Verfahren zur herstellung von mindestens einem gerbsäureprodukt und rindenprodukt mit verbessertem heizwert

Abstract

A method for production of at least one tannic product and a bark product having enhanced fuel value is disclosed. According to the invention the method comprises the steps of disintegrating bark; compressing the disintegrated bark to recover a first liquid extract comprising tannic substances; impregnating the compressed bark with a first aqueous impregnation composition at a pH below 7, and at temperature within the range of 45-80°C; dewatering the impregnated bark to recover a second liquid extract comprising tannic substances and a dewatered bark product; recirculating at least a part of the second liquid extract to the impregnation step, wherein the first aqueous impregnation composition comprises a mixture of said recirculated part of the second liquid extract and optionally fresh water; optionally combining said first liquid extract with the non-recirculated part of said second liquid extract; and adding sulphite salt to said first liquid extract and to said non-recirculated part of said second liquid extract, or to the optionally combined first and second liquid extracts in a level of 1-25 % by weight for providing a first tannic product and a second tannic product, or a combined tannic product. Also the tannic product and the bark product obtained from the method is disclosed.