Efforts to improve paper machine energy efficiency center around five basic principles:

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1 Paper machine energy conservation TIP ISSUED 2003 REVISED 2006 REVISED TAPPI The information and data contained in this document were prepared by a technical committee of the Association. The committee and the Association assume no liability or responsibility in connection with the use of such information or data, including but not limited to any liability under patent, copyright, or trade secret laws. The user is responsible for determining that this document is the most recent edition published. Scope The paper machine area is a major energy consumer in most pulp and paper mills. The high cost of energy makes it important to implement energy management and conservation measures. Paper machine energy consumption represents 50-70% of purchased energy for an otherwise efficient integrated mill. If the paper machine is inefficient in its use of energy, the mill will be uncompetitive. Reductions in energy consumption reduce operating costs and increase profitability. Reducing paper machine energy consumption requires attention to details in design, operation, maintenance, and control of nearly all aspects of the papermaking process. This TIP discusses guidelines for monitoring, benchmarking, and optimizing energy-intensive unit operations to reduce paper machine energy consumption. Safety precautions Follow normal safety precautions when working around paper machinery, including use of personal protective equipment. Do not allow loose clothing or equipment to contact rotating machinery or ropes. Beware of overhead cranes and thermal and slip hazards around the dryer section. Avoid direct contact with hot surfaces. Use hearing protection in noisy areas. Eye protection should be worn in all production areas. Safety shoes and safety helmets should also be worn where required. Energy reduction strategy Efforts to improve paper machine energy efficiency center around five basic principles: Minimize the amount of water to evaporate in the dryer section (and pressure of steam used to evaporate it). Minimize the amount of steam condensed outside the dryers. Maximize condensate return flow and condensate pressure to the powerhouse. Minimize electrical consumption for key users. Monitor and manage energy consumption and cost. Mill-wide energy savings require a multi-faceted approach, including purchasing smarter, using less, integrating processes from different parts of the mill, and generating more low-cost electricity. Human factors such as training, publicity, visibility, accountability, benchmarking, and targets can aid in achieving energy conservation goals. System monitoring Scottish mathematician and physicist Lord William Thomson Kelvin ( ) said, If you can t measure it, you can t improve it. A key first step in energy conservation activities is monitoring energy consumption and making sure flowmeters and cost information are accurate. Some mills have developed mill-wide system balances that can be used to check accuracy of individual flowmeters. Assigning a person to be responsible for energy conservation in the mill and/or paper machine area can help increase visibility and accountability of conservation efforts. Steps for an effective monitoring program include: TIP Category: Automatically Periodically Reviewed (Five-year review) TAPPI

2 TIP Paper machine energy conservation / 2 Have an energy champion responsible for monitoring and reducing energy consumption on the machines. Meter energy flows to each machine. Establish key energy parameters. Highlight variables that affect energy consumption. Include energy parameters in operator rounds and centerlining efforts. Provide information to operators, engineers, and managers to encourage continuous improvement. Develop trouble, cause, and correction (TCC) procedures to troubleshoot issues contributing to high energy consumption. Discuss energy cost and conservation efforts in production meetings. Conduct periodic check-ups of key systems. Benchmark machine operation with best in class and best achievable for the equipment installed. Utilities to be monitored include: Pressure (kpa or psig), temperature ( C or F), and flow (kg/hr or lb/hr) for each header supplying steam to the machine. Electrical consumption for each machine (MW). Natural gas (m 3 /hr or scfm) Water flows and temperatures mill water, warm or hot water from other areas of the mill, and sewer (L/min or gpm, C or F). Compressed air pressure (kpa or psig) and flow (m 3 /hr or scfm). Condensate return flow (l/min or gpm, kg/hr or lb/hr) and temperature ( C or F). Based on these measurements and paper machine production rates, specific energy indices can be calculated and tracked: Steam consumption (kg/tonne or lb steam/ton paper) Electrical consumption (kwh/tonne or kwh/ton) Natural gas consumption (m 3 /tonne or kscf/ton) Total energy consumption (kwh/tonne or MMBtu/ton) Water consumption (m 3 /tonne or gal/ton) Compressed air consumption (m 3 /tonne or kscf/ton) Condensate return (%) Total energy cost ($/ton) Determination of energy unit costs typically requires assistance from mill accounting and powerhouse personnel. Understanding the relative cost of different energy sources can help papermakers minimize total energy costs. Note that the cost of various energy sources will change based on relative cost of corresponding raw materials. Cost components that should be included in evaluation of total costs include: Net cost of steam to each paper mill supply header ($/kg or $/klb). One method is to determine fuel cost for high-pressure steam minus the value of electricity generated by turbines. Marginal cost of steam (cost of the last steam generated) should be used to measure the value of steam savings. Marginal cost is usually higher than average cost since powerhouses use more expensive fuel to top off demand. Note that this method of calculation may be an over-simplification if pressure and flow in a low-pressure steam header are maintained by highpressure make-up steam supplied from a pressure-reducing valve in the powerhouse. Net cost of natural gas cost (typically expressed in $/kcal, $/therm or $/MMBtu) Electrical cost ($/MWh). Calculating $/kwh or $/hp-hr can assist in calculating electrical energy savings. Water and sewer costs ($/M liter or $/MMgal). Both supply and sewer water treatment costs should be included to determine true value of water conservation projects. The value of condensate returned to the powerhouse. This should include associated energy, water treatment costs, wastewater treatment costs, and raw water pumping costs to get it to the water treatment plant. Cost should be adjusted downward for condensate polishing costs.

