NO176006B - Process of drying materials - Google Patents

Abstract

Process / method for removing liquids (drying) from various finely divided organic or inorganic substances by converting some of the liquids to mist that behaves like steam or gas, and thus saves the heat of evaporation so that the energy consumption is dramatically reduced compared to pure evaporation of the same liquids.

Description

The invention relates to a method for drying organic and/or inorganic materials alone or in a mixture with each other, which materials contain one or more liquids or chemicals, where drying takes place by the liquid/liquids being removed as finely divided drops from the solids, such as mist, as the mass of material exposed to an artificial gravitational field.

The invention also relates to a device for carrying out the drying of organic and/or inorganic materials alone or in a mixture with each other, which materials contain one or more liquids or chemicals, drying taking place by the liquid/liquids being removed as finely divided drops from the solids, such as fog , including a process chamber with an introduction opening for the material to be dried, and a rotatably stored rotor in the process chamber, the circumference of which, together with an opposite inner wall in the process chamber, determines an annulus in the process chamber.

Essentially, all known techniques or processes for removing liquids from such finely divided substances are either based on mechanical separation through centrifugation, sedimentation etc., or some form of complete evaporation of the liquids in the substance. This invention aims to show a new way to remove liquids from the substances which in the technical literature is referred to as drying, after some of the liquids have possibly been removed by the first-mentioned techniques.

In the literature, a number of different drying systems are known which essentially comprise different ways of supplying the energy to the substances so that the liquids can evaporate. The reason for the need for different techniques is related to the types of substances, the fine distribution of the particles, the types of liquids and not least the thermodynamic values of the substances throughout the process.

The simplest and most everyday form of drying can be found in outdoor drying of a laundry. Here the clothes are dried under the influence of sun and wind.

From the technique, the following drying methods and processes can be mentioned: Rotary dryers where the energy can either be supplied through a flame that is blown into the dryer - so-called through-firing dryers, or through variously designed heat conduction elements (pipes, plates etc.) - so-called oil or steam dryers.

Fluidized dryers which normally consist of a vertical cylinder with a cloth or other perforated plate at the bottom, where some heated gas is blown which heats the material and drives off the liquids with evaporation.

Furthermore, there are infrared dryers where the energy is delivered as infrared radiation, various types of tunnel ovens and so-called "turbo dryers" where the material is dried in a vertical cylinder by spinning fans and a counter current of hot air or other heated gas.

The processes, which are well known and are described in detail in a number of technical books such as PERRY'S CHEMICAL ENGINEERING HANDBOOK, are used for a number of different drying purposes.

The problem with all the methods is that the evaporation of the liquids requires so much energy that the finished product must normally have such a large commercial value that it far exceeds the drying costs.

Now, however, there are a number of different substance/liquid mixtures where this is not the case, but for various reasons it would be a great advantage to have them dried - not least from environmental considerations. Such substance/washing mixtures can be: All types of aqueous sludge from municipal facilities. Ordinary sewage waste.

Animal manure.

All types of filtrate from centrifuges containing liquids.

Various biological and chemical sludge compositions from refineries, the wood processing and food industry etc.

Most of these substances are characterized by the fact that they are normally considered waste, and which are therefore normally too expensive to dry by evaporation.

The aim of the present invention is to show a process or a method to be able to dry such substances with less energy than current drying processes in that the liquids are not evaporated, but removed by converting a significant part of them into fog.

During the evaporation of a liquid, the energy requirement is expressed by the equation:

Here Q is the energy requirement in Joules, m the mass of the liquid in kg, c the specific heat of the liquid in J/kg°C and dt is the temperature difference between the evaporation temperature and the initial temperature of the liquid.

When water evaporates, the equation is often expressed through:

Here h2 is the enthalpy of the steam at the evaporation temperature and hi the enthalpy of the water at the temperature of the feed, i.e. the temperature of the water when it is fed into the process together with the solid and k is equal to the loss in the process.

If we look at a quantity of sludge with water, the equation expands to:

Here, x is the weight proportion of the solid, cs is the specific heat of the solid and xv is the weight proportion of the water. If there are several different solids in the substance, the equation is expanded for each solid part with its own weight shares and specific heat.

