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1. Scope and Applicability of API Publication 2517 (1989)
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`. | Variable | Symbol | Unit | Description | |—|—|—|—| | Vapor Pressure | P | psia | True vapor pressure of the stock liquid at the storage temperature | | Molecular Weight | M | lb/lb-mole | Molecular weight of the vapor | | Rim Seal Loss Factor | K_s | lb-mole/ft·yr | Emission factor for the specific rim seal type | | Deck Fitting Loss Factor | K_f | lb-mole/hr | Emission factor for each deck fitting type | | Deck Seam Length | L_D | ft | Total length of exposed deck seams on a welded deck | | Deck Seam Loss Factor | S_D | lb-mole/ft·yr | Emission factor for deck seams | A:…
| Loss Component | Primary Variables | Source of Loss |
|---|---|---|
| Rim Seal Loss (L_R) | Vapor Pressure (P), Wind Speed (U), Tank Diameter (D), Seal Factor (K_s) | Shear and wind-driven convection across the rim seal gap. |
| Deck Fitting Loss (L_F) | Vapor Pressure (P), Number of Fittings, Fitting Factor (K_f) | Vapor escaping through openings in the roof (e.g., gauge hatches, vents). |
| Deck Seam Loss (L_D) | Vapor Pressure (P), Deck Seam Length (L_D), Seam Factor (S_D) | Permeation through welded or bolted seams in the floating deck. |
| Withdrawal Loss (L_W) | Product Withdrawal Rate, Vapor Pressure (P), Molecular Weight (M) | Vapor displaced as the roof falls during liquid withdrawal. |
Data Quality Advisory: The accuracy of the emission estimate is highly dependent on the quality of the input data. True Vapor Pressure (TVP) must be calculated based on the actual stored liquid composition and storage temperature, not the Reid Vapor Pressure (RVP). RVP is a standardized volatility measurement and does not represent dynamic storage conditions.
Implementation Tip: For rim seal losses, using a primary seal combined with a secondary weather shield significantly reduces the rim seal loss factor K_s. Many compliance inventories default to secondary seal factors as the baseline, providing both environmental and product loss benefits.
Regulatory Compliance Risk: While API Publ 2517-1989 was a foundational document, many environmental regulatory bodies (e.g., the US EPA) have since adopted API MPMS Chapter 19.2 (Evaporative Loss from Floating-Roof Tanks) as the required method for emissions reporting. Using the 1989 edition might result in non-compliant emission calculations.
Audit Success Factor: Maintaining rigorous documentation of the tank roof surveys, seal type specifications, and vapor pressure calculations is the cornerstone of a successful compliance audit. A clear audit trail demonstrating adherence to the calculation methodology is essential.
Q: How does API Publ 2517-1989 differ from the current API MPMS Chapter 19.2 standard?
A: API 2517-1989 was the predecessor to API MPMS Chapter 19.2. The current Chapter 19.2 standard includes significantly more detailed emission factors, expanded guidance on calculations for specific tank configurations (such as tanks with geodesic domes or vapor recovery systems), and more rigorous methods for handling true vapor pressure calculations. The 1989 edition is generally considered outdated for modern regulatory reporting.
A: API 2517-1989 was the predecessor to API MPMS Chapter 19.2. The current Chapter 19.2 standard includes significantly more detailed emission factors, expanded guidance on calculations for specific tank configurations (such as tanks with geodesic domes or vapor recovery systems), and more rigorous methods for handling true vapor pressure calculations. The 1989 edition is generally considered outdated for modern regulatory reporting.
Q: Can I use API Publ 2517-1989 to calculate total emissions for my facility if my tanks are very old?
A: While it is technically possible, it is not recommended for compliance purposes. Most regulatory agencies require the use of the latest industry standards (API MPMS Ch 19.2). However, the fundamental physics and loss concepts outlined in the 1989 edition remain valid. The main difference lies in the specific numeric factors (K_s, K_f, S_D) used in the equations. Using the 1989 factors will likely lead to less accurate results compared to the updated data in Chapter 19.2.
