WO2013156668A1 - Procédé et agencement pour l'intensification et le contrôle d'évaporation - Google Patents

Procédé et agencement pour l'intensification et le contrôle d'évaporation Download PDF

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Publication number
WO2013156668A1
WO2013156668A1 PCT/FI2013/000021 FI2013000021W WO2013156668A1 WO 2013156668 A1 WO2013156668 A1 WO 2013156668A1 FI 2013000021 W FI2013000021 W FI 2013000021W WO 2013156668 A1 WO2013156668 A1 WO 2013156668A1
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Prior art keywords
vapor
evaporation
liquid
condensate
duct
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PCT/FI2013/000021
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English (en)
Inventor
Carl-Gustav Berg
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Andritz Oy
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Publication of WO2013156668A1 publication Critical patent/WO2013156668A1/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/06—Flash distillation
    • B01D3/065—Multiple-effect flash distillation (more than two traps)
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D5/00—Condensation of vapours; Recovering volatile solvents by condensation
    • B01D5/0027—Condensation of vapours; Recovering volatile solvents by condensation by direct contact between vapours or gases and the cooling medium
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C11/00—Regeneration of pulp liquors or effluent waste waters
    • D21C11/10—Concentrating spent liquor by evaporation

Definitions

  • the present invention relates to a method and arrangement for intensifying and controlling evaporation of a solution, Preferably it relates to a method and an arrangement for intensifying evaporation of waste liquor from chemical pulp production processes in a multi-effect evaporation plant.
  • the invention can be widely applied in various evaporation processes and evaporation arrangements and it is not limited to the evaporation of a cer- tain solution.
  • Methanol is one of the most important causes of chemical (COD) and biological (BOD) oxygen demand in biomass waste streams or black liquor streams. Due to tightening environmental regulations, active methanol segregation and its control are of high im- portance. Alkaline pulping of wood chips at chemical pulp plants normally produces 5-20 kg of MeOH/ton of pulp (and several other easily volatile compounds, such as TRS- compounds, turpentines, ammonia etc.) and thus methanol is present in various amounts in the discharge streams of the digester plant, most important of which is weak black liquor stream. Easily volatile compounds may produce odorous condensates which are poor- ly usable.
  • Weak black liquor is an essential stream to be reused for production of usable clean water, since it simultaneously forms the most important energy source for the chemical pulp mill when it is concentrated by evaporation to so-called firing black liquor and thereafter combusted for regeneration of chemicals in a recovery boiler, A modern recovery process may in a chemical pulp mill of modern technology produce both heat and electricity in amounts exceeding the needs of the mill.
  • Water removed from weak black liquor in the evaporation plant can contain abundantly of volatile compounds such a methanol, ethanol, acetone, turpentine and multiple sulfur compounds. Thus, all these components are present in firing black liquor, but most of them are separated to secondary condensates and non-condensable off-gases.
  • the purpose of modern separation processes of evaporators is to segregate secondary condensates so that a major part of the methanol is enriched to one relatively small condensate fraction (often referred to as foul condensate), which can be purified with ac- ceptable expenses.
  • Concentrated methanol and other volatile organic compounds can then be combusted in a recovery boiler, in a dedicated incinerator for non-condensable gases or in a lime kiln, This in turn reduces the environmental impact of biomass-based methanol, as well accumulation of methanol, thereby decreasing the consumption of fresh water.
  • black liquor evaporation is a highly essential part in modern circulation of chemicals, water and energy. This has been proven in modern chemical pulp mills having a multi-effect evaporation plant in the middle of the mill.
  • black liquor is evaporated in a multi-effect evaporation plant, where vapor formed in the first effect is used as heating medium in a second effect, etc, Vapor introduced to the vapor side of the evaporation effect heats the liquid in the liquor side, whereby new vapor is generated having a pressure and temperature lower than those of the vapor introduced to the vapor side.
  • the temperature of vapor fed into the evaporation effects decreases effect by effect, which limits the capacity of the evaporation plant.
  • the capacity e.g. the heat surface of the evaporator units or the number thereof may be increased.
  • Vapor pressure increase by means of a pressure-increasing device between the evaporator units has also been suggested.
  • a black liquor evaporation plant typically comprises a multi-effect evaporation plant with 3-7 effects (see Fig. 1 )
  • Fresh steam is introduced from a low-pressure steam distribution system typically at a pressure of 0.35—0.45 MPa (absolute pressure). This corresponds to a saturation temperature of 139 °C - 148 °C.
