L3 Waste Minimisation

8/2/2019 L3 Waste Minimisation

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WASTE &WASTE MINIMISATION

Liquid/solid and gaseous waste materials are generated during the manufacture of anyproduct.

Once this waste has been created it cannot be destroyed, although it can beconcentrated and its chemical or physical form can be changed. Apart from creating potentialenvironmental problems, wastes not only represent losses from the production process, butalso require significant investment in pollution control practices. Most effluent treatmentsystems do not actually eliminate the waste but transfer it from one place to another.For example:

Aqueous solutions of heavy metals can be treated by chemical precipitation. If thetreatment system is designed and operated correctly, the aqueous stream can then be passedon for further treatment or discharge to the receiving water. But the precipitated metallicsludge must be disposed of, usually by land fill site. Also, biological treatment is not free

from this problem. It may well dispose of the organic waste, but it leads to a disposal problemof the resulting biological sludge.

The best solution for a waste problem is avoiding the production of waste in the firstplace, i.e. waste minimisation.

Waste minimisation means the reduction, to the extent feasible, of hazardous wastethat is generated prior to treatment, storage or disposal of the waste. The terms wasteminimisation and pollution prevention are becoming key initiatives of the USEnvironmental Protection Agency and the terms are increasingly being used in all areas ofcurrent applied research and development. Figure 1 illustrates the benefits of waste

minimisation.

Waste minimisation brings the dual benefits of lower effluent treatment costs andlower raw materials costs.

In its widest context, waste can be interpreted as almost any loss or discharge of anymaterial to any medium, and with particular emphasis on specified ranges of substances forthe three environmental media - air, water and soil.

Once we have created waste we cannot destroy it. We can concentrate the waste ordilute it, change its physical form, change its chemical form, but we cannot destroy it.

Clearly, the best solution is one where we avoidthe production of waste and effluent, i.e.waste minimisation.

Waste minimisation not only brings the benefit of reduced effluent treatment cost, butthere is often a further benefit in reduced raw materials costs (Figure 1).

Before we set about minimising waste it is important to understand what and wherewaste originates.

Lets start by defining waste.Waste includes streams or materials that are:

vented to the air discharged to water


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sent to landfill

sent to incinerator

sent to a flame

sent to a biological treatment facility

Waste reduction can be accomplished by creating less waste initially or by recyclingwaste products back to the process. It is also possible to reduce emissions by operating wastetreatments units more efficiently (Figure 2).

Waste can be hazardous or non-hazardous, toxic, non-toxic, flammable or non-flammable, etc.


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INTEGRATED POLLUTION CONTROL AND WASTE MINIMISATION

Over the last two decades, attitudes to the environment have changed dramatically. The

public no longer accepts that pollution is inevitable. Instead, the public is aware that theenvironment should be improved and believes that the polluter should pay. These changes inattitude are very significant for industry.

The response of government has been to introduce new legislation and economicinstruments, and to establish regulatory authorities with increased powers to enforcecompliance.

Industry is affected directly by increased regulation and more subtly by the change inpublic attitude to the environment. In order to respond positively to this new climate,companies need to reappraise their activities and to explore the possible introduction of waste

minimisation, clean technology and energy saving schemes. In this way pollution can beavoided.

Regulatory pressureOver the past decade the UK parliament has passed many Acts, Orders and regulations

to protect the environment. Much of this activity was prompted by legislation from theEuropean Union, which the UK government was then required to incorporate in similardomestic legislation. The UK government pioneered the concept of Integrated PollutionControl (IPC) and implemented it with the Environmental Protection Act (1990) (EPA). Thistype of system is likely to be adopted throughout the rest of Europe.

The current legislation has very important consequences for industry. It follows thatmanagers with environmental responsibilities should be conversant with those parts of the lawthat are most relevant to their companies and familiar with the duties of the bodies thatregulate their industry.

In the integrated pollution control the Royal Commission on Environmental Pollutionrecommended that releases of pollutants from industrial processes should no longer be subjectto different control regimes for different media (air, water, land). They introduced the conceptof Best Practicable Environmental Option (BPEO) which is a systematic procedure forestablishing which option, at acceptable cost, is the most beneficial or the least damaging tothe environment as a whole (in the long term as well as the short term).

In addition to introducing the principle of holistic environmental protection and theassociated concept of BPEO, the IPC also introduced the fundamental principle of PollutionPrevention rather than Cure and the right of the public to have access to information about

pollution from prescribed processes. These principles are in common with the principlesbehind WASTE MINIMISATION,

How are these IPC principles to be put into practice?Part I of EPA 90 sets out a series of objectives which must be met in the operation of

prescribed processes. (Prescribed processes are those industrial processes defined inRegulations as having the potential to cause serious pollution and therefore are to be subject

to IPC.)


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1. The first objective is to use the best available techniques not entailing excessive cost(BATNEEC) for prevention releases, or where that is not practicable, for minimisingand rendering the releases harmless.

2. The second objective aligns with IPC principle of protection of the whole

environment, i.e. ensure that BATNEEC is used to minimise the pollution which maybe caused to the environment as a whole - the Best Practicable Environmental Option(BPEO).

To meet these objectives, a shift of emphasis from Best Practicable Means (which waslargely based on end-of-pipe technology) to the notion of using low-waste productiontechnologies for the whole process, was starting to take place.

BATNEEC So what does BATNEEC mean?I would expect that most of you are, by now, familiar with this acronym - even if not

feeling entirely confident about its precise meaning.

Starting with the BAT part:Best refers purely to the effect of the technique on the environment, i.e. it is that

technique (or those techniques, for there may be more than one set of techniques withcomparable effectiveness) that is most effective in preventing, minimising or renderingharmless pollution releases.

