Tuesday, February 3, 2009

Pollution Prevention Guidelines

Petroleum Refining Industry - Pollution Prevention Guidelines
Courtesy of World Bank


Pollution Prevention Guidelines to provide technical advice and guidance to staff and consultants involved in pollution-related projects. The guidelines represent state-of-the-art thinking on how to reduce pollution emissions from the production process. In many cases, the guidelines provide numerical targets for reducing pollution, as well as maximum emissions levels that are normally achievable through a combination of cleaner production and end-of-pipe treatment. The guidelines are designed to protect human health; reduce mass loadings to the environment; draw on commercially proven technologies; be cost-effective; follow current regulatory trends; and promote good industrial practices, which offer greater productivity and increased energy.

Industry Description and Practices

The petroleum industry is organized into four broad sectors: exploration and production of crude oil and natural gas; transport; refining; and marketing and distribution. This document addresses
only petroleum refining. Crude oil is fractionated into liquefied petroleum gas, naphtha (used to produce gasoline by blending with octane boosters), kerosene/aviation turbine fuel, diesel oil, and residual fuel oil.

Catalytic cracking and reforming, thermal cracking, and other secondary processes are used to achieve the desired product specifications. Certain refineries also produce feedstocks for the manufacture of lubricating oils and bitumens. Some refineries also manufacture coke.

Waste Characteristics

Boilers, process heaters, and other process equipment are responsible for the emission of particulates, carbon monoxide, nitrogen oxides (NOx), sulfur oxides (SOx), and carbon dioxide. Catalyst changeovers and cokers release particulates. Volatile organic compounds (VOCs) such as benzene, toluene, and xylene are released from storage, product loading and handling facilities, and oil-water separation systems and as fugitive emissions from flanges, valves, seals, and drains. For each ton of crude processed, emissions from refineries may be approximately as follows:

  • Particulate matter: 0.8 kilograms (kg), ranging from less than 0.1 to 3 kg.
  • Sulfur oxides: 1.3 kg, ranging 0.2–06 kg; 0.1 kg with the Claus sulfur recovery process.
  • Nitrogen oxides: 0.3 kg, ranging 0.06–0.5 kg.

Petroleum Refining

  • Benzene, toluene, and xylene (BTX): 2.5 grams (g), ranging 0.75 to 6 g; 1 g with the Claus sulfur recovery process. Of this, about 0.14 g benzene, 0.55 g toluene, and 1.8 g xylene may be
    released per ton of crude processed.
  • VOC emissions depend on the production techniques, emissions control techniques, equipment maintenance, and climate conditions and may be 1 kg per ton of crude processed (ranging from 0.5 to 6 kg/t of crude).

Petroleum refineries use relatively large volumes of water, especially for cooling systems. Surface water runoff and sanitary wastewaters are also generated. The quantity of wastewaters generated and their characteristics depend on the process configuration. As a general guide, approximately 3.5–5 cubic meters (m3) of wastewater per ton of crude are generated when cooling water is recycled. Refineries generate polluted wastewaters, containing biochemical oxygen demand (BOD) and chemical oxygen demand (COD) levels of approximately 150–250 milligrams per liter (mg/l) and 300–600 mg/l, respectively; phenol levels of 20–200 mg/l; oil levels of 100–300 mg/l in desalter water and up to 5,000 mg/l in tank bottoms; benzene levels of 1–100 mg/l; benzo(a)pyrene levels of less than 1 to 100 mg/l; heavy metals levels of 0.1–100 mg/l for chrome and 0.2–10 mg/l for lead; and other pollutants.

Refineries also generate solid wastes and sludges (ranging from 3 to 5 kg per ton of crude processed), 80% of which may be considered hazardous because of the presence of toxic organics and heavy metals. Accidental discharges of large quantities of pollutants can occur as a result of abnormal operation in a refinery and potentially pose a major local environmental hazard.

Pollution Prevention and Control

Petroleum refineries are complex plants, and the combination and sequence of processes is usually very specific to the characteristics of the raw materials (crude oil) and the products. Specific pollution prevention or source reduction measures can often be determined only by the technical staff. However, there are a number of broad areas where improvements are often possible, and site-specific waste reduction measures in these areas should be designed into the plant and targeted by management of operating plants. Areas where efforts should be concentrated are discussed here.

Reduction of Air Emissions

  • Minimize losses from storage tanks and product transfer areas by methods such as vapor recovery systems and double seals.
  • Minimize SOx emissions either through desulfurization of fuels, to the extent feasible, or by directing the use of high-sulfur fuels to units equipped with SOx emissions controls.
  • Recover sulfur from tail gases in high-efficiency sulfur recovery units.
  • Recover non-silica-based (i.e., metallic) catalysts and reduce particulate emissions.
  • Use low-NOx burners to reduce nitrogen oxide emissions.
  • Avoid and limit fugitive emissions by proper process design and maintenance.
  • Keep fuel usage to a minimum.

Elimination or Reduction of Pollutants

  • Consider reformate and other octane boosters instead of tetraethyl lead and other organic lead compounds for octane boosting.
  • Use non-chrome-based inhibitors in cooling water, where inhibitors are needed.
  • Use long-life catalysts and regenerate to extend the catalysts’ life cycle.

Recycling and Reuse

  • Recycle cooling water and, where cost-effective, treated wastewater.
  • Maximize recovery of oil from oily wastewaters and sludges. Minimize losses of oil to the effluent system.
  • Recover and reuse phenols, caustics, and solvents from their spent solutions.
  • Return oily sludges to coking units or crude distillation units.

Operating Procedures

  • Segregate oily wastewaters from stormwater systems.
  • Reduce oil losses during tank drainage carried out to remove water before product dispatch.
  • Optimize frequency of tank and equipment cleaning to avoid accumulating residue at the bottom of the tanks.
  • Prevent solids and oily wastes from entering the drainage system.
  • Institute dry sweeping instead of washdown to reduce wastewater volumes.
  • Establish and maintain an emergency preparedness and response plan and carry out frequent training.
  • Practice corrosion monitoring, prevention, and control in underground piping and tank bottoms.
  • Establish leak detection and repair programs.

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