i

بسم هللا الرحمن الرحيم

University of Khartoum

Faculty of Engineering

Mechanical Engineering Department

Gasoline Vapour Recovery

A thesis submitted in partial fulfillment of the requirements for the

degree of B.Sc. in Mechanical Engineering

Presented by:

1/Mohamed Ahmed Elsamani 2/ Mohamed Elfadil Elwadie

Supervised by:

Dr. Salah Ahmed Abdallah

August 2015

ii

Dedication

We dedicate this research with much love and

appreciation:

To the candles of our lives our beloved mothers who have

always been there for us.

To our fathers who have always been the brick walls on

whom we can lean and depend on forever.

To our brothers and sisters who mean the world to us.

To our friends, family, colleagues and teachers past and

present to everyone that we love.

iii

Acknowledgments

We would like to express my gratitude to all those who

gave us the possibility to complete this research .We

deeply indebted would like to express our great thanks to

our supervisor dr. Salah Ahmed Abdullah who helped,

stimulating suggestions and encouragement helped us

in all time of the research. His guidance, his support and

his great knowledge and experience have given us the real

accelerating power to complete this research .Of course we

can’t forget the great help and effort from Petronas &

HAM companies for advices and engineering works

.they were always cooperative and ready to help at any

time. They supported us all the way through. They

showed great care, interest and patience. Many thanks to

them.

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Abstract

Gasoline emissions in service station is one of the biggest issues that people are not

taking it under consideration especially in Sudan , because the rate of the gasoline

emissions are very high backs to the high temperature rates. Gasoline emissions should

also be taking seriously because the high value of gasoline. These emissions contribute to

the formation of smog and the control of these emissions has been applied internationally

for some years. Vapor recovery is the preferred control technology after prevention and

minimization.

The application of vapor recovery of gasoline in Sudan has never been used. Gasoline

loading data and vapor analyses date were used to determine the theoretical and

experimental filling emissions from underground tanks in three different service stations

in Khartoum:

1/Al-Oshra station.

2/Jabl Awleya station.

3/Dar AL Salam station.

The average evaporative emission per year in each station were (13800.04 liter/year),

(8822.02 liter/year) and (7825.46 liter/year) respectively.

From These values of gasoline emissions it shows that the economic losses are very high

with a range of 30000- 60000 SDG per year. So the application of Vapor recovery

System should be applied in Sudan to minimize the Gasoline losses in service stations.

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Table of contents

Introduction ....................................................................................................................... 2

Literature review .............................................................................................................. 5

2.1 Introduction ............................................................................................................. 5

2.2 Evaporative emissions ............................................................................................. 9

2.2.1 Displacement emissions .................................................................................... 9

2.2.2 Breathing and withdrawal emissions .............................................................. 9

2.2.3 Filling emissions ................................................................................................ 9

2.4 Control of emissions .............................................................................................. 11

2.4.1 Emission prevention and minimization ........................................................ 11

2.4.2 Vapor recovery ............................................................................................... 12

3.1 Introduction ........................................................................................................... 25

3.2 Working loss .......................................................................................................... 25

Working losses occur when the vapor in the vapor space over the liquid is displaced

from the tank by the addition of organic liquid during tank filling. .............................. 25

3.3 Breathing loss......................................................................................................... 27

3.4 Assumptions & givens ........................................................................................... 32

3.5 Sample of calculations ........................................................................................... 32

3.5.1 Working loss .................................................................................................... 32

3.5.2 Breathing loss .................................................................................................. 33

4.1 Results ........................................................................................................................ 35

5.1 Conclusions ................................................................................................................ 38

5.2 Recommendations ..................................................................................................... 38

References ........................................................................................................................ 39

Appendix A ...................................................................................................................... 40

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List of abbreviations

BAT Best Available Technology/Technique

EPA Environmental Protection Agency

GLO Ground Level Ozone

PLV Preloading Vapor

POCP Photochemical Ozone Creation Potential

RVP Reid Vapor Pressure

TOMA Tropospheric Ozone Management

VOCs Volatile Organic Compounds

VRU Vapor Recovery Unit

UNECE United Nations Economic Commission for Europe

vii

List of Figures

Figure 2.1 typical gasoline distribution system. …………………………….……… 5

Figure 2.2 typical gasoline distribution system. ............................................................. 9

Figure 2.3 compression-refrigeration-absorption unit by Parker Hannifin ............. 13

Figure 2.4 compression-refrigeration-absorption by Rheem Superior ..................... 14

Figure 2.5 compression-refrigeration-condensation unit by GESCO ........................ 16

Figure 2.6 compression-refrigeration-condensation unit by VAPOREX .................. 17

Figure 2.7 refrigeration vapor recovery unit by Edwards .......................................... 19

Figure 2.8 Lean oil absorption system by Southwest Industries ................................ 20

Figure 2.9 Flow diagram of a membrane gasoline-vapor recovery unit suited to a

retail gasoline station tank vent. .................................................................................... 23

viii

List of tables

Table 2.1 typical gasoline vapor composition (only VOC)…………………………7

Table 4.1 comparison of results between the three service stations ………………35

1

Chapter one

Introduction

2

1.1 Introduction

Gasoline is a transparent, petroleum-derived liquid that is used primarily as a fuel in

internal combustion engines. It consists mostly of organic compounds obtained by the

fractional distillation of petroleum, enhanced with a variety of additives. A 42-gallon

barrel of crude oil yields about 19 gallons of gasoline, when processed in an oil refinery.

Gasoline, as used worldwide in the vast number of internal combustion engines used in

transport and industry, has a significant impact on the environment, both in local effects

(e.g., smog) and in global effects (e.g., effect on the climate). Gasoline may also enter the

environment uncombusted, as liquid and as vapors, from leakage and handling during

production, transport and delivery, from storage tanks, from spills, etc.

