How to separate coal tar from water
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This post was last edited by ryn on 2009-8-11 at 16:14. It’s a relatively difficult issue – I would like to ask how coal tar and water can be separated in terms of processing; cannot centrifugation be used for this? :handshake
Coal tar and water have different densities, so they can be separated by simply allowing them to settle, or by using centrifugation
I previously shared a research paper on the application of demulsifiers in the separation of ammonia and tar: http://bbs.hcbbs.com/thread-385040-1-1.html
The moisture content of crude tar is generally around 4%; by keeping the temperature of the tar at 70–80 degrees, the moisture content usually drops to about 2–3% after it has been left to stand for some time. The common method currently used is to heat to 120–130 degrees in a tubular furnace, and then carry out flash evaporation in a disposable evaporator to reduce the moisture content to around 0.5% ； The method used in the UK is continuous dehydration via light oil azeotropy, while Japan uses pressure-driven dehydration. There should be a fairly detailed explanation in the book on coal tar technology!
There is a type of cyclone separator that operates on the principle of centrifugation, and it achieves quite good separation results
Oil and water are immiscible; by taking advantage of the difference in specific gravity, they can be separated simply by letting them settle. Of course, there are also methods that utilize different boiling points or centrifugal forces to separate coal tar from water, but these all increase costs.
During my experiments, after centrifugation the oil separated into two layers – one on top and one below – with water in between. The amount of water can be determined by distilling organic reagents, but to determine the properties of the oil it is necessary to obtain tar; at present there is no good method for this: handshake
The dehydration of tar is carried out in two steps: preliminary dehydration and final dehydration. Preliminary dehydration takes place in a tar storage tank, which is equipped with a steam indirect heater to maintain the tar temperature at 85–95°C. The mixture is left to stand for more than 36 hours, during which time water and tar separate due to their different densities. This method of dehydration can only reduce the water content in the tar to 2–3%, while the required water content in the tar entering the distillation system is no more than 0.5%; therefore, further dehydration is necessary. Ultimately, the most common method for dehydration is to heat the tar in the convection section of a tubular furnace to 120–130°C, and then carry out flash dehydration in a primary evaporator, thereby reducing the moisture content in the tar to no more than 0.5%. Furthermore, the tar can also be dehydrated in a dedicated dehydration unit under conditions of pressure (0.3–1.0 MPa) and heating (120–150°C). This method breaks down the emulsified water; the water does not vaporize, and it is discharged in liquid form, thereby reducing heat consumption.
Separation by simple settling alone is certainly not ideal; it’s difficult to separate when the tar is highly emulsified. Demulsifiers are mentioned in theory, but I’ve never seen them used in practice. Separating water actually comes down to the operation – controlling the temperature and liquid level properly