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Water Consumption at Pulp and Paper Mills Barry Malmberg, NCASI

ABSTRACT One of the definitions of water consumption is “water that is no longer available because it has been evaporated, transpired, incorporated into products, or otherwise removed from the water environment.” [1]. The concept of water consumption is gaining importance as one of the methods to manage water resources in local or regional watersheds or basins. The primary method of estimating water consumption is the use of water consumption coefficients, commonly agreed upon values less than unity, which are multiplied by the total water intake to generate consumptive water losses at a facility. The major shortcoming of the use of water consumption coefficients is the general lack of accurate, scientifically verified coefficients for use in calculations. This presentation reviews the sources of consumptive water losses at pulp and paper manufacturing facilities and presents more refined coefficients for use in water consumption calculations. Chemical pulp mills tend to have larger consumptive water losses than other types of mills at the same specific total water usage because of evaporative losses from the recovery area and cooling tower circuits.

Methods of Estimating Water Consumption Traditionally, consumptive water use has been estimated by two different techniques; subtracting the return flows + conveyance losses from overall withdrawals or by multiplying withdrawal amount by a water consumption coefficient to generate a consumptive use value. The first method involves the subtraction of two typically large numbers, with the difference being attributed to consumptive water loss. The error in volumetric measurements for total mill water intake and outflow is of the same order of magnitude as the consumptive water loss, so the first method is subject to large error. Water consumption coefficients are generally agreed upon values, less than unity, for a particular industrial category. The use of water consumption coefficients is currently the predominant method to estimate water consumption [2]. A general equation for calculating the water consumption coefficient for pulp and paper mills is given in Equation 1.

( )( )

r UsageFresh Wate TotalChemicals Purchasedin Water Material Rawin Water

- Solidsin LossesWater Product in Losses Water Losses eEvaporativ

E +++

= Eq (1)

Sources of Water Consumption at Pulp and Paper Facilities In this section, the major sources of water consumption in pulp and paper facilities are examined in detail. The important parameters affecting water consumption from these sources are listed. Evaporative Losses Gleadow et al. [3] list major sources of vapor discharges from a “recent” kraft mill in Table 1, recent being defined as a mill designed during the late 1980s and commissioned in the early 1990s. NCASI estimates of the major sources of vapor discharges are included in the table for comparison. In Gleadow et al., total water to the mill is 69.9 m3/admt, with 67.7 m3/admt being fresh water. The remaining water to the mill originates from wood (2.0 m3/admt) and purchased chemicals (0.2 m3/admt). Note that NCASI estimates of evaporative discharges include losses from secondary treatment, which can be substantial.

Table 1: Major Evaporative Discharges from “Recent” Kraft Pulp Mills [3] NCASI

Process Vapor Discharge m3/admt m3/admt Process Cooling 3.8 3.8 Secondary Treatment - 2.2b Process Vents 1.8a 2.0 Effluent Cooling 1.5 1.5 Recovery Boiler 0.6 0.8 Lime Kiln 0.2 0.3 Consumptive Water Loss 7.9 10.6 a) Losses from pulp machine, 1.2 m3/admt + miscellaneous

vent losses, 0.6 m3/admt b) Assuming an aerated stabilization basin (ASB) Process and effluent cooling. According to Carter and Gleadow, the major cooling water circuits for kraft pulp mills are the evaporator and turbine condenser cooling circuits, will smaller cooling tower circuits associated with the chlorine dioxide and chloralkali plant and vent cooling [4]. Other potentially large cooling tower circuits include the effluent treatment system cooling tower and the vacuum pump seal water circuit [5]. Given the operating parameters for the major cooling tower circuits, estimates have been made for evaporative water losses from cooling towers. Table 2 lists the estimated water consumption amounts from the various cooling tower circuits.

Table 2: Estimated Evaporative Water Losses from the Major Cooling Tower Circuits Cooling Tower Circuit Flow

(m3/admt) Inlet Temperature

(°C) Outlet Temperature

(°C) Water Consumption

(m3/admt) Evaporative surface condenser

50-75 43-48 25-32 0.90-2.8

Turbine condenser 21-50 32-41 27 0.18-1.1 Effluent cooling 17-50 50-60 37-40 0.28-1.81 Vacuum pump seal water

10-12 40-49 24-38 0.18-0.45

Chlorine dioxide plant 5-15 40-45 27 0.12-0.50

Pulp drying. The key variables for determining water consumption from the pulp drying process are the water content in pulp leaving the press section, the dryness of pulp leaving the drying system, and the existence and efficiency of the heat recovery system. A simplified schematic of the drying and heat recovery process is shown in Figure 1.

DryingDrying

Evaporated Evaporated waterwater

Pulp from thePulp from thepresspress Dried pulpDried pulp

HH22O Content: 5O Content: 5--10%10%Consistency: 33Consistency: 33--55%55%

HeatHeatRecoveryRecovery

Condensed waterCondensed watervaporvapor

Water vapor toWater vapor toatmosphereatmosphere

HH22O Content: O Content: 120120--180 g180 gH2OH2O/kg/kgdry airdry air


DryingDrying

Evaporated Evaporated waterwater

Pulp from thePulp from thepresspress Dried pulpDried pulp

HH22O Content: 5O Content: 5--10%10%Consistency: 33Consistency: 33--55%55%

HeatHeatRecoveryRecovery

Condensed waterCondensed watervaporvapor

Water vapor toWater vapor toatmosphereatmosphere



Figure 1: Schematic of Pulp Drying and Heat Recovery

Modern press sections using shoe presses and steam boxes improve water removal, and can achieve exiting press consistencies in the range of 45-50%. The theoretical maximum consistency achievable in the press section is 70%, based upon the amount of water contained within the fiber cell. Further increases in press consistencies require evaporation of water from the fiber cell. The exiting humidity of exhaust air leaving a modern heat recovery system is usually in the range of 40-70 d.a.OH /kgg

2 [6]. Table 3 shows the amount

of water vapor leaving the paper machine dryer as a function of inlet pulp consistency, outlet sheet dryness, and availability and efficiency of heat recovery. Depending upon the individual machine conditions, water consumption can range from 0.13 – 1.8 m3/admt. All calculations assume an ambient air humidity of 20

d.a.OH /kgg2

.

