Environmental Management and Technology in Oil Refineries

Abstract

A petroleum refinery separates the hydrocarbons present in the crude oil feedstock into its constituent parts by distillation and subsequent processing by a range of processes including cracking, coking, reforming and alkylation. The principal potential environmental impacts from an oil refinery are emissions to air with over 60 % relating to energy production; these are largely dependent on the composition of the fuel used but will include NOx, particulates, SOx, CO, and CO₂. Other sources of emissions to air include flare-related emissions and non-methane volatile organic compounds. Other significant environmental impacts arise from wastewater discharges; soil and groundwater contamination; waste disposal; and energy and water consumption. The best available techniques advice for managing each of these impacts are identified in terms of primary techniques to prevent production/minimise use and secondary techniques to prevent discharges to the environment.

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1 Purpose of an Oil Refinery

The process of petroleum refining is the physical, thermal and chemical separation of crude oil into marketable products. The primary products are:

• Fuels (e.g. motor gasoline, diesel and distillate fuel oil, liquefied petroleum gas (LPG), jet fuel, residual fuel oil, kerosene);

• Chemical industry feedstock (e.g. naphtha, gasoils and gases);

• Finished non fuel products:

  • Lubricating oils, greases and waxes

  • Bitumen and Asphalt

  • Petroleum Coke

  • Sulphur

• Energy as a by-product in the form of heat (steam) and power (electricity).

Crude oil is a mixture of many different hydrocarbons, other organic compounds and impurities (e.g. oxygen, nitrogen, sulphur, salt and water), with widely ranging properties from gases to substances with very high boiling points. As a result crude oils can vary greatly in their physical and chemical characteristics, depending on their origin. The size, configuration and complexity of a refinery are influenced by the market demand for the type of products, the available crude quality and requirements set by authorities. As these factors vary from location to location, no two refineries are identical.

In 2012 there were 655 refineries worldwide, with a total capacity of around 4400 Mta⁻¹ [1]. The world’s largest refining region is Asia (25 %), followed by North America and Europe (around 20 % each). In 2013 there were approximately 120 crude oil refineries in Europe. Due to overcapacity in the European refinery sector, very few refineries have been built in the last 35 years, with 95 % being built before 1981 and 44 % before 1991, i.e. in an era largely before environmental concerns were a major issue for the public, government or industry. Most refineries have since had upgrades and new units built but their overall structure will have remained essentially unchanged.

Refining can be separated into two phases (also sometimes known as simple and complex refineries) and a number of supporting processes.

• Simple Refinery which separates the crude oil into its various components or fractions based on different boiling ranges in a distillation column at atmospheric pressure. Vacuum distillation is used to lower the temperature at which the heavier fractions can be separated without thermal decomposition. The desired fractions are collected separately and sent for further processing. This is followed by a further distillation of the lighter components and naphtha to recover methane and ethane to fuel the refinery operations, LPG, gasoline-blending components and petrochemical feedstocks. The yield reflects the crude oil composition. Generally this gives relatively low yields of light products and high yields of residual fuel oil. An increasing number of refineries also have an isomerisation unit to enhance the octane rating of light naphthas. Some simple refineries have bitumen manufacturing facilities involving vacuum distillation and possibly bitumen blowing.

• Complex refinery which alters the molecular structure of some of the heavier distillation fractions into lighter molecules, with a higher commercial value, through a range of cracking, coking, reforming, and alkylation processes. This gives higher yields of light products and lower yields of heavy products than in a simple refinery. The majority of refineries worldwide have a fluid catalytic cracking (FCC) unit and an alkylation unit to increase yield and quality of the gasoline pool. In North America, where heavy fuel oil markets are limited, most refineries have a coker. In the European Union (EU), visbreakers are usually installed to reduce the quantity of residual oil produced in the distillation of crude oil and to increase the yield of more valuable middle distillates (heating oil and diesel) by the refinery. A visbreaker thermally cracks large hydrocarbon molecules in the oil by heating in a furnace to reduce its viscosity and to produce small quantities of light hydrocarbons. An Integrated Gasification Combined Cycle (IGCC) unit may also be used to convert the visbreaker residue to power, steam, hydrogen, and some waste streams. Very complex refineries can be designed to produce no residual fuel oil.

  An example of a complex refinery configuration is shown in Fig. 11.1.

  Fig. 11.1

  

  Illustrative complex refinery configuration

• Supporting operations may include waste water treatment, energy generation, sulphur recovery, additive production, waste gas treatment, heat exchanger cleaning, blowdown systems, product blending and storage.

