waste product in induswaste product in industries.docx

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"Waste" describers material that was not used for its intended purpose or

unwanted material produced as a consequence of another process. In the chemical industry, waste

is either considered inert or contaminated. Inert waste can be recycled or released into the

environment. Malformed polymer or leaking steam may be considered inert wastes, although they

are not chemically inert. Wastewater is a type of contaminated waste that needs to be treated

before the components can be recycled or released to the environment. No matter what type of

waste you have, waste costs money. Malformed polymer is either sold as scrap for much less than

the properly formed parts or it has to be reprocessed. Either scenario costs a company money.

Treating wastewater is certainly an expensive endeavor. In short, there is much motivation to

minimize waste in the chemical and other industries.

Batch Operations

When you think of a batch operation, you may not think that these smaller units produce much

waste. To the contrary, batch operations produce much more waste per unit product than do

continuous processes. Traditionally, manufacturers using batch operations could afford this high

waste content thanks to the high value of their products. In recent years, waste has become more

and more expensive to deal with while competition has forced product value down. What has raised

the cost of waste "production"? Increased solvent prices and fees for environmental permitting and

monitoring emissions.

Each run of a batch process differs in many aspects. Waste generation is no exception. For

example, one run may yield 1.5 lbs. of unwanted by-product while a small pressure variation in the

next run causes 1.7 lbs. of waste to be produced. Waste handling equipment must be designed to

handle the worst case scenario waste production conditions. Careful control of reaction conditions

can help minimize waste in such applications. Reactor loading and unloading are also opportunities

to minimize waste.

During reactor loading, add solids before liquids. This will minimize the amount of time that a

most likely volatile liquid is in contact with the atmosphere. If possible, use a solvent with a lower

vapor pressure to minimize evaporation losses. Consider using a hopper specific to your solids.

Some hoppers allow locking of the process vessel to minimize vapor losses. Also, some hoppers are

available to open and distribute solids packaged in bags (cut-in hoppers).

During batch reactor operations, consider using a vapor recycling system if necessary. The

cumulative effects can be well worth the investment. Install gaskets on all vessel openings. Use

statistical process control (SPC) to regulate reactions rather than using intermediate testing. When

discharging the reactor, try to allow the reactor to cool as much as possible to limit volatile organic

compounds from leaking.

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Process Modifications

Raw Materials

Feed quality is very important in waste minimization. Working with suppliers to improve feed

quality reduce waste dramatically. Even small impurities can lead to giant amounts of waste. For

example, a specific feed impurity may speed up catalysts degradation which in turn produces waste

that must be separated from final products. Even if these impurities are not a compromise of your

quality and are left in the product, it may increase the waste in your customer's process. Raw

materials can also be evaluated for reduction or elimination. Consider a company that uses algae

inhibitor in their cooling tower. By shielding their tower from the sun, they quickly found that they

could reduce their inhibitor use by half.

Reactors

The transition from laboratory to industrial scale can sometimes see a drastic change in product

yield if proper mixing is not employed. By using static mixers before the reactor, by-product yield

can be minimized. Constant searching for better catalyst materials can also help a reactor operate at

peak efficiency. Consider a separate, smaller reactor for recycle streams. Optimum conditions for

recycle streams can vary from those used for fresh feeds. A separate reactor allows these different,

optimum conditions to be used.

Distillation Columns

Distillation columns contribute to waste by allowing impurities to remain in the product. The

solutions to this problem include ways to better separations. It is critical that engineers analyze the

cost of waste treatment and the additional energy costs required for better separations. At times,

the additional energy may be much more expensive than waste treatment. Separations can be

bettered by the following methods:

1. Increased reflux ratio

2. Additional trays

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3. Changing feed location

4. Insulating column

5. Pre-heating column feed

6. Increasing size of vapor lines

Columns can also produce significant waste due to inadequate condensation. The vapor can find

its way to a vent or flare and add to atmospheric pollution and result in costly fines. Be sure your

condenser is operating properly.

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Pollution

Your activities may cause air pollution from the release of chemical fumes and odours, noise

pollution from processing plant and machinery, water pollution from contaminated discharges or

accidental spills, or land contamination from storing chemicals or oil. If you cause a pollution

incident you may be prosecuted or fined and have to pay clean-up costs, all of which could damage

your reputation.

Emissions to air or odours can result from:

reaction or distillation facilities combustion plant products used in specific chemical processes, eg chlorophenols storing raw materials such as solvents, eg ethyl acetate, toluene and xylene using certain chemical groups, eg volatile organic compounds (VOCs) or sulfurous

compounds

waste and wastewater treatment processes

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Safe Disposal

Waste streams are rendered completely harmless orsafeso that they do not adversely impact the environment.Here, we define this as total conversion of waste

constituents to carbon dioxide, water, and nontoxic mirerals.An example would be subsequent treatment of awastewater treatment plant effluent in a private wetlands.So-called secure landfills would not fall within this categoryunless the waste is totally encapsulated in granite.

The bookPollution Prevention: Methodology, TechnologiesandPractices 111 is a waste-minimization and pollutionprevention resource describing a novel systematic

methodology that uses a structured brainstorming

process, requiring minimum resources to identlfy chemistryand engineering changes to processes. The book

also contains an extensive fundamental waste-minimizationknowledge that is applicable to all businesses, as well

as novel problem-solving approaches that enable all plantoperations personnel to have an important role in the

identification of waste-minimization and pollution-preventionopportunities. The approaches examine process

data and information from a different perspective, leadmg

\to the identification of new opportunities for reducingwaste and increasing business revenue

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TreatforMscharge

This involves lowering the toxicity, turbidity, global

warming potential, pathogen content, etc., of the waste

stream before discharging it to the environment. Examples

include biological wastewater treatment, carbon

adsorption, filtration, chemical oxidation, and so on.

Recycle

A large number of manufacturing facilities, especially

chemical plants, have internal recycle streams that are

considered part of the process (Figure 1). Here recycle

refers to the external recycl: of materials, such as polyester

film and bottles, Tyvek envelopes, paper, and spent

solvents

Minimize Generation

Reduce to a minimum the formation of nonsalablebyproducts in chemical reaction steps, and of waste

constituents, such as tars, fines, and so on, in all

chemical and physical separation steps.

Minimize Introduction

Minimize the addition of materials to the process

that pass through the system unreacted or that aretransformed to make waste. This implies minimizing

the introduction of materials that are not essentialingredients in making the final product. Examples of

introducing nonessential ingredients include: 1) usingwater as a solvent when one of the reactants, intermediates,or products could serve the same function, and2)adding large volumes of nitrogen gas because ofthe use ofair as an oxygen source, heat sink, diluent

or conveying gas.