The descriptive approach is catching on as an effective audit method to uncover pollution preven- tion (P2) opportunities in manufacturing. Unlike the traditional prescriptive approach, which relies on generic checklists and questionnaires, descrip- tive analysis enables P2 audit teams to’develop a s fte-specfjlc characteriza- tion of a manufacturing process and associated sources of pollution. The result is P2 solutions that lead to meaningful reduc- tions in waste and im- provements in process eflcfency. This case study shows how the descriptive method was applied in a woolen mill.

Lyle Calfa, Jean Holbrook, Cheryl Keenan, and Tim Reilly

As MORE COMPANIES seek the economic and environmental benefits of pollution prevention, a new form of facility auditing known as the “descriptive approach” has emerged. Although traditional compliance audits (sometimes referred to as the “prescriptive approach”) can be used to assess pollution prevention opportunities, such audits often come up short. This is because the prescriptive approach relies on standardized questionnaires and checklists designed for generic use in a single industry. These usually do not lead to the detailed characterizations of a manufacturing process and associated sources of pollution that are needed to achieve meaningful reductions in waste and improvements in process efficiency at a specific site. By contrast, the descriptive approach is designed to make the process and associ- ated losses the central focus of the audit. [For a discussion of the differences in these approaches, see “Contrasting Approaches to Pollution Prevention Auditing,” PoZZution Prevention Reuiew, Sum- mer 1991, pages 225-235.1

The fundamental component of the descriptive approach is pro- cess flow analysis, which is integrated with activity-based costing, total quality management, and other P2 tools. These tools help the audit team identify options with the greatest potential to reduce manufacturingcosts and maximize protection of the environment and worker health and safety.

In 1993, the Northern Textile Association requested a study to examine the complete manufacturing process in a woolen mill for the purpose of identifying loss reduction and other P2 opportunities. A team from Tufts University was assembled to develop a pollution prevention guidance manual for woolen mills. The team used the descriptive approach to develop the guidance manual and to verify the manual’s effectiveness during a series of site audits at one of New

Lyle Calfa is a senior engineer with the Boston Edison Company in Boston, Massachusetts. Jean Holbrook is the compliance manager and assistant general manager with Total Waste Management Corporation in Newington, New Hampshire. Cheryl Keenan is an environmental research engineer with Abt Associates in Cambridge, Massachusetts, Tim Reilly is a section leader of t h e h o Pigmentsgroup with Hoechst Celanese in Coventry, Rho& Island.

Pollution Prevention Review /Spring 1994 I79

Lyle Calfa. Jean Holbrook, Cheryl Keenan, and Tim Reilly

Figure 1. Process Flow Diagram Overview

FIBER WOOL INPUT PREPARATION PRODUCTS

W DRY + --___ ---A WET 4--t DRY + PROCESSING I PROCESSING PROCESSING

England's largest woolen mills. Their experience, as discussed in this article, provides a detailed illustration of how the descriptive ap- proach can be applied.

Identifying Losses through Process Flow Analysis The team's first task was to determine where the losses were in

each step of the wool manufacturing processes and its ancillary activities (e.g., shippindreceiving, wastewater treatment, pollution control, and maintenance operations). Performing this analysis re- quired the construction of a process flow diagram (PFD). The PFD traces the series of steps that material inputs pass through as they are transformed into a final product. In any type of manufacturing operation, this transformation takes place in a functional sequence of events or actions, one event triggering the next until the function is complete and output is produced. The PFD is the clearest illustration of this functional sequence, which includes process inputs, outputs, or losses.' Each loss identified in the assessment represents an opportu- nity to prevent such loss.

In this study, a preliminary PFD was constructed by researching current wool industry periodicals and books on wool preparation. When this initial PFD was complete, the team visited several fabric production mills to verify the diagram. The PFD was then broken down into a more detailed map of the process steps.

The five basic processes in wool manufacturing are illustrated in the PFDs shown in Figures 1 and 2 and described below.

