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delaval milk separator manual

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delaval milk separator manualSomething went wrong. View cart for details. All Rights Reserved. User Agreement, Privacy, Cookies and AdChoice Norton Secured - powered by Verisign. It covers only those components that are used in liquid milk processing. Cheesemaking equipment, buttermaking. This was “a drum which is made to rotate and which, after turning for a time, leaves the cream floating on the surface so that it can be skimmed off in the usual fashion”. After reading this article, a young Swedish engineer, Gustaf de Laval, said, “I will show that centrifugal force will act in Sweden as well as in Germany.” The daily newspaper “Stockholms Dagblad” of 15th January 1879 reported: “A centrifugal separator for cream skimming has been on show here since yesterday and will be demonstrated every day between 11 a.m. and 12 noon on the first floor of the house of number 41, Regeringsgatan. The machine can be likened to a drum which is driven round by a belt and pulley. The cream, which is lighter than the milk, is driven by centrifugal force to the surface of the milk and flows off into a channel from which it is led into a collection vessel. Under it, the milk is forced out to the periphery of the drum and is collected in another channel, whence it is led to a separate collecting vessel.” From 1890, the separators built by Gustaf de Laval were equipped with specially-designed conical discs, the patent on which had been granted in 1888 to the German Freiherr von Bechtolsheim and had been acquired in 1889 by the Swedish company AB Separator, of which Gustaf de Laval was part-owner. Today, most makes of similar machines are equipped with conical disc stacks. Up to a hundred years ago, the technique used for separating one substance from another was the natural process of sedimentation by gravity. Sedimentation takes place all the time. Clay particles moving in puddles will soon settle, leaving the water clear. Clouds of sand stirred up by waves or by the feet of bathers do the same.http://wiktormajak.com.pl/local/userfiles/final-cut-pro-4-user-manual.xml

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Oil that escapes into the sea is lighter than water, rises and forms oil slicks on the surface. Sedimentation by gravity was also the original technique used in dairying to separate fat from milk. Milk fresh from the cow was left in a vessel. After some time the fat globules aggregated and floated to the surface where they formed a layer of cream on top of the milk. This could then be skimmed off by hand. Requirements for sedimentation The liquid to be treated must be a dispersion; a mixture of two or more phases, one of which is continuous. In milk it is the milk serum, or skim milk, that is the continuous phase. Milk also contains a third phase, consisting of dispersed solid particles such as udder cells, pulverized straw and hair, etc. The phases to be separated must not be soluble in each other. Substances in solution cannot be separated by means of sedimentation. Dissolved lactose cannot be separated by means of centrifugation. It can, however, be crystallized. The lactose crystals can then be separated by sedimentation. The phases to be separated must also have different densities. The phases in milk satisfy this requirement; the solid impurities have a higher density than skim milk, and the fat globules have a lower density. How does sedimentation work. If a stone is dropped into water, we would be surprised if it did not sink. In the same way, we expect a cork to float. We know by experience that a stone is heavier and a cork is lighter than water. But what happens if we drop a stone in mercury, a liquid metal with a very high density. Or if we drop a piece of iron into mercury. We have no experience to help us predict the result. We might expect the piece of iron to sink. In actual fact, both the stone and the piece of iron will float. Substances in solution cannot be separated by means of sedimentation. Density Stone is heavier thanwater and sinks. If we weigh a cubic metre of iron, we will find that the scale shows 7 860 kg.http://vendsol.com/userfiles/final-cut-pro-6-manual-espa-ol.xml When an object is dropped into a liquid, it is basically the density of the object, compared with the density of the liquid, that determines whether it will float or sink. If the density of the object is higher than that of the liquid, it will sink, but it will float if the density of the object is lower. Density is usually denoted by the Greek letter ?. With a density of a particle ?p and the density of the liquid. The result is a positive number, as the density of the stone is higher than that of water; the stone sinks. This time, the result is negative. Because of the low density of a cork, it will float if it is dropped into water; it will move against the direction of the force of gravity. This is called the sedimentation velocity. If the density of the particle is lower than the fluid medium the particle will float at a flotation velocity.Increases with diminishing viscosity of the continuous phase. Flotation velocity of a fat globule With fresh milk in a vessel, the fat globules will begin to move upwards, towards the surface. The flotation velocity can be calculated with the help of the formula above.At zero time, the fat globules are at the bottom of the vessel. After t minutes, a certain amount of sedimentation has taken place, and after 3 t minutes, the largest fat globule has reached the surface. By this time, the medium-sized globule has risen to a point halfway to the surface, but the smallest globule has only covered one quarter of the distance. The medium-sized globule will reach the surface in 6 t minutes, but the smallest globule will need 