Building an oil refinery will definitely come with an environmental cost to the nation. And as we seek to assess the environmental impact of building an oil refinery there are a number of factors that are worthy taking note of.
For this particular analysis we zero on one particular aspect of the environment: the air emissions that will result from the refinery construction and how the stakeholders or builders of the refinery should take on the challenge of mitigating the amounts of destructive air emissions that are likely to be released into the atmosphere as result of the refinery.
It should be noted that all emissions from the Uganda refinery will be limited in order to meet the requirements of the World Bank, except for where the Ugandan National Standards are the more stringent, or where there is no world Bank Standard for a substance regulated by the Ugandan National Standards. The World Bank Guidelines are based on the World Health Organisation Air Quality guidelines.
Air dispersion modeling is likely to be undertaken to ensure that emissions to air from any part of the refinery will meet these standards. Impacts on the quality will be minimized through adequate dispersion of pollutants and thus abatement system and stack heights will be designed to meet the requirements stated above.
The typical sources of emissions from a refinery include sulphur recovery units, process heaters, flares, boilers, heaters, incinerators, power generation units/emergency generators and fugitive emissions
During the construction phase, the main sources of air pollution are dust and exhausted gas. Dust would be generated from vegetation clearance and site filling, vehicle traffic on the roads, unloading/loading of materials and construction activities. Dust pollution will decrease air quality and the clearness of the atmosphere which will affect the sunlight absorbability and diffuseness. The other source of air pollution is exhausted gas produced from the operation of vehicles and engines. The exhausted gas contains COx, NOx, SOx and unburned hydrocarbon.
During the operations phase the main air emissions from a refinery are Cox, SOx, NOx, Volcanic Organic Compounds and particulates (dust, soot and associated heavy metals).
Here below we tell you about the different emissions in more specific detail.
Almost all the carbon present in crude oil, once produced from the oil well, will be converted into CO2 sooner or later. A small portion of the CO2 will be converted in the refinery during the processing of crude oil into marketable products. The remainder will be converted into CO2 once the refined oil products are sold and subsequently consumed by the various sectors of industry and private consumers. The main emmission sources for CO2 are the process furnances and boilers, power plants, gas turbines, FCC regenerators, flare system and incinerators. The range of CO2 emmissions range from 0.02 to 0.82 tonnes of CO2 per tonne of crude processed.
Other pollutants considered are carbon monoxide (process furnaces/ boilers, gas turbines, catalytic cracker regenerators, flare system, incinerators, cold from fire fighting equipment. Odours in a refnery are mainly created by sulphur compounds as mercaptanes but also by some hydrocarbons (e.g aromatics.) The main focus of odour in refineries is storage (e.g sour crudes), bitumen production, desalter, water, sewers, dissolved air flotation and bio treatment and flaring.
The term NOx- by convention- only refers to NO (Nitric Oxide) and NO2 (Nitrogen Oxide). N20 can also be found in fuel gases from FCCs. In most combustion processes NO contributes over 90% of the total NOx. It is rapidly oxidized to NO2 in the atmosphere. Hence emissions of NO are expressed as NO2. Combustion processes are the main source of NOx. The main emission sources for NOx are process furnances/boilers, power plant/ gas turbines, FCC regenerators, incinerators and the flare system. NOx emissions from refineries depend on the fuel type, fuel nitrogen, hydrogen content, combustor equipment design and operating conditions.
Accordingly, large differences in the NOx emission level can be expected between refineries and even between different combustion installations at the same refinery at different times. The range of NOx varies from 50 to 5000 tonnes per year. The specific emission range of NOx varies from 60 to 500 tonnes of NOx per million tonnes of crude oil processed.
Sulphur emissions to the atmosphere have always been an issue for refineries. All crude oil contains some amount of sulphur compounds. Consequently, when firing refinery fuels, SO2 and SO3 will be emitted. There is a direct relation between the Sulphur Content of the fuel and the amount of SOx emitted. The sulphur which is not extracted from the products in the refinery will remain in the various products and will be combusted to SOx by the various end users. The refinery as consumer of fuel for its energy use similarly emits SOx. Natural gas normally contains only traces of Sulphur compounds. There are both continuous and non-continuous sources of SOx emissions. The number of sources may vary from refinery to refinery. The main emission sources of SO2 are process furnaces/ boilers, gas turbines, sulphur recovery units, FCC generators, flare system, incinerators, decocking operations and treating units.
Volatile organic compounds (VOC) is the generic term applied to all compounds containing organic carbon, which evaporate at ambient temperature and contribute to the formation of summer smog and odour nuisance.
VOC losses can be calculated or directly measured (discrepancies in the emission numbers from both methods are found in many cases). The main sources of VOCs from refineries are vents, flares, air blowing, blow down systems, fugitive emissions from piping systems. Waste water systems, storage tanks (tank breathing), loading and unloading systems storage and handling.
Diffuse (fugitive) VOC emmission sources such as (single) seals from pumps, compressors, valves and flanges and leaks in pipelines and equipment may contribute 20-50% to the total VOC emmisions. The range of emmisions found in Europeans refineries (including storage farms) is from 600 to 10000 tonnes of VOC emptied per year. The specific emmision range found is from 50 to 6000 tonnes of VOC per million tonnes of Crude Oil processed.
The concern with particulate emissions (including heavy metals) stems from health effects. The main emission sources are process furnaces/ boilers, power plants (mainly those fired with (liquid) heavy fuel oil), catalytic cracker regenerators, coke plants, incinerators, decoking and soot blowing of furnaces and the flare.
However there are other emisions like odour, benzene, toluene, and dioxins also contribute to air emissions. They emerge typically from sources such as stacks of process furnaces and boilers, regenerators (FCC), individual items such as valves and pump seals and to a lesser extent from flares and incinerator stacks.
Measures to mitigate the pollution resulting from the air emissions
There are a number of ways through which resultant pollution caused by these emissions can be mitigated and there are outlined down here.
By reducing NOx emmissions
By reducing fuel consumption
By application of low NOx burners outages.
By providing a denox system where NOx emmissions are high.
By reducing Sulphur dioxide emissions through accurate quantification of sulphur emissions from various refinery sources to identify the main emmitters in each specific case
By increasing the use of gaseous fuels that have higher hydrogen to carbon ratios
Compiled from the Fosterwheeler Report on Uganda’s Oil refinery