FI20195958A1 - Drying method and device for sludge - Google Patents

Abstract

The application relates to a sludge drying process (100) according to an embodiment. In the process, water present in the sludge is separated (120) from its solid material by means of an electric field in an electric dryer and (120) water is forced out of the sludge in the electric dryer. In addition, the sludge to be dried in the ultrasonic process is pretreated (112) in order to at least weaken the sludge's cell structure in order to make it possible in the electric dryer to remove internal water stored in the sludge cells.

Description

TECHNICAL FIELD The application relates generally to a method for drying sludge and to a drying device used therein.

Background In Finland, 400,000 tonnes are burned annually in energy production, e.g. various sludges from on-site effluent treatment in the forestry industry.

Sludges are wet fibrous fractions that can be divided into fibrous sludge and bio-sludge, which consists mainly of bacterial pulp that treats wastewater.

The share of bio-sludge is significant and its relative share of all sludges has been growing steadily in recent decades.

The paste-like and sticky bio-slurry consists of a bacterial cell that is rich in intracellular water.

Filamentous bacteria interfere with dewatering, so drying sludge for incineration is very poorly achieved with existing dryer types.

As a result of poorly successful dewatering, the calorific value of the dried sludge remains low.

SUMMARY It is an object of the invention to solve the problems of the prior art, to increase the calorific value of bio-sludge and to provide cost savings in the final disposal of bio-sludge by increasing its dry matter content by means of a new bio-sludge treatment method and apparatus.

In addition, the new method and apparatus increase the energy efficiency of drying sludge and produce dried sludge with a very high level of hygiene. x An object of the invention is achieved by a method and apparatus according to the independent claims. a x In the method of drying a slurry according to an embodiment of the invention, the water in the slurry is separated from its solid material by means of an electric field in an electric dryer (electric-assisted dryer) and water is mechanically pressed from the slurry in an electric dryer.

In addition, the method - pretreates the sludge to be dried by ultrasound at least to weaken the cell structure of the sludge.

allowing the internal water stored in the sludge cells to be removed in an electric dryer. A slurry drying apparatus according to an embodiment of the invention, adapted to carry out the method according to the above embodiment. The device - comprises an electric dryer in which the water in the slurry is separated from its solid material by an electric field and the water is mechanically compressed from the slurry. The device further comprises a pretreatment section in which the sludge to be dried is sonicated at least to weaken the cell structure of the sludge, thus enabling the removal of internal water stored in the sludge cells in an electric dryer. Other embodiments of the invention are set out in the dependent claims. Exemplary embodiments of the invention are illustrated in more detail by the accompanying drawings. DETAILED DESCRIPTION OF THE DRAWINGS Fig. 1 shows a method of drying a slurry 100 as a flow chart. The sludge to be dried (sludge mass) is, for example, a primary sludge or a bacterial bio-sludge (biomass) generated as a surplus of processes. In step 110, the slurry to be dried is fed to a drying device (machine) 240 for drying the slurry, where the slurry is conveyed either directly or by means of a transfer mechanism 244 (transfer part, transfer means) 244 to its pre-treatment section 246. o In step 112 240 The slurry in the pretreatment section 246 is physically rehabilitated (pretreatment) to at least weaken its cellular structure. The pretreatment is performed by applying ultrasound generated to the slurry by the ultrasonic transmitter portion 247 mounted on the pretreatment portion 246 © 25. The UÄ transmitter section I 247 is capable of applying high power ultrasound to the slurry with a frequency of & e.g. 20-40 kHz, e.g. 20, 25, 30, 35 or 40 kHz. 00

LO 2 During pretreatment, it is possible to optimize (adjust) the power of the ultrasound 2 used, if necessary, by controlling the operation of the UA-30 transmitter portion 247 by means of the control section 242 of the device 240 in order to prevent the formation of pre-treatment fines.

Ultrasound partially disrupts and / or partially impairs the cell structure (cell membranes) of the bacteria in the sludge mass. In addition, ultrasound breaks down the bacterial structures in the slurry, which are the most sensitive structures to UA treatment.

Due to the weakening and disruption of the internal structures of the bacteria in the slurry, it is possible to more efficiently remove the internal water stored in the slurry cells after pretreatment in the electric dryer 250 of the device 240. = night 248. In step 116, the pretreated sludge containing broken and attenuated bacterial structures is chemically rehabilitated in the remediation tank 248 prior to electrical and mechanical treatment to form sludge blocks and free water in the sludge.

The slurry blocks are formed from the cleaved structures of the bacteria with a flocculation chemical having at least one of the following components: an organic polyelectrolyte, an inorganic aluminum salt and an inorganic iron salt.

The sludge treatment of steps 112 and 116 is a combination of ultrasonic physical sludge treatment and flocculation chemical sludge treatment.

