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. The shell undergoes further processing to extract cashew nut shell liquid and the residue is sometimes used as a fuel in the brick kilns. This residue is called as cashew de-oiled cake or cashew DOC. Interestingly, DOC has a very high calorific value of 4500 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.
What’s Inside The Cake?
Cashew nutshell 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 an 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 de-oiled contains 10-20% CNSL, out of which 90% is anacardic acid and 10% is cardol acid.
So, what happens when the cashew de-oiled cake, and simultaneously the cashew nut shell liquid is combusted?
- Reduction in furnace lifetime: Cashew shells liquids are a rich source of phenols which when combusted is known to attack the refractory bricks .
- Acidic fume that is corrosive and toxic: The CNSL is acidic in nature. The direct combustion of cashew doiled cake, therefore, generate toxic fumes of anacardic acid which don’t only deteriorate the components of the equipment but generates toxic flumes which pose serious threats to workers and environmental safety. 
- Handling Issues: Since CNSL is acidic in nature, handling DOC becomes difficult for the operating team. The workers have reported itching/burning sensation in the hands and skin peeling off with consistent exposure.
- Black smoke: DOC contains higher carbon content. When burned as a standalone, it tends to generate black smoke as well (if the air supply is not sufficient).
- Handling and Feeding issues: Due to the high oil content of this fuel, the fuel poses serious problems in the hopper, feeder etc. Also, due to its highly acidic nature, the fuel is difficult to handle and store.
Learning from the Mistakes
In 2016, Britannia Industries Ltd. (BIL), Orissa ran a trial on cashew 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 shut down for 1 month for coil replacement and the major accident was averted.
We recommend against using cashew DOC 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 deoiled cake 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.
How Astillas Is Different From Cashew DOC?
Though Astillas look similar to pure cashew DOC, it undergoes following transformations and processes to enhance its safety and application:
- Reduced Acidity: The Astillas have a CNSL oil content of below 8% compared to 10-20% in DOC. This is achieved by screw-pressing the DOC to extract the oil and mixing it with other high-quality local biomass fuels (dried & debarked wood chips, dried sawdust, groundnut shells, etc.)
- Improved Handling: Astillas come in reusable bags that are easier to store and handle. The bags are specifically designed for longer life to ensure re-usability.
- Worker Safety: Reduced acidity improves worker safety. The Astillas are relatively safer to be handled by bare hands.
- Clean Combustion: Reducing the oil content reduces the carbon content as well. Therefore, black smoke emissions are eliminated with this.
|1||Gross Calorific Value||>4200 Kcal/Kg|
|4||Sizing||5 to 25 mm|
Note: “Astillas” is an intellectual property of Steamax. Steamax bears the sole right of using the name and manufacturing this fuel. For details, contact at email@example.com
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How Biomass Helps In Eliminating Black Smoke Emissions? This is an actual case study of one of our clients, HIL ltd. The main problem faced by the industry was high amount of black smoke formation and more than permissible solid particulate emissions from the boiler’s chimney. All this was greatly contributing to the environmental pollution that became a matter of concern for the residents of nearby society Steamax did some improvement in their pollution control equipment (Bag filter), installed it’s multi-fuel automatic biomass feeding kit, and started providing its clean biomass fuel blend, ‘Astillas’ to the company. The picture above clearly indicates the end-results. If you are facing any such issues, we will be happy to help. Reach out to us at firstname.lastname@example.org
- Couto, H. S., Duarte, F., & Bastos-Netto, D. (2004, December). Biomass combustion chamber for cashew nut industry. In Proceedings of the Seventh Asia-Pacific International Symposium on Combustion and Energy Utilization.
- Mohod, A. G., Khandetod, Y. P., & Powar, A. G. (2008). Processed cashew shell waste as fuel supplement for heat generation. Energy for Sustainable Development, 12(4), 73-76.