PNEUMATIC S.
N.
TRANSPORTATION Revenko
and
G.
I.
OF
SODA ASH UDC
II'chenko
666.1.022:621.867.8
Pneumatic transportation, which is being used more widely in various branches of industry and agriculture, has a number of advantages over other f o r m s of transportation. Its virtues include continuity of the transportation p r o c e s s , possibility of complete mechanization and automation of the p r o c e s s , c o m p a c t ness, no l o s s e s of m a t e r i a l s during transportation, and improvement of working conditions from a health standpoint and of safety conditions. Pneumatic transportation of powdered m a t e r i a l s can be accomplished both with a minimum c o n c e n t r a tion of the mixture and with the maximum, when the solid particles move as a continuous stream, forming, as it were, a g a s - e v a c u a t e d porous piston. With a low concentration of the mixture, the particles of the material are inevitably imparted with high kinetic energies, proportional to the square of their velocity. The particles, striking one another and the wall of the pipeline, disintegrate, which leads to their c o m m i n u t[on, change of shape, and ultimately to a change of physicomechanical p r o p e r t i e s . Comminution of the particles of the material as a result of pneumatic t r a n s p o r t in some c a s e s is a favorable phenomenon, f o r example, the quality of cement is improved in so doing. However, in most c a s e s comminution leads to adverse results. Thus, the germination rate of grain becomes worse, granulated catalysts b e c o m e unfit, soda ash flows poorly, becomes lumpy, and sticks in hoppers, spouts, and batching devices. The effect of various methods of pneumatic transportation on the physicomechanical p r o p e r t i e s of soda ash is shown in this article. A t p r e s e n t at soda plants of our country the soda is sent from the calcination department to sodastorage silos by pneumatic screw pumps, produced by the K r a s n o g o r s k Cement Machine Construction Plant, along pipelines with a d i a m e t e r of 150, 200, and 250 ram. This form of transportation is c h a r a c t e r i z e d by high flow velocities of the a i r - d i s p e r s e d mixture and its low concentrations, its use showed that after
Fig. 1
Fig. 2
Fig. 1. P h o t o m i c r o g r a p h of soda ash particles before pneumatic t r a n s p o r t a t i o n (35 • Fig. 2. P h o t o m i c r o g r a p h of soda ash particles after pneumatic t r a n s portation (35 • State Scientific R e s e a r c h and Design Institute of Basic C h e m i s t r y (NIOKhIM). Steklo i Keramika, No.. t, pp. 8-10, February, 1971..
Translated from
9 1971 Consultants Bureau, a division of Plenum Publishing Corporation, 227 West 17th Street, New York, N. Y. 10011. All rights reserved. This article cannot be reproduced for any purpose whatsoever without permission of the publisher. A copy of this article is available [rom the publisher [or $15.00.
75
TABLE
1
Properties of soda after transportation by existingpneumatic transport
Index
Bulk weight, kg/m3. . . . . . . . . . . . . . . Angle of repose, deg . . . . . . . . . . . . . . . TABLE
546 38
2
Composition, %
Type of transport
In interval of dispersity, p /
1
/
/
t
t
f--~
63 Worm conveyerfromealciningfurnace . . . . . . . . . . . . Existing pneumatictransport . . . . . . . . . . . . . . . . . . . Experimental pneumatic transport in dense layer . . . . . . TABLE
3
Interval of dispersity,
Bulkweight, kg/ms
Angle of repose
I 1.8 | / 1.2 / [ 5.2 /
2.4 | 0.6 | 1.6 [
1.8
1,9
1 3.8
I 6"5
34.8 19
i.1
r 4.8
32.7
29 58.4 25,8
24.4 16.4 28.8
pneumatic transportation the flowability of soda d e c r e a s e s markedly and its capacity for sticking in large and small vessels, spouts, and batching devices increases.
The change of physicomechanical properties of soda ash after pneumatic transportation h a m p e r s its use. How30o40, 588 438 36~ ever, for p l a n t - c o n s u m e r s whose production p r o c e s s r e 41o40' 374 quires dissolution of the soda, the change of its p r o p e r t i e s does not affect the production p r o c e s s or quality of the finished product. P l a n t - c o n s u m e r s using soda in a dry form c a t e g o r i c a l l y refuse to use such soda. For instance, the main c o n s u m e r of soda ash, the glass industry, was forced to reject the use of pneumatically t r a n s p o r t e d soda, since the change of its physicomechanical p r o p e r t i e s adversely affected the process of making up the batch and its quality, which in turn affected the p r o c e s s of glass founding and the quality of the finished product. .htong with this, the poor flowabiltty and propensity for caking of soda precluded the possibility of using l a r g e - s c a l e mechanization and automation of the p r o c e s s of making up the batch. In connection with this, the State Scientific R e s e a r c h and Design Institute of Basic Chemistry (NIOKhIM) c a r r i e d out studies to determine the physicomechanical p r o p e r t i e s of pneumatically t r a n s p o r t e d soda and to find a form of pneumatic transportation which would not substantially affect the properties of soda. Total sample 250 250--125 125--74 74
500 600
44~
The following physicomechanical p r o p e r t i e s of soda were studied: bulk weight, angle of repose, and grain size. Plant.
The investigations were c a r r i e d out at the V. I. Lenin Lisichansk Soda Plant and Lisichansk Glass The data given in Tables 1 and 2 are averaged, obtained from several determinations.