Consistency (%) Humidity ( d.a.OH /kgg2

) Description

From press section

Exiting Product Entering Heat

Recovery

Exiting Heat Recovery

Consumptive Water Loss

(m3/admt)

Pulp Dryer/ No HR

33 95 - - 1.8

Pulp Dryer/ No HR

55 90 - - 0.64

Pulp Dryer/ HR 33 95 180 70 0.56 Pulp Dryer/ HR 55 90 120 40 0.13

Table 3: Parametric calculation of dryer water consumption Recovery boiler. Sources of evaporative water losses from a recovery boiler are (in order of importance)

1. Water in the black liquor 2. Water formation from the oxidation of hydrogen in the black liquor solids 3. Sootblowing steam 4. Humidity from the incoming combustion air 5. Direct heating steam for raising the black liquor temperature to firing temperature

When considering water consumption, contributions from the water formation from the oxidation of hydrogen in the black liquor solids and humidity from the incoming combustion air should be ignored. These water sources, while contributing to evaporative water losses from the recovery boiler, do not affect water losses from the local watershed or ecosystem. A typical breakdown of evaporative losses in a recovery boiler is given in Table 4. The conversion between kg H2O/100 kg black liquor solids and mt H2O/admt unbleached pulp is made by using the weight

ratio of 1.7 kg black liquor solids/1 kg of bleached pulp [7]. This ratio varies depending upon the pulping and bleaching process, i.e. mills with oxygen delignification will have a higher ratio than mills without oxygen delignification. The calculations in Table 4 assume 70% strong black liquor, direct heating steam of 1.7% of the wet black liquor, sootblowing steam use of 18 wt. % of the black liquor solids, and combustion air humidity of 13 d.a.OH /kgg

2. Consumptive water losses are calculated by subtracting the

water from hydrogen oxidation and the humidity of the combustion air.

Table 4: Evaporative Water Losses in a Recovery Boiler

kg/100 kg BLS m3/admt

Steam in stack from water in BL 42.9 0.73 H2O from hydrogen oxidation 29.7 0.51 Sootblowing steam 18.0 0.31 Humidity in air 5.7 0.10 Direct heating steam 2.4 0.04 Total water vapor 98.6 1.68 “Consumptive” water loss1 63.3 1.08

1) Excludes humidity in combustion air and H2O formed from hydrogen oxidation

Lime kiln. The primary parameter affecting consumptive water losses in the lime kiln is the mud solids percentage leaving the mud filter. Modern lime mud filters produce lime mud at 80-85% solids content, while older units produce lime mud at 65-70% solids content [8]. Three sources contribute to the evaporative water losses in the lime kiln; the water content in the incoming mud solids, the humidity of the combustion air, and the water vapor from the oxidation of hydrogen from the kiln fuel. The two primary fuel types fired in kilns are natural gas and fuel oil. Natural gas has a higher percentage of hydrogen (25 wt. % as H) compared to fuel oil (11 wt. % as H). During combustion, the hydrogen in the fuel is oxidized to water vapor, contributing to the evaporative water losses in the kiln. As with the recovery boiler, contributions from the water formation from the oxidation of hydrogen in the black liquor solids and humidity from the incoming combustion air should be ignored when calculating water consumption from lime kilns. Consumptive water losses from lime kilns are summarized in Table 5. The conversion between kg H2O/mt CaO and mt H2O/admt unbleached pulp is made by using the conversion factor of 230 kg CaO/admt of unbleached pulp [13].

Table 5: Consumptive Water Losses from Lime Kilns as a Function of Mud Solid Content Filter Solids Content

(%) mt H2O/ mt CaO

m3 H2O/admt unbleached pulp

60 1.47 0.40 65 1.20 0.33 70 0.97 0.26 75 0.76 0.21 80 0.58 0.16 85 0.42 0.12

Secondary treatment. In North America, the two predominant systems to treat wastewater are activated sludge systems and aerated stabilization basins. Aerated stabilization basins (ASBs) are large bio-reactors used to remove organic wastes from pulp and paper effluents before discharge to a receiving water. An ASB typically has a large surface area exposed to the atmosphere and mechanical aeration. These conditions are conducive to evaporative water losses, which will contribute to water consumption at a mill. Aerated stabilization basin surface aeration units are normally high-speed (~1200 rpm) floating units or low-speed (~50 rpm) fixed platform units. High speed aerators generate a larger spray area, which assists with heat transfer leading to

larger evaporation losses. Diffused aeration equipment provides oxygen to ASBs via compressed air. Fewer than 10% of ASBs in the United States are equipped with diffused aeration systems [9]. For a typical ASB design configuration the amount of water pumped through aerators is on the order of 35 times the daily influent flow. The large water throughput leads to large evaporative losses from surface aeration units. Evaporation from aerated basins consists of two processes; surface evaporation and evaporation losses from aeration. Novotny and Krenkel proposed equation 2 to describe the combined evaporation rate from these two processes [10]:

( ) ( )⎭⎬⎫

⎩⎨⎧

⎥⎦

⎤⎢⎣

⎡⎟⎠⎞⎜

⎝⎛ −+−⎟

⎠⎞⎜

⎝⎛ += −

10015302.00604.0exp392 1.0 a

aeaA

wf

TTTA

QvXE Eq (2)

Where: E: Evaporation rate (g m-2 day-1) X: Characteristic length of the basin, (m), approximately A VW: Wind velocity (tree top) (m/s-1) QA: Aerator air flow rate (m3 day-1) A: Surface area for heat transfer (m2) Ta: Air temperature (°C) Te: Equilibrium basin temperature (°C) fa: relative humidity of air (%)

Equation 2 is applicable for surface aerated systems and diffused aerated systems. Given the same power input and wind speed, air flow through the liquid, and consequently the evaporative losses, are considerably less with diffused air systems than surface aerated systems. For diffuse aeration, the air flow rate (QA) is typically measured and is equal to the total air flow to the aerator. For surface aerators QA is the air flow contribution by aeration, which is not directly known, can be estimated with equation 3. The aerator spray cross-sectional area for a surface aeration unit is shown in Figure 2.