Volatile organic compounds (VOCs) are among the most common air pollutants emitted

by chemical process industries, and include hydrocarbons such as olefins, paraffin and

aromatics. VOCs adversely affect air quality as it is one of the precursors of ground level

ozone (GLO), the primary component of smog. It can also have a negative impact on

human health due to its toxicity. During gasoline storage and distribution, VOCs are

emitted due to evaporation, where the rate of evaporation depends on factors such as the

vapor pressure of the liquid, temperature and turbulence.

Besides being an environmental hazard, these fugitive VOCs emissions actually cost a lot

money. So by minimizing the escaped vapors from bulk storage at marketing depot and

the storage tank at service station we maximize the profits of the owners of the marketing

depot and the service station.

Vapor recovery of gasoline is used extensively in Europe and the United States of

America, with legislation to enforce its use. In Sudan little attention has been given to

VOC control in general, and the use of vapor recovery systems in particular.

The objectives of this dissertation are to:

3

Evaluate vapor recovery systems used in first world countries for the control of

VOC emissions from gasoline,

Determine evaporative losses from the storage tank at service station.

In this dissertation the evaluation of vapor recovery systems and related terminology was

conducted via a literature review and is presented in Chapter 2. Methodology and

calculation of losses from the storage tank at service station in Chapter 3, followed by a

discussion of the results in Chapter 4. Conclusions and recommendations are presented in

Chapter 5

4

Chapter two

Literature review

5

Literature review

2.1 Introduction

Gasoline is a commodity used worldwide. During its use, carbon dioxide, nitrous oxides

and hydrocarbons are emitted as a result of combustion processes taking place in a

vehicle. Further emissions, consisting of hydrocarbons, take place during the storage and

distribution of gasoline due to evaporation.

The hydrocarbons emitted during gasoline storage and distribution can be broadly

classified as volatile organic compounds (VOCs). VOCs make up a major class of air

pollutants and is a brad collective term for different organic compounds. These include

pure hydrocarbons, partially oxidized hydrocarbons and organics containing chlorine,

Sulphur and nitrogen; with most VOCs being toxic and/or carcinogenic (Jo and Song,

2001).

According to Jeffery (1998), there is some discrepancy in the definition of VOCs used in

international legislation. In the United States of America a VOC is defined as any

compound of carbon that participates in atmospheric photo chemical reaction, excluding

carbon monoxide, carbon dioxide, carbonic acid, metallic carbides and carbonates and

ammonium carbonate. The United Nations Economic Commission for Europe (UNECE)

classifies VOCs based on their photochemical ozone creation potential (POCP). POCP is

defined as the change in photo chemical ozone production due to change in emission of a

particular VOC and can be determined by photochemical model calculation or laboratory

experiments (Jeffery, 1998).

In the presence of sunlight, VOCs react with nitrogen oxides forming photochemical

oxidants such as ozone. Ground level ozone (GLO) is a major component in the

formation of smog, can migrate great distances and is a known greenhouse gas. Smog

also adversely affects human health, vegetation and materials. Although VOCs and

nitrogen oxides occur naturally, anthropogenic sources have greatly increased the

concentration in the atmosphere. According to Sangster (1991), VOC emissions originate

from:

Industrial and domestic solvents (40%);

Exhaust gases from motor vehicles (25%);

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Evaporative and running losses from motor vehicles (10%);

Gasoline distribution (3%);

Vehicle refueling (2%);

Oil refining (3%); and

17% from other sources.

Although gasoline distribution and vehicle refueling contributes to only 5% of the total

VOC emissions, these emissions are concentrated at gasoline bulk storage facilities and

service station, highly frequented by people.

A typical gasoline distribution system is shown in Figure 2.1. In Sudan pipelines are

mainly used for the transportation of gasoline from product storage facilities at refineries

to bulk storage tanks at marketing depots. From the marketing depots road tankers are

used to transport the gasoline to the service stations.

Figure 2.1 typical gasoline distribution system.

7

The control of emissions that occur during the transportation of gasoline from bulk

storage facilities to the ultimate consumer is represented by three stages, namely (Figure

2.2):

Stage Ia involves the control of emissions that occur at facilities when road

tankers are loaded;

Stage Ib involves the control of emissions that occur when road tankers unload

into service station storage tanks; and

Stage II involves the control of emissions that are formed during vehicle

refueling.

During each of these stages evaporation losses occur, as shown in Figure 2.2.

Evaporation occurs whenever gasoline is introduced into a tank that has a vapor space

(Hadley et al., 1978). Unless the resultant vapor (a VOC/air mixture) is contained or

suppressed by some means, a loss of product results. The VOC composition of gasoline

vapor; gasoline being a mixture of compounds with different boiling points with the

tendency of the lower molecular weight compounds to evaporate; is shown in Table 2.1

(Hansen, 1996).

Table 2.1 Typical gasoline vapor composition (only VOC)

Compound Volume

Ethane Traces

Propane 1.5 %

Isobutene 8 %

n-Butane 10 %

Pentane 14 %

Benzene 5000 ppm

Hexane and others 6 %

TOTAL

(VOC only, remainder is air)

40 %

8

9

Figure 2.2

2.2 Evaporative emissions According to Hadley et al. (1978), the average emission from a typical European gasoline

storage and distribution system, as shown in Figure 2.2 is 0.56 volume % of the gasoline

distributed. Therefore, for every 1000 liters of gasoline distributed (that is, gasoline from

the bulk storage facilities to the remainder of the distribution system); 5.6 liters are lost to

the atmosphere through evaporative emissions. These emissions can be divided into four

types, namely displacement, breathing and withdrawal, filling and refueling emissions.

