2

OISD-GDN-224

November 2006

FOR RESTRICTED CIRCULATION ONLY

MONITORING & CONTROL

OF

VOLATILE ORGANIC COMPOUNDS EMISSION

Prepared by:

COMMITTEE ON

“MONITORING AND CONTROL OF

VOLATILE ORGANIC COMPOUNDS EMISSION”

OIL INDUSTRY SAFETY DIRECTORATE

7th FLOOR, “NEW DELHI HOUSE”,

27, BARAKHAMBA ROAD,

NEW DELHI – 110 001

3

N O T E

Oil Industry Safety Directorate (OISD) publications are prepared for use

in the Oil and Gas Industry under the Ministry of Petroleum and Natural

Gas. These are the property of Ministry of Petroleum and Natural Gas

and shall not be reproduced or copied or loaned or exhibited to others

without written consent from OISD.

Though every effort has been made to ensure the accuracy and reliability

of data contained in these documents, OISD hereby expressly disclaims

any liability or responsibility for loss or damage resulting from their use.

These documents are intended only to supplement rather than replace

the prevailing statutory requirements.

- (ii) -

4

FOREWORD

The Oil Industry in India is about 100 years old. As such, a variety of practices have been in vogue because of collaboration/association with different foreign companies and governments. Standardisation in design philosophies, operating and maintenance practices was hardly in existence at a national level. This, coupled with feedback from some serious accidents that occurred in the recent past in India and abroad, emphasised the need for the industry to review the existing state-of-the-art in designing, operating and maintaining oil and gas installations.

With this in view, the Ministry of Petroleum and Natural Gas in 1986 constituted Safety Council assisted by the Oil Industry Safety Directorate (OISD) for formulating and implementing a series of self-regulatory measures aimed at removing obsolescence, standardising and upgrading the existing standards to ensure safer operations & also develop standards in new area identified. Accordingly OISD constituted a number of functional committees comprising of experts nominated from the industry to draw up standards and guidelines on various subjects.

At every stage of production, processing, handling, transfer and distribution of hydrocarbon based products, there is potential for losses to the environment. Volatile Organic Compounds (VOCs) being high in vapour pressures significantly vapourise and participate in atmospheric photochemical reactions with oxides of nitrogen and sunlight to form ozone. Ground level ozone affects normal function of the lung in healthy humans. For this reason controlling of VOCs is an effective method of minimizing ground level ozone.

The present document “Monitoring and Control of Volatile Organic Compounds (VOCs) Emission ” was prepared by the Functional Committee on “VOC Emission control”. This document was prepared based on the accumulated experience and knowledge of industry members and various national & international codes and practices.

This document will be reviewed periodically for improvement based on the new experiences and better understanding. Suggestions may be addressed to:

The Coordinator

Committee on "Monitoring and Control of Volatile Organic Compounds (VOCs) Emission”

Oil Industry Safety Directorate

7th Floor, New Delhi House

27, Barakhamba Road,

NEW DELHI - 110 001.

-------------------------------------------------------------------------------------------------------------------------------------------------------------

- III -

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FUNCTIONAL COMMITTEE

NAME ORGANISATION

LEADER

Shri M.K.Dutta Centre for High Technology, New Delhi

MEMBERS

Shri A.K. Sharma GAIL (India) Limited, Pata

Dr.P.S.Viswanathan Kochi Refineries Limited, Kochi

Shri D.V.Dixit Engineers India Limited, New Delhi.

Shri A.D. Vyawhare Bharat Petroleum Corporation Limited. Mumbai

Dr. M.S.R. Swami Chennai Petroleum Corporation Limited, Chennai

Shri P. Sitarama Rao Hindustan Petroleum Corporation Limited, Vizag

Shri Harendra Singh Oil & Natural Gas Corporation Limited, Mumbai

Shri S.Dasgupta Indian Oil corporation Limited, New Delhi

MEMBER COORDINATOR

Shri P. Kulshreshtha Oil Industry Safety Directorate, New Delhi.

In addition to above, several other experts from industry contributed in the preparation, review

and finalisation of this document.

-(iv)-

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INDEX

SECTION DESCRIPTION PAGE NO.

1.0 Introduction 1

2.0 Scope 1

3.0 Definitions 2

4.0 Sources of Emissions 3

5.0 Estimation of Emissions 6

7.0 Prevention & Control of Emissions 7

7.0 Control of Emissions – By LDAR 8

8.0 Emission Prevention through In-built Features 11

9.0 Recommended Practices 12

10.0 References 13

ANNEXURES

I Estimation of emission from fixed roof tank 14

II Estimation of emission from floating roof tank 17

III Steps in Brief on US EPA Method 21 for monitoring fugitive emissions

19

IV Sample Calculation for Fugitive Emission Monitoring using Emission Rate Correlation Equation

21

V A Brief on Vapour Recovery systems 22

VI Sample calculation for emissions from loading operations

25

VII Typical Format for Fugitive Emission (Leak) Survey 26

_____________________________________________________________________

-v-

OISD-GDN-224 1

_______________________________________________________________________

“OISD hereby expressly disclaims any liability or responsibility for loss or damage resulting from the use of the OISD Standards/Guidelines/Recommended Practices”

Monitoring and Control of

Volatile Organic Compounds Emission

1.0 INTRODUCTION

Emission of Volatile Organic

Compounds (VOC) is an area of

significant concern. Refineries & gas

processing plants are major

contributors. Apart from causing

production loss, VOCs are partly

responsible for ground-level ozone,

which may affect normal functioning

of lungs. Many VOCs are toxic,

causing illnesses such as cancer,

neurological and respiratory diseases.