A refinery therefore consists of a complex system of stills, crackers, processing and blending units and vessels in which the various reactions take place, bulk storage tanks, and packaging units for products for immediate distribution to the retailer. Bulk storage tanks are usually grouped together in bunded tank farms. These “farms” are used for storage of both crude and refined products.

Crude oil is transferred into the refinery by a combination of pipeline, roads, rail and marine tanker. Finished products are transferred out of a refinery to smaller distribution terminals by direct pipeline, marine tanker, road or rail.

2 Main Environmental Issues

Crude oil refineries process large amounts of raw materials and consume substantial amounts of energy and water. Emissions to air, water and soil are generated as well as various solid and liquid waste streams.

2.1 Emissions to Atmosphere

Oil refining is responsible for a significant proportion of air emissions from industrial activities. Table 11.1 provides an estimation of the contribution to key atmospheric emissions parameters reported for 2007–2012 by EU Member States, Iceland, Liechtenstein, Norway, Serbia and Switzerland in the oil and gas refinery sector.

Table 11.1 Contribution of oil refining to the European air emissions (2007–2012) [2]

Typically more than 60 % of refinery air emissions are related to the production of energy for the various processes. Power plants, boilers, heaters and catalytic cracking are the main sources of emissions of carbon monoxide and dioxide, nitrogen oxides (NOx), particulates, and sulphur oxides (SOx) to the atmosphere. Sulphur recovery units and flares also contribute to these emissions. Nitrous oxide (N₂O) is released principally from FCC regenerators. Catalyst changeovers and cokers release particulates. Volatile organic compounds (VOCs) are released from storage, product loading and handling facilities, oil/water separation systems and, as fugitive emissions, from flanges, valves, seals and drains. Other emissions to the atmosphere are H₂S, NH₃, BTX (mixtures of benzene, toluene, and the three xylene isomers), CS₂, COS, HF; heavy metals are also released as particulates.

Refineries will typically have large numbers of permitted routine process release points, which will vary in size and throughput from very small to stacks from large combustion plant. Permits stipulate limits for specific, named pollutants. In order to control these emissions, the facility will be required to monitor emissions and submit findings to the regulatory authorities. In most instances it will be illegal to operate and emit pollutants to the atmosphere without a valid permit. In Europe this is controlled by the Industrial Emissions Directive 2010/75/EU (Integrated Pollution Prevention and Control).

2.1.1 Combustion Related Emissions

2.1.1.1 NOx Control

Nitrogen oxides are generated in the combustion process from the oxidation of atmospheric nitrogen and nitrogen in the fuel. The primary or process related techniques to prevent NOx emissions to air, as listed in Table 11.2, are: to reduce the nitrogen content in the fuel; to reduce the atmospheric nitrogen oxidised in the combustion process through reduction in oxygen; to reduce the residence time; and to reduce the combustion temperature. Secondary or end-of-pipe techniques serve to reduce or eliminate NOx from the discharges.

Table 11.2 Control techniques to prevent or reduce NOx emission from combustion

2.1.1.2 Dust and Metal Emissions Control

Particulate emissions are of interest because of their potential adverse impact on health, especially those with a diameter less than 10 μm (PM₁₀) and less than 2.5 μm (PM_2.5)_. Emitted refinery particulates may range in size from less than a nanometre to the coarse dusts arising from the attrition of catalyst.

The most hazardous refinery particulates contain heavy metals and polycyclic aromatic hydrocarbons, therefore, a reduction in the particle content reduces the metal emissions from the refinery.

Particulate emissions from refineries come from:

• Flue-gas from furnaces, particularly soot when firing liquid refinery fuels if there is sub-optimal combustion;

• Catalyst fines emitted from FCC regeneration units and other catalyst-based processes;

• CO boilers;

• Handling of coke, coke fines and ash generated during the incineration of sludges.

Particulate minimisation techniques include avoidance by replacement or treatment of the fuel, improved combustion and secondary particulate removal as shown in Table 11.3.

Table 11.3 Control techniques to prevent or reduce dust and metal emissions

Particulate removal techniques are dry, wet, or a combination of the two. The main dry techniques include cyclones, electrostatic precipitators and bag filters. Some wet techniques such as scrubbers may also be used mainly as finishing treatment.

The range of emissions from the majority of European refineries is between 4 and 75 tonnes of particulates per million tonnes of crude oil processed [1]. The lower end of the range being achieved in refineries using substantial amounts of gas combined with effective dust removal.