2.2.1 Displacement emissions Displacement emissions occur from fixed roof storage facilities (bulk storage tanks), as

well as underground service station tanks due to vapor displacement emissions from fixed

roof storage facilities account for0.14 % (vol.%) and from service station storage tanks

for 0.16 % of the total emissions losses (0.56%) from gasoline storage and distribution

systems (Hadley et al., 1978).

2.2.2 Breathing and withdrawal emissions Breathing emissions are caused by variations in tank contents, temperature and by

changes in barometric pressures that cause expansion and contraction to the liquid and

vapor in a tank. Withdrawal emissions occur when gasoline is pumped out of a storage

tank resulting in the intake of air through pressure/vacuum relief valves or vents. The

incoming air will dilute the VOC/air mixture previously contained in the tank, resulting

in an increase in evaporation to restore the equilibrium. Breathing and withdrawal

emissions from bulk storage tanks account for 0.02% and from service station storage

tanks for 0.01% of total emission losses. Breathing and withdrawal emissions from

tankers are not significant due to the relatively short transit times (Hadley et al., 1978).

2.2.3 Filling emissions Filling emissions occur when gasoline is transferred from storage tanks to road tankers.

Hadley et al. (1978) identified two types of vapor making up filling emissions, namely

preloading vapor (PLV) and evolution vapor (𝑉𝑒).

PLV is residual vapor originating from a tank’s previous contents, being displaced by

loading of the new product.

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Evolution vapor (𝑉𝑒) evaporates from the product itself when it is being loaded. Petrol

can be loaded into a road tanker via top splash loading, submerged top loading or bottom

loading. Most 𝑉𝑒 evaporation takes place during splash loading when the turbulence in a

tank is at its peak.

2.2.4 Emissions from vehicle refueling

When a motor vehicle is being refueled at a service station the incoming gasoline

displaces the gasoline vapor in the fuel tank, causing it to escape into the atmosphere.

These emissions contribute to 0.18 volume % of the total emissions from gasoline storage

and distribution systems (Hadley et al., 1978).

2.3 Factors affecting evaporation

The main factors affecting evaporation are product (liquid gasoline) properties,

liquid/vapor interface areas and turbulence in the relevant liquid and vapor. Product

properties that play a role during evaporation are vapor pressure and temperature. The

higher either the vapor pressure and/or the temperature of a liquid, the higher the

expected rate of evaporation. The vapor pressure of a petroleum product can be

determined by using the Reid vapor pressure (RVP) method where RVP is also a generic

term used for gasoline volatility (EPA, 2003a). RVP is a standard laboratory method that

measures the Reid vapor pressure of a substance at a temperature of 100◦F, or 37.8 ◦C

(Hadley et al., 1978). The RVP is about 10% less than the true vapor pressure. Appendix

A shows a nomogram for the determination of true vapor pressure from RVP at any

temperature for different petroleum products (EPA, 2006b).

The rate of evaporation is also proportional to the area of the liquid/vapor interface. By

decreasing the liquid/vapor interface area, the amount of evaporation will decrease due to

the limited amount of vapor space above the liquid (Hadley et al., 1978).

Turbulence in the liquid and/or vapor will increase the rate of evaporation and reduces

the time necessary to reach 100% saturation in the vapor space via two mechanisms

(Hadley et al., 1978). When light hydrocarbons evaporate, the thin liquid surface layer

becomes momentarily deficient in these molecules, slowing the rate of evaporation.

However, when fresh gasoline is loaded, the light hydrocarbons move to this region via

diffusion and evaporation continues. This process is accelerated by mixing and/or

turbulence in the liquid.

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In the vapor space above the liquid, the hydrocarbons molecules are heavier than air and

tend to accumulate as a layer just above the liquid surface, suppressing further

evaporation (Hadley et al., 1978). Turbulent movements in the vapor space cause by

thermal convection currents or pressure vacuum valve air intakes accelerate evaporation.

2.4 Control of emissions Emissions from gasoline storage and distribution systems can be controlled in four

methods. The methods are prevention, minimization, recovery and finally treatment. The

treatment will not be addressed in this dissertation.

2.4.1 Emission prevention and minimization The same techniques are followed in both the prevention and minimization of emissions.

These include decreasing the volatility of gasoline (by lowering RVP or introducing RVP

limits) and its temperature, vapor balancing, minimizing the liquid/vapor interface area

and reducing turbulence.

It is common practice in large parts of Europe and North America to blend gasoline to a

predetermined RVP limit, depending on the season (Kojima and Mayorga-Alba, 1998).

Although there has been a move in lowering the RVP limits generally, lower limits exist

to avoid combustion problems in motor vehicles (Hansen, 1996).

Lowering the temperature that gasoline is stored at will decrease the true vapor pressure

and therefore decrease the amount of evaporation. Methods in reducing gasoline

temperature include painting of storage tanks in sun reflecting colors (for example, silver

and white) and the use of underground storage tanks.

Vapor balancing involves a vapor retrieval system whereby vapor displaced from

tanks/tankers receiving gasoline is returned to the tanks/tankers delivering gasoline. For

example, vapor formed during vehicle refueling is rerouted back to the service station

storage tank. The liquid inside the service station storage tank will only evaporate until

the vapor in the air space above liquid reaches a certain pressure, therefore less

evaporation will occur due to the returned vapor (Jeffery, 1998).

The use of floating covers in storage tanks prevents contact between the product and air,

thereby decreasing the liquid/vapor interface area and therefor evaporation. According to

Hadley et al. (1978), this can reduce or even prevent displacement, withdrawal and

breathing emissions. As evaporation is either bottom or submerged top loading, instead of

top splash loading; will reduce turbulence and therefore evaporation.

