Environmental pollution and Petroleum Refining

1.1 Environmental
Potential environmental issues associated with petroleum refining include the following:
1 Air emissions
2 Wastewater
3 Hazardous materials
4 Wastes
5 Noise

Air Emissions
Exhaust gas and flue gas emissions (carbon dioxide (CO2), nitrogen oxides (NOX) and carbon monoxide (CO)) in the petroleum refining sector result from the combustion of gas and fuel oil or diesel in turbines, boilers, compressors and other engines for power and heat generation. Flue gas is also generated in waste heat boilers associated with some process units during continuous catalyst regeneration or fluid petroleum coke combustion. Flue gas is emitted from the stack to the atmosphere in the Bitumen Blowing Unit, from the catalyst regenerator in the Fluid Catalytic Cracking Unit (FCCU) and the Residue Catalytic Cracking Unit (RCCU), and in the sulfur plant, possibly containing small amounts of sulfur oxides. Low-NOX burners should be used to reduce nitrogen oxide emissions.
Air quality impacts should be estimated by the use of baseline air quality assessments and atmospheric dispersion models to establish potential ground level ambient air concentrations during facility design and operations planning.

Venting and Flaring
Venting and flaring are important operational and safety measures used in petroleum refining facilities to ensure that vapors gases are safely disposed of. Petroleum hydrocarbons are emitted from emergency process vents and safety valves discharges. These are collected into the blow-down network to be flared.

Excess gas should not be vented, but instead sent to an efficient flare gas system for disposal. Emergency venting may be acceptable under specific conditions where flaring of the gas stream is not possible, on the basis of an accurate risk analysis and integrity of the system needs to be protected. Justification for not using a gas flaring system should be fully documented before an emergency gas venting facility is considered.
Before flaring is adopted, feasible alternatives for the use of the gas should be evaluated and integrated into production design to the maximum extent possible. Flaring volumes for new facilities should be estimated during the initial commissioning period so that fixed volume flaring targets can be developed.
The volumes of gas flared for all flaring events should be recorded and reported. Continuous improvement of flaring through implementation of best practices and new technologies should be demonstrated.

Fugitive Emissions
Fugitive emissions in petroleum refining facilities are associated with vents, leaking tubing, valves, connections, flanges, packings, open-ended lines, floating roof storage tanks and pump seals, gas conveyance systems, compressor seals, pressure relief valves, tanks or open pits / containments, and loading and unloading operations of hydrocarbons. Depending on the refinery process scheme, fugitive emissions may include:
1 Hydrogen;
2 Methane;
3 Volatile organic compounds (VOCs), (e.g. ethane, ethylene, propane, propylene, butanes, butylenes, pentanes, pentenes, C6-C9 alkylate, benzene, toluene, xylenes, phenol, and C9 aromatics);
4 Polycyclic aromatic hydrocarbons (PAHs) and other semivolatile organic compounds;
5 Inorganic gases, including hydrofluoric acid from hydrogen fluoride alkylation, hydrogen sulfide, ammonia, carbon dioxide, carbon monoxide, sulfur dioxide and sulfur trioxide from sulfuric acid regeneration in the sulfuric acid alkylation
process, NOX, methyl tert-butyl ether (MTBE), ethyl tertiary butyl ether (ETBE), t-amylmethyl ether (TAME), methanol, and ethanol.
The main sources of concern include VOC emissions from cone roof storage tanks during loading and due to out-breathing; fugitive emissions of hydrocarbons through the floating roof seals of floating roof storage tanks; fugitive emissions from flanges and/or valves and machinery seals; VOC emissions from blending tanks, valves, pumps and mixing operations; and VOC emissions from oily sewage and wastewater treatment systems. Nitrogen from bitumen storage tanks may also be emitted, possibly containing hydrocarbons and sulfur compounds in the form of aerosols. Other potential fugitive emission sources include the Vapor Recovery Unit vents and gas emission from caustic oxidation.

