Six Areas of Focus For Energy Saving Across P&P Mills

• Measures for reducing the energy use in raw material preparation are presented in this chapter. These include cradle debarker, ring-style debarkers, chip conditioning, chip-conveying systems, use of secondary heat instead of steam in debarking, automatic chip handling and thickness screening, bar-type chip screens, and fine-slotted wedge wire baskets.
• Possible measures for reducing the energy use in chemical pulping are presented in this chapter. These include batch-digester modification (indirect heat, cold blow); continuous digester control systems; digester blow/flash heat recovery; use of flash heat in a continuous digester to preheat chips; optimization of the dilution factor control; use of evaporator condensates on decker showers; use of two pressure level steaming of batch digesters to maximize back-pressure power generation; use of digester additives to increase yield; use of extended delignification and oxygen delignification.  
• Possible measures for reducing energy use in bleaching are presented in this chapter. These include improved brown stock washing, washing presses, ozone bleaching, and heat recovery optimizing the filtrate recycling concept for optimum chemical and energy use.
• Possible measures for reducing the energy use in chemical recovery are presented in this chapter. These include black liquor solids concentration; lime kiln oxygen enrichment; lime kiln modification; lime kiln electrostatic precipitators; improved composite tubes for recovery boilers; quaternary air injection; recovery boiler deposition monitoring; converting evaporation to seven-effect operation (installing additional evaporator effect); performing evaporator boilout with weak black liquor; converting recovery boiler to nondirect contact and implementing high solids firing; condensate stripping; installing a methanol rectification and liquefaction system; and Tampella recovery system.
• Alternative black liquor recovery processes are presented in this chapter. Gasification processes (Manufacturing and Technology Conversion International fluidized bed gasification and Chemrec technology—atmospheric and pressurized system, catalytic hydrothermal gasification of black liquor), causticization processes (autocausticization and direct causticization), and the combination of alternative causticization and gasification processes are discussed. Environmental impact of black liquor gasification is also discussed.
• Possible measures for reducing energy use in stock preparation and papermaking are presented. These include shoe (extended nip) press; advanced dryer controls; optimization of water removal in forming and pressing; high consistency forming; Condebelt drying; hot and superhot pressing; gap formers; direct drying; cylinder firing paper machine vacuum system optimization; energy savings through heat recovery systems; implementing efficient control systems for the machine steam and condensate systems to eliminate excessive blow through and steam venting during machine breaks; optimization of pocket ventilation temperature; control of dew point; closing hoods and optimizing ventilation; infrared drying and moisture profiling; dry sheet forming.

 Source: Maklain Market Analysis Group (Nov. 2018)

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