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2.4.2 Vapor recovery In this dissertation we are interested in the vapor recovery for underground tanks in

service stations. There are five vapor recovery systems, this section reviews the vapor

recovery systems applicable to bulk terminals and assesses the efficiency, reliability,

safety and manufacturing capacity of these systems.

2.4.2.1 Compression-Refrigeration-Absorption Systems

The compression-refrigeration-absorption vapor recovery system (CRA) is based

on the absorption of gasoline vapors under pressure with cool gasoline from storage. The

primary unit in CRA systems is the absorber with the remaining components serving to

condition the vapor and liquid entering the absorber, improve absorber efficiency, reduce

thermal losses, and/or improve system safety.

Figures 2.3 and 2.4 show two CRA vapor recovery systems. Incoming vapors are first

passed through a saturator where they are sprayed with fuel to insure that the

hydrocarbon concentration of the vapors is above the explosive level. This is done as a

safety measure to reduce the hazards of compressing hydrocarbon vapors.

The partially saturated vapors are then compressed and cooled prior to entering the

absorber. In the absorber the cooled, compressed vapors are contacted by chilled

gasoline drawn from product storage and are absorbed. The remaining air containing

only a small amount of hydrocarbons is vented from the top of the absorber and gasoline

enriched with light ends is withdrawn from the bottom of the absorber and returned to the

fuel storage tanks. The operating conditions in the absorber vary with the manufacturer,

and range from -10°F to ambient temperature and from 45 psig to 210 psig. Although

dependent on terminal operating schedules and vapor storage capacity.

13

Figure 2.3 compression-refrigeration-absorption unit by Parker Hannifin

14

Figure 2.4 compression-refrigeration-absorption by Rheem Superior

The vapor collection efficiency of a CRA vapor recovery unit is difficult to define due to

its dependency on inlet hydrocarbon concentration. The outlet hydrocarbon

concentration, however, is essentially fixed by the absorber operating conditions. Field

tests have shown it to range from 1% to 4.5%, by volume. Current CRA systems on the

market can surpass 90% recovery (if so required) for inlet hydrocarbon concentrations

GJ: greater than 20% by volume. One CRA unit supplies a booster compressor to achieve

90% recovery at lower inlet hydrocarbon concentrations.

2.4.2.2 Compression-Refrigeration-Condensation Systems

Compression-Refrigeration-Condensation vapor recovery systems (CRC) were

the first type utilized by the petroleum industry. They are based on the condensation of

hydrocarbon vapors by compression and refrigeration. Figures 2.5 and 2.6 show the flow

scheme of two CRC systems. Incoming vapors are first contacted with recovered product

in a saturator, and are saturated beyond the flammability range.

The saturated vapors are then compressed in a two-stage compressor with an

inter-cooler. Condensate is withdrawn from the inter-cooler prior to second stage

compression. The compressed vapors pass through a condenser where they are cooled,

15

condensed, and returned along with condensate from the inter-cooler to the gasoline

storage tank. Essentially, hydrocarbon-free air is vented from the top of the condenser.

Each manufacturer has minor variations from this basic flow scheme.

Operation conditions vary with the manufacturer, with temperatures ranging

from -10°F to 30°F and pressures ranging from 85 psig to 410 psig. Although dependent

on terminal operating schedules and vapor storage capacity.

The efficiencies of CRC vapor recovery units are not well documented and

difficult to define due to their dependency on inlet hydrocarbon concentrations. Data

from field tests indicate that CRC units can recover 96% of the hydrocarbons in saturated

gasoline vapors and 8870 to 90% of the hydrocarbons in sub saturated gasoline vapors

from bottom loading operations. Vendors claim that adjustments and optional equipment

can improve the efficiency of CRC systems to a minimum recovery of 94.

16

Figure 2.5 compression-refrigeration-condensation unit by GESCO

17

Figure 2.6 compression-refrigeration-condensation unit by VAPOREX

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2.4.2.3 Refrigeration Systems

One of the vapor recovery systems is the straight refrigeration system, based on the

condensation of gasoline vapors by refrigeration at atmospheric pressure.

Figure 2.7 shows the flow scheme of such a system. Vapors displaced from the

terminal enter a horizontal fin-tube condenser where they are cooled to -100°F and

condensed. Because vapors are treated on demand, no vapor holder is required.

Condensate is withdrawn from the condenser bottom and the remaining air, containing

only a small amount of hydrocarbon, is vented from the condenser top. Cooling for the

condenser coils is supplied by a methyl chloride reservoir. A two-stage refrigeration unit

is used to refrigerate the stored brine solution to between -105°F a 125° F.

The vapor recovery efficiency of refrigeration systems is again dependent on the

hydrocarbon concentration of the inlet vapors. Field tests of a unit with a condenser

temperature of -100°F indicate the outlet hydrocarbon concentration is relatively fixed by

the condenser temperature at 0.6% to 2.6% by volume. Typical hydrocarbon recoveries

are 93% to 97% with recoveries reaching 99% for saturated inlet vapors.

19

Figure 2.7 refrigeration vapor recovery unit by Edwards

2.4.2.4 Lean oil absorption systems

The lean oil absorption (LOA) vapor recovery system is based on the absorption of

gasoline vapors into lean gasoline stripped of light ends.

Figure 2.8 is a flow scheme of a LOA vapor recovery system. Gasoline vapors

from the terminal are displaced through the packed absorber column where they are

absorbed by cascading lean gasoline (termed sponge oil or lean air at atmospheric

temperature and pressure. Stripped air is vented from the top of the absorber column.