Available means procurable by the operator in question. This doesnt imply that thetechnique has to be in general use in the UK or overseas, but it does recognise that noveltechnologies proven only at pilot plant scale require a degree of business confidence beforethey can be said to be available.

Techniques is defined in the Act. It embraces not only the plant and equipment inthe process, but also the way it is operated, the manning and supervision levels, the trainingand qualifications of the staff, etc.

So how does HMIP come to a view on what constitutes BAT?EPA90 lays a specific duty on the chief inspector to follow developments in

technology and techniques for preventing or reducing pollution of the environment due to thereleases of substances from the prescribed processes. To this end, HMIP commissionsresearch into available techniques either for specific production process or for wider industrialsectors.

The research is published by Guidance notes which merely represent a selection ofpossible alternatives which were available at the time of publication. If techniques have comealong since, or alternatives appear better in relation to a particular process then, of course, it isfor the applicant to put them forward and demonstrate why they are the best availabletechnique.

So far I have spoken only about BAT. The NEEC or Not Entailing Excessive Costpart requires consideration of the cost of applying the Best Available Techniques in relationboth to the nature of the industry concerned and to the degree of the environmental damage,and thus the cost of BAT that can be required before costs are considered excessive.

How does HMIP come to a view on what constitutes BATNEEC?


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For new processes, BATNEEC will often be synonymous with the best availabletechnique, but for existing processes it is usually more complicated. There is an inherentexpectation that all plant will, in time, be brought up to new plant standards (or ultimatelyclose down), so in addition to assessing the cost implications, the HMIP will establish time-scales for upgrading. The progress will vary between plants depending upon:

(1) the impact of their activities upon the environment;(2) the plants technical characteristics;(3) its rate of utilisation and length of its remaining life;(4) the nature and volume of pollution emissions from it;(5) the desirability of not entailing excessive cost for the plant concerned, having regard in

particular to the economic circumstances of the industrial sector concerned.

To summariseIntegrated Pollution Control applies to the most potentially polluting or

technologically complex industrial processes throughout England and Wales. The enforcing

authority is HMIP.

IPC is concerned with the control of releases to all three environmental media - air,water, and land. The main objectives of IPC are:

(a) to prevent or minimise the release of prescribed substances and to render harmless anysuch substances which are released;

(b) to develop an approach to pollution control that considers releases from industrialprocesses to all media in the context of the effect on the environment as a whole(BATNEEC);

(c) to minimise the pollution which may be caused to the environment taken as a whole

by the releases, having regarded the best practicable environmental options available(BPEO).

Note There are three separate lists of prescribed substances, according to whether thesubstance is to be controlled in relation to air, water or land releases.


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Waste Minimisation and IPC

What is waste?

In its widest waste minimisation context, waste can be interpreted as almost any lossor discharge of any material to any medium. Under IPC, strictly it is only releases ofsubstances prescribed in the Regulations which must be prevented or minimised; otherreleases need only be rendered harmless.

Section 75 of the Environmental Protection Act 1990 formally defines waste as:

(a) any substance which constitutes a scrap material or an effluent, or other unwantedsurplus substance arising from the application of a process, and;

(b) any substance or article which requires to be disposed of as being broken, worn out,contaminated or otherwise spoiled.

It is important to note at this stage that all emissions of materials into air, water andland, as well as energy consumption, should be considered in waste minimisation

programmes.

The concept of Waste Minimisation, like IPC, is based on the premise thatPrevention is better than cure.

Waste minimisation involves any technique, process or activity which either avoids,eliminates or reduces waste at its source, usually within the confines of the production unit.Synonymous terms include:

(a) waste minimisation;(b) waste reduction;(c) clean technologies/clean engineering/clean processing;(d) pollution prevention/reduction;(e) environmental technologies;(f) low and non-waste technologies.

The main implications of these techniques are:(i) the avoidance of reliance of end-of-pipe treatment of waste streams;(ii) the adoption of clean, low-waste technologies;

(iii) and (where some waste production is unavoidable) recycling, reclamation or use asfuel.

Whats involved in waste minimisation in practice?Generally, waste minimisation isNOTabout reducing waste after it has been

generated, so the following techniques usually have no place in a waste minimisationprogramme.

- Incineration- Chemical transformation to less harmful waste- Biological treatment- Transfer from one environmental medium to another where it might be less

harmful- Dilution or dispersion


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These techniques are end-of-pipe abatement options which in a waste minimisationprogramme are only considered as a measure of last resort to further treat releases that havealready been minimised.

So, what is waste minimisation about?It is about methodically assessing the process in question, using EPA methodology,

with the aim of advancing each waste - or release - producing part up the order of priorityfrom 7 to 1 in the following list of waste production practices.

1. Elimination of waste production2. Reduced production of waste at source3. Recycling within the process4. Reclamation for recycling or other use5. Use of the waste for energy production6. Treatment to form less harmful waste7. Disposal

* (Overheads)Hierarchy of Waste Management Practice, adopted by the UK Government. As a general

rule, the further upstream you tackle your waste problem, the more benefits you will obtain.


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The Benefits of Improved Pollution Control

Improved pollution control can reduce the impact on the environment, which is of benefit toeveryone. The direct benefits to companies through integrated measures to improve pollutioncontrol (i.e. waste minimisation) can include:

(i) reduced costs;(ii) improved company image;(iii) more effective compliance with the law.

(i) Reduced costsDischarge to the environment can cost companies money in a number of ways.(a) Disposal costs

These direct costs include:

for solid waste - landfill charges, skip costs and transport costs;

for aqueous waste - trade effluent charges, pumping costs, make-up water

replacement and treatment costs.

These costs are the most likely to be noticed, particularly as they will probablyincrease in the near future and thus are the most likely to prompt companies to considerimproved pollution control.