  • Fresh steam is led to a heating element) of the first effect (not shown in Fig. 1 ). Vapor generated in the liquor side of effect 1 is led via lines 15 to a heating element of effect 2 and from there to effect 3, etc. , as shown by lines 16.
  • the vapor exiting the last effect 6 at a temperature of 57 °C - 60 °C is con- densed in a surface condenser 8.
  • the steam flow sequence is numbered so that it passes from effect 1 to the next effect, i.e. effect 2 etc. and the black liquor typically flows to an opposite direction.
  • the heating element of the evaporators is a lamella formed of two plates attached to each other. The liquid to be evaporated falls to the outer surface of the lamella, and heating medium, such as steam, flows inside the la- mella. This is illustrated in more detail in Fig. 2.
  • the evaporation plant has several possibilities for arranging the liquor flow sequence. The optimal number of effects is dependent on the steam balance of the mill, boundary conditions comprising e.g. production of electricity, price of electricity etc. Saving steam is not always economical and mill-wide cost calculations are needed in order to find the best so- lution for each case.
  • the embodiment of Fig. 1 is typical for a Northern chemical pulp mill using soft wood as raw material.
  • the concentration effect 1 is usually divided to a number of separate sub-units which are connected in parallel in the steam side and in series in the liquor side. A sequence typical for the liquor side is counter-current with respect to the steam or a mixed-feed sequence. If the feed temperature is higher than the temperature in the last effect and a counter- current feed model is preferred, the liquor is to be flashed prior to feeding it into the last effect, The flash vapor of hot weak black liquor is mixed with suitable secondary vapor streams which provide latent heat to the colder effects. The black liquor stream is shown in Fig. 1 . Weak black liquor (or other waste liquor from chemical pulp) in line 10 is led into effect 4, where the liquor is flashed. After that the liquor is led via line 1 1 to effect 5, where it is further flashed.
  • secondary condensate can be fractioned inside the lamellas to clean and foul fractions (see Figs. 1 and 2).
  • Foul condensate thus generated is typically treated further with steam stripping.
  • the stripping process produces stripped (clean) condensate and liquid methanol fuel. Fractionation is chosen in each effect to maximize methanol recovery and to minimize foul condensate stream.
  • the amount of foul condensate from the evaporation plant is typically approximately 15% of the total condensate amount and the obtained total methanol recovery can be 70-80%.
  • the present (duct stripping) invention can help to increase methanol recovery close to 100 per cent when it is combined with evaporators having internal segregation of condensate.
  • the vapor space inside the lamellas 20 is divided by diagonal welding seams 21 to a lower 22 and an upper 23 compartments (Fig. 2). Most of the vapor fed to the evaporator via line 28 is condensed in the lower compartment producing clean condensate 24. The smaller steam fraction and with it most of the methanol and TRS-compounds are condensed in the upper compartment 23 and collected as foul condensate 25. The area of foul condensate compartment is 5-30% of the lamella area, largest in the evaporator effects of the back end. Vent vapor is dicharged from conduit 26. Liquor to be evaporated is fed via line 29 and evaporated liquor is discharged via line 30. The vapor generated in the evaporators is discharged via line 31 .
  • Fractionation is chosen in each effect to maximize methanol recovery and to minimize foul condensate stream.
  • the amount of foul condensate coming from the evaporator effects varies normally between 5-30% of the total amount of condensate.
  • the portion of foul condensate is 10% of the incoming secondary vapor flow and its MeOH-mass flow out corresponds to 80% of the incoming MeOH mass flow.
  • the corresponding figures for clean condensate is 89% of the total incoming mass flow, where MeOH outflow is 10% of the MeOH inflow, and... the__vent.
  • vapor is 10% of the incoming mass flow of secondary vapor and its MeOH mass flow out corresponds to 10% of the incoming MeOH mass flow.
  • Fig. 1 illustrates secondary condensate fractions in a 6-effect evaporator.
  • 6-effect evaporator according to Fig. 1 separation takes place in effects 2-6 and in the surface condenser.
  • the corresponding condensate streams and their compositions are shown in Table 1 .
  • Foul condensates generated in effects 2,3, 4 and 5 in Fig. 1 are collected into a flashing tank 17 and discharged via line 18.
  • the foul condensates (FC) from the surface conden- ser 8 and effect 6 are also directed to line 18.