The enriched gasoline is returned to storage. Lean gasoline for the absorber is generated

by heating gasoline from the storage tanks and evaporating off the light ends. The

20

separated light ends are compressed, condensed, and returned to storage, and the lean

gasoline is stored separately for use in the absorption column.

The vapor recovery efficiency of LOA systems is dependent on the liquid to

vapor ratio in the absorber and on the hydrocarbon content of the inlet vapors. The

manufacturer reports that normal practice is to adjust the lean oil feed rate to the absorber

such that the hydrocarbon content of the stripped air is 370 by volume. This corresponds

to a 907o or greater recovery for inlet hydrocarbon concentrations of 247° or greater.

Higher lean oil rates are used when improved recovery is required

Figure 2.8 Lean oil absorption system by Southwest Industries

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2.4.2.5 Operating Reliability

The operating reliability of terminal vapor recovery systems is generally

good. The technology is proven through use by industry over two decades. Companies

using CRA and CRC units report average downtime for properly maintained units is

about one week per year. Freezing problems have occurred with CRA, CRC, and

refrigeration systems where the vapors are subject to temperatures below 32°F. Water

vapor contained in the air freezes in the system, hindering heat transfer and clogging

lines. The two solutions to this problem have been:

Include an automatic defrost cycle which shuts down part of the system during off

periods and allows for defrosting the iced sections.

Inject methanol into the system to lower the freezing point of the aqueous layer.

Both solutions to the icing problems generally work well, however, isolated problems

with icing still occur. Another major source of problems in CRA and CRC systems is the

gasoline vapor compressor. Compressors handling heterogeneous mixtures of air, light

hydrocarbons, and water vapor have maintenance problems in rotors and bearings

normally encountered with closed loop refrigerant compressors. There have also been

reports that some lean oil absorption units are experiencing problems in obtaining

adequately stripped lean oil feed to the absorber.

2.4.2.6 Safety

Safety is always of paramount importance in designing equipment to handle flammable

materials. The manufacturers of vapor recovery equipment have been conscious of this,

and have included safety features in their designs. ORC, and CRA units have potential

safety problems whenever explosive hydrocarbon mixtures are being stored and

processed. To eliminate the possibility of explosion, these units are generally equipped

with means to saturate the incoming vapor stream which raises the hydrocarbon content

above the explosive Refrigeration systems generally operate at temperatures which

explosions are a threat. CRA and CRC systems have the problem of compressing

hydrocarbon vapors. The adiabatic heat of compression increases the outlet gas

temperature to the point where it is much more easily ignited than is the cooler inlet

vapors. Compression ratios and the corresponding outlet gas temperatures must be

maintained at levels low enough to prevent excessive heating and spontaneous

combustion.

Another potential safety problem in systems employing vapor holders has been leakage

creating explosive mixtures in the air space above the diaphragm. Regularly maintained

22

and inspected diaphragms should pose no safety problems. Because these are largely

custom made, none of the vapor recovery systems currently have obtained Underwriters

Laboratory approval.

2.4.2.7 Manufacturing Capacity

The manufacturing capacity and installation time of the vapor recovery industry is

dependent on the availability of supplies, equipment, contractors, labor, and weather.

Recent estimates by the top eight manufacturers are that their yearly production rate is

four to five hundred units although this rate could be expanded if the need arises. CRA

and CRC manufacturers have a nine to twelve month delivery time, while manufacturers

of refrigeration and LOA, units report six month delivery times. These manufacturing

capacities and delivery times may be optimistic in light of the current economic situation

and material shortages.

2.4.2.8 Summary

The four major types of vapor recovery systems for terminals are compression-

refrigeration-absorption, compression refrigeration-condensation, straight refrigeration

and lean oil absorption. The technology of each system is well developed. Each of these

vapor recovery systems are capable of meeting 90% recovery although some may require

adjustments or additional equipment to meet 90% recovery on inlet streams having a very

low hydrocarbon concentration. The reliability of vapor recovery units for bulk terminals

is good and is continuously being improved. Future stream factors, assuming proper

maintenance should be in the 95% category

2.4.2.9 Membrane separation system

Beside all the previous vapor recovery systems. A simple and small vapor recovery

system has been made to do the exact work of separating the gasoline from the vapor

mixture with lower cost.it called membrane separation system.

In the last few years, several hundred retail gasoline stations have installed small

membrane systems to treat their tank vents. A flow scheme of this type of system is

shown in Figure 2.9. Air from the gas station dispenser is collected and sent to the

gasoline storage tank. When the pressure in the tank reaches a preset value, a pressure

switch activates a small compressor that draws off excess vapor-laden air. A portion of

the hydrocarbon vapors condense and is returned to the tank as a liquid. The remaining

hydrocarbons permeate the membrane and are returned to the tank as concentrated vapor.

Air, stripped of 95-99% of the hydrocarbons, is vented. In addition to eliminating

23

hydrocarbon emissions, the unit essentially pays for itself with the value of the recovered

gasoline.

Figure 2.9 Flow diagram of a membrane gasoline-vapor recovery unit suited to a retail gasoline station tank vent.

Typical systems are small, containing a single 1-2 m2 membrane module and costing

from $5,000 to 15,000. Several hundred, perhaps as many as1000 of these systems have

been installed around the world.

24

Chapter three

Methodology

25

Methodology

3.1 Introduction This chapter is structured in the theoretical evaporation emissions calculations, using

Sudan product (gasoline) data, are presented. Thereafter experimental evaporation

emissions for Sudan’s service stations are calculated in three different service stations

based on the gasoline consumption rate in each station. One with High consumption rate,

second with medium consumption rate and third with low consumption rate.

