Chapter 13: Environmental Impacts of Petroleum Refining Processes

Overview In this chapter, we will briefly study: The different types of pollutants from petroleum refineries and how they are discharged to environment Pollutants discharges from major refinery processes World regulations on pollutants discharges from petroleum refineries Reduction of pollutants discharges to environment and treatment of wastes

Some Important Terminologies Process Vent is a point of emission from a unit operation (e.g., reactor) having a gaseous stream that is discharged to the atmosphere. Fugitive Emissions are emissions of gases or vapors from pressurized equipments due to leaks and various other unintended releases of gases, and is not routed to a pollution control device. Heater Stack Gases are side products of the combustion of fossil fuels used by heaters and furnaces.

Air Emissions (Air Pollutants) Heater Stack Gas (CO, NOx, SOx) CO2 Volatile hydrocarbons (e.g., Benzene, Toluene, Xylene, Propane and others) Solid particulate (e.g., metals and dust) NH3 H2S HCl AIR EMISSIONS 1 bbl=0.15899 cm~0.136 t, density of crude oil~0.8 to 1.0 g/cc

Sources of Air Emissions Combustion Emissions: associated with the burning of fuels in the refinery, including fuels used in the generation of electricity. Equipment Leak Emissions (Fugitive Emissions): released through leaking valves, pumps, or other process devices. They are primarily composed of volatile compounds such as ammonia, benzene, toluene, propylene, xylene, and others. Process Vent Emissions: typically include emissions generated during the refining process itself. Gas streams from all refinery processes contain varying amounts of refinery fuel gas , hydrogen sulfide and ammonia.

Water Effluents (Water Pollutants) Oil H2S NH3 Phenols Suspended and dissolved solids Chlorides Mercaptans Alkalines BOD (Biochemical Oxygen Demand) COD (Chemical Oxygen Demand) Cynides H2SO4 Amines Heavy metals Approximately 3.5-5 cubic meters of wastewater per ton of crude are generated.

BOD (Biochemical Oxygen Demand) BOD= amount of oxygen consumed by microorganisms (e.g., bacteria) to utilize organic wastes as food and/or energy. From BOD we can estimate the amount of organic wastes in wastewater Example:

COD (Chemical Oxygen Demand) COD= amount of oxygen required to fully oxidize organic wastes in wastewater. From COD we can estimate the amount of organic wastes in wastewater Example:

Sources and Types of Wastewater Produced in Refineries Cooling Water: which normally does not come into contact with oil streams and contains less contaminants than process wastewater. It may contain chemical additives used to prevent biological growth in heat exchanger pipes. Process Wastewater: that has been contaminated by direct contact with oil accounts for a significant portion of total refinery wastewater. Surface Water Runoff: is generated intermittently (either by rainfall or human) and may contain constituents from spills to the surface, leaks in equipment and materials in drains.

Solid Wastes Refineries generate solid wastes and sludges ranging from 3 to 5 kg per ton of crude processed, 80% of this sludges may be considered hazardous because of the presence of harmful organics and heavy metals.

Residual Wastes Most refinery residuals are in the form of sludge, spent caustics, spent process catalysts, and incinerator ash. These residuals could be classified as follows: Non-hazardous Residuals: are incinerated, landfilled or regenerated to provide products that can be sold off-site or returned for re-use at a refinery. Hazardous Wastes: Listed hazardous wastes include oily sludge, leads tank bottom corrosion solids and wastes from the cleaning of heat exchanger bundles. Toxic Chemicals: These are very dangerous materials that require extreme handling care. Many toxic chemicals are produced/used in large quantities by refineries.

Types and Sources of Residual Wastes Crude oil/desalted sludge: Contains iron rust, clay, sand, metals, emulsified oil and wax. Coke dust: Contains carbon particles and hydrocarbons Spent catalysts: May contain metals, fine particles, phosphoric acid, and/or alumina silicate. Neutralized alkylation sludge: Contains sulfuric acid or calcium fluoride and hydrocarbons. Heat exchanger sludge: Contains oil, metals and suspended solids Tank bottom sludge: Contains iron rust, clay, sand, metal, emulsified oil and wax.

Desalting Purpose of Desalting: remove corrosive salts along with some of the metals and suspended solids from crude oil before processing. Environmental impact of Desalting: Air Emissions: CO, SOx, NOx, particulates and fugitive emissions (hydrocarbons). Effluent to Water: Oil, H2S, NH3, phenol, high levels of suspended solids, dissolved solids and high BOD. Amount of wastewater produced = 2.1 Gal/Bbl crude oil processed. 1 Bbl= 31 Gal Residual waste generated: Sludge contains salts, iron rust, clay, sand, metals, emulsified oil and wax.

