Manual of Petroleum Measurement Standards Chapter 19.6.2

Evaporative Loss from the Cleaning of Storage Tanks

FIRST EDITION, SEPTEMBER 2019

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Foreword

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Contents

Page

1. Scope 1

2. Normative References 1

3. Variables and Symbols 2

4. Standing Idle Emissions 7

   1. General 7

   2. Fixed-roof Tanks 7

   3. Floating-roof Tanks 7

5. Vapor Space Purge Emissions 9

   1. General 9

   2. Fixed-roof Tanks 11

   3. Floating-roof Tanks 12

6. Continued Forced Ventilation Emissions 14

   1. Overview of Methodology 14

   2. Derivation of the Vapor Concentration Method Equations 17

7. Refilling Emissions 20

   1. General 20

   2. Fixed-roof Tanks 20

   3. Floating-roof Tanks 21

8. Controlling Emissions During Cleaning 21

9. Example 21

   1. General 21

   2. Description 21

   3. Days 1-2 Standing Idle After Normal Pumpout. 24

   4. Day 3 Continued Forced Ventilation (with Prior Stock Remaining) 27

   5. Days 4-5 Sludge Removal (with Diluent) 30

   6. Days 6-7 Sludge Removal (No Free-standing Liquid Remaining) 32

   7. Refilling Emissions 33

   8. Total Emissions 34

10. Summary 35

Annex A (informative) Alternative Methods of Estimating Sludge Removal Emissions 36

Annex B (informative) LEL Monitors and Response Factors 42

Annex C (informative) Data Collection Forms 44

Annex D (informative) Distillate Flushing Study Bench and Field Testing Report 47

Annex E (informative) Storage Tank Cleaning Process 72

Bibliography 78

Figures

1. Height of the Vapor Space Under a Landed Floating Roof 5

2. Equations of the Daily Tank Cleaning Cycle 16

1. Test Assembly Drum for Low Leg Position 50

2. Fabricated Test Assemblies 51

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   Contents

   Page

3. Fill/Empty Tube and Probe Ports 51

4. Vent and Probe Port 52

5. Dilution Probe 53

6. TCEQ Slide Depicting FID Response Factors 54

7. TVA Probe Inserted into Probe Port 55

8. Results from Round 1, Series 2—Concentration vs Time 59

9. Results from Round 2, Series 1—Concentration vs Time 60

10. Results from Round 2, Series 1—Percent Reduction vs Time 60

11. Results from Round 2, Series 2—Concentration vs Time 61

12. Results from Round 2, Series 2—Percent Reduction vs Time 61

13. Results from Round 2, Series 3—Concentration vs Time 62

14. Results from Round 2, Series 3—Concentration vs Time (Detail) 62

15. Results from Round 2, Series 3—Concentration vs Time (One Graph Line per Drum) 63

16. Sample Port at the Second Field Site 67

1. Daily Tank Cleaning Cycle 76

2. Flow Diagram of Tank Cleaning Tasks 77

Tables

1. Height of the Vapor Space Under a Floating Roof 5

2. Summary of Tank Cleaning Emissions 6

3. Summary of Saturation Factors (S) for Vapor Space Purge 10

4. Saturation Factors (S) for the Initital Vapor Space Purge of Floating-roof Tanks 13

5. LEL Values for Selection Compounds 14

6. Tank Cleaning Emissions for the Example 34

1. Comparison of Example Results by Sludge Removal Estimating Method 36

2. Sludge Depth in Storage Tanks 37

3. Comparison of Sludge Removal Emission Estimating Methods 39

4. Comparison of Vapor Concentration and Sludge Volume Methods 40

B.1 Response Factors of Individual Instruments for Selection Target Compounds 43

1. Comparison of Response Factors 53

2. Round 1, Series 1 56

3. Round 1, Series 2 57

4. Round 2, Series 1 57

5. Round 2, Series 2 57

6. Round 2, Series 3 58

7. First Field Site TVA Readings 66

E.1 Tank Cleaning Steps 73

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Introduction

The purpose of this standard is to provide guidance for estimating emissions that result from forced ventilation of a storage tank, such as is commonly utilized while cleaning the bottoms of aboveground storage tanks. This forced ventilation is sometimes referred to as degassing.

While a given tank may be cleaned only once every 10 to 20 years, regulations may require reporting the resulting emissions when this does occur. Furthermore, petroleum industry facilities may be required to estimate emissions from all sources within their plant sites. These regulatory requirements include Toxic Release Inventory reporting under EPCRA Section 313 and annual emissions reporting under the Part 70 operating permit program. Given these requirements to report emissions, there is a need for guidance on how to estimate them.

Emission factors have been developed for most of the routine sources of emissions from petroleum-related facilities, but little guidance has been available for estimating emissions from non-routine sources. When non-routine events occur, companies often expend a significant effort in preparing a good-faith estimate of the resulting emissions. In the absence of any industry-wide practice or guidance, however, these estimates may vary widely.

This standard is intended to reduce the effort required to generate a good-faith estimate of tank cleaning emissions, and to result in more uniformity in the resulting emission estimates.

This standard replaces API Technical Report 2568, Evaporative Loss from the Cleaning of Storage Tanks, 1st Edition, November 2007. TR 2568 has been withdrawn.

Evaporative Loss from the Cleaning of Storage Tanks

1. Scope

   
   

   This standard provides guidance for estimating emissions that result from forced ventilation of storage tanks such as may occur while removing the liquid heel (free-standing stock liquid) and cleaning the remaining deposits of stock liquid mixed with residue and water (sludge) from the bottoms of aboveground storage tanks.

   
   

   The emissions addressed in this report are those that leave the tank during forced ventilation. This standard does not address:

   
   

   • the fate of vapors after they have left the tank (other than accounting for the efficiency of a control device, as discussed in Section 8),

     
     

   • the fate of sludge after it has left the tank (or emissions that may occur during sludge treatment or disposal), or

     
     

   • emissions that may be expelled by the vacuum pump of a vacuum truck or suction pump, if such devices are used in the tank cleaning process.

   
   

   In other words, this report addresses the estimation of the mass of volatile organic compounds that leave the tank as vapor during forced ventilation of the tank, such as may occur during a tank cleaning process such as is described in Annex E. It does not address emissions that may result from the handling of liquids or sludge after such materials have been removed from the tank.

   
   

   This standard is not a guide for entering and cleaning storage tanks. Such procedures are addressed in API 2015 [1] and API 2016 [2].

   
   

2. Normative References

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

API Manual of Petroleum Measurement Standards (MPMS) Chapter 19.1, Evaporative Loss from Fixed-roof Tanks, Fifth Edition, June 2017

API Manual of Petroleum Measurement Standards (MPMS) Chapter 19.4, Evaporative Loss Reference Information and Speciation Methodology, Third Edition, October 2012 (including Addendum 2, June 2017)

API Manual of Petroleum Measurement Standards (MPMS) Chapter 19.6.1, Evaporative Loss from Storage Tank Floating-roof Landings, First Edition, February 2017

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