Though Yemen is not contributing a lot to GHG emissions, it is, on the other hand, highly vulnerable to climate change-related impacts, and the hydrocarbons in this regard are among the most perilous air pollutants that are emitted from almost all refining processes in petroleum refineries; and Yemen in this sector is not well established and owns & operates two refineries only "the Aden Refinery-170,000 bpd and Marib Refinery-10,000 bpd”. Though such refineries are necessary for providing the best suited fuel to accommodate the growing fuel demand, yet are responsible of the emission of several hazardous pollutants into the atmosphere which are yet to be properly estimated & quantified. The uncertainties in such estimates are associated with data access/constraints, potential unsuitability of generic emission factors, and an incomplete understanding of the processes associated with such emissions. Therefore, the author in this post presenting the results of the methodology that might be employed in estimating air emissions in such sectors and Marib Oil Refinery facilities was selected for this purpose .
1. Emission Factors for Estimating Emission Rates
Air Emission Calculations Write up
The Marib refinery plant area comprises two processing units along with the utilities and tank farm facilities and the source of air emissions during the refinery operational are as depicted in Table 1.1 below
Table 1.1: Environmental Sources “Releases” in Marib Refinery
Due to the absence of credible & reliable information related to the refinery emission rates/factors, the USEPA AP-42 Emission Factors and World Bank guidelines applicable for refinery operations was used for estimating the emissions. The USEPA Emission Factors present average emission rates of pollutants based on data collected for a number of similar sources over a period of time and provide conservative emission rates of pollutants.
Sources
Based on field data collected and facilities documents reviewed "such as process flow schemes, P&IDs, design bases, Material Balance, Heat Balance, etc," the following are the main sources of air emissions:
Point Air Emission Sources
These include the following:
5 Process heaters – 2 Crude Heater (F-101/102),
3 Reformer Heater (F-201, F-202 and F-203),
1 Flare (25,000 kg/d); and
1 Standby DG Unit (1 MW).
Table 1.2. below provides summary of the calculations results of the estimated emissions rates of pollutants from the above stationary point sources at the process units and utilities.
Table 1.2. Emissions from Stationary Point Sources
The emission factors used for estimating above emission rates of pollutants, the engineering data used and the calculations details are presented in details in attached Appendix "Tables 1A to 1E" and are primarily based on USEPA emission factors (AP-42; https://www.epa.gov/air-emissions-factors-and-quantification/ap-42-compilation-air-emissions-factors) and some assumptions in applying these factors.
Fugitive Air Emission Sources
On the other hand, the fugitive emissions from the refinery are mainly from the storage tanks and the product loading racks and mainly include the following:
10 Fixed Roof Tanks - 2 for Diesel, 2 for Gasoline, 2 for Fuel Oil (LSWR); 2 for Crude oil and 2 for plant inventory "slop" storage tank; and
3 Loading Racks - One set for Gasoline, one set for Diesel, one set for Fuel Oil
The emission rates are estimated using USEPA Tank 4.0 software tool (https://www.epa.gov/air-emissions-factors-and-quantification/emissions-estimation-tools) and for emissions from loading racks, we have again employed AP-42 emission factors and the results are presented in Table 1. 3. below. .
Table 1.3. Fugitive Emissions
Likewise, the details of calculations and engineering data & assumptions used for the above fugitive emissions calculations are presented in the attached Appendix 1 "Tables 2A to 2C".
Summary of the assumptions & data considered for this calculations are as follows:
Equipment Assumptions & Data Input Used
Note: Other mobile source emissions “e.g. Vehicles & mobile equipment” , or Fugitive emissions “such as Valves, pumps, etc.” couldn’t be estimated.
CONCLUSION
From the above obtained figures (Table 1.2 & Table 1.3) it might be concluded that the emission rates of pollution in Marib Refinery area are huge and incomparable to pollution emitted “on a pro-rate basis” from similar facilities*1.2.3. which might be attributed to the old technology the refinery design was based on such as absence of low-Nox burners, fixed roof vs. floating roofs storage, conventional vs. submerged filling with vapor capture/recovery system loading racks…etc.
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