text: what is kappa number in pulp manufacture ?what does residual alkali signify in spent liquor ?   kappa number measures the delignification of the pulp.  pulp will be at a reference kappa between 60 and 100 usually, depending on the product.    residual alkalai is simply the amount of equivalent sodium hydroxide left in the pulp at the point it is measured.  this can be used to predict how much further deliginification can take place.