180 Pollution Prevention Review / Spring 1994

Case Study: The Descriptive Approach to Pollution Prevention in a Woolen Mill

Figure 2. Wool Process Flow Diagram

. . . . . . . . . . . . . . . . . . . . . . . I

_ _ _ _ _ _ _ _ _ _ - _ - _ _ - ' WOOL PREPARATION I I YARN FORMATION I

INCOMING WOOL

l , - I - - - - - - - - - _ _ - - - _ - - - \ ' . I I ' _ / ',-

- ' . ,. " I .-,' ' C ' ,, ", . , ,-p~!~b. '. DYEING DRYING 2 RINSING A I

B

I ,- - ; 1 I / I 1 . \ , , I , # , , - -

. . . . . . . . . . . . . . . . . . . . . I I

STEAM FINISHED WOOL PRODUCT -- NAPPING + DECATING- .A+ C

SIZING I I I

FINISHING I . . . . . . . . . . . . . . . . . . . . . .

Wool preparation The operation starts with the raw wool, which is processed into

wool fabric. Wool preparation can include scouring, stock dyeing, and blending operations, In most New England mills, scoured raw wool is delivered to the mill, and the first processing step is blending. Due to the wide variation in raw wool from lot to lot, blending is nec- essary to achieve a uniform product. During blending, the wool is also oiled. Oiling of the wool ensures proper lubrication for carding and spinning.

Yarn formation Yarn formation processes convert the bulk, raw wool to spools of

yarn. The first step in yarn formation is carding. Carding is a process that aligns the randomly placed fibers parallel to each other so they can be properly twisted into yarn in the spinning process. Spinning is performed after initial fiber preparation and consists of drawing out the fibers, twisting them into yarn, and then winding the newly made

181 Pollution Prevention Review I Spring 1994

Lyle Calfa, Jean Holbrook, Che yl Keenan, and Tim Reilly

yarn onto a bobbin. Yarn from several bobbins is then wound to a cone that holds a lengih of yarn suitable for the warping and weaving processes. At this point the yarn is ready for conversion to fabric.

Fabric formation In fabric formation, the yarn is woven into fabric. A warping

machine winds numerous separate strands of yarn onto a beam. These fibers will run in the lengthwise direction of the woven cloth. The yarn is then woven into griege, or unfinished fabric. The fabric then goes through a process called carbonizing. In this process the fabric is impregnated with sulfuric acid, dried, and baked to oxidize the vegetable matter impurities remaining in the wool. After carbon- izing, the wool may be washed and neutralized, or it may go into the fulling process, which tightens the flat weave into a dense three- dimensional fabric.

Finishing and dyeing The final process, finishing, varies with the fabric and use.

Finishing can include napping, polishing, steam sizing, and dyeing. Dyeing can be done at various stages in the process. If the raw wool or yarn was not dyed (stock dyeing or yarn dyeing), the fabric is dyed before entering the finishing process (piece dyeing). These processes are designed to impart qualities such as color fastness, feel, and protection from shrinkage.

As shown in Figure 1, all the steps in the process can be placed into two broad categories-dry and wetidepending on whether or not a liquid is involved. Usually the process is considered dry until final dyeing and finishing. An example of a PFD that breaks down the process steps, sources of wastes, and releases into even more detail is shown in Figure 3. PFDs at this level were prepared for each of the production steps discussed above.

To test the effectiveness of the guidance manual, the team tailored the PFDs for a specific facility. Initial modifications were made based on literature and plant records at the mill. This information was verified during several facility tours and brainstorming sessions with plant personnel. The PFD was broken down in the same detail as the manual for each of the major process steps (wool preparatiodyarn formation, fabric formation, and dyeinglfinishing). Inputs and losses for each step were identified. The information on losses, along with cost data from the various processes, was later helpful in prioritizing losses targeted for P2 solutions.

... it is essential that all costs associated with the implementation of the project be compared with the costs ofnotdofng the project.

Act ivi ty-Based Costing When considering the costs associated with any P2 project, it is

essential that all costs associated with the implementation of the project be compared with the costs of not doing the project. Tradi- tional accounting methods that rely on direct costs (labor, raw materials, capital equipment, and waste disposal) do not adequately

182 Pollution Prevention Review / Spring 1994

Case Study: The Descriptive Approach to Pollution Prevention in a Woolen Mill

1 !

