RU2547741C2 - Method of flushing of fine precipitate on filter web - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to washing off fine precipitates of organic pigments from water-soluble impurities at filter web and can be used in chemical industries. Removal of water-soluble impurities is conducted at intermittent feed of flushing water. Note here that after filtering said precipitate is blown by compressed air at 0.25-0.35 MPa. After queen cell is removed from precipitate, flushing water is fed for a time interval that ensures the termination of decrease in concentration of water-soluble impurities by used flushing water. Then, flushing water feed is terminated and held in precipitate flow pores for a time required for increase in concentration of water-soluble impurities in flushing water to equilibrium concentration or that approximating thereto. Flushing water is displaced from precipitate flow pores by compressed air. Cycle jobs are reiterated unless required concentration of water-soluble impurities in the paste.

EFFECT: one and a half to three times acceleration in the process, two-to-four-fold decreased in flushing water consumption.

4 cl, 1 dwg, 7 tbl, 3 ex

Description

The invention relates to processes for the separation of fine suspensions with subsequent washing of the precipitate and can be used in chemical, petrochemical, pharmaceutical food and other industries.

To date, in industry, the process of washing sediments on filtering equipment is carried out on filter presses, which are a set of filter plates installed between the thrust plate and the rod of the clamping mechanism to which the pressure plate is attached, interconnected by beams. Each chamber filter plate is a support for the filter partition and is a sheet with a drainage surface and a protrusion around the perimeter (mating surface). In the center of the plate there is an opening for supplying a suspension, at the corners of the plate there are holes with internal channels for collecting and discharging the filtrate and for supplying and discharging the washing liquid. The supply of washing liquid and air to purge the sludge through the holes and channels of the filtrate discharge is carried out only on one side of the plate. The plates are combined in a package so that the channels of adjacent plates are arranged alternately on the left and right (or above and below). When clamping the plates into a single package, the holes for feeding the suspension and for removing the filtrate form collectors, and chambers are formed between the internal drainage surfaces of adjacent plates. Each chamber is surrounded on both sides by a filter wall. The design of the filter septum provides for the possibility of the suspension entering the chamber.

The filtering and washing process (described in a monograph by V.A. Zhuzhikov. Filtering. Theory and practice of separation of suspensions. - M .: Chemistry, 1971. - 440 p.) Is carried out according to the following scheme.

1. Filter plates using a clamping mechanism are connected in a single package, then a suspension is fed into the central channel, which is divided on a filter partition installed on the drainage system of each plate. First, the chambers are filled with suspension. Upon further supply of the suspension, a precipitate layer forms on the filter baffle, filling the entire chamber at the end of the filtering process. The process is carried out until the termination or decrease below a predetermined value of the filtrate flow rate, which is discharged through the internal channels in the filter plate to the side channels and is removed from the filter.

2. At the end of the filtration, the suspension is stopped, washing water is fed into one of the side channels, which through the internal holes enters the drainage system of each odd plate, passes through the filtering layer of the sediment layer through the drainage system and the internal holes of each even plate, then the washing water is collected in the channel opposite to the input and is output from the filter. If necessary, the direction of movement of the wash water is reversed, supplying the wash water, interchanging the channels of the outlet and supply of the wash water. Washing is carried out until the desired concentration of impurities in the formed precipitate is achieved.

3. The purge process is carried out similarly to the washing process, instead of washing water, compressed air is supplied to the channels.

4. At the end of the purge process, the plates are expanded and the sediment is discharged from the filter cavity.

The disadvantage of this method is the high consumption of washing water required to achieve standard values for the content of water-soluble impurities in the sediment, significant time spent on the process, the loss of the target substance due to its ablation by washing water, a decrease in the unit capacity of the equipment resulting from the formation of gaps with incomplete filling the filter chambers with sediment or transport pores with a complete and uniform filling of the filter chambers through which the washing liquid flows spine without its participation in the process of removing water-soluble impurities.

There are also known methods of washing sediments on the filter screen.

According to the certificate of authorship 710583 B01D 37/100 (published on September 12, 1975), a method for washing the filter cake is proposed, which consists in displacing the mother liquor from the filtered cake by washing with a liquid, in which it is proposed to use as washing liquid suspension containing a solid phase in an amount of 0.5-200 kg / m ³ .

The introduction of a washing liquid containing a solid phase eliminates the leakage of washing liquid through cracks and pores of large diameter.

