There are quite a few methods of removal of water and solid particles from diesel and motor fuels. The most wide spread methods are settling, centrifuge separation and filtration. Without a doubt, all the methods have both advantages and drawbacks, therefore the research into new methods of fuel purification, chemical and physical, is ongoing. These methods can be divided into one-time and continuous.
The methods of the first group use preliminary treatment of fuel. In the general case, the process is performed by hot water wash or steam purge. The need to use water is dictated by its properties as a surfactant, which can remove most contaminants from the phase boundary between fuel and water. In turn, to completely remove water after the wash, de-emulsifiers are needed. This method does not allow to completely remove contaminants from the processed liquid. Particles smaller than 3 micron mostly remain in the fuel.
This is not the only method. Hydrodynamic method involves passing fuel at 21 – 35 MPa pressure through a special conical valve with reduction of pressure to atmospheric. With the rapid change of velocity and pressure, asphalt and tar are destroyed. The drawback of this method is that nonorganic solids are not destroyed, and the total amount of contaminants in the fuel does not change. However, the size of contaminant particles becomes smaller, which allows to eliminate the risk of rapid clogging of filters, pipelines and nozzles.
Fuel can also be purified by sound waves. In this case, the particles become larger instead of smaller due to acoustic coagulation and can then be filtered out.
Electric separators can remove water from petrochemical fuels. Electric field cases water droplets in the fuel to coagulate, and these droplets can then be separated by gravity or centrifuge.
Physical and chemical methods of one-time water removal from fuel are complicated and cumbersome, even through they are quite efficient. They rely on filtration through adsorbents (charcoal, zeolite, silica gel and alumina gel).
Long-term physical and chemical methods are relatives simpler. They maintain fuel purity for storage and transportation, as well as operation. The method involves injection of small amounts of special additives. Their influence remains constant from the moment of injection to the moment of combustion in the cylinder. Known additive spectrum is quite wide. They limit or prevent corrosion of engine parts, prevent formation of tar, coagulate solid particles etc.
Method selection depends on the specific requirements to fuel.