In Sudan there’s an Agreement between the petroleum companies and service provider in

which the amount of loss due evaporation must not exceed 0.3 in percentage and In case

of exceeding the company is obligated to compensate the difference.

Theoretical filling emission Calculations in Service station:

The theoretical evaporation emissions is calculated based on Equations found EPA

methodology using gasoline RVP (Reid vapor pressure), product temperature and vapor

characteristics . The Gasoline Produced in Sudan (Khartoum Refinery) has an average

Reid Vapor Pressure 8.3.

According to EPA (2006) the equations to estimate the working losses and breathing

losses from underground and aboveground gasoline storage tanks are

3.2 Working loss

Working losses occur when the vapor in the vapor space over the liquid is displaced from

the tank by the addition of organic liquid during tank filling.

The following equation was used for the estimation of working loss from underground

and aboveground gasoline storage tanks:

𝑊𝐿 = (0.0010) ∗ 𝑄 ∗ 𝑀𝑉 ∗ 𝑃𝑉𝐴 ∗ 𝐾𝑁 ∗ 𝐾𝑝 (3.1)

Where:

WL= storage tank working loss (lb. /year)

Q= annual net gasoline throughput (bbl. /year)

26

MV= gasoline vapor molecular weight (lb./lb.-mole)

PVA= vapor pressure at daily average liquid surface temperature (psia)

KN= working loss turnover (saturation) factor, dimensionless;

KP= working loss product factor, dimensionless;

0.0010= integrated conversion factor to yield the units of lb. /year for the working loss

Q = the annual net gasoline throughput.

MV= the gasoline vapor molecular weight (MV) was calculated by using equation (3.2)

MV = 63 + 0.1053 (T − 15.55) (3.2)

Where

T= site specific mean daily temperature during warm and cold season, respectively (oC)

PVA=the vapor pressure of gasoline at daily average liquid surface temperature was

calculated using appendix A

KN=the working loss turnover (saturation) factor (KN) was estimated from the following

USEPA model:

For turnovers per year (N) > 36

𝐾𝑁 = (180 + 𝑁)

6𝑁 (3.3)

For turnovers per year (N) ≤ 36

KN = 1

N=the turnover rate is estimated using equation (3.4).

N = 5.614 ∗Q1

VLX (3.4)

Where:

Q1= annual net gasoline throughput (bbl. /year)

27

VLX= storage tank working volume (gallon or liter, converted as appropriate); VLX was

estimated from equation (3.5).

𝑉𝐿𝑋 = Vtotal– Vsegment (3.5)

Where:

V Total= Volume of gasoline storage tank (liters).

V Segment= Volume of gasoline remaining at the base of the tanks (liters) estimated from

equation (3.6).

VSegment = L ∗ [r2 ∗ COS−1[(r−h)

r−(r−h)] ∗ √ (2rh − h2) ] (3.6)

Where:

H= height of the remaining liquid at the bottom of tank (ft.)

L= length of the tank (ft.)

r= radius of the tank (ft.); Tank radius and length were calculated from the volume of the

tank reported by respondents using industry/manufacturers standard tank radiuses and

volumes.

KP=the working loss product factor (KP) for gasoline was set to 1.

3.3 Breathing loss Breathing losses occur because differences in temperature (such as changes between day

and night temperatures) affect the vapor space pressure inside storage tanks

Equation (3.7) was used for the estimation of breathing loss from underground and

aboveground gasoline storage tanks:

BL = 365 ∗ KE ∗ ( 3.1416

4∗DE2 ) ∗ HVO ∗ KS ∗ WV (3.7)

Where:

28

BL= storage tank breathing loss (lb. /year)

365= constant, the number of daily events in a year.

KE= vapor space expansion factor, dimensionless

3.1416= mathematical constant; the standard ratio of 22/7 for circle circumference to its

diameter

DE= effective tank diameter for horizontal tanks (ft.)

HVO= vapor space outage (ft.)

KS= vented vapor saturation factor, dimensionless

WV= gasoline vapor density (lb. /ft3)

KE=the vapor space expansion factor (KE) was calculated by using equation (3.8).

KE = ( ∆TV

TLA ) + (ΔPV − ΔPB) / (PA − PVA) (3.8)

Where:

KE= vapor space expansion factor, dimensionless

ΔTV= daily vapor temperature range (°R, Degrees Rankin)

TLA= daily average liquid surface temperature (°R)

ΔPV= daily vapor pressure range (psia)

ΔPB= breather vent pressure setting range (psia)

PA= atmospheric pressure (psia)

PVA= vapor pressure at daily average liquid surface temperature (psia)

ΔTV=the daily vapor temperature range (ΔTV) was calculated by using equation (3.9).

ΔTV = 0.72 ∗ ΔTA + ( 0.028 α ∗ I) (3.9)

Where:

ΔTV= daily vapor temperature range (°R)

ΔTA= daily ambient temperature range (°R); the daily ambient temperature range (ΔTA)

is the difference between the average maximum and average minimum ambient

temperatures during each season, as expressed by equation (3.10):

ΔTA = TAX − TAN (3.10)

29

Where:

TAX= daily average maximum ambient temperature (°R)

TAN= daily average minimum ambient temperature (°R)

α= tank paint solar absorbance, dimensionless; the tank paint solar absorbance (α) data

for aboveground tanks are provided by the USEPA. For underground tanks, this

parameter assumes the value of zero.

I= daily total solar insolation factor (Btu/ft2 d); the daily total insolation factor (I) data for

aboveground tanks are provided by the USEPA. For underground storage tanks, this

parameter assumes the value of zero.

