Short-term Evaporative Loss Estimation from Atmospheric Storage Tanks
API TECHNICAL TECHNICAL REPORT REPORT 2576 2576 FIRST EDITION, JULY 2016
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Special Notes API publications necessarily necessarily address problems of a general nature. With respect to particular circumstances, local, state, and federal laws and regulations should be reviewed. Neither API nor any of API's employees, subcontractors, consultants, committees, or other assignees make any warranty or representation, either express or implied, with respect to the accuracy, completeness, or usefulness of the information contained herein, or assume any liability or responsibility for any use, or the results of such use, of any information or process disclosed in this publication. Neither API nor any of API's employees, subcontractors, consultants, or other assignees represent that use of this publication would not infringe upon privately owned rights. API publications publications may be used by anyone anyone desiring to do so. Every effort effort has been been made by the Institute Institute to assure assure the accuracy and reliability of the data contained in them; however, the Institute makes no representation, warranty, or guarantee in connection with this publication and hereby expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any authorities having jurisdiction with which this publication may conflict. API publications publications are published published to facilitate the broad availability availability of proven, sound engineering engineering and operating practices. These publications are not intended to obviate the need for applying sound engineering judgment regarding when and where these publications should be utilized. The formulation and publication of API publications is not intended in any way to inhibit anyone from using any other practices. Any manufacturer manufacturer marking marking equipment equipment or materials materials in conformance conformance with the marking marking requirements requirements of of an API standard standard is solely responsible for complying with all the applicable requirements of that standard. API does not represent, warrant, or guarantee that such products do in fact conform to the applicable API standard.
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Foreword Nothing contained in any API publication is to be construed as granting any right, by implication or otherwise, for the manufacture, sale, or use of any method, apparatus, or product covered by letters patent. Neither should anything contained in the publication be construed as insuring anyone against liability for infringement of letters patent. This document was produced under API standardization procedures that ensure appropriate notification and participation in the developmental process and is designated as an API standard. Questions concerning the interpretation of the content of this publication or comments and questions concerning the procedures under which this publication was developed should be directed in writing to the Director of Standards, American Petroleum Institute, 1220 L Street, NW, Washington, DC 20005. Requests for permission to reproduce or translate all or any part of the material published herein should also be addressed to the director. Generally, API standards are reviewed and revised, reaffirmed, or withdrawn at least every five years. A one-time extension of up to two years may be added to this review cycle. Status of the publication can be ascertained from the API Standards Department, Department, telephone (202) 682-8000. 682-8000. A catalog of API publications publications and materials is published published annually by API, 1220 L Street, NW, Washington, DC 20005. Suggested revisions are invited and should be submitted to the Standards Department, API, 1220 L Street, NW, Washington, DC 20005,
[email protected].
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Contents Page
1
Scope Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2
Normativ Normative e Referen References ces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
3 3.1 3.2 3.3 3.4
Estimati Estimating ng Reason Reasonable able Worst-c Worst-case ase Short-te Short-term rm Emissi Emissions ons from an Indivi Individual dual Storage Storage Tank. . . . . . . . . . 1 Liquid Storage Storage Temperatur Temperature e . . . . . . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . .. . . . . . . . . . . .. . . 1 Product Product Stora Storage ge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Fixed-roof Fixed-roof Tanks Tanks (Vented (Vented to Atmosphere, Atmosphere, No Floating Floating Roof) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 FloatingFloating-roof roof Tanks Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4 4.1 4.2
