1、Evaporative Loss from the Cleaning of Storage TanksTECHNICAL REPORT 2568NOVEMBER 2007Evaporative Loss from theCleaning of Storage TanksMeasurement CoordinationTECHNICAL REPORT 2568NOVEMBER 2007Special NotesAPI publications necessarily address problems of a general nature. With respect to particular
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15、submitted to the Standards Department, API, 1220 L Street, NW,Washington, D.C. 20005, standardsapi.org.iiiTABLE OF CONTENTS Section Page 0. EXECUTIVE SUMMARY 1 0.1 Statement of Purpose 1 0.2 Estimating Method . 3 1. INTRODUCTION. 4 2. NOMENCLATURE 4 3. OVERVIEW. 9 4. STANDING IDLE EMISSIONS 14 4.1 F
16、ixed-Roof Tanks. 14 4.2 Floating-Roof Tanks. 14 4.2.1 Internal Floating-Roof Tanks with a Full or Partial Liquid Heel 14 4.2.2 External Floating-Roof Tanks with a Full or Partial Liquid Heel. 15 4.2.3 Drain Dry Floating-Roof Tanks 15 5. VAPOR SPACE PURGE EMISSIONS 16 5.1 Fixed-Roof Tanks. 17 5.2 Flo
17、ating-Roof Tanks. 18 6. SLUDGE REMOVAL EMISSIONS 19 6.1 Overview of Methodology. 19 6.2 Derivation of the Vapor Concentration Method Equations . 22 7. REFILLING EMISSIONS. 25 7.1 Fixed-Roof Tanks 25 7.2 Floating-Roof Tanks 25 8. CONTROLLING EMISSIONS DURING CLEANING. 25 9. EXAMPLE . 26 9.1 Descripti
18、on . 26 9.2 Days 12 Standing Idle after Normal Pumpout. 28 9.3 Day 3 Sludge Removal (with Prior Stock Remaining). 30 9.3.1 Standing Idle Emissions during Day 3 . 30 9.3.2 Vapor Space Purge Emissions during Day 3. 30 9.3.3 Sludge Removal Emissions during Day 3 31 9.4 Days 45 Sludge Removal (with Dilu
19、ent) 32 9.4.1 Standing Idle Emissions during Days 45 . 32 9.4.2 Vapor Space Purge Emissions during Days 45 . 32 9.4.3 Sludge Removal Emissions during Days 45 33 9.5 Days 67 Sludge Removal (No Free-standing Liquid Remaining) 34 9.5.1 Standing Idle Emissions during Days 67 . 34 9.5.2 Vapor Space Purge
20、 Emissions during Days 67 . 34 9.5.3 Sludge Removal Emissions during Days 67 34 9.6 Refilling Emissions . 35 9.7 Total Emissions 35 v 10. SUMMARY 36 APPENDIX AALTERNATIVE METHODS OF ESTIMATING SLUDGE REMOVAL EMISSIONS .37 APPENDIX BLEL MONITORS AND RESPONSE FACTORS 42 APPENDIX CDATA COLLECTION FORMS
21、 .44 REFERENCES .46 Tables Table 1. Summary of Tank Cleaning Emissions 3 Table 2. Nomenclature .5 Table 3. Typical Properties of Selected Petroleum Stocks 7 Table 4. Height of the Vapor Space under a Floating Roof 8 Table 5. Summary of Saturation Factors (S) for Vapor Space Purge .16 Table 6. Satura
22、tion Factors (S) for the Initial Vapor Space Purge of Floating-Roof Tanks 19 Table 7. LEL Values for Selected Compounds 20 Table 8. Sludge Depth in Storage Tanks .37 Table 9. Comparison of Sludge Removal Emission Estimating Methods 39 Table 10. Comparison of Vapor Concentration and Sludge Volume Met
23、hods .40 Table 11. Comparison of Example Results by Sludge Removal Estimating Method .41 Table 12. Response Factors of Individual Instruments for Selected Target Compounds .43 Figures Figure 1. Daily Tank Cleaning Cycle .2 Figure 2. Height of the Vapor Space under a Landed Floating Roof.8 Figure 3.