12 t minutes to get there. The sedimentation distance in this case is h 1 m. The time to complete separation can be reduced if the sedimentation distance is reduced. The height of the vessel (B) has been reduced and the area increased so that it still has the same volume.On the way, the particles settle at different rates, due to their different diameters. Baffles increase the capacity The capacity of the sedimentation vessel can be increased if the total area is increased, but this makes it large and unwieldy. It is instead possible to increase the area available for separation by inserting horizontal baffle plates in the vessel, as illustrated in Figure 6.2.9. There are now a number of “separation channels”, in which sedimentation of particles can proceed at the same rate as in the vessel in Figure 6.2.8. The total capacity of the vessel is multiplied by the number of separation channels. The total area available ( i.e. the total number of baffle plate areas) for separation, multiplied by the number of separation channels, determines the maximum capacity that can flow through the vessel without loss of efficiency, i.e. without allowing any particles, larger than the designated limit size to escape with the clarified liquid. When a suspension is continuously separated in a vessel with horizontal baffle plates, the separation channels will eventually be blocked by the accumulation of sedimented particles. Separation will then come to a halt. If the vessel has inclined baffles instead, as in Figure 6.2.10, the particles that settle on the baffles under the influence of gravity will slide down the baffles and collect at the bottom of the vessel. Why are particles that have settled on the baffles not swept along by the liquid that flows upwards between the baffles. The explanation is given in Figure 6.2.11, which shows a section through part of a separation channel. As the liquid passes between the baffles, the boundary layer of liquid closest to the baffles is braked by friction so that the velocity drops to zero. This stationary boundary layer exerts a braking effect on the next layer, and so on, towards the centre of the channel, where the velocity is highest. The sedimented particles in the stationary boundary zone are consequently subjected only to the force of gravity. The projected area is used when the maximum flow through a vessel with inclined baffle plates is calculated. In order to utilize the capacity of a separation vessel to the full, it is necessary to install a maximum amount of surface area for particles to settle on. The sedimentation distance does not affect the capacity directly, but a certain minimum channel width must be maintained, to avoid blockage of the channels by sedimenting particles. The length of an arrow corresponds to the velocity of a particle. The dispersion passes downwards from the inlet through the opening B. An interface layer then flows horizontally at the level of B. From this level, the solid particles (which have a higher density than both liquids) settle to the bottom of the vessel. The less dense of the two liquid phases rises toward the surface and runs off over overflow outlet B 1. The denser liquid phase moves downward and passes below baffle B 2, out of the lower outlet. Baffle B 2 prevents the lighter liquid from going in the wrong direction. The centrifugal acceleration increases with distance from the axis of rotation (radius, r) and with the speed of rotation, expressed as angular velocity ?, (Figure 6.2.14). The acceleration can be calculated by the formula 2). The result is a sectional view of a centrifugal separator. Separation channels Figure 6.2.15 also shows that the centrifuge bowl has baffle inserts in the form of conical discs. This increases the area available for sedimentation. The discs rest on each other and form a unit known as the disc stack. Radial strips called caulks are welded to the discs and keep them the correct distance apart. This forms the separation channels. The thickness of the caulks determines the width. Figure 6.2.16 shows how the liquid enters the channel at the outer edge (radius r 1 ), leaves at the inner edge (radius r 2 ) and continues to the outlet. During passage through the channel, the particles settle outward towards the disc, which forms the upper boundary of the channel. The velocity w of the liquid is not the same in all parts of the channel. It varies from almost zero, closest to the discs, to a maximum value in the centre of the channel. The centrifugal force acts on all particles, forcing them towards the periphery of the separator at a sedimentation velocity, v. A particle consequently moves simultaneously at velocity w with the liquid, and at sedimentation velocity, v radially towards the periphery. The resulting velocity, v p, is the sum of these two motions. The particle moves in the direction indicated by vector arrow v p. For the sake of simplicity it is assumed that the particle moves in a straight path as shown by the broken line in the figure. In order to be separated, the particle must settle on the upper plate before reaching point B', i.e. at a radius equal to or greater than r 2. Once the particle has settled, the liquid velocity at the surface of the disc is so small that the particle is no longer carried along with the liquid. It therefore slides outwards along the underside of the disc under the influence of the centrifugal force, is thrown off the outer edge at B and deposited on the peripheral wall of the centrifuge bowl. All particles larger than the limit particle will be separated. The figure shows that some particles smaller than the limit particle will also be separated if they enter the channel at point C somewhere between A and B. The smaller the particle, the closer C must be to B in order to achieve separation. There they are collected in the sediment