- ment of at least one optical characteristic of said condensate; and controlling the value of at least one process parameter of said pretreatment part based on results obtained from said optical measurement. Said results indicate content of one or more impurities in said condensate.

According to an embodiment, said optical meas- urement comprises a spectrophotometric absorbance meas- urement on at least one wavelength or wavelength range between 200 and 700 nanometres. This involves at least the advantage that a relatively well known and docu- mented measurement method may be used with little addi- tional complicatedness in instrumentation.

According to an embodiment, said optical meas- urement comprises a spectrophotometric absorbance meas- urement on at least one wavelength or wavelength range between 300 and 400 nanometres. This involves at least the advantage that relatively close correlation between measurement results and measured guantities can be re- lied upon.

According to an embodiment, said optical meas- urement comprises a Fourier Transform Infrared measure- ment. This involves at least the advantage that a fur- ther dimension of measurement information may be ob- tained and utilized, with proven correlation between measurement results and measured quantities.

N According to an embodiment, said optical meas-

N urement comprises a refractometric measurement. This 3 30 involves at least the advantage that a further dimension 2 of measurement information may be obtained and utilized.

E According to an embodiment, said optical meas- * urement comprises a Raman spectroscopy measurement. This 3 involves at least the advantage that a further dimension 2 35 of measurement information may be obtained and utilized. < According to an embodiment, said optical meas- urement is performed as an inline measurement at one or more measurement points in a vessel or conduit that forms a part of a steam condensing and energy recovery system of said manufacturing process. This involves at least the advantage that additional complicatedness in process hardware may be minimized, and the measured con- densate can be taken to represent a true snapshot of actual conditions at the measurement location.

According to an embodiment, the method com- prises taking a sample of said condensate from a steam condensing and energy recovery system of said manufac- turing process and performing said optical measurement on said sample. This involves at least the advantage that the measurement can be made under conditions that are not disturbed in any way by the ongoing activity in the process proper.

According to an embodiment, said pretreatment part in the manufacturing process of chemical bioprod- ucts comprises impregnating wood particles in an acidic impregnating solution before taking the impregnated wood particles into said hemi-hydrolysis reactor. Said con- trolling of the value of at least one process parameter of said pretreatment part may then comprise at least one of: changing an acid concentration of the impregnating solution, changing a residence time of the wood parti- cles in said impregnating solution, changing a storage time of the impregnated wood particles between said im- pregnating and said taking of the impregnated wood par-

N ticles into said hemihydrolysis reactor. This involves

N at least the advantage that accurately defined actions 3 30 are available as possible ways of responding to obtained 2 measurement results in all conditions.

E According to an embodiment, said controlling - of the value of at least one process parameter of said 3 pretreatment part comprises changing a selected feed- 2 35 stock composition, wherein said feedstock comprises said

I wood particles before said impregnating. This involves at least the advantage that the conditions in the process may be influenced from very early on in the process.1

According to an embodiment, said controlling of the value of at least one process parameter of said 5 pretreatment part comprises at least one of: changing a residence time of the process stream in said hemihy- drolysis reactor, changing a temperature to which the process stream is subjected in said hemihydrolysis re- actor, changing a pressure to which the process stream is subjected in said hemihydrolysis reactor. This in- volves at least the advantage that accurately defined actions are available as possible ways of responding to obtained measurement results in all conditions.

According to a second aspect, there is provided an arrangement for controlling a pretreatment part in a manufacturing process of chemical bioproducts. The ar- rangement comprises a steam separating and condensing arrangement configured to separate steam from an output flow of a hemihydrolysis reactor that forms a part of said pretreatment part, and configured to condense at least a part of the separated steam into a condensate.

The arrangement comprises an optical measurement device configured to perform a measurement of at least one optical characteristic of said condensate, and a control unit configured to control the value of at least one process parameter of said pretreatment part based on results obtained from said optical measurement. Said

N results indicate content of one or more impurities in

N said condensate. 3 30 According to an embodiment, the arrangement 2 comprises a condensate vessel for temporarily holding

E at least a portion of said condensate. The optical meas- - urement device may then comprise a measurement head in 3 or adjacent to said condensate vessel. This involves at 2 35 least the advantage that additional complicatedness in

S process hardware may be minimized, and the measured condensate can be taken to represent a true snapshot of actual conditions at the measurement location.

According to an embodiment, the arrangement comprises a condensate conduit for conveying at least a portion of said condensate, wherein the optical meas- urement device comprises a measurement point along said condensate conduit. This involves at least the advantage that additional complicatedness in process hardware may be minimized, and the measured condensate can be taken to represent a true snapshot of actual conditions at the measurement location.