(b) Wasted resourcesMaterial discharges into effluents and emissions, by definition, have been

incorporated into the product or consumed usefully in the manufacturing process. These costsare the main hidden costs of pollution. They include:

wasted raw materials;

wasted product;

all of the production costs associated with wasted products.

(c) Operating costs of pollution control equipmentThese direct costs could include:

electricity for motors, fans, pumps;

fuel for heaters or burners;

labour to operate and maintain equipment;

consumables such as chemical additives;

depreciation of capital equipment;

disposal charges for any waste arising from the treatment process.

(d) Non-compliance with legislationThese associated costs include:

fines and legal fees;

paying for remedial work following pollution incident;

staff time;

increased insurance premiums.

(e) Lost businessThese associated hidden costs could include:

lost revenue from wasted product;

loss of potential extra sales to customers that refuse to trade with a companywith a poor environmental performance.


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(ii) Improved company imagePublic interest in companies environmental performance has greatly increased in

recent years. Poor environmental performance can affect the company by:

reducing sales opportunities;

reducing the stock market value of the company;

increasing advertising and marketing costs to recover from poor public

perception;

increasing the cost of public relations activities.

(iii) Complying with current and future legislationEnvironmental legislation is by far the main reason why companies modify their

pollution control systems. Companies that do not comply with legislative requirements can beprosecuted.

All businesses are covered by environmental legislation to some extent, e.g. the Duty

to Care provisions of the Environmental Protection Act 1990. Prescribed processes with themost potential for pollution are covered by Integrated Pollution Control (IPC), while less

polluting prescribed processes are covered by Local Air Pollution Control.

The table summarises the main environmental legislation affecting businesses inEngland and Wales.

When taking a strategic view of waste minimisation and pollution control, we need toconsider possible future legal requirements and ensure that any measures we adopt now areconsistent with foreseeable changes.


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Process and utility wasteBefore we set about minimising waste, it is important to understand where the waste

originates. There is a clear hierarchy intrinsic to chemical processes which is illustrated bythe onion diagram.

We start with the reactor in the core of the onion. Whatever design is chosen for thereactor dictates the separation problems and process recycles. Once these two layers are fixedwe know the material and energy balance and these allow us to design the heat recoverysystem (the third layer in the figure).

After exhausting the economic possibilities for heat recovery we add utilities(furnaces, boilers, refrigeration systems, and so on), which make up the outer layer of theonion.

So from the onion diagram we can identify two basic classes of waste

Process waste + Utility waste

Process waste represents a loss of raw materials, intermediates, by products, mainproducts and purge streams.

The outer layer of the diagram is the source of utility waste. This could be flue gasemissions, ash from fuel, waste from boiler feed water treatment and boiler blowdown.

(1) Sources of process waste:There are three basic sources of process waste: reactors, separators and recycle

systems and process operations.

(a) Reactors produce waste in a number of ways (even under normal operatingconditions):(i) if it is not possible to recycle unreacted feed material to the reactor inlet, then low

conversion will lead to waste of that untreated feed;(ii) waste is produced through the formation of waste by-products, either from the primary

reaction or through secondary reactions;(iii) waste is produced in the reactor when feed impurities undergo reaction and when

catalyst is degraded or lost and requires recycling.

(b) Separation and recycle systems produce waste through the imperfect recovery andrecycling of valuable materials from waste streams.

The third source of process waste we can classify under the general category of(c) Process operations such as start up and shut down of continuous processes, product

changeover, equipment cleaning for maintenance, and tank filling all produce waste.(2) Sources of utility waste

The principal sources of utility waste are associated with hot utilities (includingcogeneration systems) and cold utilities.

Furnaces, steam boilers, gas turbines and diesel engines all produce waste as gaseouscombustion products. These contribute in various ways to the greenhouse effects and acidrain, and they are also a direct health hazard if they form smog.

As well as gaseous waste, steam generation produces aqueous waste from boiler feed

water treatment and boiler blowdown. The recirculating cooling water systems used on mostchemical processes also create aqueous waste through cooling tower blowdown.


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Clearly, the waste streams created by utility systems tend, on the whole, to be lessenvironmentally harmful than process waste. However, given problems such as thegreenhouse effects and acid rain we, as chemical engineers, cannot afford to be complacent.

Also, there is non direct waste, or what we call the seven elements of waste.The seven elements of waste are:

1) over-production - making too many, just in case;2) waiting - time is an important element of competitiveness;3) transporting - reorganise production to minimise material handling;4) inappropriate processing - using a hammer to crack a nut;5) unnecessary inventory - cover up quality problems;6) unnecessary motions - ergonomics;7) defects - a challenge to improve.


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WASTE MINIMISATION TECHNIQUES AND TECHNOLOGIES

Waste minimisation techniques can be applied to any manufacturing process andrange from easy operational charges to state-of-the-art recovery equipment. The common

factor in the technique is that they reduce operational costs.

Waste minimisation techniques can be divided into four general classifications:1. Good practice2. production/ process modification;3. volume reduction;4. recovery.

Because the classifications are broad, there will be some overlap. In practice, wasteminimisation techniques are generally used in combination so as to achieve maximum effectat the lowest cost.

The selection of a specific minimisation technique by the individual business must bebased on accurate and current information on waste stream generation and waste managementcosts. This is accomplished by developing and implementing a waste minimisation

programme as a key part of a comprehensive waste management plan. Components of theprogramme should include procedures for collecting information, evaluation of options andidentifying cost effective waste minimisation techniques. Once identified, the techniques can

be implemented and become an established part of the management and operation of thebusiness.

1. Good practice1.1 Good design

This section was discussed in class.1.2 Good house keeping1.2.1 Inventory Management

Proper control of raw materials, intermediate products, final products and associatedwaste streams in the manufacturing process is an important way to reduce waste generation.In many cases, waste is just out-of-date, off-specification, contaminated or unnecessary rawmaterials, spill residues or damaged final products.