Estimati Estimating ng Reason Reasonable able Worst-c Worst-case ase Short-te Short-term rm Emissi Emissions ons from a Batter Battery y of Stora Storage ge Tanks. Tanks. . . . . . . . . . 5 Overview Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Overlayin Overlaying g Equipme Equipment nt Limitati Limitations. ons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Annex A (informative) (informative) Limitations Limitations on Applicability Applicability to Actual Short-term Short-term Emission Emission Estimates Estimates . . . . . . . . . . . . . 7
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Introduction This Technical Report provides guidance on how to determine reasonable worst-case short-term hourly emissions from individual tanks and from a battery of tanks. Currently available estimation methodologies are based on factors that rely on averaging throughputs and meteorological conditions on a yearly or monthly frequency and may deviate significantly when compared to a reasonable worst-case short-term duration of hours to days. This guidance document presents a standardized approach for estimating reasonable worst-case short-term emissions, but it does not address estimation of actual short-term emissions (see Annex A for limitations on applying this methodology to actual scenarios). This short-term approach combined with the dispersion model will provide the user the ability to assess potential higher mass scenarios relative to yearly averages and can be used for process safety assessments, structure siting, area classifications, determining the need for additional controls, assessing risk of potentially elevated hazardous air pollutants (HAPs) from a confluence of conditions, and other possible concerns associated with short-term scenarios such as approach to lower explosive limit (LEL) or odor potential. Hourly and annual emissions are used in air dispersion models that evaluate a facility's risk against the National Ambient Air Quality Quality Standards Standards for for the purpose of issuing issuing construction construction and operating operating air permits. permits. Hourly Hourly emission emission rates rates are also used to evaluate whether or not there has been an emission increase to determine if a tank has been “modified” and has become subject to a New Source Performance Standard (NSPS) or a New Source Review (NSR). EPA's 2011 Refinery MACT Information Collection Request (ICR) Protocol required reporting “maximum hourly average emission rates” based on “the reasonable worst-case (high emission rate) situation,” but did not provide a methodology.
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Short-term Evaporative Loss Estimation from Atmospheric Storage Tanks Tanks 1
Scope
This Technical Report provides methodology on how to estimate short-term individual tank and facility-wide emissions. The methodology is intended to generate reasonable worst-case short-term emission estimates, and not necessarily an estimate of actual short-term emissions (see Annex A for limitations on applying this methodology to actual scenarios). The methodology is applicable to routine tank operations and not applicable to emissions associated with maintenance activities or tank roof landings. The methodology is applicable for estimating short-term emissions from tanks with fittings and seals in good condition and not applicable for tanks with damaged seals or roof fittings. Also, this methodology is not intended for situations where a tank has a malfunction, the emission controls are not working as intended, or there is other structural damage. The calculated mass emissions using this methodology can be used as input for short-term air dispersion modeling. The Technical Report does not provide guidance on applicability of any particular air dispersion models or modeling protocol.
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 ( Standards (MPMS MPMS)) Chapter 19.1, Evaporative Loss from Fixed-Roof Tanks, Tanks, 4th Edition, 2012. API MPMS Chapter MPMS Chapter 19.2, Evaporative Loss from Floating-Roof Tanks, Tanks, 3rd Edition, 2012. API MPMS Chapter MPMS Chapter 19.4, Evaporative Loss Reference Information and Speciation Methodology , 3rd Edition, 2012.
3
Estimating Reasonable Worst-case Short-term Emissions from an Individual Storage Tank
NOTE While units from these calculations are typically in pounds/year from the referenced API MPMS MPMS Ch. 19.1 and 19.2 standards, the short-term emissions durations are usually calculated on the order of hours to days. See Annex A for a more complete explanation of limitations.
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SHORT-TERM EVAPORATIVE LOSS ESTIMATION FROM ATMOSPHERIC STORAGE T ANKS
question, rather than the average daily ambient temperature, 0.5.The expression then becomes T LX =
T AA.
2
This is for the default condition of H s /D, equal to
0.4TMAX + 0.6TB + 0.005α I 2
where T LX
is the average daily maximum liquid surface temperature,
T MAX is
the average daily maximum ambient temperature (°R),
T B
is the average liquid bulk temperature (°R),
α
is the tank surface solar absorptance (dimensionless), and
I
is the average daily total insolation on a horizontal surface (Btu/(ft2 day)).
The variables should be evaluated as follows. T MAX is
determined from ambient temperature data for the month identified for each tank type below.