According to an embodiment, said condensate vessel or condensate conduit constitutes a part of a steam condensing and energy recovery system of said man- ufacturing process. This involves at least the advantage that the optical measurement may be combined with a part of the process that is economically and ecologically sound.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and constitute a part of this specification, illustrate em- bodiments of the invention and together with the de- scription help to explain the principles of the inven- tion. In the drawings: n Figure 1 is a high-level block diagram of a

S manufacturing process of chemical bioproducts, b figure 2 illustrates the process steps of an = 30 exemplary pretreatment process, © figure 3 illustrates the processing of an out-

E put flow of a hemihydrolysis reactor on a general level, = figure 4 illustrates the processing of an out- © put flow of a hemihydrolysis reactor on a general level, & 35 figure 5 illustrates an example of utilization

N of separated steam,

figure 6 illustrates measured values of guan- tities related to condensate samples, figure 7 illustrates optical absorption spec- tra of condensate samples, figure 8 illustrates calculated correlations between optical absorption spectra and measured values of quantities, figure 9 illustrates calculated correlations between derivatives of optical absorption spectra and measured values of quantities, figure 10 illustrates measured values of quan- tities related to condensate samples, figure 11 illustrates FTIR absorption spectra of condensate samples, figure 12 illustrates FTIR absorption spectra of condensate samples figure 13 illustrates FTIR absorption spectra of condensate samples, figure 14 illustrates calculated correlations between FTIR absorption spectra and measured values of quantities, figure 15 illustrates calculated correlations between FTIR absorption spectra and measured values of quantities, figure 16 illustrates calculated correlations between FTIR absorption spectra and measured values of quantities, & figure 17 illustrates calculated correlations

N between 1st derivative of FTIR absorption spectra and

S 30 measured values of quantities, 2 figure 18 illustrates calculated correlations

E between 1st derivative of FTIR absorption spectra and * measured values of quantities, 3 figure 19 illustrates calculated correlations 2 35 between 1st derivative of FTIR absorption spectra and

S measured values of quantities,

figure 20 illustrates calculated correlations between 2nd derivative of FTIR absorption spectra and measured values of quantities, figure 21 illustrates calculated correlations between 2nd derivative of FTIR absorption spectra and measured values of quantities, and figure 22 illustrates calculated correlations between 2nd derivative of FTIR absorption spectra and measured values of quantities.

DETAILED DESCRIPTION

In the context of this text, cellulose is taken to mean at least one or even all of: fibers, fiber particles, cellulose, glucane, oligomeric glucose. In the context of this text, hemicellulose is taken to mean at least one or even all of: xylan (like glucuronoxylan and arabinoxylan), xylooligomers, other hemicellulosic oligomeric sugars.

In the context of this text, wood material may be selected from a group consisting of hardwood, soft- wood, and their combination. The wood material may e.g. originate from pine, poplar, beech, aspen, spruce, or birch. The wood material may also be any combination or mixture of these. Preferably the wood material is broad- leaf wood due to its relatively high inherent sugar content, but the use of other kinds of wood is not n excluded. The expressions wood particles, wood chips,

S and chips are used interchangeably and mean wood mate- b rial that has been mechanically broken, chipped, and/or = 30 crushed to have a distribution of particle sizes mainly © ranging from a few millimetres to a few centimetres.

E Fig. 1 illustrates schematically a manufactur-

N ing process of chemical bioproducts from wood material. 3 The process can be roughly divided into a wood handling & 35 phase 101, a wood-to-sugar phase 102, and a sugar-to-

N chemical phase 103.

The wood handling phase 101 comprises mainly mechanical processing such as debarking 111 and chipping 112.

The wood-to-sugar phase 102, which is also called the wood-to-sugar process, comprises a pre-treat- ment part where the wood chips from the wood handling phase 101 are taken through impregnating 121, hemihy- drolysis 122, and steam explosion 123 in order to break down the structure of the wood material and to remove the C5 sugars. Impregnating is typically part of pro- cesses that utilize an acid catalyst, so it may be omit- ted in processes that rely upon autohydrolysis. The main process stream continues into enzymatic hydrolysis 124, where the aim is to convert polysaccharides into C6 monomers, essentially converting glucan into glucose.

Lignin and other remaining solids are removed after the enzymatic hydrolysis, and the obtained C6 sugars are fed further to a sugar-to-chemical phase 103. The removed lignin may be utilized further in other processes.

