County Sanitation Districts of Los Angeles County

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

Pollution Prevention Opportunities for Chemical Manufacturing

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/NOpportunitiesComments
 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 improvePrerequisite 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 tanktrucksTo 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 streamsTo 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 temperatureTo 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 usedTo 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:
  1. Allowing impurities to remain in a product from inadequate separation
  2. Forming waste within the column itself through polymerization from the high reboiler temperature in the column
  3. Losing products through venting or flaring from inadequate condensing
 
 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 weatherEspecially 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 columnTo 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 fluidTo 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 liningTo 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 wasteTo 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 samplesWastes 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 toxicityTo maximize recovery potential

Acknowledgement

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)


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Last Updated: January 8, 1996