2.1.1.3 SOx Emissions Control

The main source of SOx emissions in the refinery is during energy production. During combustion, the sulphur in the fuel is transformed to a mixture of SO₂ and SO₃. As sulphur is a component of crude oil there is a direct relation between the sulphur in the feed to a combustion process and the sulphur oxides in its flue-gas.

SOx emissions also emanate from the catalytic cracking process and sulphur removal and recovery operations. To control SOx emissions, refiners can adopt one or more of the measures in Table 11.4.

Table 11.4 Control techniques to prevent or reduce SOx emissions

In a Sulphur Recovery Unit, the fuel gases (methane and ethane) are separated from the hydrogen sulphide (H₂S) using a solvent (typically amine) to dissolve the H₂S. The fuel gases are removed for use in other refinery processes and the solution is heated and the steam stripped to remove the H₂S gas. The H₂S rich gas streams are then treated in a high efficiency sulphur recovery unit using the Claus process for bulk sulphur removal and a tail gas treatment process to bring sulphur recovery yield to 99 % or more [3].

2.1.1.4 CO Emissions Control

Carbon monoxide (CO) is an intermediate product of the combustion processes, in particular in understoichiometric combustion conditions. CO emissions may actually be increased with the application of combustion modifications to reduce NOx emissions. This can be limited by careful control of the operational parameters. In addition, the following techniques may also be used:

• Constant delivery of liquid fuel in the secondary heating;

• Good mixing of the exhaust gases;

• Catalytic afterburning;

• Catalysts with oxidation promoters.

2.1.1.5 CO₂ Emissions Control

A feasible abatement technology for CO₂ is not available. CO₂ separation techniques are available but the problem is the storage and the recycling of the CO₂ and therefore the emphasis must be on emissions reduction. Options to reduce CO₂ emissions are:

• Effective energy management;

• Use of fuels with high hydrogen contents;

• Effective energy production techniques.

2.1.2 Flare-Related Emissions

Flares are used for safety and the environmental control of discharges of undesired or excess combustibles and for surges of gases in emergency situations, upsets, unplanned events or unanticipated equipment failure. Flaring is a source of air emissions and leads to the burning of potential valuable products.

Techniques for the reduction of emissions are given in Table 11.5.

Table 11.5 Control techniques to prevent or reduce flare-related emissions

2.1.3 Non-Methane Volatile Organic Compound (NMVOC) Emissions

NMVOC emissions originate from the evaporation and leakage of hydrocarbon fractions associated with potentially all refining activities, e.g. fugitive emissions from pressurised equipment in process units, storage and distribution losses, and waste water treatment evaporation. Typical sources are control valve stems, flanges, compressor/pump seals, tanks and loading facilities.

The main sources are:

• Fugitive emissions from piping;

• The flare system;

• The waste water treatment plant;

• Storage tanks and refinery dispatch stations.

Techniques to reduce NMVOC emissions focus on prevention and detection of fugitive emissions as shown in Table 11.6.

Table 11.6 Control techniques to prevent or reduce VOC emissions

2.1.4 Odours

The majority of all public complaints regarding refineries are due to odours. Hydrogen sulphide and methyl mercaptan are among the most common odorants from a refinery and are typically generated from storage tanks, sewage systems and oil/water separators. Although they have odour thresholds significantly lower than levels known to cause toxicity, they are nonetheless most often associated with annoyance at levels just exceeding their odour threshold.

The main reduction techniques are covered under atmospheric (see Sect. 2.1) and waste water emissions (see Sect. 2.2).

2.2 Emissions to Water

Potential water contaminants in refinery effluent are:

• Acids, alkalis (pH);

• Oil (free and dissolved);

• Sulphides;

• Ammonia/nitrates;

• Cyanides;

• Heavy metals;

• Heat;

• Other organic materials;

• Nutrients;

• Settleable solids;

• Colour;

• Taste and odour producers;

• Toxic compounds.

Table 11.7 shows the contribution of oil and gas refining to European water emissions 2007–2012.

Table 11.7 Contribution of oil refining to European water emissions (2007–2012) [2]

The largest volume of waste water arises from the distillation, catalytic cracking, and catalytic reforming processes. The waste water from distillation includes condensed steam from the tower (called oily sour water), which contains hydrogen sulphide, ammonia, and oily waste water if barometric condensers are used for vacuum distillation.

Other waste water pollutants include spent potassium hydroxide steam from alkylation, and sour water from visbreaking.

Rainwater falling into process areas may also become contaminated due to entry into production areas, tank systems, secondary containment systems and loading/off loading areas. Good housekeeping practices are required to minimise such contamination.