The subsequent utilization of the sugars in the sugar-to-chemical phase 103 may comprise steps such as purification 131 of the sugars (both C5 and/or C6 car- bohydrates) and one or several sugar conversion pro- cesses 132. The sugar conversion processes 132 may in- clude processes such as fermentation to produce alcohols or catalytical hydrotreatment to produce glycols.

Fig. 2 illustrates an example of a product flow & through various stages that all belong to the pretreat-

N ment part of fig. 1. Wood particles or chips are washed 3 30 in a washing 201, which is done with water, removing 2 some mainly inorganic impurities such as sand. Washed

T wood particles are taken to steam treatment 202 for the * purpose of removing air from inside the wood particles 3 and to preheat them to an elevated temperature. Steam- 2 35 treated wood particles are taken to dilute acid treat-

I ment 203 for impregnating them with a dilute acid solu- tion. The aim of the dilute acid treatment 203 is to make the dilute acid solution penetrate into the wood particles as evenly as possible.

The acid-impregnated wood particles are taken to hemihydrolysis at 204 where they are under elevated pressure and temperature. At the output of the hemihy- drolysis 204 the wood particles undergo a steam explo- sion that breaks their structure. The output stream from the hemihydrolysis and steam explosion 204 goes through steam separation (not separately shown) to mixing 205 where water is added and the resulting mass is homoge- nized mechanically to break up agglomerates. Solids and liquids may then be separated at 206 for feeding into later process stages.

Fig. 3 illustrates how a manufacturing process of the kind explained above may comprise steam separa- tion after the hemihydrolysis and steam explosion step 204. At the output of the hemihydrolysis reactor, the process stream comprises the actual product to be pro- cessed, as well as steam. The steam that gets separated from the actual product to be processed carries signif- icant amounts of energy, which should be extracted and circulated back into the process. Extracting the energy makes the steam condense into a liquid condensate. Ac- cording to a novel insight, the content of one or more impurities in the condensate may serve as an important indicator of how successful the manufacturing process currently is in terms of enabling the eventual produc-

N tion of the desired chemical bioproducts as efficiently

N and economically as possible. 3 30 In the sense of the following description, the 2 term "impurity” is taken to mean all other constituents

T of the condensate than water. Such other constituents > may comprise, for example, carboxylic acid, acetates, 3 furans, methanol, formiates, formic acid, acetic acid, 2 35 and/or sugars. As an alternative designation, instead

S of impurities one could characterise such other-than- water constituents of the condensate as chemical components of the condensate. In addition to chemical components, the condensate may also contain impurities in the form of small amounts of solid matter that the steam has brought along from the steam separation step.

The concentrations of any such impurities in the condensate are typically rather small, in the order of less than a gram or at most some grams per litre.

Consequently, the condensate is relatively clear in col- our and transparent or at least translucent to light and near ultraviolet radiation. For this reason, it may be possible to perform an optical measurement of at least one optical characteristic of the condensate. The re- sults obtained from the optical measurement may then indicate the content of one or more impurities in the condensate. Performing such an optical measurement is shown schematically as step 301 in fig. 3.

An example of an optical characteristic that can be measured is absorbance on at least one wave- length. Impurities such as those mentioned above tend to cause absorption of visible light and/or near ultra- violet radiation in the condensate. It has been found that important information about the current operation of the manufacturing process may be gained by performing a spectrophotometric absorbance measurement on at least one wavelength or wavelength range between 200 and 700 nanometres. It has also been found that particularly significant information about the current operation of & the manufacturing process may be gained by performing

N the spectrophotometric absorbance measurement on at 3 30 least one wavelength or wavelength range between 300 and 2 400 nanometres. = Additionally, impurities such as those men- q tioned above tend to cause changes in the way in which 3 the condensate absorbs and/or reflects infrared radia- 2 35 tion. Correspondingly, the optical measurement men-

I tioned above and shown as step 301 in fig. 3 may comprise an FTIR measurement, where the acronym FTIR comes from

Fourier Transform InfraRed.

Additionally, impurities such as those men- tioned above tend to cause changes in the index of re- fraction of the condensate. Correspondingly, the optical measurement mentioned above and shown as step 301 in fig. 3 may comprise a refractometric measurement.

Additionally, impurities such as those men- tioned above tend to cause changes in the inelastic scattering of photons in the condensate. Correspond- ingly, the optical measurement mentioned above and shown as step 301 in fig. 3 may comprise a Raman spectroscopy measurement.

To complete the schematic shown in fig. 3 as a method for controlling the pretreatment part in a man- ufacturing process of chemical bioproducts the method comprises step 302, which involves controlling the value of at least one process parameter of the pretreatment part based on results obtained from the optical meas- urement.

