39 a large quantity of energy can be recovered with turbine steam being used only on the order of magnitude of about 9 metric tons hour at a pressure level of about 8 bar while the accumulating condensate is returned to the boiler with this quantity of steam at least 8 metric tons of chemical pulp can be bleached while it is diluted in stages by the addition of water to obtain a concentration of about 3 percent of dry substance whereby more than 400 metric tons of liquid per hour are passed through during some of the stages this data is pertinent when using mgo as the caustic agent when using naoh as a caustic agent heat consumption is even lower fig2 illustrates the delignification apparatus 10 which is in the form of two vessels 1 1 39 that are operated with varying pressures and temperatures chemical pulp is charged through the pipe 24 in the circulation system 8 of the pressure vessel 1 the circulation system 8 is provided with a connection 5 in a head chamber 4 of the vessel 1 in which gas accumulated within the head chamber 4 is drawn in and brought into contact in a gassing device 6 with the liquid chemical pulp having a concentration of about 3 percent ats due to the intensity of the contact delignification will continue after mechanical gassing has been completed so that in order to.