Pulp and Paper 



Table 25-11 



3127 



-Yietds and electrical energy requirements of four hardwood pulping 

 processes (Swartz 1962) 



Process 



Pulp 

 Yield' 



Electrical energy 

 requirement- 



Percent 



Mechanical stone groundwood, conventional^ 90-95 



Chemi-groundwood and chemi-thermomechanical pulp, 



including cold soda pulp 85-92 



Semi-chemical, including neutral sulfite semichemical 60-85 



Extensive chemical, including hot soda, kraft, and acid 



sulfite and bisulfite 43-52 



Hp days/ton 

 65-75 



40-70 

 10-20 



5-10 



'Percent of ovendry weight of wood. 

 ^Per ton of ovendry pulp. 



•^Thermomechanical pulp disk-refined from chips requires about 50 percent more energy than 

 conventional groundwood. 



One possibility for decreasing energy required for production of TMP is use of 

 natural lignin-degrading organisms to loosen lignin bonds in chips before they 

 are fiberized. 



In spite of high energy costs, mechanical pulps have low total manufacturing 

 costs because of their high pulping yields and low capital requirement. 



Readers interested in further study of the technology of pulping chips with 

 disk refiners will find useful the review of Franzen (1985). 



25-6 SEMICHEMICAL PULPING 



Semichemical pulping consists of a mild chemical treatment (but more severe 

 than in chemi-mechanical pulping) to remove sufficient of the ligno-cellulose 

 fiber encrustants to allow mechanical treatment to complete fiberizing. Pulps 

 produced from southern hardwood by semichemical pulping are principally used 

 for corrugating medium (fig. 25-18 top). 



TRENDS IN MECHANICAL AND SEMICHEMICAL PULP 

 PRODUCTION^ 



Production of mechanical pulps (steam-gun exploded fiber^ stone ground- 

 wood, and disk-defibrated fiber) and semichemical pulps in the southern United 

 States in 1974 was 5.25 million tons, but 2.20 million tons were conventional 

 groundwood pulp which contained little hardwood. The remaining 3.05 million 

 tons were 56 percent semichemical and 44 percent coarse fiber (exploded and 

 disk defibrated) pulps which amounted to 10 percent of the total production of 



^Text under this heading is condensed from McGovem and Auchter (1976). 

 ^For a discussion of this technology see sections 18-27 and 23-6. 