space. As the milk passes along the full radial width of the discs, the time of passage also allows very small particles to be separated. The most typical difference between a centrifugal clarifier and a separator is the design of the disk stack. A clarifier has no distribution holes or open holes at the periphery.A more detailed illustration of this phenomenon is shown in Figure 6.2.20. The milk is introduced through vertically-aligned distribution holes in the discs at a certain distance from the edge of the disc stack. Under the influence of centrifugal force, the sediment and fat globules in the milk begin to settle radially outwards or inwards in the separation channels, according to their density relative to that of the continuous medium (skim milk). As in the clarifier, the high-density solid impurities in the milk will quickly settle outwards towards the periphery of the separator and collect in the sediment space. Sedimentation of solids is assisted by the fact that the skim milk in the channels in this case moves outwards towards the periphery of the disc stack. The cream, i.e. the fat globules, has a lower density than the skim milk and therefore moves inwards in the channels, towards the axis of rotation. The cream continues to an axial outlet. The skim milk moves outwards to the space outside the disc stack and from there through a channel between the top of the disc stack and the conical hood of the separator bowl to a concentric skim milk outlet. The smallest fat globules, normally The flow velocity through the separation channels will be reduced if the flow rate through the machine is reduced. This gives the fat globules more time to rise and be discharged through the cream outlet. The skimming efficiency of a separator consequently increases with reduced throughput and vice versa. The proportion discharged as cream determines the fat content of the cream.This amount of fat must be diluted with a certain amount of skim milk. The total amount of liquid discharged as 40 cream will then be The size of fat globules varies during the cow’s lactation period, i.e. from parturition to going dry. Large globules tend to predominate just after parturition, while the number of small globules increases towards the end of the lactation period. Solids ejection The solids that collect in the sediment space of the separator bowl consist of straw and hairs, udder cells, white blood corpuscles (leucocytes), red blood corpuscles, bacteria, etc. In milk separators of the solids-retaining type it is necessary to dismantle the bowl manually and clean the sediment space at relatively frequent intervals. This involves a great deal of manual labour. Self-cleaning or solids-ejecting separator bowls are equipped for automatic ejection of accumulated sediment at pre-set intervals. This eliminates the need for manual cleaning. The system for solids discharge is described at the end of this chapter under “The discharge system”. Solids ejection is normally carried out at 30 to 60 minute intervals during milk separation. They are held together by a threaded lock ring. The disc stack is clamped between the hood and the distributor at the centre of the bowl. There are two types of modern separators: semi-open and hermetic. Semi-open design Centrifugal separators with paring discs at the outlet, (Figure 6.2.23), are known as semi-open types (as opposed to the older open models with overflow discharge). In the semi-open separator, the milk is supplied to the separator bowl from an inlet, normally in the top, through a stationary axial inlet tube. When the milk enters the ribbed distributor (4), it is accelerated to the speed of rotation of the bowl, before it continues into the separation channels in the disc stack (3). The centrifugal force throws the milk outwards to form a ring with a cylindrical inner surface. This is in contact with air at atmospheric pressure, which means that the pressure of the milk at the surface is also atmospheric. The pressure increases progressively, with increasing distance from the axis of rotation, to a maximum at the periphery of the bowl. The heavier solid particles settle outwards and are deposited in the sediment space. Cream moves inwards towards the axis of rotation and passes through channels to the cream paring chamber (2). The skim milk leaves the disc stack at the outer edge and passes between the top disc and the bowl hood to the skim milk paring chamber (1). The kinetic energy of the rotating liquid is converted into pressure in the paring disc, and the pressure is always equal to the pressure drop in the downstream line. An increase in downstream pressure means that the liquid level in the bowl moves inwards. In this way, the effects of throttling at the outlets are automatically counteracted. In order to prevent aeration of the product, it is important that the paring discs are sufficiently covered with liquid. It is accelerated to the same speed of rotation as the bowl and then continues through the distribution holes in the disc stack. The bowl of a hermetic separator is completely filled with milk during operation. There is no air in the centre. The hermetic separator can therefore be regarded as part of a closed piping system. The pressure generated by the external product pump is sufficient to overcome the flow resistance through the separator to the discharge pump at the outlets for cream and skim milk. The diameter of the pump impellers can be engineered to suit the outlet pressure requirements. Increasingly larger amounts of cream, with a progressively diminishing fat content, will be discharged from the cream outlet, if the valve is gradually opened. A given rate of discharge consequently corresponds to a given fat content in the cream. The pressure on the skim milk outlet, (1) in Figure 6.2.27, is set by means of a regulating valve at a certain