WO2021089924A1 - Drying method and device for sludge - Google Patents

Drying method and device for sludge Download PDF

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Publication number
WO2021089924A1
WO2021089924A1 PCT/FI2020/050736 FI2020050736W WO2021089924A1 WO 2021089924 A1 WO2021089924 A1 WO 2021089924A1 FI 2020050736 W FI2020050736 W FI 2020050736W WO 2021089924 A1 WO2021089924 A1 WO 2021089924A1
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WO
WIPO (PCT)
Prior art keywords
sludge
ultrasound
drying
unit
dried
Prior art date
Application number
PCT/FI2020/050736
Other languages
French (fr)
Inventor
Timo RAHIKAINEN
Juha KUUTTI
Harry PIIRAINEN
Original Assignee
Eco Wws Oy
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Filing date
Publication date
Application filed by Eco Wws Oy filed Critical Eco Wws Oy
Priority to EP20884881.2A priority Critical patent/EP4054985A4/en
Publication of WO2021089924A1 publication Critical patent/WO2021089924A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F9/00—Multistage treatment of water, waste water or sewage
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/42—Electrodialysis; Electro-osmosis ; Electro-ultrafiltration; Membrane capacitive deionization
    • B01D61/56—Electro-osmotic dewatering
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F11/00—Treatment of sludge; Devices therefor
    • C02F11/006—Electrochemical treatment, e.g. electro-oxidation or electro-osmosis
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F11/00—Treatment of sludge; Devices therefor
    • C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
    • C02F11/121—Treatment of sludge; Devices therefor by de-watering, drying or thickening by mechanical de-watering
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F11/00—Treatment of sludge; Devices therefor
    • C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
    • C02F11/13—Treatment of sludge; Devices therefor by de-watering, drying or thickening by heating
    • C02F11/131—Treatment of sludge; Devices therefor by de-watering, drying or thickening by heating using electromagnetic or ultrasonic waves
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F11/00—Treatment of sludge; Devices therefor
    • C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
    • C02F11/14—Treatment of sludge; Devices therefor by de-watering, drying or thickening with addition of chemical agents
    • C02F11/143—Treatment of sludge; Devices therefor by de-watering, drying or thickening with addition of chemical agents using inorganic substances
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F11/00—Treatment of sludge; Devices therefor
    • C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
    • C02F11/14—Treatment of sludge; Devices therefor by de-watering, drying or thickening with addition of chemical agents
    • C02F11/147—Treatment of sludge; Devices therefor by de-watering, drying or thickening with addition of chemical agents using organic substances
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F11/00—Treatment of sludge; Devices therefor
    • C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
    • C02F11/15—Treatment of sludge; Devices therefor by de-watering, drying or thickening by treatment with electric, magnetic or electromagnetic fields; by treatment with ultrasonic waves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B1/00—Preliminary treatment of solid materials or objects to facilitate drying, e.g. mixing or backmixing the materials to be dried with predominantly dry solids
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B3/00—Drying solid materials or objects by processes involving the application of heat
    • F26B3/32—Drying solid materials or objects by processes involving the application of heat by development of heat within the materials or objects to be dried, e.g. by fermentation or other microbiological action
    • F26B3/34—Drying solid materials or objects by processes involving the application of heat by development of heat within the materials or objects to be dried, e.g. by fermentation or other microbiological action by using electrical effects
    • F26B3/347—Electromagnetic heating, e.g. induction heating or heating using microwave energy
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B5/00—Drying solid materials or objects by processes not involving the application of heat
    • F26B5/02—Drying solid materials or objects by processes not involving the application of heat by using ultrasonic vibrations
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B5/00—Drying solid materials or objects by processes not involving the application of heat
    • F26B5/14—Drying solid materials or objects by processes not involving the application of heat by applying pressure, e.g. wringing; by brushing; by wiping
    • 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
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3563—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing solids; Preparation of samples therefor
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F11/00—Treatment of sludge; Devices therefor
    • C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
    • C02F11/121—Treatment of sludge; Devices therefor by de-watering, drying or thickening by mechanical de-watering
    • C02F11/123—Treatment of sludge; Devices therefor by de-watering, drying or thickening by mechanical de-watering using belt or band filters
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B2200/00—Drying processes and machines for solid materials characterised by the specific requirements of the drying good
    • F26B2200/02—Biomass, e.g. waste vegetative matter, straw
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B2200/00—Drying processes and machines for solid materials characterised by the specific requirements of the drying good
    • F26B2200/18—Sludges, e.g. sewage, waste, industrial processes, cooling towers

Definitions

  • the application relates generally to a sludge drying method and a device used therein.