I INCOMING WOOL

I

I i

Figure 3. Yarn Formation

energy - CLEANING --c wool

fibers water soluble tint t J + oil + emulsifier dirt f--

2 OILING - oil/

water

mechnical energy 1c

wool fibers

FEED f - 1 TOWER

I L energy

CARDING

energy fibers

energy COMBING

- *m I SLIVERING p- s I ive rs

energy slivers (worsted)

l!“

L energy slivers I

electrical SPINNING heat energy

e n e r g y J t 1 L-+ friction yarn

energy -4’ CONING 1~ energy

‘O MULTI-PLY -4 TWISTING energy

I I

1 * energy

- t m t - - l!“

SPUN YARN KEY: Print in outline type is fim&hy.

estimate the actual costs and savings of projects, because they leave out the indirect costs that are usually associated with P2.

An alternative accounting method, activity-based costing (ABC), is designed to assign these indirect costs to specific activities. With ABC, each indirect cost is analyzed and allocated to the appropriate process. In a P2 project, a company can apply the principles of ABC to

I I

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Lyle Cava, Jean Holbrook, Cheryl Keenan. and Tim Reflly

assess the actual cost of losses associated with each step of the manufacturingprocess. Thus, ABC can be used as a management tool to reduce overall waste and identify the sources of waste that repre- sent the largest portion of production costs.

To assess these costs in the woolen mill, the team interviewed individuals in the facility involved with the purchasing, materials control, quality assurance, production and maintenance activities, and health and safety functions. But precise cost data for each functional area were not immediately available. Therefore, the team used qualitative cost rankings (i.e., “low,” “medium,” and “high”). Ratings were based on the estimated data available from plant records and personnel. These qualitative rankings served as a rough guide to identify areas of primary interest for further study.

... A3C can be used as a management tool to reduce overall waste ... -

Prioritizing Losses Brainstorming was used to better understand the sources of losses

from all the processes, and a relative ranking system was used to narrow the field of P2 possibilities to the highest priority areas.

Relative rankings In this study, the team used information from discussions with

plant personnel, literature, and their best engineering judgment to select criteria for ranking the losses. (Criteria may change depending on the type of process and conditions.) First, losses were examined for each unit process step. These were (1) energy loss, (2) fiber loss, (3) chemical loss, and (4) water loss. Relative rankings of losses for each stage in the manufacturing process were ranked with either a “+,” “zero” or “-” against the following criteria:

0 Environmental impacts 0 Regulatory issues

Health and safety impacts Cost of waste treatment and disposal Cost of material lost to the process

In this context, the “+” indicated that the elimination of the loss would have a major impact. A “-”meant a minor impact. A“O” signified a neutral or undetermined impact. Figure 4 illustrates how the relative ranking system was applied to the carbonizing and stock dyeing processes. For example, chemical losses in the stock dyeing process were given a “+” ranking for wastewater treatment and disposal because of the high cost of treating the residual dyestuffs. If the chemical losses from this process were reduced, the financial burden associated with wastewater treatment would also be reduced. In the carbonizing process, energy losses were given a “+” ranking based on the high level of material loss from this process. Because the effects on personnel health and safety of heat escaping from the carbonizing unit were considered insignificant, a “0” rating was

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Case Study: The Descrlptlve Approach to Pollution Prevention in a Woolen MfZZ

Chemical Loss

Energy Loss

(rejecthework) Fabric Loss

Figure 4. Relative Rankings

T

Vapors from the acid bath and smoke + + + + 0 4

Heat escaping from the Carbonizing unit. - - 0 - + -2

on fabric. - - - o + - 2

from the carbonizer are released to the environment and inhaled by workers. ~-____l_. L

Oil builds up inside carbonizer and drips

a

Process/ Associated Loss

Chemical Loss

Energy Loss

Water Loss

Fiber Loss (flock)

Source of LQSS E R HS W$ M$ SUM

Dyestuff additions are inconsistent. + + o + o 3

Heat from spent bath is not recovered. 0 - - - Kettles are flushed until water runs clear. 0 - + Flock left in kettle after dyeing. - - + 0 -2

+ -2

-2 - No measurement or control.

- _ _ ~ _ _ _ ~ _

KEY

Environmental (E) Regulatory (R) Health and Safety (HS)

Cost of Waste TreatmenVOisposal (W$) Cost of the Lost Material (M$)

assigned to health and safety concerns associated with energy loss from carbonizing.

