Kraft chemical pulping recovery systems

Melville, S., and Williams, T., Application of Economic Optimization to the Chemical Recovery System of a Kraft Pulping Process, Laboratory for Applied Industrial Control, Report 107. Purdue University, West Lafayette, IN, 1977. 

While the Kraft process initially had two distinct disadvantages, it produced a dark pulp and required chemical recovery, the pulp is stronger and has better dimensional stability than in the old soda process. Chemical recovery systems rapidly became quite advanced and most advanced mills are now aiming for 98-99% chemical recovery. 

A feature of the kraft process vital to continued success is its integral, well-tested chemical recovery system. The digestion liquor for each batch of chips to be pulped is mainly obtained from the chemicals recovered from the spent liquor of previous digestions, and has approximately the composition given in Table 15.8. For kraft pulping it is usual to specify all of the components of the digestion liquor on a NaiO equivalent basis. This puts all the active constituents on the same sodium ion content basis. Thus, the actual concentration of sodium hydroxide present for a 73 g/F, NaiO equivalent is given by Eq. 15.12. 

The US pulp and paper industry operates over 550 facilities which employ over 200,000 people. Total shipments are 60 billion with an additional 80 billion in converted products. Several proeesses eontribute to the emission of solvents. These include chemical pulping kraft process (terpenes, alcohols, methanol, acetone, chloroform), bleaching (acetone, dichloromethane, chloroform, methyl ethyl ketone, carbon disulfide, chloromethane, and trichloroethane), wastewater treatment (terpenes, alcohols, methanol, acetone, chloroform and methyl ethyl ketone), and evaporators in chemical recovery systems (alcohols and terpenes). 

Figure 20-1 Simplified overview of a typical kraft process showing chemical pulping, oxygen delignification, pulp bleaching, and chemical recovery systems. Important mixing operations are indicated by the NAMF mixing icon.

The overall system that we will analyze comprises the unbleached Kraft pulp line, chemicals and energy recovery zones of a specific paper mill (Melville and Williams, 1977). We will employ a somewhat simplified but still realistic representation of the plant, originally developed in a series of research projects at Purdue University (Adler and Goodson, 1972 Foster et al., 1973 Melville and Williams, 1977). The records of simulated operation data, used to support the application of our learning architecture, were generated by a reimplementation, with only minor changes, of steady-state models (for each individual module and the system as a... 

Waste water treatment Recovery of heavy metal ions from effluent of the galvanizing process,36 treatment of waste from galvanizing baths (Cr, Zn, etc.),37 recovery of precious metals, regeneration of chemical plating baths,38 removal of radioactive elements,39 removal of ions such as chloride ions from a Kraft pulp mill,40 completion of closed system of waste water in factories,41 treatment of adsorption solution of flue gases,42 removal of salt from landfill leachate.43... 

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