24、Flow Diagram of Tank Cleaning Tasks 13 Figure 4. Equations of the Daily Tank Cleaning Cycle 22 Evaporative Loss from the Cleaning of Storage Tanks 0. EXECUTIVE SUMMARY 0.1 Statement of Purpose The purpose of this report is to provide guidance for estimating emissions that result from cleaning the bo
25、ttoms of aboveground storage tanks. This report addresses vapors that leave the tank during the tank-cleaning process, but it 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 slud
26、ge 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. The tank-cleaning process may be considered, for purposes of
27、 estimating emissions, as involving the following steps: a) Normal Pumpout: As much stock liquid as possible is pumped out through the tank outlet in the normal manner (i.e., until the liquid level has dropped below the open end of the outlet line, and no more liquid moves through the outlet). As th
28、e liquid level drops during normal pumpout, flow of air through the tank vents is from outside the tank to inside the tank. Given this inward direction of air flow, it is assumed that no emissions occur during normal pumpout. b) Standing Idle: The defining characteristics of the standing idle condit
29、ion are: volatile material, capable of generating vapors, remains in the tank (as a full or partial liquid heel, or as clingage on the tank bottom), the height of the vapor space is reasonably constant (change is limited to stripping of the heel, or pump in of diluent) during the period in question,
30、 and there is no forced ventilation of the vapor space (i.e., no eductors, fans, or blowers are engaged in expelling the air/hydrocarbon mixture (i.e., vapors) from the tank). During a standing idle period, vapors are generated inside the tank by evaporation at the surface of the remaining volatile
31、material. The diurnal temperature cycle causes expansion and contraction of the vapors in the tank, thereby causing some of these vapors to be expelled from the tank (in the same manner as for breathing losses from a fixed-roof tank). c) Vapor Space Purge: As used in this report, forced ventilation
32、refers to any expulsion of vapors from a tank by means of eductors, fans, or blowers, regardless of whether or not the vapors are collected or treated upon being expelled from the tank. When forced ventilation begins, outside air is drawn into the tank, displacing the vapors that remain from the pri
33、or period of standing idle. While it may require multiple air changes to actually remove all of these vapors, for purposes of estimating emissions these vapors are accounted for in the first air change. This first air change, then, represents the vapor space purge. Emissions associated with subseque
34、nt air changes are accounted for in the sludge removal step. d) Sludge Removal: As used in this report, sludge removal refers to the removal of volatile materials from a tank while the tank is subject to forced ventilation. Volatile materials evaporate during sludge removal, thereby producing vapors
35、 that are expelled from the tank by the eductors, fans, or blowers. Sludge removal may take place as part of a daily cycle that includes periods of standing idle and vapor space purge. This cycle is illustrated in Figure 1. 1 2 API TECHNICAL REPORT 2568 Vapor Space PurgeSludge RemovalStanding Idlest
36、art up ventilationfirst air changein the morningforced ventilationdaytime tank cleaningoperationsventilation offoperations shutdownovernightFigure 1Daily Tank Cleaning Cycle e) Remain Clean: Once the tank has been cleaned, it may remain in the clean condition for some period of time. In that there a
37、re no remaining sources of vapors once the tank has been cleaned, no further emissions will occur for as long as the tank remains clean. f) Refilling: The clean tank is refilled. The incoming stock liquid generates vapors, which are then displaced from the tank as the stock liquid level rises. The n
38、ormal pumpout and remain clean steps do not involve emissions. Methods for estimating emissions from the standing idle and refilling steps are given in the API document Evaporative Loss from Storage Tank Floating Roof Landings API Landing Loss Report.1The purpose of this report is to provide guidanc
39、e for applying the methods from the API Landing Loss Report2to the standing idle and refilling steps as they pertain to tank cleaning, as well as to provide guidance for estimating emissions from the other two steps: vapor space purge and sludge removal. EVAPORATIVE LOSS FROM THE CLEANING OF STORAGE
40、 TANKS 3 0.2 Estimating Method The estimating method presented in this report is summarized in Table 1. Table 1Summary of Tank Cleaning Emissions Standing Idle Emissions Fixed Roof Tanks Internal Floating Roof Tanks with a Liquid Heel External Floating Roof Tanks with a Liquid Heel Drain-Dry Floatin
41、g-Roof Tanks Initial standing idle period upon emptying the tank (Section 4): Included with normal standing storage (breathing) losses (see API 19.13) Thus LS= 0 equations 9 & 10 LS= SVVEdKMRTPVKn 0.25 0.25 0.25 (16) S 0.5 (17) 5.2 Floating-Roof Tanks The volume of the vapor space for estimating the
42、 vapor space purge loss from a floating-roof tank is limited to the space under the floating roof: VV= volume (ft3) of the vapor space under the floating roof, = (hv) ( D2/4), (6) where: hv= the height (ft) of the vapor space under the floating roof for the given vapor space purge (see Table 4) The
43、saturation factor (S) is evaluated as specified for the filling saturation factor in the API Landing Loss Report.25This approach is conservative in that filling losses have both an arrival component, from resident vapors, and a generated component, from vapors generated by incoming liquid (e.g., 25%
44、 of the filling saturation factor for an internal floating-roof tank with a full liquid heel may be attributable to the incoming liquid the contribution of the incoming liquid to the vapor concentration varies with the filling scenario). The vapor space purge does not involve incoming liquid, howeve
45、r, and therefore would have only the arrival component of vapors. It is conservative, therefore, to use saturation factors that include allowance for the generated component of vapors. Values to be used are summarized in Table 6. The factors for external floating-roof tanks given in Table 6 are dete
46、rmined from the Csf S term given in the API Landing Loss Report Table 1:26CsfS = SSMRTPVKMRTPVKnKMRTPVKnMDPnVVSVVEdSVVEdVd+)/()/()/(*57.01 Where the number of days, nd, is taken as one day. This reduces to: CsfS = SSKKKKPVRTDPSESEV+)/(*57.01 (18) EVAPORATIVE LOSS FROM THE CLEANING OF STORAGE TANKS 1
47、9 Table 6Saturation Factors (S) for the Initial* Vapor Space Purge of Floating-Roof Tanks Tank Type Value for S (Csf S for EFRTs) in Equation 14 Full liquid heel Internal floating-roof tank (IFRT) 0.6 External floating-roof tank (EFRT) +6.0*57.016.0SESEVKKKKPVRTDPPartial liquid heel Internal floatin
48、g-roof tank (IFRT) 0.5 External floating-roof tank (EFRT) +5.0*57.015.0SESEVKKKKPVRTDPDrain dry (IFRT or EFRT) 0.0 Clingage has been accounted for, and there is no incoming liquid to generate more vapors. *The initial vapor space purge occurs at the end of the standing idle period that immediately f
49、ollows normal pumpout. Saturation factors for subsequent vapor space purges (i.e., those that follow overnight periods of standing idle, for which emissions are not calculated) are discussed in Section 6. 6. SLUDGE REMOVAL EMISSIONS 6.1 Overview of Methodology The calculation of vapor space purge emissions accounted for the vapors that were expelled by the first air change of the vapor space upon commencing forced ventilation at the end of a standing idle period. There still may be volatile