Sulfur Oxides
Sulfur oxides (SOx) and hydrogen sulfide may be emitted from boilers, heaters, and other process equipment, based on the sulfur content of the processed crude oil. Sulfur dioxide and sulfur trioxide may be emitted from sulfuric acid regeneration in the sulfuric acid alkylation process. Sulfur dioxide in refinery waste gases may have pre-abatement concentration levels of 1500 -7500 milligrams per cubic meter (mg/m3).

Particulate Matter
Particulate emissions from refinery units are associated with flue gas from furnaces; catalyst fines emitted from fluidized catalytic cracking regeneration units and other catalyst based processes; the handling of coke; and fines and ash generated during incineration of sludges. Particulates may contain metals (e.g. vanadium, nickels). Measures to control particulate may also contribute to control of metal emissions from petroleum refining.

Carbon and Nitrogen Oxides
Carbon dioxide (CO2) may be produced in significant amounts during petroleum refining from combustion processes (e.g. electric power production), flares, and hydrogen plants. Carbon dioxide and other gases (e.g. nitrogen oxides and carbon monoxide) may be discharged to atmosphere during in-situ
catalyst regeneration of noble metals.
Operators should aim to maximize energy efficiency and design facilities (e.g. opportunities for efficiency improvements in utilities, fired heaters, process optimization, heat exchangers, motor and motor applications) to minimize energy use. The overall objective should be to reduce air emissions and evaluate cost-effective options for reducing emissions that are technically
feasible.








Wastewater
Industrial Process Wastewater
The largest volume effluents in petroleum refining include “sour” process water and non-oily/non-sour but highly alkaline process water. Sour water is generated from desalting, topping, vacuum distillation, pretreating, light and middle distillate hydrodesulphurization, hydrocracking, catalytic cracking, coking, visbreaking / thermal cracking. Sour water may be contaminated
with hydrocarbons, hydrogen sulfide, ammonia, organic sulfur compounds, organic acids, and phenol. Process water is treated in the sour water stripper unit (SWS) to remove hydrocarbons, hydrogen sulfide, ammonia and other compounds, before recycling for internal process uses, or final treatment and
disposal through an onsite wastewater treatment unit. Non-oily / non-sour but highly alkaline process water has the potential to cause Waste Water Treatment Plant upsets. Boiler blowdown and demineralization plant reject streams in particular, if incorrectly neutralized, have the potential to extract phenolics from the oil phase into the water phase, as well as cause
emulsions in the WWTP. Liquid effluent may also result from accidental releases or leaks of small quantities of products from process equipment, machinery and storage areas/tanks.

Process Wastewater Treatment
Techniques for treating industrial process wastewater in this sector include source segregation and pretreatment of concentrated wastewater streams. Typical wastewater treatment steps include: grease traps, skimmers, dissolved air floatation or oil water separators for separation of oils and floatable solids; filtration for separation of filterable solids; flow and load
equalization; sedimentation for suspended solids reduction using clarifiers; biological treatment, typically aerobic treatment, for reduction of soluble organic matter (BOD); chemical or biological nutrient removal for reduction in nitrogen and phosphorus; chlorination of effluent when disinfection is
required; dewatering and disposal of residuals in designated hazardous waste landfills. Additional engineering controls may be required for:
(i) containment and treatment of volatile organics stripped from various unit operations in the wastewater treatment system,
(ii) advanced metals removal using membrane filtration or other physical/chemical treatment technologies,
(iii) removal of recalcitrant organics and non biodegradable COD using activated carbon or advanced chemical oxidation,
(iv) reduction in effluent toxicity using appropriate technology (such as reverse osmosis, ion exchange, activated carbon, etc.),
(v) and (iv) containment and neutralization of nuisance odors.

Other Wastewater Streams & Water Consumption
Other wastewater streams and water consumption like , non-contaminated wastewater from utility operations, non-contaminated storm water, and sanitary sewage.
Contaminated streams should be routed to the treatment system for industrial process wastewater.