. The manufacture of pulp and paper : a textbook of modern pulp and paper mill practice. be able to reducethe pressure quickly before blowing. The circulation is un-doubtedly also better, and the distribution of temperature istherefore more uniform, with the gas space created by side reliefor by draining for a short period through the bottom valve, apractice which is also followed at times. 102. Relief Gas Strengthens Acid.—While the relieving ofacid and gas is an important part of the cooking process itself,it is also very essential, for the manufacture of the cooking acid,that this operation
. The manufacture of pulp and paper : a textbook of modern pulp and paper mill practice. be able to reducethe pressure quickly before blowing. The circulation is un-doubtedly also better, and the distribution of temperature istherefore more uniform, with the gas space created by side reliefor by draining for a short period through the bottom valve, apractice which is also followed at times. 102. Relief Gas Strengthens Acid.—While the relieving ofacid and gas is an important part of the cooking process itself,it is also very essential, for the manufacture of the cooking acid,that this operation be properly conducted. §4 THE COOKING PROCESS 69 The reclaiming process, and the building up of a strong acid,has become very important and typical for this continent, onaccount of the necessity of using a strong acid to cook the usuallyvery wet wood in a comparatively short time. If the acid shouldbecome weak on account of too much weak relief liquor beingreturned to the acid, the relief liquor must pass through theseparator, and only the gas may then be returned to the reclaim-. Fio. 29. ing system, the liquor not being used. But even more necessarythan a strong acid is a uniform acid; and in order to obtainuniform reclamation, the digesters must be properly spaced,that is to say, there should be a certain time between the steam-ing of each digester in the mill, of 1, 2, or 3 hours, dependingupon number of digesters and cooking time. 103. No Standard Method of Cooking.—It is not possible togive any standard method of cooking; the process depends toomuch upon the nature of the wood, the composition of the acid, 70 MANUFACTURE OF SULPHITE PULP §4 the desired quality of pulp, and, especially, upon the instructionsissued at each plant, which are based upon particular 10 or 11 hours cooking for easy-bleaching pulp, a tem-perature of 105° to 110°C. is usually reached after 4 hours, andthis is gradually increased to 145° or 155°C, depending uponthe wood an
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