The disadvantages of implementing this washing method on frame and chamber filter presses include the possibility of supplying washing liquid only through the central suspension feed channel, which will lead to an uneven distribution of the washing liquid over the sediment volume and, as a result, to the formation of non-washed paste zones.

According to the patent of the Russian Federation No. 2369560 (IPC 5, C01F 7/46, published 10.10.2008), a method for producing active aluminum hydroxyl by precipitation from an aluminate solution, followed by filtration and washing on a filter, is proposed. The washing process is carried out by displacing the mother liquor with water or a washing solution with alternating supply of a washing solution containing aluminum hydroxyl particles and air or steam.

The implementation of this method of washing allows you to eliminate the breakthrough of the washing liquid through cracks and pores of large diameter and to remove the mother liquor and the washing liquid from the pores of the precipitate by blowing with compressed air or steam.

The disadvantages of implementing this washing method on frame and chamber filter presses include the possibility of supplying the washing liquid only through the central channel for supplying the suspension and, as a result, the ineffective distribution of the washing liquid over the volume of the washed precipitate. As the authors themselves note, the use of this washing method does not completely remove water-soluble impurities.

Closest to the patented solution is a method of washing precipitates on filters, including displacing the mother liquor from the filtered precipitate with washing liquid by creating a pressure differential in the sediment. The process is carried out with periodic equalization of the differential pressure, the holding time of the equalized pressure is 10-20 s, and the time of one washing period is 50-80 s (copyright certificate SU No. 1022723 A (published on 15.06.1983).

The implementation of this method of washing can reduce the washing time and the volume of washing liquid by increasing the completeness of mass transfer processes in large pores and in cracks.

The disadvantage of this method is the low rate of removal of the washing liquid in the pores of small diameter and, as a result, the formation of a concentration gradient of water-soluble impurities by volume of the washed precipitate.

The technical result of the patented invention consists in a short-term increase in the rate of outflow of wash water in the pores, which forms a uniform filling of flowing pores and the elimination of stagnant zones, which allows you to remove water-soluble impurities from the sediment while reducing the process time by 1.5-3 times. Stopping the supply of washing water with its subsequent removal by blowing with compressed air allows to reduce the flow of washing water by 2-4 times, which leads to a decrease in the loss of the target substance with washing water and to reduce the volume of wastewater requiring treatment from organic compounds, salts and acids.

The technical result is achieved due to the implementation of the process of washing fine sediment on the filter screen with a cyclical flow of wash water, which consists in the fact that:

at the end of the filtering process, the mother liquor is displaced from the sediment with compressed air, the process is carried out until it expires from the "drain" channel of the filter press;

at the end of the first purge, a wash water is supplied to the filter baffle through the washing water supply channel, openings in the plates and the water distribution system.

As a result of purging the precipitate with compressed air, the mother liquor is displaced from the washing channels and the resistance of the sediment layer is small, the distribution of washing water occurs at an increased flow rate as follows: first, pores of a larger diameter are filled, which leads to an increase in their resistance and, as a result, filling of pores of a smaller diameter rinse water.

When all pores are filled with washing water, its supply is stopped and its exposure is given; during this period of time, water-soluble impurities are transferred from the paste to the pore washing water. Upon reaching equilibrium concentration or values close to it, the wash water is displaced from the flowing pores of the sediment by supplying compressed air to the channel for entering the wash water of the filter press. Further, the components of the washing cycle are repeated.

The following is a description of embodiments of the washing process on the filter baffle of finely divided precipitates during a cyclical flow of wash water.

The process of filtering and washing fine suspensions was carried out in the installation shown in figure 1.

The suspension with the help of a centrifugal pump is fed for filtration to a filter press with a flow rate (0.05 - 0.1 m ³ / h per 1 m ^{2 of} filter surface) at the initial time, ensuring uniform filling of the filter chambers, and pressure (0.6 -0.8 MPa), forming a dense precipitate not prone to the formation of ravines and transport pores. At the end of the filtering process, the suspension, determined by the fact that the flow rate is reduced to a value of 0.001 m ³ / h per 1 m ^{2 of the} filter surface, is supplied with compressed air with a pressure of 0.25-0.35 MPa to the upper channel of the filter press, the purging process is carried out for 2.5-5 minutes until the mother liquor is displaced from the flowing pores of the sediment. At the end of the purge, washing liquid is supplied to the same channel - artesian water or river water purified from mechanical impurities or water vapor condensate with a flow rate of 0.08 - 0.25 m ³ / h (per 1 m ^{2 of} filter surface), at a temperature of 18- 22 ° C. The washing liquid supply process is stopped after 5-12 minutes or upon the fact that the decrease in the concentration of water-soluble impurities in the washing water is stopped. Then the wash water supply is stopped for 5-10 minutes. The washing liquid is stationary in the sediment without excess pressure until the equilibrium state of the concentration of water-soluble impurities in the paste and the washing water of the pores or values close to it is reached. Next, the wash water from the pores is replaced by compressed air according to the procedure described above. The components of the cycle are repeated until the desired concentration of water-soluble impurities in the paste is achieved.