3 3 / Paper machine energy conservation TIP The combination of production rates, energy consumption, and cost information can be used to determine energy cost per ton of product. It is also important to understand energy contracts. Generally managing energy savings downward is the correct move; however, with some peak energy contracts unless you are able to save off of peak there are no apparent savings and conversely if you can save off of peak there is an immediate benefit. Additional specific energy flows can also be useful, including dryer section steam, if it is metered separately from total steam to the machine. There are three areas that are typically poorly monitored that can help a mill identify steam waste; the steam flow to the wire pit or silo, the steam flow used to heat shower water, and the energy loss to the dryer vacuum condenser (water flow, temp in, temp out). Looking at valve position is one way of tracking these energy flows but does not tell the entire story. Most mills have no idea how much energy they are using in the silo or for shower water heating. The normal response from papermakers is "not much" but in reality it can be a significant use. Dryer drainage system vacuum condenser tracking is also recommended. It is a sure way to assess and maintain the health of the dryer drainage system. The percent energy loss can be tracked and trended. This identifies bad vent valves, open vent valves, high wet end dryer losses, air leaks, high water flow, etc. The vacuum condenser is often a piece of equipment that is poorly controlled. Poor control often results in high water flow that dilutes and upsets the fresh water system. Performance indices Performance indices can be used to benchmark energy consumption and identify opportunities for improvement. TAPPI TIP Paper machine performance guidelines (1) provides a broad range of indices for different grades of paper. Target values for key indices applicable to energy consumption are shown in Table 1 for various grades. Key factors Each machine typically has several key factors that influence energy consumption on the machine. Green/yellow/red indicators can be used for key process conditions that affect energy consumption to show whether values are in desired ranges. DCS and/or data historian trending can be used to track trends of key parameters. Sheet consistency out of the press section is often the primary variable affecting paper machine energy consumption. Regular grab samples (TAPPI TIP Determination of water removal by wet presses discusses the proper procedure) or the use of portable or fixed sheet moisture gauges specifically designed for use in the press section are recommended to track solids. Press solids can also be calculated based on press section and/or dryer section water balances. Typical additional key factors include: Venting from dryer section thermocompressor or cascade sections Condenser water valve output/condensate flow Differential pressure (especially for lead dryers) Wire pit steam water heating steam valve positions Mill water make-up into whitewater or warm water systems. Basis weight versus standard Press section weir flows Size press starch solids and pick-up Pocket ventilation temperature Temperatures through hood exhaust heat recovery systems Warm water flow, pressure, and temperature from pulp mill Winter/summer operating strategy for machine room ventilation Any additional steam venting Centerlining Centerlining is often a tool used to help ensure consistent paper machine operation and quality. The tool can also be used to help monitor and control energy consumption. Centerlining of energy parameters can often be divided into two categories: process setpoints and factors reflective of system health.

4 TIP Paper machine energy conservation / 4 Table 1. Energy performance indices Grade Corru- Recycled Bleached gated Market Fluff paper- News- Kraft Index Fine board Liner medium pulp pulp board print LWC paper Uptime, % First quality, % Overall machine Efficiency, % Total steam consumption lb/ton 4,000 4,000 2,800 2,750 2,000 2,500 2,800 2,800 3,000 5,000 kg/ton 2,000 2,000 1,400 1,400 1,000 1,250 1,400 1,400 1,500 2,500 Electrical consumption kwh/ton kwh/tonne Total energy cons. MMBtu/ton GJ/tonne Water consumption gal/ton 2,000 2,000 1,500 1,500 1,000 1,000 <1, m 3 /ton < Couch solids, % NA 21/18 22/18 20/19 Press solids, % 42/ /50 42/ /48 43/49 42/46 Size press moisture, % NA NA NA NA NA NA NA NA Reel moisture, % > Drying steam lb steam / lb water evaporated PV supply temperature F <180 <180 <180 <180 NA NA <180 <180 <180 <180 C <80 <80 <80 <80 NA NA <80 <80 <80 <80 Condensate return

5 5 / Paper machine energy conservation TIP Examples of process setpoints that can be used in Centerlining include: Wire pit and other water heating temperatures Pocket ventilation, blow box, and other air heating temperatures Dryer section differential pressures (or blowthrough flows) Press loads Sheet moisture at the reel Refining kw, freeness, hpd/t and/or kwh/t Examples of factors reflective of system health include: Overall consumption indices such as ton steam/ton paper, kwh/ton, and energy cost/ton Dryer section ton steam/ton Warm water flow and temperature from the pulp mill Mill water flow Silo and process heat exchanger valve positions Warm water make-up valve positions Mill water make-up valve positions into the white water or warm water systems Venting from dryer sections (dp or blowthrough vent valve positions) Pulper pump and agitator amps Press section weir flows Operator rounds Operator rounds should be utilized to manage systems that are not visible in DCS or data historians. Examples of areas where operator round may be required include: Roof or mezzanine rounds to check for leaking vent or safety-relief valves. Roof supply and machine room ventilation temperatures. Hydraulic cooling/heating systems. Condenser systems. Steam leaks. No dumping of condensate. Some mills utilize an infrared temperature gun to check stock and water system temperatures and detect cold-water infiltration. Note that flat black spray paint should be used to mark areas on piping where infrared measurements are used to ensure uniform emissivity. Energy surveys Energy audits can provide useful first steps to identify and prioritize opportunities to reduce paper machine energy consumption. Data can be collected from direct observation; data historians; discussions with mill operating; maintenance, and engineering personnel; and previous reports conducted on subsystems of the paper machine. A computer simulation of the papermaking process can help validate data and determine potential benefits from process changes. Keys to successful implementation of recommendations from an energy audit include: Obtaining buy-in from all parties involved Focusing on optimal measures, but not forgetting incremental gains Understanding the costs, risks, and benefits of potential projects Considering life cycle costs in project evaluation Thoroughly planning implementation Training