There are two basic aspects to inventory management;

(a) inventory control - controlling the type and quantities of materials in the plantinventory, including techniques to reduce inventory size and chemical use while

increasing inventory turn-over;

(b) material control - controlling the handling of raw materials, along with the finishedproducts and waste streams in production facility, including methods to reduce rawmaterials and finished product loss and damage due to handling, production andstorage.

1.2.2 Inventory controlInventory control is a waste minimisation technique that is applicable to all types of

industry, regardless of their size. The great advantage of this approach is that it is not

expensive or difficult to implement.


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Purchasing only the amount of raw materials required for a production run or a setperiod of time is one of the keys to proper inventory control. This requires the establishmentof a strict inventory tracking system. In many instances, excess or out-of-date material issimply disposed of as waste. The disposal cost will greatly exceed the original purchase cost.Thus, purchase procedures must be implemented which ensure that materials are ordered only

on an as-needed basis and that only the amount needed for a specific period of time isordered.

Another approach to inventory control is to purchase the material in the properamount and the proper size of container.

If large quantities of a material are used, then purchasing it in bulk will produce lesswaste, both in product loss and empty packaging, than if it were purchased in drums or bags.On the other hand, small containers may be better than bulk purchases if the material itselfhas a short shelf life or is not used in large quantities.

The ultimate in inventory control procedures is just-in-time (JIT) manufacturing, sincethis system eliminates the existence of any inventory by directly moving raw materials fromthe receiving areas to the manufacturing area for immediate use. The final product is thentransported out without any intermediate storage. JIT manufacturing is a complex programmeto implement and cannot be used by all facilities; however, when applicable, it can minimisewaste significantly.

Developing review procedures for all material purchased is another step inestablishing an inventory control programme. Procedures should require that all materials beapproved prior to purchase. In the approval process all production materials should beevaluated to determine if they contain hazardous constituents and if so, what alternative non-

hazardous substitute materials are available. Also, brief evaluation procedures should beestablished for all incoming raw materials to avoid the acceptance of incorrect, off-specification or defective materials.

Material ControlMaterial control procedures include storage of raw materials, product and process

waste and the transfer of these items within the process and around the facility. Propermaterial control procedures will ensure that raw materials will reach the production processwithout loss through spills, leaks or contamination. It will also ensure that the material isefficiently handled and used in the production process and does not become waste. Examples

of potential sources of material loss are shown in Table 1.1.

Area SourceLoading Leaking fill hose or fill line connections

Draining of fill lines between fillingPunctured, leaking or rusting containersLeaking valves, piping and pumps

Storage Overfilling of tanksImproper or malfunctioning overflow alarms

Punctured, leaking or rusted containersLeaking transfer pumps, valves and pipes


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Improper material transfer proceduresLack of regular inspectionLack of training programme

Process Leaking process tanks

Improperly operated and maintained process equipmentLeaking valves, pipes and pumpsOverflow of process tanks; improper overflow controlsLeaks and spills during material transferInadequate checkingOpen drainsEquipment and tank cleaningOff-specification raw materialsOff-specification products

Table 1.1 Potential Sources of Process Material Loss

Material loss can be greatly reduced through improved process operation, increasedmaintenance and additional employee training. Many sources of material loss, such as leaksand spills, can be easily identified and corrected.

2. Production Process ModificationImproving the efficiency of a production process can significantly reduce waste

generation. Use of this approach helps reduce waste at the source of generation. Thepotential waste minimisation techniques can be divided into three general categories:improved operations and maintenance procedures, material change and process equipment

modification.

2.1 Operational and maintenance procedureImprovements in the way a production process is operated and maintained can result

in significant waste reduction. A wide range of methods are available to operate a productionprocess at peak efficiency. But firstly, a thorough knowledge of the production process isessential.

(a) Operational procedures: Improved operation procedures are quite simply methodswhich make optimum use of the raw materials used in the production processes.

Some examples are:

reduce raw materials and product loss due to leaks, spills and off specificationprocess material;

schedule production to reduce equipment cleaning;

consolidate types of equipment or chemical to reduce quantity and variety of

waste;

improve cleaning procedures to reduce generation of dilute mixed waste;

segregate wastes to increase recoverability;

optimise operational parameters (temperature, pressure, reaction time,

concentration and chemicals) to reduce by-products or waste generation;

develop employee training procedures on waste reduction;

evaluate the need for each operational step and eliminate steps that are not

necessary; collect spilled or leaked material for re-use.


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Once proper operating procedures are established they must be fully documented andmade part of the employee training programme. A comprehensive training programme is akey element of any effective waste minimisation programme.

(b) Maintenance programme: A maintenance programme which stresses corrective andpreventive maintenance can reduce waste generation caused by equipment failure. To beeffective, a maintenance programme should be developed followed for each operational stepin the production process, with special attention to potential problem points. A strict scheduleand accurate records on all maintenance activities should be maintained. The type ofinformation which should be collected and updated regularly in order to establish a preventivemaintenance is:

a list of plant equipment and location;

operating time for each item or area;

which items are critical to the process(es);

problem equipment; previous maintenance history;

vendor maintenance manuals;

a database of equipment repair histories.

Maintenance procedures themselves produce waste, such as process materials, rags,scrap parts, oils and clean-up residue. These wastes can be reduced by using standard wasteminimisation techniques such as revised operational procedures, equipment modification,source regeneration and recovery.

2.2 Material change

Hazardous material used in either a product formation or in a production process maybe replaced with a less hazardous or non-hazardous material. Reformulating a product tocontain less hazardous material will reduce the amount of hazardous waste generated during

both the products formulation and its end use. Using a less hazardous material in aproduction process will generally reduce the amount of hazardous waste produced.

