NMVOC Training

8/10/2019 NMVOC Training

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VOC Management Plan

Frequently asked Questions

(FAQs)

Training Guidance

and

understanding the Principles


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What is a VOC Management Plan?

and, Why do you need it?

A VOC Management Plan is a plan that is Crude Oil

Tanker specific and compiled in accordance with IMO

Guidelines (MEPC 185 (59) and MEPC Circ 680) to

supply guidance for the limitation of VOC emissionsfrom Crude Oil cargoes during its transportation and

handling (loading or discharge (COW)).

In accordance with MEPC Resolution 181 (59) the

Plan will be inspected by Port State Control officers

pursuant to the requirements of Regulation 15.6 of

MARPOL Annex VI.


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What is NMVOC?

and Why control it?

Non Methane Volatile Organic Compounds

(NMVOC) evolve in differing proportions

from Crude Oil cargoes and, subject to

conditions, are released to the atmosphere

during loading and carriage.

VOC gases are harmful and a pollutant to

the atmosphere and Maritime Environment.

They also act a precursor gas to the

formation of OZONE which is a recognised

Greenhouse Gas.


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What arethe Critical Criteria

impacting Tanker Operations?

There are two main criteria impacting the

necessity for NMVOC control for tanker

operations. They are: Pressurenecessitating a release for control

Temperaturegenerating vapour pressure

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

Any other energy input into the cargoRolling and

pitching at sea; rate of loading and turbulence in the

cargo tanks.


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Cargo Tank Gas Phases

Crude Oil Cargo Tanks contain two

gas/vapour phases that individually and

together have an impact upon Pressure

generation in the Cargo Tank gas phase

system. These are:

The Inert Gas (I.G.) component of the total

The NMVOC component of the total

Each of these gases should be considered

separately and together for NMVOC Control


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The Impactof Pressure

Cargo Tanks have a limiting pressure controlled by the P/Vvalve setting.

How is Pressure generated by I.G.?

IG Pressure is dependent upon the temperature of Gas

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

sunlight

How is Pressure generated by NMVOC?

NMVOC pressure is dependent upon the Liquidtemperature of the crude oil and the amount of volatile

components in the crude oil cargo which evolve into the

vapour space at varying concentrations (temperature

dependent). This varies with differing Crude Oil types.


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NMVOC concentrations during

loading

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90 100

%V

OCConcentration

% Fill of Cargo Tanks

Orig Vapour %

Evolved Vapour %

Total Vapour %


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The Impact of Temperature

The Impact of temperature is different for the

two types of gases present in the vapour phase

system onboard a crude oil tanker.

IG temperature will causes daily fluctuations in

the pressure contribution from this gas.

NMVOC liquid phase temperature determinesthe amount of evolved vapour and associated

concentration to that found in the liquid phase

Henrys Law or Raoults Law and Saturated

Vapour Pressure (SVP).


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A Pressure/Temperature Profile

of a crude oil during a voyage

0

200

400

600

800

1000

1200

1400

1600

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35 40 45 50

PressuremmWG

TemperatureDegC

Day Number

Tank temp

Pressure

P/V Valve Opening Pressure

Maximium NormalControl Operating

Pressure before ManualRelease by Vessel's

Command


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Cargo Tank Pressure

(necessitating release)

The cargo tank pressure shown on pressure

gauges on the IG system reflects the total

pressure in the system and is the

combination/addition of the IG and NMVOC

pressuresDaltons Law of Partial Pressure

Cargo Tank P/V valves are typically set at

around 1400 mmWG (16.53 psia).

When the total or combined pressures exceed

the opening pressure a proportion of NMVOC

will be released.


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Where Do you get the information from

to determine Pressure?

The NMVOC pressure is found on the MaterialSafety Data Sheet (MSDS) for the cargo.

When carrying more than one grade of cargo a

rough average of the vapour pressures willsupply guidance.

The MSDS could supply data as:

The Reid Vapour Pressure (RVP) but this ismeasured at approx 38 Deg C

Saturated Vapour Pressure (SVP) but here the

standardised conditions for measurement must also

be known.


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Tanker Operations

covered by the Management Plan

The Crude Oil Tanker operations required to be

covered by the VOC Management Plan are: Control of Emissions during Loading

Control of Emissions during the Voyage

Control of Emissions during DischargeCrude Oil

Washing

Control of Emissions using Specialist Equipmentif fitted

Additional considerations should be given to

Maintenance routines for: P/V valves and other vapour control systems

Tank openings and vapour leakage


13/19

Control of Emissions

on Loading (1) Prior to loading the cargo tanks need to be fully inerted. To limit

the extent of emissions the over pressure in the cargo tanks

should be set to the lowest deemed safe.

This will allow the NMVOC to evolve to generate its own Partial Pressure

at its Saturated Vapour Pressure which will contribute to the Total

Pressure within the tank vapour system

During loading NMVOC is evolved from the incoming cargo and

combined with existing NMVOC in the cargo tanks. There are

two pressure control methods:

Release to atmosphere via mast riser but maintaining the highestpossible pressure within the tank vapour system

Using the Vapour Return Manifold connection and return the vapour

ashore as per IMO MSC Circ. 585. again maintaining the highest

possible tank pressure.


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on Loading (2) Evolution of NMVOC during loading is mainly caused

by pressure drops in the loading pipeline system

throttled valves etc.

The main cause of vapour evolution during loadingis the pressure drop at the top of the loading drop

line. At this point vapour bubbles evolve and are

carried into the cargo tanks where they boil off

until the Equilibrium Pressure (Saturated Vapour

Pressure of the crude oil) in the cargo tank vapour

system is achieved. This pressure is independent

of the Inert Gas pressure.


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during the Voyage

NMVOC will evolve from the crude oil cargo during the

voyage. This will cease when the pressure in the

vapour phase pressure is in equilibrium with the

liquid phase SVP. Any change in cargo temperaturewill impact the equilibrium pressure. Higher

temperature will increase the pressure and vice versa.

During the voyage the SVP should be maintained in

the cargo vapour system and any required manual

vapour releases should not go below this pressure

reference VOCON Procedure. LOW CLOSING

PRESSURES SHOULD BE AVOIDED after a release.


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during Discharge

Vapour emissions should not occur during a discharge

programme unless heavy weather ballast is to be placed in a

cargo tank.

During discharge care should be exercised with the supply ofIG into the cargo tanks and avoiding excessive pressure in the

system. A low pressure cargo tank IG regime will assist in

efficient discharging/stripping.

During Crude Oil Washing (COW) selection of crude oil type

(multi parcel loadings) with lowest SVP is preferred. Closed

Cycle COW will limit VOC generation during this process and

avoid excessive VOC for displacement at next loading.


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Knowledge of Operation of

Special Control Equipment

There are numerous differing types of VOC

control equipment being marketed. Become

acquainted with the operation of this equipment

through it instruction manuals.

One popular method being employed is the

increased opening pressure settings of P/V

valves from 1400 mmWG to around 2000

mmWG together with avoidance of manual

releases during a voyage.


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Record Calculation and Sheet

The VOC Management Plan requires the

recording and estimation of the extent of VOC

emissions during a voyage.

This can only be done with manually controlled

releasessee next slide for proposed

spreadsheet calculation/recording method.

The extent of release during loading can be

estimated from the volume of the loaded cargo

and, thus, the extent of displaced vapour.


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Record of Releases

Manually controlled discharge

Voyage NMVOC Emission Calculation Spreads heet

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

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