Prepared by Philip Lo, CSDLA, 12/90.
AA I Road
Whittier, CA 90601 4998
Mailing Address:
P.O. Box 4998
Whittier, CA 90607 4998
Charles W. Carry
Chief Engineer and General Manager
(213) 699 7411
(213) 685-5217
Fax: (213) 695-6139
For further information, contact:
Industrial Waste Section
County Sanitation Districts of Los Angeles County
P. 0. Box 4998
Whittier, CA 90607
Telephone (213) 699-7411 or 685-5217, extension 2900
FAX (213) 692-5103
The keys to pollution prevention are good operating practices and production process modifications. Wastes are usually generated from the mishandling of materials and the inadvertent production of off-spec materials.
Y/N | Opportunities | Comments | |
---|---|---|---|
1. Material Input, Storage and Handling | |||
Inventory control | |||
First in, first out to prevent expiration | |||
Designate material storage | |||
Provide protection, spill area containment keep area clean and organized give one person the responsibility to maintain the area | |||
Return obsolete materials | |||
Suppliers are the best persons to suppliers to handle them | |||
Segregate wastestreams, especially nonhazardous from hazardous | |||
Store packages properly and shelter from weather | |||
Prevent and contain spills leaks via proper equipment maintenance and increased employee training and supervision | |||
Minimize traffic through material storage area | |||
Improve quality of feed by working with suppliers or installing purification equipment | |||
Reexamine need for each raw material | |||
Use off-spec material | |||
Improve product quality | |||
Use inhibitors and continuously improve | Prerequisite for recovery and reuse To prevent damage, contamination and product degradation To prevent the generation of wastes To reduce contamination and dispersal of materials | ||
Impurities in feedstream can be major contributors to waste eliminated by modifying the process and improving control | |||
Occasionally, a process can use off-spec material because the particular quality that makes the material off-spec is not important to the process | |||
Product Impurities may be creating wastes at customers' plants; effect should be discussed with customers | |||
Inhibitors prevent unwanted side reactions or polymer formation | |||
Reformulate products from powder to pellet | |||
Reuse inert ingredients when flushing solids handling equipment change shipping containers, both for raw materials and products | |||
Recover product from tankcars and tanktrucks | To reduce dust emissions and waste generation To minimize need for disposal To avoid disposal, change to reusable containers, totebins or bulk shipments. To minimize product drained from tanks going to waste | ||
II. Production Process Modifications | |||
Reactors | |||
The reactor is the heart of the process and can be a primary source for waste products. The quality of mixing is the key. | |||
Improve physical mixing in a reactor | |||
Distribute feeds better for better yield and conversion, both for inlet and outlet | |||
Improve ways reactants are introduced into the reactor | |||
Improve catalyst and continuously upgrade | |||
Provide separate reactor for recycle streams | |||
Better heating and cooling techniques for reactors | |||
Install baffles, a high rpm motor for the agitator, a different mixing blade design, multiple impellers, pump recirculation or an in-line static mixer | |||
Add feed distributor to equalize residence time through fixed bed reactor to minimize under- and over reactions that form by-products | |||
Get closer to the ideal reactant concentrations before the feeds enter the reactor to avoid secondary reactions which form unwanted by-products in the premixing of reactants | |||
Catalyst has a significant effect on reactor conversion and product mix; changes in the chemical makeup of a catalyst, the method by which it is prepared, or its physical characteristics can lead to substantial Improvements in catalyst life and effectiveness | |||
The ideal reactor conditions for converting reactor streams to usable products are different from those in the primary reactor; this separation affords optimization for both streams | To avoid hot spots that would give unwanted by-products | ||
Consider different | The classic stirred-tank back mix reactor design reactor is not necessarily the best choice. A plug flow reactor off are the advantage that it can be staged, and each stage can be run at different conditions for optimum product mix and minimum waste generation | ||
Improve control to | To increase yield and decrease maintain optimal conditions by-product; at a minimum, stabilizing in reactor conditions in reactor operation frequently if advanced computer control is not available | ||
Heat Exchangers | |||
Heat exchangers can be a source of waste, especially with products that are temperature-sensitive. Reducing tube-wall temperature is the key. | |||
Use lower pressure steam | |||
Desuperheat steam | |||
Install a thermocompressor | |||
Use staged heating | |||
Use on-line cleaning techniques for exchangers | |||
Use scraped-wall exchanger | |||
Monitor exchanger fouling | |||
Use noncorroding tube to reduce tube-wall temperature | To reduce tube-wall temperatures and increase the effective surface area of the exchanger because the heat transfer coefficient of condensing steam is ten times greater than that of superheated steam To reduce tube-wall temperature by combining high and low pressure steam To minimize degradation, staged heating can be accomplished first using waste heat, then low pressure steam and finally, desuperheated high pressure steam | ||
Recirculating sponge balls and reversing brushes can be used to reduce exchanger maintenance, and also to keep the tube surface clean so that lower temperature heat sources can be used | To recover saleable products from viscous streams, e.g. monomers from polymer tar | ||
Sometimes an exchanger fouls rapidly when plant operating conditions are changed too f heat or when a process upset occurs; monitoring can help to reduce such fouling | |||
Corroded tube surfaces foul more quickly than noncorroded ones | |||
Pumps | |||
Preventing leaks is the key. | |||
Recover seal flushes where possible | |||
Recycled to the process and purges | |||
Use sealless pumps | |||
