Therefore, certain very important precautions are taken in designing a Solvent Extraction Plant and operating the same as enumarated below
1.   No naked fire is allowed in the vicinity of a solvent extraction plant. All the heating, necessary in the plant is carried out by only steam and not by naked fire or electrical fire, as the naked fire and electrical heating are not controllable below the ignition temperature of hexane and therefore, can cause the fire.

2. For the ignition to occur in a hexane atmosphere there must be a proper mixture of oxygen (air) and hexane as well as ignition temperature. Once the oxidation (burning) of hexane starts the reaction is highly exothermic and produces enough heat to continue the reaction (i.e. burning) and the fire quickly spreads. The reaction produces (mainly carbon dioxide) are released in great volumes creating the pressure inside the burning enclosures and the explosion results. Therefore, to avoid fire and/or explosion in a solvent plant it is necessary to see that the air and hexane vapours do not exist in explosive limits. The explosive limits for hexane and air are below 6.9% and above 1.2% hexane in air by volume. In a plant which is working normally, the atmosphere inside the equipment is full of saturated vapours of hexane containing negligible amount of air. And hence, it does not constitute a dangerous atmosphere. But, during the starting and stopping of a plant, the proportion of air inside the equipment is much higher and that may pose a potential hazard. Therefore, during this period it is necessary to ensure that no ignition temperature is reached in any part of the plant. A safe plant design shall take this into consideration.

3.   While the atmosphere inside the equipment is free from hazard in a working plant, any leak of solvent vapours from the equipment constitutes a serious hazard. The leaking vapours meet with enough amount of atmospheric air just outside the leaky spot and can catch fire in case of ignition. Therefore, it is absolutely necessary to block all the leaks in a plant, not only to prevent hazards but also to reduce hexane loss. The potential leaky areas are
(a) Flanges not properly tightened.
(b) Damaged packings between the flanges.
(c) Welding leaks due to inferior workmanship
(d) Screw joints not properly tightening
(e) Damaged mechanical seals
(f) Pump glands
(g) Glands of valves in process lines.
It is good practice to take hydraulic test of the plant periodically to locate any such leaks and plug them.

NEXT>>