TLA=the daily average liquid surface temperature (TLA) was calculated by using equation

(3.11):

TLA = ( 0.44 ∗ TAA) + (0.56 ∗ TB ) + ( 0.0079 ∗ α ∗ I) (3.11)

Where:

TLA= daily average liquid surface temperature (°R)

TAA= daily average ambient temperature (°R)

TB= liquid bulk temperature (°R)

α= tank paint solar absorbance, dimensionless

I= daily total solar insolation factor (Btu/ft2 d)

Daily average ambient temperature (TAA) was calculated by using equation (3.12):

TAA = (TAX + TAN)

2 (3.12)

Where:

TAX= daily average maximum ambient temperature (°R)

TAN= daily average minimum ambient temperature (°R)

𝑇𝐵 =for aboveground tanks, the liquid bulk temperature (TB) was calculated by using

equation (3.13), while for underground tanks, it was assumed to be equal to the average

underground temperature during the particular season.

30

TB = TAA + (6 α − 1 ) (3.13)

Where:

TAA= daily average ambient temperature (°R)

α= tank paint solar absorbance, dimensionless

ΔPV=the daily vapor pressure range (ΔPV) was calculated by using equation (3.14).

𝛥𝑃𝑉 = 𝑃𝑉𝑋 − 𝑃𝑉𝑁 (3.14)

Where:

ΔPV= daily vapor pressure range (psi)

PVX= vapor pressure at the daily maximum liquid surface temperature (psi)

PVN= vapor pressure at the daily minimum liquid surface temperature (psi)

ΔPB =the breather vent pressure setting range (ΔPB) was calculated by using equation

(3.15)

ΔPB = PBP − PBV (3.15)

Where:

ΔPB= breather vent pressure setting range (psi)

PBP= breather vent pressure setting (psi)

PBV= breather vent vacuum setting (psi)

PVA=the vapor pressure at daily average liquid surface temperature (PVA)

DE =the effective tank diameter was calculated by using equation (3.16).

DE = [L∗D

π

4

]−

1

2 (3.16)

Where:

DE= effective tank diameter (ft.)

L= length of the horizontal tank (ft.)

31

D= diameter of the horizontal tank (ft.)

HVO =the vapor space outage (HVO) for horizontal tanks is equal to half of the effective

tank height, calculated by using equation (3.17).

𝐻𝑉𝑂 = 𝐻𝐸

2 (3.17)

Where:

HE= effective height of horizontal tanks (ft.)

HE=the effective height of a horizontal tank (HE) corresponds to the height of a vertical

tank having the same volume as the horizontal tank in question; it was calculated using

equation (3.18).

𝐻𝐸 = 3.1416∗ D

4 (3.18)

Where:

D=is the diameter of the horizontal tank

KS=the vented vapor saturation factor (KS) was calculated by using equation (3.19).

𝐾𝑆 = 1

(1+0.053∗𝑃𝑉𝐴∗𝐻𝑉𝑂) (3.19)

Where:

PVA= vapor pressure at daily average liquid surface temperature (psi)

HVO= vapor space outage (ft.), the vapor space outage (HVO) was calculated by using

equation (3.17) above.

WV = the gasoline vapor density (WV) was calculated by using equation (3.20).

WV = MV ∗PVA

(R∗TLA) (3.20)

32

Where:

MV= gasoline vapor molecular weight (lb./lb.-mole), the gasoline vapor molecular weight

(MV) was calculated by using equation (3.2) above.

PVA= vapor pressure at daily average liquid surface temperature (psi)

R= ideal gas constant (10.731 psia ft3/lb.-mole °R)

TLA= daily average liquid surface temperature (°R), the daily average liquid surface

temperature (TLA) was calculated by using equation (3.11).

3.4 Assumptions & givens Site average daily temperature T=31.5 oC.

Effective height 𝐻𝐸=30 cm.

Vapor pressure at daily average liquid surface temperature 𝑷𝑽𝑨=49 kPa. (7.12 psi)

Gasoline vapor molecular weight MV=100.

Daily average maximum ambient temperature TAX =37 oC.

Daily average minimum ambient temperature TAN =26 oC.

PVX=8.63616 psi from Appendix A at TAX =37 oC.

PVN=6.062 psi from Appendix A at TAN =26 oC.

Tank paint solar absorbance α= 0, for underground tanks, this parameter assumes

the value of zero.

Breather vent pressure setting range ΔPB =0 in the absence of pressure and

vacuum vents, ΔPB assumes the value of zero.

Storage tank working volume VLX= 95% of VTotal

𝑉𝑇𝑜𝑡𝑎𝑙 for the three stations =45000 liters

The working loss product factor KP= 1.

R= ideal gas constant (10.731 psi ft3/lb.-mole °R)

3.5 Sample of calculations The calculation of working loss and breathing loss in the medium consumption rate

service station (Jabl Awleya)

3.5.1 Working loss

Q=409613.476 liter per year (25760 bbl. per year)

MV=100

𝑷𝑽𝑨=49 kPa. (7.12 psi)

KP= 1

VLX= 95% of 𝑉𝑇𝑜𝑡𝑎𝑙 =0.95*45000=427500 liters

33

Use equation (3.4) N=95

Use equation (3.3) 𝐾𝑁= 0.48

Use equation (3.1) WL= 5576.97 liter per year (8848.786 lb. per year)

3.5.2 Breathing loss

Use equation (3.14) ΔPV=2.5743 psi.

Use equation (3.12) TAA=31.5 oC (548.37 °R)

Use equation (3.13) 𝑇𝐵 =30.5 oC

Use equation (3.11) TLA≈31.5 oC

Use equation (3.10) ΔTA=19.8 oR

Use equation (3.9) ΔTV=14.256 oR

Use equation (3.20) WV = 0.12

Use equation (3.18) HE=7.98 ft.

