NATL INST OF STAND ,& TECH

AlllOt

NBS

PUBLICATIONS

NBSIR 83-2640

Sensors for Efficient Energy

Utilization in the Paper Industry

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Chemical Engineering

Washington, DC 20234

December 1 981

Final Report

Issued January 1983

Prepared for • QC —1 partment of Energy

2 j j der Contract No. EA-77- A01 -601 0

. U56

<43-2640

1963

NBSIR 83-2640

SENSORS FOR EFFICIENT ENERGY

UTILIZATION IN THE PAPER INDUSTRY

NATIONAL BUREAU

OF STANDARDS

LIBRARY FEB 7 1383

no~Vo.CC . 'CjO

1 CTT,—

§3 -51=^0

J. R. Whetstone

E. G. Johnsen

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Chemical Engineering

Washington, DC 20234

December 1 981

Final Report

Issued January 1983

Prepared for Department of Energy

Under Contract No. EA-77-A-01 -601 0

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Table of Contents

Page

Executive Summary 1

1. Purpose of Survey 3

a. Survey Approach 4

b. Types of Pulp and Paper Mills 7

2. Pulp and Paper Making Measurement 9

Technology Requirements

a. Feedstock 9

b. Pulping Processes 12

1. Mechanical Pulping 12

2. Chemical Pulping 13

3. The Sulfite Process 14

4. The Kraft or Sulfate Process 14

c. Pulp Washing and Bleaching 18

d. Process Steam 24

3. Chemical Recovery - Kraft Process 24

a. Recovery Boiler 27

b. Smelt Bed 31

c. Lime Kiln 31

4. DOE-Sponsored Measurement Technology

Research and Development 33

5. Conclusion and Observations 34

Appendix - Survey Questionnaire 38

Executive Summary

Seven pulp and paper mills, two research institutions, an

instrumentation manufacturer, and one corporate Instrumentation and

Control group were visited to obtain the points of view of the plant

operating personnel and others concerned about the need for new

sensors and measurement instruments. Most of the information

developed is in agreement with the generally perceived needs that

have been reported in the literature during the past several years.

Acknowledging that six mills is a very limited sample of the large

pulp and paper industry, several of the points of view were

significant either because the mills were unanimous in voicing a

need, or conversely, the mills placed the needs for some sensors as

low priority items. For example, sensors to measure the moisture in

the wood chips did not appear to be an important need, particularly

in the mills located in climates where freezing is an unusual

condition

.

On the other hand, all of the mills expressed a need for a

reliable, on-line sensor capable of measuring the consistency of

multi-phase flows. Associated with the need for consistency sensors

was a desire for a sensor to measure the "freeness" of the furnish,

i.e., the drainage characteristic of the water comprising the

majority of the pulp slurry to drain from the sheet formed by the

cellulose fibers when the slurry is incident on a screen. Such is

the initial procedure in forming the paper sheet. In this case, some

agreement needs to be established on the characteristics of

"freeness .

1
The pulping process is the least controlled of the papermaking

processes. Several measurement needs were identified in this area.

On-line measurement of the degree of completion of the digestion

process would provide the required information to control the

digestion process. Also various measurement technologies are needed

to improve process control of the chemical recovery cycle. The

prominent energy-intensive processes of this cycle are the recovery

boiler and the lime kiln. The recovery boiler is of most interest

since its chemical reduction capacity limits pulp production rates in

many mills. Some parameters of interest here are: (1) fuel value of

black liquor; (2) solids concentration; (3) combustion zone temperature; and (4) smelt bed parameter, i.e., degree of chemical

reduction.

Several additional sensor needs were also discussed, and these

sensors are identified in this report.

It is apparent that the continuing increase in fuel costs is of

concern to the pulp and paper industry. New sensors that would

result in the decreased use of energy would be welcome. However, it

is improbable that any sensor would be accepted unless it has been

proven to be reliable, to require infrequent calibration, to be

relatively maintenance free, and to not require a very high level of

training to operate.

2
1. PURPOSE OF SURVEY

A survey of selected paper mills was conducted in order to identify

the needs for improved sensors and measurement techniques. By visiting

selected paper mills and reviewing applicable documents, the survey

gathered experiences and recommendations from paper plant operating

personnel, and paper plant instrumentation engineers.

This report of the survey includes an assessment of the process

control equipment used in the pulp and paper industry and discusses the

future needs for sensors as perceived by the industry. The survey

revealed that the priorities of needs for sensors as viewed by the

personnel responsible for paper production may be significantly different

from the priorities as seen by the instrumentation specialist.

The following pulp and paper mills were visited to obtain the

information discussed in the field survey.

Mead

Westvaco

St. Regis

Intemat ional

Scott

Southwest Forest Industries

North Pacific Paper

Chilicothe, Ohio

Luke, Maryland

Pensacola, Florida

Mobile, A1 ab ama

Mobile, Alabama

Panama City, Florida

Longview, Washington

Visits were made to the Accuray Corporation, Columbus, Ohio; a

manufacturer of instrumentation and control systems used by the pulp and

paper industry. Two research institutions were visited: The Institute of

Paper Chemistry, Appleton, Wisconsin; and the Weyerhaueser Technology

Center, Tacoma, Washington. The Instrumentation and Control Group of the

Crown Zellerbach Company at Vancouver, Washington was also visited.

3
a. Survey Approach

The pulp and paper industry can be characterized as a "mature"

industry involving processes that require large amounts of energy.

Although approximately one-half of the energy used is derived from forest

and pulp waste products, the remaining energy requirements are supplied by

oil, gas, and/or coal. The majority of the pulp and paper mills now in

operation were built during the years when the costs of fossil fuel energy

were very low, and consequently the design of energy efficient systems was

not given the attention it would be in today's era of high energy cost.

All of the mills surveyed have improved or expanded their plant facilities

since construction, one has been in operation only a short time, but the

primary emphasis has been on improving the paper making process.

Improving energy efficiencies is a part of many recent plant improvement

programs, but these improvements still appear to be of secondary

importance. There are strong indications, however, that if fossil fuel

prices continue to increase faster than the inflation rate, most mills

must improve their energy efficiencies if they are to remain competitive.

The interviews followed the general line of questions that are listed

in the last section of this report. These interviews with the technical

staff of several operating paper mills indicate an awareness of the need

for better instruments in order to improve energy efficiencies, but the

interviews also revealed a practical concern regarding the cost/benef its

of improved instrumentation and computer control. Much of this concern is

the result of unsatisfactory experiences with instruments that were

unreliable, or required constant maintenance, or required highly trained

(and highly-paid) technicians to operate.

