4 GENERIC EMISSIONS
4.2 Water pollutants
The Paris workshop [CITEPA, 1997 #47] considered that the water pollution issues of a process were different for:
- non-aqueous processes
- processes with process water contact as steam, diluent or absorbent - processes with a liquid phase reaction system
- batch processes where water is used for cleaning operations.
All but batch processes are likely to be used in LVOC production.
4.2.1 Emission sources
Again, the generic LVOC process provides a useful structure for identifying the source of water emissions. For all sources, attention should not only be paid to effluent streams that enter surface waters (rivers, lakes, seas), but also discharges to groundwater – either directly or indirectly (via the contamination of soil). The sources may include:
Raw material supply and work-up
• storage tank overflows
• mixing vessels (e.g. overflows, wash-down).
Synthesis
• water is added (as reactant solvent or carrier)
• reaction water is formed in the process (e.g. from a condensation reaction)
• water is present in the raw material
• process purges and bleeds (especially of ‘mother liquors’)
• quenching of organic vapour streams.
Product separation and refinement
• water is used for product washing and picks up traces of products / wastes
• spent neutralising agents (acid or alkali)
• regeneration of ion exchange resins
• solvent recovery.
Product storage and handling
Detailed information on emission sources may be found in the Storage BREF [EIPPCB, Draft
#49], but in general terms emissions may arise from:
Chapter 4
74 Production of Large Volume Organic Chemicals
• tank overflow
• spills during loading/unloading
• leakage from tanks and pipe systems
• spillage from drums and IBCs.
Emission abatement
• effluents may utilise neutralising agents (acid or alkali)
• air abatement systems (e.g. spent scrubber liquor)
• dewatering of sludges
• water bleed from seals drums and knock-out drums.
Energy / utilities
• hydrocarbon contamination of water cooling systems (e.g. from equipment leakage)
• bleed on boiler feed water (containing corrosion-inhibitors, biocides and scale)
• bleed on water demineralisation plant
• cooling system blowdown
• steam condensate contaminated with raw material, product, or waste (e.g. from equipment leakage).
Infrastructure
• cleaning operations (washing of vessels, pipes and other equipment to facilitate access e.g.
for maintenance purposes)
• fire-fighting water
• rain water run-off from roofs and hardstanding
• diffuse sources (e.g. leaks, spills from process equipment)
• oil from mechanical equipment (compressors etc)
• contamination of condensate from steam ejectors used to create vacuum
• water gland seals on vacuum pumps
• vapour condensates in pipe runs
• general site effluents from offices, canteens, laboratories and workshops
• water-curtains for hydrocarbons containment and /or acid gases absorption.
Management systems
Emissions may occur from process upsets or incidents that are attributable to the inadequacies of management systems or the failure of operators to adhere to procedures.
4.2.2 Pollutant types
The nature of pollutants in effluents is very specific to the process, but several generic effluent characteristics are encountered in LVOC processes:
• mixtures of oil/organics in water. Oils are so widely used in processes that they pose a high risk of contaminating effluents. Other organic contaminants may arise from raw materials, by-products and the use of solvents. These may occur as an emulsion or a distinct phase
• biodegradable organics (typically as measured by BOD)
• recalcitrant organics that are not amenable to conventional biological degradation. This may be measured by tests such as Chemical Oxygen Demand (COD), Total Organic Carbon (TOC), Adsorbable Organic Halogens (AOX) or Extractable Organic Halogens (EOX)
• volatile organics
• heavy metals – resulting from use of catalysts
• nitrogen-compounds (NH4-N, NO3-N, NO2-N) and phosphate – where used in a process
• acid / alkaline effluents
• suspended solids
• heat.
Chapter 4
Production of Large Volume Organic Chemicals 75
4.3 Wastes
4.3.1 Emission sources
Wastes are very specific to a process, but the key pollutants in wastes can be derived from:
knowledge of the process; materials of construction; corrosion/erosion mechanisms and materials related to maintenance. In generic terms wastes may include:
Raw material supply and work-up
• off-specification raw materials.
Synthesis
• spent catalyst and catalyst support. Catalysts may become spent because of chemical deactivation, physical degradation or fouling. The composition of catalysts varies greatly and is often subject to a high level of confidentiality. Many are based on expensive, exotic metals and this prompts recovery (either on or off site)
• wastes on shutdown (e.g. organic residues)
• corrosion and erosion products inside equipment (e.g. oxides of iron and other metals).
Product separation and refinement
• spent purification media. A variety of media are used to remove impurities such as water or unwanted side products (e.g. activated carbon, molecular sieves, filter media, desiccants, ion exchange resins)
• unwanted by-products
• process residues (e.g. heavy organic residues from distillation columns (e.g. tars and waxes), sludges in vessels). May have value as a by-product, feedstock for another process or as a fuel
• spent reagents (e.g. organic solvents – these may be valuable to recover/re-use, or to use a fuel to capture the calorific value)
• off-specification products.
Product storage and handling
Detailed information on emission sources may be found in the Storage BREF [EIPPCB, Draft
#49], but in general terms emissions may arise from:
• waste packaging (e.g. spent drums, sacks)
• product polymerisation in tanks.
Emission abatement
• adsorbents used for spill clean-up
• solids produced by the abatement of air pollutants (e.g. dust from electrostatic precipitators, bag filters)
• solids produced by the abatement of water pollutants (e.g. catalyst solids settled from waste water, filter cake).
Energy / utilities
• ashes / soots from furnaces, heaters and other combustion equipment.
Infrastructure
• decommissioned plant equipment
• construction materials (e.g. metal, concrete, insulation)
• general site wastes from offices, canteens and laboratories
• spent cleaning agents (e.g. phosphoric acid)
• spent oils (lubrication, hydraulic etc)
• spent heat transfer fluids.
Chapter 4
76 Production of Large Volume Organic Chemicals
Management systems
Emissions may occur from process upsets or incidents that are attributable to the inadequacies of management systems or the failure of operators to adhere to procedures.
4.3.2 Pollutant types
The form of wastes may range from discrete solid items to highly fluid sludges with significant water content. The nature of wastes is very dependent on the process. Wastes may be hazardous due to the presence of toxic organic substances or heavy metals.