Use can-type or magnetically driven sealless pumps | |||
Furnaces | |||
Avoiding the hot tube-wall temperature is the key. | |||
Replace coil | |||
Alternative designs should be investigated wherever replacement becomes necessary | |||
Replace furnace with | |||
Use a high temperature intermediate intermediate exchanger heat transfer fluid to eliminate direct heat | |||
Making use of existing Sufficient superheat may be available steam super heat to heat a process stream, avoiding exposure of the fluid to hot tube-wall temperature of a furnace | |||
Distillation Column | |||
Distillation column typically produces waste in three ways:
| |||
Increase reflux ratio if column capacity is adequate for better separation | |||
Add section to column for better separation | |||
Retray or repack column for better separation | |||
Change feed tray for better separation | |||
Insulate | |||
Improve feed distribution | |||
Preheat column feed | |||
Increase the ratio by raising the the pressure drop across the column and increasing the reboiler temperature using additional energy | |||
The new section can have a different diameter and can use trays or high efficiency packing | |||
Repack to lower pressure drop across a column and decrease the reboiler temperature, large diameter columns have been successfully packed | |||
Match the feed conditions with the right feed tray in the column through valving changes | |||
Good insulation prevents heat losses and fluctuation of column conditions with weather | Especially for a packed column | ||
Preheating improves column efficiency and also requires lower temperatures than supplying the same heat to the reboiler Often the feed can be preheated by cross exchange with another stream | |||
Remove overhead products from tray near top of column | |||
Increase size of vapor line | |||
Modify reboiler design | |||
Reduce reboiler temperature | |||
Lower column pressure | |||
Improve overhead condensers | |||
condensers | |||
Improve column control | |||
Forward vapor overhead to the next column | To obtain a higher purity product if it contains a light impurity To reduce pressure drop and decrease the reboiler temperature | ||
A falling film reboiler, a pumped recirculation reboiler, or high-flux tubes may be preferred to the conventional thermosiphon reboiler for heat-sensitive fluids | |||
General temperature reduction techniques include using lower pressure steam or desuperheated steam, installing a thermocompressor and using an intermediate transfer fluid | To decrease reboiler temperature; the overhead temperature, however, will also be reduced which may create a condensing problem To capture any overhead losses through retubing, condenser replacement or supplemental vent condenser addition Similar to improving reactor control | ||
Use a partial condenser and introduce the vapor stream to the downstream column | |||
Piping | |||
A simple piping change can result in a major reduction of waste. | |||
Recover individual | |||
Segregation is crucial for reuse wastestream | |||
Avoid overheated lines | |||
Review the amount and temperature of heat-sensitive materials in lines and in vessel tracing and jacketing | |||
Avoid sending hot to prevent excessive venting and materials to storage degradation of products | |||
Eliminate leaks | |||
Change metallurgy or use lining | To prevent waste generation | ||
Metal may cause a color problem or act as a catalyst for the formation of by-products monitor major vents and flare system and recover vented products | |||
Storage tanks, tankcars and tank trucks are common sources of vented products install a condenser or vent compressor for recovery | |||
Process control | |||
Modern technology allows computer control system to respond more quickly and accurately than human beings. This capability can be used. | |||
Improve on-line control | |||
Optimize daily operation | |||
Automate startups, shutdowns and product changeover | |||
Program plant to handle unexpected upsets and trips | |||
Miscellaneous | |||
Avoid unexpected trips and shutdowns | |||
Use wastestreams from other plants | |||
Reduce number and quantity of samples | |||
Find a market for waste product | |||
Install reusable insulation | |||
III. Equipment Cleaning and Changeover | |||
Avoid unnecessary equipment cleaning | |||
Good process control reduces waste by optimizing process conditions and reducing plant trips and wastes | |||
A computer can be programmed to analyze the process continually and optimize the conditions to prevent waste | To bring the plant to stabilize conditions quickly to minimize the generation of off-spec wastes To minimize downtime, spill, equipment loss and waste generation | ||
A good preventive maintenance program, adequate sparing of equipment and adequate warning system for critical equipment | |||
Internal waste exchanges are feasible, but wastestreams should be adequately characterized | |||
Review sampling frequency and procedure and recycle the samples | Wastes can be converted to saleable by-products with additional processing and creative salesmanship Particularly effective on equipment where the insulation is removed regularly to perform maintenance | ||
Explore the feasibility of eliminating cleaning step between batches | |||
Maximize equipment dedication | |||
Recover more products | |||
Use less cleaner | |||
Reuse cleaner | |||
Consider alternative cleaning methods and less hazardous cleaners | |||
Standardize cleaning products used in plant | |||
Dedicating tanks to one product will reduce clean-out and save time and labor cost for changeover scraping down tanks, pigging or blowing lines can recover more product and reduce wastes | |||
High pressure sprays, pressurized air, steam and heated cleaning bath can reduce the amount of cleaner used and disposed of as waste | |||
Reclaim and reuse cleaner if feasible | |||
Mechanical cleaning such as plastic media blasting and ultrasonic cleaning, together with more biodegradable cleaner, can reduce waste volume and toxicity | To maximize recovery potential |
Materials for production process modification were adopted from Ken Nelson, Dow Chemical USA, " Use These Ideas to Cut Waste, "Hydrocarbon Processing, March 1990.
(WP, Chemical, Manual)
Last Updated: January 8, 1996