Practical exercise 4

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PRACTICAL EXERCISE 4

Technological calculations of the filtration process

Carbonization columns use a filtration process to separate sodium bicarbonate from the suspension. The formed crystals are fed to the calcination unit, and the liquid phase leaving the filter is fed to the distillation unit for regeneration of ammonia.

In addition, due to the partial reaction, the loss of sodium bicarbonate is observed:
NaHCO3+NH4Cl⇄NaCl+NH4HCO3

Wash water temperature450Cand with an increase in the amount and when the integrity of the filter barrier is broken, it is observed that the amount of losses during the filtration process increases. The following table shows the dependence of heat consumption on the moisture content of sodium bicarbonate in the calcination step and the amount of evaporated moisture.

Moisture content, %	100 kgthe amount of moisture extracted into finished soda, kg	Relative consumption of heat to evaporate water in the calcination stage, %	100 kgoutput of soda to wet* sodium bicarbonate, kg
22,23	45	139.7	49
20.75	41.3	126.1	50
19,16	37.5	114.7	51
17.58	33.8	100	52
15.99	30.2	91.7	53
14.31	26.5	80.3	54

*Maximum theoretical yield of soda per 100 kg of wet sodium bicarbonate-63 kg.

Continuous drum vacuum filters are the main equipment of the filtration unit.

BS-5, 6-1, 8/1 drum vacuum filter is widely used in soda production technology.
Below are the technical specifications of the drum vacuum filter BS-5, 6-1, 8/1:
Filtration surface, m2………………………………5,6
Drum diameter, m …………………….....1.8
Drum length, m…………………………...1.0
Angle, degree:
Sinking of the drum into the suspension………...130
Filtering zone………………………………...53
Drying and washing zone…………………….189
Liquid gravity and gazmol
regeneration zone………………………..…...48
Secondary of the mixer in 1 minute
number of vibrations……………………………….35
Since the drum vacuum filter is equipped with 18 cells and a distribution device, several processes take place on its surface at the same time. According to the process taking place in the filter drum, it can be conditionally divided into the following zones:
- self-filtering zone; under vacuum conditions, the filtered liquid is drawn into the drum, sodium bicarbonate crystals are caught on the surface of the filter gas and form a precipitate;
- initial drying zone; at this time, the surface of the drum is located on the suspension, and filter liquid is drawn from the sediment into the drum;
-sediment washing zone; washing water is supplied to the surface of the drum; this water passes through the sediment to the drum and squeezes the filter liquid from the intercrystalline area of ​​the sediment;
- main drying zone; air is supplied here, and it passes through the sedimentary layer of sodium bicarbonate, squeezes the washing water from the intercrystalline area of ​​the sediment and reduces the moisture content in the sediment;
- closed zone; sodium bicarbonate deposits are removed from the surface of the drum with the help of a special knife, therefore air is not allowed to pass between the special knife inside the drum and the filter liquid drawing zone (if air passes, the vacuum in the system may be lost);
- filter fluid attraction zone; "wet" blowing of gas oil before blowing with compressed air to increase the service life of gas oil with a filter;
- blowing zone; Compressed air is supplied to the drum cell against the flow of the mixture to regenerate the filtering gas. The gas-liquid mixture enters the drum due to non-vacuum.
The filter liquid extraction zone squeezes the incoming filter liquid from the compressed air cells. The filtered liquid from the gazmol squeezes out small crystals of sodium hydrogen carbonate from the holes of the gazmol and dissolves them in itself. This in turn accelerates the regeneration process. After that, the holes of the gas cylinder with a filter are cleaned with compressed air:
- transition zone; It is designed so that the compressed air supplied for blowing does not pass into the vacuum part of the drum.
In one rotation of the drum, a complete cycle of the filtering process is carried out, and each cell passes through all the zones. Drum vacuum filter performance can be determined by the following formula:
Qf.l.=60F_gnW
Qf.l - efficiency of a drum vacuum filter designed for a standard product, t/s
G' is the filtering surface, m2 (G'=dL, diameter of D-vacuum filter, m; width of the sodium bicarbonate layer in the L-filter, m);-sediment thickness, m;_g- the density of concentrated sodium bicarbonate in a vacuum filter, t/m3; usually taken as 1.32 t/m3; n-vacuum-filter rotation number; Soda release from W-sodium bicarbonate (W=0.52);-reduction coefficient.
Usually on the blade of the filter 5-8 mma layer of uncut sodium bicarbonate remains. If he6 mmis assumed to be:=(-6)/.
The above equation can be written as:
Qf.l.=129.3DL(-6) n
Recently, drum vacuum filters with a filtering surface of 32 m2 are used in soda factories.
The main technological and technical data of the following drum vacuum filter are provided:
Sediment moisture,% …………………………...13-18
Chloride in sodium bicarbonate
amount of ions,%…………………..0.25
Losses in filtration, %…………….up to 3.5
Filtration surface, m2…………………………32
Productivity, t/milk……………………...650
Length, m……………………………….....9.2
Width, m ……………………………….....4.0
Height, m……………………………….....4.1
Mass, kg ………………………………....21500
The number of drum revolutions ……………….0.3-1.69
Construction material………………..steel OX17N13MZT
Specified productivity, kW……………11.4


Matter
Calculate the performance of the drum vacuum filter. BS 5.6–1.8/1.0 for bicarbonate filter. Drum-filter diameter D = 1.8 m, drum length 1 m. The width of the bicarbonate layer in the filter is L = 0.98 m. Drum-filter rotation speed is 1 min–1. The thickness of the sediment layer in the filter is  = 40 mm. After cutting with a knife, a thick sediment layer remains on the filter  = 5 mm. Coefficient of soda production from bicarbonate  = 0.52; sediment density
 = 1320 kg/m3.