Blending/Commingling of LPG Cargoes On Board Gas Carriers

Leading the way; making a difference

INTERTANKO GAS AND MARINE SEMINAR

Blending/Commingling of LPG Cargoes On Board

Gas Carriers. Mr Stefanos Karakelles

Senior Manager Gas(LPG)


LPG Blending and SOLAS Regulation VI 5-2

• At its 90th session in 2012, the IMO Maritime Safety

Committee adopted SOLAS Regulation VI 5-2. • SOLAS Regulation VI 5-2 consists of 4 paragraphs and is

the result of lengthy deliberations at IMO beginning in 2005 and finally concluding in 2011 when MSC 89 approved the draft of SOLAS Regulation VI 5-2 and authorized its circulation for subsequent approval at MSC 90

• The paragraph which is of importance with regards to LPG blending is para .1:



.1 The physical blending of bulk liquid cargoes during sea voyages is prohibited. Physical blending refers to the process whereby the ship's cargo pumps and pipelines are used to internally circulate two or more different cargoes with the intent to achieve a cargo with a new product designation. This prohibition does not preclude the master from undertaking cargo transfers for the safety of the ship or protection of the marine environment.



This Paragraph makes it clear that LPG Blending during sea voyages is prohibited. Although IMO decided that LPG blending cannot be performed during sea voyages, it felt that it was beyond its remit to specify if LPG blending should be allowed within port limits. It has therefore been left to each port state/port authority to define the respective port location, limits and circumstances under which blending may be undertaken in each port.


Reasons for Blending

LPG Blending is being performed on board gas carriers for one of the following reasons. • The reception facility might not have the tank space

required for blending.

• The reception facility might not have the equipment/expertise needed for LPG blending.

• Blending might be interfering with shore facility’

loading/discharging schedule.


Reasons for Blending

• Importing Butane in countries where the ambient temperature drops below – 5C.

• The avoidance or reduction of tax (either import or manufacturing tax).

• Quicker turnaround of the cargo being imported, as the LPG mix would be directly fed to bottling plants, without delay.


Propane to Butane or Butane to Propane?

Propane to Butane

When propane is introduced to a butane tank, there will be rapid rise in tank pressure as the cooler propane tends to produce a large quantity of flash gas. If the propane is not introduced in a controlled manner, the vessel’s cargo compressors may not be able to cope up with the rise in tank pressures. Also the temperature gradient needs to be monitored, as temperature will tend to fall with introduction of propane. The risk of thermal stresses / shock should be considered during the blending process.


Propane to Butane or Butane to Propane?

Butane to Propane

When butane is introduced in a propane tank, the rise in tank pressure may not be immediate, but will tend to rise after a time lag. This can take place once the vessel proceeds to sea. Hence introducing of butane into a propane tank has higher associated risks, as the rise in tank pressure may not be apparent. It will tend to rise suddenly and could lead to uncontrolled venting if not monitored carefully. The heavier butane will also tend to stay in the bottom so the need for circulating the cargo arises.


Ways of Blending

1. Blending during Loading

2. Blending while at safe anchorage or at layby berth

3. Blending during Discharging


Blending in Various Ship Types • On board Fully Pressurized vessels: Is not a concern. Vessels are designed to withstand the pressure of all cargoes they are carrying even if the cargo reaches ambient temperature. • On board Semi-refrigerated vessels: Is not considered a major safety issue, although the relief valve settings can vary (MARVS Setting: 5~8.0 Bar) and the pressure of the resultant mix could exceed the MARVS setting. • On board a Fully refrigerated vessels: Can cause major concerns as these ships cannot carry the cargo at ambient temperatures. The cargo carried, is cooled below its boiling point. (MARVS Setting: 0.45 Bar)

PRODUCT Chemical Symbol Atmospheric Boiling Point Vapour Pressure at 37.8ºC (Bars Absolute)

PROPANE C3H8 -42.3 12.9

n-BUTANE C4H10 -0.5 3.6

i-BUTANE C4H10 -11.7 4.9

SHIP TYPE FULLY REF SEMI PRESS FULLY PRESS

MARVS BarG 0.45-0.50 5-8 17


Hazards associated with Blending

1. Generation of flash gas

2. Loss of power

3. Miscommunication with shore

4. Cargo roll-over due to density inversion.


Hazards associated with Blending

5. Stability and stress issues

6. Accuracy and sloshing issues

7. Thermal stress


HUMAN FACTOR

Biggest Hazard also the Biggest Safeguard Crew experience is a hazard common to each way of blending. On the other hand Crew experience can prove to be the most important safety buffer when conducting blending. It has become common in the industry for instructions on LPG blending to be issued without taking into account whether those on board have any previous experience of such operations.


General Guidance

1. Carry out risk assessment of the operation. 2. Plan the operation and brief all personnel involved. 3. Specify the tank pressure at which the operation must be

halted. 4. Consider the mechanical and technical limitations of vessel’s

equipment. 5. Evaluate and monitor stability and stress conditions affecting

the vessel during every stage of the blending operation. 6. Ensure sufficient ullage is available in the tanks. 7. Monitor the hourly trend of change in tank pressure and tank

temperature. In case of an upward trend, reduce rate of blending in order to stabilize pressure.

8. No other operations to be carried out during LPG blending.


Commercial Implications for Owners

• Cargo calculations and Deadfreight

• Bunkers used for Blending

• Time used for Blending

• Tanks’ condition upon completion of discharge



• Cargo calculations and Deadfreight. After the blending operation, the density of the mixture will not be a mathematical average of the two cargoes because the molecular composition of the mixture will be different. This can lead in cargo shortage claims. A prudent Owner should get indemnification from Charterers in this regard. The quantity the vessel would have been able to load in case mixing was not required must be taken into account by the Chartering department when calculating the freight rate. A relevant deadfreight letter of protest and a statement should be prepared by master.



• Bunkers/Time used for Blending Time Charter Clearly communicate to Time Charterers that all costs for the blending operation will be for their account and get their written agreement to avoid future disputes. Clearly communicate an estimate of the time and bunkers required. Spot Charters If a spot chartered vessel is requested to perform blending operations, in absence of a blending clause in the fixture, an addendum to the charter should be agreed identifying clearly that the owner will be compensated for time lost (at the demurrage rate) and for additional bunkers consumed. Clearly communicate an estimate of the time and bunkers required.



• Tanks condition upon completion of discharge Due consideration should be given to the condition of the tanks upon completion of discharge as LPG mix heel might not be suitable for the vessel’s next employment. For example, if the next cargo is a full propane cargo, certain terminals require the vessel to arrive fully ref in order to be allowed to load. This would mean that the owner will be facing a cost in order to arrive at that condition and should consider if this cost should be passed to Charterers.


Thank you

Port of Gotheburg, Sweden: Photo: Johan Gahnström

Stefanos Karakelles INTERTANKO Senior Manager,Gas (Secondee) London office: St Clare House, 30-33 Minories, London EC3N 1DD, UK T: +44 (0)20 7977 7037 (Dir) T: +44 20 7977 7010 (S/B) M: + 44 (0)7885897522 M(2): +30 69 55 666 423 E: [email protected]

Blending/Commingling of LPG Cargoes On Board Gas Carriers

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