Product reformulation is one of the most difficult waste minimisation techniques, yet itcan be very effective. As more manufacturers implement inventory management

programmes, pressure will increase on chemical supply companies to produce products withlower quantities of hazardous materials.

Hazardous materials used in the production process can also be replaced with lesshazardous or non-hazardous materials. This is a very widely used waste minimisationtechnique where changes can range from using purer raw materials to replacing solvents withwater-based products.

One important area which is sometimes overlooked in making material change is itsimpact on the total water stream. Switching from solvent-based to water-based products canincrease wastewater volumes and concentrations, which could adversely affect the currentwastewater treatment systems, course effluent limits to be exceeded and possibly increasewastewater treatment sludge production. Thus, before any change is made, its impact on allemissions must be evaluated.


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Minimising or eliminating hazardous materials from the production process candecrease not only hazardous waste generation, but also the quantity of hazardous materials inair emissions and wastewater effluents.

2.3 Process equipment modification

Waste generation may be reduced by installing more efficient process equipment ormodifying existing equipment to take advantage of better production techniques. New andupdated equipment can use process materials more efficiently, producing less waste.Additionally, higher efficiency systems may reduce the number of rejects or off-specification

products, thereby reducing the amount of material which has to be treated. The use of moreefficient equipment or processes can pay for itself through higher productivity, reduced rawmaterial costs and reduced waste management costs.

Modifying existing process equipment can be a very cost-effective method ofminimising waste generation. In many cases, the modification can be relatively simple withinexpensive changes in the way the materials are handled within the process to ensure that

they are not wasted. Modifying production equipment to improve operational efficiencyrequires a thorough understanding of both the production process and waste streamgeneration.

In many cases it is best to phase in the required process modifications over a period oftime to reduce any potential effects on the whole production process and to evaluate itsimpact on the waste stream. Some examples of modifications to existing process equipmentwhich can minimise waste generation are shown in Table 1.2.

Process step Technique

Chemical reaction Optimise reaction variables and reactor design.Optimise reactant addition method.Eliminate use of toxic catalysts.

Filtration and washing Eliminate or reduce use of filter aids anddisposable filters.Drain filter before opening.Use countercurrent washing.Recycle spent washwater.Maximise sludge dewatering.

Table 1.2 Examples of Production Process Modifications for Waste Minimisation

An important factor in evaluating the cost effectiveness of equipment modifications isthe cost associated with treating or disposing of off-specification products. This can be veryexpensive, not only in terms of labour and materials but also in waste management costs.

3. Volume reductionVolume reduction includes techniques to separate hazardous waste from recoverable

wastes from the total waste stream. These techniques are usually used to increaserecoverability, reduce volume and thus the cost of waste treatment or disposal. They can be

divided into two general categories; source segregator and waste concentration.


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3.1 Source segregationSegregation of wastes is in many cases a simple and economical technique for waste

minimisation. By segregating wastes at the source of generation and handling the hazardousand non-hazardous wastes separately, the volume and disposal cost of the waste can bereduced. Additionally, the non-contaminated or undiluted wastes may be reusable in the

production process or may be sent off-site for recovery.

The segregation technique is applicable to a wide variety of waste streams andindustries and usually involves simple changes in operational procedures.

A commonly used waste segregation technique is to collect and reuse in the product,dust and excess materials generated during the manufacturing process.

3.2 ConcentrationVarious techniques are available to reduce the volume of a waste through physical

treatment. Such techniques usually remove a portion of a waste, such as water. For example,

concentration techniques are commonly used to dewater waste water treatment sludges andreduce the volume by as much as 90%. Available concentration methods include gravity andvacuum filtration, evaporation, ultrafiltration, reverse osmosis, freeze vapourisation, filter

press, heat drying and compaction. Concentration techniques are available for all types ofwaste streams and are used by a wide range of industries.

In some cases, concentration of a waste stream may also increase the likelihood that thmaterial can be reused or recycled.

4. RecoveryRecovering waste can provide a very cost effective management alternative. This

technique can help eliminate waste disposal costs, reduce raw material costs and possiblyprovide income from a reliable waste. Recovery of waste is a widely used practice in manymanufacturing processes and can be carried out on-site or at an off-site facility.

Waste recovery should only be considered after all other waste minimisation optionshave been instituted. Actually reducing the amount of waste generated at the source willusually be more cost effective than recycling. In many cases this is because a waste is lost rawmaterial or product which requires time and money to manage and recover. Also, simplygenerating and handling a waste product produces a range of regulatory health andenvironmental liabilities.

The effective use of recovery will depend on the segregation of the recoverable wastefrom other process waste. This will ensure that the waste is uncontaminated and theconcentration of recoverable material is maximised.

4.1 On-site recoveryIn most cases the best place to recover process wastes is within the production facility.

Wastes, which are simply contaminated versions of the process raw materials, are goodcandidates for in-plant recycling. Such recovery can significantly reduce raw material

purchases and waste disposal costs. Waste can be most efficiently recovered at the point ofgeneration, because the possibility of contamination with other waste materials is reduced, asis the risk involved in handling and transporting waste materials.


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Some waste streams can be reused directly in the original production process as rawmaterials. This can usually be accomplished when the waste material is only slightlycontaminated or is excess raw material.

Some waste may have to undergo some type of purification before it can be reused. A

number of physical and chemical techniques which can be used are shown in Table 1.3.These techniques range from simple filtration to state-of-the-art techniques such as freezecrystallisation. The method of choice will depend on the physical and chemicalcharacterisation of the waste stream on the recovery economics and on operationalrequirements.

Most on-site recovery systems will generate some type of residue. This residue caneither be processed for further recovery or properly disposed of. For example, a solventdistillation system will usually recover only 90% of the input spent solvent for reuse. Theresidues or distillation bottoms are a hazardous waste and as such must be managed in anapproved manner.

