GB2111843A - Method for the agitation of liquid masses under vacuum by means of pneumatic injection - Google Patents

Abstract

Solutions which are to be concentrated under vacuum in heating vessels are agitated by injecting air alone or air enriched with water vapour thereinto.

Description

SPECIFICATION Method for agitation of liquid masses under vacuum by means of pneumatic injection The present description, which is an application for the registration of a patent of invention, relates to a "method for the agitation of liquid masses under vacuum by means of pneumatic injection", the novel features of which provide it with the capacity of imparting advantages to the object set which are more than sufficient for the registration which is hereby applied for, rendering possible energy saving, an increase in productivity and an improved performance of the processes to which it is applied.

It represents a lower consumption of energy.

An evaporator with mechanical agitation usually has a motor of 20 to 25 H.P. which operates at 80% of its nominal potential during baking, but which, when actuated freely in the first part of baking, produces a considerable reduction in the cosine of the electrical installation whilst in the final stages of baking the life of the motor has to depend on the actuation of the intensity relays, with excessive consumption.

In the case of agitation with air the consumption per evaporator is from 5 to 6 H.P. There is a difference of approximately 15 to 30 H.P. per evaporator with respect to energy consumption which is an important factor in a sugar refinery, whose actual production is limited and almost always slight.

It involves a smaller investment since the mechanically agitated evaporator has a motor with a double winding in order to operate at two different speeds as a function of the consistency of the mass. Apart from the higher price of this type of motor there is the disadvantage of the speed reducer which is necessarily bulky and expensive owing to its increased reduction relation from 1,500 r.p.m. to 40 to 60 which is the speed of the agitation screw.

The agitation screw is always a manufactured part of expensive metal which has to meet specific and very strict conditions with respect to its casting and in order to be dismountable into parts, so that it may be introduced into its place of operation, it has to be precisely manufactured.

The transmission shaft, inside the evaporator, has to be wide, with a large diameter and of very high grade steel which is divided into two or more parts connected by means of mechanical handles which are expensive. There must be one or more special bearings inside the evaporator which require automatic remote lubrication in addition to irrigation with pressurized water so as to avoid the mass in the chamber entering these bearings and rapidly destroying them. The pressurized water which washes the bearings has to evaporate in the chamber, which involves the consumption of vapour.

The closing or sealing device for the bearing, which is borne by the shaft at the outlet of the evaporator and requires perfect air-tightness at its upper part - which necessitates careful yearly repairing - raises the reducer. Owing to its location in the upper part of the evaporator it requires a costly framework; when installing a fixed passage above each agitating evaporator which enables the reducer and the motor to be dismantled. Failure of the seal during operation involves an uncontrolled inrush of air and the repair of this fault requires this evaporator to be out of service for many hours.

All the above conditions are eliminated by the invention described.

Afurther advantage is its versatility.

Mechanical agitation requires special evaporators which have to have a central hole in their tubular body, wherein the agitating screw may be housed, its vapour outlet may be altered and drops may be recovered, in order to install the motor unit.

On the other hand, agitation of the evaporator with air and or a portion of water vapour enables, with little effort and the minimum expense, evaporators with the most varied type of tubular body to be agitated: evaporators with floating calenders, without a central hole, with an annular space on their periphery, with a flat surface or with its upper tubular plate inclined to a greater or lesser degree, etc..

It is readily possible in each particular case to study the form of the evaporator and the insertion of the air and/or part water vapour injectors at the most suitable points in order to obtain optimum agitation; and this improves the quality of the grain.

It is a proven fact in all sugar refineries that the agitation of the mass results in the reduction of the number of twin crystals and the considerable increase of single crystals. This signifies the reduction of occlusions of beet juice between the faces of the twin crystals and the retention of beet juice in the actute angles which the secondary crystals form with the principal crystal in the twin crystals which entails the reduction in the remains of the content of the sugar crystals obtained with the same syrup in a chamber with or without agitation.

The same also occurs with the ICUMSA colour of the sugar crystals. The reduction of the remains is of the order of 35% and that of the colour 30% when using the proposed method.

On the other hand, whatever type of agitation is used it avoids centres of excessive super-saturation and thus the formation of false grain during the course of baking, improving the uniformity of the grain obtained.

Hereinafter there will be discussed the incidence of this improvement in the uniformity during centrifugation, increasing the advantages obtained.

This thus represents a reduction in baking time and vapour consumption.