wA vFNmQ ⋅⋅⋅= Eq (3) Where

QA: Aerator air flow rate (m3 day-1) vw: Wind velocity (tree top) (m/s-1) N: Number of aerators F: Aerator spray cross-sectional area (m2) m: wind height proportionality coefficient converting wind velocity at tree-top level to

aerator spray level (~ 0.5) Spray cross-sectional area, FSpray cross-sectional area, F

Figure 2: Schematic Diagram of a Surface Aerator, 1) Floatation Ring, 2) Draft Tube, 3) Propeller, 4)

Electric Motor

A parametric sensitivity analysis was performed to study the effect of parameters on evaporation rate using the comprehensive ASB heat balance model of Argaman and Adams Jr. [11] and operating data from a U.S. Northwestern kraft pulp mill. The Argaman and Adams model uses the evaporation rate equation, Equation 2, and the air flow rate equation for ASBs with surface aerators, equation 3, proposed by Novotny and Krenkel [10]. Parametric sensitivity results indicated that wind speed and aeration area are the most important parameters affecting evaporation, followed by relative humidity. Estimates were made of the evaporation rate from a U.S. Northwestern kraft pulp mill’s aerated stabilization basin over a period of one year, Figure 3. An average of 0.88 MGD of water (2.6% of the total daily flow) was evaporated from the ASB with peak evaporation of 1.52 MGD of water (4.5% of the total daily flow) occurring in July. Specific water consumption for this particular mill from the ASB would be 2.2 mt H2O/admt on average with a peak water consumption amount of 3.9 mt H2O/admt during July.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Evap

orat

ion

Rat

e (M

GD

)

Average: 0.88 MGDStandard Deviation: 0.39 MGD

Figure 3: Predicted Evaporation Rate for the Aerated Stabilization Basin

U.S. Northwestern kraft pulp mill Argaman and Adams Jr. provided process data for two aerated lagoons: one operating with surface aerators and one operating with diffused air. For the surface aerated lagoon, 6.0% of the incoming water was evaporated with 59% of the water evaporated via surface evaporation and 41% of the water evaporated via aeration evaporation. For the diffused aerated lagoon, 2.9% of the incoming water was evaporated with 97% of the water evaporated via surface evaporation and 3% of the water evaporated via aeration evaporation. It can be concluded that surface aerated systems will have substantially higher consumptive water losses than diffused aerated systems, which is further confirmed by the work of Talati and Stenstrom [12]. As with ASBs, evaporative water losses from activated sludge treatment (ASTs) are dependent upon the aeration system. Even though the use the use of diffuse (subsurface) aeration is more prevalent in activated sludge systems than in aerated stabilization basins, the majority of active sludge processes within the pulp and paper industry are still surface aerated. Because of the smaller aeration surface area and more highly controlled operation, evaporative losses from activated sludge plants will be less dependent upon seasonal conditions compared to aerated stabilization basins. The smaller aeration basin surface area also leads to less evaporative losses compared to ASBs. Equations 2 and 3 are applicable to activated sludge plants and have been used to estimate evaporative losses from AST plants under summer and winter conditions.

Evaporative losses from activated sludge aeration basins will be approximately 1.0-2.5% of the total influent flow. Miscellaneous vents. Pulp and paper mills have a number of diffuse process vents that contribute to the overall consumptive water loss. NCASI has compiled information on process vents from a number of sources in various types of pulp mills [13, 14]. Table 6 lists consumptive water losses from the largest miscellaneous vent sources. Note the large standard deviations compared to average values for most of the categories.

Table 6: Evaporative Water Losses from the Largest Miscellaneous Vents in Kraft Pulp Mills Vent Average

(m3 H2O/admt ) Standard Deviation

(m3 H2O/admt) Black liquor oxidation tank vents 0.51 0.50 Smelt dissolving tank vents 0.40 0.21 Total brownstock washing vents 0.33 0.28 Total bleach plant vents 0.16 0.10 Thermal oxidizer vents 0.14 0.08 Oxygen delignification vents 0.083 0.058 Pulp deckers 0.057 0.038

Evaporative losses from mechanical pulp mills. Mechanical pulping is extremely electricity intensive compared to chemical pulping. Stone groundwood requires 1.0-2.0 MW-h/bdmt while thermomechanical (TMP) pulping requires 1.6-3.0 MW-h/bdmt. Jackson and Wild examine the energy aspects of mechanical pulping in detail [15]. They show that for mechanical pulping of newsprint grade TMP, over 80% of the total energy requirements for the mill can be attributed to refiner operation. Of the refiner input energy, approximately 70-75% of the electricity input can be recovered in efficient recovery systems. The recoverable heat from the refining process is in the form of contaminated steam from pressurized cyclones and pressurized and/or atmospheric vents from refiners. Smaller pressurized stream contributions are from stock chest vents. Pressurized cyclones usually operate in the pressure range of 2.4 bar (22 psig) – 5.0 bar (58 psig). Pressurize cyclones are normally located on the discharge lines from pressurized refiners (typically the primary refiners). Other sources of pressurized steam can come from secondary refiners or from pressurized stone grinders. When pressurized refiners are employed, the heat recovery can be 90 – 95% of the excess refiner steam [16]. Atmospheric steams originates from the operation of atmospheric secondary refiners and reject refiners, and stock chests under atmospheric pressure. Heat is recovered from refiner steam via indirect heat exchangers or a reboiler. Contaminated steam at 2.5 to 5.0 bar passes through a heat exchange device to generate clean steam at 3.7 - 4.2 bar. Approximately 1.1 metric ton of steam is generated/MW-h refining energy [17]. The efficiency of the heat recovery system will determine how much of this steam is emitted to the atmosphere, contributing to the mill water consumption fraction, and how much of the steam in condensed to extract the energy from the latent heat of vaporization. In mechanical pulping heat recovery, ~5% of the steam is vented before the reboiler to avoid NCG buildup [17]. Table 7 lists the consumptive water losses from mechanical pulp mill’s wood processing step with and without heat recovery. Stone groundwood processes will have significant water vapor losses compared to other mechanical pulp mill types because they operate at near-atmospheric refiner pressure, limiting the economic feasibility of heat recovery.

