In modern kraft mills extra
electricity is also produced and sold to the market. The mills using
an acidic process (using either magnesium bisulphite, ammonium
bisulphite or calcium bisulphite), which today produce less than
10% of the pulps, can be considered as even more complete biorefineries:
in addition to the production of cellulose they can produce bioethanol, vanillin or lignosulphonates