Absorption Activated carbon

Molecular separation Reverse osmosisIon exchangeUltrafiltrationElectrolysis

Phase transition CondensationDistillationEvaporation

RefrigerationElectrolytic recovery

Chemical modification PrecipitationReduction

Physical separation FiltrationFlotationLiquid-liquid extractionCentrifugationSedimentation

Table 1.3 Examples of Physical and Chemical Techniques for Waste Recovery


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WASTE MINIMISATION IN PROCESS OPERATIONS

Waste from process operations is generally brought about by unsteady-state conditions away

from the conditions under which the process was designed to operate. Start-up, shutdown andproduct changeovers are obvious cases. However, poor operating practice can also keep theprocess away from the conditions under which it was designed to operate.

Typical operations which bring about waste include:- start-up/shut-down- product changeover - poor control and operation- equipment cleaning- tank filling- fugitive emissions.

Process Operations as Sources of Waste:(a) Start-up/shut-down of continuous processes

- reactors give lower than design conversion rates;- reactors at non-optimal conditions produce additional unwanted products;- separators working at unsteady conditions produce intermediates with

compositions which do not allow them to be recycled;- process intermediates are generated which, because the downstream process is

not operational, cannot be processed further;- separators working at unsteady conditions produce products which do not meet

the required sales specifications.

(b) Product changeovers- in continuous processes all these sources of process waste associated with

start-up and shut-down also apply to product changeover in multi-productplants;

- in batch and continuous processes it may be necessary to clean equipment toprevent contamination of new product. Materials used for equipment cleaningoften cannot be recycled, leading to waste.

(c) Poor control and operation- even at steady state, reactors generate waste if operated at non-optimal

conditions;- separators which split useful materials from waste streams can lose material atsteady state if operated at non-optimal conditions.

(d) Equipment cleaning for maintenance- equipment needs to be cleaned and made safe for maintenance.

(e) Tank filling- when process tanks or road tankers are filled, material in the vapour space is

forced out of the tank and lost to atmosphere;- accidental spillages can occur from tank filling operations.

(f) Fugitive emissions


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- material transfer requires pipework, valves, pumps and compressors. Fugitiveemissions occur from pipe flanges, valve glands and pump and compressorseals.

We will now make suggestions on what can be done, particularly in design, to

overcome such waste from operations.

(1) Start up/Shut down of continuous processes- minimise the number of shutdowns. Install more reliable or stand-by

equipment.- plan maintenance to avoid unnecessary shutdown.- design for flexible operations, e.g. high turndown rate rather than shutdown.

(1.1) Batch processesBatch processes, by their very nature, are always at steady-state so they are difficult to

maintain at optimum conditions. We should, therefore, question whether it would be

advisable and possible to change to continuous operations. If we choose to maintain batchoperation then the production schedule can have a major influence on the production of wastefrom batch processes. The production schedule is important in two ways:

the time-limiting step in batch process dictates the batch cycle time and hence the

level of production. If the plant is capacity-limited then there is pressure to speed upthe limiting step and this can lead to waste. As an example, consider the common casewhere the reaction is the limiting step in a batch process. Pressure to shorten the timefor the reaction can lead to low reactor conversion. Alternatively, using more extremeconditions to shorten the cycle time can lead to excessive waste by-product formation;

batch processes are often multi-product. Changeover between products causes waste

since equipment must be cleaned. Such waste can be minimised by scheduling

operations to minimise product changeovers; Right first time is the goal. Getting a process to work right first time, every time is

the low-waste goal. Right first time is the key to rapid changeovers, flexibility andgood service at low cost;

Remember that when more preparation is done off-machine then downtime and waste

are reduced.Example:Each start-up after a meal-break, for example, leads to waste. Staggering meal-breaksis one way to running more continuous and less wasteful. Discontinuous feeds to acontinuous process can also lead to stoppages and be a source of waste. Automatedfeeds such as pallet chargers to eliminate such stoppages.

(2) Equipment cleaning

(2.1) Introduction - Examples of cutting cleaning losses:- use the cheapest mix: mixtures of solvents are often used for cleaning but

prices of solvents change over time and you may be able to reduce your costsby reformulating. Set up some trials to ensure you are getting the best cleaningpower per ;

- resin production can be a source of free cleaning solvent. Solvents may be by-products of chemical reactions used to produce resins. Installing separationtank allows recovery of the solvent which is suitable for use in cleaning. One

plant saved 200,000/year this way.


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- dirty solvent can still be clean. What looks dirty solvent still has lots morecleaning power. In fact solvents can still be effective for cleaning when itcontains up to 15% solids, particularly if filtered effectively.

In both continuous and batch processes, equipment needs to be maintained. In such

circumstances the equipment must be emptied of process fluids and cleaned. This might firstrequire flushing with an organic solvent. The equipment will then be flushed with water orsteam cleaned. Such equipment is clearly a source of waste and more reliable equipment isone answer.

Also effective vessel washing is essential to ensure product quality and prevent cross-contamination particularly where batch plant is used for a range of different products.Furthermore, this need to maintain product quality can lead to companies being over-cautiousin their vessel washing. However, product quality can be protected by focusing on betterwashing technique rather than more washing. The result is often lower wash liquorconsumption, reduced effluent generation, shorter down time periods and fewer labour inputs.

(2.2) Collecting and segregation of wasteProcess waste streams are usually mixed in an effort to render pollutants as diluted as

possible ready for treatment (biological treatment). However, the mixing of streamsprematurely can often inhibit recovery of useful materials. The following measures to collectand segregate waste can help in the recovery and recycling of useful materials:- install a process sewer when processing organic materials, draining to a sump tank.Recycle the contents if possible;- install separate facilities for the collection of aqueous waste. This water sewer shouldhave facilities to separate materials. Solids and organics can often be separated by setting.Recycle material if possible.