The invention is further explained with reference to specific examples of the method.

Example 1

Filtering-washing was carried out using a suspension of Pigment orange G, having the characteristics shown in table 1.

Table 1
The component composition of the suspension Pigment orange G Pigment t,% wt. NaCl,% wt. Na ₂ SO ₄ ,% wt. HCl,% wt. H ₂ SO ₄ ,% wt. Organ. approx. % of the mass. H ₂ O,% wt. Disp. composition of tv. phase, microns sol. not sol. 3,5 1.28 0.04 0.39 0.02 0,07 0.09 94.56 1-12

The filtering process was carried out on a DIEMME filter press (114 - chamber plates, plate size 1,500 × 1,500 mm, total filtering area 480 m ² ) with the systems for supplying slurry, washing water and compressed air shown in Fig. 1 (1) as follows way:

The wash water supply valves (2, 3, 4, 5) were closed, and the suspension supply valves (6) and the mother liquor outlet valves (7, 8) were opened, the suspension supply pump (9) was turned on and filtration was started with a suspension flow rate of 25 m ³ / h , which is 0.0525 m ³ / (m ³ × h) (per 1 m ^{2 of} filter surface), the process was carried out for 3 h 45 min at a maximum pressure of 0.6 MPa until a suspension flow rate of 0.45 m ³ / h, measured by a flow meter (10).

Upon the fact that the suspension flow rate was reduced below the set value, the electric motor of the suspension feed pump was stopped (9), the suspension feed valves (6) and the mother liquor drain from the upper channel (8) were closed, the compressed air supply valve (11) and main valves (3, 4) were opened and compressed air was supplied to the filter press at a pressure of 0.3 MPa for 4 minutes and monitored using a pressure sensor (12) and a time relay (13). After the purge time has elapsed, the compressed air supply valve (11) was closed, and the washing water supply valve (14) was opened. Wash water was supplied using a centrifugal pump (15) with a flow rate of 45 m ³ / h. within 11 minutes The volume of water supplied for flushing 5.25 m ³ is determined using a flow meter (16). At the end of the wash water supply, the tap (14) was closed, after 9 minutes the compressed air supply tap (11) was opened, and the components of the purge - flush - shutter cycle were repeated 6 times. Data on the results of filtering processes - washing suspension of Pigment orange G are shown in table 2.

table 2
Technical characteristics of the processes of filtering and washing paste Pigment orange Zh Parameter Name Units rev. Value Initial parameters Orange Pigment Suspension Volume m ³ 63.5 Pigment concentration in suspension kg / m ³ 34.98 The concentration of water-soluble impurities in suspension kg / m ³ 13.74 The mass of the paste Pigment orange W kg 10820 Pigment paste volume Orange Zh m ³ 9.45 Set and calculated process parameters The number of washing cycles PC. 6 The volume of wash water used for 1 cycle m ³ 5.25 Flushing time min eleven Holding time min 9 Monitored parameters The concentration of water-soluble impurities in the paste Pigment orange W at the end of the process kg / m ³ 0.405 Total Wash Water m ³ 49.5

Example 2

Filtration-washing was carried out using a red FGR Pigment suspension having the characteristics shown in Table 3.

Table 3
The composition of the suspension of the Pigment red FGR Pigment,% wt. NaCl,% wt. Na₂SO_four, % of the mass. HCl,% wt. Organ. approx.,% mass. H ₂ O,% wt. Disp. composition of tv. phase, microns sol. not sol. 2.77 1.29 1.51 0.04 0.54 0.14 93.71 3-24

The filtering process was carried out on a filter press with 83-chamber plates, a plate size of 1250 × 1250 mm, a total filtration area of 240 m ² , with systems for supplying slurry, washing water and compressed air according to Fig. 1 as follows.