VOCs are present in crude oil and the

produced petroleum fractions viz.

LPG, motor spirit, kerosene, naphtha,

benzene, hexane, cyclohexane, fuel

gas etc. Volatile hydrocarbon vapours

get released to atmosphere from

storage, pumping, loading / unloading

and processing of crude & petroleum

products. However, fugitive emission

(leakage to atmosphere) of VOCs

usually occurs through seals of

equipment, wastewater collection &

treatment facilities, cold vents,

leakages etc. Actions taken in recent

years have shown substantial

reduction in VOC emission.

These guidelines include

identification of fugitive emission

sources alongwith quantification and

control techniques through design

measures, inspection, repair &

maintenance schedules,

administrative actions, reporting and

record keeping in a systematic

manner.

2.0 SCOPE

This document lays down guidelines

applicable for refineries and gas

processing plants, for identification

and control of fugitive VOC

emissions.

2

3.0 DEFINITIONS

3.1 VOLATILE ORGANIC COMPOUNDS

(VOC):

These are the organic compounds

whose vapour pressure at 20oC

exceeds 1.0 kPa (0.145 psi). As a

result, these can easily become

vapour or gas from the solid or liquid

state.

3.2 COMPONENT:

Equipment or accessories which

include pump seals, compressor seals,

seal oil degassing vents, flanges of

heat exchangers, pipeline valves,

flanges and other connections,

pressure relief devices, process

drains, open-ended pipes, sampling

connections etc. that could potentially

leak to emit VOCs into the

atmosphere.

3.3 FUGITIVE EMISSIONS:

Also known as “equipment leaks”,

the fugitive emissions are the result

of leaks of volatile organic

compounds from components as

above including the hydrocarbon

transfer lines and associated

equipment. Valves are usually the

single largest source of fugitive

emissions.

3.4 BACKGROUND CONCENTRATION

LEVEL:

It is the concentration of VOC

measured through the portable

hydrocarbon detection instrument

which is taken upwind (atleast three

metres) from any component to be

inspected (e.g. pump or compressor)

so that it is unaffected by any specific

emission point.

3.5 ESSENTIAL EQUIPMENT:

Any equipment in the process whose

outage from service will cause cut in

unit throughput by > 33%.

3.6 LEAK:

Gaseous hydrocarbon emission found

to be in excess of 10,000 ppm above

background concentration level,

when measured by a portable

hydrocarbon detector at a distance of

one (1) centimeter from the surface of

potential source with the instrument

calibrated with methane. However, in

case of Benzene, which is highly

carcinogenic, the leak is defined as

the emission value measured in

3

excess of 3000 ppm above the

background concentration level.

Regardless of concentration, a leak is

also identified by sight, sound or

smell at a component caused by

liquid dripping or vapour leak, which

is sometimes visible through bubbles

in presence of soap solution. The

dripping of liquid VOCs at a rate of

more than three (3) drops per minutes

can be construed as leak.

3.7 REFERENCE COMPOUND :

This is VOC used for instrument

calibration.

3.8 EMISSION CONTROL SYSTEM:

It is a combination of capture

system(s) and control equipment used

to recover, reduce, remove or control

the release of VOC to atmosphere.

Such equipment includes vapour

recovery system, compressor,

incineration system, flare system,

process heaters etc.

3.9 LEAK DETECTION AND REPAIR

(LDAR) :

It is a tracking programme to ensure

that all components are monitored on

regular basis and repaired in timely

manner to reduce/eliminate VOC

emissions from leaking components.

3.10 RESPONSE FACTORS (RF):

Response factor is required to provide

an accurate relationship while using

an analyzer calibrated for one gas to

measure leaks of other compounds.

The response factor is defined as

Concentration in actual = RF x

Concentration measured. A

response factor of 1.0 means the

instrument reads out identical to

actual concentration of chemical in

the gas sample.

3.11 EMISSIONS:

“VOC Emissions” shall hereinafter

be expressed as “Emissions” in this

document.

4.0 SOURCES OF EMISSIONS:

In oil and gas installations, probable

sources of emissions are as follows:

1. Process Vents, which are mostly

controlled.