In step 118, the chemically treated slurry containing the slurry blocks and free water is directed by a screening mechanism 244 from the recovery tank 248 to the electric dryer 250 of the device 240 for electrically assisted drying (electric drying). = In step 120, the chemically treated slurry is subjected to an electric drying field formed in an electric dryer 250 = 25 to separate at least the free water contained therein from the solid material in the slurry, and mechanically squeeze at least free water out of the slurry.

D In the electric drying field, the water contained in the flocculated sludge is removed by electro-osmosis and electrophoresis when the ultrasonic digestion and accumulation of N-shaped filamentous bacteria does not interfere with dewatering.

In the electric drying field, in addition to free water, capillary water

water and intracellular water released from the cells during the sonication of step 112.

Known electric field dewatering solutions based on electro-osmosis and milling become energy inefficient at the latest when intracellular water remains in the sludge to be dried. In this case, the energy consumption of the known electric dryers rises sharply and the drying capacity drops substantially if an attempt is made to pump intracellular water through the cell membrane or if the structure of the cell membrane is to be broken by significantly increasing the electric field strength.

- Ultrasonic technology, on the other hand, can break the cell membranes of sludge e.g. forces based on cavitation. When the cell membranes break down, the sludge is broken down and the amount of fines contained in the sludge increases, whereby the sludge becomes denser. The mechanical or thermal drying of the dense sludge with suitable equipment is impaired because air and water have poor permeability to the dense sludge as the flow resistance caused by the fines increases.

By using ultrasound as a pre-treatment for electric drying, it is possible to take advantage of the strengths of both techniques when ultrasound breaks, or at least significantly weakens cell membranes, making it possible to remove water cost-effectively in the electric field of an electric dryer.

- In addition, the weaknesses of the ultrasonic treatment do not impair the success of the electric drying, since the growth of the fines formed therein and the consequent condensation of the sludge only slightly interfere with the electric drying, since the electric field allows water to flow through even small pores.

& NL 25 - If the device 240 does not include a post-processing section 252, then after step 120, and in step 126, the electrically and compression-treated, i.e., electrically dried, slurry is directed away from the device 240 for re-utilization or storage to await further utilization.

O If the device 240 includes a post-treatment section 252, then after step 120, 3 30 - in step 122, the electrically dried slurry is directed to the foot treatment section 252 by a transfer mechanism 244.

In step 124, the slurry in the post-treatment section 252 is post-treated (post-drying) to further enhance the removal of water from the slurry, improving the drying result. The post-treatment is performed by applying to the slurry the microwave radiation generated by the microwave transmitter section 253 mounted on the post-treatment section 252. The MA transmitter section 253 is capable of directing microwave radiation having a frequency of 300-3000 MHz, e.g., 300, 500, 800, 1000, 2000 or 3000 MHz, to the slurry.

Microwave treatment makes it possible to increase the amount of final dry matter and to better control the drying result when the dried slurry is obtained in a uniform manner.

After further processing of step 124, just as described above in the case of the electrically dried slurry in step 120, step 126 directs the microwave-treated, i.e., post-processed, slurry from the device 240 for further utilization or storage by means of a transfer mechanism 244.

- If the device 240 comprises a thermal camera part 254 comprising at least one thermal camera, it is possible during the method 100 to monitor the progress of sludge drying and its success by online measurement with the thermal camera part 254. The monitoring can be performed in at least one of the following parts 240: pretreatment part 246 , in the recovery tank 248, an electric dryer 250 and a foot treatment section 252.

Drying power control plays an important role in energy efficiency. In addition to the need for and proper alignment of drying power control, thermal camera technology can be utilized to prevent inadvertent local overheating of device 240.

O = 25 - The drying treatment of sludges, eg bio-sludges, must be gentle, but o nevertheless the filamentous bacteria must be broken and the intracellular water must be accessible without increasing unprofitable energy consumption. Therefore, ultrasonic pretreatment is well suited for this purpose. Microwave drying, on the other hand, is an excellent energy-efficient drying method, especially for post-drying. o N With the method 100 and the device 240, the calorific value of the sludge dried is higher than before, the carbon dioxide emissions from its combustion are reduced and

The increased dry matter content of tea enables new recovery and nutrient recycling sites.

Fig. 2 shows a schematic view of an apparatus 240 used to dry a slurry for carrying out the method 100 shown in connection with the previous figure.

The device 240 has a power supply section 241 by means of which the device 240 takes the operating current it needs.

The device 240 further has a control part 242 by means of which the device 240 controls its own operation, i.e. the operation of its parts 241, 244, 246, 247, 248, 250, 252, 253, 254, so that the device 240 operates as shown in connection with the previous figure.

The control section 242 includes a processor section 256 for executing control commands defined by the user of the application programs and the device 240, as well as for processing information.

Processor section 256 includes at least one processor, e.g., one, two, three, or more processors.