4
Since the purpose of this field survey was to obtain the views of the

pulp and paper industry personnel regarding the needs for new or improved

sensors, the industry's concern with the practical usefulness of

instrumentation in a relatively unsophisticated production environment was

found to be an important factor in the selection of any sensor research

and development program.

In order to relate the specific comments of mill personnel to

specific mill operations, this report will include brief generic

descriptions of typical mill processes, followed by the recommendations

and comments received during the survey. The basic unit operations and

intermediate products in the making of paper using the Kraft or sulfate

process are diagrammed in Fig. 1.
KRAFT PAPER MAKING PROCESS

6
b . Types of Pulp and Paper Mills

Over 350 companies manufacture paper and paper products and over 700

mills are located in the U.S. to produce pulp and paper. Producers vary

in size from very large installations that produce wood products, as well

as pulp and paper, down to relatively small specialty paper mills.

Although some mills produce quality paper from rags and other fibrous

materials, most of the raw material for paper is obtained from trees and

recycled waste paper.

Mills are generally classified as either integrated mills, or

non-integrated mills. The distinguishing difference is whether a mill

produces its own pulp to be made into paper, in which case it is an

integrated mill, or whether it purchases its pulp and/or waste paper,

which identifies it as a non-integrated mill.

It has been estimated that 60-70% of the production capacity is in

integrated mills. The average capacity of an integrated mill is 300,000

tons per year. However, the large new mills have production capacities of

500,000 to 1,000,000 tons per year. These mills produce their own

electric power unless they are located in an area where electric power

such as hydro-electric power is relatively cheap. According to the

American Paper Institute, all paper mills in the U.S. with annual

capacities greater than 360,000 tons are fully integrated.

The non-integrated mills that manufacture paper from purchased pulp

and waste paper have paperraaking capacities ranging from 3,000 to 30,000

tons per year. Almost all of the non-integrated mills purchase their

electric power as well as the feedstock for- the paper. Recognizing that

although some new sensors may be needed by non-integrated mills, it is

apparent that most of the needs for new or better sensors and instruments

7
will come from integrated mills, especially sensors needed in the

digesting and chemical recovery processes. Consequently,

emphasized visiting and interviewing personnel from fully

mills

.

this survey

integrated

8
2. PULP AND PAPER MAKING MEASUREMENT TECHNOLOGY REQUIREMENTS

a. Feedstock

With the exception of specialty paper mills that use rags and other

non-wood fibrous materials as feedstock, the feedstock for integrated

mills is almost exclusively wood in the form of sawdust, chips, or

mill residues. By far the largest percentage of feedstock is in the form

of wood chips, and an increasing amount of the chips is produced in the

forest by machines that chip the whole tree instead of just the tree

trunk. Unless the wood is obtained from a plantation in which all of the

trees are of the same species, the wood chips from a hardwood forest will

be from a number of tree species. Variability in hardwoods will result in

differences in paper properties. Most mills do not pulp mixtures of

hardwood and softwood chips because they respond differently to liquor

penetration and pulping kinetics.

In looking to future requirements, the supply of good long fiber

softwoods might not be adequate to meet the increasing demand for pulp.

If this type of supply /demand condition should develop, it would result in

an increase in demand for short-fiber hardwoods and probably lower quality

feedstocks in general with possible changes in requirements for facilities

and instrumentation. An increase in usage of lower quality wood would

also require more intensive bleaching to produce white papers.

These expected changes in the feedstock could initiate or accentuate

the demands for new sensors, particularly on-line measurement of the Kappa

number, and the wood-to-alkali measurements. Kappa number is a measure of

the concentration of lignin compounds in a sample of pulp or process

liquor, usually spent digestion liquor. This process variable results

from an off-line titration involving permanganate solutions.

9
The sources of wood fibers are: (1) roundwood or wood chips obtained

from forests owned by the pulp and paper mills, or (2) log or wood chips

purchased from private suppliers within the general area surrounding the

mill. Some mills reported problems in digesting purchased chips. In

particular wood chips from some undesirable species such as swamp cypress

can cause problems, and chips containing waste material from plywood

plants are particularly troublesome because of the glue used in the

plywood. Mill operators would welcome a sensor that could detect these

contaminants prior to storage and pulping.

Wood chips, either purchased or chipped by the mill, are normally

stored in a stockpile of sufficient size to insure that continuous pulp

production would not be affected by any small-duration interruption in the

wood supply. During its storage, the moisture content of chip can change,

depending principally on weather conditions.

In the colder climates, rain and melting snow can be troublesome if

this moisture is frozen around the chips. The moisture of chips in the

stockpile will vary with respect to its location in the pile.

Knowledge of the chip moisture content is needed in order to

regulate the cooking schedule to meet the target Kappa number. Many mills

sample chips, usually twice during a work shift for moisture determination

in the laboratory. The moisture content information is then transmitted

to the personnel responsible for digester operations, and adjustments are

made to the cooking schedule to compensate for any changes in the moisture

content. Obviously, infrequent samples that are analyzed off-line can be

effectively used only if the moisture content is subject to relatively

slow changes, which is usually the case in warmer climates. All of

10
the paper mills visited use off-line sampling, and most do not

consider on-line moisture content to be a high priority need.

However, one mill was testing an on-line sensor at the time of the

plant visit. The results of these tests were reported to be

favorable at the 12th Annual Instrumentation and Control for the Pulp

and Paper Industry held at Miami University of Ohio, May 1981. The

indications are that the mills in the colder climates might use

on-line moisture sensors if they are low cost and reliable.

In order to avoid the problem of frozen chips, some mills in the

colder climates stockpile the chips in silos or bunkers. In this

case, one mill expressed a need for a reliable instrument to indicate

the level of chips in the bunkers.

11
b . Pulping Process

The three principal commercial processes used to convert wood into

pulp are: (1) mechanical pulping, (2) sulfite chemical processes, and (3)

sulfate (or kraft) chemical processes ( ~ 70% of U.S. pulp production).

1

.

Mechanical Pulping

This process produces pulp through the direct mechanical abrasion of

wood either in chip form or in the form of round wood. Four types of

processes are used:

1. Stone grinding of wood,

2. Refiner mechanical pulping (RMP),

3. Thermomechanical pulping (TMP),

4. Chemi thermomechanical pulping (CTMP).

These processes have approximately twice the yield (~ 90-95%) of the

kraft process since the lignin binding the cellulose fibers together is

not removed. These processes are electrical energy intensive.