The wash water supply valves (2, 3, 4, 5) were closed, and the suspension supply valves (6) and the mother liquor outlet valves (7, 8) were opened, the suspension supply pump (9) was turned on and filtration was started with a suspension flow rate of 24 m ³ / h , which is 0.1 m ³ / (m ³ × h), the process was carried out for 2 h 55 min at a maximum pressure of 0.8 MPa until a suspension flow rate of 0.24 m ³ / h measured by a flow meter (10) was reached.

Upon the fact that the suspension flow rate was reduced below the set value, the electric motor of the suspension feed pump was stopped (9), the suspension feed valves (6) and the mother liquor outlet from the upper channel (8) were closed, the compressed air supply valve (11) and main valves 3.4) were opened and compressed air was supplied to the filter press at a pressure of 0.3 MPa for 3 minutes and monitored using a pressure sensor (12) and a time relay (13).

After the purge time has elapsed, the compressed air supply valve (11) was closed, and the washing water supply valve (14) was opened. Wash water was supplied using a centrifugal pump (15) with a flow rate of 45 m ³ / h for 6 minutes. The volume of supplied water for washing with 4.5 m ^{3 was} determined using a flow meter (16). At the end of the flushing fluid supply, the valve (14) was closed, after 7 minutes the compressed air valve (11) was opened, and the components of the purge-flush-soak cycle were repeated 10 times. Data on the results of filtering-washing processes of a suspension of Pigment red FGR are shown in table 4.

Table 4
Technical characteristics of the processes of filtering and washing paste Pigment red FGR Parameter Name Units rev. Value Initial parameters Red FGR Pigment Suspension Volume m ³ 38.7 Pigment concentration in suspension kg / m ³ 27.22 The concentration of water-soluble impurities in suspension kg / m ³ 33.54 Pigment paste mass red FGR kg 5045 Pigment paste volume red FGR m ³ 4,5 Set and calculated process parameters The number of washing cycles PC. 10 The volume of wash water used for 1 cycle m ³ 4,5 Flushing time min 6 Holding time min 7 Monitored parameters The concentration of water-soluble impurities in the paste Pigment red FGR at the end of the process kg / m ³ 0.39 Total amount of wash water m ³ 45

Example 3

Filtering-washing was carried out using a suspension of Pigment orange G, having the characteristics shown in table 5.

Table 5
The component composition of the suspension Pigment orange G Pigman
t,% of the mass. NaCl,% wt. Na₂SO_four, % of the mass. HCl,% wt. H ₂ SO ₄ ,% wt. Organ. approx. % of the mass. H ₂ O,% wt. Disp. composition of tv. phase, microns sol. not sol. 3.63 1.29 0.04 0.39 0.01 0.08 0.09 94.47 1-12

The filtering process was carried out on a DIEMME filter press (114 - chamber plates, plate size 1,500 × 1,500 mm, total filtering area 480 m ² ) with systems for supplying slurry, washing water and compressed air according to Fig. 1, (1) as follows.

The wash water supply valves (2, 3, 4, 5) were closed, and the suspension supply valves (6) and the mother liquor outlet valves (7, 8) were opened, the suspension supply pump (pos. 18) was turned on and filtration was started with a suspension flow rate of 25 m ³ / h, which is 0.0525 m ³ / (m ³ × h), the process was conducted for 3 h 45 min at a maximum pressure of 0.6 MPa until a suspension flow rate of 0.40 m ³ / h measured by a flow meter was reached (10 )

Upon the fact that the suspension flow rate was reduced below the set value, the electric motor of the suspension feed pump was stopped (9), the suspension feed valves (6) and the mother liquor drain from the upper channel (8) were closed, the compressed air supply valve (11) and main valves (3, 4) were opened and compressed air was supplied to the filter press at a pressure of 0.35 MPa for 3 minutes and monitored using a pressure sensor (12) and a time relay (13).

After the purge time has elapsed, the compressed air supply valve (11) was closed, and the washing water supply valve (14) was opened. Wash water was supplied using a centrifugal pump (15) with a flow rate of 40 m / h until the condition is satisfied, reducing the concentration of water-soluble impurities in the wastewater taken from the filter press outlet channel with a time interval of 15 seconds by less than 1%, determined using a flow meter (16).

