RU2458978C1 - Method of producing granular synthetic detergent - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method is realised in an apparatus shown on dwg.1. The method involves dividing a synthetic detergent composition into two streams, one of which is sprayed by nozzles uniformly fitted in the horizontal plane on the periphery of the upper level of a cylindrical drying chamber. The second stream is sprayed by nozzles lying below the spraying level of the first stream. Moisture content of particles of the synthetic detergent in the drying chamber on the spraying level of the second stream must in the range of 15-25%. The sprayed composition is dehydrated in an ascending stream of a heat carrier which is fed on the lower level of the drying chamber and comes out from the upper level into a cleaning system. Dust from the heat carrier cleaning system is fed into the zone of the bottom of the drying chamber and mixed with the discharged powder. The dust fraction is separated from the powder in an airlift separator and comes out of the process as the ready product - granular synthetic detergent with residual dust content. The dust separated from the powder is returned into the drying chamber and fed into the spraying zone of the second stream, wherein the dust is fed into the near-wall annular region of the drying chamber towards the bottom with minimum distance from the axis of the drying chamber 0.85R, where R is the radius of the drying chamber.

EFFECT: efficient utilisation of dust when feeding it into the drying chamber, avoiding significant accumulation of dust in the apparatus and providing high consumer properties of the product.

1 cl, 4 ex, 4 tbl, 2 dwg

Description

The invention relates to a spray drying technique, primarily to the production of powdered synthetic detergents (CMC) with a minimum content of fine fraction (dust). This fraction makes packing difficult, irritates the mucous membrane of the respiratory tract, and causes allergic diseases of personnel.

A known method of producing granular powders in installations of spray dryers equipped with apparatuses with a fluidized bed. According to this method, dry fine powder from the dryer is fed to a fluidized bed apparatus, where dust is also introduced from the unit’s aspiration systems [1]. The powder is agglomerated with the supply of a binder in the layer. A combination of agglomeration in the fluidized bed and dust recycle with its introduction into the spray zone of the dryer are also used [2]. However, in CMC production, these methods are not widely used due to the abrasion of CMC particles in the fluidization process and the need for additional functional systems.

A known method for the disposal of dust, in which the dust from the suction or separation systems is fed into the dryer and introduced into the spray zone. In this case, part of the dust particles collides with droplets of atomized liquid and aggregates with them, forming agglomerates [3, 4]. The main obstacle to using the method is the lack of efficiency of the agglomeration process. With a single entry into the spray zone due to the low probability of contact of dust particles and droplets of the sprayed product, not more than 10-20% of the introduced dust is utilized. In a continuous process, dust consumption in recycling increases. According to the method proposed in the patent [4], the consumption of circulating dust is more than an order of magnitude higher than the productivity of a powder with a target particle size distribution.

Closest to the proposed invention are methods for producing granular powders described in the patent [5] and copyright certificates [6, 7]

US Pat. [5] proposes a dryer for dewatering high-cost CMC compositions. A composition with a moisture content of 35-45% and a temperature of 70-90 ° C is divided into several streams, one of which is sprayed with nozzles uniformly installed in a horizontal plane at the periphery of the upper level of the cylindrical drying chamber, and the remaining composition is sprayed with nozzles also uniformly installed in a horizontal plane on the periphery of the zone of the drying chamber at levels below the spray level of the first stream. The sprayed composition is dehydrated in an upward flow of coolant, which is introduced with a temperature of up to 350 ° C at the lower level of the drying chamber and is withdrawn to the cleaning system from its upper level with a temperature of up to 90 ° C. The dry powder is removed from the bottom of the drying chamber. Countercurrent drying and spraying of the composition at several levels contribute to self-organization in the drying chamber of a rather long agglomeration zone. By analogy with the process in a scrubber, dust particles, which are saturated with the upward flow of coolant, are in contact with a curtain of falling drops and agglomerate. The two-spray dryer of this patent is currently widely used in CMC manufacturing. The powder from the dryer contains up to 8% of dust (fractions with a particle size of up to 0.2 mm), however, after mixing with the cyclone fraction, dust is at least 15%. This is less than the dust content of the powder from the installation of a similar dryer with a single spray level, however, the powder is significantly dusty.

