ph of 12 5 a kappa no of 15 and contains 15 kg of oxygen per metric ton of air dried pulp the mixture of pulp alkali and oxygen flows upward through the reactor at a residence time of 50 minutes at the top of the reactor but prior to dilution the pulp temperature is 95 u00b0 c due to the exothermic delignification reaction and the pressure is 60 psig pulp filtrate is injected through 16 nozzles each 38 mm i d in the reactor head as illustrated in fig1 to dilute the pulp is a consistency of 7 5 which cools the diluted pulp to 85 u00b0 c and the pulp is withdrawn through discharge pipe 17 the delignified pulp which now has a kappa no of 90 is ready for washing and bleaching prior to the final papermaking step the reactor of the present invention differs from prior art reactors and has several unique features and advantages over such reactors first the present reactor utilizes no mechanical devices for pulp feed distribution or discharge this reduces capital and operating costs and also introduces no agitation which could cause the small dispersed oxygen bubbles to coalesce as earlier described coalescence is undesirable because it reduces the oxygen gas interfacial area thus reducing the oxygen dissolution rate and therefore the delignification rate in addition large oxygen bubbles in the reactor may induce channeling resulting in a nonhomogeneous product the reactor also differs from the reactor described in earlier cited u s pat no 5 034 095 which utilizes conical top and bottom reactor sections having convergence angles between 20 and 60 degrees in contrast to the conical bottom chamber of the present invention which has a convergence angle greater than 60 and less than 90.