The control section 242 further includes a communication section 258 by means of which the device 240 transmits a control command and information to the other parts 241, 244, 246, 247, 248, 250, 252, 253, 254 of the device 240 and receives the information transmitted by them.

The control part 242 may optionally further have a physical user interface part 260, by means of which the user can give control commands and information to the device 240, in particular to its parts 241, 244, 246, 247, 248, 250, 252, 253, 254, and - receive from the device 240 information, instructions and control command requests.

The user interface section 260 includes at least one of the following components: physical function keys, keyboard, display, and touch screen. The control section 242 also has a memory section 262 in which the application programs controlling the operation of the device 240 = and used by it are stored, as well as the data used in the operation.

The memory section 262 includes at least one memory, e.g., one, two, z three or more memories. The memory section 262 has a communication application 264 for controlling the operation of the communication section 258, a user interface application 266 for controlling the operation of the physical user interface section 260, such as the control section 2 242, a power supply application 268 for controlling the operation of the power supply section 241, 246, 247, 248, 250, 252, 253, 254 control application 270.

The application 270 comprises computer program code (instructions) for controlling the device 240 to operate as shown in the previous figure when the application 270 is executed by the processor portion 256 with the aid of the memory portion 262 in the device 240. The device 240 further has, as already shown in the previous figure, a (slurry) transfer mechanism 244 and a pretreatment section 246 and associated UA transmitter section 247 for sonicating the sludge to be dried to at least degrade its cellular structure to remove internal water stored in the sludge cells in the electric dryer 250.

The device 240 further comprises, as already shown in connection with the previous figure, a sludge chemical recovery tank 248 and an electric dryer 250 for the electric drying of the sludge to separate the water in the sludge from its solid material by an electric field and to mechanically compress it.

- The device 240 may additionally have, as already shown in connection with the previous figure, an after-treatment part 252 for the MA or UV treatment of the slurry and in connection therewith an MA transmitter unit 253 or a UV transmitter part.

The device 240 may further have, as already shown in connection with the previous figure, a thermal camera section 254 for online monitoring of the progress and success of sludge drying.

With the method 100 and the device 240, the cost of transporting the dried sludge to the sludge disposal site is reduced when the sludge is lighter when it contains less water than before.

O N With the aid of the method 100 and the device 240, the port charges for e.g. a biogas plant, composting or other disposal site are also reduced when the 2 sludges to be loaded are lighter.

Only exemplary embodiments of the invention have been described above. 3 The principle according to it can, of course, be modified within the scope of protection defined by the requirements, eg with regard to the details of implementation and the areas of use> 30.

Claims (11)

Standard A method of drying a slurry (100), comprising (120) separating (120) water in a slurry in an electric dryer (250) from its solid material and mechanically pressing (120) water from the slurry in an electric dryer, characterized in that the slurry to be dried is sonicated (112) at least to weaken the field, allowing the internal water stored in the sludge cells to be removed in an electric dryer. The method of the preceding claim, wherein the pretreatment is performed in a pretreatment section (246), wherein the slurry is subjected to ultrasound generated by the ultrasonic transmitter portion (247), which breaks down the sludge-like structures and weakens and breaks down the sludge's cellular structures. The method of claim 2, wherein the frequency of the high power ultrasound applied to the slurry is 20-40 kHz. A method according to any one of the preceding claims, wherein the power of the ultrasound used is optimized to prevent the formation of fines resulting from the treatment. A method according to any preceding claim, wherein in the chemical rehabilitation tank (248) the sludge is chemically treated (116) prior to electrical and mechanical treatment to form sludge blocks in the sludge. The method of claim 5, wherein the slurry blocks are formed with a = flocculation chemical comprising at least one of an organic polyelectrolyte, an inorganic aluminum salt, and an inorganic iron salt. © 25 A method according to any preceding claim, wherein the electrically dried I and the compressed slurry are post-treated (124) in a post-treatment section (252), wherein the slurry is subjected to microwave radiation generated by the microwave transmitter section (253) to improve the drying result. LO 2 The method of claim 7, wherein the frequency of the N 30 microwave radiation applied to the slurry is 300-3000 MHz. A method according to any one of the preceding claims, wherein the drying of the slurry is monitored by a thermal camera section (254) in at least one of a pre-treatment section, a recovery tank, an electric dryer and a foot treatment section. A method according to any one of the preceding claims, wherein the slurry bio-slurry is to be dried. A sludge drying device (240) adapted to implement a method (100) according to any preceding claim, comprising an electric dryer (250) for separating (120) water in the slurry from its solid material by an electric field, mechanically squeezing (120) the separated water - a sonication and pretreatment section (246) for sonicating (112) the sludge to be dried, at least to weaken the cell structure of the sludge, thus allowing the internal water stored in the sludge cells to be removed in an electric dryer. oO O No. O I a a 00 LO o LO o O OF