A refinery site therefore generates a mix of waste water streams containing both soluble and insoluble substances which become pollutants when released. Historically, treatment techniques were directed at reducing the amount of pollutants and the oxygen demand exerted by the waste water prior to release. These end-of-pipe techniques are mature and emphasis is now shifting to prevention and reduction of contaminated waste water streams prior to final treatment units (Table 11.8).

Table 11.8 Control techniques for the control of aqueous emissions

2.3 Soil and Groundwater Contamination

Contamination of soil and groundwater may arise due to the loss of crude, refined products or water containing hydrocarbons as a result of storage, transfer and transport operations. Most refineries have some areas that are contaminated by historical product losses. Current refinery practices are designed to prevent spillages and leaks to the ground. Historically however, the awareness of the potential risks of these contaminated areas was low. The two main issues therefore are the prevention of new spills and the remediation or the remedial control of historic contamination.

2.3.1 Prevention

Measures to control new spills are basically the same as those to control aqueous emissions together with ensuring that areas where oil is regularly handled are covered with an impermeable surface and drain to a dedicated oily water sewer and than tanks are double lined or bunded.

2.3.2 Remediation

Small quantities of contaminated soils or liquids may be managed as hazardous wastes and either treated on site or removed off site for treatment and/or disposal. Larger quantities and gross contamination may require more significant intervention and clean up, especially where it is a hazard or migrating off site. Monitoring regimes are often necessary.

2.4 Waste

The amount of waste generated by refineries is small if it is compared to the amount of raw materials and products that they process. Table 11.9 shows the generation and different waste routes according to the European Pollutant Release and Transfer Register (E-PRTR) declarations.

Table 11.9 Contribution of oil refining to European waste transfers (2007–2012) [2]

Waste is classified in Europe according to the European List of Wastes [4] as either hazardous or non-hazardous depending on properties defined in the Waste Framework Directive (WFD) [5] Annex III. It is a requirement under the WFD that wastes are managed according to the proximity principle i.e. as close to the source as possible, but in some cases e.g. where no appropriate facilities exist within the country, it will be necessary to send the wastes outside the country for disposal or recovery.

The WFD introduced the concept of the waste hierarchy which states that wastes should be managed in the following order of priority:

• Prevention;

• Preparing for reuse;

• Recycling;

• Other recovery, particularly energy recovery;

• Disposal.

Most oil refinery waste consists of:

• Sludges, both oily (e.g. tanks bottoms) and non-oily (e.g. from waste water treatment facilities);

• Other refinery wastes in liquid, semi-liquid or solid form (e.g. contaminated soil, spent catalysts from conversion processes, oily wastes, incinerator ash, spent caustic, spent clay, spent chemicals, acid tar);

• Non-refining wastes, e.g. domestic, demolition and construction.

Oil retained in sludges or other types of waste represents a loss of product and, where possible, efforts are made to recover such oil. Waste disposal depends very much on its composition and on the local refinery situation. The high operating costs of waste disposal mean that much priority has been given to waste minimisation schemes and management (Table 11.10).

Table 11.10 Control techniques for the management of waste

Segregation of waste by its characteristics is fundamental to ensuring efficient management according to the waste hierarchy. Good plant operation, materials handling and storage, housekeeping and economy in the use of chemicals will result in the minimisation of wastes for disposal.

Recycling waste materials for reuse may in many circumstances provide a cost-effective alternative to treatment and disposal. The success of recycling depends on both the ability to segregate recoverable and valuable materials from a waste and the ability to reuse waste materials as a substitute for an input material.

Petroleum sludge wastes are typically water-in-oil emulsions that are stabilised by fine solids. Sludge accumulates in refineries from equipment failure, training and periodic tank cleaning.

Processes for treating petroleum sludge include centrifugation, thermal desorption, solvent extraction, and hydrothermal processing. Electrokinetics is a developing technology that is used for in situ remediation of heavy metals and organic contaminants from saturated or unsaturated soils and sediments.

Process wastes should be tested and classified as hazardous or non-hazardous based on local regulatory requirements and international good practice and disposed of appropriately using authorised and licensed waste disposal operators.

A significant proportion of the non-petroleum outputs can be recovered and sold as by-products, e.g. sulphur, acetic acid, phosphoric acid and recovered metals from catalysts.

Increased use is made of third party waste contractors for off-site treatment, reclamation and disposal. Materials commonly reprocessed off-site by chemical and physical methods include oils, solvents, and recovered metals from catalysts and scrap metal. A strong commitment is required from the recycler not only to upgrade the waste materials for sale or exchange but also in finding suitable markets. The waste producer has a “duty of care” to ensure that the waste is correctly treated and disposed of by any third parties used.

