Control questions

1. Call the basic stages of technological process at powder production.

2. Call the basic methods of powder production.

3. Which ways of powder drying are used in periodic methods of powder production? Call temperatures of heat-transfer agent.

4. On which stage of powder production the thermal instable additives are entered?

5. Explain the way of waste gas clearing at powder production.

3.7 Capital equipment at granulated synthetic detergents manufacture

A drying tower (fig.3.4) is made from acid resistant and carbonaceous steel and is covered inside by aluminium or zinc layer. The case of tower is collected from separate parts welded to each other. Outside the case is isolated for reduction of heat losses. The working part of tower is the vertical cylinder having in the bottom part a cone through which a powder is unloaded. On the roof is situated the manifold for removal of exhaust gases at counter-current flow and for input of drying agent at co-current flow. In the top part of manifold there is a valve. At counter-current flow hot gases are given on ring gas duct, at co-current flow on this pipe exhaust gases are removed. In the top part of cylinder atomizers are established. The cone of tower represents the unloader-refrigerator. Sometimes in column by special fan cold air is submitted for cooling of powder up to 70⁰С before unloading from the tower. The cone can be supplied with vibrator for simplification of powder unloading. The cooled powder from tower through flexible sleeve is given on conveyor.

A scrubber (fig.3.5) represents a steel cylinder with a conic bottom. Inside it in three circles jalousie are located, lengthening the way of gas movement and holding drops of suspension. For dispersion of solution on height of scrubber atomizers are located with torch of pulverization from below upwards, that allows to receive the uniform stream on section of the device. Flowing down suspension gathers in the cone and is given in reservoirs, located after scrubber. From reservoirs suspension comes back in the top part of scrubber.

Bunkers represent metal cylindrical reservoirs with conic bottoms. In the bottom there are special adaptations which prevent the formation of deposits, caking of powder and provide the uniform structure of loose material at unloading. The bunker is supplied by top 1 and bottom 2 funnels, which have identical diameter of apertures. The loose material from central part of bunker is given through top funnel. The located at walls of bunker material goes on pipes 3, in which is fed through vertical cracks. In bottom funnel it is mixed with the material, giving from the central part of bunker. For elimination of deposits in bunkers the mechanical mixers, compressed air, vibrators are used. Compressed air is submitted to the bottoms through porous elements or nozzles. More effective for storage of synthetic detergents are bunkers with vibrating bottom.

Keys: 1 – safety valve; 2 – cap; 3 – branch pipe of cap; 4 – atomizer; 5 – drying chamber; 6 – ring pipe-line; 7 – lower cylinder; 8 – soft valve

Fig.3.4 – Drying tower

Keys: 1 – cylinder; 2 – bottom; 3 – atomizer

Fig.3.5 – Scrubber

The ways of powder production described above are characterized by the following parameters.

Table 5. Dependence of basic technological parameters from production capacity.

Parameter	Value of parameter at power of factory, thousand tons
	30	60	120	200
Power of one unit, ths t.	30	60	60	120
Output of production on one worker, t/year	64	75	92	143
Specific capital investments, rouble/t including in the basic manufacture	220	208	200	180
	110	104	100	88
Cost price, rouble/t	575	558	553	543

Structure of cost price of the powders produced by spray drying:

Raw material and materials 85,4

Electric power 0,7

Steam and fuel 0,8

Water 0,5

Wages 5,2

Depreciation charges 2,4

Other expenses 5,0

The charge of power resources depends on technology and volume of manufacture. By manufacture of 1 ton of a powder by spray drying are spent on the average 120-200 kilowatt-hour (kw/hr) of the electric power, 160-200 kg of water steam, 1-5 m³ of water, 20-40м³ of compressed air and 90-120 m³ of fuel gas.

Using of spray drying method, the loose powders are received which not contain the dust, are quickly dissolved in water, have homogeneous structure. The content of particles in the size of 0,2-2,5 mm, according to the accepted norms, should make 80 %.

Disadvantages of production of powders by spray drying:

- Decomposition of some components at high temperatures of drying;

- Low density of product, that leads to the significant charge of packing materials;

- The high charge of fuel;

- Significant specific capital investments.