Checklist of potential projects for energy conservation in the pulp and paper industry

Extracted from : Energy management and conservation in pulp and paper mills, Matthew Coleman, Miller Freeman Publications Inc (1981), Chapter 6.

In other references, even more detailed listings can be found for specific processes.

  1. Pulp processing

    Batch cooking
Utilize indirect steaming of digesters.
Consider recovery of blow heat utilizing:
  1. Standard blow-heat recovery systems
  2. Blow-heat evaporation systems
  3. Vapor-recompression systems
  4. Use of paper mill wastewater for exchanger medium in blow-heat economizer systems.
Optimize utilization of energy during cooking cycles utilizing computer control for:
  1. Minimizing gas-off
  2. Maximizing pulp yield
  3. Minimizing cooking temperature (balancing alkali/wood ratio with cooking temperature)
  4. Control of two-stage digester heating utilizing low-pressure (wash) steam in first stage.
Minimize liquor-to-wood ratio.

Continuous cooking

Reevaluate ways and means of recovering heat from flashed steam, considering the dilution of cooking liquor and turpentine losses.
Reduce liquor-to-wood ratio.
Use computer control to:
  1. Maximize pulp yield
  2. Minimize cooking temperature.
Utilize waste low-pressure steam for indirect heating of cooking liquor.
Washing and screening
Optimize use of wash water relative to savings from recovered cooking and papermaking chemicals.
Consider diffusion washing.
Consider pressure washing with recirculation of air to conserve heat and reduce volume of emission required to be incinerated.
Recycle all liquor spills to system.
Utilize recycled water for washing pulp.
Utilize hot stock screening where compatible with product quality requirements.
Consider methods and equipment for increasing consistency of washed brownstock from 30% to 40%.
Utilize excess water as woodyard flume makeup.
  1. Liquor/recovery

Vacuum evaporators

Reappraise multiple-effect evaporator system optimum number of stages.
Evaluate use of vapor-recompression techniques.
Reappraise techniques to increase overall temperature drop across stages, and also to increase overall heat-transfer coefficient.
Collect and recycle all liquor spills.
Segregate condensates for stripping, i.e.:
  1. Those which require no stripping
  2. Those which require stripping of malodorous substances
  3. Those which require stripping of methanol.
Maximize use of multistage evaporation in thickening black liquor.
Reclaim demineralizer regenerant to weak black liquor.
Reevaluate efficiency of vacuum-producing equipment, i.e., use of vacuum pumps in place of ejectors.
Recovery furnaces
Maximize black-liquor solids to boiler.
Maximize temperature drop across boilers. Higher pressures and lower cold end temperatures.
Utilize indirect heating of black liquor at liquor heaters.
Investigate uses of waste heat in preheating air and boiler feedwater.
Design to insure condensate return.
Utilize recovery-furnace computer control to reduce heat losses and maximize steam production and reduction efficiency, and minimize blowdown.
  1. Causticizing
Recover heat from slaking for reuse.
Evaluate all methods to reduce addition of freshwater to the system:
  1. Use mechanical seals
  2. Use dirty condensate in place of freshwater for showers.
  3. Cascade water used for bearings, trunnions, and cooling water, etc., to system before freshwater is used.
Collect and return all spills to system.
Insulate or cover lime kiln, particularly at hot end. Also design and operate for maximum fuel economy by:
  1. Utilizing product coolers
  2. Minimizing dust recycle.
Reevaluate use of fluidized-bed techniques for burning lime.
Evaluate oxygen enrichment to reduce energy consumption in lime kilns.
Evaluate methods to maximize concentration of white liquor.
  1. Bleaching
Consider methods of:
  1. Maximizing pulp consistency in each stage 2. Minimizing bleaching temperatures
  2. Design for countercurrent reuse of wash water.
Use paper-mill (bleached) whitewater on last stage wash.
Design for the reuse of chlorination-stage effluent for brownstock high-density dilution.
Eliminate all freshwater on washer showers or seal-box showers.
Consider methods for reusing extraction-stage effluent for caustic makeup.
Recover all Cl02 generator effluent as pulp-mill chemical makeup.
Reevaluate energy savings compared to bleaching economy and product quality by reducing the number of bleaching stages.
Consider economics of diffusion washing.
Reevaluate economics of in-plant generation of chlorine, caustic soda utilizing offgas H2 for fuel.
Use pulp-mill condensate flash steam, blow heat, or BSW hood economizers to heat bleaching chemicals (particularly ClO2).
Evaluate oxygen bleaching for minimizing effluent and reducing bleach-plant steam consumption.
  1. Paper/board manufacture
Design/operate saveall systems to produce wash water of sufficient cleanliness and reliability for general reuse in stock preparation and paper mill, i.e.:
  1. Fourdrinier showers
  2. Saveall showers
  3. Headbox showers
  4. Consistency dilution
  5. Wash-up hoses
  6. Dilution of chemical additives
  7. Bleach-plant washers
  8. Dilution in mechanical pulping operations.
Cooling, seal, gland, bearing waters, etc., should be segregated for temperature and reused where possible.
Reduce water content of paper entering dryers to minimum by mechanical means.
Evaluate economics of press-section rebuilds compared to energy expenditures for:
  1. Heating wire pit with steam
  2. Utilizing steam boxes
  3. Using drainage aides.
Reuse vacuum-pump seal water in wash-water system.
Utilize low-energy wet-end formers.
Reevaluate design/operation of paper-machine dryers from an overall steam usage, mill energy balance point of view, considering:
  1. Minimizing the dryer pressure level required
  2. Dryer drainage systems for control and economy
  3. Improved methods of utilizing vapor recompression to reclaim blow-through steam
Reevaluate design/operation of dryer hoods for controlled operation and recovery of heat, e.g. for heating wire-pit wash water.
Install paper-machine hood economizers for heating shower waters.
  1. Power generation
Install additional feedwater heating.
Reduce excess air for combustion by 02 monitoring.
Improve water treating to minimize boiler blowdown.
Improve condensate returns.
Recover heat from blowdown flash steam.
Use condensate for desuperheating.
Investigate auxiliary power consumption for possible improvements.
Recover sand-filter backwash by recirculating to clarifier.
Eliminate throttling of high pressure steam through PRVíS.
Optimize cascading of energy use about the plant.
Use boiler fluegases to dry bark and woodwaste before firing.
  1. Mill - general
Maintain or replace steam-trap stations that are leaking steam.
Eliminate leakage and misuse of water.
Evaluate feasibility of using exhaust steam for vapor-absorption refrigeration for cooling and air conditioning.
Review and adjust temperature drops across all heat exchangers to minimize usage of cooling water.