6 TIP Paper machine energy conservation / 6 Documenting results Optimizing the system after the project Additional surveys A detailed review of various paper machine systems can ensure that systems and equipment are operating efficiently. Some of these recommended surveys and suggested frequency are listed below. Steam trap surveys (annual) Compressed air system surveys (annual) Refining optimization (on-going) and mechanical surveys (annual) Saveall audit to check capacity and filtrate quality (annual) Showering surveys (every 2 years) Press section optimization (on-going) Press section nip surveys (every 2-3 years) Vacuum pump boroscopes or orifice plate testing (annual) Vacuum system surveys/optimization (every 3 years) Thermography to check for leaks and hot spots (annual) Steambox surveys (annual) Dryer steam and condensate system surveys (annual) Hood air system surveys (annual) Machine room ventilation studies (every 5 years) Pulp dryer maintenance/capacity reviews (annual) Tissue machine hood balances/inspections (annual) System optimization Key process areas to consider when in a program to reduce paper machine energy consumption are discussed below. Reducing the amount of water to evaporate Drying steam represents the majority of energy consumption on a paper machine. A step in minimizing energy consumption is reducing the amount of water to evaporate in the dryers. Opportunities to do this include: Increase press dryness (high-load, shoe presses) Optimize press fabrics and roll cover designs (venting and hardness, nip dewatering vs. Uhle box dewatering) Reduce basis weight (while meeting the product specifications) Trim the sheet at the wet end rather than at the dry end Improve cross-machine moisture profile uniformity Increase starch solids used in size press (metering size press) Minimize water added to the sheet through rewet showers Increase moisture content of the sheet at the reel (when sheet properties and profiles allow). Machine efficiency Increasing overall machine efficiency has a direct effect on specific energy consumption since it takes as much or more energy to produce a ton of broke as it does to make a ton of first-quality paper. Some steps to increase machine efficiency include: Reduce sheet break and grade change times. Shorten open press-to-dryer draws, provide direct sheet support. Minimize trim losses with good edge control and coordination with business logistics. Full machine threading - including features that minimize break recovery and thread times. Optimize performance of trim squirts.

7 7 / Paper machine energy conservation TIP Utilize camera systems to identify and characterize breaks. Optimize quality control system (QCS) performance to ensure good machine-direction (MD) and cross-machine direction (CD) profiles. Control sheet in open draws in the dryer section. Utilize capability of distributive control systems (DCS) and data historians to impact efficiency and troubleshooting. Optimize process chemistry for runnability and maximizing ash content - closed loop control of retention, charge, etc. Manage broke to maintain stability. Optimize whitewater saveall to maximize overall retention, to stabilize wet end during break conditions, and to increase clear filtrate quality and quantity for replacement of mill water in showers. Agitation Chest agitation is a significant contributor to paper machine electrical consumption. Opportunities to reduce energy consumption with design and operation of agitation include: Do not overestimate consistency when designing systems Design chests for the optimum dimensional ratios (cube is best) Do not underestimate temperature Allow for a larger manhole to install a larger impeller at low speed Keep flow impediments [ladders, etc] out of chest design Only operate the number of pulper agitators necessary Consider variable-speed or two-speed agitator motors Utilize zone agitation where complete mixing is not required. Consider top-entry instead of side-entry agitators Do not put pump suction behind the impeller Slow down an agitator and reduce horsepower if operating consistency has dropped substantially from design. Make sure there is not excessive motion when you look in a chest. Work with a supplier that understands the mixing process intimately Pump and motor systems U.S. Department of Energy (DOE) information indicates that average motor energy cost/mill/year is $1.7 MM for pulp mills, $4.6 MM for paper mills, and $3.0 MM for board mills. Average available motor savings opportunities per year are estimated to be $483,000 for pulp mills, $679,000 for paper mills, and $492,000 for board mills. The U.S. DOE Office of Industrial Technologies web site (3) includes information on pump and motor systems, compressed air systems, steam, and other opportunities to conserve energy. Approximately 30% of paper mill electrical energy consumption is by pumps, 20% by fans, 5% by compressors, and 45% by drive motors and other electrical equipment. Potential electrical energy savings opportunities are available through pumps and fans (53%), motor efficiency upgrades (23%), air compressors (6%), rewind improvements (6%), motor downsizing (6%), and other systems (6%). Pump-based systems represent the largest single group of energy-consuming equipment and offer greatest potential savings. DOE indicates that 80% of electrical consumption is by 10% of the motor population (motors greater than 50 hp) hp motors typically have the largest percentage of savings opportunities. The primary reasons pumps waste energy are over-design, change in process conditions, or degradation. Overdesign can be the result of overestimating design conditions, contingencies, safety factors, catch-up capability, room to grow, or design for a wide range of process conditions. Energy is wasted when a pump system is changed; resulting in a lower flow rate or lower head pressure requirements, but the pump, motor, and/or piping are not downsized to meet the change. Energy is also wasted when