Approximately 1500 kwh is needed to produce a ton of pulp using the ground

wood process with RMP and TMP consuming 2000 to 2500 kwh/ton. Plants

employing these processes tend to be located in regions of cheap electric

power. The U.S. Pacific Northwest and Canada contain most plants using

this process. The ground wood and RMP processes employ little pretreating

of the wood while TMP and CTMP use presteaming or presteaming combined

with mild chemical treatment before the wood goes to the refiner. One or

two refiner stages may be used to produce the pulp depending upon its use.

A primary control parameter for this process is freeness which is a

measure of the ability of a pulp to release the water used to transport it

once it is placed on the fourdrinier screen of a paper machine as well as

a predictor of some paper strength properties.

12
Freeness and consistency are the primary parameters used for control

of the thermomechanical pulping (TMP) process. This process consumes a

large amount of electrical power to produce pulp. In the newest plant

visited, each refiner plate was driven by a 5,000-horsepower electric

motor. Approximately 250,000 horsepower is used to process pulp for two

large paper machines producing newsprint. Freeness values were obtained

from grab samples and laboratory derived results were entered into the

automatic control system by the operator of the process. Approximately

two hours elapsed between samples. In this particular mill the level of

automatic control capability is extremely high. Every attempt has been

made to use on-line measurements. In the case of freeness these on-line

sensors required a high level of maintenance and were felt to be

unreliable by mill personnel. Mill operation relied upon off-line

laboratory measurements for process control information. Reliable

freeness measurements on-line would allow active control of the TMP

process resulting in a significant savings of electrical power through

more rapid and effective feedback control of the TMP process .

2 . Chemical Pulping

The purpose of a chemical pulping process is to separate cellulose

fibers from the major non-cellulose constituents of wood; the major

constituents are cellulose, heraicellulose , and lignin. Cellulose is a

colorless carybohydrate . The whiteness of the fiber, which is mostly

cellulose, is caused by dispersion of light in the fiber body. Cellulose

is fairly resistant to the action of the chemicals normally used in the

papermaking process. Lignin, the name for a complex polymeric organic

compound, is the second main constituent and is the substance that binds

the fibers together. Of particular importance to the pulping process is

13
the fact that hardwood lignins are quite different from softwood lignins.

A considerable body of work has been published on the characteristics of

these lignins. A definitive reference work on the subject has been

published by Sarkanen and Ludwig [1],

3 . Sulfite Process

The sulfite pulping process uses an acid sulfite solution to digest

the wood chips. Although once a relatively popular pulping process, the

number of mills using the sulfite process has remained approximately

constant since 1940. The difficulty of pollution abatement has played a

strong role in decreasing the attractiveness of these process in recent

years. The growth of the U.S. pulp and paper industry during this century

has been based largely on the Kraft pulping process. The advantages of

the sulfite process on a commercial basis are:

1. High yield,

2. Low cost of process chemicals (sulfurous acid and calcium

bisulfite) relative to the Kraft process,

3. High brightness of unbleached pulps,

4. Ease of bleaching without use of chlorine dioxide.

However, two major disadvantages of the sulfite process relative to

the Kraft process are:

1. A limit of range of woods are suitable as feedstock,

2. Significantly reduced strength of the pulp,

3. Difficult pollution abatement.

4 . Kraft or Sulfate Process

The kraft or sulfate pulping process is the predominant alkaline

process in use today. The kraft process uses sodium hydroxide and sodium

sulfide as the pulping chemicals. The advantages of the process are:

14
1 . The pulp has high strength,

2. Any wood specie can be used,

3. Substantial bark can be tolerated in the chips,

4. The digestion process is short,

5. Problems with pitch are less prevalent,

6. Chemical recovery is a well understood process,

7. Commercially useful by-products (turpentine and tall oil)

are available from some softwood species.

The remaining portion of this report will deal largely with the Kraft

process, since most of the paper mills surveyed for this report use it.

In the Kraft process, alkaline chemicals with a pH of greater than 12

are used to chemically remove most of the lignin and hemicellulose in

order to free the desired cellulose fibers. The digestion process is

operated at elevated temperatures and pressures in large vertical

cylindrical digesters. The digester is charged with wood chips and

"white” cooking liquor and black liquor. It is then closed and the wood

chips are cooked or digested from two to three hours at temperatures of

340 to 350°F, and at pressures of about 100 to 150 psig. The active

chemicals in the cooking liquor are sodium sulfide and sodium hydroxide.

The strength of the white liquor is expressed in terms of active or

effective alkali, which is defined as the combination of concentrations of

sodium hydroxide and sodium sulfide expressed in terras of the equivalent

sodium oxide. All of the mills surveyed using the kraft process used

off-line titration to measure the effective alkali in the liquor. Some

types of on-line sensing for active or effective alkali are in commercial

use. These use titration or conductivity sensing.

15
All of the kraft mills surveyed used banks of batch digesters. Up to

18 batch digesters are in use in some mills. Since continuous digesters

are relatively recent systems, batch digesters were the only kinds of

digesters in use when these mills were built. Within recent years at

least two of the mills visited have added continuous digesters, and

another mill is planning to add a continuous digester. Some mills have

automated chip charging systems, but most batch digesters are still

charged manually. The batch digesting cooking cycle normally consists of

three steps:

1. Pressure raising and penetration of liquor,

2. Cooking period under full pressure at the cooking temperature,

3. Pressure reducing step. The pulp is usually blown from the

digester under pressure.

Batch digesters are either heated by direct steaming of the

wood-liquor mixture or by indirect steaming of the cooking liquor as it is

circulated through side-arm heat exchangers connected to the digester

vessel itself. The process control variables involved in the digestion

process are:

1. Composition of cooking liquor,

2. Concentration of cooking liquor,

3. Chemical to wood ratio,

4. Temperature and time.

The most important factors are the temperature and time of the

digestion process. In addition the liquor volume must be controlled to

assure an optimum consistency of the pulp when it is blown from the bottom

of the digester. The flash steam released in the blowing process is

partially recovered in the form of hot water. This hot water is then used

16
for washing and bleaching the pulp. In continuous digesters, the three

steps of heating, cooking, and blowing take place in different zones of

the digester. The flash steam is captured and used to heat the chips

being fed into the digester.

The cooking time for batch digesters is determined by the Kappa

number of the previously cooked pulp, i.e., the measure of the lignin

compound concentration of the pulp. A sample of the pulp is taken during

the pulp-blowing step, and is analyzed to determine its kappa number.