  • Sludges are wet fiber-rich fractions that can be divided into fiber sludge and biosludge made up mostly of wastewater-purifying bacterial mass.
  • the amount of biosludge is significant and its proportional share of all sludges has been in steady increase over the past decades.
  • the pasty and sticky biosludge consists of a bacterial cell structure with a high content of intracellular water. Filamentous bacteria hamper dewatering, so the drying of biosludge necessary for incineration is achieved very poorly with the available dryer types. As a result of poorly achieved dewatering, the heating value of dried biosludge remains low.
  • One objective of the invention is to solve some of the prior art problems, to in crease the heating value of biosludge, and to achieve cost savings in the final disposal of biosludge by increasing its dry content by means of a novel bi osludge treatment method and device.
  • the novel method and de vice enable enhancement of the energy efficiency of biosludge drying and pro duction of dried sludge with a very high level of hygiene.
  • the sludge drying method comprises using an electric dryer (electrically assisted dryer) for separating, by means of an elec tric field, water contained in the sludge from its solid material and compressing (squeezing) water mechanically out of the sludge in the electric dryer.
  • the method further comprises pre-treating the to-be-dried sludge with ultrasound for at least weakening the cell structure of the sludge, thereby enabling the in ternal water stored in sludge cells to be removed in the electric dryer.
  • One embodiment relates to a sludge drying device, which is adapted to imple ment the method according to the foregoing embodiment.
  • the device compris es an electric dryer, wherein water contained in the sludge is separated by means of an electric field from its solid material and water is mechanically compressed (squeezed) out of the sludge.
  • the device further comprises a pre treatment unit, wherein the to-be-dried sludge is pre-treated with ultrasound for at least weakening the sludge’s cell structure, thereby enabling the internal wa ter stored in sludge cells to be removed in the electric dryer.
  • Fig. 1 shows a sludge drying method 100 in the form of a flowchart.
  • the sludge to be dried (sludge mass) consists e.g. of primary sludge or biosludge (biomass) generated as processing residue and made up of bacteria.
  • step 110 the sludge intended for drying is delivered into a drying device (machine, dryer) 240 used in drying, in which the sludge proceeds either di rectly or by means of the device’s 240 transfer mechanism (transfer element, transfer means) 244, intended for the transfer of material, into its pretreatment unit 246.
  • a drying device machine, dryer
  • transfer mechanism transfer element, transfer means
  • the sludge present in the pretreatment unit 246 of the device 240 is subjected to physical conditioning (pretreatment) for at least weakening its cell structure.
  • the pretreatment is conducted by subjecting the sludge to fo cused ultrasound generated by an ultrasound transmitter unit (ultrasound transmitter, sender) 247 installed in the pretreatment unit 246.
  • the US trans mitter unit 247 is capable of subjecting the sludge to high intensity focused ul trasound with a frequency of e.g. 20-40 kHz, e.g. 20, 25, 30, 35, or 40 kHz.
  • the pretreatment it is possible, when necessary, to optimize (adjust) the intensity of the applied ultrasound by using the device’s 240 control unit (con- trailer) 242 for controlling operation of the US transmitter unit 247 for a capabil ity of suppressing the formation of fines generated in the pretreatment.
  • the ultrasound partially disrupts and/or partially weakens the cell structure (cell membranes) of bacteria present in the sludge mass.
  • the ultrasound chops up the bacterial structures, which are included in the sludge and which are structures most sensitive to US treatment. It is by virtue of weakening and disrupting the intra-sludge bacterial structures that a removal after the pre treatment of the internal water stored in sludge cells is possible more effective ly than before in an electric dryer (electrically assisted dryer) 250 of the device 240.
  • step 114 the ultrasound-pretreated sludge is conveyed by means of the transfer mechanism 244 from the pretreatment unit (pretreater) 246 into a chemical sludge conditioning tank (sludge conditioner) 248 of the device 240.
  • pretreatment unit pretreater
  • sludge conditioner chemical sludge conditioning tank
  • step 116 the pretreated sludge, containing disrupted and weakened bacte rial structures, is subjected in the conditioning tank 248 to chemical condition ing before electrical and mechanical treatment for providing the sludge with sludge floes and free water.