8 TIP Paper machine energy conservation / 8 a larger pump than required is used for the purpose of commonality of spares. This also highlights the need to build to what will be required instead of building to some future incremental capacity. Pumps that operate in caustic or solids applications tend to experience impeller and wear ring degradation, causing a loss in pump efficiency. Routine inspection of pumps in these applications is recommended. Parts should be maintained and/or replaced as necessary. DOE promotes identifying motors with the greatest saving potential for further investigation. The greatest savings potential is typically centrifugal loads with a high duty cycle. These motors are referred to as the vital few. The following steps can identify them: 1. Categorize motors by size times operating time. Establish a threshold for more detailed consideration. (Should be a one-day effort in most plants a plant-wide motor inventory is not necessary). 2. Segregate by load type (focus on centrifugal loads) 3. Look for symptoms in pumping systems that indicate potential opportunity: Systems controlled by throttling valves Recirculation line normally open Systems with multiple parallel pumps with the same number of pumps always operating Constant pump operation in a batch environment or frequent cycle batch operation in a continuous process. Cavitation noise (at pump or elsewhere in the system) High system maintenance Systems that have undergone a change in function. 4. Establish policies to replace seldom-used, small-load, and large, non-centrifugal systems with high-efficiency motors. The Pumping System Assessment Tool (PSAT) (3) can be used to quantify energy consumption and cost savings potential from a pump. The assessment requires flow rate, pressure, and motor current or power data. Note that cost to buy a pumping system is usually much less than its operating cost. Life cycle cost should be used for evaluating pumps. Opportunities to reduce energy consumption by pumps and motor systems include: Replace throttling valves with speed controls where appropriate Reduce speed for fixed-load pumps Install parallel system for highly variable loads Equalize flows using surge vessels Replace motors and/or pumps with more efficient models Avoid recirculation control Avoid incompatible duties on common pumps Do not operate in startup configurations permanently Design systems with proper line sizes Avoid tanks where feasible Optimize process configuration, consistency and pressure setpoints Determine what can be shut off or bypassed during slow backs. Refining Refiners must be in good mechanical condition to minimize energy consumption and optimize fiber development. Effective life of refiners between rebuilds is typically years. Mechanical condition can be estimated by checking no-load horsepower by backing off refiners while stock is running through them. Higher than normal noload power indicates mechanical problems such as bad bearings, sticking quill, improperly greased slide coupling, etc. Lower than normal no-load horsepower indicates worn refiner plates. Poor mechanical condition can increase no-load horsepower by over 10%. Refiners should be inspected annually to check mechanical condition.

9 9 / Paper machine energy conservation TIP Some questions to ask when evaluating a refining system include: Are you running in Specific Energy control (either HPD/T or kwh/t)? Specific Energy control will minimize over-refining and optimize energy usage. Is the Net Specific Energy applied within normal guidelines for the grade/pulp? Is the refiner operating properly alignment and no sticking (e.g., splined shaft conversions can prevent sticking and alignment problems)? Is plate design matched properly to the fiber and refiner to achieve effective compression index and number of fiber treatments (optimize strength lift per unit of freeness loss)? Is the impact of refining on water retention value (WRV) and dewatering understood, i.e., run just enough refining? Is the stock consistency to the refiners between % for best energy transfer and fiber development? Does the consistency fluctuate to the refiners? A consistency that swings will cause fiber development to swing and lead to over-refining. Is the hardware run within proper flow limits? Opportunities to optimize refining energy include: Select refiner type, size, speed, and plates to minimize pumping and no-load energy losses. Operate refiners within design hydraulic flow range. Stocks flow above and below design capacity will reduce refining efficiency. Select refiner plate patterns to provide desired fiber property development with the lowest net energy applied. Operate with recommended refiner rpm. No-load horsepower increases exponentially with higher refiner rpm. Operate with lowest plate diameter consistent with stock flow and refining intensity requirements. No-load horsepower increases exponentially with refiner plate diameter. Bypass and shut down unnecessary and underused refiners. Normal refiner operation is most energy efficient at motor loads >80% of motor rating. Check freeness drop per hpd/t regularly to monitor refining efficiency and determine whether refiners are working correctly. Typical Canadian Standard Freeness (CSF) drops per net hpd/t are for Southern bleached softwood kraft and CSF/net hpd/t for bleached hardwood. Rebuild double-disk refiners to utilize splined shafts. Energy consumption can typically be reduced by 10-15% compared to floating-shaft arrangements. Some new conical and cylindrical refiner designs have lower no-load horsepower and provide more uniform refining than conventional disk refiners. Approach systems Opportunities to reduce energy consumption in the stock approach system include: Determine whether cleaners are needed. Size system properly for machine wet end. Utilize cleaners designed for low pressure drops (less than 207 kpa or 30 psi pressure drop). Conduct flow balances and verify operating conditions (consistency, pressure drop, efficiency, and debris removal) of cleaners. Reduce flows to fiber recovery stages based on balancing the system properly. Shut down cleaners where product quality permits. Determine whether deaeration is needed. Monitor pressure screen differential pressure and reject flows. Minimize stuff box flow and recirculation. Install variable-speed drives for machine chest pump (to eliminate stuff box), fan pumps, and other variableflow requirements. Design for low friction losses in piping. Consider installing compact stock approach systems offered by several suppliers. Some systems have reported energy savings as much as 25% from elimination of tanks and pumps.