Table 7: Water Consumption from Mechanical Pulping Wood Processing Step Description Consumptive water loss

(m3 H2O/admt ) Stone groundwood, no HR 1.0-2.0 Pressurized stone groundwood, HR 0.5-0.7 TMP, no HR 1.6-3.0 TMP, older HR 0.5-0.8 TMP, efficient HR 0.08-0.15

Evaporative losses from sulfite pulp mills. The primary source of evaporative losses in sulfite pulping is gas from the SO2 absorption units or scrubber units treating flue gas from the recovery furnace. The average evaporative losses from the recovery system exhaust vent for two sulfite mills in which NCASI has data was 2.32 ± 0.32 m3 H2O/admt pulp [13].

Water Losses in Product Water leaving with the final product is considered a source of water consumption if the product leaves the ecosystem. Product leaving pulp and paper facilities usually have a moisture content ranging from 2%-10%. The exception is mills that produce wet lap. Wet lap is very thick sheets of pulp of approximately 50% moisture content produced from mechanically pressing pulp using a series of roll presses. The sheets of pulp are cut, stacked into bales, compressed, and wrapped for storage on-site or shipment off-site. Table 8 lists consumptive water losses from the product at various moisture contents.

Table 8: Water Consumption from Product Description Consumptive water loss

(m3 H2O/admt ) Product, 10 % moisture 0.10 Product, 5 % moisture 0.05 Wet lap, 50% moisture 0.90

Water Leaving with Solid Wastes A number of different types of solid wastes are generated during the production of pulp and paper products. These solids wastes can include pulping rejects, treatment plant residuals, and inorganic wastes such as lime mud, slaker grits, and recovery boiler ash. NCASI has previously reviewed the state of solid waste management practices in the U.S. paper industry [18]. The NCASI review compiles data on generation rates and disposal options for solids wastes. Water bearing solid residuals leaving the ecosystem could be considered a consumptive water loss. Total solid residue production was 270 dry lb/adst (0.14 dry mt/admt) based upon 1995 data. The residual generation rate is dependent upon the mill type, with deinked mills generating 2-3 times the solids residuals as other types of mills. Combined solids residuals are usually dewatered using a belt filter press or screw press and then disposed of in a landfill, land applied, burned, or using some other beneficial use. In 1995, approximately 50% of combined residuals were land-filled, which would not contribute to consumptive water loss according to the definition of water consumption used. Assuming a dry solids content of 35%, and that 50% of the solid residuals are disposed of in a fashion that would contribute to water consumption, the consumptive water loss for solid wastes for different mill types are given in Table 9. Consumptive water losses from solid waste in deinked pulp mills are substantially greater than other mill types.

Table 9: Water Consumption from Solid Wastes Mill Type Residuals Median

Generation Rate (mt dry solids/admt)

Consumptive water loss (m3 H2O/admt )

Bleached Kraft 0.05 0.05 Unbleached Kraft 0.02 0.02 Mechanical 0.08 0.07 Recycled, Nondeinked 0.02 0.02 Deinked 0.36 0.33 Average 0.14 0.13

Water in Raw Material and Purchased Chemicals Wood chips entering the pulping process have approximately 50% moisture content. The water content in the wood can be calculated on a specific water content based upon final product by considering the wood moisture content and total yield, Equation 4.

( )MY

MW −⎟⎠⎞⎜

⎝⎛= 11

Eq (4)

Where: W: Water content (m3/admt) Y: Overall yield (fraction) M: Moisture content (fraction) Water content in purchased chemicals for bleached chemical pulp mills has been estimated to be 0.2 m3/admt [3]. The water content in purchased chemicals is likely less for other types of mills. Water Consumption Coefficients Once the sources of consumptive water losses have been identified, Equation 1 can be used to estimate water consumption coefficients for various mill types as a function of total fresh water usage. Figure 4 presents a summary figure for water consumption coefficients for various mill types. The lines in the Figure 4 have been generated by the synthesis of data from a number of published full mill mass balances and best judgment calculations. Figure 4 should be viewed as an initial estimate for water consumption coefficients at pulp and paper mills. Individual facilities may have a different water consumption profile based upon water use and management practices.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0 25 50 75 100 125

Total Fresh Water Usage (mt/admt)

Wat

er C

onsu

mpt

ion

Coe

ffici

ent (

unit-

less

)

KraftMechanicalRecycledFine Paper

Figure 4: Water Consumption Coefficients as a Function of Total Fresh Water Usage

SUMMARY The major sources of water consumption were analyzed. Water consumption coefficients were generated as a function of total water usage for each of the major production sectors. At the same specific water usage, water consumption coefficients for chemical pulping (bleached and unbleached) are larger than for mechanical, recycled, and non-integrated paper mill types. Water consumption coefficients for all pulp and paper production categories are a function of total water usage, with the functional dependence more pronounced for tightly closed mills. As mills reduce water usage, consumptive water losses will also increase on a total mass flow basis as temperature management issues become increasingly important.