  • the sludge floes are produced from chopped-up structures of bacteria with a flocking chemical containing at least one of the fol lowing ingredients: organic polyelectrolyte, inorganic aluminum salt, and inor ganic iron salt.
  • the sludge treatment of steps 112 and 116 is a combination of the ultrasound- effected physical and flocking chemicals-effected chemical sludge condition ing.
  • step 118 the chemically treated sludge, containing sludge floes and free water, is conveyed by means of the transfer mechanism 244 from the condi tioning tank 248 to the electric drying element (dryer, electric dryer unit) 250 of the device 240 for electrically assisted drying (electro-drying).
  • the electric drying element dryer, electric dryer unit
  • the transfer mechanism 244 used in step 118 may include a transfer belt dryer section (dryer), wherein the chemically treated sludge is carried on an inclined or horizontally placed wire section (wire) and at the same the sludge can be re lieved of easily removable water before reaching the electric dryer 250.
  • the transfer belt dryer section includes lower and upper lip elements (bottom and top lips) intended for holding the sludge on the wire, as well as a roll section provided with multiple rolls and intended for squeezing the sludge.
  • Gravitation al dewatering in the transfer belt dryer section can be enhanced with an in clined wire designed to convey the sludge “uphill”, thereby discharging water from the sludge by gravity more effectively than with a wire placed in a horizon tal plane prior to a press-treatment in which more water is removed from the sludge by squeezing between the rolls.
  • step 120 the chemically treated sludge is exposed to the effect of an elec tric drying field generated in the electric dryer 250 for an ability to separate from the flocculated sludge at least the free water contained therein from solid material present in the sludge, and at least the free water is compressed (squeezed) in the electric dryer 250 mechanically out of the sludge.
  • ultrasonic technology enables the cell membranes of sludge to be disrupted e.g. with forces based on cavitation.
  • the sludge is chopped up and the amount of fines con tained in the sludge increases, the sludge becoming thicker.
  • the mechanical or thermal drying of thick sludge with appropriate equipment becomes less ef fective since the thick sludge is poorly permeable to air and water as a result of increasing flow resistance caused by the fines.
  • the use of ultrasound as a pretreatment for electric drying enables utilization of the strengths of each technique as the cell membranes are disrupted, or at least significantly weakened, by ultrasound, enabling the dewatering in the electric dryer’s electric field to be conducted cost-effectively.
  • the deficiencies of ultrasound treatment do not have an undermin ing effect on the success of electric drying because the increase of fines gen erated therein, and the thickening of sludge as a result thereof, disturb the electric drying only slightly as water flow is enabled by the electric field even through small pores.
  • step 120 is followed by conveying in step 126 the electro- and press- treated, i.e. electro-dried, sludge by means of the transfer mechanism 244 out of the device 240 for further use or for storage to wait for further use.
  • step 126 the electro- and press- treated, i.e. electro-dried, sludge by means of the transfer mechanism 244 out of the device 240 for further use or for storage to wait for further use.
  • step 120 is followed by conveying in step 122 the electro-dried sludge by means of the transfer mechanism 244 to the after-treatment unit 252.
  • the electro-dried sludge present in the after-treatment unit 252 is after-treated (after-dried) in order to further enhance the dewatering of sludge for improved drying result.
  • the after-treatment is conducted by subjecting the sludge to focused microwave radiation generated by a microwave transmitter element (microwave transmitter, sender) 253 installed in the after-treatment unit 252.
  • the MW transmitter element 253 is able to expose the sludge to fo cused microwave radiation with a frequency of 300-3000 MHz, e.g. 300, 500, 800, 1000, 2000, or 3000 MHz.
  • the microwave treatment enables increasing the final amount of dry matter and improving management of the drying result by resulting in dried sludge of more consistent quality.
  • step 124 The after-treatment of step 124, exactly the same way as described in the case of electro-dried sludge in 120, is followed by conveying in step 126 the micro- wave-treated, i.e. after-treated, sludge by means of the transfer mechanism 244 out of the device 240 for further use or storage.
  • the device 240 includes a thermal camera unit (thermal camera) 254 comprising at least one thermal camera, then it is possible during the method 100 to monitor the progress of drying and its success by using the thermal camera unit 254 for online measuring. It is possible to perform the monitoring in at least one of the following units of the device 240: pretreatment unit 246, conditioning tank 248, electric dryer 250, and after-treatment unit 252.