10 TIP Paper machine energy conservation / 10 Recycled fiber systems Opportunities to minimize energy consumption in recycled fiber systems include: Install energy-efficient pulper rotor and extraction plate designs. Ensure that pumps are not oversized. Install frequency control on motors to reduce energy waste. Reduce pulp and water volume. Increase consistency as much as possible to reduce hydraulic volume for pumping and agitating. Simplify process configuration. Run equipment at optimum operation point. Make process stable and homogeneous. Increase process temperature to gain additional production, being careful not to exceed the stickies activation temperature. Close water loops. Refine and disperse pulp as little as necessary. Use latest development of machinery equipment to increase overall efficiency. Water heating Substantial savings in water consumption can be accomplished with limitations in retention, quality, and energy dissipation. The reduction in water-usage will also lead to an equivalent saving in energy consumption. The most energy-efficient systems have no continuous usage of steam to the silo or warm water system. Basic rules for water conservation include reduce, reuse, and recycle. Reduce simply means reducing fresh water usage. A systematic approach is recommended with clear identification of every stream. Paper mill water usage varies between 0 and 60 ton of water per ton of paper produced. Approximately 4-6 tons per ton represent a practical minimum. Zero consumption is possible, but only with serious quality drawbacks on some grades depending on wet end chemistry. Zero discharge is generally only achievable with products such as recycled fiber grades. Simple water reduction possibilities are often overlooked, so it is sometimes possible to achieve reduction of water and wet end energy consumption by up to 50%. Wet end water consumption can represent 20-45% of overall paper machine energy consumption. Reuse can require a systematic study of possibilities of substitution. New process equipment, such as filters, will be required to allow whitewater streams to be reused. Recycling can result in significant water and energy reduction, but extra equipment such as filters and/or evaporators may be required. Heat dissipation and chemical concentration can become issues as water systems are closed. Opportunities to minimize steam required for water heating include: Maximize stock temperature from the pulp mill (at least 5 F, 3 C warmer than silo temperature). Utilize waste heat from the pulp mill (water stream at least 5 F, 3 C warmer than silo temperature) and/or hood exhaust heat recovery instead of steam to heat whitewater and warm water. Return only warm/hot water streams to the warm/hot water systems. Minimize mill water infiltration into whitewater and warm water systems. Minimize flow and maximize temperature of water from condenser systems. Maximize strained/polished whitewater reuse in paper machine showers. Ensure proper saveall design, maintenance, and operation. Utilize strainers and polishing filters after saveall clear legs to allow reuse in showers. Circulate vacuum pump seal water using strainers and a cooling tower. Utilize stock/whitewater or warm water instead of mill water for additive make-up and carrier water when feasible.

11 11 / Paper machine energy conservation TIP Use warm (approximately 10 F, 38 C) water instead of cold mill water for seals. Utilize dead-band control logic for emergency water make-up into whitewater storage chests. Determine optimum silo temperature for the machine. Minimize total steam consumption. Savealls Effective saveall design and operation are essential for minimizing material losses and reducing water consumption on the machine. Increasing capacity, improving maintenance, and/or installing post-saveall strainers and filters can improve filtrate water quality to allow saveall filtrate to be reused in place of fresh water. Key saveall parameters to evaluate include: Installation and equipment, including size (number of installed discs and available blanked-off discs), droplegs (diameter and layout), and sector type (cover type and condition). Operation, including proper sweetener type and quantity, well-tuned vat level control, dilution of recovered stock with rich white water bypass, and cloudy filtrate recycle. Optimize split between cloudy and clear legs to match usage and prevent mill water make-up into the system. Maintenance including sector cover condition, sector-to-rotor seals, and knock-off and oscillating cleaning showers. Dissolved air flotation (DAF) savealls can be used in addition to or instead of disk or drum savealls to help improve whitewater quality. Showering Showering is a major source of fresh water consumption on many machines. Any shower water used on the former that is below whitewater temperature requires steam to return the silo to desired temperature. Cool showers in the press section can lead to deposits and reduced press solids. From an energy and water conservation perspective, showers should utilize filtered/polished whitewater wherever feasible. One approach to optimize shower performance is to assign a whitewater reuse risk factor for each shower based on: Water filtered with current technology Likelihood nozzles will plug Potential fabric plugging from fines Negative effect on paper making process Typical low-risk showers include: Breast roll showers Knock-off showers Medium-risk showers typically include: Lubrication showers Wetting showers High-risk showers include: High-pressure wire cleaning High-pressure felt cleaning Steps for optimizing shower performance include: Determine optimum shower flows, shower and nozzle design, and water quality requirements. Calculate potential energy and fiber savings from utilizing whitewater instead of fresh/warm water. Improve saveall and filtering to achieve water quality requirements.