Determination of the kappa number of the sample is accomplished with an

off-line wet-chemistry test. Depending upon the type of pulp to be

produced, the kappa number is used to determine the alkali-to-wood ratio,

and the temperature and cooking time to be used for the next batch. Only

one of the mills visited had batch digesters equipped with devices that

enable the extraction of pulp samples during digestion. These samples are

also analyzed off-line and could be used to modify the cooking process to

meet the pulp quality desired. Normally, the test results of these

samples were used to control the processing of the next batch. None of

the mills visited use any on-line sensors to determine the Kappa number

during a cook, nor were the mill personnel familiar with any sensor that

could make on-line Kappa number or equivalent measurements.

In fact, if an on-line Kappa number sensor were developed, there may

be a reluctance to use such a sensor in some mills. Old-time pulp mill

operators take pride in their abilities to grab hand samples of the pulp

during the digester blow, and to estimate its Kappa number by its color,

texture, and feel. On the other hand, mill and corporate personnel

responsible for instrumentation and control agreed that a low cost,

reliable on-line Kappa number sensor must be developed in order to

eventually achieve real-time computer control of this process.

17
Another method for controlling the Kappa number of the pulp is to

blend the pulp after digestion. By mixing a number of batches of pulp in

the pulp storage tanks, the kappa number for the pulp that will go to the

paper machine can be controlled within a desired range suitable for the

type of paper to be manufactured.

One of the documents reviewed during this survey listed the Nu and

permittivity measurement tests as other pulp quality measurement tests.

None of the mills visited make these tests, nor did there appear to be any

interest in them.

c . Pulp Washing and Bleaching

All chemical pulps must have additional treatment after the pulp is

discharged from the digester. The first step in the treatment is to wash

the pulp with hot water in order to remove a major portion of the lignin

still adhering to the cellulose fibers and residual alkali chemicals. The

washing process is usually performed in a series of steps. Before the

washing process, uncooked wood pieces (knots and shives) are removed, and

bundles of fibers are broken into separate fibers.

From an energy conservation point of view, control of the pulp

washing (sometimes called brown stock washing) is important because the

efficiencies with which the chemicals are recovered and the hot water

reused will determine the amount of process heat that will be required.

Effective evaporator efficiency will minimize the amount of dilution which

the black liquor will experience before passing to the evaporators. Since

evaporation requires process heat, a high concentration of solids in the

black liquor will decrease the amount of steam required to increase the

solids concentration in black liquor to be safely fired in the recovery

boiler (60-65% solids). An alternate process using freeze crystallization

18
of the water in black-liquor-dissolved organic and inorganic salts is

currently the subject of research efforts. It is anticipated that use of

this process for black liquor dewatering will provide a significant energy

reduction.

Following the washing process, the pulp is bleached to varying

degrees of brightness determined by the type of paper to be produced.

Brightness measurements are based upon reflectance intensities in several

regions of the visible spectrum. Typically, these colors (red, green,

blue) are used although others may be used for particular types of paper

or pulp. For example, kraft pulp which will be made into liner board is

not bleached, while pulps to be used for high quality writing papers are

bleached to a high degree of brightness. Bleaching is a process of

solubilization and removal of colored material from the pulp after

digestion. Kraft pulps are dark in color as they leave the digester, due

to residual lignin adhering to the cellulose fibers. Since lignin is

easily chlorinated, it can be efficiently removed if the first step in

bleaching is chlorination followed by alkaline extraction. Caustic is

used to extract the chlorol ignins formed in the first stages — for the

most pert, and chlorine, hypochlorites, and chlorine dioxide are used to

remove lignin in the subsequent stages. The use of chlorine dioxide will

produce high-strength, high-white pulps. However, chlorine dioxide is one

of the most expensive chemicals used in the paper making process and

itself is produced in an energy intensive process.

Bleaching is usually either a three stage or a five stage process.

The plants surveyed used the five stage bleaching process. The bleaching

process involves several washings, chlorination, alkaline extraction,

hypochlorite, and/or chlorine dioxide treatment. Each stage is usually

19
subjected to an appropriate form of measurement to achieve process

control. Chlorine is the principal bleaching chemical, and between 125

and 150 lbs of chlorine are required for each ton of white paper. The

chlorine bleaching process is usually controlled by measuring the

brightness of the treated pulp using optical reflectance methods. This

particular measurement technique was used by all of the mills surveyed.

The degree of alkaline extraction is determined off-line in the

laboratory. Measurement of the concentration of hypochlorite is also

performed off-line usually by using the oxidation-reduction-potential

(ORP) technique. On-line measurement is used but not in the mills

visited. All of the mills surveyed stated that the existing techniques of

measuring and controlling the bleaching process were effective and did not

give the mills any significant problems. Therefore, the mills did not

consider the development of on-line bleach process sensors to be urgently

needed

.

After the pulp has been bleached, it is filtered, thickened and then

stored in a thick stock tank before beginning preparation for paper

making. This final processing procedure or approach flow to the paper

machine is highly dependent upon the type of paper to be made. A wide

variety of additives may be used to obtain the desired paper

characteristics

.

A major energy consumer in this final processing stage is the

refining or beating process. The refining process is electrical energy

intensive. Refiners generally consist of a stator and rotor or two

rotors, either conical or disc shaped, driven by large electric motors (

500-1000 hp). Control of the procedure is accomplished through variation

of the residence time, consistency, and gap between the stator and rotor.

Paper pulp having a consistency of approximately 4 to 6% is mechanically

20
abraded changing the physical characteristics of the cellulose fiber to

produce desirable properties of the paper sheet formed from them.

(Consistency is defined as the mass fraction of cellulose in the pulp

slurry, i.e., it is the solid phase fraction of this particular

solid-liquid system.) Sheet strength and sheet formation are strongly

influenced by refining. The process variable used extensively to measure

the degree of refining is freeness. Freeness is a measure of the drainage

of water from the fiber mass formed by the pulp as it drains over a screen.

The standard test most often used in the U.S. is the Canadian Standard

Freeness test which is an off-line test. On-line sensors which measure

drainage characteristics were not given a high degree of confidence by the

operating personnel surveyed. High levels of maintenance were claimed

necessary to maintain operation and there was a general lack of confidence

in the measured values derived from these devices. Since this parameter is

of such importance to the paper making process, a high level of interest

was expressed in the development of reliable and effective freeness

measurement techniques with reliability and low maintenance being primary

considerations.