  • the adjustment of drying capacity has an important role in terms of energy ef ficiency. It is possible to make use of thermal imaging technology not only for determining the need of and properly focusing the adjustment of drying capaci ty but also for avoiding inadvertent local overheating occurrences of the device 240.
  • sludges e.g. biosludges
  • the drying treatment of sludges must be gentle, but filamen tous bacteria must nevertheless be chopped up and access to intracellular wa ter must be provided without energy consumption rising to an unsustainable level. Therefore, the ultrasound-effected pretreatment is quite suitable for this purpose.
  • Microwave drying on the other hand, being an energy-efficient drying method, is excellently suitable for after-drying.
  • Fig. 2 shows a principle view of a device 240 intended for implementing the method 100 presented in connection with the previous figure and used in the drying of sludge.
  • the device 240 comprises a power supply unit (power supply) 241, by means of which the device 240 obtains its required operating current.
  • a power supply unit power supply
  • the device 240 further comprises a control unit 242, by means of which the device 240 controls its own operation, i.e. the operation of its units 241, 244, 246, 247, 248, 250, 252, 253, 254, in such a manner that the device 240 func tions as described in connection with the previous figure.
  • a control unit 242 by means of which the device 240 controls its own operation, i.e. the operation of its units 241, 244, 246, 247, 248, 250, 252, 253, 254, in such a manner that the device 240 func tions as described in connection with the previous figure.
  • the control unit 242 comprises a processor component 256, which is used for executing control commands defined by application programs and by a user of the device 240, as well as for processing information.
  • the processor compo nent 256 comprises at least one processor, e.g. one, two, three or more pro cessors.
  • the control unit 242 further comprises a data transfer component 258, by means of which the device 240 transmits control commands and information to other units 241 , 244, 246, 247, 248, 250, 252, 253, 254 of the device 240 and receives information transmitted thereby.
  • the control unit 242 further possibly comprises a physical user interface com ponent 260, by means of which the user is able to supply the device 240, es pecially its units 241 , 244, 246, 247, 248, 250, 252, 253, 254, with control commands and information needed thereby, as well as to receive from the de vice 240 information, instructions, and control command requests presented thereby.
  • the user interface component 260 comprises at least one of the fol lowing elements: physical function keys, keyboard, display, and touchscreen.
  • the control unit 242 further comprises a memory component 262, having stored therein application programs controlling the operation of and being run by the device 240, as well as data used in the operation.
  • the memory compo nent 262 comprises at least one memory, e.g. one, two, three or more memo ries.
  • the memory component 262 comprises a data transfer application 264 control ling the operation of the data transfer component 258, a user interface applica tion 266 controlling the operation of the physical user interface component 260 - when such is included in the control unit 242, a power supply application 268 controlling the operation of the power supply unit 241 , and an application 270 controlling the operation of the device’s 240 units 241 , 244, 246, 247, 248, 250, 252, 253, 254.
  • the application 270 comprises a computer program code (instructions), whereby the device 240 is directed to function as presented in connection with the previous figure as the application 270 is executed with the processor com ponent 256 assisted by the memory component 262 in the device 240.
  • the device 240 further comprises, as already pointed out in connection with the previous figure, a transfer mechanism 244, which is intended for conveying the material (sludge) to be transferred in the device 240 and which possibly in- eludes a transfer belt dryer element described in connection with the previous figure, as well as a pretreatment unit 246 and a US transmitter unit 247 in as sociation therewith for pretreating the to-be-dried sludge with ultrasound for at least weakening its cell structure for an ability to remove in the electric dryer 250 the internal water stored in sludge cells.
  • a transfer mechanism 244 which is intended for conveying the material (sludge) to be transferred in the device 240 and which possibly in- eludes a transfer belt dryer element described in connection with the previous figure, as well as a pretreatment unit 246 and a US transmitter unit 247 in as sociation therewith for pretreating the to-be-dried sludge with ultrasound for at least weakening its cell structure for an ability to remove in the electric dryer 250 the
  • the device 240 further comprises, as already pointed out in connection with the previous figure, a conditioning tank 248 intended for the chemical condi tioning of sludge, and an electric dryer 250 intended for the electric drying of sludge, for separating the water present in the sludge from its solid material by means of an electric field and for squeezing the same mechanically out of the sludge.
  • a conditioning tank 248 intended for the chemical condi tioning of sludge
  • an electric dryer 250 intended for the electric drying of sludge, for separating the water present in the sludge from its solid material by means of an electric field and for squeezing the same mechanically out of the sludge.