As an example, it may be assumed that the pre- treatment part in the manufacturing process of chemical bioproducts comprises impregnating wood particles in an acidic impregnating solution, as in step 203 of fig. 2, before taking the impregnated wood particles into the hemihydrolysis reactor as in step 204 of fig. 2. In such a case, the controlling of the value of at least one & process parameter of the pretreatment part may comprise

N changing an acid concentration of the impregnating so- 3 30 lution and/or changing a residence time of the wood 2 particles in said impregnating solution. Typically, if

T the results obtained from the optical measurement can * be interpreted as being indicative of an insufficient 3 severity of the reaction in the hemihydrolysis reactor, 2 35 one may increase the acid concentration and/or the res-

I idence time of the wood particles in the impregnating solution. Correspondingly, if the results obtained from the optical measurement can be interpreted as being in- dicative of too severe a reaction in the hemihydrolysis reactor, one may decrease the acid concentration and/or the residence time of the wood particles in the impreg- nating solution.

Additionally or alternatively, the controlling of the value of at least one process parameter of the pretreatment part may comprise changing a storage time of the impregnated wood particles between the impreg- nating in the impregnation vessel and the input of said hemihydrolysis reactor. After removing from the impreg- nation vessel, the impregnated wood particles may not go directly to the hemihydrolysis reactor but to an intermediate silo or other kind of temporary storage.

At least to a certain extent, the longer the impregnated wood particles are kept in such a temporary storage, the better the remaining impregnating solution penetrates into their inner parts, which has essentially the same effect as a longer residence time in the impregnating solution.

The results obtained from the optical measure- ment may also be interpreted as being indicative of suboptimal quality and/or composition of the feedstock, meaning the wood particles before impregnating. A man- ufacturing plant of chemical bioproducts may obtain its feedstock from its own chipping facility, and/or it may acquire the wood particles ready chipped from one or & more subcontractors. The plant may have stockpiles of

N different kinds of wood particles, and these may differ 3 30 from each other in e.g. coarseness, wood species, stor- 2 age age, moisture content, rot content, or the like.

E Some kind of a feeding mechanism is used to feed a - selected feedstock composition to the pretreatment part 3 of the process. The controlling of the value of at least 2 35 one process parameter of said pretreatment part may com-

S prise changing the selected feedstock composition. For example, aged wood is known to behave differently in the hemihydrolysis reaction than fresh wood. If the results obtained from the optical measurement can be interpreted as being indicative of the hemihydrolysis reaction ex- hibiting too dominant features typical to aged wood, one may change the selected feedstock composition to include a larger proportion of fresh wood.

Additionally or alternatively, the controlling of the value of at least one process parameter of the pretreatment part may comprise changing a residence time of the process stream in the hemihydrolysis reactor, and/or changing the temperature and pressure to which the process stream is subjected in the hemihydrolysis reactor. The temperature and pressure in the hemihy- drolysis reactor are typically closely interlinked to- gether. Longer residence time, higher temperature, and higher pressure increase the severity of the reaction, while shorter residence time, lower temperature, and lower pressure decrease it. Consequently, if the results obtained from the optical measurement can be interpreted as being indicative of too severe a reaction or insuf- ficient severity of the reaction in the hemihydrolysis reactor, the residence time, temperature, and/or pres- sure may be decreased or increased correspondingly.

Fig. 4 illustrates schematically some process streams towards the end of the pretreatment part in an example of a manufacturing process of chemical bioprod- ucts. The reactor, shown with reference designator 401,

N is for maintaining the hemihydrolysis reaction mentioned

N above in step 204 of figs. 2 and 3. At the output of the 3 30 reactor 401 the steam explosion takes place, after which 2 the process stream that comprises steam and the actual

T product to be processed is taken to a solids separator * 402, possibly with the aid of driving means such as a 3 jet of compressed air. From the solids separator 402 the 2 35 actual product to be processed continues to a conveyor

I 403, while steam from the solids separator 402 goes to a steam recovery part 403.

The recovered steam releases heat to a stream of fresh water, producing fresh steam that can be used for example as one of the inputs to the reactor 401.

Releasing heat condenses the steam into a condensate, which may be taken to waste waters processing and/or at least partly circulated to other purposes. Such partial circulation could mean for example recovering any such species of the previously described impurities that may have other uses. One purpose in steam recovery 1s to extract remaining heat and transfer it to incoming fresh water, producing hot water for other uses in the pro- cess. The output from the steam recovery part 403 is a stream of cooled condensate.