The agitation of evaporators with air and/or part water vapour guarantees a reduction in baking time which is greater than 25 or 30%. This effect is more marked in evaporators of secondary and tertiary products, i.e. of a low degree of purity, in which the formation of bubbles in the inner part of the mass activates boiling and improves to a surprising degree the heat transmission, even with very high viscosities.

It may be estimated that in the evaporators the vapour consumption is of the order of 130% of the water evaporated therein, owing to the heat losses during the long period of time during which the mass remains in the evaporator.

For each thousand tons of beet proceses the vapour consumption in the evaporators may be separated into: Vapour for evaporating and concentrating 107,700kg Vapurconsumed over the whole period of time ........................................ 32,230 kg Total , 140,000 kg vapour If the backing time is reduced by 25%, logically the vapour consumption in terms of losses will be reduced by the same proportion, i.e. 8,075 kg.

To this saving in vapour, there should be added, principally in the crystallization of products of low purity, the vapour necessry for evaporating the water which the boiler introduces into the chamber so as to maintain boiling - "the movement" - of the chamber, and which will not be estimated here, although it is not preposterous to rate if at 700 Kg. for each 1,000 tonnes of beet processed.

A further advantage is the production of improved fluidity in the increase of the baking operations: practical experience with evaporators has shown that when an evaporator is not agitated if it has to be raised rapidly, owing to the manufacturing step, it has to be raised "closed" from below, since, if it is diluted, whereby improved crystals would be obtained, when the attempt is made to concentrate it when the evaporator is full, the process is so slow that it is reached by the syrup and the very liquid evaporator has to be emptied and a low yield of crystals and large quantity of beet juices are obtained.

Whether the agitation is performed with air or mechanically it enables the chamber to be closed at the appropriate moment, thus obtaining a greater quantity of crystals and a more degraded beet juice.

From the formula provided by the crystal yield: Crystal yield % = - mass purity - beet juice purity x 100 100 - beet juice purity it may be seen that for the reduction from 79.5 to 78.5 of the beet juice purity, the mass having a degree of purity of 90.0, the crystal yield increases from 51.22% to 53.49%, i.e. an increase of 4.5% in the quantity of crystals.

Maintaining the baking "liquid" i.e. slightly concentrated, prevents the formation of new grains when the chamber is raised, which hitherto has rendered turbination difficult and increases the remains and the colour of the sugar obtained. It also reduces the base volume.

In many of the chambers constructed the requirement of covering the tubular cavity with the syrup, for concentration and crystallization, necessitates the use of an excessively bulky "baking base" which causes some sugar grains to be extremely thin.

If agitation occurs, as is proposed, this base may be substantially reduced, since, although the syrup is not sufficient to cover the tubular body completely, it is performed with an approximately constant admission of an additional volume of air, which causes the mass to move over the upper tubular plate thus avoiding local overheating and the (socarrones) which are produced since they do not move.

In particular cases such a substantial reduction of the baking time enables the process to be performed according to a new method, which in turn enables sugar crystals of a greater size to be obtained without having to use more than one evaporator for the production of crystallization, in which there is a large baking base which is practically double the normal and once crystallization and clarification has occurred half of this base is passed to another evaportor and the two two evaporators are raised simultaneously or one slightly after the other.

It should be noted that this facilitates the incorporation of the beet juice.

When baking the first product it is normal practice to add to the evaporator, when the baking is advanced, the beet juice obtained in previous baking operations, generally that having the highest degree of purity or richest beet juice, whereby it is possible to degrade the beet juice and lower the proportion of crystals in the mass, providing them with improved fluidity, which facilitates their passage to the turbines.

However, it is well known that it it not always easy to achieve rapid incorporation of the beet juice in the mass, as a short time occurs comprising two different phases. It is at this time that the small crystals which always accompany the beet juice grow. If the evaporator is agitated with air and/or a portion of water vapour in accordance with this description, on making it more diluted, the mixture with the beet juice is scraped off and it is possible forthe very small crystals to be removed.

When baking products with a lower degree of purity there is often added at the end of baking a beet juice with a lower degree of purity in order to be able degrade it to concentrate or "seal" the chamber and which simultaneously assists the fluidity of the mass. The speed at which this beet juice is incorporated is fundamental for obtaining optimum degrading. It also signifies facility of turbination.

It has been stated above, that whatever type of agitation of the evaporator is used, by avoiding points of excessive supersaturation it avoids the formation of false grain and twin crystals, with the result that the proportion of single crystals in the mass increases considerably and thus the uniformity of the crystals increases.