  • the device 240 possibly further comprises, as already pointed out in connec tion with the previous figure, an after-treatment unit 252 intended for the MW or UV treatment of sludge and, in association therewith, an MW transmitter unit 253 or a UV transmitter unit.
  • the device 240 possibly further comprises, as already pointed out in connec tion with the previous figure, a thermal camera unit 254 intended for online monitoring the sludge drying process for its progress and success.

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Abstract

The application relates to a sludge drying method (100) according to one embodiment. The method comprises treating (116) sludge chemically in a chemical conditioning tank (248) for producing sludge floes in the sludge, separating (120), in an electric dryer by means of an electric field, water present in the sludge from its solid material, and compressing (120), in the electric dryer, water mechanically out of the sludge. The method further comprises pretreating (112) the to-be-dried sludge with ultrasound for at least weakening the cell structure of the sludge, thereby enabling the internal water stored in sludge cells to be removed in the electric dryer.

Description

DRYING METHOD AND DEVICE FOR SLUDGE
Technical field
The application relates generally to a sludge drying method and a device used therein. Background
The energy production in Finland involves annually the incineration of 400.000 tons of various sludges generated e.g. in forest industry during the treatment of wastewaters. Sludges are wet fiber-rich fractions that can be divided into fiber sludge and biosludge made up mostly of wastewater-purifying bacterial mass. The amount of biosludge is significant and its proportional share of all sludges has been in steady increase over the past decades.
The pasty and sticky biosludge consists of a bacterial cell structure with a high content of intracellular water. Filamentous bacteria hamper dewatering, so the drying of biosludge necessary for incineration is achieved very poorly with the available dryer types. As a result of poorly achieved dewatering, the heating value of dried biosludge remains low.
Summary
One objective of the invention is to solve some of the prior art problems, to in crease the heating value of biosludge, and to achieve cost savings in the final disposal of biosludge by increasing its dry content by means of a novel bi osludge treatment method and device. In addition, the novel method and de vice enable enhancement of the energy efficiency of biosludge drying and pro duction of dried sludge with a very high level of hygiene.
One objective of the invention is attained with a drying method and a device according to the independent claims and embodiments of the invention are presented in said independent claims.
The sludge drying method according to one embodiment comprises using an electric dryer (electrically assisted dryer) for separating, by means of an elec tric field, water contained in the sludge from its solid material and compressing (squeezing) water mechanically out of the sludge in the electric dryer. The method further comprises pre-treating the to-be-dried sludge with ultrasound for at least weakening the cell structure of the sludge, thereby enabling the in ternal water stored in sludge cells to be removed in the electric dryer.
One embodiment relates to a sludge drying device, which is adapted to imple ment the method according to the foregoing embodiment. The device compris es an electric dryer, wherein water contained in the sludge is separated by means of an electric field from its solid material and water is mechanically compressed (squeezed) out of the sludge. The device further comprises a pre treatment unit, wherein the to-be-dried sludge is pre-treated with ultrasound for at least weakening the sludge’s cell structure, thereby enabling the internal wa ter stored in sludge cells to be removed in the electric dryer.
Other embodiments of the invention are presented in the dependent claims.
Exemplary embodiments of the invention are described in more detail by means of the accompanying figures.
Detailed description of the figures
Fig. 1 shows a sludge drying method 100 in the form of a flowchart. The sludge to be dried (sludge mass) consists e.g. of primary sludge or biosludge (biomass) generated as processing residue and made up of bacteria.
In step 110, the sludge intended for drying is delivered into a drying device (machine, dryer) 240 used in drying, in which the sludge proceeds either di rectly or by means of the device’s 240 transfer mechanism (transfer element, transfer means) 244, intended for the transfer of material, into its pretreatment unit 246.
In step 112, the sludge present in the pretreatment unit 246 of the device 240 is subjected to physical conditioning (pretreatment) for at least weakening its cell structure. The pretreatment is conducted by subjecting the sludge to fo cused ultrasound generated by an ultrasound transmitter unit (ultrasound transmitter, sender) 247 installed in the pretreatment unit 246. The US trans mitter unit 247 is capable of subjecting the sludge to high intensity focused ul trasound with a frequency of e.g. 20-40 kHz, e.g. 20, 25, 30, 35, or 40 kHz.
During the pretreatment it is possible, when necessary, to optimize (adjust) the intensity of the applied ultrasound by using the device’s 240 control unit (con- trailer) 242 for controlling operation of the US transmitter unit 247 for a capabil ity of suppressing the formation of fines generated in the pretreatment.