12 TIP Paper machine energy conservation / 12 Chemistry Chemistry can impact paper machine energy consumption by affecting sheet properties and improving drainage. Make-down and introduction of chemicals into the system can also affect energy consumption. Opportunities to reduce energy consumption through chemical systems include: Utilize polyamine products to increase strength. This can provide savings through reduced refining, reduced basis weight, increased couch and press solids, and /or reduced starch usage. Utilize enzymes for fiber modification to reduce refining needs. Utilize silica and microparticles to improve drainage. Utilize whitewater instead of mill water for chemical injection. Maximize ash content in the sheet. Headboxes Basis weight profiles ultimately impact pressing, runnability, and dryer operation. Pressure drop through headboxes have increased with headbox design evolution. Turbulence level and nozzle convergence impact MD/CD ratio capability. Consistency profiled designs require lower flow from the cleaner system. Some areas where headboxes affect paper machine energy consumption include: Minimize MD and CD basis weight variability to improve runnability and maximize dewatering and drying efficiency Improve moisture profile to allow maximum possible moisture content at the reel Optimize turbulence level and nozzle convergence. The impact on MD/CD ratio capability can help optimize required strength characteristics to allow for reduced basis weight or reduced refining levels Impact MD/CD ratio capability Optimize headbox contribution to formation and sheet uniformity to aid forming, pressing, and drying rates, improve runnability, and to improve strength allowing the use of higher freeness furnishes. Operate headbox within designed flow range. Over-designed flow capability generally has very poor results Maintain cleanliness for efficiency. Formers Formers consume energy directly through drive load and vacuum systems. Formation and drainage affect performance of downstream processes. Areas where the former affects energy consumption include: Utilize former type and headbox that provide optimum formation results at higher consistency Match hardware to drainage needs Avoid sealing the sheet early in the forming process. Graduate vacuum down the table to reduce drag load and provide proper sheet consolidation. Utilize multi-compartment high-vacuum boxes. Evaluate drainage element materials for impact on drag load Avoid couch re-wet (suction box orientation, double doctors, air doctors) Optimize headbox and forming temperatures for impact on drainage and solids Monitor former solids frequently, maintain high level of solids Paper machine clothing Properly designed clothing can have an impact on energy consumption that far exceeds the cost of the fabrics. Forming fabrics affect energy efficiency in much the same way as formers:

13 13 / Paper machine energy conservation TIP Consistency off the couch, with ~10% of solids improvement transferring to the dryers Improved formation resulting in better pressing uniformity Flatbox vacuum requirements Reduced drive loads Press fabrics are an important part of press section optimization. Opportunities include: Pressure uniformity through micro-pressing Increasing consistency into dryers Minimizing sheet rewet Nip dewatering Opportunities to reduce Uhle box vacuum Dryer fabrics can affect capacity and energy efficiency through: Fabric tension Surface contact heat transfer Pocket ventilation mass transfer Resistance to contamination Vacuum systems The vacuum system is often the second largest process in the paper mill for electrical energy consumption (after paper machine drives), and is frequently one of the least understood parts of the papermaking process. Vacuum systems can have from 1,000 to 10,000 installed horsepower. Often vacuum systems can use 10 20% more horsepower than is necessary for paper production. Some of the most common vacuum system problems that can increase energy consumption and/or reduce system efficiency include: Hot seal water. High backpressure on vacuum pumps. High seal water pressure, resulting in high seal water flow. Use of synchronous versus induction motors can affect power factor for the entire paper mill. Recirculated seal water system with no cooling, or poorly functioning cooling system. Usually, this is done with a cooling tower. Worn or missing seal water orifices and nozzles. Scale build-up in pumps and piping. Worn pump rotor, casing, or lobes. Old, obsolete, and less efficient vacuum pumps. High piping losses and incorrect system design. Guidelines to minimize vacuum system energy consumption include: Use fans or exhausters instead of vacuum pumps for low-vacuum applications such as vacuum foils. Control vacuum level by bleeding air into the system instead of by throttling liquid ring pumps. Graduate flatbox vacuum to maximize dryness and minimize drag load. Eliminate unnecessary vacuum boxes (remove or drop out of contact with the fabrics). In addition to requiring additional vacuum pumps, sucking excessive air through the sheet can cool the sheet and cause press solids to drop more than the small amount of water that comes out with the air, especially on lightweight, open webs. Extra flatboxes also add drag load to the table. Proper flatbox setup can remove more water while reducing table drive load by as much as 10%. Ensure proper Uhle box slot size to provide required flow capacity and dwell time. Ensure proper vacuum pump application (high-vacuum vs. low-vacuum pump design).