As we see from the tables, soda ash is greatly pulverized as a result of pneumatic transportation, which a d v e r s e l y affects its friability. The deterioration of the friability of soda is expressed by a marked increase of the angle of repose, which reaches 44 ~ The bulk weight of soda in the case of free pouring after the t r a n s p o r t i n g pipeline has a minimum value of 516 k g / m 3 at the entrance to the silo. After ensiling the bulk weight of soda i n c r e a s e s to 610 k g / m 3 as a result of its compaction. The i n c r e a s e of the bulk weight and caking of soda in silos and in various means of transportation is related with r e c r y s t a l l i z a t i o n of the highly dispersed fraction obtained as a result of pneumatic transportation and with crystallization Of monohydrate formed due to the moisture absorbed by the soda f r o m the air flow in which it is transported. After pneumatic transportation the moisture content of soda increased by 0.7-1.5~. P r i m a r i l y the d i s p e r s i t y of soda ash changes. The fraction with a particle size less than 100 # reaches 75~, i.e., its content i n c r e a s e s 20-25~. That the change of d i s p e r s i t y of soda determines mainly
76
TA BLE
o
-C 1-insolu~2eresidue
Composition of batch
ICI g,
~ I ~ 1 9
the deterioration of its physicomechanical properties was confirmed by a study of the bulk weight and angle of repose of individual fractions.
4
17,5" r~ t >
o
,
~
:
~, *. . . . 12" ~ ~- 18,"9"a)~ ~ .y, '~> .o
0221=011731_0101001,83, 001
As we see from Table 3, the bulk weight d e c r e a s e s and the angle of r e p o s e i n c r e a s e s with a d e c r e a s e of p a r t i cle size. On the other hand, as the small fractions are separated the angle of repose d e c r e a s e s .
Thus, the poor flowability of soda after pneumatic t r a n s p o r t a t i o n is due p r i m a r i l y to its high d i s p e r s i t y and also to an increased moisture content. ~s a consequence of the high dispersity, and consequently of the large r e a c 7 58.91-2,5 / 18,9/+1,4 t 1,8 (+0,6,9,1 +0,2 tion surface, the soda readily absorbs moisture from the air ;'-Percentage ratio of components in compositionof and subsequently cakes. Caking of soda particles of small batch required by recipe, fractions o c c u r s even during screening on l a b o r a t o r y sieves. The ability of finely dispersed soda to absorb moisture readily f r o m the air results in its caking during conveyance by various means of transportation. Thus, caking greatly h a m p e r s unloading the soda f r o m railroad cars.
2 3 4 5 6
62,01--0,4 [ 17,5[:1:0,0] 1,5 -[-0,3 19,0 +0,11 62,0/--0,4 / 17,8[+0,3[ 1,3 {+0,11 18,8 --0,1 62 5]+0,1[ 17,5[+0,0] 2,1 [-[-0,0117,9 --1,0 62,3[--0,2 / 17,3i--0,2{ 2,0 l+0,8 18,4 --0,5 62,1{--0,3{ 17,6]+0,11 1,6 /+0,4 18,7--0,2[
An x - r a y analysis showed that the lumps of caked soda contain monohydrate, which f o r m s as a r e sult of the absorption of w a t e r vapor f r o m the a i r by the hot soda charged into the soda c a r s . The high t e m p e r a t u r e of the soda p r o m o t e s its r e c r y s t a l l i z a t i o n and c r y s t a l l i z a t i o n of monohydrate. If we a s s u m e that 1% of the m o i s t u r e present in the pneumatically t r a n s p o r t e d soda f o r m s monohydrate, this is sufficient to bind about 6~ of the soda. Figures 1 and 2 show photomicrographs of p a r t i c l e s of soda ash before and after pneumatic t r a n s p o r tation by a pneumatic s c r e w pump. The data of the photomicrographs c l e a r l y show the effect of pneumatic t r a n s p o r t a t i o n on the d i s p e r s i t y of soda particles. To reduce the degree of comminution and caking of soda it is n e c e s s a r y to t r a n s p o r t it with a small amount of air, which is secured by using the method [1] developed by the Institute of Organic Chemistry, Academy of Sciences of the Armenian SSI1. On the basis of this method, in 1969 we developed and tested at the Lisichansk Soda plant a l a b o r a t o r y device consisting of three c h a m b e r feeders with top delivery of the material, each with a capacity of 0.25 m 3. Two c h a m b e r s alternately pump the s o d a - a i r mixture into the third c h a m b e r in which the p r o c e s s of demixing and formation o c c u r s with its continuous delivery to the main pipeline. The operating p a r a m e t e r s of the device are: productivity 6.5-7 tons/h, flow of c o m p r e s s e d air 70-80 m3/h, s~arting p r e s s u r e 5.2 gauge aim, t r a n s p o r t i n g p r e s s u r e 3-3.2 gauge aim, reduced length of the main pipeline 130 m, d i a m e t e r 45 x 3 ram. By means of the device we tranported an experimental lot of soda in a quantity of 23 tons (cement r a i l r o a d car) which was sent to the Lisichansk Glass Plant for testing. The physicomechanical p r o p e r t i e s of the soda ash t r a n s p o r t e d by this device are given in Tables 1 and 2. Testing of the experimental lot of soda at the Lisichansk Plant did not result in any difficulties in unloading the car, delivering it to the hopper by the existing t r a n s p o r t i n g system, or adding it to the batch. The r e s u l t s of analyzing the batch obtained by the plant l a b o r a t o r y are given in Table 4. .As we see from Table 4, soda does not substantially affect the mesh size of the batch, its behavior in the batch is s i m i l a r to the behavior of soda which has not been t r a n s p o r t e d pneumatically, although a slight i n c r e a s e of d i s p e r s i t y is noted. We can conclude from these investigations that pneumatic t r a n s p o r t a t i o n at low velocities and with high concentrations of the mixture, i.e., pneumatic transportation in a dense layer, does not substantially change the physicomechanical p r o p e r t i e s of soda ash. LtTERATUR 1.
E CITED
A u t h o r ' s Certificate No. 107815.
77