Use equation (3.17) HVO =3.99 ft.

Use equation (3.19) KS=0.4

Use equation (3.16) DE =0.062 ft.

Use equation (3.8) KE=0.365

Use equation (3.7) BL= 3245.05 liter per year (5148.81 lb. per year)

34

Chapter four

Results & Discussion

35

4.1 Results

Our pervious calculations have been made to calculate the fuel emission in three different

service stations in Khartoum City. The three service stations with different consumption

rate in each station:

Al-Oshara station (high consumption rate).

Jabl Awleya station (medium consumption rate).

Dar AL Salam station (low consumption rate).

The calculations contain the measure of the working loss, the breathing loss,

total loss and the percentage of the total loss to the total volume in each service station to

compute the fuel losses per year.

Table 4.1 comparison of results between the three stations

Service Station

Working loss

Liter/year

Breathing

loss

Liter/year

Total loss

Liter/year

Number of

Filling liters

per year

Percentage

of the total

loss to

number of

filling liter

per year

1/ Al-Oshara 10554.99 3245.05 13800.04 7022231.263 0.196519%

2/ Jabl Awleya 5576.97 3245.05 8822.02 4096136.476 0.215374%

3/ Dar AL Salam 4580.41 3245.05 7825.46 1912000 0.409281%

36

The cost of the total loss of gasoline for the three service stations:

Al-Oshara 64446..187 SDG

Jabl Awleya 41198.8 SDG

Dar AL Salam 36544.9 SDG

4.2 Discussion

The breathing loss is constant for the three stations because it depends on the total

volume of the tank and their volume is constant

As we had mentioned before in chapter 3 that In Sudan there’s an Agreement between

the petroleum companies and service provider in which the amount of loss due

evaporation must not exceed 0.3 in percentage and In case of exceeding the company is

obligated to compensate the difference.

Our results showing that two of the three service stations is in the allowable range of the

0.3%, Al-Oshara and Jabl Awleya with 0.196519% and 0.215374% respectively.

The Third station Dar AL Salam with 0.409281% evaporation losses which exceed the

Limit of 0.3%. The service station owner must demand the company to compensate the

losses.

37

Chapter five

Conclusions & Recommendations

38

5.1 Conclusions

The evaporation loss from underground tanks in some service stations in Sudan is

about 0.41%.This is significantly higher that set by the petroleum companies and

stations provider (0.3%).

A loss percentage of 0.41% if gained means an annually saving of 36544 SDG

for a certain Service Station.

From the results we found that it is important to use vapor recovery system

VOC controls can take many forms and the type of control method used will be

determined by the characteristics of the VOC emissions. Minimization

techniques, such as the lowering of RVP, can be implemented but only to a

certain degree, as there is a lower limit with regard to petrol volatility. Vapor

recovery is the preferred technique for the control Of VOC emissions from petrol

storage and distribution systems. This also has added advantage Of monetary

savings from recovered petrol vapor. There are various VOC treatment

techniques, but this must only be used in situations were other control options are

not viable.

5.2 Recommendations

Install automatic Tank gauge system to eliminate the use to dip stick to minimize

the residual losses caused when we open the tank to measure the fuel volume.

Replace the splash loading method with submerged loading method. As

evaporation is a function of turbulence in liquid and/or vapor interface.

Evaporation reduction or recovery measures need to be developed, declared and

implemented.

Install simple and small membrane vapor recovery system

39

References

1. Cornelia Venter (2003) master of engineering dissertation “recovery of petrol

vapour at a bulk storage facility.

2. EPA (2003a) Volatility (RVP), Gasoline fuels, EPA,

http://www.epa.gov/otaq/volatility.htm

3. EPA (2006b) Emission Factor Documentation for AP-42 Section 7.1

4. EPA (1975) “ a study of vapor control methods for gasoline marketing operations

volume 1”

5. HADLEY PV, DEVOS F, ESTY W, GOMMEL PG, ISING U, LILIE RH,

VERBEEK GPM AND WILLIAMS LJ (1978) Hydrocarbon Emissions from

Gasoline Storage and DistributiN1 Systems, Report nr. 4178, CONCAWE, Haag.

6. HANSEN MR (1996) Hydrocarbon vapor emission reduction by recovery, Paper

presented at Danish Days in Ukraine conference, 5-9 February 1996. Kiev,

Ukraine.

7. JEFFERY K (1998) Bulk Liquids Vapor Control, Hazardous Cargo Bulletin. IIR

Publications, London.

8. JO W AND SONG K (2001) Exposure to volatile organic compounds for

individuals with occupations associated with potential exposure to motor vehicle

exhaust and/or gasoline vapor emissions, The Science of the Total Environment,

269, 25-37.

9. KOJIMA M AND MAYORGA-ALBA EO (1998) Cleaner Transportation Fuels

for Air Quality Management, Energy Issues, No. 13, July 1998, The World Bank,

http://www.worIdbank.org'htrnl/fpd/energy/enls13.pdf (23 October 2002).

10. K. Ohlrogge and J. Wind, “Method and Apparatus for reducing Emissions from

Breather-lined Storage Tanks, U.S. Patent 6,059,856 (May 2000).

11. SANGSTER A (1991) Vapor Recovery from Petrol Distribution, Petroleum

Review, March 1991, 45(530), 130-132, 134.

12. Statistics Canada http://www.statcan.gc.ca/pub/16-001-m/2012015/part-partie1-

eng.htm

13. Richard W. Baker Membrane Technology and Research, Inc. “MEMBRANES

FOR VAPOR/GAS SEPARATION”

40

Appendix A