2. Fugitive releases of hydrocarbon

vapour caused by leaks in process

equipment or evaporation from

open areas. These are the major

source of emission,which include:

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a. Evaporative emission

sources viz hydrocarbon

storage & transfer facility

(loading/ unloading),

wastewater transfer &

treatment facility, cooling

tower, waste management

area e.g. oily sludge

lagoons, sludge pits, etc.

b. Process Equipment

Emission Sources viz

pumps, valves (from gland,

bonnets etc.), compressors,

pressure relief valves,

connectors and flanges,

agitators, open ended lines,

sampling connections.

4.1 EMISSIONS FROM STORAGE TANKS:

Emissions from fixed roof storage

tank include standing losses and

working losses. Standing losses occur

due to variation in ambient

temperature (thermal breathing).

Working losses occur during filling

operation.

Emissions from floating roof tanks

include standing losses and

withdrawal losses. The standing

losses occur from roof rim seals, deck

fittings, deck seams, still wells etc.

The withdrawal losses pertain to

evaporation loss of liquid stock that

clings to the shell, guide pole etc

while the stock is being pumped out.

Emissions from Pressurised storage

tanks (e.g. dome roof tanks or

nitrogen blanketed fixed roof tanks)

occur when their safety valves /

controlled vents discharge to

atmosphere. Similarly, emissions

from the other pressurized storages

(e.g. spheres & bullets) occur when

their safety valves/ controlled vents

discharge to atmosphere. In order to

minimize these discharges to

atmosphere, safety valves / vents of

horton spheres and bullets should

normally be connected to flare

header.

4.2 EMISSIONS FROM LOADING

FACILITIES:

Emission is significant during filling

of road tankers and rail wagons in

case of lighter products like

naphtha/gasoline.

4.3 EMISSIONS FROM EFFLUENT

TREATMENT FACILITIES:

Drainage routing from process units,

storage tanks, loading areas etc. to the

Effluent Treatment Plant (ETP)

5

through Oily Water Sewer (OWS)

involve considerable emission from

the open inlet chamber of ETP, API

oil separator, other open storages etc.

depending upon the oil content in the

influent streams and the temperature.

Recommended system for reduction

of emission from wastewater

treatment is to have a closed system

for contaminated and odorous

wastewater stream with provision of

water seals on sewers & drains and

gas tight covers on junction boxes.

4.4 EMISSIONS FROM COOLING

TOWERS:

Cooling towers, under normal

circumstances, do not contribute to

emissions. However, leakages in the

water cooled exchangers can lead to

hydrocarbon carryover to cooling

towers resulting in emissions.

Hydrocarbon detectors should be

provided at cooling tower return

stream from units.

4.5 EMISSIONS FROM OILY SLUDGE:

The main sources of generation of

oily sludge are tank cleaning, ETP,

oil catchers, API separators, and

spillages from bitumen plant, crude

oil and product storage tanks. For

API separators and oil catchers, oil

content and temperature have major

effect on emission. Sludge removed

from these sources and stored in open

pits, contributes to emissions in

significant quantity. Oil should be

removed from the oily sludge before

disposal. The residual sludge should

not have hydrocarbon content more

than 10% v/v.

4.6 EMISSIONS FROM PROCESS UNITS:

In process units, VOC emissions can

occur through leaks, vents, drains,

flanged joints, instrument

connections, PSVs open to

atmosphere, pump seals, compressor

seals, valve gland/ bonnet, sample

connections etc. These should be

minimised through an effective

LDAR programme. Significant

amount of emission can also occur

while preparing the equipment /

vessels for handing over to

maintenance for repairs or during

start up/ emergency shut down of the

unit. Such emissions should be

minimised by adopting standard

operational practices of emptying out

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the equipment/vessel completely into

close blowdown system for

reprocessing instead of routing to

ETP via Oily Water Sewer.

5.0 ESTIMATION OF

EMISSIONS

Estimation of emissions from storage

tanks, loading facility and equipment

leaks can be done as described below:

5.1 ESTIMATION OF EMISSIONS FROM

STORAGE

Fixed Roof Tanks: Working losses

for the fixed roof tanks are

estimated on the basis of tank filling

rate. Standing losses from the fixed

roof tanks are estimated based on

thermal breathing from the tank.

See Annexure-I for guideline to

estimate annual average emission

loss of VOCs from a fixed roof

tank.

Floating Roof Tanks: The method

to determine annual average

emission loss of VOCs from

internal/ external floating roof tanks

is provided at Annexure-II.

Pressurised storage tanks and

vessels: Annual average emission

loss of VOCs for low-pressure

storage tanks (upto 2.5 psig) can be

estimated based on method

provided at Annexure-I. For high-

pressure storage tanks (2.5 to 15

psig) and vessels, the atmospheric

emissions are considered

insignificant with proper

maintenance measures in place.

5.2 ESTIMATION OF EMISSIONS FROM

LOADING FACILITIES:

Estimation of emissions from loading

gantries is done on the basis of

loading flow rates and the

concentration of the vapours emitted

from the vent nozzle of the tanker/

wagons. Typical parameters, which

should be collected for estimating

emissions from loading gantries,

include Product information (i.e.

name, vapour pressure, density,

composition, molecular weight of

vapour), number of loading points,

flow rate per loading point and

concentration of vapour being

emitted to atmosphere.