When this mass, with a greater uniformity of crystals, passes to the centrifuges a "cushion" or filtering mass of crystals forms, the openings of which are not blocked by small crystals and the beet juice flows easily therethrough. This allows the load of the mass per turbine to be increased, utilizing its capacity and at the same time reducing the total time of centrifugation.

This also occurs with the washing processes which may be reduced without impairing the quality of the sugar obtained, reducing the amount of water and thus reducing the beet juices which form to a far greater degree.

Referring in particular to the ASEA centrifuges, which are used practically everywhere in Spain for the turbination of primary products, these have a cycle per turbine of approximately 145 seconds. The reduction of this cycle by seven seconds, which is easy to achieve by improving the uniformity of the grain - as is provided by the invention - signifies an increase of 5.2% of the turbination power of each machine and, in addition, the mass load per turbine is greater.

In the case of continous centrifuges, which today are used to turbinate products of a low degree of purity, the greater uniformity of the crystals enables more use to be made of the machine's capacity, providing a better flow of the mass, whilst the product obtained is not impaired and the limit of the amperage of the motor is not reached.

A lower consumption of water in the washing process of the sugar is also obtained. The improvement in the uniformity of the grain results in the reduction of water for washing the sugar grains.

In the centrifugation of primary material mass, the spreader tube of the ASEA centrifuges provides a flow of approximately 73 litres/minute. The reduction of only 2 seconds in the washing processes from the 14 to 15 which it normally takes, implies a reduction of 73 60 which, when the external film of crystal dissolves, is transformed into 2.43 = 12.15kg.

0.20 of beet juice of 80 Brix.

As approximately 800 cycles are performed for 1,000 tons of beet, the following reduction in first class beet juice is obtained: 800 x 12.15 kg = 9,620 kg. of beet juice.

In the turbination of intermediate products (second class products, refined, intermediate, etc.) it is possible to obtain a reduction of water in the continuous centrifuges of approximately 360 litres for each 1,000 tons of beet and an equal quantity is obtained in the centrifuges which separate the final molasses. If this is expressed in beet juice of intermediate products and in molasses, of 83 and 84 Brix respectively the following results are obtained: Reduction of secondary product beet juice 360 ~ 0.17- = 2,118 kg beet juice Reduction of tertiary product molasses 360 = 2,250 kg molasses 0.16 In this latter case this lower quantity of molasses signifies an approximate reduction of 0.1 kg saccharose which becomes molasses for each 100 Kg of beet processed.

The possibility of improved grinding in the factory is also a further advantage. The large investment which is required for a factory in the sugar field means that the factories which have a large grinding and evaporating capacity are obliged to retain a large part of the syrup in large deposits in order that this syrup may be converted into crystallized sugar when the grinding of the beet is completed, for which a great deal of energy is required.

The reduction in baking time per evaporator is equivalent to a corrsponding expansion of the sugar proportion and therefore to the increase in its beet grinding and processing capacity, which is achieved in a manner which is not expensive and with simple means.

All these above features lead to improved sugar sales.

Whatever the improvement in the finished product may be, in this case the reduction of the ICUMSA colour and the content of the sugar remains, together with the improved grain quality, it renders it easier to sell or possible to be sold at a better price.

Summarizing what has been stated above, the agitation of the chambers with compressed air and/or with part water vapour may be assessed as follows: 1. - It requires average investment for its installation which may be expanded according to the conditions of each factory with the installation of a new vacuum pump and the extension of the collector which carries the non-condensable substances from the barometric column to the vacuum pump; 2. A reduction in the energy consumed between an evaporator with mechanical agitation and agitation by air according to Kw consumption; 3. Reduction in investment of the order of 2 to 5 million Pesetas per chamber with mechanical agitation to an investment of 0.9 to 1.3 for agitation with air and/or part water vapour according to the features of the installation to be produced; 4.Possibility of agitating any type of chamber where mechanical agitation is not possible; 5. Reduction of vapour consumption of 8,775 kg. for each 1,000 tonnes/day of beet, which, assuming an evaporation in boilers of 12 kg vapour per kg. fuel, heating vapour of chambers of the secondary evaporation effect and afuel price of 23 Pesetas/kg., signifies: 8,775 xffix 23 = 8,410 Pesetas/day; 2 12 6. For an improved degrading of the best juice having 1 degree of purity in the primary product, the increase in crystals is estimated to be 4.5% since the crystals increase from 51.22% of the mass to 53.49%, i.e an increase of 2.27 kg crystals per 100 kg mass.Logically this signifies a reduction of the beet juice of 2.27/0.785 = 2.89 kg beet juice with a 78.5% degree of purity.