T B
is the average liquid bulk temperature for the month identified for each tank type below, which may be determined from actual measurements or process knowledge. In the event that the average liquid bulk temperature is not known, it may be estimated for tanks that are in nominal equilibrium with ambient conditions (see API MPMS Ch. MPMS Ch. 19.1, 4th Edition, Equation (12) or API MPMS Ch. MPMS Ch. 19.2, 3rd Edition, Equation (18)).
α
is determined from the tank color and surface condition (see API MPMS Ch. MPMS Ch. 19.4, 3rd Edition, Section 4.8).
I
is the average daily total insolation on a horizontal surface for the month identified for each tank type below (see API MPMS Ch. MPMS Ch. 19.4, 3rd Edition, Table 1).
Refer to API MPMS Ch. MPMS Ch. 19.1 for guidance on calculating the liquid surface temperature in an insulated tank.
3.2
Product Storage
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3
API T ECHNICAL REPORT 2576
3.3
Fixed-roof Tanks Tanks (Vented to Atmosphere, No Floating Roof)
The maximum short-term emission rate, L MAX , is to be determined using the working loss, LW , which is calculated with the throughput based on the maximum filling rate and with the turnover (saturation) factor, K N , set equal to 1. The liquid surface temperature is to be set using the liquid surface temperature equation in 3.1. An annual working loss, MPMS Ch. 19.1 equations. If the tank stores different stocks during the course LW , can then be determined from API MPMS Ch. of a year, then each stock should be evaluated separately. Given that the working loss would typically be the dominant mechanism driving short-term emission rates for fixed-roof tanks, the calculation of short-term emission rates for typically controlled fixed-roof tanks without vapor recovery may be based on only the working loss. (i.e. the standing loss may be neglected). Follow the following steps. Step 1: Use API MPMS Ch. MPMS Ch. 19.1, Section 4.3.1, Equation (21)5 to calculate annual working loss, LW , with: —
throughput calculated from the maximum filling rate,
—
the turnover (saturation) factor, K N , set to 1.0,
—
the product factor, Kc, for crude oil stocks is set to 1.0, and
—
the liquid surface temperature determined from 3.1 of this document.
Step 2: Divide this annual annual working working loss by 8760 8760 hr/yr to obtain the the maximum short-term short-term emission emission rate, L MAX .
3.4 3.4.1
Floating-roof Floating-r oof Tanks Overview
For floating-roof tanks, the type of floating-roof construction, including all deck fitting data, has to be known in order to accurately estimate emissions. The short-term emission rate for floating-roof tanks is based on the highest monthly average emission rate for standing loss coupled with the maximum pumping rate for working loss. If the tank stores different stocks during the course of a year, then each stock should be evaluated separately for the portion of the year it is stored (e.g. summer and winter gasoline).
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SHORT-TERM EVAPORATIVE LOSS ESTIMATION FROM ATMOSPHERIC STORAGE T ANKS
3.4.2
4
Internal Floating-roof Tanks (and Domed External Floating-roof Tanks) Tanks)
For an internal floating-roof tank (or domed external floating-roof tank), standing losses are estimated as a fairly steady-state process of vapors escaping past the floating roof to the headspace above. When estimating short-term emissions, however, the concern is the rate at which the vapors leave the tank. This rate will be maximized when the tank is being filled. On the other hand, working (withdrawal) losses occur while the tank is being emptied. In that both fill and withdrawal rates can affect short-term emission rates for an internal floating-roof tank, the maximum short-term working loss, LWD, for these tanks shall be calculated with the throughput based on the greater of the maximum fill rate or the maximum withdrawal rate. The maximum short-term standing loss, LS , for an internal floating-roof tank is taken as the highest average monthly standing loss rate. In that emissions from an internal floating-roof tank (or domed external floating-roof tank) are not wind dependent, the highest average monthly standing loss rate for these tanks will occur during the warmest month. Follow the following steps. Step 1: Calculate the maximum short-term working loss rate, LWD. Use API MPMS Ch. MPMS Ch. 19.2, Section 4.3.1 6 to calculate annual working loss, LW , with: —
throughput calculated from the greater of the maximum fill rate or the maximum withdrawal rate;
—
select the month with the highest average temperature and determine the liquid surface temperature from 3.1;
—
divide this annual working loss by 8760 hr/yr to obtain the maximum short-term working loss rate, LWD.