Having been refined, the pulp slurry has entered the approach flow

system to the paper machine. This stage of the process will produce the

final pulp slurry or furnish which contains all necessary components to

the paper sheet having specific ranges of properties. The furnish may be

a complex blend of selected pulps, fillers, dyes and/or whiteners such as

titanium dioxide for producing high quality writing or printing grades of

paper or may contain unbleached stock for producing linerboard, whose

primary specifications relate to strength characteristics. These

processes occur before the stock is diluted to a consistency of 0.1 to 1%

21
and may use unit processes of a specialized nature to obtain the desired

paper properties. These procedures were not surveyed and tend to be

either proprietary or nonenergy-use specific and were, therefore, not

considered in this survey. Dilution of the stock from the 3 to 4%

consistency level to the proper consistency is done using the white water

taken from the paper machine. This is the water used to carry the furnish

through the head box to the Fourdrinier screen. This water falls through

the screen or is sucked off through the couch roll and recirculated to the

blending point. Once again, consistency is the controlling parameter for

the dilution. Although this is not an energy-intensive procedure it is

very important to paper making since sheet properties, e.g., basis weight

(mass per unit area of paper sheet) and variation in it, are sensitive to

the final consistency in the head box and at the slice (the orifice through

which the pulp slurry passes from the headbox onto the fourdrinier screen).

Feed forward control of the linear speed of the paper machine is common and

based in part upon the consistency measurement of the furnish. At this

point, accuracy of the consistency measurement is more important than

previously since sheet properties depend directly upon absolute consistency

measurements rather than relative variations.

All of the mills surveyed state that they would place a high priority

on developing a reliable and accurate on-line instrument for measuring

consistency. Several indicated that not only is it important to measure

the consistency at the headbox and in the blending process, but such an

instrument would also be useful in other parts of the process particularly

in the digesting, bleaching, cleaning, and refining operations where

consistencies are in the 3 to 12 percent range. Great care is exercised in

measuring the volumes or weights of water and materials but, in spite

22
of this, variations in consistency will occur, requiring frequent

checking. Taking a sample of stock from any point in the system is not a

reliable technique. Experience has demonstrated that such samples can

vary by 10 percent in the consistency value. Although numerous types of

consistency sensors are available and in use, many of the mills surveyed

were not satisfied with their performance. In particular, the sensors

based on hydrodynamic drag of the flowing stock required frequent

maintenance and were generally claimed to be unsatisfactory but better than

no sensor at all.

In a recent survey by the American Paper Institute of technical

support personnel in pulp C

'— 30 % of the respondents) and paper (~70% of

the respondents) mills, devices based on hydrodynamic drag were

predominant (~95%). The primary deficiencies of these devices were their

sensitivity to flow conditions, vibration induced by high flow velocities,

and plugging. The majority of the respondents felt that further

instrument development work was needed. Poor reliability and excessive

maintenance were often cited as problems with this type of device. These

devices appear to be used for relative consistency measurement. Absolute

consistency measurements are not considered possible presently but would

be a desirable feature.

Freeness plays an important role in the papermaking process.

Freeness will affect the first step in the drying process and the initial

drainage of water from the screen on the fourdrinier screen followed by

additional water removal by a suction coach roll at the end of the screen.

As the sheet enters the machine's rolls, the first rolls remove more water

by pressing the sheet against a felt roll. The remaining water is removed

by evaporation which occurs on steam-heated rolls of the paper sheet

23
passes through the drying sections of the paper machine. The dryer section

of a paper machine is enclosed by hoods to reduce the amount of process

steam required, some of the mills surveyed expressed a need for reliable

humidity sensors in the hood area. Humidity sensing was being used in at

least two mills, but these sensors required frequent maintenance. The

humidity sensors provide information for control of the recirculation

of air in the dryer hoods, thereby reducing a tendency to overdry the paper

sheet

e . Process Steam

Process steam is consumed primarily in the digestion process, in

drying the paper sheet once it has been formed through various evaporation

processes. It is the most energy-intensive fluid found in a paper mill.

In most cases, the metering of steam to the various unit processes was not

done. There was a general feeling among those interviewed that a reliable

and accurate steam flow measurement would induce more efficient use of

steam throughout a mill. Accurate measurement would also provide a method

for energy usage in the various unit processes of papermaking and could

provide an incentive to improve efficient utilization of it.

One mill visited did not produce process steam since the pulping

process was therraoraechanical . Steam was purchased from a nearby producer.

Both producer and user emphasized the need to measure the energy content

of the steam. The user stressed the need for improved steam flow

measurements having increased dynamic range in the flowrate (current

devices have a 3:1 range) and the capability to measure the energy content

of the steam. Improved control and energy utilization characteristics of

the papermaking as a whole could result from such measurements of this

primary form of energy.

24
CHEMICAL RECOVERY PROCESS

25
3 . Chemical Recovery

The kraft pulping process that is described in the first sections of

this report is a sulfate chemical process. One of the advantages of this

process is its ability to recover and recycle most of the chemicals used.

In addition to the recovery of valuable chemicals, the chemical recovery

system generates enough heat in the combustion of the waste lignin and

carbohydrates to provide a substantial portion of the process heat needed

to operate the mill. A schematic of a typical chemical recovery loop is

shown in Fig. 2. The two most energy-intensive processes are the recovery

boiler and the lime kiln. Energy is produced in the boiler and consumed

in the kiln.

The chemical recovery process starts with the washing of the pulp to

remove the dissolved lignin, hemicellulose, and process chemicals. The

wash water remaining after the pulp has been cleaned is called black

liquor because of the characteristic black color caused by the dissolved

organics. A substantial portion of the black liquor is recycled and added

to the white liquor to be used in the digestion of another batch of chips.

The remaining black liquor is oxidized to reduce odors and then sent to

evaporators where the concentration of solids is increased by multi-effect

evaporation to remove the water.

Multi-effect evaporators use water evaporated from one stage to act

as the heating fluid for the succeeding stage. Typical evaporators will

have as many as six stages, and can increase the concentration of solids

from about 15% to 50%. Recent safety standards require the black liquor

to have 60-65% solids before it can be burned in the recovery boiler.

Since corrosion and high viscosity preclude the use of multi-effect

evaporators above concentrations of 50%, the final concentration step is

26
achieved by heating the black liquor in the hot flue gas stream from the

boiler. Optical ref ractometers were used in all cases to assure that

concentration of solids will be a minimum of 65% before injection into the

recovery furnace. None of the mills surveyed indicated any problems with

using refractometers , although some of the technical personnel at the

mills felt that a more direct measurement of solids concentration would be

des irable

.

