Duqm refinery Project Team carried out a site visit to the Duqm refinery site. During the visit preliminary discussions were held with the Ministry of Environment and Climate Affairs. A number of environmental issues were identified during the site visit and appropriate mitigation have been proposed. In this blog, one of these issues is going to be discussed and illustrated with the best practice.
One of the most environmental issues related to the operation of the petroleum refineries are emissions to air, water and soil. The common atmospheric pollutants are SOx, NOx, VOCs and particulates. In this blog, emissions to the air considerations and techniques are going to be listed, based on the refinery current configuration and the proper techniques to reduce the emissions will be discussed as well.
Development of the Outcome for Alternative
Most of the pollutants from the refineries are CO2, CO, NOx, Sox, VOCs and particulate. Although most of these pollutants are generated from Crude Oil being processing, Figure.1 shows that almost 60% of these pollutants are from fuel combustion sourcing the generation of energy.
Fiugre.1 Contribution of different emission sources in petroleum refineries .
In this blog, NOx and SOx emissions are going to be discussed.
NOx Emissions: These atmospheric pollutants include major oxides of nitrogen including NO, NO2 and N2O. The main sources of NOx generation are from the fuel combustion processes including furnaces, boilers and gas turbines.
Sox Emissions: SOx is an atmospheric pollutants include major oxides of sulphur, mainly SO2 (sulphur dioxide) and SO3 (sulphur trioxide). The main source of SOx generation is from fuel combustion processes including process furnaces, boilers, gas turbines, sulphur recovery units, FCC generators, flares, incinerators and de-coking operations
Selection of Criteria
Techniques used to reduce the emissions of both NOx and SOx are falling into two categories: Primary Techniques and Secondray, This blog will only concentrating on the primary techniques, hence they contribute the major reduction of the emissions. Primary for both NOx and SOx techniques as follows:
1) NOx emissions:
Primary techniques: Involve the control of Nox production through pre-combustion operational changes and combustion modifications. These include the use of:
- Low and Ultra Low Nox burners: Precise mixing of fuel and air is used to keep the flame temperature low and to dissipate heat quickly through the use of low excess air, off stoichiometric combustion.
- Flue gas circulation: involves recycling a portion of the combustion gases from the stack to the boiler wind-box.
- Re-burning: providing the gas stream residence time is long enough to allow the re-burn fuel to burn completely .
- Combustion Tempering: utilizes the injection of water or steam injection into the combustion zone to reduce the firing temperature, has been traditionally associated with minimizing NOX emissions from combustion turbines. However, this combustion control technology has also been applied to furnaces. Adding water or steam in the combustion zone can uppress NOX formation by up to 25% .
Table.1 below, summaries some of reduction techniques used and NOx emission reduction rate in percentage of the overall emission.
Table.1 Summary of NOx reduction techniques.
2) SOx emissions:
Primary techniques: Involve the control of SOX production through pre-combustion operational changes. These include:
- Using low sulphur fuels (LPG, Natural Gas).
- Processing low sulphur crudes.
- Increased Sulphur Recovery Unit (SRU) efficiency.
Analysis and Comparison of the Alternative
So far, there are many methods can be carried out to reduce the emissions of the NOx and SOx. For the NOx, most of the techniques used are based on the re-processing techniques to reduce the NOx emission to the air, while in SOx the idea is to reduce the sulphur contents by either using low sulphur contents fuel/crude.
Selection of the Preferred Alternative
In order to comply with the local and international standard, Duqm refinery has to implement the most optimum design and the desirable crude oil with the minimum pollutants contents that will efficiently meet the objective. Most of the techniques mentioned are either will add more costs and complexity to the refinery design, cause modifications to the refinery design or demanding the use of crude/fuel that will reduce the emission level. Further workshops and design reviews need to be commenced in order to come up with most optimum design with respect to cost, efficiency and less environmental impacts.
Best Available Techniques (BAT) document for Oil and Gas Refineries provides general guidelines on technological solutions which may be applied to mitigate the environmental impact of the refining process by reducing the emissions produced as a result of normal operations, and accidental discharges.
(a) “Techniques” includes both the technology used and the way in which the installation is designed, built, maintained, operated and decommissioned;
(b) “Available” techniques means those developed on a scale which allows implementation in the relevant industrial sector, under economically and technically viable conditions, taking into consideration the costs and advantages, whether or not the techniques are used or produced inside the Member State in question, as long as they are reasonably accessible to the operator;
(c) “Best” means most effective in achieving a high general level of protection of the environment as a whole.
Performance Monitoring and the Post Evaluation of Result
Significant reduction in NOx/SOx emissions can be achieved by making operational changes at your facility and by reducing the sulphur contents fuel and crude that is used in the process. The blog shows that NOx emissions in refinery, comes mainly from the internal combustion engines, boilers, furnaces, and process heaters. While it shows, most of the techniques that are used to reduce the emission of the SOx is to reduce the contents of sulphre in the crude oil used by the refinery or by simply, increasing the efficiency of the sulphur recovery unit. Making the proper operation design can be effective reduction techniques that results in lower NOx/SOx emissions. There are some action can be taken and followed to continuing the process of NOx/SOx reduction, Such as:
- Reduced or rescheduled emergency generator
- Testing the Air quality and the products contents (NOx/SOx).
- Modification, maintaining and tuning.
- Combustion Equipment
- Fuel switching
1) Available and Emerging Technologies for Reducing Greenhouse Gas Emissions from the Petroleum Refining Industry. (2010, October 1). . Retrieved June 24, 2014, from http://www.epa.gov/nsr/ghgdocs/refineries.pdf
2) NOx Reduction Techniques and Control Measures . (2000, September 1). . Retrieved June 24, 2014, from http://charmeck.org/mecklenburg/county/airquality/educationandoutreach/documents/noxreductionhandoutfinal.pdf
3) D., B. R. (n.d.). AN OVERVIEW OF TECHNOLOGIES FOR REDUCTION OF OXIDES OF NITROGEN FROM COMBUSTION FURNACES. . Retrieved June 24, 2014, from http://www.mpr.com/uploads/news/nox-reduction-coal-fired.pdf
4) James, L. (2010, September 17). Definition of Best Available Techniques. . Retrieved June 24, 2014,from http://www.elni.org/fileadmin/elni/dokumente/elni_forum/2010/Pres_LesleyJames.pdf