  • Clean condensates from effects 2, 3 and 4 are discharged via line 19 as secondary condensate 1 (SC1 ).
  • Clean condensates from effects 5, 6 and the surface condenser 8 are discharged via line 27 as secondary condensate 2 (SC2).
  • Foul condensates are typically cleaned with steam in a stripping column (stripper), which is a cylindrical vessel, where stripping liquid flows downwards under gravity and steam rises upwards.
  • the mass transfer process is assisted by intermediate bottoms in the column, which divide the liquid into heating and degasification stages,
  • the foul condensate stripper is located between evaporator effect 1 and 2 or 2 and 3. Secondary vapor coming from a preceding effect is used in the stripper as heat source.
  • the next effect has its own lamella package, where vapor from the top of the stripper, enriched with MeOH and TRS- compounds is partially condensed (inside) and black liquor is evaporated (outside) .
  • Non- condensable vapor is further condensed partially in a liquor pre-heater and the rest of the stripper gases flow through a trim-condenser.
  • the MeOH-content of the stripper off-gases is adapted to a value of approximately 30%, if the gases are still processed to liquid methanol, or to a value of approximately 30-50% if the gases are combusted in a gas phase.
  • the stripped clean condensate coming from the bottom of the stripper can be combined with clean secondary condensate.
  • the stripper off-gases can be combusted (in a dedicated burner for non-condensable gases/in a lime kiln/recovery boiler) or rectified in a MeOH-column into liquid methanol.
  • Fl-application 20106079 describes a method with which contaminants are separated from liquids, such a condensates of waste liquor, by stripping setting the condensate to direct contact with vapor by spraying or distributing it into the vapor flowing in the vapor pipe or onto the wall surfaces of the vapor pipe, thus reducing the contaminants-content of the condensate and producing cleaner liquid.
  • Contaminants are enriched in the vapor and the cleaned liquid is collected.
  • the secondary condensate is sprayed into the vapor flowing in the vapor discharge pipe of the evaporator, which vapor strips off contaminants from the condensate.
  • An object of the invention is to provide a solution which allows reducing or completely avoiding above-mentioned problems of the prior art.
  • the present invention relates to a method of intensifying the evaporation of solutions, according to which method secondary vapor is formed. from_a_solution to- be- evaporated and which is carried out in at least one evaporation device, which is provided with a secondary vapor discharge duct, and liquid, such as condensate is introduced, e.g.
  • the liquid to be fed such as condensate
  • the liquid to be fed is cooled for controlling its temperature prior to introduction into the secondary vapor flow.
  • the liquid stream to be fed is cooled in a heat transfer device.
  • the heat being released from the liquid stream can be used typically for producing hot water for the mill.
  • the liquid stream to be fed is cooled by decreasing its pressure in a flashing tank. This can be accomplished also as an additional measure in addition to the heat transfer device.
  • the liquid to be fed into secondary vapor stream may be a process water to be cleaned, containing volatile contaminants.
  • the process water may originate e.g. from a debarking plant of a chemical pulp mill or from a pulp treatment line containing cooking, bleaching and drying.
  • condensate to be fed into a secondary vapor stream is formed at the evaporation plant, where evaporation of liquid takes place or it contains condensates from another evaporation plant.
  • the evaporation takes place in a multi-effect evaporation plant, in the evaporation devices of which secondary vapor is generated, and secondary vapor is condensed to at least one condensate stream in at least one evaporation device, which condensate stream and/or condensate stream from a condenser of the evaporation plant is fed into the secondary vapor flow of at least one evaporation device.
  • the solution to be evaporated can contain volatile compounds, whereby secondary vapor is condensed in at least one evaporation jevice-to-a-first " and " a ⁇ second "" p ⁇ ial ⁇ sTrea " m of condensate, the first of which contains a larger amount of volatile compounds.
  • the second condensate streams from one or more evaporation effect and/or condensers of the evaporation plant are cooled prior to feeding them into the secondary vapor stream of one or more evaporation effect/s.
  • the liquid stream to be sprayed or fed is cooled in evaporators following the feed and operating at a lower pressure or by flashing into these.
  • This method can utilize the fact that foul process waters, such as secondary condensates of the evaporation plant can be cleaned in the plant internally with a so-called stripping- like process,
  • process waters, such as condensates are led into the evaporator effects by spraying them into the secondary vapor lines, whereby easily volatile compounds in the process waters such as condensates, such as methanol, are transferred into a gas phase and liquefied again only later when concentrated, whereby they can be recovered for further treatment, or they end up into non-condensable gases (so- called NCG) for downstream processing.