14 TIP Paper machine energy conservation / 14 Prevent carryover of process fluids from suction point. Provide water/air separation ahead of the pump to prevent two-phase flow at the pump. Use proper separator removal pump design. Check vacuum pump internal clearances and/or capacity annually. Rebuild pumps operating at less than 80% of design capacity. Conduct routine maintenance of vacuum pumps and auxiliary equipment, including belt and gear drives and motors. Replace and calibrate gauges and process instrumentation (vacuum gauges, seal water pressure gauges, level transmitters in vacuum pump sumps, amp meters for motors) Remove old, inefficient vacuum pumps from service. Do not rebuild obsolete pumps with inefficient designs. Modern blower systems consume much less electricity than liquid ring vacuum pumps and do not require seal water. Some mills with hard water have installed blowers to avoid calcium carbonate buildup in conventional vacuum pumps. System audits can be used to help reduce wasted energy. Replacing or calibrating gauges can ensure proper indication of vacuum levels. Key operating data should be monitored, reviewed and recorded. Sheet and fabric moisture should be checked regularly to ensure effective use of vacuum. One of the most effective ways to manage vacuum system energy is through EMBWA (Energy Management By Wandering Around). Additional information on vacuum system optimization is included in TAPPI TIP Performance evaluation techniques for paper machine vacuum systems (4). Press section On a typical paper machine with 0.5% headbox consistency, 20% couch solids, 40% press solids, and 5% reel moisture, 195 kg water is removed per kg fiber in the forming section, 2.5 kg water per kg fiber in the press section, and 1.45 kg water per kg fiber in the dryer section. However, the cost of water removal is significantly lower in the forming and pressing sections than in the dryer section. Removal of the water content after the press section represents more than 50% of the energy consumption in the paper machine system. Each one percentage-point improvement in solids out of the press section results in 3-5% less water that needs to be evaporated in the dryer section. Maximizing press performance is thus one of the most important aspects of paper machine energy conservation. Primary opportunities in the press section are increased water removal, dryer section steam savings, increased production, more efficient water removal, sheet property improvements, and fiber savings on bulk sensitive and strength grades. Factors influencing press water removal are furnish, time, temperature, and pressure. Press performance can be improved by increasing nip load and by increasing the time during which the press load is applied. Press impulse (press nip pressure x nip residence time) has been shown to be a good performance indicator for press water removal. Development of shoe presses has significantly increased time available in the nip, resulting in higher press impulse without the damaging effects of raising nip load. Press performance can also be improved by increasing temperature of the web during pressing. Experience indicates that solids content of the pressed web can be increased by one percentage point for each 10 C (18 F) increase in web temperature. Methods to increase temperature in the press section include increased stock temperature, steam shower applications on the sheet or on the fabric, heated press rolls, or hot water flooded nip showers. Energy efficiency of heating the sheet in the press section should be compared with that in the dryer section (typically 1.3 kg steam per kg water evaporated). Operating felt showers with cool water (such as fresh water) cools press fabrics and reduces sheet dewatering. Trials have indicated that sheet dewatering can be increased by one percentage point by increasing shower water temperature by 10 o C. High-pressure and low-pressure shower water should be at least equal to the temperature of stock at the headbox. Shower water temperature of 54 C (130 F) or above is beneficial in maintaining fabric temperatures. Shower water heating is an excellent application for direct or indirect heat recovery. Shower water temperature on the last press fabric should have priority for use of warm water on the wet end of paper machines.

15 15 / Paper machine energy conservation TIP Uniformity of pressure applied to the sheet in the press is important, especially with modern shoe press technology, because of increased nip dwell times and lower peak nip pressures. Modern press fabric designs provide improved pressure uniformity and higher sheet solids content. Multi-axial laminated fabrics provide superior pressure uniformity, excellent bridging on vented/drilled rolls, and more steady-state pressing compared to conventional fabrics. Flat batt fibers can offer contact area equal to round fine denier batt without sacrificing wear volume. TAPPI TIP Press Section Optimization (5) provides guidelines for evaluating and improving press section performance. The TAPPI Paper Machine Wet Press Manual (6) provides more complete coverage of press section optimization. Opportunities to optimize pressing include: Shoe pressing increases dryness potential, and for bulk-sensitive grades, adds degree of freedom (bulk vs. dryness). Double felting improves dewatering on heavyweight grades. Graduate press loads. Maximize loading throughout the grade mix (within sheet quality limitations). Steam boxes increase sheet temperature and increase exiting dryness; can also be used for profile improvement. Felt heating will help clean the fabric as well as help maintain or increase sheet temperature. Optimizing roll cover hardness and use of blind drilled or other cover designs can improve press dewatering. Balance between nip and Uhle box dewatering over fabric life. Maintain shower temperature at or above sheet temperature. Nip dewatering efficiency, press geometry, fabric selection, and operations can result in improved profiles, solids, and in vacuum for uhle boxes. Felt and belt design optimization - press fabric design greatly impacts press efficiency, solids level. Minimize rewet (fabric runs / sheet runs; sleeve doctors, double doctors, air doctors, use of catch pans on high dewatering nips that generate water spray). Minimize draw to maximize CD strength on grades requiring high CD strength properties. Check nip profiles and optimize crowns, dubs, and fabric cleaning to improve moisture profiles. Monitoring of pressing performance throughout fabric life on-line monitoring of press water flows, frequent CD and MD monitoring of fabric permeability, moisture, and temperature. Check couch and press solids at least once every outage cycle. Maintain a database of results. Steam showers Steam shower efficiency depends on the product being made, where the steambox is installed and how it is operated. TAPPI TIP discusses steam shower applications in the forming and press sections. Steam showers are most energy efficient with low steam ratios on relatively cool systems with vacuum assist beneath the steambox. Better steam utilization efficiency occurs when steam showers are located ahead of the last press nip since there is less water to heat. For most applications, efficient steam flow ratios are 0.10 lb steam/lb paper for fourdrinier applications, lb/lb for press section applications, and 0.05 lb/lb for Uhle box steam showers. Mills should determine the value of steamboxes for specific applications and operate accordingly. Some modern steambox designs can operate with much greater energy efficiency than some older models. Opportunities to optimize steam shower performance include: Utilize low pressure waste or vented steam. Reduce steam flow when producing grades that are not drying limited. Operate steambox at clearance recommended by manufacturer. Apply only as much steam as can be condensed in or on the sheet. Lower steam supply to reduce excess fog in the machine room. Use profiling capability to apply steam only where needed. Reduce vacuum to reduce sheet cooling and air infiltration under the steam shower. Increase vacuum to improve steam penetration into sheet.