Emission rate from loading gantry

can be estimated using the following

7

equation (valid for bottom loading /

top submerged loading):

· Emissions from loading operation of Petroleum Liquids : (Reference AP-42 of EPA Chapter 5.2 )

LL = 12.46 SPM / T Where,

LL = Loading loss, lb per

1000 gal of liquid loaded

S = A saturation factor

P = True vapour pressure

of liquid loaded in psia

M = Molecular weight of

vapours , lb/lb-mole

T = Temperature of bulk

liquid loaded, 0R ( 0F + 460).

· Sample calculation is given in annexure VI.

5.3 ESTIMATION OF EMISSIONS FROM

EQUIPMENT LEAK

Emissions due to equipment leak (i.e.

valves, flanges, other connections,

pumps, compressors etc) should be

estimated using US EPA Method 21.

Procedural steps in brief alongwith a

typical example calculation are

illustrated in Annexure-III and

Annexure-IV respectively. The

instrument used for detection of VOC

leakage should be able to detect VOC

concentrations in parts per million

volume (ppmv) and % LEL in line

with leak definition concentration.

The instrument must be intrinsically

safe for use in the hazardous area of

the process units. Typical

specification of the instrument as per

EPA Reference method 21 are given

at Annexure-III.

6.0 PREVENTION & CONTROL

OF EMISSIONS

Two primary techniques of equipment

leak emission control are:

a. Equipment modification for

Emission Prevention (on case to

case basis, such as replacing

standard valve with seal less

type).

b. Implementing a regular and

structured leak detection and

repair programme (LDAR) for

Emission Control.

Equipment reliability improvement

is recommended on following lines:

i) Valves: Use of better quality of

packing, proper engineering

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specifications, use of special

type of valves e.g. bellow type.

ii) Flanges: minimization of flange

connections in number, proper

rating & gasket material.

iii) Pumps: Provision of double

mechanical seals, other high

performance seals etc.

Compressors: Connecting the

packing vent of reciprocating

compressor preferably to the

flare system. Use of seals

permitting minimum gas

leakage, other high performance

seals, collection and safe routing

to Emission Control system.

iv) Safety Valves: Connecting to

flare.

v) Wastewater Treatment: Covered

processing and storage, pre-

treatment for toxics.

vi) Storage: Proper type of storage

and Seals, inclusion of Vapour

recovery system for fixed roof

tanks.

vii) Loading: Installing vapour

recovery system (See

Annexure-V for information on

typical VRS).

viii) Route the flushing from

sampling points preferably to

Closed Blowdown system.

7.0 CONTROL OF EMISSIONS

- BY LDAR

LDAR programme should be

implemented in three phases:

Components identification to

determine which of them requires to

be monitored, the same to be tagged

by using weatherproof tags.

Components may be identified from

P&ids and Unit inspection. Process

streams should be followed in logical

order to identify all potential leak

sources.

7.1 Monitoring potential fugitive

emission sources for leaks and

tagging the detected leaking

components.

7.2 Repair or replacement of leaking

component—first attempt at repair of

component within 5 days of leak

detection and final repair within 15

days. If the leaking component is

essentially required for sustaining the

process operations and cannot be

repaired within 15 days after

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detection, one of the following

actions should follow:

i. Replace the leaking component and

inspect for leaks within 5 days after

detection.

ii. Vent out emissions to vapour

recovery system operating at 95%

efficiency (min) or to a flare.

iii. Plan for repair/replacement of the

essential component in the next

shutdown of the process unit but

within a reasonable time as per

management’s decision( say, one

year from the date of the original

leak). It should be accordingly

marked/tagged distinctly. Similarly,

a component which is not getting

isolated for repair, should be tagged

and short-listed for action in next

shutdown.

iv. After repair is done, the component

should be re-tested within 15 days

for the residual leak assessment.

A cost effective LDAR programme

should be developed by focusing

attention to locate very high leaking

points and repair them on priority.

Any deviations from schedule and

procedure should be identified and

corrected on monthly basis. Each leak

not detected remains unrepaired and

results in a lost opportunity to reduce

emissions from the installation. In

facilities, where contractors are

involved in implementation of LDAR

programme and test of leak including

first attempt at repair, internal quality

control should be ensured through

accountability for the LDAR

programme.

7.3 PROCEDURE FOR MONITORING

· The VOC analyzer should be

assembled and started in open and

clean atmosphere.

· The instrument should be

calibrated before use.

· Concentration of VOCs emitted

by the leaking component should

be checked at the surface interface

(e.g. at the interface between a

valve stem and packing).

· The probe inlet should be placed

at the surface of the component

interface where leakage could

10

occur. It should then be moved

along the periphery while

observing the instrument readings.

The interface where leakage is

indicated should be sampled

slowly until the maximum meter

reading is obtained. Retain the

probe at this maximum observed

meter reading location for about

two times the instrument response

time. If the maximum observed

meter reading is greater than

the leak definition , record and

report the result.