Measurement of the dew point in the contact evaporator was cited as a

useful measurement. Condensation of sulfuric acid on the metal surfaces

of the evaporator causes excessive corrosion ultimately leading to

replacement of the evaporator. A sensor to do this measurement was

considered desirable although direct energy conservation would not result

from its use.

a. Recovery Boiler

The recovery furnace is a major component in a kraft paper mill. Not

only is it necessary in the chemical recovery step, but it usually also

supplies enough heat energy as process steam to operate the digesters. The

operating principle of a recovery furnace is to bum the combustible lignin

in the black liquor in a staged combustion process. Two types of furnace

designs are used. The first [2], sprays the black liquor from two nozzles

located in opposite walls of the furnace. The nozzles are on oscillating

mounts; the flow through them and their shape are selected to spray the

liquor through the combustion zone of the furnace so that it strikes the

opposite wall where it adheres, dries, and may begin combustion. After

drying on the wall, the dry residue slumps 'off the wall and falls onto the

bottom of the furnace into the smelt bed where it completes combustion of

the hydrocarbons and the chemical reduction of the liquor. The smelt flows

27
out the bottom of the furnace through spouts into the dissolving tank.

Steam jets break up these smelt streams before they hit the surface of the

liquid in the tank to avoid explosion of the hot smelt as it comes into

contact with water. This type of furnace uses three locations for the

introduction of combustion air. Primary air is introduced near the top of

the smelt bed, secondary air enters immediately above the liquor injection

ports, and tertiary air is admitted 10 to 15 feet above the secondary air

ports

.

The second type of recovery furnace is similar in general

characteristics but differs in the method of introduction of the black

liquor and combustion air. In this case the black liquor is sprayed

through a system of nozzles located on all four sides of the furnace at the

same level. Up to four individual nozzles may be located on each side of

the furnace. The spray of black liquor from a nozzle is a dispersed spray

of droplets whose trajectories carry them into the combustion zone of the

furnace where they fall to the surface of the smelt bed. During transit

the droplets dry and burn. Again, primary combustion air is introduced

near the top of the smelt bed. Secondary combustion air is introduced

approximately 15 to 20 feet above the black liquor injection point. In

both types of furnace designs sufficient heat is released by the burning

lignin to maintain the reduction reaction in the smelt bed producing the

desired sodium sulfide.

Although easy to describe in generalities, the operation of a recovery

furnace is relatively complicated. While the lignins and other organic

matter in the black liquor are the primary fuels, supplementary gas or oil

may also be burned simultaneously to provide combustion stability or to

make up for low black liquor availability should the digestion process not

be providing a sufficient supply. Enhanced combustion stability is

28
considered possible if the fuel or calorific value of black liquor were

measured to adjust firing levels to compensate for the fuel's variable

energy content. No on-line sensor is available to measure this variable,

therefore furnace control and operation must allow a substantial safety

margin. Unfortunately, catastrophic furnace explosions have occurred due

to either large breaks in the water walls of the furnace or to firing black

liquor containing too much water. This latter cause is one of dispute

within the community. In any case, the need for on-line fuel content

measurement as a control variable for the recovery boiler was voiced by

operating and technical personnel and would provide increased automatic

control capability. In this case the time necessary for an acceptable

sensor to provide fuel content information would be on the order of every

few minutes (5 to 10). This was claimed to be entirely acceptable.

The other major variable of the recovery boiler combustion process,

air was either not measured or done poorly in the mill personnel's

opinions. At least two of the mills surveyed were strong in their

criticism of existing techniques, and expressed a conviction that more

accurate air mass flow instruments could be beneficial in improving the

operating efficiency of the furnace. Generally, few if any direct

measurements are available from the combustion region itself.

Additional parameters which were cited as being needed but not

presently available, or available but at an unacceptable level of operation

are listed below:

1. Oxygen and CO concentration in the furnace cavity. Presently

sensors are available for both variables to be measured in the

stack emissions. These measurements have been shown to improve

control of the boiler.

29
2 . Instrumentation to monitor particulate emissions from the recovery

furnace cavity. These are primarily sodium sulfate and sodium

carbonate. These inorganic salts exit the furnace ( 1700*F) and

enter the boiler tube banks ( 1200°F) where fouling and corrosive

effects may be severe. The level of "stickiness" of these

particulates is dependent upon temperature. Corrosion of the

boiler tubes results from excessive temperature in the furnace

which is frequently overfired to increase chemical production.

Surface temperature measurements on the boiler tubes would be used

to control the temperature of the furnace to keep particulate

temperatures below critical values.

3. Various black liquor parameters need to be measured:

a. Flowrate of liquor as it is fed to the boiler's spray

nozzles

,

b. Droplet size distribution as it is sprayed from the nozzles

droplet sizes should influence the drying and combustion

characteristics of the liquor,

c. More accurate solid concentration,

d. Viscosity - influence on droplet size is the object here,

e. Surface tension, a key parameter of the spray-droplet

formation process.

4. Detection of leaks in the boiler tubes at the pinhole size.

5. Vertical temperature profile of the furnace from the smelt bed to

the boiler tubes.

No on-line sensors are presently being used to measure the combustion

properties of the recovery boiler. This dearth of available sensors must be

30
remedied to effectively control the boiler's operation efficiently.

b . Smelt Bed of the Recovery Boiler

The primary function of the recovery boiler is the reduction of

sodium sulfate to sodium sulfide. These reduction reactions occur in

the smelt bed which lies on the hearth of the furnace. The boiler is

operated such that the smelt bed is maintained between 1700 and

2200°F. The smelt is drawn off from the furnace hearth while still

molten and dissolved in weak liquor and water. The smelt bed

parameters which were most frequently given as critical measurements

needed for control purposes are listed below:

1. Surface temperature profile,

2. Smelt bed height and/or profile (topography),

3. Smelt bed inventory or density,

4. Temperature a’nd flowrate of the liquid smelt as it comes

from the bed,

5. Sulfate to sulfide conversion rate, bed reaction rates

generally,

6. Sodium carbonate concentration in the smelt and the green

liquor produced from it.

The harshness of this environment is such that few if any bed

parameters are made even on an intermittent basis. Periodic visual

inspection is the usual practice. Visual inspection allows the bed

height to be maintained at 2 to 3 feet.

c . Lime Kiln

Although the recovery furnace is a ma-jor component in the

recovery and recycling of chemicals, additional chemical processes

and equipment are needed to return the chemicals to the state from

which they can be used again in the pulping process. As shown in

31
Fig. 2, the smelt is drawn from the furnace hearth while it is still

liquid, and is then dissolved in weak liquor and water. The

resulting solution is transported to a clarifying tank in which the

solids settle out, after which it is called green liquor, a color

caused by dissolved iron sulfide.

The green liquor contains sodium sulfide and sodium carbonate.

The sodium carbonate is converted into caustic soda by treatment with

slaked lime (CaO) and calcium carbonate is precipitated as lime mud.