  • solutions can be made in accord- ance with the invention, which allow increasing the evaporation capacity of the evaporation plant.
  • These solutions being cost-efficient, provide savings for the mill either by increasing the solid matter in the liquor stream exiting the evaporation plant, or by recovering more heat, or by removing the bottle neck of production, if the evaporation plant has been such for the production.
  • cold or cooled liquid such as condensate
  • the aim in cooling is to cool a part of the secondary vapor stream, and thus the method allows condensing approximately 0.1 -20 %, typically 0.4-5 % of the secondary vapor stream.
  • the method has shown that even with a small condensing amount, e.g. approximately 0.01 -1 % of the secondary vapor stream, an increase in the amount of several per cents can be achieved in the evaporation efficiency of the evaporation plant, and thus actively impact the functioning of the evaporation plant.
  • Spraying is especially advantageous to be performed in the back end of the evaporation plant and/or upstream of the surface condenser, which corresponds to the end with the lowest vapor pressure.
  • the stages following the spraying can form a bottle neck for the flow of secondary vapor, e.g. due to excessive pressure loss or carry over, or for the flow of flash vapors.
  • Each ton of secondary vapor that is condensed in the vapor duct increases the capacity of the evaporation plant with respect to the evaporation effect, from which the vapor comes.
  • condensate streams from different evaporation devices are combined prior to cooling or after that,
  • large amounts of condensate or other liquid is sprayed into the secondary vapor stream , which liquid has a temperature of at least 1 °C lower than the saturated condensing temperature of secondary vapor and it is desired to heat the liquid and / or simultaneously clean it in the secondary vapor stream of the process.
  • Condensates of the evaporation process are for many reasons advantageously used as cooling liquid in the secondary vapor duct. Then the fractions in the condensates of the evaporation process are diffused into the secondary vapor (or condense from the vapor into the condensate) at the same time when the evaporation is intensified and heat is transferred under control e. g . from the back end of the evaporation process towards the front end of the evaporation. This allows reducing or eliminating the carryover of the back end of the evaporation plant and also pressure losses caused by the back end, and thus achieving evaporation with quality functioning also with overload .
  • the solution according to the invention provides clear advantages in view of the prior art.
  • the capacity is increased because, as mentioned earlier, the cold liquid sprayed into the secondary vapor stream is in direct contact with the secondary vapor stream and thus more condensing surface is activated.
  • This additional condensing surface is in analogy with adding evaporation heat surface in the evaporation plant, such as lamellas, but in addition the decrease in the secondary vapor stream in the back end of the evaporation plant decreases the pressure loss of the back end.
  • the new method allows transferring of the heat distribution and its new distribution so that the evaporation plant operates better than before. This is because the pressure losses can be directed there where they cause the least adverse effects. Simultaneously the method also eliminates superheating and thus many effects are provided acting to the same direction and all having an increasing impact on the evaporation efficiency. The method can also be used for eliminating carry over in the back end, of the risk thereof.
  • the present invention also relates to an arrangement for intensifying evaporation of a solution in an evaporation plant comprising at least one evaporation device provided with a secondary vapor discharge duct, said secondary vapor discharge duct being provided with a feed device for spraying or distributing liquid, such as condensate, into vapor flowing in the discharge duct or onto the wall surfaces of the discharge duct setting the liquid being fed into direct contact with the vapor. It is essential that the liquid feed device is connected to the device for cooling the liquid to be fed prior to introducing it into the vapor discharge duct, where vapor is condensed.
  • the evaporation plant comprises several in-series connected evaporation devices, and in the vapor flow direction the last evaporation device or devices is/are provided with a liquid feed device.
  • the secondary vapor duct is a duct that is connected to the evaporator and via which the vapor generated in the evaporator is led out,
  • the duct can be arranged so that the vapor is led into another evaporator vessel.
  • This method and arrangement allows separating various contaminants from liquids.
  • the contaminants can comprise methanol and/or TRS-compounds (total reduced sulphur compounds), which are common volatile or odorous contaminants in condensates of a chemical pulp mill.
  • Gontaminated-liquidr such as a " s “ meth “ a ro d/or TRS-enriched liquid, can be sprayed at at least one location either co-currently with respect to the vapor stream or counter-currently with respect to the vapor stream in the duct, or to any other direction with respect to the vapor stream. Often counter-current provides a better separation.