For each 1,000 tons of beet/day this would be: 336,000 x 2.89/100 = 9,710 kg beet juice which added to the 9,620 by which the beet juice is reduced for the lower consumption of water in the washing process for white sugar results in 18,330 kg., which converted into the mass of the secondary products gives approximately 17,100 kg which in turn gives 46% crystals and 54/080 = 67.5 secondary product beet juice with degrees of purity of 83.6% and 69.7% of the mass and beet juice respectively. If this is transformed for grinding 1,000 tons beet/day the result would be: Reduction of sugar crystals to be remelted 17,100 x 0.46 = 7,860.

Reduction of secondary product beet juice to be baked to form the tertiary product 17,100 x 0.675 = 11,542.

The sugar crystals to be remelted, dissolved in juice or water produce 7,860 = 11,228 kg. remelted syrup, 0.70 which will pass to evaporators containing the primary product, producing 8,733 kg. of mass of 900Brix. That is to say, the amount of the mass of 336,000 kg. for each 1,000 tons of beet is reduced to 327,270 kg., i.e. a reduction of 2.6%. The 11,542 kg. of beet juice which has been reduced added to the 2,188 kg. owing to the reduced consumption of water in the secondary product will give 13,730 kg. beet juice which would be reduced and which would give 11,828 kg. reduced mass of the tertiary product when it is concentrated to 80 to 93 Brix.

The 71,000 kg. of tertiary product mass which are produced, assuming that there are 71 kg. per ton of processed beet, will be reduced to 71,000 - 1,828 = 59,200 kg. of tertiary product mass.

There would be obtained from this reduced mass, if the degrees of purity were 73% in the mass and 58.0 in the final beet juice or molasses, 35.7% crystals and 64.3/0.84 = 76.5 molasses, i.e.: Reduction of crystals to.be refined from the tertiary product ....................................... 11,828 x 0.357 = 4,222 Reduction of molasses in the tank ........................................ 11,828 x 0.765 = 9,04E Adding to this amount of molasses the 2,250 kg. by which it is reduced by the reduced use of water in the centrifuges of the tertiary product, 1 1,298 kg. will result for each 1,000 tons of beet, which are to go to the molasses tank.

At first sight these calculations appear optimistic since it is assumed that all the water which enters the centrifuges dissolves sugar and does not dilute the beet juices, but the influence which a reduction in the production of mass has for the beet juices obtained in the product with the lowest degree of purity has not been taken into account.

It is only being attempted with these calculations to provide a general idea of the importance which agitation of the baked mass in chambers with air and/or part water vapour may have with respect to the technical evaluation of the results on completion of an operation, which is definitely what decides the improvements and amendments to be made in intermediate operations.

It essentially consists in the introduction of a novel procedure not known hitherto owing to its apparent incongruity, due to the fact that it has never been thought advantageous for air and/or part water vapour to be injected into a unit in which a vacuum is produced for particular operations.

In practice it is performed by incorporating suitable mechanical elements programmed so as to be subordinate to the cycle for which it is intended and assembled at different positions, advantageously in the baking apparatus, these incorporated elements connecting with the material to be treated which, by means of air and/or part water vapour pulses, establish the desired intensity and duration of agitation, resulting in the very rapid finishing of this product.

As may be seen from the above, the system enjoys a high degree of versatility and there are no mechanical restrictions on its application which is possible in a wide range of industrial processes and, on a small scale, experimental processes.

The parts used for the injection of air and/or mixed with water vapour, as well as their incorporation in the reactors in which they may be used, are either available on the market or are very simple to manufacture, which renders their use highly attractive and, since they are robust, give them a long useful life.

The invention and an embodiment thereof having been described it is stated that details thereof may be modified provided that these do not affect the fundamental principle of the invention.

Note Summarizing: the Patent Of Invention is based on the special features which are as follows:

Claims (1)

1. Method for the agitation of liquid masses under vacuum by means of pneumatic injection, characterised in that these liquid masses are constituted by diluted solutions to be concentrated in heat boilers; there are incorporated in these boilers means for injecting air alone or enriched with water vapour, in such a way that the stream of fluid causes agitation owing to the reaction which is established in the internal vacuum of the boilers or reactors in which this method is used; in that the flow of the said stream may be controlled so that its magnitude may be subordinate to the effect which may be established in a predetermined manner.