Arrow shows location of monitoring

· Precautions :

o The probe of instrument should be about 1 cm from leaking interface.

o Tip of the probe should not touch greasy areas. It should always remain clean and through.

o Monitoring activities may be avoided during rain to protect the analyzer from bad weather.

o Well trained LDAR inspection personnel should be deployed.

o Target planning should be made with regard to number of components to be checked for leaks in a day or shift, based on the response time of the instrument.

· Calibration:

o Calibration frequency for the instrument should be as specified by the supplier.

· Frequency:

o Pumps seals, pipeline valves in liquid service, process drains should be monitored once in six months.

o Compressor seals, pipeline valves in gas service, pressure relief in gas service should be monitored quarterly (four times per year).

o Whenever liquid is observed dripping from a pump seal, the seal shall be checked immediately with portable

11

detector to determine if there is a leak of VOC taking place.

· Reporting :

Leak Survey Report should be

compiled in a structured format as

given in the Annexure-VI and

should be circulated to the

concerned sections viz.

Mechanical maintenance,

Operations/Process unit,

Instrument maintenance within

one working day of detection.

Reporting and regular follow up

will be done by responsible

personnel. The leaks which cannot

be repaired during operation, must

be tagged separately to attend

them during next shutdown of the

facility.

· Review and action

1. Follow up with concerned

plant officers

2. Ensure repeat survey after

attending the leaks

3. Review the record again and

communicate

4. Generate report for internal

circulation

5. Ensure co-ordination with

operating and maintenance

crew

The individual installation should

initiate LDAR programme with

collection of baseline data as the first

step forward. Further improvement

should be achieved through target

setting on continuous basis.

8.0 EMISSION PREVENTION

THROUGH IN-BUILT

FEATURES

8.1 RECOMMENDED FEATURES FOR

STORAGE TANK AREA

Emission should be reduced by

preferably using floating roof tanks.

8.1.1 For floating roof tanks reduction of

VOC emissions can be achieved by

following measures:

· Provide double rim seals,

primary as well as secondary,

for new tanks storing lighter

hydrocarbons e.g. MS, naphtha,

crude oil etc. Old tanks with

single seal should be provided

with secondary seal based on

engineering feasibility.

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· Providing still well sleeve to

minimize emissions from still

well slots.

· Regular maintenance of rim

seal.

8.1.2 In case of fixed roof tanks, reduction

of VOC emissions can be achieved

by following measures:

· Convert existing fixed roof

tanks storing VOCs to floating

roof / fixed cum floating roof

tanks based on engineering

feasibility.

· Provide pressure vacuum relief

valve for small capacity tanks.

· Provide vapour balancing line,

where a group of tanks storing

same products exists.

· Provide tank vapour recovery

systems.

8.2 RECOMMENDED FEATURES FOR

LOADING / UNLOADING FACILITIES

The recommended measures include.

· Provide vapour balancing line to

storage tanks, if it is fixed roof

type.

· Providing vapour recovery

systems.

· Bottom loading of truck and top

submerged loading of rail

wagons, to reduces evaporation

losses.

8.3 VAPOUR RECOVERY SYSTEMS

Three types of vapour recovery units

(VRU) are normally in use with

minor variations. These are

Adsorption/ Absorption system,

Membrane Systems and Chiller

Systems. VRU is a part of vapour

recovery system which comprises of

vapour recovery arms (in case of

trucks/ tank wagons), piping, VRU,

safety instrumentation. On a case to

case basis, the vapour recovery

system may also include a knock out

drum and a blower. Typical sketch of

a vapour recovery system is included

at Annexure-V alongwith a brief

description.

9.0 RECOMMENDED

PRACTICES

1. Chronic or very high leaking

components should receive

appropriate attention through more

frequent surveys & repair.

Significant emissions reduction

13

could be achieved through repair at

appropriate periodicity.

2. Following LDAR programme,

loading arms/ valves/ hoses should

be checked with portable analysers.

3. Technological advancements

should be explored at reasonable

cost for quick detection of large

leaks.

4. Covered separation basins should be

adopted for Waste water treatment.

5. For storage of volatile products,

floating root tanks are used. Actual

Seal gaps for new and in-service

tanks should be monitored and

corrected within acceptable values

by regular maintenance to get the

best results. These are crucial for

actual VOC emissions from tanks.

6. The accuracy of leak detection

depends considerably on Operators’

skill, background concentration

level, response to different

chemicals and instrument accuracy/

calibration. Administrative initiative

should be taken to develop the

required proficiency for making

LDAR an effective and purposeful

programme on regular basis.

7. Water sealing should be ensured for

emergency drains of floating roof

tank.

10.0 REFERENCES:

1. API Publication Number 4612 on

Refinery Fugitive Emissions from

Equipment Leaks).

2. US EPA’s reference Method-21

regarding Determination of

Volatile Organic Compound

Leaks, CFR40, Part 60

3. US EPA-453, the Protocol for

Equipment Leak Emission

Estimates.

4. Charter on Corporate

Responsibility for Environmental

Protection from the Central

Pollution Control Board.