Step 2: Calculate the maximum short-term standing loss rate, LS . —
Use the API MPMS Ch. MPMS Ch. 19.2, Section 4.2.1, Equation (2) 5 to calculate standing loss for the rim seal, deck fittings, and deck seams (if bolted) on a monthly basis; the product factor, Kc, for crude oil stocks is set to 0.6;
—
select the month with the highest average temperature and determine the liquid surface temperature from 3.1;
—
divide this maximum monthly standing loss rate by the number of hours in the month to obtain the maximum
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5
API T ECHNICAL REPORT 2576
3.4.3.2
Wind Speed
The function of the fixed roof on an internal floating-roof tank and a domed external floating-roof tank is not to act as a vapor barrier, but to block the wind. Wind speed is a large contributor to emissions for external floating-roof tanks from the rim seals and deck fittings. Higher wind speeds will generate more emissions, but will also induce more dispersion. Lower wind speeds will generally have lesser emissions but with less dispersion. Seasonal archived wind data may be available from an airport or other local source, or from archived sources such as the United States National Solar Radiation Data Base (http://rredc.nrel.gov/solar/old_data/nsrdb/), or internationally, the NASA Surface Meteorology and Solar Energy Data Set (http://eosweb.larc.nasa.gov/sse/), or from API MPMS Ch. 19.4, 3rd Edition, Table 1. Follow the following steps. Step 1: Calculate the maximum short-term working loss rate, LWD. Use API MPMS Ch. MPMS Ch. 19.2, Section 4.3.1, Equation (19) 5 to calculate annual working loss, LW , with: —
throughput calculated from the maximum withdrawal rate;
—
liquid surface temperature, as determined from 3.1, for the month selected for standing loss in Step 2 below;
—
divide this annual working loss by 8760 hr/yr to obtain the maximum short-term working loss rate, LWD.
Step 2: Calculate the maximum short-term standing loss rate, LS .
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SHORT-TERM EVAPORATIVE LOSS ESTIMATION FROM ATMOSPHERIC STORAGE T ANKS
4.2.2
6
Pumps
Available Available pumps for a site at any given time should be considered considered when evaluating evaluating site-wide hourly emissions. emissions. Actively working tanks tanks should should be restricted restricted to the the number of both inbound inbound and and outbound outbound pumps available available for for floatingroof tanks, and inbound pumps for fixed-roof tanks. Product transfer configurations vary and pumps may not be located at each tank or available for all tanks, so assuming that all tanks are “working” would grossly overestimate the short-term emissions from the site. 4.2.3
Piping Availability
Available Available piping for a site at any given time should be considered considered when evaluating evaluating site-wide short-term emissions. emissions. Similar to pumps, tanks may be manifolded together and share inbound/outbound lines. Actively working tanks should be restricted to the volume of transfer capacity in the number of outbound pipes available for floating-roof tanks and inbound pipes for fixed-roof tanks. The piping availability should be overlaid with the pump availability and the restricting parameters should prevail. 4.2.4
Control Device
A control control device used either at the point of transfer or to control roof landing should be evaluated for availability availability and capacity/pump rates. There is often a limited number of control devices at a site with a restricted pump rate that should be considered when evaluate site-wide short-term emissions. 4.2.5
Combined Process Restrictions
The piping availability should be overlaid with the pump availability and control device availability/pump rate and the
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Annex A (informative) Limitations on Applicability to Actual Short-term Emission Estimates The methodology in this technical report is expressly intended for estimating a short-term emission rate in the hypothetical case of a reasonable worst-case scenario and not for estimating actual short-term emission rates. The methodology relies on the equations in the API MPMS Ch. MPMS Ch. 19 series of standards, which are intended for estimating routine annual emissions. There are numerous issues that render the equations in the API MPMS Ch. MPMS Ch. 19 standards inappropriate for time periods shorter than one month, as noted below. However, these equations may be applied to a hypothetical reasonable worst-case scenario, in that parameters may be assigned values for a hypothetical scenario that are not necessarily representative of reality. Compliance with a short-term emissions limit can be demonstrated by showing that none of the parameter values