REFERENCES 1 Solley, Wayne, B., Merk, Charles, F., Pierce R.R., Estimated Use of Water in the United States in 1985. U.S. Geologic Survey Circular 1004. U.S. Department of the Interior, U.S. Geologic Survey. 82 pages, (1988). 2 Pebbles, V., Measuring and Estimating Consumptive Use of the Great Lakes Water, Great Lakes Commission, Ann Arbor, 2003. 3 Gleadow, P., Hastings, C., Barynin, J., Schroderus, S., Warnqvist, B., Towards closed-cycle kraft: ECF versus TCF case studies, Pulp & Paper Canada, 98(4), 27-37, (1997). 4 Browne, T.C. (technical editor), Water Use Reduction in the Pulp and Paper Industry, 2nd Edition, Paprican, December 2001. 5 Sweet, D.F., Vacuum pump seal water conservation and cooling tower applications, 1992 Tappi Papermakers Conference, 371-377, (1992). 6 Thorp, B.A. (editor), Pulp and Paper Manufacture Volume 7 Paper Machine Operations, Tappi Press, (1991). 7 Gullichsen, J., Fogelholm, C.-J., Recovery Boiler Chapter 13. In Chemical Pulp, Part 2, Papermaking Science and Technology, book 6, Fapet Oy, Helsinki, Finland Page B95, ISBN 952-5216-06-3. 8 Pulp and Paper Industry Energy Bandwidth Study, Report for American Institute of Chemical Engineers (AIChE), Prepared by Jacobs Engineering and IPST, August 2006. 9 NCASI Environmental Resource Handbook for Pulp and Paper Mil, Chapter 11: Effluent Treatment Systems and water Quality Issues, 2004. 10 Novotny, V., Krenkel, P., Evaporation and Heat Balance in Aerated Basins, Paper presented at the 7th national meeting and 7th petroleum exposition, New Orleans, Louisiana, USA, 150-159, (1973). 11 Argaman, Y., Adams, Jr., C.E., Comprehensive Temperature Model for Aerated Biological Systems, Progress in Water Technology, 9, 397-409, (1977). 12 Talati, S.N., Stenstrom, M.K., Aeration-Basin Heat Loss, Journal of Environmental Engineering, 116(1), 70-86, (1990). 13 National Council for Air and Stream Improvement, Inc. (NCASI). 1994. Volatile Organic Emissions from Pulp and Paper Mill Sources Part I-X, Technical Bulletin No. 675-684. New York, N.Y.: National Council for Air and Stream Improvement, Inc. 14 National Council for Air and Stream Improvement, Inc. (NCASI). 1994. Volatile Organic Compound Emissions from Non-Chemical Pulp and Paper Mill Sources, Part I-VI, Technical Bulletin No. 736-741. New York, N.Y.: National Council for Air and Stream Improvement, Inc. 15 Williamson, P.N (editor), Energy Cost Reduction in the Pulp and Paper Industry, Chapter on Mechanical Pulp Mills, 97-118, Paprican, November 1999 16 Reside, D.A., Energy efficiency for mechanical pulp mills in Western Canada, 1994 CPPA Pacific Coast and Western Branches Join Conference, Jasper, Alberta. 17 Leask, R.A. (editor), Pulp and Paper Manufacture, 3rd Edition, Mechanical Pulping, Chapter XII Heat Recovery, page 166, (1987). 18 NCASI Technical Bulletin No 793, Solid Waste Management Practices in the U.S. Paper Industry – 1995, September 1999.

Water Consumption at Pulp Water Consumption at Pulp and Paper Millsand Paper Mills

Barry MalmbergBarry MalmbergNCASINCASI

2007 Engineering, Pulping & 2007 Engineering, Pulping & Environmental ConferenceEnvironmental Conference

One of the Definitions of One of the Definitions of Water ConsumptionWater Consumption

Consumptive water useConsumptive water use: The portion : The portion of water removed from the local of water removed from the local watershed or ecosystem that is not watershed or ecosystem that is not directly returned to the immediate directly returned to the immediate environment in the form of liquid environment in the form of liquid discharge from a mill. Examples discharge from a mill. Examples include evaporative losses and include evaporative losses and water content in the end product.water content in the end product.

Methods for Estimating Methods for Estimating Consumptive Water Use Consumptive Water Use

•• Subtracting return flows from overall Subtracting return flows from overall withdrawalswithdrawals

•• Use of water consumption coefficients Use of water consumption coefficients (predominant method)(predominant method)

•• Overall material and energy balance Overall material and energy balance methods and analyses of process datamethods and analyses of process data

–– Full mill material and energy balance Full mill material and energy balance calculations for summer and winter conditionscalculations for summer and winter conditions

–– Spreadsheet material and energy balance Spreadsheet material and energy balance calculations for individual unit operationscalculations for individual unit operations

Water Consumption CoefficientsWater Consumption Coefficients

•• USGS CoefficientsUSGS Coefficients

•• Great Lakes Consumptive Use CoefficientsGreat Lakes Consumptive Use Coefficients0.10.1--0.40.419951995

0.030.03--0.80.819901990

0.070.07--0.720.7219851985IndustrialIndustrialYearYear

0.060.06

IndianaIndiana

0.250.25

New New YorkYork

0.10.1--0.150.15

MichiganMichigan

0.10.1

OhioOhio

0.10.1aa

QuebecQuebec

0.10.1

WisconsinWisconsin

SelfSelf--Supply Supply IndustrialIndustrial

a)a) Specific to pulp and paper facilitiesSpecific to pulp and paper facilities** All other great lakes states and the province of Ontario use watAll other great lakes states and the province of Ontario use water consumption coefficientser consumption coefficients

that vary by plant type and standard industrial classification (that vary by plant type and standard industrial classification (SIC) code.SIC) code.

Necessary Information to Necessary Information to Estimate Water Consumption Estimate Water Consumption

CoefficientsCoefficients

•• Overall estimate of consumptive Overall estimate of consumptive water losseswater losses

•• Overall water usageOverall water usage

(Evaporative Losses + Water Losses in Product + (Evaporative Losses + Water Losses in Product + Water Losses in Solids) Water Losses in Solids) ––

(Water in Raw Material + Water in Purchased Chemicals(Water in Raw Material + Water in Purchased Chemicals))

Total Fresh Water UsageTotal Fresh Water Usage

E =E =

Consumptive Water LossesConsumptive Water Losses

•• Kraft pulp mills (bleached and Kraft pulp mills (bleached and unbleached)unbleached)

•• Mechanical pulp millsMechanical pulp mills•• Recycle millsRecycle mills•• Sulfite millsSulfite mills•• NonNon--integrated paper millsintegrated paper mills

Major Vapor Discharges for Major Vapor Discharges for Modern Kraft Pulp MillsModern Kraft Pulp Mills

2.22.2bbSecondary TreatmentSecondary Treatment7.97.9

0.20.20.60.61.51.51.81.8aa

3.83.8

mm33/admt /admt [c][c]

