Control questions
Which methods are used for drying of synthetic detergents compositions?
Explain the difference between convection and contact drying.
Explain the arrangement and principle of action of spray drier.
Advantages and lacks of counter-current and co-current drier.
Call the duration of drying and the density of powder synthetic detergents at different regimes of drying.
3.6 Basic technological circuits of powdery synthetic detergent manufacture by periodic and continuous ways
A technological circuit of powders’ manufacture includes the following stages: reception, storage and preparation of raw material, preparation and drying of composition, introduction of thermal-instable components, packaging and packing, clearing of waste gases.
There are two methods of powders manufacture by periodic way with productivity of 30 thousand tons in one year: method of "Kestner" firm and method of "Lurgi" firm. The technological circuit of powder manufacture by "Kestner" firm method is presented on fig.3.1. Preparation of initial composition is spend by periodic way in two reactors 9 with volume 8м3 everyone. The ready composition by pump of high pressure 19 is submitted in atomizers of drying tower 20 having 6 m diameter. Drying of sprayed composition in drying tower conduct by counter-current regime at temperature of heat-transfer agent 300-3500С. Heat-transfer agent from gas generator by fan is given in collector of tower.
Exhaust heat-transfer agent has temperature 105-1200С and represents a mix of air with water vapours and fine-dispersed fractions of synthetic detergent. Exhaust gases leave the top part of tower 20 and are given on dry clearing in group of 4 cyclones 22 connected in parallel. In cyclones large powder particles are separated and through sluice gates are submitted on a conveyor of ready product 29. Dusty air from cyclones by fan 23 is submitted on wet clearing to scrubbers 24 where there is additional removal of dust particles. After scrubbers exhaust air is directed in atmosphere and liquid phase - in reactors 15.
The powder with temperature 700С from bottom part of tower by conveyors 28, 29 and bucket elevator 30 through vibrating screen 31 is submitted to reception bunker. From the bunker by weigher 33 it is submitted to drum-type amalgamator 34 in which thermal-instable components are added.
Sodium perborate and enzymes are entered by weigher 36, from bunker 35 aromatic substances and non-ionogenic SAS are added in amalgamator 34. The powder from amalgamator is given in reception bunker 37, and then by bucket elevator 38 and conveyor 39 is distributed on bunkers of ready product. Then it is submitted on automatic packaging in cardboard packs or a film. Packs with the powder are packed in boxes, paper or polyethylene film.
The technological circuit of powder production by method of "Lurgi" firm is presented on fig.3.2. The initial composition is prepared also by periodic way in reactors 11 with volume about 15 m3 and by pump of high pressure 14 it is submitted to atomizers of tower 15. Tower diameter is 8 m. The volume of drying chamber of this tower is more than volume of tower of "Kestner" firm. It allows to conduct the powder drying at input temperature of heat-transfer agent 250-2800С. Heat-transfer agent is submitted to the tower from gas generator 18. The powder from the tower is given on tape conveyor 23. On the same conveyor automatically sodium perborate and enzymes from bunkers 24 are dosed and aromatic substances and non-ionogenic SAS acting of tanks 25 are sprayed on atomizers. The received powder by bucket elevator 26 is submitted on vibrating screen 27. Then the powder by tape 28 and scraper 29 conveyors is submitted to bunkers of ready product. Exhaust gases are cleared from dust in preliminary dust separator 19, then in system of cyclones 20 and multicyclones 21 then send in atmosphere.
The technology of powder production by continuous way includes the same stages as periodic way however it has the following advantages:
- high productivity (600 thousand tons of a powder in year);
- application of pneumotransport for moving of loose materials;
- continuous preparation of initial composition;
- automatic raw material weighing;
- automatic control of all process.
The technological circuit of powder production by continuous way is submitted on fig.3.3. An initial composition by pump of high pressure 14 is submitted to collector of high pressure which is situated in the top part of drying tower 16. From collector suspension is given on atomizers.
Hot heat-transfer agent from gas generator 18 with speed 0,3-0,6 km/s is submitted to the bottom part of tower. The formed powder settles down and through the bottom of tower at temperature 60-700С is given on conveyor 19. By this conveyor the powder is directed to the bottom part of air lift 20 in which the fan 23 creates vacuum. The powder by air stream moves in separator 21. At movement in air lift the powder is cooled up to 30-400С. In separator air is separated from powder and by fan is directed to battery of cyclones. In cyclones air is cleared from fine-dispersed dust. Then air is given in scrubber for final clearing and put out in atmosphere.
The separated from air powder is directed on vibrating screen 27. Agglomerates are given on dissolution, and the powder passes through the device for input of aromatic substances 28 and by conveyor 30 moves in intermediate bunkers 31. Then powder is unloaded from bunker and directed to system of introduction of thermal instable components (sodium perborate, enzymes, sodium hydrocarbonate).
The basic device of unit of introduction of thermal instable components is the drum-type amalgamator. It represents the inclined rotating cylinder inside which atomizers are fixed. From atomizers non-ionogenic surface-active substances and (if necessary) aromatic substances are sprayed on powder. Then the powder is given in bunkers of ready product.
Exhaust air after tower passes the system of cyclones in which the basic mass of powder carried away from the dryer is separated. The powder comes back in tower. After clearing in cyclones the dust-gas mixture is given in scrubber for wet clearing. The scrubber is irrigated by suspension of ready composition or water solution of sodium silicate and carboxylmethilcellulose. The cleared gas mix is given in atmosphere through fan 25.