VOC Management PlanVOC Management Plan

Frequently asked Questions Frequently asked Questions (FAQs)(FAQs)

Training GuidanceTraining Guidance

and and

understanding the Principlesunderstanding the Principles

What is a VOC Management Plan?What is a VOC Management Plan?and, Why do you need it?and, Why do you need it?

A VOC Management Plan is a plan that is Crude Oil A VOC Management Plan is a plan that is Crude Oil Tanker specific and compiled in accordance with IMO Tanker specific and compiled in accordance with IMO Guidelines (MEPC 185 (59) and MEPC Circ 680) to Guidelines (MEPC 185 (59) and MEPC Circ 680) to supply guidance for the limitation of VOC emissions supply guidance for the limitation of VOC emissions from Crude Oil cargoes during its transportation and from Crude Oil cargoes during its transportation and handling (loading or discharge (COW)).handling (loading or discharge (COW)).

In accordance with MEPC Resolution 181 (59) the In accordance with MEPC Resolution 181 (59) the Plan will be inspected by Port State Control officers Plan will be inspected by Port State Control officers pursuant to the requirements of Regulation 15.6 of pursuant to the requirements of Regulation 15.6 of MARPOL Annex VI. MARPOL Annex VI.

What is NMVOC?What is NMVOC?and Why control it?and Why control it?

Non Methane Volatile Organic Compounds Non Methane Volatile Organic Compounds (NMVOC) evolve in differing proportions from (NMVOC) evolve in differing proportions from Crude Oil cargoes and, subject to conditions, Crude Oil cargoes and, subject to conditions, are released to the atmosphere during loading are released to the atmosphere during loading and carriage.and carriage.

VOC gases are harmful and a pollutant to the VOC gases are harmful and a pollutant to the atmosphere and Maritime Environment. They atmosphere and Maritime Environment. They also act a precursor gas to the formation of also act a precursor gas to the formation of OZONE which is a recognised Greenhouse OZONE which is a recognised Greenhouse Gas.Gas.

What What areare the Critical Criteria the Critical Criteria impacting Tanker Operations?impacting Tanker Operations?

There are two main criteria impacting the There are two main criteria impacting the necessity for NMVOC control for tanker necessity for NMVOC control for tanker operations. They are:operations. They are:

Pressure – necessitating a release for controlPressure – necessitating a release for control Temperature – generating vapour pressureTemperature – generating vapour pressure

There are other operational criteria that will There are other operational criteria that will impact the generation of NMVOC such as:impact the generation of NMVOC such as:

Any other energy input into the cargo – Rolling and Any other energy input into the cargo – Rolling and pitching at sea; rate of loading and turbulence in the pitching at sea; rate of loading and turbulence in the cargo tanks.cargo tanks.

Cargo Tank Gas PhasesCargo Tank Gas Phases

Crude Oil Cargo Tanks contain two Crude Oil Cargo Tanks contain two gas/vapour phases that individually and gas/vapour phases that individually and together have an impact upon Pressure together have an impact upon Pressure generation in the Cargo Tank gas phase generation in the Cargo Tank gas phase system. These are:system. These are:– The Inert Gas (I.G.) component of the totalThe Inert Gas (I.G.) component of the total– The NMVOC component of the totalThe NMVOC component of the total

Each of these gases should be considered Each of these gases should be considered separately and together for NMVOC Controlseparately and together for NMVOC Control

The The ImpactImpact of Pressure of Pressure Cargo Tanks have a limiting pressure controlled by the P/V Cargo Tanks have a limiting pressure controlled by the P/V

valve setting.valve setting.

How is Pressure generated by I.G.?How is Pressure generated by I.G.? IG Pressure is dependent upon the temperature of Gas IG Pressure is dependent upon the temperature of Gas

and follows the “Ideal Gas” Lawand follows the “Ideal Gas” Law It varies throughout the Day and Night with heating from It varies throughout the Day and Night with heating from

sunlightsunlight

How is Pressure generated by NMVOC?How is Pressure generated by NMVOC? NMVOC pressure is dependent upon the Liquid NMVOC pressure is dependent upon the Liquid

temperature of the crude oil and the amount of volatile temperature of the crude oil and the amount of volatile components in the crude oil cargo which evolve into the components in the crude oil cargo which evolve into the vapour space at varying concentrations (temperature vapour space at varying concentrations (temperature dependent). This varies with differing Crude Oil types.dependent). This varies with differing Crude Oil types.

NMVOC concentrations during NMVOC concentrations during loadingloading

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Orig Vapour %

Evolved Vapour %

Total Vapour %

The Impact of TemperatureThe Impact of Temperature

The Impact of temperature is different for the The Impact of temperature is different for the two types of gases present in the vapour phase two types of gases present in the vapour phase system onboard a crude oil tanker.system onboard a crude oil tanker.

IG temperature will causes daily fluctuations in IG temperature will causes daily fluctuations in the pressure contribution from this gas.the pressure contribution from this gas.

