Limestone is used for uniform ashing and starch is used as a binder. Borax, Yes Borax! is used to help release the briquettes from the press, and sodium nitrate and sawdust are used to aid in ignition. A lot of experienced BBQ folks out there seem to voice concern about the borax, limestone.
Lignite also referred to as brown coal, is used to make coal briquettes that are extremely easy to light, produce less ash than other fuels and are more resistant to damp. Coal Briquette Uses Lignite coal briquettes are widely used for open fires and multi-fuel stoves.
If you are targeting high end markets like USA, go ahead and use sodium nitrate as an accelerant in your briquettes for that market is willing to pay more for quality. If you are targeting low end markets in developing countries, forget about sodium nitrate. Instead, use sawdust as accelerant.
Starch Starch is the most common binder though it is usually expensive. It doesn't have to be an food grade. In general, about 4-8% of starch is needed to make the briquettes. Starch sources can be corn starch, wheat starch, maize flour, wheat flour, rice flour, cassava flour, potato starch, etc.
Charcoal briquettes have higher caloric power than wood briquettes; they burn for longer and they produce more heat and less (almost zero) smoke. Also, they’re lighter. In order to DIY charcoal/char, you’ll require wood scraps. The best material for making charcoal is hardwood such as birch, beech, hickory, maple and oak.