10.610.6TotalTotal

0.30.3Lime KilnLime Kiln0.80.8Recovery BoilerRecovery Boiler1.51.5Effluent CoolingEffluent Cooling2.02.0Process VentsProcess Vents3.83.8Process CoolingProcess Cooling

mm33/admt /admt [NCASI][NCASI]

Process Vapor Process Vapor DischargeDischarge

a)a) Losses from pulp machine, 1.2 mLosses from pulp machine, 1.2 m33/Adt, + miscellaneous vent losses, 0.6 m/Adt, + miscellaneous vent losses, 0.6 m33/Adt/Adtb)b) Authors did not consider evaporative losses from secondary treatAuthors did not consider evaporative losses from secondary treatmentmentc)c) Gleadow, P., Hastings, C., Barynin, J., Schroderus, S., WarnqvisGleadow, P., Hastings, C., Barynin, J., Schroderus, S., Warnqvist, B., Towards t, B., Towards

closedclosed--cycle kraft: ECF versus TCF case studies, Pulp & Paper Canada, 9cycle kraft: ECF versus TCF case studies, Pulp & Paper Canada, 98(4), 278(4), 27--37, (1997). 37, (1997).

Water Consumption in the Water Consumption in the Major Cooling Tower CircuitsMajor Cooling Tower Circuits

0.170.17--0.450.4524-3840-457-15Chlorine Dioxide Plant

0.18 0.18 –– 0.450.4524-3840-4910-12Vacuum Pump Seal Water

0.28 0.28 –– 1.811.8137-4050-6017-50Effluent Cooling

0.18 0.18 –– 1.11.12732-4121-50Turbine Condenser

0.9 0.9 –– 2.82.825-3243-4850-75Evaporative Surface Condenser

Water Consumption

(m3/admt)

Outlet Temperature

(°C)

Inlet Temperature

(°C)

Flow(m3/admt)

Description

Cooling Tower Loads, Cooling Tower Loads, Summer vs. Winter ConditionsSummer vs. Winter Conditions11

y = 0.0178x + 0.2064R2 = 0.9884

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 5 10 15 20 25 30 35

Raw Water Temperature (°C)

Frac

tion

of H

eat D

isch

arge

d vi

a C

oolin

g To

wer

(CT/

(CT

+ E

fflue

nt)

1)1) Data from: Syberg, O., Barynin, J., Impact of Water Reduction onData from: Syberg, O., Barynin, J., Impact of Water Reduction on Kraft Mill Heat Balance, Kraft Mill Heat Balance, Proceedings of the 1998 Tappi Engineering Conference, 1167Proceedings of the 1998 Tappi Engineering Conference, 1167--1172, (1998). 1172, (1998).

Consumptive Water Losses, Consumptive Water Losses, Recovery AreaRecovery Area

•• Recovery BoilerRecovery Boiler–– 60 60 -- 85% solids: 1.3 85% solids: 1.3 –– 0.6 m0.6 m33 HH22O/admtO/admt

•• Lime KilnLime Kiln–– 60 60 -- 85% solids: 0.4 85% solids: 0.4 –– 0.12 m0.12 m33 HH22O/admtO/admt

•• Black Liquor Oxidation VentsBlack Liquor Oxidation Vents–– 0.4 0.4 ±± 0.4 m0.4 m33 HH22O/admtO/admt

•• Smelt Dissolving Tank VentsSmelt Dissolving Tank Vents–– 0.3 0.3 ±± 0.2 m0.2 m33 HH22O/admtO/admt

•• Slaking/Causticizing VentsSlaking/Causticizing Vents–– ~0.05 m~0.05 m33 HH22O/admtO/admt

Consumptive Water Losses, Consumptive Water Losses, Fiber LineFiber Line

•• Brownstock ventsBrownstock vents–– 0.28 0.28 ±± 0.24 m0.24 m33 HH22O/admtO/admt

•• Bleach plant ventsBleach plant vents–– 0.14 0.14 ±± 0.09 m0.09 m33 HH22O/admtO/admt

•• Oxygen delignification ventsOxygen delignification vents–– 0.07 0.07 ±± 0.04 m0.04 m33 HH22O/admtO/admt

Evaporation from Effluent Evaporation from Effluent TreatmentTreatment

•• Aerated Stabilization Basins Aerated Stabilization Basins –– 2.5 2.5 –– 6% of total inflow evaporated6% of total inflow evaporated

•• Activated SludgeActivated Sludge–– 1.0 1.0 –– 2.5% of total inflow evaporated2.5% of total inflow evaporated

•• Polishing PondsPolishing Ponds–– 0.1 0.1 –– 0.25% inflow evaporated0.25% inflow evaporated

•• Primary and Secondary ClarificationPrimary and Secondary Clarification–– Primary: 0.06 Primary: 0.06 –– 0.15% inflow evaporated0.15% inflow evaporated–– Secondary: 0.01 Secondary: 0.01 –– 0.1% inflow evaporated0.1% inflow evaporated

Importance of Aeration Equipment Importance of Aeration Equipment in Evaporation from ASBsin Evaporation from ASBs11

•• Surface Aeration (6% of incoming water Surface Aeration (6% of incoming water evaporated)evaporated)

–– 59% of water evaporated via surface 59% of water evaporated via surface evaporationevaporation

–– 41% of water evaporation via aeration 41% of water evaporation via aeration evaporationevaporation

•• Diffuse Aeration (2.9% of incoming water Diffuse Aeration (2.9% of incoming water evaporated)evaporated)

–– 97% of water evaporated via surface 97% of water evaporated via surface evaporationevaporation

–– 3% of water evaporation via aeration 3% of water evaporation via aeration evaporationevaporation

1)1) From: Argaman, Y., Adams, Jr., C.E., Comprehensive Temperature MFrom: Argaman, Y., Adams, Jr., C.E., Comprehensive Temperature Model for Aerated odel for Aerated Biological Systems, Progress in Water Technology, 9, 397Biological Systems, Progress in Water Technology, 9, 397--409, (1977).409, (1977).