The causticized liquor, now called "white" liquor is clarified and

ready for recycling in the pulping process. Fresh white liquor is

diluted with black liquor up to 60% by volume to maintain the water

balance favoring energy conservation in the recovery process. The

lime mud (calcium carbonate) is passed through a lime kiln to be

reformed into CaO. The lime mud is injected into the high end (gas

exhaust end) of a rotary kiln and progresses through the slowly

turning kiln until the calcined product, (CaO) is discharged at the

lower end. Oil or natural gas is used for heating the kiln. The

burners are located at the lower end of the kiln and the hot gases

pass to the high end, or counterflow to the mud flow.

Although the kiln is a major consumer of fuel, most of the mills

surveyed have not installed sophisticated control systems. The mills

visited were using manual controls. The temperature at the burner

end is measured with an optical pyrometer, and the temperature

composition of the exhaust gases is measured with standard sensors.

Host mills have yet to install air preheaters to recover some of the

sensible heat from the discharged CaO. No active attempts to control

airflow into the kiln were observed. The parameters for which

measurements were desired are listed here:

32
1 . Flame temperature profiles and emissivity,

2. Lime temperature profile along the kiln length,

3. Mass flow of lime mud into the upper end of the kiln,

4. Quality of the discharged lime in terms of actual CaO available to

convert Na2 C 03 to white liquor.

Due to concentration and reaction equilibrium the reaction proceeds usually

at less than 90% efficiency. Hence, unreacted lime and sodium carbonate

circulate through the kiln as a "dead load." Energy is wasted in the calcining

process since these materials must be dewatered and converted again.

The lime kiln is a large user of energy. Several corporate research

personnel have stated that research directed toward the use of alternate energy

sensors in this process could be useful to decrease the industry's dependence on

natural gas. Combustion-related research was also suggested for the effective

burning of less desirable fuels such as bark, waste paper, and wood unsuitable

for paper making or other uses.

4. DOE-Sponsored Measurement Technology Research and Development

As part of the contract under which this report has been written, the

Department of Energy is supporting a research and development effort directed

toward producing measurement technology which will provide the basis for the

private sector to develop new on-line sensor technologies which will be

available in a paper mill environment. The objective is to enhance the

efficient utilization of energy through the increased use of automatic control

systems. At this time the barrier to broadened use of these systems, which are

> well developed, is process variable measurement information, e.g., consistency,

freeness or black liquor properties.

33
As part of this effort, an industry working group has been assembled to

provide expertise. As part of the initial phase of this activity, this working

group compiled a list of sensor needs for the paper industry which would improve

energy utilization and the process generally. The following lists the process

parameters chosen by the committee as those of highest interest and potential

impact to the industry in this area.

1. Kappa number (lignin concentration in the pulp mass),

2. Pulp quality (freeness),

3. Steam flow,

4. Active alkali,

5. Black liquor combustion,

6. Smelt bed parameters,

7. Black liquor characteristics,

8. Lime kiln temperature profile,

9. Solids concentration of black liquor,'

10. Consistency,

11. Chip moisture,

12. Bulk chip density.

This list is not given in priority order. In generating the list the

working group used energy conservation as a general guideline along with the

conclusion of previous analyses which indicated that the pulping and recovery

areas were those in which the use of new sensor technology would significantly

enhance the use of automatic control system in these areas.

5 . Conclusion and Observations

The need for new and better process instrumentation and controls for pulp

and paper mills has been the subject of several technical conferences during the

34
late 70 's and has also been studied by consultants under contract to the

Department of Energy. A review of applicable proceedings and reports indicate

that while there has been a considerable amount of discussion about the need for

better sensors, there is a diversity of opinions concerning the feasibility of

using new sophisticated instruments in existing facilities. The survey of the

mills visited for this report indicate that the operators of the paper mills are

well informed on instrumentation and control systems, and would favorably

consider using new sensors and techniques. As one of the technical staff at a

paper mill observed, " . . . any on-line sensor technology would be of use”.

However, reliability in the plant environment is a key consideration to the

acceptance and use of new measurement technologies.

The need for new measurement technologies which will improve energy

utilization in the paper industry is most pronounced at the pulping end of the

process. The kraft and thermomechanical pulping processes are energy intensive

and presently cannot be effectively controlled because no sensor technology

exists to do the job. Specific needs have been listed in this report for these

processes. Research efforts directed toward developing the basic knowledge

needed to support the development of on-line sensor technology is sparse.

Although many of the paper companies maintain research and development

activities, these efforts tend to be short range and do not emphasize the type

°f research, i.e. instrumentation technology, needed which will ultimately

provide the basis for development of on-line sensors for the pulping process.

Ihe same situation exists with the instrumentation and control companies with

process control hardware. Although control algorithm system production

capability is well developed in these companies, they are not supporting long
term research which may provide the basis for an on-line measurement technique

unless fruit ition of the effort is expected in a reasonably short period of

time

The American Paper Institute supports research activities at The Institute

of Paper Chemistry and universities. These tend to be of various types but few

in the area of new process measurement technology. At this time the U.S.

Department of Energy has supported and is supporting research related to energy

conervation technologies and some of these are long-term research oriented.

The following areas are ones which will be useful throughout the pulping

and paper making processes in addition to being required for achieving efficient

control of the pulping process.

a. Thermomechanical Pulping (TMP)

1. Freeness - The prevailing opinion in the community is that a

correlation(s) must be found between fiber properties which can

be sensed remotely, and drainage of water from the paper sheet on

the fourdrinier screen. Some work has been done here but either it

is not available to U.S. manufacturers or it has not been successful. A broader definition of the properties of interest is usually

designated as pulp quality, i.e. those fiber or pulp characteristics which combine to form paper of a desired type. This parameter

not only applies to TMP-produced pulp but also to pulp produced by

any process as that pulp is refined for final properties in the

approach flow to the paper machine.

2. Consistency - Currently available sensors are not doing the job in

the opinion of most of the people and companies surveyed. New and

different methods are needed to produce a sensor insensitive to

36
other parameters; e.g., flow velocity or other fluid dynamic

properties. Again this variable is a key one in the refining

operation of the approach flow to the paper machine.

b. Kraft Pulping Process

The sensor needs here lie in two distinct areas. The first which relates

to the digestion process is the need for measurement of the residual lignin

adhering to the cellulose fibers during or immediately after completion of

digestion. Kappa number is the most frequently mentioned parameter here.

Effective or active alkali concentration measurement during digestion would be

effective here. The primary barrier here is the harshness of the environment,

i.e. high temperature, pressure, and a highly corrosive environment.