  • Cleaned condensate can be used in the mill to replace fresh water.
  • the collection point of cleaned/foul liquid (such as condensate) in vertical ducts is located after the elbow in the bottom of the vapor duct.
  • Condensate or other liquid is preferably fed along a feed pipe extending through the wall of the vapor duct into the vapor duct and being provided with at least one nozzle, via which the liquid is sprayed in form of droplets into the vapor stream. If there are several nozzles, they are distributed evenly along the width of the duct.
  • the liquid can also be sprayed from openings in the form of a nozzle, which are arranged around the circumference of the duct for feeding liquid from the inner wall of the duct.
  • the liquid can also be fed via openings in the wall of the duct, whereby the liquid is distributed evenly so that it flows as a film along the inner surface of the duct.
  • the openings are arranged along the circumference of the duct.
  • Liquid such as condensate
  • the present invention is characterized in that cold or cooled liquid, such as condensate is fed into a secondary vapor stream for cooling it, whereas in US-patent 5382321 A (Fa- gerlind, Agren 1992) the condensate is flashed into the vapor stream in order to obtain a bigger temperature difference in the stage following the spraying. It is also known to feed condensate e.g. into a vapor stream of the compressor evaporator, after the vapor pressure has been risen by means of a compressor. Then the purpose is only the removal of superheating from the vapor and not condensing of the vapor.
  • MVR/compressor evaporators it is not optimal to feed downstream of the compressor very large amounts of water or condensate colder than the saturated temperature of secondary vapor (e.g. 5°C below the saturated temperature of secondary vapor or colder), but this should be done upstream of the compressor, if the use of cold water is necessary for the process. This would then require also removal of large droplets, since otherwise the process is subjected to erosion wearing. In the present method, evaporation capacity is increased by condensing secondary vapor.
  • Segregating reboilers or the like apparatuses where secondary vapor is condensed on a flowing liquid film is in view of the phenomena and the operation comparable to the operation of a multi-effect evaporation plant or a MVR-evaporator.
  • the present method can be utilized also in this kind of apparatuses. It is advantageous to spray or feed the liquid into the secondary vapor duct going into the evaporator or reboiler so that the duct area and duct volume preceding or succeeding the spraying together form a good reaction volume. A minimum volume or duct area is obtained when the distance of the spraying taking place counter-currently with respect to secondary vapor prior to condensing, i.e.
  • upstream of the inlet to the evaporator or the reboiler is 0*D (i.e. zero times the diameter D of the secondary vapor duct).
  • Inlet refers to the infeed point for secondary vapor (inlet feed opening, at which the secondary vapor duct terminates) in the evaporation device, or con- denser or reboiler, An almost optimal result is achieved in large duct already at a distance of (4-10)*D (4 to 10 times the diameter D of the secondary vapor duct). The best segregation result and also the heating of the liquid to be sprayed is achieved when the reaction volume is increased by moving the spraying point further from said inlet.
  • Liquid to be cleaned or heated can in all cases (evaporator, reboiler etc.) also be sprayed co-currently, but then an optimal result requires a larger distance from the inlet, mostly approximately (5-20)*D (5 to 20 times the diameter).
  • the heating and condensing benefit i.e. capacity increase, is achieved already at a distance of 0*D from the inlet when the spraying is accomplished counter-currently with respect to the flow di- rection of the secondary vapor.
  • achieving the best separation level most often requires a distance that is many times larger than the diameter D.
  • Fig. 1 illustrates schematically a known multi-effect evaporation plant for black liquor
  • Fig. 2 illustrates the structure of known lamella-evaporator, in which evaporator condensate is separated into clean and foul condensate;
  • Fig. 3 illustrates schematically a duct-stripping arrangement as presented in Fl patent application 20106079;
  • Figs. 4 and 5 illustrate schematically embodiments of the present invention.
  • Fig. 3 illustrates one arrangement for carrying out the stripping-based process being uti- lized in connection with the present invention.
  • the Figure illustrates effects x and x+1 of a multi-effect evaporation plant, These effects can be e.g. effects V and VI of a black liquor evaporation plant.
  • Black liquor is evaporated in effect x so that vapor is formed, The vapor is led via duct 100 to a next effect x+1 .
  • Liquid, such as foul condensate, containing methanol and other volatile compounds is led via line 102 and sprayed by means of a nozzle or nozzles 104 into a vapor duct 100.