in the “reasonable worst-case scenario” have been exceeded, such as maximum monthly average TVP and pump rate. Situations may exist where a facility may have exceeded one of the parameters for a tank, but wanted to run the equation to show that they had not exceeded the emission limit. For the demonstration noted above, it is important to have an equal basis of comparison. Consequently, the Kc product factors for crude oil stocks should be selected to match the permit or compliance Kc factors used in 19.1 and 19.2 at 0.75 for fixed-roof tanks and 0.4 for floating-roof tanks. While use of the short-term equation can be used to check compliance, it would not be characterized as a calculation of the “actual” short-term emission rate. Rather, it would be characterized as having compared the combined effects of parameters X, Y, and Z (e.g. pump rate, liquid bulk temperature and ambient temperature) and demonstrates that
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SHORT-TERM EVAPORATIVE LOSS ESTIMATION FROM ATMOSPHERIC STORAGE T ANKS
8
b) Changes in the liquid bulk temperature. The parameters that are accounted for as variables in the equations for routine emissions are evaluated in a manner that does not account for short-term phenomena. For example, calculations of temperature variables in the equations for routine emissions are based on the liquid and vapor phases within the tank having achieved a state of thermal equilibrium. The calculations do not, however, account for how long it may take for thermal equilibrium to be achieved after there has been a change in the thermal balance, such as the receipt of a batch of liquid. It is demonstrated in API MPMS Ch.19.4, MPMS Ch.19.4, Annex I, Sections 2.1, 3.3, and 3.4.8 that a typical time period for approaching thermal equilibrium may be approximately nine days and thus a tank that has received liquid within the prior nine days would be expected to not be in thermal equilibrium. c) Changes in ambient temperature. As temperature. As ambient temperature changes, there would be an associated change in the vapor space temperature and subsequently in the liquid surface temperature. There would, however, be a time lag between a change in the ambient temperature and the associated change in the liquid surface temperature. This time lag is deemed inconsequential for the estimation of annual or monthly emissions, but would be expected to be more significant for shorter periods of time. Shorter time periods would also be more significantly influenced by abrupt short-term meteorological phenomena, such as cooling due to cloud cover or precipitation. d) Saturation factors. factors. The saturation level of vapors in the headspace of a fixed roof tank is a similarly timedependent phenomenon. The equations for routine emissions do not fully account for the time lag required to achieve saturation equilibrium in response to short-term fluctuations in the values of applicable parameters. e) Vapor expansion rate. The calculation of standing loss for a fixed-roof tank is based on the total amount of vapor expansion that is expected to occur between the coolest night time temperature and the warmest day time temperature. The equation does not, however, calculate the hourly rate at which the vapor expansion takes place or the distribution of vapor expansion over the course of a day. This hourly rate would be dependent on several of the variables noted in (a) above, as well as on whether the tank shell is insulated. As discussed in API MPMS Ch. 19.1 Section 4.2.1, a fixed-roof tank with an insulated shell but an uninsulated roof would be expected to have
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9
API T ECHNICAL REPORT 2576
k) Vapor space outage. The outage. The calculation of standing loss for a fixed-roof tank is based on an assumed vapor space outage corresponding to the average liquid height. However, at any given point in time the tank may be nearly empty or nearly full, thus resulting in very different scenarios of vapor space outage. For example, if the vapor space expansion factor is 0.15, that indicates 15 % of the vapor space will be expelled by daytime warming, and expelling 15 % of the vapor space when the tank is nearly empty would constitute a far greater volume than 15 % of the vapor space when the tank is nearly full. l)
Vented vapor saturation factor. The factor. The saturation factor used in the calculation of standing loss for a fixed-roof tank is similarly dependent on the vapor space outage. Annual emission estimates are based on the average liquid height, but the calculation would indicate lower vapor saturation when the tank is nearly empty and higher vapor saturation when the tank is nearly full.
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