NMVOC liquid phase temperature determines NMVOC liquid phase temperature determines the amount of evolved vapour and associated the amount of evolved vapour and associated concentration to that found in the liquid phase – concentration to that found in the liquid phase – Henry’s Law or Raoult’s Law and Saturated Henry’s Law or Raoult’s Law and Saturated Vapour Pressure (SVP).Vapour Pressure (SVP).

A Pressure/Temperature ProfileA Pressure/Temperature Profileof a crude oil during a voyage of a crude oil during a voyage

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Pressure

P/V Valve Opening Pressure

Maximium Normal Control Operating

Pressure before Manual Release by Vessel's

Command

Cargo Tank PressureCargo Tank Pressure(necessitating release)(necessitating release)

The cargo tank pressure shown on pressure The cargo tank pressure shown on pressure gauges on the IG system reflects the total gauges on the IG system reflects the total pressure in the system and is the pressure in the system and is the combination/addition of the IG and NMVOC combination/addition of the IG and NMVOC pressures – Dalton’s Law of Partial Pressurepressures – Dalton’s Law of Partial Pressure

Cargo Tank P/V valves are typically set at Cargo Tank P/V valves are typically set at around 1400 mmWG (16.53 psia).around 1400 mmWG (16.53 psia).

When the total or combined pressures exceed When the total or combined pressures exceed the opening pressure a proportion of NMVOC the opening pressure a proportion of NMVOC will be released.will be released.

Where Do you get the information from Where Do you get the information from to determine Pressure?to determine Pressure?

The NMVOC pressure is found on the Material The NMVOC pressure is found on the Material Safety Data Sheet (MSDS) for the cargo. Safety Data Sheet (MSDS) for the cargo. When carrying more than one grade of cargo a When carrying more than one grade of cargo a rough average of the vapour pressures will rough average of the vapour pressures will supply guidance.supply guidance.

The MSDS could supply data as:The MSDS could supply data as:– The Reid Vapour Pressure (RVP) but this is The Reid Vapour Pressure (RVP) but this is

measured at approx 38 Deg Cmeasured at approx 38 Deg C– Saturated Vapour Pressure (SVP) but here the Saturated Vapour Pressure (SVP) but here the

standardised conditions for measurement must also standardised conditions for measurement must also be known.be known.

Tanker OperationsTanker Operationscovered by the Management Plancovered by the Management Plan

The Crude Oil Tanker operations required to be The Crude Oil Tanker operations required to be covered by the VOC Management Plan are:covered by the VOC Management Plan are:

Control of Emissions during LoadingControl of Emissions during Loading Control of Emissions during the VoyageControl of Emissions during the Voyage Control of Emissions during Discharge – Crude Oil Control of Emissions during Discharge – Crude Oil

WashingWashing Control of Emissions using Specialist Equipment – if fittedControl of Emissions using Specialist Equipment – if fitted

Additional considerations should be given to Additional considerations should be given to Maintenance routines for:Maintenance routines for:

P/V valves and other vapour control systemsP/V valves and other vapour control systems Tank openings and vapour leakageTank openings and vapour leakage

Control of EmissionsControl of Emissionson Loading (1)on Loading (1)

Prior to loading the cargo tanks need to be fully inerted. To limit Prior to loading the cargo tanks need to be fully inerted. To limit the extent of emissions the over pressure in the cargo tanks the extent of emissions the over pressure in the cargo tanks should be set to the lowest deemed safe.should be set to the lowest deemed safe.– This will allow the NMVOC to evolve to generate its own Partial Pressure This will allow the NMVOC to evolve to generate its own Partial Pressure

at its Saturated Vapour Pressure which will contribute to the Total at its Saturated Vapour Pressure which will contribute to the Total Pressure within the tank vapour systemPressure within the tank vapour system

During loading NMVOC is evolved from the incoming cargo and During loading NMVOC is evolved from the incoming cargo and combined with existing NMVOC in the cargo tanks. There are combined with existing NMVOC in the cargo tanks. There are two pressure control methods:two pressure control methods:

Release to atmosphere via mast riser but maintaining the highest Release to atmosphere via mast riser but maintaining the highest possible pressure within the tank vapour systempossible pressure within the tank vapour system

Using the Vapour Return Manifold connection and return the vapour Using the Vapour Return Manifold connection and return the vapour ashore as per IMO MSC Circ. 585. again maintaining the highest ashore as per IMO MSC Circ. 585. again maintaining the highest

possible tank pressurepossible tank pressure. .

Control of EmissionsControl of Emissionson Loading (2)on Loading (2)

Evolution of NMVOC during loading is mainly caused Evolution of NMVOC during loading is mainly caused by pressure drops in the loading pipeline system – by pressure drops in the loading pipeline system – throttled valves etc.throttled valves etc. The main cause of vapour evolution during loading The main cause of vapour evolution during loading

is the pressure drop at the top of the loading drop is the pressure drop at the top of the loading drop line. At this point vapour bubbles evolve and are line. At this point vapour bubbles evolve and are carried into the cargo tanks where they “boil off” carried into the cargo tanks where they “boil off” until the “Equilibrium Pressure” (Saturated Vapour until the “Equilibrium Pressure” (Saturated Vapour Pressure of the crude oil) in the cargo tank vapour Pressure of the crude oil) in the cargo tank vapour system is achieved. This pressure is independent system is achieved. This pressure is independent of the Inert Gas pressure.of the Inert Gas pressure.