  • Liquid droplets end up in direct contact with vapor so that the vapor stream picks up methanol and other contaminants.
  • Cleaned liquid which is referred to as duct-stripped liquid, flows downwards along a wall of the vapor duct and it is collected preferably after an elbow 106 on the bottom of the vapor duct prior to the inlet 120 of effect x+ 1 .
  • Vapor with an increased amount of volatile contaminants, flows in duct 100 to a following evaporation effect x+ 1 , where it is condensed .
  • the heating element of effect x+ 1 is a lamella 1 10, as described in connection with Fig .
  • the condensate is segregated and clean condensate 1 14 and foul condensate 1 1 2 are formed in the lamella 1 10.
  • the foul condensate can be treated further in the stripping column plant of the mill,
  • the duct-stripped liquid, such as condensate in line 1 16 can be pumped from the vapor duct 100 directly into a process, where it is used as process water.
  • the duct-stripped liquid and clean condensate 1 14 can be combined, but this depends on the impurity-content thereof, such as methanol-contents, and the optimal use of condensates in a later process.
  • Decisive variables for a well operating duct-stripping system and also for condensing system are the mass flow (m 6 , m 3 ) of vapor and foul (or clean) condensate, pressure drop over the spray nozzle (p3-p5), characteristics of the nozzle (i .e.
  • spray geometry (hollow cone or full cone), distribution of droplet size (average diameter) , opening angle of the spray (a) , droplet velocity (w d ), temperature of the droplets and saturation temperature of the vapor ( 7 ⁇ 3, p6), velocity of the droplets and the vapor (w d , w v ), retention time in the duct ( ⁇ ), duct geometry, equilibrium of vapor and liquid (x and y), interfacial equilibrium (net mass transfer of water vapor or not, this impacts the methanol transfer) , heat and mass transfer both inside the droplet and on the walls of the duct (impact net mass transfer of water vapor), see Table 2 and Fig . 3.
  • An appropriate nozzle size and nozzle number are dependent on the process size and the volume flow of the liquid being sprayed.
  • the internal film area inside the duct can be increased by elements inside the duct.
  • the film area can be increased e.g. by means of a pipe arranged inside the steam duct.
  • the structure of the component inside the duct is simple.
  • duct-stripping system it is preferable to design the duct-stripping system so that the methanol net mass transfer is maximized by optimizing the above-listed variables to be as cost-efficient as possible, while ensuring a maximum separation, e.g . methanol separation close to 100% .
  • Fig . 4 illustrates a multi-effect evaporation plant 200 comprising six effects, of which four last in the vapor flow direction are shown.
  • This is a typical black liquor evaporation plant, but only the vapor and condensate streams are shown , not the black liquor stream.
  • the black liquor mainly flows counter-currently with respect to the vapor.
  • Evaporation effect 4 has two evaporation devices 201 and 202, which are connected parallel with respect to the vapor, while effects 5 and 6 have each one evaporation device 203 and 204, respectively.
  • the last evaporation device is followed by a surface condenser 205. Secondary vapor formed in each evaporation effect is used in the following stage as heating medium.
  • the evaporators 201 and 202 of evaporation effect 4 are typically supplied with vapor generated in evaporation effect 3 (not shown) via line 206. Secondary vapors of evaporation devices 201 and 202 are taken via line 207 into a fifth evaporation effect, from where the vapor generated therein flows via line 208 into a sixth evaporation effect. Secondary vapor of the last evaporation device 204 from line 209 is condensed in the surface con- denser 205. Also flash vapor generated in the condensate flashing tanks is combined to the secondary vapor stream .
  • the heat surface of the evaporation devices in Figure 4 is formed of lamellas, which are provided with an internal intermediate wall 21 1 for dividing the condensate stream into at least two parts, foul condensate and cleaner condensate.
  • Foul condensates are discharged from the evaporation devices via lines 212.
  • Clean condensates are transferred via lines 21 3 and 214.
  • Foul condensates of evaporation devices 201 and 202 and 203 are flashed in tanks 21 5 and 216, from where they are taken into line 21 7 together with foul condensates of effect 6 and the surface condenser 205, and further e.g. as known per se to the stripping column of the mill. Clean condensates also contain contaminants, and often they are to be cleaned, depending on the further use, as described below.