Fig. 5 illustrates, in a somewhat more appa- ratus-like approach, an example of how some process streams related to steam and condensate may be routed.

In particular, fig. 5 will be used below to consider, where to obtain the condensate that will be subjected to the optical measurement discussed above.

From a stream of separated steam 501, a small side stream 502 may be branched out for separate con- densing in small scale. The resulting condensate may be subjected to an optical measurement at the point sche- matically shown as 503. The condensate in the side stream 502 may then be routed back to the main stream of steam, or it may be lead to disposal of waste liquids.

A condensing device 504 may work as a heat

N exchanger, so that the thermal energy released by con-

N densing the steam may be utilised to heat some other 3 30 medium, like water for example. Condensate that flows 2 out from the condensing device 504 may be subjected to

E optical measurement at the point schematically shown as - 505. Additionally or alternatively, there may be a 3 branch 506 for taking samples of condensate to more 2 35 accurate laboratory measurements, shown schematically

I as 507.

A pump 508 is shown in fig. 5 for pumping the condensate both into a circulation loop 509 and to an output line 510. A further possibility for a measurement point along the output line 510 is shown schematically as 511.

In one possible implementation there is an evaporator, a preheater, two condensers , two circula- tion pumps, as well as a heat exchanger. Pressurized steam from a solids separator releases a first portion of its thermal energy in the evaporator before at least a part of it continues first to the preheater and then to the first condenser. The evaporator and the preheater belong to a steam-producing loop in which fresh water is first preheated in the preheater and then converted to steam in the evaporator. The first circulation pump may maintain a local circulation of some of the conden- sate formed of the pressurized steam in the evaporator for stabilising purposes, while it may also pump some of said condensate into the first condenser. Condensate from the preheater may return by gravity to the evapo- rator.

The first condenser may combine the unpressur- ized steam from the product conveyor, the remnants of the pressurized steam from the preheater, and the con- densate pumped therein by the first circulation pump.

The purpose of the first condenser is to heat incoming warm water to make hot water that can be used elsewhere & in the manufacturing process. The second circulation

N pump may maintain some circulation of condensate in the 3 30 first condenser. Any remaining steam, which is thor- 2 oughly unpressurized at this stage, may go to the second

T condenser for final condensing. Also the second conden- - ser may produce hot or warm water for other purposes in 3 the process. 2 35 The heat exchanger extracts remaining heat from

S condensate pumped therein by the second circulation pump, transferring said extracted heat to incoming fresh water than can then be used as an input to the water- heating loop in the first condenser, for example. The eventual outputs of cooled condensate from the second condenser and the heat exchanger may be taken to waste water processing and/or circulation as explained above with reference to fig. 4.

It should be noted that the arrangements shown in figs. 4 and 5 are only examples, as steam condensing and energy recovery systems may take different forms in different manufacturing processes. For example, it is not necessary to have separate collection paths for pressurized and unpressurized steam, but all steam may come into the condensing part of the process in unpres- surized form.

As seen in fig. 5, there are typically a vari- ety of locations in the process streams where the con- densate could be subjected to an optical measurement of the kind - and for the purposes - described above. As a general rule, irrespective of the detailed form of the steam condensing and energy recovery system, the con- densate the optical characteristics of which are to be subjected to the optical measurement should be "fresh” in the sense that it would represent very recent devel- opments in the hemihydrolysis reaction. Circulation loops, and all further routes that the condensate takes towards the end of the process, cause both delay and dilution so that any portion of condensate examined only

N later in the process will have a somewhat more vague

N relationship with the characteristics of the product 3 30 that was most recently output from the hemihydrolysis 2 reaction.

E Another factor to consider, when deciding the - point where to optically measure the condensate, is the 3 possible appearance of solids in the condensate. On one 2 35 hand, solids that were carried along by the steam and

S that consequently ended up in the condensate may inter- fere with the optical measurement, meaning that the optical measurement should be made on a portion of con- densate that is as free of solids as possible. On the other hand, if the way in which the appearance of solids affects the optical measurement is known, and if a con- sistent relation can be shown between such solids-in- flicted effect on the optical measurement and some re- cent characteristic of the reaction in the hemihydrol- ysis reactor that affected the appearance of solids, solids appearing in the condensate might be even desir- able as their measured effect may be of assistance in making the control decisions. As a yet further aspect is that if solids are not wanted in the optical meas- urement, it may be possible to remove them by filtering before making the measurement.