The ultrasound partially disrupts and/or partially weakens the cell structure (cell membranes) of bacteria present in the sludge mass. In addition, the ultrasound chops up the bacterial structures, which are included in the sludge and which are structures most sensitive to US treatment. It is by virtue of weakening and disrupting the intra-sludge bacterial structures that a removal after the pre treatment of the internal water stored in sludge cells is possible more effective ly than before in an electric dryer (electrically assisted dryer) 250 of the device 240.
In step 114, the ultrasound-pretreated sludge is conveyed by means of the transfer mechanism 244 from the pretreatment unit (pretreater) 246 into a chemical sludge conditioning tank (sludge conditioner) 248 of the device 240.
In step 116, the pretreated sludge, containing disrupted and weakened bacte rial structures, is subjected in the conditioning tank 248 to chemical condition ing before electrical and mechanical treatment for providing the sludge with sludge floes and free water. The sludge floes are produced from chopped-up structures of bacteria with a flocking chemical containing at least one of the fol lowing ingredients: organic polyelectrolyte, inorganic aluminum salt, and inor ganic iron salt.
The sludge treatment of steps 112 and 116 is a combination of the ultrasound- effected physical and flocking chemicals-effected chemical sludge condition ing.
In step 118, the chemically treated sludge, containing sludge floes and free water, is conveyed by means of the transfer mechanism 244 from the condi tioning tank 248 to the electric drying element (dryer, electric dryer unit) 250 of the device 240 for electrically assisted drying (electro-drying).
The transfer mechanism 244 used in step 118 may include a transfer belt dryer section (dryer), wherein the chemically treated sludge is carried on an inclined or horizontally placed wire section (wire) and at the same the sludge can be re lieved of easily removable water before reaching the electric dryer 250. The transfer belt dryer section includes lower and upper lip elements (bottom and top lips) intended for holding the sludge on the wire, as well as a roll section provided with multiple rolls and intended for squeezing the sludge. Gravitation al dewatering in the transfer belt dryer section can be enhanced with an in clined wire designed to convey the sludge “uphill”, thereby discharging water from the sludge by gravity more effectively than with a wire placed in a horizon tal plane prior to a press-treatment in which more water is removed from the sludge by squeezing between the rolls.
In step 120, the chemically treated sludge is exposed to the effect of an elec tric drying field generated in the electric dryer 250 for an ability to separate from the flocculated sludge at least the free water contained therein from solid material present in the sludge, and at least the free water is compressed (squeezed) in the electric dryer 250 mechanically out of the sludge.
It is in the electric drying field that the water contained in flocculated sludge is removed in response to electro-osmosis and electrophresis as dewatering is not hampered by filamentous bacteria chopped up by ultrasound and agglom erated into floes. It is in the electric drying field that the sludge is relieved not only of free water but also of capillary water, absorbed water, and intracellular water which has been released from the cells during the ultrasound treatment of step 112.
The prior known dewatering solutions, based on electro-osmosis and -phresis and carried out in electric field, become energy inefficient at the latest when the to-be-dried sludge is left with the intracellular water. At this point, the ener gy consumption of prior known electric dryers rises drastically and the drying capacity falls substantially in case the intracellular water is sought to be pumped through the cell membrane or the structure of the cell membrane is sought to be disrupted by significantly increasing the strength of the electric field.
On the other hand, ultrasonic technology enables the cell membranes of sludge to be disrupted e.g. with forces based on cavitation. Upon the disrup tion of cell membranes, the sludge is chopped up and the amount of fines con tained in the sludge increases, the sludge becoming thicker. The mechanical or thermal drying of thick sludge with appropriate equipment becomes less ef fective since the thick sludge is poorly permeable to air and water as a result of increasing flow resistance caused by the fines. The use of ultrasound as a pretreatment for electric drying enables utilization of the strengths of each technique as the cell membranes are disrupted, or at least significantly weakened, by ultrasound, enabling the dewatering in the electric dryer’s electric field to be conducted cost-effectively.
In addition, the deficiencies of ultrasound treatment do not have an undermin ing effect on the success of electric drying because the increase of fines gen erated therein, and the thickening of sludge as a result thereof, disturb the electric drying only slightly as water flow is enabled by the electric field even through small pores.