After the team ranked each loss according to the five criteria, an overall score was calculated. The highest scores were attributed to four areas: (1) chemical loss in carbonizing, (2) chemical loss in stock dyeing, (3) chemical loss in piece dyeing, and (4) chemical loss from storage. Although all the areas were closely ranked, chemical loss from carbonizing presented the most promising P2 opportunity. This process was selected over the others, because it had losses to several media, including air, water, and solid waste. Also, the carbonizing process has been a source of continuing concern at the mill, because losses of sulfuric acid in the eMuent and atmospheric problems in the plant pose serious risks to worker health and safety. I

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MANPOWER \

Figure 5. Cause and Effect Diagram: Vapors from Bath

\

MATERIALS More Tlme To Get Wet \ \

h Dry Fabric

Hydrometer Use

Sullfuric Acid On Floor

Wool Contaminants

Grease Wool Lubricating Oil (Fibers)

New Employees

Employees New To Task

* VAPORS

Large Surface Area Conductance Readings

Exhaust Rollers

Sulfuric Acid Addition

SOP? Filling New Tank Full

Materials of Constuction Frequency of Bath Dump

Overflow To Drain PMllnspection /MACHINEAYJ

Case Study: The Descriptive Approach to Pollution Prevention in a Woolen Mill

Focus on primary loss Next, the team studied the carbonizing process in more detail.

From current studies and interviews with academic personnel knowl- edgeable in this area, the team gained a better understanding of the theoretical process operation. In particular, they learned that proper controI of the process parameters was extremely important. For example, acid concentration, exposure time, and temperature must be carefully controlled to assure that acid that contacts the wool is chemically absorbed or bound to the wool. If these parameters are not properly controlled, the fabric can be damaged. Bath strength, immer- sion time, drying temperature, bakingtemperature, and the moisture content of the cloth prior to baking were also discovered to be critical process parameters.

Armed with this information, the team returned to the plant floor to observe the process again. This time they identified three potential loss factors from the carbonizing process: (1) vapors from the acid bath, (2) smoke or haze escaping from the carbonizing oven, and (3) sulfuric acid loss to the eflluent. Atmospheric problems and odor in the carbonizing area were readily apparent from the tour. Operators complained of respiratory and eye discomfort. Additionally, sulfuric acid emissions from the system are reportable under the Toxic Release Inventory (TRI), and stack opacity values are a source of concern to the state regulatory agency. Sulfuric acid losses in the area appeared at that time to be mainly due to the large quantity of spent acid dumped from the bath to the wastewater pretreatment system. (The bath was then cleaned out and refilled with fresh acid and water.) When the facility disposed of the acid, it also needed many additional operations to maintain the required pH.

In addition to their observations from the floor, the team conducted a brainstorming session with plant personnel involved with the carbon- izing process and a maintenance engineer experienced with the carbonizer’s past problems. Subsequent interviews with individual equipment operators validated ideas generated in this session.

Selecting and Implementing Solutions The team used these ideas and information collected on losses to

construct a cause-and-effect (Ishikawa or “fishbone”) diagram to determine the causes of each of the three major loss factors from carbonizing. Figure 6, a fishbone diagram of vapors from the acid bath, is one example. As shown, the causal groups of manpower, machinery, methods, and materials were used to construct the dia- grams. Specific causes in each group are listed along the ribs of the diagram. For example, under materials, spills, and accidents, sulfuric acid concentration and bath contaminants are listed as possible causes of vapors from the acid bath.

The team used the multi-voting technique to select the most likely cause(s) for each of the problems. Multi-voting is a simple technique

The team used the multi- ‘Oting technique to the most likely cause(s) for each of the problems.

used to prioritize multiple ideas generated through brainstorming.

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Lyle Calfa, Jean Holbrook, Cheryl Keenan, and Tim Reilly

Extending the bath IiJe could reduce acid use and potentially reduce the volume of wastewater generated and treated.

Ideas were included in this list if at least half the team agreed that the idea had merit. The team members brainstormed again to generate solutions for each problem. The solutions were then evaluated based on their potential to achieve the following:

Reduce the identified losses in the carbonizing area Increase operating eficiency of the process Reduce labor in rework of soiled fabric Eliminate or reduce stack emissions problems

Potential solutions for reducing sulfuric acid vapors entering the atmosphere from the tank are discussed below.