In an arrangement of the kind explained ear- lier, one possible point for examining relatively “fresh” condensate is the condensate return line from the preheater to the evaporator. That portion of pres- surized steam that made it through the evaporator had come quite recently from the solids separator and thus fulfils the criterion of being “fresh”. If it condenses in the preheater, it appears quite quickly in said re- turn line and becomes available for optical measurement.

As the amount of condensate needed for the op- tical measurement is small, it is also possible to con- struct a completely separate, dedicated condensing and measuring loop into which one would direct a small por- & tion of the steam that comes directly from steam sepa-

N ration. Even if one may thus loose some thermal energy 3 30 that would otherwise be recoverable, the loss will be 2 relatively small, and it may even become compensated

E economically if such an arrangement enables making more * accurate control decisions that optimise the operation 3 of the pretreatment part better. In the arrangement of 2 35 fig. 5, an example of such a dedicated condensing and

S measuring loop is shown with the reference designator 502.

Irrespective of location, the optical measure- ment described above may be performed as an inline meas- urement at one or more measurement points in a vessel or conduit that forms a part of a steam condensing and energy recovery system of the manufacturing process. If in a conduit, the measurement may be arranged by in- stalling optically transparent lenses that allow optical radiation to pass transversally through a section of the conduit. Alternatively, there may be a whole section of the conduit that is optically transparent for the opti- cal radiation to pass through that is used for the meas- urement. In in a vessel, the measurement may be arranged by using a measurement head protruding into the vessel, with an optical transmitter and optical receiver in the measurement head separated by some free space. An inline measurement involves the advantage of allowing truly constant monitoring of the measured quantity as well as full automatization.

As an alternative, the method may comprise tak- ing a sample of condensate from the steam condensing and energy recovery system of the manufacturing process and performing the optical measurement on said sample. In such an embodiment, the sampling and measuring may be partly or fully automatized. A further possibility is manual sampling, in which the sample is taken manually and carried to a separate measurement location for the measurement.

N It is obvious to a person skilled in the art

N that with the advancement of technology, the basic idea 3 30 of the invention may be implemented in various ways. The 2 invention and its embodiments are thus not limited to

T the examples described above, instead they may vary - within the scope of the claims. g

Q 35 EXAMPLE 1

S Nine samples of condensate were taken from the steam condensing and energy recovery system of a manufacturing process of chemical bioproducts. The man- ufacturing process was of the kind shown in figs. 1 and 2, and it was deliberately run with slightly different values of various process parameters such as acid con- centration and residence time in impregnation; residence time, temperature, and pressure in hemihydrolysis; and feedstock composition. After each change in process pa- rameter values, the process was allowed to run long enough for the change to take full effect on the severity of the reaction in the hemihydrolysis reactor.

The nine samples were analysed in laboratory regarding their total carboxylic acids content, furans content, Brix value, ICUMSA value, COD value, methanol content, acetate content, formiate content, formic acid content, acetic acid content, and conductivity. The re- sults of the laboratory analyses are given in the table of fig. 6.

Each of the nine samples was also subjected to a spectrophotometric absorbance measurement on a wave- length range between 200 and 700 nanometres. The meas- ured absorbance spectra are shown in fig. 7.

For each integral wavelength A, Ae€[200, 700], there was formed a nine-element vector Ay = [A (A), As (A), .. Ag (A) ], the components A; (A) of which were the measured absorbances of the i:th sample (i€[1,9]) at the wave- length A. Additionally, for each integral wavelength A, he [200, 700], there were formed two other nine-element & vectors A’, = [A':(A), A’.(A), .. A/o(M)] and Arn, =

N [A "3 (ÅA), AO(X), .. ATS (AA) ] . The components A’; (A) and 3 30 A’’;(A) of these were the calculated first-order and 2 second-order derivatives, respectively, of the measured

T absorbance curves of the i:th sample (i€[1,9]) at each - wavelength A. 3 A correlation coefficient was calculated of 2 35 each vector Ax, A'1, and A’’; with the corresponding

S nine-element vector obtained from the respective column in the table of fig. 6. The calculation of the correla- tion coefficient followed the formula 2ilxi-X)Yi-7I)

Cor X,Y) = = =r .

Thus, for example, the correlation coefficient calculated for a vector A;y and the first column in the table of fig. 6 indicates, using the value range [0,1], how well the variation in measured methanol content be- tween samples correlated with the variation in measured absorbance between samples at the wavelength 200 nano- metres. The larger the calculated correlation coeffi- cient, the better the correlation.

