FAQ about coal powder briquette press
1.What should we use for binder?
Some of our customers might use Corn starch, molasses, and cement. However, PVA is most welcomed by our customers. And our engineers also suggest you use this. I would like to explain the PVA in detail.
PVA ie Polyvinyl alcohol resin is a polymer. It’s usually a white or light yellow floccule, flake, granular or powder solid. Its molecular formula is: [CH2CHOH]n Part of PVA resin’s molecular formula is [CH2CHOH]n[CH2CHOCOCH3]N.
It’s nontoxic, tasteless, non-polluting. PVA is a water-soluble resin and has good chemical stability. It also has good adhesion, film-forming ability, insulation, oil resistance, abrasion resistance and gas barrier properties, and has typical chemical properties of polyols, and can make esterification, etherification and acetalization reactions.
2. Why the PVA is not the same with that in the factory?
What the factory used is the same with this. But what you need to do is to make the PVA into liquid. I would like to show you how to use the PVA in the following.
Use Methods of Products
I When PVA products are used, they're required to be formulated into solution. Water is a good solvent for PVA. According to the features of different brands and shapes of PVA products, we should adopt appropriate dissolving methods to improve the dissolving efficiency of PVA.
1 Dissolving facilities
a: Dissolving kettles: Use dissolving kettles with stirrers. Dissolving kettles should be made with rustless, non-corrosive materials, such as stainless steel, enamel or ironwork internally lined with synthetic resins to avoid pollution to PVA solution.
b: Stirres: The rotating speed of the stirrers should be 70-100 rounds per minute. If their speed is too slow, PVA will be easily sink to the bottom of the kettle and agglomerate; but if too fast, air will be easily involved into PVA solution and form excessive air bubbles.
c: Heat supply: Heat PVA solution by directly blowing steam into the solution. If supplemented with jacket steam heating, the dissolving time can be greatly shortened. Avoid heating the solution directly with fire. If PVA solution is directly heated with fire, PVA will easily be burnt into coke on the bottom and walls of the container in case of bad stirring.
2 Dissolving temperature and concentration of PVA
The solubility of PVA products mainly depends on their degree of alcoholysis and their degree of polymerization. When their degree of polymerization increases, their solubility decreases. When their degree of alcoholysis decreases, their water-solubility increases and their dissolving temperature can be reduced accordingly. PVA products with complete alcoholysis have greater dependence on temperature. Below a certain temperature, they can't be dissolved or only partially dissolved or swell. The dissolving temperature of PVA products with partial alcoholysis shouldn't be too high. Otherwise, the PVA solution will easily foam and overflow out of the kettle. This will bring inconvenience to the operation. So different brands of PV products should be dissolved at an appropriate temperature range.
For the PVA when delivery to you, the suitable temperature is 90-96 degree. The max dissolving concentration is12%.
3 Dissolving method. a Measure the needed water at the room temperature and then add it into the dissolving kettle. b Start the stirrer and then slowly put the measured PVA products into the dissolving kettle. Because PVA products with partial alcoholysis can dissolve fast but easily agglomerate, you should put them into the dissolving kettle a little slowly and not pour a whole bag of them into the dissolving kettle. c Stir PVA solution fully for about 10-20 minutes to make PVA disperse and swell as much as possible, then gradually raise its temperature at a rate of 2 degree centigrade. Don't raise the temperature too fast. Otherwise, the solution will easily foam and overflow. d Gradually raise the temperature to the required dissolving temperature, and then continue to stir the solution for about one hour to make PVA fully dissolved, and then filter the solution.
* Don't put PVA directly into hot water to dissolve, in order to avoid agglomerating and partially dissolving.
*Avoid heating the solution directly on fire.
* The solution must be stirred in the whole dissolving process.
*If the concentration of the PVA solution is high during the dissolving process, when it is stirred fast, it will produce a few bubbles. In order to inhibit foaming, you should add a small amount of defoamer, such as 0.05-0.10% (PVA as a benchmark) Octanol, TBP or 0.01-0.05% (PVA as a benchmark) silicone emulsion, into the solution before it is dissolved.
II Preservation and storage of PVA solution
Antiseptic: PVA solution can be preserved almost without chemical changes. At room temperature, its viscosity will gradually increase as its storage time extends. At low temperatures, it can turn into a gel, which can become a solution again when heated. If stored for a long time, the solution should be added with some antiseptic agent, such as 1.01-0.05% (PVA as a benchmark) of formaldehyde and salicylic acid. But pay attention to the impact of the additives on the quality and performance of PVA solution.
Antirust: When the solution is stored in iron containers, weak alkali should be added into it. When it is stored in bronze containers, it should be added with 0.02-0.05%. (PVA as a benchmark) of sodium nitrite. Had better use stainless steel or plastic containers to store PVA solution.
Packaging and Storage
Packaging: Floccule PVA products should be packaged with polypropylene weaving sacks containing colorless medium-density polyethylene plastic film inside, having net weight 12.5kg per sack; granular or powered products should be packaged with polypropylene weaving sacks containing colorless medium-density polyethylene plastic film inside and having an inside lining of colorless high-density polyethylene plastic, having net weight 20.0kg/sack or 25.0kg/sack.
Storage: Store the products in dry, well-ventilated rooms, and pay attention to preventing them from damp and avoid exposing them to sunlight and rain.
Transport: Take up and lay down the products lightly when transporting them. Don't break their sacks. Keep them far away from fire. When they're caught with a fire, use any fire extinguishers to put out the fire.
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