value, according to the separator and the throughput. The throttling valve (2) in the cream outlet is then adjusted to give the flow volume corresponding to the required fat content. Any change in the cream discharge will be matched by an equal (and opposite) alteration in the skim milk discharge. An automatic constant pressure unit is fitted in the skim milk outlet to keep the back pressure at the outlet constant, regardless of changes in the rate of cream flow. The size of the valve aperture is adjusted with a screw, and the throttled flow passes through a graduated glass tube. A spool-shaped float, within the tube, is lifted by the cream flow to a position on the graduated scale, varying according to the flow rate and viscosity of the cream. By analysing the fat content of the incoming whole milk and calculating the volume of the cream flow at the required fat content, it is possible to arrive at a coarse setting of the flow rate and to adjust the throttling screw accordingly. Fine adjustment can be made when the fat content of the cream has been analysed. The operator then knows the float reading when the fat content of the cream is correct. The fat content of the cream is affected by variations in the fat content of the incoming whole milk and by flow variations in the line. Other types of instruments are used, (e.g. automatic in-line systems) to measure the fat content of cream in combination with control systems which keep the fat content at a constant value. Hermetic separator An automatic constant pressure unit for a hermetic separator is shown in Figure 6.2.28. The valve shown is a diaphragm valve and the required product pressure is adjusted by means of compressed air above the diaphragm. During separation, the diaphragm is affected by the constant air pressure above and the product (skim milk) pressure below. The pre-set air pressure will force the diaphragm down if the pressure in the skim milk drops. The valve plug, fixed to the diaphragm, then moves downwards and reduces the passage. This throttling increases the skim milk outlet pressure to the pre-set value. The opposite reaction takes place when there is an increase in the skim milk pressure, and the pre-set pressure is again restored. It also shows an important difference between these two machines. In the paring-disc separator, the outer diameter of the paring disc must penetrate into the rotating liquid column. The distance is determined by the fat content of the cream. The fat content is highest at the inner, free cream level in the separator. From there, the fat content is gradually reduced, as the diameter increases. An increased fat content in the cream from the separator increases the distance from the inner, free-liquid level of the cream to the outer periphery of the paring disc by the cream level being forced inwards. The fat content at the inner, free-cream level must consequently be considerably higher if, for instance, 40 cream is to be discharged. This could cause destruction of the fat globules in the innermost zone facing the air column, as a result of increased friction. The outcome will be disruption of fat globules causing sticking problems and increased sensitivity to oxidation and hydrolysis. Cream from the hermetic separator is removed from the centre, where the fat content is highest. Over-concentration is therefore not necessary. When removing cream that has a high fat content, the difference in outlet performance is even more important. At 72 , the fat is concentrated to such an extent that the fat globules are actually touching each other. It would be impossible to obtain cream with higher fat content from a paring-disc separator, as the cream would have to be considerably over-concentrated. The required pressure cannot be created in a paring-disc separator. High pressures can be created in the hermetic separator, which makes it possible to separate cream with a fat content exceeding 72 globular fat. Sediment from the product and the CIP solutions are collected in the sediment space at the periphery of the bowl, until a discharge is triggered. To clean the larger surfaces in the bowl of bigger centrifuges efficiently, a larger volume of sediment and liquid is discharged during water rinsing in the cleaning cycle. Discharge A sediment discharge sequence may be triggered automatically by a pre-set timer, a sensor of some kind in the process, or manually by a push button. The details in a sediment discharge sequence vary, depending on centrifuge type, but basically a fixed water volume is added to initiate drainage of the balance water. When the water is drained from the space below the sliding bowl bottom, it drops instantly and the sediment can escape at the periphery of the bowl. New balance water is automatically supplied from the service system (operating water module), to close the bowl. The water moves the sliding bowl bottom upwards, to tighten against the seal ring. A sediment discharge has taken place, in tenths of a second. The centrifuge frame absorbs the energy of the sediment leaving the rotating bowl. The sediment is discharged from the frame by gravity to a vessel, pump or to sewage. In most centrifuges, the vertical shaft is connected to the motor axis by a worm gear on a horizontal axis, giving an appropriate speed, and a coupling. Various types of friction couplings exist, but friction is inconsistent, so direct couplings with a controlled start sequence are often preferred. Standardization of fat and protein Principle calculation methods for blending of products Various methods exist for calculating the quantities of products with different fat contents that must be blended to obtain a given final fat content. These cover mixtures of whole milk with skim milk, cream with whole milk, cream with skim milk and skim milk with anhydrous milk fat (AMF). One of these