Thermal desorption process

The thermal desorption technique is the one of the most recongized technique for treating the drilling wastes. As the name indicates, it is based on 'desorption'; the phenomenon of removing the adsorbed particles from the surface over which they are absorbed. In this process the oil components which are present in the drilling waste are effectively removed by heating them at very high temperature. All the volatile hydrocarbon that are present in the waste are removed but, still some impurities which are very harmful for the environment as well as toxic for the drilling system aren't affected but this method. Heavy metal impurities such as barite, mercury, cadmium etc. and some saline additives still remain as unremoved impurities.
This process is mostly used in onshore since there is the high transportation cost involved in offshore. In onshore, the waste is sent to the desorption system by truck or by any other available transportation means. Then after the waste is weighted, it is kept segregated by the generator. Soon after that they are screened for foreign materials and finally they are feed into the hooper for heating. The heating temperature in the kiln is round about 500°C.
Rotary kiln is widely used for heating the drilling waste. In it the waste is heated at 500°C by passing the high temperature silicone oil around it. It should be noted that the oil is again provided by the hollow auger. Other method is also used in which the waste is heated by hammer, which uses the heat released by the friction.
Cautions:
Nitrogen should be used in order to remove the excess oxygen from the system as it can harm the waste in 2 hazardous ways:

• If the temperature of the system is higher than the flash point of the oil and at the same conditions if the amount of vapours available in the system is high then the presence of oxygen can produce fire. 
•  Moreover, hydrocarbons have tendency to crack at very high temperature. Now, at very high temperature if the oxygen is available to them than they can from the carcinogens and other harmful contaminants.

So, in order to avoid all these problems nitrogen is supplied into the system.
Apart of this a special care is taken for cooling the cuttings rapidly before exposing them in air.
Advantages:

•  The oily componets can be separated out from the drilled waste.
•  The additional oil can be reclaimed and it can be processed to used for different purposes.

Disadvantages:

•  Only oily componets can be obtained from this method, whereas other harmful componets still remain in the waste.
•  Special expertise is required by the operator in order to handle this process.
•  The quality of the oil that is obtained is not consistent. 
•  There are safety issues related to this process.
•  Air emission should be controlled.
•  Maintainance cost is high.
•  The thermal desorption process is the expensive one.