The second area is that of chemical recovery and power generation. The

primary needs here relate to combustion science; temperature measurements in the

combustion zone for recovery and utility boilers and for the lime kiln; fuel

property measurements; and measurements related to the process product, e.g.,

smelt bed parameter measurements in the recovery boiler and lime kiln

temperature profile.

37
APPENDIX I

The variety of opinions regarding the use of existing instruments and

the need for new sensors can be illustrated by reporting the response

given to a list of questions that were verbally answered by the personnel

in the mills that were surveyed. The questions and responses are

presented in the following summary. The numbers following each response

indicates the number of mills giving this answer.

Pulp and Paper Industry Field Survey

1. Feedstock

1.1 What is the raw material used in this facility?

Response: Wood chips (7), ground wood (1), short wood (1),

plywood waste (1)

1.2 Is the moisture content measured? If so, how and when?

Response: Occasional check, samples analyzed in lab (5), None

( 2 )

2. Chemical Pulp and Bleaching

2.1 Does this facility use batch digesters, continuous digesters or

both?

Response: Batch only (3), batch and continuous (3)

2.2 If this facility uses batch digesters, how is the flash steam

that is released during blowing used?

Response: Accumulated as hot water and used to wash pulp (5),

preheat boiler feed water (1)

2.3 What characteristics of the pulp, in addition to its kappa

number, are used to determine its readiness to leave the

digester?

38
Response: None (4), alkalinity test of white liquor (1), visual

examination of "pull" sample (1)

2.4 Is the active alkali measured? When and how?

Response: Manual titration (6)

2.5 How is the alkali-to-wood ratio determined?

Response: Off-line coulometric titration (4), by formula (2)

2.6 Are any of the following measurements made in this mill?

a. Nu number Response: No (6)

b. Permittivity Response: No (6)

c. Optical reflectance Response: Brightness of samples (4)

Prior to chlorination (2)

d. Gamma ray densitometer Response: Wood density (2)

Clarifier (1)

Green liquor (2)

Blow line on continuous

digester (2)

No (1)

Chip stock level (1)

Response: Laboratory only (3)

No (3)

Response: 3lack liquor (6)

e. Spectrophotometry

3 .

f. Refractometry

2.7 Is chlorination measured? If so, how?

Response: Oxidation reduction potential (ORP) (3),

optical measurement (3), extracted kappa number (1)

Chemical Recovery System

3.1 Which of the following measurements are made? How?

White liquor causticity Response: Laboratory titration (6)

39
Flue gas temperature

Stack emissions

Furnace temperature Response: Hand held optical (3)

None (3)

Response: Thermocouple (4)

None (2)

Response: 0 meters (4)

Unknown (2)

Black liquor dry solids Response: Ref ractometer s (6)

Off-line analysis (1)

Response: None (4)

Off-line (2)

Response: None (6)

Black liquor viscosity

Response: None (6)

Black liquor surface

tens ion

Smelt bed weight

Sodium bed light intensity Response: None (6)

Paper Making

4.1 How is consistency measured?

Response: Vane type instruments (3), strain gauges (2), shear

pipe (2)

Sensor Needs

5.1 What new kinds of sensors would be useful if they were available?

1. Better consistency measurement instruments

2. Humidity sensor in paper machine drying section

3. Portable and accurate non-intrusive flowmeters for liquids

4. Portable chip moisture sensor

5. Accurate and reliable air mass flow measurement instrument -

recovery boiler

6. Sensors to warn of imminent sodium explosion

-40-
7. On-line density sensors for green liquid

8. BTU sensor for black liquor

9. On-line viscosity meter for black liquor

10. System to optimize use of electric power

11. On-line active alkali sensor

12. Sensor to measure dew point at bottom of wet precipitator

In summary, this survey of six large pulp and paper mills belonging

to six different corporations reinforces previous studies that indicate a

need for better sensors in the paper industry. Some plants indicated that

their needs were urgent, while at the other end of the scale, one plant

production manager felt that his plant was "over-controlled" with the

exception of a few instruments. An almost universal opinion expressed

dissatisfaction with existing commercially available instruments.

41

References

[1] Sarkenen, K. V. and Ludwig, C. H. , Lignins - Occurrence, Formation,

Structure and Reactions , Wiley-Interscience, John Wiley & Sons,

New York, N.Y., ISBN 0-471-75422-6.

General References

1. Pulp and Paper - Chemistry and Chemical Technology , edited by J. P. Casey,

Vol. 1-3, John Wiley and Son, New York, N.Y., ISBN 0-471-03175-5.

2. Clark, J. d'A. , "Pulp Technology Treatment for Paper", p. 504, Miller

Freeman, San Francisco, 1978.

3. Steam/Its Generation and Use , Chapter 26, Babcock and Wilcox, Inc., 1978,

New York.

4. S. S. Fam, "Impact on Energy Conservation of Automatic Control Systems

Utilization in the U.S. Pulp and Paper Industry", Thermo-electron Report

#TE4265-20-80 (1979).

5. "Concise Notes for Students of Papermaking and Boardmaking," The Paper

Maker , July 1979 through January 1972.

. M U

NBS-114A (REV. 2-80

U.S. DEFT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date BIBLIOGRAPHIC DATA

REPORT NO.

FEBRUARY 1983 SHEET (See instructions) NBSIR 83-2640

4. TITLE AND SUBTITLE

Sensors for Efficient Energy Utilization in the Paper Industry

5. AUTHOR(S)

J. R. Whetstone , E. G. Johnsen

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/ Grant No. EA-77-A-01-6010

8. Type of Report & Period Covered

Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

Department of Energy

Washington, DC 20585

10. SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bi bl iography or literature survey, mention it here)

A survey of the on-line process measuremsmt needs of the paper industry has been

completed. The survey focused on pulp and paper mills with one corporate Instrumentation and Control group and one instrumentation and control systens manufacturer included. The results of the survey strongly indicate the need for

new measurement technology at the pulping end of the process. Important unit

processes identified are: (1) chemical recovery (recovery boiler and lime kiln

combustion measurements) ; (2) digestion (lignin concentration measurement in the

pulp or spent liquor) ; and (3) thernonechanical pulping (consistency measurement)

All of the processes are energy intensive and cannot be controlled either partially

or completely due to the lack of measurement of specific process parameter.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

Instrumentation; measurement technology; paper manufacturing; pulping; recovery

boiler.

13. AVAILABILITY 14. NO. OF

PRINTED PAGES

j y| Uni imited

| | For Official Distribution. Do Not Release to NTIS

|

j Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

Order From National Technical Information Service (NTIS), Springfield, VA. 22161

45

15. Price

$8 . 50

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