India is the third largest producer and processor of cashew nuts shells in the world, after Vietnam and Nigeria. As per one data, India accounts for 23% of the total cashew production in the world.

This cashew comprises 32.5% nut and 67.5% shell. While the nut is edible but the shell remains the waste product of the cashew processing industry.  Interestingly, this shell has a very high calorific value of 4800 Kcal/kg which is superior to most biomass fuels including groundnut shell, firewood, wood chips, mustard straw, rice husk etc. but can we use it as a fuel for the industries? Well, high calorific value isn’t the only criterion for selecting the fuel.

Cashew nut shell contains 15-25% dark reddish-brown viscous liquid called as cashew nut shell liquid (CNSL). This CNSL is a natural, low-cost source of phenol and therefore finds numerous applications in polymer-based industries such as paints, brake linings, epoxy resins, rubber compounding resins etc.

The properties of CNSL are quite similar to light furnace oil (LFO) with average calorific value of 11380 Kcal/Kg. However, CNSL has a pH of 4.5 to 5.2 because of the presence of the acids. The cashew nut shell contains 90% anacardic acid and 10% cardol acid. So, what happens when the cashew shell, and simultaneously the cashew nut shell liquid is combusted?

1. Reduction in furnace lifetime: Cashew shells are a rich source of phenols which when combusted is known to attack the refractory bricks.
2. Acidic fume that are corrosive and toxic: The CNSL are acidic in nature. The direct combustion of cashew shells, therefore, generate toxic fumes of anacardic acid which doesn’t only detoriate the components of the equipment but generates toxic flumes which poses serious threats to workers and environmental safety.
3. Black smoke: CNS contains higher carbon content. When burned as a standalone, it tends to generate black smoke as well (if air supply is not sufficient).
4. Handling and Feeding issues: Due to high oil content of this fuel, the fuel pose serious problems in the hopper, feeder etc. Also, due to its highly acidic nature, the fuel is difficult to handle and store.

In 2016, a FMCG based out of Orissa ran a trial on cashew de-oiled cake (DOC) as a stand-alone fuel in their thermic fluid heater. Within 10 to 15 days of operation, the coils were damaged beyond repair and the heater had to be shutdown for 1 month for coil replacement but a major accident was averted.

We recommend against using cashew shells as a standalone fuel in any equipment. Considering these issues with cashew shells, we have come up with a new fuel “Astillas” which has cashew shells as one of the raw materials but they are processed to reduce the CNSL content as well as the toxicity of the fuel. The fuel is safer to use in all the equipment, doesn’t generate toxic and/or black smoke and is easier to handle.

Is your industry looking for an alternate fuel? Do you know any fuel which has better properties than this? Feel free to reach for any questions and case discussions.