In the copyright certificates [6, 7], adopted as a prototype, a method for producing granular CMC in a countercurrent spray dryer with one spray level is proposed. The CMC component, finely dispersed sodium tripolyphosphate, is blown tangentially into the side of the drying chamber in two streams. It is essential that for the efficiency of the agglomeration process, sodium tripolyphosphate is blown into the zone of the drying chamber with a moisture content of particles of the composition of 18-25%. In this moisture range, CMC compositions have the highest adhesion to dusty, dry particles. Additionally, sharp steam is supplied to the input zone. The resulting powder contains by weight up to 8.3% fraction up to 0.25 mm, particles over 3 mm in powder up to 4.3%. The disadvantage of this method is to obtain a powder with a wide range of dispersed composition, which reduces its consumer performance, in particular bulk density and solubility. In addition, the application of the method limits the use of steam and the lack of data on the agglomeration of dust discharged from the heat treatment system. It should be assumed that dust recycling was not used and dust from cyclones (up to 10% of the powder productivity) was removed from the process.

The aim of the invention is the effective utilization of dust when entering it into the drying chamber, eliminating the substantial accumulation of dust in the installation and ensuring high consumer performance of the product.

This goal is achieved in that the CMC composition with a moisture content of 35-48% is divided into two streams, the first stream is sprayed with nozzles uniformly installed in a horizontal plane on the periphery of the upper level of the cylindrical drying chamber, the second stream is sprayed with nozzles located below the spray level of the first stream in horizontal planes on the periphery of the zone of the drying chamber with a moisture content of particles of the sprayed composition of 15-25%, dehydrate the sprayed composition in an upward flow of coolant, which drive at the lower level of the drying chamber and withdrawn to the cleaning system from its upper level, the dust fraction from the heat carrier cleaning system is introduced into the zone of the bottom of the drying chamber, powder containing the dust fraction is unloaded from the bottom of the drying chamber, the dust fraction is extracted from the unloaded powder and removed as the finished product is a powder with a residual dust fraction, the extracted dust fraction is introduced into the drying chamber in the spray zone of the second stream, and the dust fraction is introduced into the wall ring region of the drying sill chamber towards the bottom at a minimum distance from the axis of the drying chamber 0,85R, where R is the radius of the drying chamber.

The invention is illustrated by the accompanying drawings, in which Fig. 1 shows a block diagram of an installation in which the proposed method is carried out, Fig. 2 is a graph of the distribution of irrigation density and humidity of the sprayed CMC composition in the cross section of the drying chamber at the spray level of the second composition stream.

The installation of Fig. 1 includes a spray dryer 1, which contains a drying chamber 2, a bottom 3, a gas supply 4, an upper 5 and a lower 6 nozzle manifolds 7, and also includes: a heat generator 8, a preparation and supply unit 9, cyclones 10, an airlift 11 , airlift separator 12, bag filters 13, dust pneumatic conveying lines 14 and 15. Dust communication 16 is used when operating the unit without dust recycling.

The graphs of figure 2 presents the experimentally obtained distribution of the density of the irrigation density "G" (mass flow rate of the sprayed composition CMC per unit cross-sectional area of the drying chamber, dimension in kg / m ² h) and the moisture content of the particles of the composition "W" (dimension in mass% moisture content ) The distributions are shown depending on the relative radius r / R, where r is the current radius, R is the radius of the camera. The graphs show that at the spraying level of the second composition stream in the wall zone of the drying chamber in the annular space from the composition flow in the wall zone of the drying chamber in the annular space with a radius of more than 0.85R, where R is the radius of the chamber, a downward concentrated stream of particles with a moisture content of 20 -25%, and the average value of the density of irrigation in this zone is more than twice the density of irrigation in the rest of the radial section. The conditions for agglomeration in this zone are optimal: an increased concentration of wet particles provides a high probability of their contact with dust particles, and moisture content - an effective agglomeration of particles upon contact. The preferred direction of dust input is toward the bottom of the drying chamber. In this case, a unidirectional mixed flow of dust and wet particles is realized, which prevents the penetration of dust into the central zone of the drying chamber, i.e. the return of dust to recycling by means of ablation from the chamber by an upward flow of coolant. Thus, the introduction of the dust fraction into the spray zone of the second stream of the composition into the wall annular region of the drying chamber towards the bottom at a minimum distance from the axis of the drying chamber of 0.85R ensures efficient dust utilization and eliminates significant dust accumulation in recycling.