Water in Solid DischargesWater in Solid Discharges

•• ProductProduct–– 0.02 0.02 –– 0.1 m0.1 m33 HH22O/admtO/admt

•• InorganicsInorganics•• Sludge from secondary treatmentSludge from secondary treatment•• RejectsRejects•• Deinked ResidualsDeinked ResidualsAll small with the exception of deinked All small with the exception of deinked residualsresiduals

Miscellaneous Vent Losses, Miscellaneous Vent Losses, Kraft Pulp MillsKraft Pulp Mills

0

20

40

60

80

100

10 20 30 40 50 60 70 80 90 100

Vent Temperature (°C)

H2O

in V

ent (

wt.

%)

0

20

40

60

80

100

Vapo

r Pre

ssur

e (k

Pa)

1)1) Data from: Someshwar, A.V., Compilation of Speciated Reduced SulData from: Someshwar, A.V., Compilation of Speciated Reduced Sulfur Compounds and Total Reduced fur Compounds and Total Reduced Sulfur Emissions Data from Kraft Mill Sources, NCASI Technical BSulfur Emissions Data from Kraft Mill Sources, NCASI Technical Bulletin No. 849, August 2002.ulletin No. 849, August 2002.

Miscellaneous Vent Losses, Miscellaneous Vent Losses, Kraft Pulp MillsKraft Pulp Mills

0.0

0.5

1.0

1.5

0.0 0.5 1.0 1.5

Measured (m3 H2O/admt)

Cal

cula

ted

(m3 H

2O/a

dmt)

Consumptive Water Losses, Consumptive Water Losses, Mechanical Pulp MillsMechanical Pulp Mills

•• Major consumptive loss is steam Major consumptive loss is steam from the refining processfrom the refining process

–– SGW and PGW 1.0 SGW and PGW 1.0 –– 2.0 MW2.0 MW--h/bdmth/bdmt–– TMP 1.6 TMP 1.6 –– 3.0 MW3.0 MW--h/bdmth/bdmt–– ~1.1 mt steam/MW~1.1 mt steam/MW--h refining energyh refining energy

•• Heat RecoveryHeat Recovery–– Modern heat recovery systems can Modern heat recovery systems can

recover 70recover 70--75% of the refining energy 75% of the refining energy in the form of clean steamin the form of clean steam

Consumptive Water Losses Consumptive Water Losses from the Refining Step in from the Refining Step in

Mechanical Pulp MillsMechanical Pulp Mills

0.5 0.5 -- 0.70.7Pressurized SGW, HRPressurized SGW, HR

0.08 0.08 –– 0.150.15TMP, modern HRTMP, modern HR

0.5 0.5 –– 1.61.6TMP, older HRTMP, older HR

1.6 1.6 –– 3.03.0TMP, no HRTMP, no HR

1.0 1.0 –– 2.02.0Stone Groundwood, no HRStone Groundwood, no HR

Consumptive water Consumptive water lossloss

(m(m33 HH22O/admt)O/admt)

ProcessProcess

Miscellaneous Vent Losses, Miscellaneous Vent Losses, Mechanical Pulp MillsMechanical Pulp Mills11

0102030405060708090

100

20 30 40 50 60 70 80 90 100 110


H2O

in V

ent (

wt.

%)

1)1) Data From: Volatile Organic Compound Emissions from NonData From: Volatile Organic Compound Emissions from Non--Chemical Pulp and Paper Mill Chemical Pulp and Paper Mill Sources Part III Sources Part III –– Mechanical Pulping, NCASI Technical Bulletin 738, July 1997Mechanical Pulping, NCASI Technical Bulletin 738, July 1997

Miscellaneous Vent Losses, Miscellaneous Vent Losses, Mechanical Pulp MillsMechanical Pulp Mills11

1)1) Data From: Volatile Organic Compound Emissions from NonData From: Volatile Organic Compound Emissions from Non--Chemical Pulp and Paper Mill Chemical Pulp and Paper Mill Sources Part III Sources Part III –– Mechanical Pulping, NCASI Technical Bulletin 738, July 1997Mechanical Pulping, NCASI Technical Bulletin 738, July 1997

0.0

0.5

1.0

1.5

0.0 0.5 1.0 1.5

Measured (m3 H2O/odmt)

Cal

cula

ted

(m3 H

2O/o

dmt)



•• Mechanical pulp millsMechanical pulp mills•• Recycle millsRecycle mills•• Sulfite and semiSulfite and semi--chemical millschemical mills•• NonNon--integrated paper millsintegrated paper mills

Miscellaneous Vent Losses, Miscellaneous Vent Losses, Deinked MillsDeinked Mills11

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70 80 90


H2O

in V

ent (

wt.

%)

1)1) Data From: Volatile Organic Compound Emissions from NonData From: Volatile Organic Compound Emissions from Non--Chemical Pulp and Paper Mill Chemical Pulp and Paper Mill Sources Part IV Sources Part IV –– Deinking Processes, NCASI Technical Bulletin 739, July 1997Deinking Processes, NCASI Technical Bulletin 739, July 1997

Miscellaneous Vent Losses, Miscellaneous Vent Losses, Deinked MillsDeinked Mills11

1)1) Data From: Volatile Organic Compound Emissions from NonData From: Volatile Organic Compound Emissions from Non--Chemical Pulp and Paper Mill Chemical Pulp and Paper Mill Sources Part IV Sources Part IV –– Deinking Processes, NCASI Technical Bulletin 739, July 1997Deinking Processes, NCASI Technical Bulletin 739, July 1997

0.00

0.05

0.10

0.15

0.20

0.00 0.05 0.10 0.15 0.20

Measured (m3 H2O/odmt)

Cal

cula

ted

(m3 H

2O/o

dmt)

Consumptive Water Losses Consumptive Water Losses Sulfite Pulp MillsSulfite Pulp Mills

•• Only 6 operating sulfite mills in the Only 6 operating sulfite mills in the United StatesUnited States

•• Major consumptive water loss Major consumptive water loss –– flue flue gas from the SOgas from the SO22 absorption units absorption units or scrubber units treating flue gas or scrubber units treating flue gas from the recovery furnacefrom the recovery furnace

–– 2.0 +/2.0 +/-- 0.2 m0.2 m33 HH22O/admtO/admt

Consumptive Water Losses, Consumptive Water Losses, Sulfite Pulp MillsSulfite Pulp Mills11

1)1) From Volatile Organic Compound Emission from Pulp and Paper MillFrom Volatile Organic Compound Emission from Pulp and Paper Mill SourcesSourcesPart VIII Part VIII –– Sulfite Mills, NCASI Technical Bulletin 682, November 1994Sulfite Mills, NCASI Technical Bulletin 682, November 1994

0102030405060708090

100

0 25 50 75 100 125Vent Temperature (°C)

H2O

in V

ent (

wt.