5. AP-42 of US Environmental

Protection Agency

6. Information on “VOC Emission &

LDAR Programme” available

from internet including TANKS-

4.0 software package developed

by US EPA.

14

ANNEXURE-I

ESTIMATION OF EMISSION FROM FIXED ROOF TANK

For vertical fixed roof tanks, the following equations apply.

LT = LS + LW

LS = 365 x WVVVKEKS

LW = 0.0010 x MVPVAQKNKP

Where,

LT = total loss, lb/yr

LS = standing storage loss, lb/yr

LW = working loss, lb/yr

VV = tank vapour space volume, ft3

VV = P /4 x D2 x HVO

D = tank diameter, ft

HVO = tank vapour space equivalent height, ft

= HS - HL + HRO

HS = tank shell height, ft

HL = liquid height, ft

HRO = roof outage (shell height equivalent to the volume contained in the roof), ft

= 1/3 x (D/2) x SR

SR = tank cone roof slope, if unknown, a standard value of 0.0625 ft/ft is used

WV = vapour density, lb/ft3

= MVPVA/ RTLA

KE = vapour space expansion factor, dimensionless

= [∆TV / TLA ] + [∆PV-∆PB]/ [PA- PVA]

KS = vented vapour space saturation factor, dimensionless

= 1 / [1 + 0.053 x PVA x HVO]

MV = molecular weight of vapour, lb/lb.mole

PVA = vapour pressure at the daily average liquid surface temperature, psia

R = ideal gas constant

15

TLA = daily average liquid surface temperature, °R

∆TV = daily vapour temperature range, °R

∆PV = daily vapour pressure range, psia

∆PB = breather vent pressure setting range, psia

PA = atmospheric pressure, psia

Q = annual net throughput, bbl/yr, (tank working capacity multiplied by number of

turnovers)

KN = working loss turnover factor, dimensionless

= (180+N)/ 6N, for per year turnovers > 36,

= 1, for turnovers £ 36

N = number of turnovers per year

KP = working loss product factor, dimensionless

= 0.75 for crude oils, 1 for all other organic liquids

Notes:

1. Refer Chapter 7, Compilation of Air Pollutant Emission Factors (AP-42), of US

Environmental Protection Agency. This model for emission estimation is available in

the TANKS-4.0 software package developed by US EPA, and can be accessed

through the website http://www.epa.gov/ttn/chief/software/tanks.

16

Sample calculation for Emissions from Fixed Roof Tanks (taken from an

EPA manual on Storage Tanks)

Given:

WV = vapour density, lb/ft3 = 1.26 x 10-2 lb/ft3

VV = tank vapour space volume, ft3 = 114.86 ft3

KE = vapour space expansion factor, dimensionless = 0.077

KS = vented vapour space saturation factor, dimensionless = 0.841

MV = molecular weight of vapour, lb/lb.mole = 78.6 lb/lb-mole

PVA = vap pressure at the daily average liquid surface temperature, psia = 0.880 psia

Q = annual net throughput, bbl/yr = 8,450 gal/yr x 2.381 bbl/100 gal = 201 bbl/yr

KP = working loss product factor, dimensionless = 1

KN = working loss turnover factor, dimensionless = 1

Calculation:

LS = 365 x WVVVKEKS

= 365 ( 1.26 x 10-2) (114.86) (0.077) (0.841)

= 34.2 lb/yr

LW = 0.0010 x MVPVAQKNKP

= (0.0010) (78.6) (0.880) (201) (1) (1) = 13.9 lb/yr

Therefore, total losses,

LT = LS + LW

= 34.2 + 13.9

= 48.1 lb/yr

17

ANNEXURE-II

ESTIMATION OF EMISSION FROM FLOATING ROOF TANK

For external and internal floating roof tanks, the following equations apply.

LT = LWD + LR + LF + LD

LWD = 0.943 x (QCWL/ D) x [1 + NCFC/D]

LR = [KRA + KRB vn] P D MVKC

LF = FFPMVKC

LD = KDSDD2PMVKC (this factor is calculated only for internal floating roof tanks)

Where,

LT = total loss, lb/yr

LWD = withdrawal loss, lb/yr

LR = rim seal loss from external floating roof tanks, lb/yr

LF = deck fitting loss, lb/yr

LD = deck seam loss, lb/yr=0 for external floating roof tanks

Q = product average throughput, bbl/yr

C = product withdrawal shell clingage factors, bbl/ 1000ft2

WL = density of liquid, lb/ft3

D = tank diameter, ft

KRA = zero wind speed rim seal loss factor, lb-mole/ ft.yr

KRB = wind speed dependent rim seal loss factor, lb-mole/ (mph)nft.yr

v = average ambient wind speed for the tank site, mph

n = seal wind speed exponent, dimensionless

P = the vapour pressure function, dimensionless

= [PVA/PA]/ [1 + (1 - PVA/PA)0.5]2

PVA = the true vapour pressure of the materials stored, psia

PA = atmospheric pressure, psia

MV = molecular weight of product vapour, lb/lb-mole

KC = product factor, dimensionless

18

= 0.4 for crude oils; = 1 for all other organic liquids

FF = the total deck fitting loss factor, lb-mole/yr

= Si=1 to nf [NFiKFi]

NFi = number of fittings of a particular type for the specific tank under consideration

See Note-2 at the bottom of Annexure.