Control of EmissionsControl of Emissionsduring the Voyageduring the Voyage

NMVOC will evolve from the crude oil cargo during the NMVOC will evolve from the crude oil cargo during the voyage. This will cease when the pressure in the voyage. This will cease when the pressure in the vapour phase pressure is in “equilibrium” with the vapour phase pressure is in “equilibrium” with the liquid phase SVP. Any change in cargo temperature liquid phase SVP. Any change in cargo temperature will impact the equilibrium pressure. Higher will impact the equilibrium pressure. Higher temperature will increase the pressure and vice versa.temperature will increase the pressure and vice versa.

During the voyage the SVP should be maintained in During the voyage the SVP should be maintained in the cargo vapour system and any required manual the cargo vapour system and any required manual vapour releases should not go below this pressure – vapour releases should not go below this pressure – reference VOCON Procedure. reference VOCON Procedure. LOW CLOSING LOW CLOSING PRESSURES SHOULD BE AVOIDED PRESSURES SHOULD BE AVOIDED after a release. after a release.

Control of EmissionsControl of Emissionsduring Discharge during Discharge

Vapour emissions should not occur during a discharge Vapour emissions should not occur during a discharge programme unless heavy weather ballast is to be placed in a programme unless heavy weather ballast is to be placed in a cargo tank.cargo tank.

During discharge care should be exercised with the supply of During discharge care should be exercised with the supply of IG into the cargo tanks and avoiding excessive pressure in the IG into the cargo tanks and avoiding excessive pressure in the system. A low pressure cargo tank IG regime will assist in system. A low pressure cargo tank IG regime will assist in efficient discharging/stripping.efficient discharging/stripping.

During Crude Oil Washing (COW) selection of crude oil type During Crude Oil Washing (COW) selection of crude oil type (multi parcel loadings) with lowest SVP is preferred. Closed (multi parcel loadings) with lowest SVP is preferred. Closed Cycle COW will limit VOC generation during this process and Cycle COW will limit VOC generation during this process and avoid excessive VOC for displacement at next loading.avoid excessive VOC for displacement at next loading.

Knowledge of Operation ofKnowledge of Operation ofSpecial Control EquipmentSpecial Control Equipment

There are numerous differing types of VOC There are numerous differing types of VOC control equipment being marketed. Become control equipment being marketed. Become acquainted with the operation of this equipment acquainted with the operation of this equipment through it instruction manuals.through it instruction manuals.

One popular method being employed is the One popular method being employed is the increased opening pressure settings of P/V increased opening pressure settings of P/V valves from 1400 mmWG to around 2000 valves from 1400 mmWG to around 2000 mmWG together with avoidance of manual mmWG together with avoidance of manual releases during a voyage.releases during a voyage.

Record Calculation and SheetRecord Calculation and Sheet

The VOC Management Plan requires the The VOC Management Plan requires the recording and estimation of the extent of VOC recording and estimation of the extent of VOC emissions during a voyage.emissions during a voyage.

This can only be done with manually controlled This can only be done with manually controlled releases – see next slide for proposed releases – see next slide for proposed spreadsheet calculation/recording method.spreadsheet calculation/recording method.

The extent of release during loading can be The extent of release during loading can be estimated from the volume of the loaded cargo estimated from the volume of the loaded cargo and, thus, the extent of displaced vapour.and, thus, the extent of displaced vapour.

Record of Releases – Record of Releases – Manually controlled dischargeManually controlled discharge

Voyage NMVOC Emission Calculation Spreadsheet

Date

Time at Start of Release

Time at Stop of Release

Duration of Release

(Minutes)

Tank Pressure at

Start of release

(mmWG)

Tank Pressure at

Stop of Release

(mmWG)

Mean Pressure

during Release

(Metres WG)

Diameter of Release

pipeline opening (Metres)

Length of Release Pipeline

from Tank (Metres)

Mean Velocity of

Release (Metres/sec)

Total Vapour Volume of Release

(Metres ^3)% of

NMVOC

NMVOC Vapour Release

(Metres^3)

NMVOC equiv. Liquid

Release (Metres^3)

NMVOC equiv.

Weight Release (Tonnes)

29th Sept 1020 1028 8 1200 800 1.072 0.508 30 4.22 410.60 80 328.48 1.314 0.716

The main shipboard input criteria for this spreadsheet are the accurate recordings for:• The Start and Stop Times for the manual release• The Tank Pressure at the start and stop of the release• A measurement or estimation of the % NMVOC in the vapour phase of the tanks