alkali used is 11 of the bone dry raw material based on sodium hydroxide anthraquinone added is 0 8 liquor ratio is 1 4 and the mixture is heated to 130 u00b0 c for the first time insulated at the temperature for 40 min then relieved for 30 min heated to 173 u00b0 c for 60 min for the second time and insulated for 60 min high hardness pulp obtained after cooking has hardness of 25 equivalent to 45 kappa number and beating degree of 12 u00b0 sr and is conveyed to a single spiral press master with variable diameter for extracting the black liquor in the prior art for pressing the high hardness pulp with concentration of 20 obtained after pressing is conveyed to a hop sieve for coarse pulp screening with hop sieve loss of 0 2 and delagged by a high concentration slag separator with loss of 0 1 the pulp obtained after deslagging is fed into a horizontal belt pulp washer for washing pulp concentration is 2 0 while washing the pulp from the pulp washer has concentration of 9 temperature is kept at 68 70 u00b0 c during the washing process and the pulp is heated to 70 u00b0 c and conveyed to a medium concentration pulp pipe by a spiral conveyor after adjusting concentration the pulp.