In case the device 240 does not include an after-treatment unit (-treater) 252, then step 120 is followed by conveying in step 126 the electro- and press- treated, i.e. electro-dried, sludge by means of the transfer mechanism 244 out of the device 240 for further use or for storage to wait for further use.
In case the device 240 includes an after-treatment unit 252, then step 120 is followed by conveying in step 122 the electro-dried sludge by means of the transfer mechanism 244 to the after-treatment unit 252.
In step 124, the electro-dried sludge present in the after-treatment unit 252 is after-treated (after-dried) in order to further enhance the dewatering of sludge for improved drying result. The after-treatment is conducted by subjecting the sludge to focused microwave radiation generated by a microwave transmitter element (microwave transmitter, sender) 253 installed in the after-treatment unit 252. The MW transmitter element 253 is able to expose the sludge to fo cused microwave radiation with a frequency of 300-3000 MHz, e.g. 300, 500, 800, 1000, 2000, or 3000 MHz.
The microwave treatment enables increasing the final amount of dry matter and improving management of the drying result by resulting in dried sludge of more consistent quality.
The after-treatment of step 124, exactly the same way as described in the case of electro-dried sludge in 120, is followed by conveying in step 126 the micro- wave-treated, i.e. after-treated, sludge by means of the transfer mechanism 244 out of the device 240 for further use or storage. In case the device 240 includes a thermal camera unit (thermal camera) 254 comprising at least one thermal camera, then it is possible during the method 100 to monitor the progress of drying and its success by using the thermal camera unit 254 for online measuring. It is possible to perform the monitoring in at least one of the following units of the device 240: pretreatment unit 246, conditioning tank 248, electric dryer 250, and after-treatment unit 252.
The adjustment of drying capacity has an important role in terms of energy ef ficiency. It is possible to make use of thermal imaging technology not only for determining the need of and properly focusing the adjustment of drying capaci ty but also for avoiding inadvertent local overheating occurrences of the device 240.
The drying treatment of sludges, e.g. biosludges, must be gentle, but filamen tous bacteria must nevertheless be chopped up and access to intracellular wa ter must be provided without energy consumption rising to an unsustainable level. Therefore, the ultrasound-effected pretreatment is quite suitable for this purpose. Microwave drying, on the other hand, being an energy-efficient drying method, is excellently suitable for after-drying.
It is by virtue of the method 100 and the device 240 that the heating value of dried sludge becomes higher than before, the carbon dioxide emissions gen erated by its incineration are reduced, and the increased dry content of sludge provides new utilization and recycling possibilities for nutrients.
Fig. 2 shows a principle view of a device 240 intended for implementing the method 100 presented in connection with the previous figure and used in the drying of sludge.
The device 240 comprises a power supply unit (power supply) 241, by means of which the device 240 obtains its required operating current.
The device 240 further comprises a control unit 242, by means of which the device 240 controls its own operation, i.e. the operation of its units 241, 244, 246, 247, 248, 250, 252, 253, 254, in such a manner that the device 240 func tions as described in connection with the previous figure.
The control unit 242 comprises a processor component 256, which is used for executing control commands defined by application programs and by a user of the device 240, as well as for processing information. The processor compo nent 256 comprises at least one processor, e.g. one, two, three or more pro cessors.
The control unit 242 further comprises a data transfer component 258, by means of which the device 240 transmits control commands and information to other units 241 , 244, 246, 247, 248, 250, 252, 253, 254 of the device 240 and receives information transmitted thereby.
The control unit 242 further possibly comprises a physical user interface com ponent 260, by means of which the user is able to supply the device 240, es pecially its units 241 , 244, 246, 247, 248, 250, 252, 253, 254, with control commands and information needed thereby, as well as to receive from the de vice 240 information, instructions, and control command requests presented thereby. The user interface component 260 comprises at least one of the fol lowing elements: physical function keys, keyboard, display, and touchscreen.
The control unit 242 further comprises a memory component 262, having stored therein application programs controlling the operation of and being run by the device 240, as well as data used in the operation. The memory compo nent 262 comprises at least one memory, e.g. one, two, three or more memo ries.
The memory component 262 comprises a data transfer application 264 control ling the operation of the data transfer component 258, a user interface applica tion 266 controlling the operation of the physical user interface component 260 - when such is included in the control unit 242, a power supply application 268 controlling the operation of the power supply unit 241 , and an application 270 controlling the operation of the device’s 240 units 241 , 244, 246, 247, 248, 250, 252, 253, 254.