Monitor bath parameters Bath temperature, room temperature, humidity, acid concentration,

sludge buildup, and impurities in the bath may contribute to the atmo- spheric problem. Establishing connections between these parameters and a subjective evaluation of discomfort and a record of employee com- plaints may yield potential control strategies. Initially, it is suggested that parameters and atmospheric conditions should be monitored at the beginning, middle, and end of each shift, with data reviewed weekly.

Determine optimal frequency of tank dump The sulfuric acid tank is dumped when it is qualitatively deter-

mined that the bath is spent. Analyzing the carbonizing process to determine the optimum time to dump the sulfuric tank can lower costs by increasing the life of the bath. Extending the bath life could reduce acid use and potentially reduce the volume of wastewater generated and treated.

Clean sludge fiom tank each time it is dumped Sludge buildup in the bath may contribute to excess acid use and

the vapor problem. The impurities in the sludge can also contribute to increased vapors.

Pre-wet the fabric The fabric is passed in and out of an acid bath by a roller system.

This method of soaking the fabric may contribute significantly to the atmospheric problems in the area, because the acid bath is open to the atmosphere, and acid is continually transferred to the air as it is soaked into the fabric. Pre-wetting the fabric allows the acid to penetrate more quickly, reducing the soaking time required. Pre-wet fabric could require fewer passes through the bath, and thus reduce contact time between the acid-soaked fabric and the air.

Pre-scour the fabric Pre-scouring removes the oils from the fabric, but also leaves the

fabric wet. This method would have the same advantages as pre-wetting.

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Case Study: The Descriptive Approach to Pollution Prevention in a Woolen Mill

Enlarge the mid bath Reduced contact time between the acid-soaked fabric and the air

could be accommodated if the acid bath were enlarged to allow the acidfabriccontact to take place in the bath rather than in the air space above the bath.

Lower the upper roller height in the acid bath Contact between the acid-soaked fabric and the air may be a source

of acid transfer to the air. Lowering the rollers so that the fabric spends minimal time in the air may improve the acid vapor problem. This alternative is enhanced if coupled with either pre-wetting the fabric or increasing the bath size to allow for longer acidfabric contact time.

Enclose the carbonizing tank Transfer of acid to the atmosphere may be prevented by construct-

ing an airtight enclosure around the entire acid tankholler assembly. Entry and exit doors for fabric would require appropriate seals.

Solutions to losses in the carbonizing area were also prioritized according to whether they were considered short- or long-term alter- natives. Short-term alternatives that could be quickly and easily implemented, and required minimal capital expenditure, were prima- rily related to maintenance and training (e.g., monitoring bath pa- rameters). Longer-term solutions involving process changes, materi- als substitution, or equipment modifications included pre-wetting fabric and lowering rollers over the bath. Because personnel time and capital were very limited at the facility, it was recommended that short-term solutions be implemented first. These changes could potentially result in significant loss reduction, so that the longer-term alternatives would not be necessary.

Conclusion The descriptive approach illustrated in this case study can be used

to develop a P2 project at any manufacturing facility. Key characteristics of the descriptive approach that distinguish it from the prescriptive alternative include the various levels and types of analysis that must be conducted to create a detailed picture of the process. It is also flexible; the methodology can be used for any process and modified from a general process level to perform a Sik-Specific analysis. h a result, the teanl WaS

... the descriptiue approach ... can be used

for any process and modified from a aeneral

I O I

process leuel to perform a site-speclflc analysis.

able to zero in on opportunities that were relatively easy to implement, cost-effective, and had the greatest potential to enhance planuequip- ment efficiency, improve working conditions, and reduce pollution.

Notes 1. Pojasek, Robert B., and Cali, Lawrence J. “Contrasting Approaches to Pollution Prevention Auditing,” Pollution Prevention Review, Summer 1991, p. 230.

2. Pailthrope, Michael T. “Developments in Wool Carbonizing,” Review of Progress in Coloration, Vol. 21, The Society of Dyers and Colorists, 1991, p. 11.

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