The method is as follows (see figure 1). Prepared in block 9 according to a given recipe, the composition is divided into two streams, fed at a pressure of 50-70 kg / cm ² at a temperature of 60-90 ° C and with a moisture content of 35-48% in collectors 5 and 6 of dryer 1 and sprayed with nozzles 7 on two levels of the drying chamber 2. Nozzles of each level are uniformly located in one plane on the periphery of the drying chamber. The sprayed composition is dehydrated in an upward flow of coolant, which is prepared in a heat generator 8 and introduced into the lower level of the drying chamber through a gas supply 4. The spent dusty coolant is removed from the upper level of the drying chamber to cyclones 10, the dust from which is returned via a pneumatic conveying line 14 to the dryer in the bottom zone 3, where it is mixed with poured powder. Dry powder with a moisture content of up to 11% and a dust fraction of up to 20% is unloaded from the bottom 3 of the drying chamber. Next, the powder is cooled in an upward flow of cold air in the airlift 11. The extraction of the dust fraction from the powder is carried out in the airlift separator 12. The finished product - granular CMC with a residual dust content (particles up to 0.15 mm) of not more than 5% - is discharged from the airlift separator and removed from the process. Dusty air is taken out of the airlift separator and cleaned in bag filters 13, dust from which is fed through the pneumatic conveyor line 15 for disposal to the dryer. In order to achieve the most complete utilization of dust and to prevent accumulation of dust in recycling, the dust is introduced into the zone of the drying chamber located at the lower spray level of the composition into the wall annular region towards the bottom. The minimum radius of the annular input region is 0.85R, where R is the radius of the chamber. The agglomeration conditions in this area and the method of introducing dust are most favorable for achieving the objective of the invention.

The proposed method can be used to obtain granular CMC with various desired composition. The following are specific examples of the application of the method to obtain a powder with the following components in wt.%:

surfactants 22 sodium tripolyphosphate 40 sodium methyl silicate one carbomethyl cellulose 2 optical brightener 0.1 sodium sulfate 24 water 10

Examples 1-3 show the effectiveness of the proposed method for reducing dust content in CMC powder. In example 4, the granulometric compositions of the powders obtained by the known method [7] and the proposed one are compared.

Work is carried out on the installation of figure 1. The diameter of the drying chamber is 8 m, the height of the active drying zone is 14.9 m. The composition is sprayed on two levels. The number of installed nozzles at the upper and lower levels, respectively, 12 and 20. The distance between the levels of the nozzles is 8.6 m. Dust from cyclones is introduced into the bottom of the dryer, dust from bag filters is introduced into the drying chamber according to the proposed method. In the method without recycle, the dust discharged from the bag filters 13 is introduced via communication 16 into a powder discharged from the airlift separator 12. The dust consumption is measured at the outlet of the bag filters.

Example 1. The temperature of the coolant at the inlet 210 ° C, at the outlet 68 ° C. The moisture content of the composition is 48%, the moisture content of the powder is 8-9%. Number of working nozzles: top - 4 pcs., Bottom - 11 pcs. Powder performance 13100 kg / h. The powder and dust consumption in table 1.