A: While it is technically possible, it is not recommended for compliance purposes. Most regulatory agencies require the use of the latest industry standards (API MPMS Ch 19.2). However, the fundamental physics and loss concepts outlined in the 1989 edition remain valid. The main difference lies in the specific numeric factors (K_s, K_f, S_D) used in the equations. Using the 1989 factors will likely lead to less accurate results compared to the updated data in Chapter 19.2.
Q: What is the most critical parameter to get right in the calculation?
A: Without a doubt, the True Vapor Pressure (TVP) of the stored liquid at the bulk liquid temperature. Errors in TVP propagate multiplicatively through all components of the loss equation. A 10% error in TVP equalizes to a 10% error in the calculated total emission rate. Using the correct characterization of the stored fluid (e.g., via a lab analysis of the stored product) is the most impactful step an operator can take.
A: Without a doubt, the True Vapor Pressure (TVP) of the stored liquid at the bulk liquid temperature. Errors in TVP propagate multiplicatively through all components of the loss equation. A 10% error in TVP equalizes to a 10% error in the calculated total emission rate. Using the correct characterization of the stored fluid (e.g., via a lab analysis of the stored product) is the most impactful step an operator can take.
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1. Scope and Applicability of API Publication 2517 (1989)
API Publication 2517, formally titled “Evaporative Loss from External Floating-Roof Tanks” (Third Edition, February 1989), establishes the standard methodology for estimating the evaporative loss of volatile organic liquids stored in external floating-roof tanks. The scope of this publication is strictly limited to standing storage losses. It does not comprehensively cover working losses, withdrawal losses, or losses from internal floating-roof tanks, which are addressed in subsequent industry standards such as API MPMS Chapter 19.2 and 19.3.
The standard is applicable to petroleum products and volatile organic compounds (VOCs) stored at or near atmospheric pressure. The fundamental principle is that the floating roof acts as a vapor suppression system, and the remaining loss is primarily governed by wind-induced convection across the rim seal, vapor leaks through deck fittings, and permeation through deck seams.
2. Technical Requirements and Key Calculation Variables
The core of the standard requires the summation of individual loss components. The total standing storage loss (L_T) is calculated as: L_T = L_R + L_F + L_D Where L_R is the rim seal loss, L_F is the deck fitting loss, and L_D is the deck seam loss.
| Loss Component | Primary Variables | Physical Source of Loss |
|---|---|---|
| Rim Seal Loss (L_R) | True Vapor Pressure (P), Wind Speed (U), Tank Diameter (D), Rim Seal Factor (K_s) | Wind-driven convection and vapor diffusion across the annular space between the tank shell and the floating roof rim seal. |
| Deck Fitting Loss (L_F) | True Vapor Pressure (P), Number of Fittings per Type, Fitting Factor (K_f) | Vapor escaping through openings in the deck structure (e.g., gauge hatches, sampling wells, column sleeves, vents). |
| Deck Seam Loss (L_D) | True Vapor Pressure (P), Total Seam Length (L_D), Seam Factor (S_D) | Permeation of vapor through the interstices of welded or bolted deck seams. |
Critical Data Quality Advisory: The accuracy of the entire emission estimate hinges on the True Vapor Pressure (TVP) of the stored liquid at the bulk storage temperature. Using Reid Vapor Pressure (RVP) as a direct substitute for TVP will introduce significant errors in the calculation. TVP must be determined from compositional analysis of the stored fluid or through certified laboratory vapor pressure tests at the corresponding storage temperature.
3. Implementation Highlights and Best Practices
Accurate implementation of API Publ 2517-1989 requires meticulous field data collection. Operators must perform detailed roof surveys to catalog every deck fitting, measure rim seal gap widths (when using gap-based seal factors), and confirm the deck construction type (welded, bolted, or floating pontoon).
Implementation Tip: For minimizing rim seal losses, the standard provides different factors for various seal configurations. A tank equipped with a primary seal and a secondary weather shield demonstrates significantly