KFi = deck fitting loss factor for a particular type of fitting, lb-mole/yr. See Note-2 at

bottom of Annexure.

nf = number of different types of fittings

KD = deck seam loss per unit seam length factor, lb-mole/ft/yr

SD = deck seam length factor, ft/ft2

NC = number of fixed roof support columns (= 0 for self supporting fixed roof or

external floating roof)

FC = effective column diameter, ft (perimeter/ p)

Notes:

· Refer Chapter 7, Compilation of Air Pollutant Emission Factors (AP-42), of US

Environmental Protection Agency. This model for emission estimation is available in

the TANKS-4.0 software package developed by US EPA and can be accessed

through the website http://www.epa.gov/ttn/chief/software/tanks.

· For determination of various factors such as FF, C, KRA, KRB, KD, SD etc. refer tables /

values provided in the reference given at Note-1.

19

ANNEXURE-III

US EPA METHOD – 21 : STEPS IN BRIEF

1. This is the currently accepted regulatory method for monitoring of fugitive emissions.

2. Available emission-estimating co-relations were developed based on this method.

3. This technique is commonly called “sniffing”.

4. For non-moving components e.g. valves, flanges, connectors, readings are obtained by

placing the instrument probe at the surface of interface where the leakage could occur.

5. For moving components e.g. pumps, compressors etc., the probe is placed within one

centimeter of the interface. Probe should be perpendicular and tangential to the leak

interface. Probe should be moved along the entire leak interface to find the maximum

reading. It should be moved more slowly along those areas where leakage is indicated.

6. The probe inlet should be left at the location of the maximum reading for approx. two

times the instrument response time.

7. The “leak rate screening value” is the maximum concentration recorded by the

instrument.

8. Prior to commencing to monitor, the leak detector should be tested and calibrated

according to manufacturer’s instructions.

9. Initial calibration usually consists of setting the zero value and calibration gas value.

10. The calibration gas should be in the range of expected field instrument.

11. In cases where maximum exceeds instrument range, dilution probe adaptor may be used

to extend the range of instrument. The instrument should re-calibrated with dilution probe

using a reference gas.

20

Typical Specifications for the monitoring instrument ( as per EPA Reference method 21

given in API Publication Number 4612 on Refinery Fugitive Emissions from Equipment

Leaks):

· Analyzer response factor less than 10

· Analyzer response time less than, equal to 30 seconds

· Calibration precision less than, equal to 10% of calibration gas value

· Internal pump capable to pulling point 0.1 to 3.0 liters per minute

· Intrinsically safe

· Single hole probe with maximum ¼ inch outer diameter

· Both, the linear response range and the measurable range of the instrument are in line

with the leak definition

· Instrument should be readable to +/- 2.5% of specified leak definition concentration –

e.g. 0-10,000 ppmv)

· No detectable emission value defined as + / - 2.5 % of leak definition (i.e. +/- 500

ppm)

· It should be able to respond to the compounds being processed.

21

ANNEXURE-IV

Sample Calculation for Fugitive Emission Monitoring

Using Emission Rate Correlation Equation

Based on industry experience, certain correlations have been developed for calculation of the

emissions utilizing meter readings of the portable gas detector, calibrated on methane gas.

These correlations (a list given in the table below) depend on the services (such as vapour, light

liquid etc.) and the type of the component tested (e.g. flange, open-end drain, pump seal, valve

gland etc.).

COMPONENT TYPE

SERVICE CORRELATION #

Valve Light liquid ( vap pr. > 0.3 kPa (3.84 x 10-5) x (ppmv)0.74

Valves Gas/ Vapour (9.81 x 10-7) x (ppmv)1.14 Valves Hydrogen (1.77 x 10-6) x (ppmv)0.98 Pumps Light Liquid (2.22 x 10-4) x (ppmv)0.77 Pumps Heavy Liquid (3.13 x 10-5) x (ppmv)0.97 Compressors Hydrocarbon (2.28 x 10-4) x (ppm)0.77 Compressors Hyd-rogen (1.77 x 10-6) x (ppmv)0.98 Safety relief Valves All (2.28 x 10-4) x (ppmv)0.77 Flanges All (1.7 x 10-5) x (ppmv)0.82 Drains All (1.43 x 10-4) x (ppmv)1.02 # Reference US EPA

1. Assumption: A flange leak

2. Instrument calibration basis: 1% LEL = 500 ppmv ( based on methane)

3. Instrument Reading assumed: indicating 20% LEL value on instrument

4. Equivalent LEL in ppmv: 500 ppmv x 20 = 10,000 ppmv

5. Calculation using correlation for flange leak: (from the above table)

Emission , kg/hr/source = (1.7 x 10-5) x (measured in ppmv x R.F.)0.82

= (1.7 x 10-5) x (10,000)0.82 (R.F. factor assumed 1.0)

= 0.0324 kg/hr = 0.77 kg/day

22

ANNEXURE-V

A BRIEF ON VAPOUR RECOVERY SYSTEMS

A vapour recovery system (VRS) comprises vapour collection piping, which is routed to

a vapour recovery unit (VRU). The VRU can be of various types, viz. Adsorption/

Absorption system, membrane system, vent condenser system or combination of these

technologies. A VRS may necessitate a blower for pushing the vapours to the VRU or an

intermediate vessel depending on case to case. A brief description of the VRU

technologies is given below.

