spent cooking liquor typically holds full cooking temperature i e 130 160 u00b0 c at withdrawal said temperatures obtained after using live steam from the medium pressure steam net of the mill this high heat value is preferably used to heat the polysulfide liquor that conventionally is made on site of the mill and is stored in atmospheric tanks holding a temperature of about 70 80 u00b0 c thus the polysulfide liquor may thus be heated easily to a temperature of about 110 130 u00b0 c before addition to the system using heat exchangers in the most preferred embodiment and as disclosed in fig1 is the second heat exchanger he 2 system using the heat value of low pressure steam using live steam from the low pressure steam net of the mill the low pressure steam is most often available at abundance at the mill in contrast to medium pressure steam but is most suitable for heating purposes in the range 100 130 u00b0 c the heating obtained in the circulation by the second heat exchanger preferably in combination with the heating of the polysulfide liquor is most often sufficient for effective steaming of the cellulose material in warm climate where.