At the end of the wash water supply, the valve (14) was closed, after 7 minutes the compressed air valve (11) was opened, and the components of the purge-flush-soak cycle were repeated 6 times. Data on the results of filtering-washing processes of a suspension of Pigment orange G are shown in table 6.

Table 6
Technical characteristics of the processes of filtering and washing paste Pigment orange Zh Parameter Name Units rev. Value Initial parameters Orange Pigment Suspension Volume m ³ 63.5 Pigment concentration in suspension kg / m ³ 34.92 The concentration of water-soluble impurities in suspension kg / m ³ 13.74 The mass of the paste Pigment orange W kg 10820 Pigment paste volume Orange Zh m ³ 9.45 Set and calculated process parameters The number of washing cycles PC. 8 The volume of wash water used for 1 cycle m ³ 5.25 Holding time min 12 Monitored parameters Flushing time of the first flushing cycle min 21,2 Flushing time of the second flushing cycle min 14.2 Flushing time of the third flushing cycle min 9.5 Flushing time of the fourth flushing cycle min 6.4 Rinse time of the fifth rinse cycle min 4.8 Flushing time of the sixth flushing cycle min 4.3 Volume of rinse water for the first rinse m ³ 14.13 Volume of wash water for a second wash m ³ 9.45 Volume of wash water for the third wash m ³ 6.33 Fourth flush volume m ³ 4.26 The volume of wash water for the fifth wash m ³ 3.17 Volume of wash water for sixth wash m ³ 2.87 The concentration of water-soluble impurities in the paste Pigment orange W at the end of the process kg / m ³ 0.405 Total Wash Water m ³ 40,2

Carrying out the filtering-washing processes of finely dispersed suspensions by the technology of cyclic supply of washing liquid-purge given in the examples allows to reduce the amount of washing water required to achieve the required concentration of water-soluble impurities in the paste; reduce the loss of the target substance at the washing stage and reduce the time of the washing process, the data are shown in table 7.

Table 7 Pigment name Process time, min The volume of washing liquid, m ³ The loss of the target substance,% of the mass. one* 2 ** one* 2 ** one* 2 ** Pigment Orange F 455 154 90 40,2 1.8 1,1 Pigment Red FGR 420 160 92 45 1,2 0.9 1 * - Continuous supply of wash water to the filter press.
2 ** - Cycle supply of washing water to the filter press with purge of sludge after each cycle.

Claims (4)

1. The method of washing finely dispersed sediments of organic pigments from water-soluble impurities on the filter screen, characterized in that the process of removing water-soluble impurities is carried out with a cyclic supply of washing water as follows: the precipitate formed as a result of filtration is blown with compressed air at a pressure of 0.25-0.35 MPa , upon the release of the precipitate from the mother liquor, wash water is supplied for a period of time ensuring the cessation of the decrease in the concentration of water-soluble impurities of the spent wash water s, then the flow of wash water is stopped, and the wash water is kept in the flow pores of the sediment for the time required to increase the concentration of water-soluble impurities in the wash water until an equilibrium or close concentration is reached, the wash water is displaced from the flow pores of the sediment with compressed air, then the components of the cycle are repeated until the desired concentration of water-soluble impurities in the paste is achieved. 2. The method according to p. 1, characterized in that the orange Pigment paste W is washed with a particle size of 1-12 μm, the purge time of the sediment is 4 minutes, the pressure of compressed air is 0.3 MPa, the time of continuous supply of washing water is 11 minutes, the volume of washing water for each cycle of 5.25 m ³ , the residence time of the washing water 9 minutes, the number of cycles required 6. 3. The method according to p. 1, characterized in that the Pigment paste is red FGR with a particle size of 3-24 μm, the purge time of the sediment was 3 minutes, the pressure of compressed air 0.3 MPa, the time of continuous supply of washing water 6 minutes, the volume of washing water per cycle 4.5 m ³ , the stationary time of the wash water 7 minutes, the number of required cycles 10. 4. The method according to p. 1, characterized in that the orange P pigment paste is washed with a particle size of 1-12 microns, the purge time of the sediment is 3 minutes, the pressure of compressed air is 0.35 MPa, the time of continuous supply of wash water varies from cycle to 21.2 to 4.3 minutes, while each time the condition was met, the concentration of water-soluble impurities in wastewater was reduced by less than 1% for a time interval of 15 seconds, the volume of wash water for each cycle also varied in the range 14.13-2, 87 m ^3, the stationary residence time 12 min wash water, the number t ebuemyh 8 cycles.

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