Adsorption/ Absorption system

In this process, the air vapour mixture from which hydrocarbons are to be recovered is

passed through activated carbon bed. HC vapours from the mixture are adsorbed in the

bed, whereas remaining gases (mostly O2 and N2) are vented to atmosphere. Normally,

two beds are provided. One of the beds is in adsorption mode while the other is in

regeneration mode. Regeneration of carbon bed is accomplished with a combination of

high vacuum (about 90 % vacuum) and purge air/ steam stripping. Vacuum is pulled

using Liquid Ring Vacuum Pump (LRVP). Some of hydrocarbon vapours which get

desorbed due to reduction of pressure, condense in the vacuum pump itself. The multi-

phase mixture from the vacuum pump is routed to a three phase separator where three

phases (uncondensed vapours, seal fluid of the LRVP and the condensed hydrocarbon)

are separated. Non-condensed vapours are then passed through an absorption tower

where they are absorbed in a stream of cold absorbent. Normally, the same hydrocarbon

liquid whose vapour is being recovered is used as an absorbent at lower temperatures.

The recovered hydrocarbons are recycled as slop oil for further processing. Monitoring

is done at vent.

23

Membrane system

In this process, the air vapour mixture is drawn into the system using a compressor. The

type of compressor is normally a Liquid Ring Compressor. A part of the hydrocarbons

are condensed inside the compressor. The multi-phase mixture at the compressor outlet

is routed to a scrubber. Inside the scrubber, vapours are separated from liquid and are

further absorbed in cold absorbent liquid which is sprayed from the top. Vapours from

the scrubber are then routed to the membrane separation unit. A vacuum is maintained

on the other side of the membrane. This creates a pressure difference across the

membrane causing the hydrocarbon vapours to preferentially pass through the

membrane. The permeate stream rich with HC is recycled back to the suction of inlet

compressor and is recovered in the scrubber. The clean residual stream(offgas) with

negligible amount of hydrocarbons is released to atmosphere. With this process, the

hydrocarbon concentration in offgas can be reduced to 2-3 gm/m3. In case, the pollutant

content in the emissions is to be reduced further, this stream can be routed to a PSA

system.

Vent condensers with chiller unit

In this process, the air plus vapour mixture is initially cooled to about 2 to –10°C in

pre-coolers. At this temperature, bulk of moisture and a small amount of VOCs

condense and is separated out. Uncondensed vapours are further cooled to –30 to –

37°C. At this temperature about 85 to 95 % of the vapours condense and are separated

out. Remaining non-condensable gases, which mostly contain air and a small amount

of hydrocarbons are either incinerated or routed to an engine generator to generate

power. A chiller package is provided with the system, which provides required

refrigeration duty to the coolers.

Certain variation of these three technologies alongwith supplementary processes are

also being offered by specialized vendors.. Simplified sketch of a vapour recovery

system is as follows:

24

TRUCK TANKER

VOCs

V

SDV

TO ATM.

VAPOUR RECOVERY SYSTEM

RAIL WAGONS RECOVERED

LIQUID TO TANK

VENT GASES

TYPICAL VOC RECOVERY SCHEME FOR LOADING GANTRY

25

ANNEXURE-VI

Sample calculation for Emissions from the Loading Operations

Loading losses (LL) from a gasoline tank truck in dedicated vapor balance service and practicing vapor recovery would be calculated as follows, using Equation 1:

Design basis –

Tank truck volume is 8000 gal

Gasoline Reid vapor pressure (RVP) is 9 psia

Product temperature is 800 F

Vapor recovery efficiency is 95 percent

Vapor collection efficiency is 90 percent (for vessels passing annual leak test)

Loading loss equation –

LL = 12.46 (SPM / T) (1-eff)/100

Where :

S = saturation factor ( refer table in AP 42 chapter 5.2) = 1.0

P = true vapor pressure of gasoline (see Figure 7.1-6) = 6.6 psia

M= molecular weight of gasoline vapors (see Table 7.1-2) =66

T = temperature of gasoline = 5400 R

EFF = overall reduction efficiency (95 percent control x 90 percent collection ) = 85 percent

LL = 12.46 (1.00) (6.6) (66)/540 1 – 85 / 100

= 1.5 lb /103 gal

Total loading losses are :

(1.5 lb/103 gal (8.0 x 103 gal ) = 12 lb