If you consider a typical sludge from the wood processing industry that contains 30% wood fiber and 70% water, the energy consumption per kg if we assume that dt = 100 - 20 = 80° C, cs = 1500 J/kg°C = 1.5 kJ/kg°C, h2 = 2,676,000 J/kg°C = 2,676 kJ/kg°C and h-L = 83,900 J/kg°C = 83.9 kJ/kg°C.

Q = 1[0.3-1.5*80+0.7(2676-83.9)] = 1,850 kJ/kg = 1,850,000 kJ/ton = 514 kWh/ton net.

In addition to this, there are the thermal losses from the process which can vary from 10% and upwards to several hundred percent. An energy consumption of three times the net amount is not unusual.

If you now look at the energy required for converting water into fog, you must start from the sizes of the fog droplets, which are between 0.01-lOum. If one chooses to use (0.01+10)/2 = 5 um as a kind of average, one liter of water will be able to form the number of fog drops expressed by: N = V/dV where V is the volume of one liter of water = 100.0003 pm<3 > and dV is the volume of each drop = d^/6. From this: N = 100,000<3->6/53n = 1.53-1013

The energy required to create these droplets can be assumed to correspond to the energy in the total surface tension between water and air. The surface tension for pure water is of = 71.4 dyn/cm = 7140 dyn/m = 7140 dyn'm/m<2> = 7140•10~<5>Nm/m<2> = 7145 • 10_5J/m2 .

The total surface area of the fog droplets is:

The total energy is:

This is in the order of approx. 20,000 times less energy than with pure evaporation of water.

This phenomenon becomes, among other things, today used in so-called air humidifiers. Earlier models were based on pure evaporation in that an electric heating flask was arranged in a container which heated the water until it boiled and evaporated. Today, instead of an electric heating bulb, a piezoelectric crystal is used which oscillates with approx. 20 kHz. When a drop of water hits the crystal, it cavitates into millions of tiny water droplets that together form a mist, which humidifies the room at room temperature.

The frequency of the sonic power required to achieve this is given by F.D. Smith who

where r is the radius of the droplets, u is the specific heat of the gas in the droplets, PG is the external hydrostatic pressure, o is the specific gravity (density) of the liquid and a is the surface tension between liquid and gas.

The equation relates to the cavitation of a liquid when exposed to sonic energy. Calculations for different droplet sizes show that the frequency will lie in the size range IO<4> to IO<6> Hz.

Now, however, the substances that are desired to be dried are far from a homogeneous mass. They can consist of a number of different substances in addition to both one and several different types of liquid, but where the predominant part is most often water.

It is a well-known fact that the liquids in such mixtures can be present as freely moving liquid and liquid bound by physical forces in the substances and which for the most part are constituted by capillary forces. To overcome these forces in a normal drying process, the vapor pressure must overcome the capillary pressure which increases with decreasing pore structure. In a normal drying process, this is achieved by drying the fabric at such a temperature that the steam pressure overcomes the capillary pressure. Very often one then has to use temperatures that are far above the strictly required evaporation temperature. Another condition that intervenes with pure thermal drying is that the thermodynamic values in the fabric change during the process. They get worse. This in turn must be compensated with higher temperatures and larger heating surfaces, which in turn lead to higher costs through equipment and operation.

In order to achieve what this invention aims at - drying by a combination of fogging and evaporation, the elements that will supply the sonic and thermal energy to the fabric must be able to supply these in such a turbulent state that all parts of the fabric are treated . Putting the material in a strong turbulent state will, in addition to obtaining a state with almost constant thermodynamic data, prevent the mass from becoming stuck in the process chamber and the parts it consists of - which is a major problem with all other known drying processes.

According to the invention, a method as mentioned in the introduction is therefore proposed, characterized by the fact that in the artificial gravity field, vibrational forces are induced suitable for tearing up liquid for the formation of fog.

Advantageously, hot gas can be supplied as additional energy for the drying.