  • Condensate from the front end (not shown) of the evaporation plant is fed into flashing tank 21 8 and the vapor generated from the condensate is taken via line 219 into the fourth evaporation effect, and the flashed condensate is taken via line 220 together with clean condensates 21 3 of effect 4 to further treatment.
  • the clean condensate of effect 5 is flashed in tank 221 and taken together with the clean condensates of effect 6 and the surface condenser via line 223 back into tank 222, wherein also other condensates and pro- cess waters of the mill, e.g. from the digester plant, are introduced.
  • the last-mentioned tank 222 acts as a feed tank, from where condensate is pumped by means of pump 225 via line 224 into the secondary vapor ducts of the evaporation devices in the back end of the evaporation plant, the condensate being e .g. sprayed into the vapor flowing in the ducts.
  • the condensate stream Prior to spraying, the condensate stream is cooled in a heat exchanger 226 by means of indirect heat transfer with a cooling medium, which typically is liquid required in processes, such as water.
  • the cooling medium flows in line 227.
  • the condensate stream is cooled " colder tharfthe condensing temperature of the secondary vapor is prior to spraying or feeding of the condensate into the secondary vapor stream in question .
  • the condensate is already colder than the condensing temperature of the secondary vapor prior to spraying or feeding into said secondary vapor stream , so that it does not need separate cooling ,
  • the heat exchanger 226 typically produces hot water, while the condensate stream is cooled.
  • the cooled condensate is transferred via line 228 and spraying with a nozzle or nozzles 229 into vapor ducts 207, 208 and 209.
  • the condensate droplets end up in direct contact with vapor so that the vapor stream catches contaminants.
  • the cleaned condensate referred to as duct-stripped condensate, flows downwards along the wall of the vapor duct and it is collected preferably via the bottom of the vapor duct, after the elbow on the bottom , into line 230.
  • the cleaned condensate can further be flashed, such the con- densate that is stripped in the vapor duct of effect 4, in flashing tank 231 .
  • Vapors having an increased amount of volatile contaminants flow into the next evaporation effect 5 or 6 or into the surface condenser, where they are condensed.
  • the duct-stripped condensate is led via line 230 to further treatment as process water, e.g. to pulp washers of a chemical pulp mill.
  • the cooling liquid amount can be approximately 0.2 - 10 -fold, typically 0.4 - 3-fold with respect to the secondary vapor stream.
  • an aim is to actively condense a part of the secondary vapor stream, and thus with the method it is possible to typically condense approximately 0.1 - 20%, typically 0.4 - 5% of the secondary vapor stream.
  • the method has shown that even with a small condensing amount, e.g. approximately 0.1 - 1 & of the secondary vapor stream, the evaporation efficiency of the evaporation plant can be increased by several per cents and thus it is possible to actively influence the functioning of the evaporation plant.
  • Fig. 5 illustrates a second embodiment of the present invention.
  • the arrangement is oth- erwise similar to that of Fig. 4, but instead of an indirect heat exchanger the condensate stream or other liquid stream is cooled by flashing in tank 240.
  • the flashed and cooled condensate stream in line 228' is led for spraying into secondary vapor ducts 207', 208' and 209' in the same way as in Fig. 4.
  • the flashing vapor formed from the condensate in the flashing tank 240 is taken via line 241 into a heat exchanger 242, where the flashing vapor releases its heat into the medium to be heated, such as cold water in duct 243.
  • the condensate stream can, instead of a separate flashing tank, be cooled also by flash- ing in an evaporation device that is located downstream of condensate spraying and operates at a lower pressure than the evaporation device, into the secondary vapor from which the condensate is fed.
  • the condensate to be fed into the secondary vapor duct 207 can be flashed into evaporation device 203 or 204 for cooling the condensate.
  • the condensate stream to be fed into different secondary vapor ducts is formed by combining condensates or other liquids from various sources and cooling the combined stream.
  • the condensate to be fed into each vapor duct can also be cooled separately, depending on the need for cooling. It is also possible that the condensates are cooled separately and mixed after that. Possibly some condensate does not require cooling.
  • Hot cleaned condensate replaces the raw water of the mill ⁇ thereby minimum heating expenses are obtained when the cold condensate to be cleaned is sprayed at the back end of the evaporation plant:
  • Some mills can have production limitations, whereby effluents limit the production. If such is the case, removing the bottle neck of the mill provides additional income due to in- creased pulp production. The benefit is then 0-1 5 euro/adt. Increased evaporation capacity provides benefit 1 -25 euro/adt, this being dependent on the final capacity improvement.