%)

Consumptive Water Losses, Consumptive Water Losses, Sulfite Pulp MillsSulfite Pulp Mills11

1)1) From Volatile Organic Compound Emission from Pulp and Paper MillFrom Volatile Organic Compound Emission from Pulp and Paper Mill SourcesSourcesPart VIII Part VIII –– Sulfite Mills, NCASI Technical Bulletin 682, November 1994Sulfite Mills, NCASI Technical Bulletin 682, November 1994

0.0

0.5

1.0

1.5

2.0

2.5

0.0 0.5 1.0 1.5 2.0 2.5

Measured (m3 H2O/admt)

Cal

cula

ted

(m3 H

2O/a

dmt)


•• Kraft pulp millsKraft pulp mills•• Mechanical pulp millsMechanical pulp mills•• Deinked millsDeinked mills•• Sulfite millsSulfite mills•• NonNon--integrated paper millsintegrated paper mills

Water Balance for a Modern Paper Water Balance for a Modern Paper MillMill

COOLINGCOOLING-- lubricationlubrication-- hydraulicshydraulics-- condenserscondensers-- etc.etc.

CHEMICAL CHEMICAL PREPARATIONPREPARATION-- fillersfillers-- dyesdyes-- etc.etc.

MISCELLANEOUSMISCELLANEOUS-- seal waterseal water-- washingwashing-- etc.etc.

PAPER MACHINE AND PAPER MACHINE AND AUXILIARY SYSTEMSAUXILIARY SYSTEMS

WARM WARM WATERWATER

VACUUM SYSTEM VACUUM SYSTEM SEAL WATERSEAL WATER

1.5 m1.5 m33/admt/admt






FRESH WATERFRESH WATER10.5 m10.5 m33/admt/admt

EVAPORATIONEVAPORATIONin the dryer sectionin the dryer section


FRESH WATER FRESH WATER SHOWERSSHOWERS


EFFLUENT TOEFFLUENT TOpulping department or pulping department or waste water treatmentwaste water treatment8.7 m8.7 m33/admt/admt



EVAPORATIONEVAPORATIONin cooling in cooling towertower0.3 m0.3 m33/admt/admt

EVAPORATIONEVAPORATIONin cooling towerin cooling tower0.3 m0.3 m33/admt/admt

Necessary Information to Necessary Information to Estimate Water Consumption Estimate Water Consumption

CoefficientsCoefficients

•• Overall estimate of consumptive Overall estimate of consumptive water losseswater losses

•• Overall water usageOverall water usage

Water Use in Pulp and Paper Water Use in Pulp and Paper Mills in North AmericaMills in North America

39.639.63636Deinked Secondary Deinked Secondary FiberFiber

18.818.899Market Sulfite, BCTMPMarket Sulfite, BCTMP

40.540.54040Newsprint (mechanical)Newsprint (mechanical)50.150.1135135Paper mill <100 tons/dayPaper mill <100 tons/day15.015.0218218Paper mill >100 tons/dayPaper mill >100 tons/day42.242.24444Integrated UnbleachedIntegrated Unbleached

95.695.6103103Integrated BleachedIntegrated Bleached

MedianMedian(m(m33/admt)/admt)

Number of MillsNumber of MillsMill TypeMill Type

1) Bryant, P.S., Malcolm, E.W, Woitkovich, C.P., Pulp and Pape1) Bryant, P.S., Malcolm, E.W, Woitkovich, C.P., Pulp and Paper Mill Water Use in North America, r Mill Water Use in North America, Tappi International Environmental Conference & Exhibits, 451Tappi International Environmental Conference & Exhibits, 451--460, (1996). 460, (1996).

Water Consumption Coefficients, Water Consumption Coefficients, Kraft Pulp MillsKraft Pulp Mills

y = 3.583x-0.920

R2 = 0.869

0.00.10.20.30.40.50.60.70.80.91.0

0 25 50 75 100 125

Total Fresh Water Usage (m3/admt)

Wat

er C

onsu

mpt

ion

Coe

ffici

ent

(uni

t-les

s)

Comparison of Water Comparison of Water Consumption Among Mill TypesConsumption Among Mill Types

0.00.10.20.30.40.50.60.70.80.91.0

0 10 20 30 40 50 60 70 80 90 100

Total Fresh Water Usage (m3/admt)

Wat

er C

onsu

mpt

ion

Coe

ffici

ent

(uni

t-les

s)

Triangles Triangles –– Bleached and Unbleached Kraft Mills, Diamonds Bleached and Unbleached Kraft Mills, Diamonds –– Recycle Mills, Recycle Mills, Squares Squares –– Mechanical Mills, Circles Mechanical Mills, Circles –– NonNon--Integrated Paper Mills Integrated Paper Mills

Key PointsKey Points

•• As mills reduce water usage, water As mills reduce water usage, water consumption will:consumption will:

–– increase as a fraction of total water increase as a fraction of total water usageusage

–– increase on a mass flow basis as increase on a mass flow basis as temperature management becomes temperature management becomes increasingly importantincreasingly important

•• At the same specific water usage, At the same specific water usage, water consumption coefficients are water consumption coefficients are larger for chemical pulp mills larger for chemical pulp mills compared to other mill typescompared to other mill types

ResourcesResources

•• Water consumption material has Water consumption material has been compiled into a NCASI been compiled into a NCASI Technical BulletinTechnical Bulletin

•• ExcelExcel--based tools will be available based tools will be available onon--line to assist mills in estimating line to assist mills in estimating their consumptive water lossestheir consumptive water losses

water consumption at pulp and paper millss3.amazonaws.com/zanran_storage/ · water consumption at...

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