The calculated correlation coefficients were plotted in the form of a graph for each of the labora- tory-measured values separately. The plotted graphs for the correlation between measured absorbance and each laboratory-measured value are shown in fig. 8. The plot- ted graphs for the correlation between the first-order derivative of the measured absorbance and each labora- tory-measured value are shown in fig. 9. Relatively large values of correlation coefficients are seen par- ticularly at wavelengths in the range between 300 and 400 nanometres.

Based on these results, it is plausible that the results obtained from an optical measurement can be n taken as indicative of the content of one or more impu-

S rities in the condensate. In a simple embodiment, opti-

O cal measurement results on a wavelength (or wave number) = 30 at which good correlation has been found are used as © indications of the corresponding impurity content. Even

E better accuracy may be advantageously obtained by making

K a chemometric analysis and/or regression analysis using 3 the optical measurement results on a plurality of those & 35 wavelengths or wave numbers at which good correlation

N has been found. As the content of such impurities in the condensate are, in turn, indicative of the quality of the product output from the hemihydrolysis reactor, the results obtained from the optical measurement can be used as a basis for making decisions about values of at least one process parameter of the pretreatment part in the manufacturing process of chemical bioproducts.

EXAMPLE 2

Twelve further samples of condensate were taken from the steam condensing and energy recovery system of a manufacturing process of chemical bioproducts. Similar to Example 1, the manufacturing process was of the kind shown in figs. 1 and 2, and it was deliberately run with slightly different values of various process parameters such as acid concentration and residence time in im- pregnation; residence time, temperature, and pressure in hemihydrolysis; and feedstock composition. After each change in process parameter values, the process was al- lowed to run long enough for the change to take full effect on the severity of the reaction in the hemihy- drolysis reactor.

The twelve further samples were analysed in laboratory regarding their total carboxylic acids con- tent, furans content, Brix value, ICUMSA value, COD value, methanol content, acetate content, formiate con- tent, formic acid content, acetic acid content, and con- ductivity. The results of the laboratory analyses are given in the table of fig. 10. Particularly promising & results were obtained in association with the total car-

N boxylic acids content, furan content, COD content, and 3 30 formiate content. 2 Each of the nine samples mentioned in Example

T 1 and the twelve further samples was also subjected to * a FTIR (Fourier Transform InfraRed) absorbance measure- 3 ment on a wave number range between 648 and 4000 1/cm. 2 35 The measured absorbance spectra are shown in figs. 11,

I 12, and 13.

For each integral wave number A, A€[648, 4000], there was formed a 21-element vector By = [Bi (A), Bo (A), .. Bo1(A)], the components Bi; (A) of which were the meas- ured FTIR absorbances of the i:th sample (iec€[1,21]) at the wave number A.

A correlation coefficient was calculated of each vector Bi with the corresponding 21-element vector obtained from the respective column in a combination table made by stacking the data lines of the tables of figs. 6 and 10 together. The calculation of the corre- lation coefficient followed the formula 2ilxi-X)Yi-7I)

Cor X,Y) = = =r .

Thus, for example, the correlation coefficient calculated for a vector Bsss and the first column in said combination table indicates, using the value range [0,1], how well the variation in measured methanol con- tent between samples correlated with the variation in measured FTIR absorbance between samples at the wave number 648 1/cm. The larger the calculated correlation coefficient, the better the correlation.

The calculated correlation coefficients were plotted in the form of a graph for each of the labora- tory-measured values separately. The plotted graphs for the correlation between measured FTIR absorbance and e each laboratory-measured value are shown in figs. 14,

S 15, and 16. Relatively large values of correlation co-

O efficients are seen at different wave numbers depending = 30 on which laboratory-measured value is considered. © Similar to the absorbance measurements between

E 200 and 700 nanometres, there were also formed two other

K 21-element vectors B', = [B',(4), B'>(X), .. B"/21(4)] and 3 B'/; = [B'"'1(A), B''>(4), .. B'/21(A)]. The components & 35 B';(A) and B’’; (A) of these were the calculated first-

N order and second-order derivatives, respectively, of the measured absorbance curves of the i:th sample (ie€[1,21])

at each wave number A. Good correlation was found also between the vectors B', and Bi, and the laboratory- measurement value vectors on at least some wave numbers and/or wave number ranges. The plotted graphs for the correlation between the first-order derivative of the measured FTIR absorbance and each laboratory-measured value are shown in figs. 17, 18, and 19. The plotted graphs for the correlation between the second-order de- rivative of the measured FTIR absorbance and each la- boratory-measured value are shown in figs. 20, 21, and 22.