2.5 Energy Consumption

Refineries consume large amounts of energy to generate electricity, heat and steam. Some refineries have installed combined heat and power plants. Typically more than 60 % of refinery air emissions are related to the production of energy [1].

Typical resource and energy consumption of process crude oil for an oil refinery utilising between 200 and 500 ha for land-use would require [6]:

• Total energy between 2100 and 2900 Mjt⁻¹ of processed crude oil;

• Electric power between 25 and 48 kWht⁻¹ of processed crude oil;

• Fresh make-up water between 0.07 and 014 m³t⁻¹ of processed crude oil.

Good design and management of energy systems are important aspects of minimising the environmental impact of a refinery, bearing in mind the highly integrated and interdependent nature of most processes (Table 11.11).

Table 11.11 Control techniques for the management of energy consumption

2.6 Water Consumption

Large volumes of water are used on a continuous basis in a refinery to maintain the water balance in the steam, cooling water, utility service water and emergency fire water supply circuits.

The water usage depends both on purpose and complexity of the refinery. The CONCAWE 2010 survey of 100 refineries [7] reports annual median total fresh water intake of 5.7 Mm³a⁻¹ but these range from 0.14 to 37.8 Mm³a⁻¹ with the annual median fresh water per tonne throughput being 0.70 m³a⁻¹ but similarly ranging from 0.1 to 8.6 m³a⁻¹.

It is typical for abstraction or water use permits to detail the volumes of water abstraction allowed, as over abstraction can affect local communities and also natural resources.

Drinking water sources, whether public or private, should be protected so that they meet or exceed applicable national standards or in their absence the current edition of World Health Organisation (WHO) Guidelines for Drinking Water Quality [8].

Water requirements for site workers and staff can be met through mains water supply or ground/surface water abstraction which should be properly assessed using testing techniques/lab analysis and water drawdown modelling.

In most refineries, some internal water streams are commonly used as desalter wash water, such as condensate water and steam-stripped sour water. There is scope for increased water reduction and reuse in refineries, which will lead to reduced size and costs of both water make-up and end-of-pipe treatment facilities. This is known as water stream integration where whenever possible steps are taken to prevent, reduce, recycle and reuse process water, rainwater, cooling and even contaminated groundwater to reduce the amount of fresh water intake and process water for end-of-pipe treatment.

Potential improvements include:

• Reusing unstripped/stripped sour water as wash water;

• Passing sour water from atmospheric and vacuum unit condensates to a stripper in enclosed systems;

• Segregation of non-contaminated water streams to enable reuse as process water;

• Prevention of spillages and leaks;

• Use of vacuum pumps to replace steam ejectors;

• Reuse of waste water generated by the overhead reflux drum, e.g. as a desalter wash water;

• Optimising water reuse by application of side-stream softening to blowdown streams.

3 Environmental Management Systems (EMS)

Environmental management is an integral part of the management process in most oil refineries and in Europe it is a permit requirement to demonstrate the application of Best Available Techniques (BAT). This includes that an EMS is implemented and adhered to that incorporates the following features [1]:

• 1. Commitment of the management, including senior management.

• 2. Definition of an environmental policy that includes the continuous improvement for the installation by the management.

• 3. Planning and establishing the necessary procedures, objectives and targets, in conjunction with financial planning and investment.

• 4. Implementation of the procedures paying particular attention to:

  • (a) Structure and responsibility

  • (b) Training, awareness and competence

  • (c) Communication

  • (d) Employee involvement

  • (e) Documentation

  • (f) Efficient process control

  • (g) Maintenance programmes

  • (h) Emergency preparedness and response

  • (i) Safeguarding compliance with environmental legislation

• 5. Checking performance and taking corrective action, paying particular attention to:

  • (a) Monitoring and measurement

  • (b) Corrective and preventive action

  • (c) Maintenance of records

  • (d) Independent internal and external auditing in order to determine whether or not the EMS conforms to planned arrangements and has been properly implemented and maintained.

• 6. Review of the EMS and its continuing suitability, adequacy and effectiveness by senior management.

• 7. Following the development of cleaner technologies.

• 8. Consideration for the environmental impacts from the eventual decommissioning of the installation at the stage of designing a new plant, and throughout its operating life.

• 9. Application of sectoral benchmarking on a regular basis.

The level of detail and nature of the EMS will generally be related to the nature, scale and complexity of the installation, and the range of environmental impacts identified. Many refineries have EMS certified against ISO 14001:2004 [9] or EMAS [10] which require continuous improvement in performance.