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API MPMS 19.2 Document Information:
Title
Manual of Petroleum Measurement Standards Chapter 19 - Evaporative Loss Measurement Section 2 - Evaporative Loss from Floating-Roof Tanks
American Petroleum Institute
Publication Date:
Sep 1, 2003
Scope:
This publication contains methods for estimating the total
evaporative losses or the equivalent atmospheric hydrocarbon
emissions from external floating-roof tanks (EFRTs) and freely
vented internal floating-roof tanks (IFRTs), as well as for tanks
with external-type floating roofs that also have a freely vented
fixed roof. This type of tank is referred to as a covered
floating-roof tank (CFRT) in this document.
The equations that appeared separately in API Publ 2517 [1] and
API Publ 2519 [2] are combined in this document. The standing
storage loss factors have been revised to reflect the results of
the most recent testing.
This publication was developed by the API Environmental
Technical Advisory Group. The equations and factors presented are
based on recent laboratory, test-tank, and field-tank data and
supercede previous publications. The equations are intended to
provide loss estimates for general equipment types, since it is not
within the scope of this publication to address proprietary
equipment designs.
Typical currently available types of floating roofs, rim-seal
systems, and deck fittings are described for information only. This
publication is not intended to be used as a guide for equipment
design, selection, or operation.
The equations are intended to be used to estimate annual losses
from floating-roof tanks that contain multicomponent hydrocarbon
mixtures (such as petroleum stock liquid like crude oils and
gasolines) or single-component hydrocarbon stocks (such as
petrochemicals). The equations are applicable to the various types
of tank construction, floating-roof construction, rim-seal systems,
and deck fittings, as described in Section 8, as well as for
various stock liquid, stock vapor pressures, tank sizes, and wind
speeds (EFRTs). The equations are applicable to properly maintained
equipment under normal working conditions.
The equations were developed for liquids that are not boiling,
stocks with a true vapor pressure ranging from approximately 0.1 to
less than 14.7 pounds per square in. absolute (but not greater than
the atmospheric pressure at the tank location), average wind speeds
ranging from 0 miles per hour (mph) – 15 mph (EFRTs), and tank
diameters greater than 20 ft. The estimation techniques become more
approximate when used to estimate losses for time periods shorter
than one year. The estimation may be improved by using detailed
field information, including climatic data and operational data for
the appropriate time period.
The equations are not intended to be used in the following
applications:
a. To estimate losses from unstable or boiling stocks or from
petroleum liquids or petrochemicals for which the vapor pressure is
not known or cannot readily be predicted.
b. To estimate losses from tanks in which the materials used in
the rim seal, deck fittings, or deck seams have either deteriorated
or been significantly permeated by the stored stock.
c. To estimate losses from storage tanks that do not have a
floating roof of any kind.
d. To estimate losses from closed internal or covered floating-
roof tanks (that is, tanks vented only through a pressurevacuum
relief vent, blanketed with an inert gas, vented to a vapor
processing unit, or otherwise restricted from being freely
vented).
The equations for estimating evaporative stock loss or the
equivalent total atmospheric emissions from volatile stocks stored
in floating-roof tanks are given in Section 4. The factors for the
standing storage loss equation are discussed in Section 5 and for
the withdrawal loss equation in Section 6. Sample problems
illustrating the use of the equations are provided in Section
7.
These loss-estimating procedures are applicable only to EFRTs
(as described in Appendix C of API Std 650 Welded Steel Tanks for
Oil Storage ) [3], IFRTs of freely vented design (as described in
Appendix H of API Std 650) [3], and CFRTs (as described in Appendix
G of API Std 650) [3] of freely vented design (as described in
Appendix H of API Std 650) [3]. Descriptions of the types of
construction covered by this publication are given in Section
8.
The bases and development of the loss-estimation procedures
presented in Sections 4 through 7 are described in Section 9.
The estimation procedures were developed to provide estimates of
typical losses from floating-roof tanks that are properly
maintained and in normal working condition. Losses from poorly
maintained tanks may be greater. Because the loss equations are
based on equipment conditions that represent a large population of
tanks, a loss estimate for a group of floating-roof tanks will be
more accurate than a loss estimate for an individual tank. It is
difficult to determine precise values of the loss-related
parameters for any individual tank.
Equipment should not be selected for use based solely on
evaporative-loss considerations. Many other factors not addressed
in this publication, such as tank operation, maintenance, and
safety, are important in designing and selecting tank equipment for
a given application.
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