The application 270 comprises a computer program code (instructions), whereby the device 240 is directed to function as presented in connection with the previous figure as the application 270 is executed with the processor com ponent 256 assisted by the memory component 262 in the device 240.
The device 240 further comprises, as already pointed out in connection with the previous figure, a transfer mechanism 244, which is intended for conveying the material (sludge) to be transferred in the device 240 and which possibly in- eludes a transfer belt dryer element described in connection with the previous figure, as well as a pretreatment unit 246 and a US transmitter unit 247 in as sociation therewith for pretreating the to-be-dried sludge with ultrasound for at least weakening its cell structure for an ability to remove in the electric dryer 250 the internal water stored in sludge cells.
The device 240 further comprises, as already pointed out in connection with the previous figure, a conditioning tank 248 intended for the chemical condi tioning of sludge, and an electric dryer 250 intended for the electric drying of sludge, for separating the water present in the sludge from its solid material by means of an electric field and for squeezing the same mechanically out of the sludge.
The device 240 possibly further comprises, as already pointed out in connec tion with the previous figure, an after-treatment unit 252 intended for the MW or UV treatment of sludge and, in association therewith, an MW transmitter unit 253 or a UV transmitter unit.
The device 240 possibly further comprises, as already pointed out in connec tion with the previous figure, a thermal camera unit 254 intended for online monitoring the sludge drying process for its progress and success.
It is by virtue of the method 100 and the device 240 that the transportation costs of sludge to a final disposal site will be reduced as the sludge is lighter by containing less water than before.
It is likewise by virtue of the method 100 and the device 240 that the gate fees for e.g. a biogas facility, composting or other final disposal site will also be re duced as the sludge to be loaded is lighter.
The foregoing description only reveals exemplary embodiments of the inven tion. The underlying principle thereof can naturally be diversified within the scope of protection defined by the claims, regarding e.g. implementation de tails and fields of use.

Claims

Claims
1. A sludge drying method (100), comprising treating (116) sludge chemically in a chemical conditioning tank (248) for producing sludge floes in the sludge, separating (120), in an electric dryer (250) by means of an electric field, water present in the chemically treated sludge from its solid material, and compressing (120), in the electric dryer, mechanically water out of the sludge, characterized in that the to-be-dried sludge is pretreated (112) with ultrasound prior to the chemical treatment for at least weakening the cell structure of the sludge, in which case the internal water stored in sludge cells being thereby removed in the electric dryer.
2. The method according to the preceding claim, wherein the pretreatment is conducted in a pretreatment unit (246) in which the sludge is subjected to focused ultrasound, which is generated by an ultrasound transmitter unit (247) and which chops up the sludge’s filamentous structures as well as weakens and disrupts the sludge’s cell structures.
3. The method according to claim 2, wherein the ultrasound focused on the sludge has a frequency of 20-40 kHz.
4. The method according to any of the preceding claims, wherein the inten sity of employed ultrasound is optimized for impeding the formation of fines generated as a result of the treatment.
5. The method according to any of the preceding claims, wherein sludge floes are produced with a flocking chemical, which comprises at least one of the following: organic polyelectrolyte, inorganic aluminum salt, and inorganic iron salt.
6. The method according to any of the preceding claims, wherein the elec tro-dried and compressed sludge is after-treated (124) in an after-treatment unit (252) in which the sludge is subjected to focused microwave radiation generated by a microwave transmitter unit (253) for improving the drying result.
7. The method according to claim 6, wherein the microwave radiation fo cused on the sludge has a frequency of 300-3000 MHz.
8. The method according to any of the preceding claims, wherein the drying of sludge is monitored with a thermal camera unit (254) at least in one of the following: pretreatment unit, conditioning tank, electric dryer and after- treatment unit.
9. A method according to any of the preceding claims, wherein the sludge to be dried consists of biosludge.
10. A sludge drying device (240), which is adapted to implement the method (100) according to any of the preceding claims, comprises a pretreatment unit (246) for weakening the cell structure of to-be-dried sludge with ultrasound, a chemical conditioning tank (248) for producing sludge floes in the pre treated sludge, and an electric dryer (250) for separating (120) at least the internal water, which is present in the chemically treated, weakened cell structure-comprising sludge and stored in sludge cells, from the solid material by means of an elec tric field, and for compressing (120) the separated water mechanically out of the sludge.
PCT/FI2020/050736 2019-11-08 2020-11-06 Drying method and device for sludge WO2021089924A1 (en)

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