(3) Tanks, pumps and valvesTank filling causes waste when the rise in the liquid level causes vapour in the tank tobe expelled to atmosphere. The vapour carries process materials to atmosphere and createswaste. To reduce waste from tank filling we must prevent the vapour space from breathing tothe atmosphere. There are three broad methods of avoiding such breathing:(i) send vapours from the tank space to recovery system (condenser, adsorption, etc.)

before venting;(ii) use tanks with floating roofs. This eliminates the vapour space but sealing the edge

can be a problem;(iii) use a tank with a flexible membrane in the roof.

The best way to avoid fugitive waste is by using leak-tight equipment (e.g. changingfrom packing to mechanical seals or even using seal-less pumps). If this is not possible thenregular maintenance checks can reduce fugitive waste. If all else fails the equipment can beenclosed and ventilation provided; the ventilation air would be treated before passing toatmosphere.

Example on valves:One-way valves can prevent fall back of materials. Suction pipes are often used for liftingliquids from tanks. Where the pump is higher than the tank, liquid will inevitably fall backinto the tank from the pipe, with a loss of up to 1-2 kg of chemicals in one operation. A one-way valve will prevent the fall back; the liquid in the tube can be recovered by lifting the pipe

higher than the pump.


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Pumps:Pumps dont usually contribute to waste except in two areas:(i) recover seal flushes and purges:

Each pump seal and purge needs to be examined as a possible source of waste. Mostcan be recycled to the process with little difficulty;

(ii) use seal-less pumps:Leaking pump seals lose product and create problems. Using seal-less pumps ormagnetically driven seal-less pumps eliminates these losses.

(4) Control and monitoringThe problems associated with process operations are generally unsteady-state.

Optimising procedures for start-up, shutdown and product changeover can cut waste. Perhapsthe most powerful method is improved instrumentation and increased automation.

As pointed out earlier, poor operating practice can mean that the process operatesunder conditions for which it was not designed, leading to waste. Whilst increasedautomation can solve such problems, this will not always be cost effective. If this is the case

then a system of monitoring and targeting to improve the process operating practice should beconsidered.

Note: Final RemarkWhen reducing waste from process operations a balance which takes into account

start-up, shutdown and product changeovers is required. Better operating procedures andimproved instrumentation and automation can also have a significant effect.


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Stages in Waste Minimisation:

obtain commitment from senior management for a waste minimisation initiative;

appoint a waste manager who will be responsible for co-ordinating waste

minimisation activities;

gather available information on the types and amounts of major waste generated bythe companys operations. Where possible, you should estimate the direct costs toyour companys wastes;

identify priority areas for action in terms of either waste costs or quantities;

seek ideas from the waste reduction team and other staff about how to eliminate or

reduce these priority waste streams. Keep an open mind on suggestions and thinkabout:- alternative production techniques;- alternative raw materials, solvent or fuel, etc.;- improved process control measures.

Consider possible waste minimisation options and select the most feasible and cost-effective to implement. Start with no-cost and low-cost measures that will produceimmediate savings. These fast starters on obvious waste reduction opportunitieswill help to establish confidence in the waste minimisation plan.

Implement your selected measures, making sure you:

- prepare an action plan;- identify roles and responsibilities clearly;- involve the staff controlling the operations that produce the waste;

measure waste production, raw material use and utility use regularly to demonstrate

that the expected savings are being made;

review progress regularly and publicise success. Cost savings achieved from initial

products will help to justify further action to prevent waste;

incorporate waste minimisation to your companys continuous improvement

programme.

2. Process flowsheet(i) process inputs and outputs:

Notes:- explain the principle of identifying:- all material and other inputs to the process;- all the wastes from the process.

do not consider quantities at this stage.

emphasise the importance of taking the time to complete this analysis.

Overhead The diagram highlights the range of possible process inputs and wastes.Identify as many process inputs and wastes as possible for each step of the

production process.

(ii) the process flowsheet:

emphasise the need to consider the business operation as a series of separate

processes each with its own suppliers and customers. These may be internal orexternal.


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each step of the process adds value to the product and incurs a cost from the

labour, materials and utilities (gas, water, electricity, compressed air, etc.) usedin that process.

The true cost of waste includes:

- cost of wasted resources- cost of rejects at each stage in the process- the value of lost sales from rejects.

The cost of rejects includes the value added to the material by the time it was rejected. Thecost of the reject therefore increases as the material progresses towards the final product.

Inserting this information into the process flow sheet helps to identify and track waste. Thisprocess flow sheet, which is called a waste tracking model, forms the first key stage of thewaste minimisation methodology. This waste tracking model is the core of the wasteminimisation procedure; it provides the means by which priority action areas can be

identified. Effort must be targeted on areas where it will deliver the greatest cost saving.


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TutorialExample process flowsheet:Process flowsheet for nail manufacturer:

The example of the overhead shows the main processes involved in the manufacture of

nails at a fictitious company.

Raw materials and storage:The major raw materials are steel rods and bars, which are normally stored before use.Point out that fork-lift trucks, labour, utilities and some consumables are used in this step, butlittle value is added to the material.

Acid pickling: From storage, the metal is cleaned by acid pickling. This process uses acid,water, heat, protective equipment and labour.Class should identify wastes.This process adds some value to the product.

Extrusion: To reduce the metal bar to correct diameter, it is pushed through a die.Class should be encouraged to think about inputs, outputs and wastes, e.g. energy, labour,machine maintenance, material loss at batch change over and lubricant.

Nail making: The extruded wire is then cut and shaped. Again, the class should identifyinputs and wastes. At this point, the majority of the value has been added to the product. Anyrejects and need for reworking will waste all this added value.This is an important point because many people do not appreciate the true cost of rework.