Based on these results, it is plausible that the results obtained from an FTIR measurement, which is another form of an optical measurement, can be taken as indicative of the content of one or more impurities in the condensate. In a simple embodiment, FTIR measurement results on a wavelength (or wave number) at which good correlation has been found are used as indications of the corresponding impurity content. Even better accuracy may be advantageously obtained by making a chemometric analysis and/or regression analysis using the FTIR meas- urement results on a plurality of those wavelengths or wave numbers at which good correlation has been found.

As the content of such impurities in the condensate are, in turn, indicative of the quality of the product output from the hemihydrolysis reactor, the results obtained from the optical measurement can be used as a basis for & making decisions about values of at least one process

N parameter of the pretreatment part in the manufacturing

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Claims

1. A method for controlling a pretreatment part in a manufacturing process of chemical bioprod- ucts, the method comprising: - separating steam from an output flow of a hemihy- drolysis reactor that forms a part of said pretreat- ment part, - condensing a portion of said separated steam into a condensate, - performing an optical measurement of at least one optical characteristic of said condensate, and - controlling the value of at least one process param- eter of said pretreatment part based on results ob- tained from said optical measurement; wherein said results indicate content of one or more impurities in said condensate.

2. A method according to claim 1, wherein said optical measurement comprises a spectrophotomet- ric absorbance measurement on at least one wavelength or wavelength range between 200 and 700 nanometres.

3. A method according to claim 2, wherein said optical measurement comprises a spectrophotomet- ric absorbance measurement on at least one wavelength or wavelength range between 300 and 400 nanometres. D 25

4. A method according to claim 1, wherein & said optical measurement comprises a Fourier Transform O Infrared measurement. @

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5. A method according to claim 1, wherein E said optical measurement comprises a refractometric N 30 measurement. O

Q

6. A method according to claim 1, wherein R said optical measurement comprises a Raman spectros- copy measurement.

7. A method according to any of the preceding claims, wherein said optical measurement is performed as an inline measurement at one or more measurement points in a vessel or conduit that forms a part of a steam condensing and energy recovery system of said manufacturing process.

8. A method according to any of claims 1-6, comprising: - taking a sample of said condensate from a steam con- densing and energy recovery system of said manufactur- ing process and - performing said optical measurement on said sample.

9. A method according to any of the preceding claims, wherein: - said pretreatment part in the manufacturing process of chemical bioproducts comprises impregnating wood particles in an acidic impregnating solution before taking the impregnated wood particles into said hemi- hydrolysis reactor, and - said controlling of the value of at least one pro- cess parameter of said pretreatment part comprises at least one of: changing an acid concentration of the impregnating solution, changing a residence time of the wood particles in said impregnating solution, changing a storage time of the impregnated wood parti- n cles between said impregnating and said taking of the S impregnated wood particles into said hemihydrolysis 8 reactor. S

10. A method according to claim 9, wherein = 30 said controlling of the value of at least one process q parameter of said pretreatment part comprises changing 3 a selected feedstock composition, wherein said feed- 2 stock comprises said wood particles before said im- S pregnating.

11. A method according to any of the preced- ing claims, wherein said controlling of the value of at least one process parameter of said pretreatment part comprises at least one of: changing a residence time of the process stream in said hemihydrolysis re- actor, changing a temperature to which the process stream is subjected in said hemihydrolysis reactor, changing a pressure to which the process stream is subjected in said hemihydrolysis reactor.

12. An arrangement for controlling a pre- treatment part in a manufacturing process of chemical bioproducts, the arrangement comprising: - a steam separating and condensing arrangement con- figured to separate steam from an output flow of a hemihydrolysis reactor that forms a part of said pre- treatment part, and configured to condense at least a part of the separated steam into a condensate, - an optical measurement device configured to perform a measurement of at least one optical characteristic of said condensate, and - a control unit configured to control the value of at least one process parameter of said pretreatment part based on results obtained from said optical measure- ment; wherein said results indicate content of one or more impurities in said condensate. O N

13. An arrangement according to claim 12, N comprising a condensate vessel for temporarily holding = at least a portion of said condensate, wherein the op- © 30 tical measurement device comprises a measurement head E in or adjacent to said condensate vessel. 3

14. An arrangement according to claim 10, 2 comprising a condensate conduit for conveying at least S a portion of said condensate, wherein the optical measurement device comprises a measurement point along sald condensate conduit.

15. An arrangement according to claim 13 or 14, wherein said condensate vessel or condensate con- duit constitutes a part of a steam condensing and en- ergy recovery system of said manufacturing process. O N O N O <Q o O I a a N + O O 0 N O N