methods, frequently used, is taken from the Dictionary of Dairying by J.G. Davis and is illustrated by the following example: How many kilograms of cream of A fat must be blended with skim milk of B fat to make a mixture containing C fat. The answer is obtained from a rectangle (Figure 6.2.31) where the given figures for fat contents are placed. From the equations below, it is then possible to calculate the amounts of A and B needed to obtain the desired quantity (X) of C. The requirement is to produce an optimal amount of 3 standardized milk and surplus cream containing 40 fat. Separation of 100 kg of whole milk yields 90.35 kg of skim milk with 0.05 fat and 9.65 kg of cream with 40 fat.Previously, standardization was done manually, but, along with increased volumes to process, the need for fast, accurate standardization methods, independent of seasonal fluctuations of the raw milk fat content, has increased. Control valves, flow and density meters and a computerized control loop are used to adjust the fat content of milk and cream to desired values. This equipment is usually assembled in units (Figure 6.2.33). The pressure in the skim milk outlet must be kept constant in order to enable accurate standardization. This pressure must be maintained, regardless of variations in flow or pressure drop caused by the equipment after separation, and this is done with a constant-pressure valve located close to the skim milk outlet. For precision in the process, it is necessary to measure variable parameters such as: Fluctuations in the fat content of the incoming milk Fluctuations in throughput Fluctuations in pre-heating temperature Most of the variables are interdependent; any deviation in one stage of the process often results in deviations in all stages. Following separation, the cream is standardized to a pre-set fat content. To achieve this, the calculated amount of cream intended for standardization is routed and remixed with an adequate amount of skim milk. The surplus cream is directed to the cream pasteurizer. The course of events are illustrated in Figure 6.2.34. Under certain circumstances, it is also possible to apply an in-line standardization system to a cold milk centrifugal separator. The reason is that the density will vary with the degree of crystallization and will thus affect the measuring accuracy of the density transmitter, which is always calibrated after installation. The cream fat content is inversely proportional to the flow rate. Some standardization systems therefore use flow meters to control the fat content. The fat content will be wrong if these parameters change. Various types of instruments can be used for continuous measurement of the fat content in cream. The signal from the instrument adjusts the cream flow so that the correct fat content is obtained. This method is accurate and sensitive to variations in the temperature and fat content of the milk. However, the control is slow and it takes a long time for the system to return to the correct fat content when a disturbance has occurred. There are two transmitters in Figure 6.2.35 measuring the flow of standardized cream and skim milk respectively. With these two flow data, the control system (4) calculates the flow of whole milk to the separator. A density transmitter (1) measures the cream density and converts this value into fat content. Combining fat content and flow rate data, the control system activates the modulating valve (3), to obtain the required cream fat content. The computer monitors the fat content of the cream, the flow rate of the cream and the setting of the cream regulating valve. The density transmitter transmits continuous density readings to the computer in the form of an electric signal. The strength of the signal is proportional to the density of the cream. Increasing density means that there is less fat in the cream and the signal will increase. Any change in density modifies the signal from the density transmitter to the computer; the measured value will then deviate from the setpoint value which is programmed into the computer. The computer responds by changing the output signal to the regulating valve by an amount corresponding to the deviation between measured and set-point values. The position of the regulating valve changes and restores the density (fat content) to the correct value. In Figure 6.2.35 the flow transmitter (2) in the control circuit measures the flow in the cream line continuously and transmits a signal to the computer. The transmitters in the control circuit measure the flow and density in the cream line continuously and transmit a signal to the computer. Cascade control is used to make necessary corrections due to variations in the fat content in the incoming whole milk. Cascade control works by comparing: The flow through the flow transmitter, which is proportional to the cream fat content, and The density measured by the density transmitter, which is revised according to the cream fat content. The computer in the control panel (4) then calculates the actual whole milk fat content and alters the control valves to make the necessary adjustments. The standardized milk fat content is recorded continuously. The fat content varies inversely with density because the fat in cream is lighter than the milk serum. In this context, it is important to remember that the density of cream is also affected by temperature and gas content. Much of the gas, which is the lightest phase in the milk, will follow the cream phase, reducing the density of the cream. It is therefore important that the amount of gas in the milk is kept at a constant level. Milk can contain varying levels of air and gases, but 6 can be taken as an average figure. More air than that can cause problems such as inaccuracy in volumetric measurement of milk, increased fouling of equipment during heating, etc.