Table 1 The method without dust recycling The proposed method Granulometric composition, mm less than 0.15 0.15 ... 0.425 0.425 ... 1.18 more than 1.18 less than 0.15 0.15 ... 0.425 0.425 ... 1.18 more than 1.18 Wt% 16.53 48,2 33.97 1.3 5.02 34.09 56.45 4.26 Bulk weight kg / m ³ 365 360 Dust consumption, kg / h 2280 2540

Example 2. The temperature of the coolant at the inlet 270 ° C, at the outlet 72 ° C. The moisture content of the composition is 40.6%, the moisture content of the powder is 11.5%. Number of working nozzles: top - 7 pcs., Bottom - 9 pcs. Powder performance 15500 kg / h. The powder and dust consumption in table 2.

table 2 The method without dust recycling The proposed method Grading less than 0.15 0.15 ... 0.425 0.425 ... 1.18 more than 1.18 less than 0.15 0.15 ... 0.425 0.425 ... 1.18 more than 1.18 Wt% 16.58 48.29 31.83 3.3 3.21 28.41 61.28 7.1 Bulk weight, kg / m ³ 415 405 Dust consumption, kg / h 2560 2960

Example 3. The temperature of the coolant at the inlet 255 ° C, at the outlet 70 ° C. The moisture content of the composition is 45%, the moisture content of the powder is 11%. Number of working nozzles: top - 7 pcs., Bottom - 5 pcs. Powder production 14,200 kg / h. The powder and dust consumption in table 3.

Table 3 The method without dust recycling The proposed method Grading less than 0.15 0.15 ... 0.425 0.425 ... 1.18 more than 1.18 less than 0.15 0.15 ... 0.425 0.425 ... 1.18 more than 1.18 Wt% 13.57 44,42 39.26 2.95 4,56 33.18 55.84 6.42 Bulk weight kg / m ³ 420 410 Dust consumption, kg / h 2100 2540

From examples 1-3 it follows that the use of recycling according to the proposed method provides an average of 3-fold reduction in the fraction content of less than 0.15 mm in the product. Significant dust accumulation in the recycling system does not occur: dust consumption during drying without recycling is 5-17%, while drying with recycling 18-19% of the powder productivity.

Example 4. Table 4 shows a comparison of the particle size distribution of the powders obtained by the known method [7] and the proposed. The composition of the powders obtained by the proposed method is given according to the results of 9 experiments. The table shows that the granular CMC obtained by the proposed method is superior to that obtained by the method of the prototype in terms of particle size distribution.

Table 4 Granulometric composition, mm The content of fractions of the powder, wt.% Known method The proposed method more than 3 1.1-4.3 absent 2 ... 3 23.8-24.5 absent 1 ... 2 28.9-30.3 twenty 0.5 ... 1 23.2-26.4 57.5 0.25 ... 0.5 5.1-5.4 fifteen less than 0.25 6.9-8.3 no more than 7.5

Literature

1. German patent No. 2352894, A23C 1/04, 04/30/1975.

2. Popov A.E. et al. Investigation of the process of granulation of Belofor in a spray dryer. Proceedings of TSPU, Tula, 2007.

3. German patent 1629016, F26B 3/12, 01/10/1970.

4. RF patent 2006494, C05B 7/00, 01/30/1994.

5. US patent No. 3629955, 34/17, 159 / 4.04, C11D 11/02, B01D 1/16, 06/31/1970.

6. USSR author's certificate No. 536222, C11D 11/02, 03/04/1977.

7. USSR copyright certificate No. 697560, C11D 11/02, 11/15/1979.

Claims (1)

The method of obtaining granular synthetic detergent, which consists in the fact that the CMC composition with a moisture content of 35-48% is divided into two streams, the first stream is sprayed with nozzles uniformly installed in a horizontal plane on the periphery of the upper level of the cylindrical drying chamber, the second stream is sprayed with nozzles located below the level of spraying the first stream in a horizontal plane at the periphery of the zone of the drying chamber with a moisture content of particles of the sprayed composition of 15-25%, the composition in the upward flow of the coolant, which is introduced at the lower level of the drying chamber and discharged into the cleaning system from its upper level, the dust from the coolant cleaning system is introduced into the zone of the bottom of the drying chamber, powder containing the dust fraction is discharged from the bottom of the drying chamber, dust is extracted from the powder the fraction and the powder with the residual content of the dust fraction is removed as a finished product, the extracted dust fraction is introduced into the drying chamber in the spray zone of the second stream, characterized in that the dust fraction w is introduced into the near-wall region of the annular drying chamber towards the bottom at a minimum distance from the axis of the drying chamber 0,85R where R - radius of the drying chamber.

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