Packing, warehousing and dispatch: excessive use of consumables, packaging, utilities and

labour.


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3. Identifying waste minimisation opportunitiesNow that we have a taste of the power of using a process flowsheet to track waste, we

can be equipped with a good tool to get started.

(Fishbone diagram)

Once the priority areas for action have been identified, a cause and effect diagramcan be used to identify opportunities for eliminating waste.

people causes processes

effect(waste)

product procedures

For each effect, i.e. too much process waste, there are likely to be several causes.

In manufacturing industry, the key causes are:

people

methods

materials

machinery

Why is waste generated? Remember to look for ways to cure the cause or causes, of theproblem and not just the symptoms.

One practical method of identifying the reasons for waste is to brainstorm ideas and thenrank them to determine root causes.

By starting a team off with a cause and effect session you develop the shared understandingthat is needed to go on and develop solutions to the waste problems.

The fishbone diagram is a useful record of the thinking.

Generating ideas:Once the causes of waste have been identified, it is important to involve everyone in

generating solutions. Cause and effect diagrams are a standard tool for qualityimprovement. The best recipe for success is to:

ask the people who work on the process to suggest reasons for the problem

list their suggestions against each cause

involve everyone in the development of a solution

implement no-cost measures as soon as possible.

4. The Action PlanEarly success is essential to prove that waste minimisation is worth the effort.

Drawing up an action plan will help to achieve this. Since almost everything in business ismeasured in cost terms, it is important to take detailed measurements and translate them into

costs.


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Waste Minimisation in Reactors

The reactor is the heart of the process and can be a primary source of waste products.

Under normal operating conditions there are five major sources of waste from reactions.

(a) Low conversion if recycling is difficultIf it is not possible to recycle unreacted feed material back to the reactor inlet then lowconversion in the reactor will lead to waste of that unreacted feed.

(b) Waste by-products from the primary reactionsThe primary reaction can produce waste by-products, e.g.Feed 1 + Feed 2 product + waste by-product

(c) Waste by-products from secondary reactions

Secondary reactions can produce waste by-products, e.g.Feed 1 + Feed 2 product waste by-product

(d) Feed impurities undergo reactionImpurities in the feed materials can react to produce additional waste by-products.

(e) Catalyst wasteCatalyst is either degraded and requires changing or is lost and cannot be recycled.

(a) Low conversion if recycling is difficultIf recycling is not possible we should, in general, try to achieve a high conversion in

the reactor. If the reaction system involves a single, irreversible reaction then a higherconversion can be achieved using longer residence time, higher temperature or higherpressure.

The problem of forcing a high conversion with single reactions becomes acute if thedifficulty of separation and recycling coincides with the reaction being reversible. There is amaximum conversion, the equilibrium conversion, which we cannot exceed even with longresidence time.

What can we do to force a higher conversion for reversible reaction?We have a number of options available to shift the equilibrium and therefore force a higherconversion.

We can change:(a) the feed ratio, e.g. use an excess of one reactant;(b) inert concentration, e.g. add inert material if reaction leads to increased number of

moles;(c) temperature, e.g. raise temperature for enothermic reactions;(d) pressure, e.g. increase the pressure if reaction leads to a decrease in the number of

moles.

Alternatively, intermediate separation of products as the reaction proceeds can be an effectivemeans of forcing higher conversion. A common example of this technique is in the

manufacture of sulphuric acid where, to force a higher conversion of SO2 to SO3, the productgases undergo reaction followed by a first stage absorption to remove SO3. The remaining


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over of a catalyst, the method by which it is prepared, or its physical characterisation (size,shape, porosity, etc.) can lead to substantial improvements in catalyst life and effectiveness.

(3) Improve physical mixing in the reactorModifications to the reactor such as adding or improving baffles, installing a higher

rpm motor on the agitator(s) or using a different mixer blade design (or multiple impellers)can improve mixing. Pumped recirculation can be added or increased. Two fluids goingthrough a pump, however, do not necessarily mix well and a static mixer may be needed toensure good contacting.

(4) Improve way in which reactants are addedThe idea here is to get closer to ideal reactant concentrations before the feed enters the

reactor. This helps avoid secondary reactions which form unwanted by-products. The wayNOT to add reactants is shown in the upper half of Figure 2. It is doubtful that the idealconcentration exists anywhere in this reactor. A consumable catalyst, especially, should bediluted in one of the feed streams (one which does not react in the presence of the catalyst).

Part 2 of the figure illustrates one approach to improving the situation by improving mixingusing three in-line static mixtures.

(5) Consider different reactor designThe classic stirred-tank back mix reactor is not necessarily the best choice. A plug

flow reactor offers the advantage that it can be staged and each stage can be run at differentconditions (especially temperature), closely controlling the reaction for optimum product mixand minimum waste.

(6) Provide separate reactor for recycle streamsRecycling by-product and waste streams is an excellent technique for reducing waste,

but often the ideal reactor conditions for converting recycle streams back to useable productsare considerably different from conditions in the primary reactors. One solution is to providea separate, smaller reactor for handling recycle and waste streams as illustrated in Figure 3.Temperature, pressure and concentrations can then be optimised in both reactors to takemaximum advantage of reaction kinetics.

(7) Improve control For a given reactor configuration, there is one set of operating conditions that is

optimum at any given time. The control system should know that condition and make itoccur, with little fluctuation. Such control may be complex, particularly in the case of batchreactor operation which frequently reduces the formation of waste products.

Advanced computer control systems are capable of responding to process upsets andproduct changes swiftly and smoothly, producing a minimum of unwanted by-products.

(8) Examine heating and/or cooling techniquesThe technique for heating or cooling the reactor needs to be examined, especially to

avoid hot-spots or overheated feed streams, both of which cause unwanted by-products.

L3 Waste Minimisation

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