Distillation Purpose of Distillation: To separate the ingredients of crude oil into several valuable products. Environmental impact of Distillation: Air Emissions: CO, SOx, NOx, and particulates. Vent and fugitive emissions (hydrocarbons). Effluent to Water: Oil, H2S, NH3, suspended solids, chlorides, mercaptans, phenol and alkalines. Amount of wastewater produced= 26 Gal/Bbl crude oil processed Residual waste generated: Typically little or no residual waste generated.

Coking Purpose of Coking: To produce distillate naphtha and gas oils from heavy residuum. Environmental impact of Coking: Air Emissions: CO, SOx, NOx, and particulates. Vents and fugitive emissions (hydrocarbons). Decoking emissions (hydrocarbons and particulates). Effluent to Water: H2S, NH3, suspended solids, alkalines and COD. Amount of wastewater produced= 1.0 Gal/Bbl crude oil processed Residual waste generated: Coke dust (carbon particles and hydrocarbons).

Heat Exchanger Cleaning Purpose of Heat Exchanger Cleaning is to remove foulings from the inside surfaces of heat exchangers. Environmental impact of Heat Exchanger Cleaning: Air Emissions: Periodic fugitive emissions (hydrocarbons) Effluent to Water: Oily wastewater generated Residual waste generated: Heat exchanger sludge (contains oil, metals and suspended solids)

Storage Tanks Purpose of Storage Tanks is to store refinery feedstocks and products. Environmental impact of Storage Tanks: Air Emissions: Fugitive emissions (hydrocarbons) Effluent to Water: Water drained from tanks contaminated with tank contents. Residual waste generated: Tank bottom sludge (contains iron rust, metals, emulsified oil and wax)

World General Regulations on Discharges from Refineries The World Bank, has established emission levels for the design and operation of refineries, although country legislation should be accomplished. The guidelines given below present emissions levels normally acceptable to the World Bank Group. Water Effluents from the Petroleum Industry(g/m3 crude processed) Gas Emissions from the Petroleum Industry (mg/m3 crude processed) (Total Suspended Solid) Generation of sludges should be minimized to 0.3 kg per ton of crude processed, with a maximum of 0.5 kg per ton of crude processed. Solid Wastes

Reduction of Air Emissions Preserving air quality around a refinery involves controlling the gas and hydrocarbon vapor emissions to the atmosphere. Reduction of CO Emissions: through complete burning of CO to CO2 and then using CO2 capture and sequestration (or biological) methods to dispose CO2. Preventing H2S Emissions: by converting it into elemental sulfur Reduction of SOx Emissions: through sulfur recovery from tail gases in high-efficiency sulfur recovery units Reduction of NOx Emissions: through converting it to less harmful and useful chemicals such as NH3 and N2

Reduction of Air Emissions.. Continued Reduction of NH3 Emissions: By converting it to useful chemicals such as urea. Minimization of fugitive emissions of hydrocarbons and organic solvents: Through Proper design with regular maintenance of refinery equipments. By installing floating roofs in storage tanks to prevent evaporation and so that there is no space for vapor to gather in the tanks. Vapour recovery system - absorbed back into the product stream. Prevent leakage in pumps and valves Prevention of particulate emissions: through removal of particulates from gases (by, for example, filtration) and dispose the particulates appropriately.

Wastewater Treatment Refinery wastewater treatment plants are integrated systems that use both primary and secondary treatment. Settling pond for sedimentation. Also known as settling pond or decant pond. Oil water separator

Primary Treatment Primary treatment: Used to separate oil and solids from water in two stages. First stage: API oil-water separator based on differences in specific gravities. Process: allow sufficient time for free oil to float to the surface and be skimmed off, while solids settle to the bottom of the unit and are removed by mechanical scraping and depositing of the sludge into a collection hopper. Second stage: relies on physical or chemical methods to separate emulsified oils and fine particles from the wastewater: Physical methods are typically a series of settling ponds designed to have long retention times to allow settling. Chemicals such as ferric hydroxide or aluminum hydroxide are used to coagulate impurities into a froth or sludge, which can be skimmed off the surface.

Solid Waste Treatment Sludge treatment use bioremediation or solvent extraction, followed by combustion of the residues or using it as asphalt additive. The residue could require stabilization before disposal to reduce the leachability of toxic metals.

End of Environmental Impacts of Petroleum Refining Processes