  • the overall total benefit is approximately 2-30 euro/adt.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)

Abstract

La présente invention concerne un procédé et un agencement pour l'intensification d'évaporation, permettant la formation d'une vapeur secondaire à partir d'une solution en cours d'évaporation. L'évaporation est réalisée dans au moins un appareil évaporateur équipé d'un conduit de sortie pour la vapeur secondaire. Du liquide, tel qu'un condensat, est alimenté, par exemple par pulvérisation, dans le flux de vapeur secondaire dans le conduit de sortie de l'appareil évaporateur. Au moins une partie de la vapeur secondaire est condensée de sorte que la température du liquide alimenté soit inférieure à la température de condensation de la vapeur secondaire avant l'alimentation du liquide dans ledit flux de vapeur secondaire.
PCT/FI2013/000021 2012-04-17 2013-04-17 Procédé et agencement pour l'intensification et le contrôle d'évaporation WO2013156668A1 (fr)

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FI20125419 2012-04-17

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Publication number Priority date Publication date Assignee Title
CN103816687A (zh) * 2014-03-18 2014-05-28 天津市恒脉机电科技有限公司 一种造纸黑液蒸发用自汽提式板式蒸发装置
CN112221179A (zh) * 2020-09-26 2021-01-15 安徽金禾实业股份有限公司 一种安赛蜜生产中二次浓缩釜的喷淋方法
CN115959732A (zh) * 2022-02-25 2023-04-14 光大环境修复(江苏)有限公司 一种吹蒸装置及吹蒸方法和吹蒸装置的冲洗方法

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US3232029A (en) * 1960-10-14 1966-02-01 Celanese Corp Recovery of organic solvents from gaseous media
GB2019233A (en) * 1978-02-08 1979-10-31 Addikiss Ltd Improvements in or relating to the condensation of steam
DE3149847A1 (de) * 1981-12-16 1983-07-21 Linde Ag, 6200 Wiesbaden "verfahren zur entfernung von kohlenwasserstoffen und anderen verunreinigungen aus einem gas"
DE4223392A1 (de) * 1992-07-16 1994-01-20 Dietrich Fette Vorrichtung zur Kondensation von Wasserdampfanteilen in einem Brüden-Luft-Gemisch, insb. bei der Zuckerfabrikation
US5382321A (en) 1991-04-15 1995-01-17 A. Ahlstrom Corporation Process for the concentration of spent liquors
US20090192285A1 (en) * 2004-02-27 2009-07-30 Fritz Wilhelm Method and device for the production of polyesters and copolyesters
FI20106079A (fi) 2010-10-18 2012-04-19 Andritz Oy Menetelmä epäpuhtauksien erottamiseksi nesteistä tai höyryistä

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3232029A (en) * 1960-10-14 1966-02-01 Celanese Corp Recovery of organic solvents from gaseous media
GB2019233A (en) * 1978-02-08 1979-10-31 Addikiss Ltd Improvements in or relating to the condensation of steam
DE3149847A1 (de) * 1981-12-16 1983-07-21 Linde Ag, 6200 Wiesbaden "verfahren zur entfernung von kohlenwasserstoffen und anderen verunreinigungen aus einem gas"
US5382321A (en) 1991-04-15 1995-01-17 A. Ahlstrom Corporation Process for the concentration of spent liquors
DE4223392A1 (de) * 1992-07-16 1994-01-20 Dietrich Fette Vorrichtung zur Kondensation von Wasserdampfanteilen in einem Brüden-Luft-Gemisch, insb. bei der Zuckerfabrikation
US20090192285A1 (en) * 2004-02-27 2009-07-30 Fritz Wilhelm Method and device for the production of polyesters and copolyesters
FI20106079A (fi) 2010-10-18 2012-04-19 Andritz Oy Menetelmä epäpuhtauksien erottamiseksi nesteistä tai höyryistä

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103816687A (zh) * 2014-03-18 2014-05-28 天津市恒脉机电科技有限公司 一种造纸黑液蒸发用自汽提式板式蒸发装置
CN112221179A (zh) * 2020-09-26 2021-01-15 安徽金禾实业股份有限公司 一种安赛蜜生产中二次浓缩釜的喷淋方法
CN115959732A (zh) * 2022-02-25 2023-04-14 光大环境修复(江苏)有限公司 一种吹蒸装置及吹蒸方法和吹蒸装置的冲洗方法

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