The invention also proposes a device as mentioned at the outset, characterized by the fact that the rotor carries rotor blades capable of turning on its circumference, and that mainly axially oriented ribs are arranged on the said inner wall of the process chamber.

In a vertical or horizontal cylindrical container, a stirrer is arranged which is driven by a rotating energy source, - electric motor or a combustion engine. The agitator has a series of blades which, when the rotor rotates, are thrown out by the centrifugal force.

On the process chamber itself, there is an inlet opening for the material to be dried, an outlet opening for the dried material and an opening for evacuating steam and mist.

In order to supply the turbulent mass with the sonic energy, this can be done in the following ways: On the inside of the process chamber, longitudinal ribs are arranged over the entire inner periphery of the chamber. The ribs have such a shape that they are approximately parallel to the blades when they pass the ribs. When the rotor rotates at n revolutions/min. and has N blades/arm, at each revolution n*N pressure impulses will form between the rib and the blade which are transferred to the turbulent mass in the chamber. With e.g. a diameter of 2 m and 179 ribs at 35 mm intervals, 12 blades around the rotor running at 2500 rpm. pressure waves with a frequency of 179*2500/60 = 7458 pulses per Sec. These pressure waves will tear up the liquid and cause a good part of it to cavitate and form mist. IN in addition to this, heat will develop from the blades due to internal friction in the mass and because heated air or another gas can also be added, e.g. CO2 from an internal combustion engine. Together with these added gases, the mist will lead to the formation of an extremely low partial pressure in the process chamber for the part of the liquid that is evaporated. In experiments, it has been shown that the partial pressure of the vapors becomes so low that evaporation can range from 40 - 75°C.

The gases, mist and steam that leave the process chamber through the outlet opening from these can either be condensed or led to air - depending on what the gases consist of.

Another way to increase the frequency and thus the mechanical influence of the liquids is to design the blades as tuning forks, so that when these pass a rib, they are set into self-oscillations and help to increase the sonic energy. As an alternative to the purely mechanical influence of the tuning forks, these can be electromagnetically influenced by an externally arranged magnetic oscillator. This is arranged in such a way that the magnetic field is allowed to pass through the wall of the process chamber by making this in a non-magnetic material (e.g. stainless steel). The magnetic field will affect each of the blades designed as an oscillating element with the same frequency as the magnetic field. A further way to enhance this effect is to arrange on the blades a magnetostrictive material such as e.g. Terfonol^ which is made from the elements Ferrum, Terbium and Dysprosium. Under the influence of a magnetic field, the alloy will expand by approx. 1-2 0/00. This expansion can directly affect the leaves and thus the pulp to be processed.

Another possibility to establish a strong sonic field in the process chamber is to mount the ribs on piezo-electric ceramics or magnetostrictive materials. By establishing the right impedance between the mass in the ribs, one with a frequency modulator on the outside will be able to make the ribs oscillate at any chosen frequency within the practical range we are talking about here. In the frequency range of 20,000 Hz, you will not be able to see the movements of the ribs, as they will oscillate around their elastic range.

The vibrations can also be thought of as added in other ways, e.g. by designing the leaves so that when they move in the mass, they emit a sound analogous to a flute. This can be easily and practically achieved by designing the back of the blades in such a way that an enormous turbulence is formed behind them. In addition to emitting vibrations, the turbulence will also form a trailing vacuum which will make fog formation and evaporation more efficient at a low temperature.

Through experiments, it has been demonstrated that it is possible to reduce the energy consumption to less than half of the theoretical energy consumption for drying e.g. wood fiber sludge.

The process is controlled automatically by the following parameters:

Process temperature.

Load on the engine.

Moisture in the dried fabric.

This means that the output of the dried material starts at the selected operating temperature and humidity. The reduced load that thus occurs on the motor causes the feed to start until the load has peaked again. During the feed, the temperature drops and the output starts. If the system is set correctly, this happens continuously so that the input balances with the output, i.e. output and input take place continuously.