16 TIP Paper machine energy conservation / 16 Control steam temperature to improve condensation rates. Typical recommended temperatures are 5-10 F (3-6 C) of superheat above saturation temperature. Provide proper mist elimination when utilizing flash steam. In many cases, some high-pressure make-up steam is required to introduce a small amount of superheat. Isolate non-profiling preheat section of profiling steam shower. Extend and contain steam in wedges and tunnels. Maintain pressure and temperature gauges. Maintain profiling mechanisms in good working condition. Eliminate pulp splatter from trim squirts. Utilize Teflon and/or polished surfaces to minimize build-up and allow operation at design clearances. Consider applying a little steam to multiple locations in the press section instead of a lot of steam in only one location. Elevate press fabric temperatures to the same as the sheet to encourage water movement in the press nip. Dryer section The dryer section represents the largest thermal energy consumer on the paper machine. Information on monitoring dryer section performance is included in TAPPI TIP Dryer section performance monitoring (7). The 10 Commandments of energy efficient drying are: 1. Don t dry any more than you must 2. Don t vent steam anywhere 3. Match the ventilation air flow to drying requirements 4. Use steam from lowest header pressure possible 5. Keep the machine running (minimize break times) 6. Improve the moisture profile 7. Increase the heat transfer rate 8. Measure what you must control 9. Keep the steam system calibrated 10. Don t use motive steam when make-up steam can be used Five rules for dryer steam system energy efficiency are: 1. Keep the system tight 2. Efficiently utilize flash steam from high temperature condensate 3. Maximize use of low pressure steam 4. Minimize heat used for hood supply air heating 5. Manage the steam system Energy efficient drying requires a combination of steam system design, equipment, operation, maintenance, and control. Dryer arrangement Dryer section arrangement primarily affects drying energy consumption by changing machine or heat transfer efficiency. Examples include: Single tier arrangements have high dryer-sheet wrap angles and short unsupported sheet lengths. Heat transfer rates and threading efficiency are thereby improved. Increased sheet restraint from wrap angles and fabric pressure improves thermal contact with dryers and reduces CD shrinkage. Vacuum-assisted devices and/or blow boxes and placement and quantity of draw points affect total draw requirements. Draw reduction increases CD strength. Windage control impacts runnability Fabric tension affects drying heat transfer by increasing sheet-dryer thermal contact. Felt design affects uniformity of sheet contact with dryer surface and heat transfer.

17 17 / Paper machine energy conservation TIP Fabric and dryer cleanliness impacts heat transfer performance. Blow box systems can improve high speed runnability and machine efficiency. Thermocompressor systems Thermocompressor steam systems utilize high-pressure motive steam to recompress low-pressure blowthrough steam and reuse it in the same dryer section. Good steam separators, proper piping design, and adequate motive steam pressure are critical for efficient operation. Opportunities to minimize energy consumption using thermocompressor systems include: Ensure no steam venting during normal operation. Utilize blow-through control and/or automatic pressure and differential-pressure letdown to minimize venting during sheet breaks. Optimize differential pressures for condensate evacuation and blow-through flows. Utilize properly sized thermocompressors. (Note that thermocompressors, by design, are most effective over a narrow operating range. Machines with wide variations in condensing loads may not be appropriate applications for thermocompressors.) Optimize motive steam pressure to minimize amount of motive steam flow required and net thermal energy cost. Utilize steam bleed in low-pressure dryers or other low-pressure steam user such as air pre-heat coils to purge non-condensable gases from the steam system. Cascade systems Cascade steam systems reuse flash and blowthrough steam from a high-pressure dryer section in a different dryer section that operates at lower steam pressure. Opportunities to reduce energy consumption with cascade steam systems include: Group dryer steam sections to minimize steam venting Minimize number of dryers draining to a condenser and amount of blowthrough steam from these dryers. Ensure proper section splits to prevent venting during normal operation. Utilize blow-through control and/or automatic pressure/differential-pressure letdown to minimize venting during sheet breaks. Provide make-up steam from the lowest available steam pressure header that will support section pressure requirements. Steam system design There is no one and only correct solution for steam and condensate system design. The proper system design depends on the mill steam supply and condensate return systems and production requirements. Proper sizing of piping and equipment are critical, using well-established procedures and guidelines. Detailed piping design should be done and reviewed by a qualified party to ensure proper system operation. Considerations for energy-efficient steam system designs include: Ensure no steam venting during normal operation. Utilize low-pressure instead of high-pressure steam where appropriate. Utilize blow-through control and/or automatic pressure letdown to minimize venting during sheet breaks. Provide high steam separator efficiency, especially with blow through control. Measure condenser water temperature at outlet rather than inlet. Recover flash steam from separator tanks. Return condensate to the boiler house at high temperature (> 230 F, 110 C). Do not valve off dryers to control drying capacity. Improve flexibility of the steam and condensate system instead.