The invention is shown in more detail in subsequent drawings, where

Fig. 1 shows a schematic representation of the process, fig. 2 shows a detail of the process chamber and blade i

the passing moment,

fig. 3 shows a detail of one of the blades designed as a

tuning fork,

fig. 4 shows the same fork biased with the magnetostrictive material Terfonol<R> with an oscillating magnet generator,

fig. 5 shows a detail of a rib attached to a

piezoelectric or magnetostrictive material, fig. 6 shows a side view of an exemplary embodiment of

an appliance of 450 kWQ,

fig. 7 shows an elevation of the same embodiment, fig. 8 shows the embodiment seen from one side

the end,

In fig. 1 is a process chamber with rotor 2 and blades 3 driven by the motor 4. The mass is fed into the process chamber by the feed screw 5 from the hopper 6. The feed screw is driven by the motor 7. In the process chamber the mass is whipped by the blades 3 and applied with sonic energy or vibrations from these and the ribs

8. As additional energy, some heated gas can be supplied from the unit 9. The gases, mist and vapors leave the process chamber 1 via the outlet opening via an exhaust fan 11 and from there either to the open air and or to a condenser. The dried substance is led out through the discharge opening 12 via the rotating sluice 13. As mentioned, Fig. 2 shows a detail of the process chamber and the blade at the moment of passage. Fig. 3 shows a detail of one of the blades designed as a tuning fork. Fig. 4 shows the same tuning fork biased with the magnetostrictive material Terfonol^ 14, with an oscillating magnetic generator 15. Fig. 5 shows a detail of a rib 4 attached to a piezoelectric or magnetostrictive material 20 which receives swing energies via the cables 21 and 22 from the generator 23 .

In fig. 6, where the numerical references have the same meaning as in figure 1, a screw conveyor 15 for the dry material and the machine skid 16 on which the construction stands are also shown. You can also see the exhaust pipe 17 for the exhaust gases and mist which are led to the open air. At the end of the engine, the control cabinet 18 for the process is located. The whole thing is built into a 20-foot standard ISO container 19. Fig. 7 shows a plan view of the same design example where you can see the exhaust opening 10 for the exhaust gases and the fog, the exhaust fan 11 and the feed screw 5 in the hopper 6. There are 4 pieces in the hopper transverse feed screws which only have the function of feeding the material up to the feed screw 5. Fig. 8 shows the design example seen from one end with the same reference number as mentioned above.

Claims (9)

1. Procedure for drying organic and/or inorganic materials alone or in a mixture with each other, which materials contain one or more liquids or chemicals, where drying takes place by the liquid/liquids being removed as finely divided drops from the solids, such as fog, as the mass of material is exposed to a artificial gravity field, characterized by the fact that in the artificial gravity field, vibrational forces are induced suitable for tearing up liquid to form fog. 2. Method according to claim 1, characterized in that hot gas is supplied as additional energy for the drying. 3. Device for carrying out the drying of organic and/or inorganic materials alone or in a mixture with each other, which materials contain one or more liquids or chemicals, as drying takes place by the liquid/liquids being removed as finely divided drops from the solids, such as fog, including a process chamber (1) with an introduction opening (5) for the material to be dried, and a rotatably stored rotor (2) in the process chamber (1) whose circumference together with an opposite inner wall in the process chamber (1) determines an annular space in the process chamber, characterized in that the rotor (2) carries pivotable rotor blades (3) on its circumference, and mainly axially oriented ribs (8) are arranged on the said inner wall of the process chamber (1). 4. Device according to claim 3, characterized in that each rotor blade (3) is rotatably supported about an axis parallel to the axis of rotation of the rotor (2). 5 . Device according to claim 3 or 4, characterized in that the rotor blades (3) are designed with strong turbulence-forming backsides, seen in the direction of rotation. 6. Device according to claim 3 or 4, characterized in that the rotor blades (3) are designed as tuning forks. 7. Device according to claims 3-6, characterized in that a magnetic oscillator (15) is arranged outside the annular space and that the rotor blades (3) are assigned a magnetostrictive material (14). 8. Device according to one of the preceding claims 3-7, characterized in that the ribs (8) are designed as oscillating elements. 9. Device according to claim 8, characterized in that the ribs (8) are mounted on piezoelectric ceramics or magnetostrictive materials (20).