Ch16 cargo handling

16 CARGO HANDLING16.1 Change of Grade Propane/Butane Propane Loading The term "fully cooled ready to load" means:  The cargo tank bottom is cooled down to a maximum of -39 Celsius and t

16 CARGO HANDLING

16.1 Change of Grade Propane/Butane

Propane Loading

The term "fully cooled ready to load" means:

 The cargo tank bottom is cooled down to a maximum of -39 Celsius and the maximum mean temperature above the mid - depth of the cargo tank, in the range between two thirds and three quarters of the Maximum Allowable Tank Filling Level (MATFL), excluding any

temperature indicated in the cargo tank dome vapour space, in no warmer than -25C

The cargo tank pressure is to be no more than 70MB on arrival at the berth

Butane loading

The term "fully cooled ready to load" means:

 The cargo tank bottom is cooled down to a maximum of 0 Celsius and the maximum mean temperature above the mid depth of the cargo tank, in the range between two thirds and threequarters of the MATFL and excluding any temperature indicated in the cargo tank dome vapour space, no warmer than + 14C

Cargo tank pressure is to be no more than 70 mb on arrival at the berth

Changing Propane tanks to Butane

There are two possible ways to change two Propane tanks to receive Butane

 The first is to be utilised only if there is insufficient Butane retained on board to allow the complete or partial displacement of the propane vapour by Butane vapour The method is to merely puddle heat the Propane liquid heel and to reliquify the resulting excess vapour into the remaining Propane tank, on completion the excess

propane can be pumped into the deck pressure vessel, according to the filling table in the cargo operations manual, and ensuring that there is sufficient coolant left in the remaining Propane tank so that it will be fully cooled on arrival Kuwait On completion of this operation the tanks

are hot gassed until they are approximately -5 degrees average vapour temperature, the tanks are

then ready to load the Butane

 The second method must be utilised when there is sufficient Butane retained on board

to partially or fully replace the propane atmosphere in the tanks to be changed In this method thePropane heel is puddle heated and, as before, the resultant vapour is reliquified to the remaining Propane tank The tanks are warmed up to approx zero degrees and Butane vapour is then

introduced to the bottom of the tanks, the Butane vapour is generated either by liquid through the

vaporiser or by puddle heating the Butane heel and thus generating Butane vapour The propane vapour is drawn from the top of the tanks and is reliquified to the remaining Propane tank, the interface between the Propane and Butane is easily detectable b9 monitoring the condensing pressure in the reliquifaction plant or the temperature after the expansion valve It is particularly important that the interface is carefully monitored because if the recovered Propane is heavily contaminated with Butane it will be difficult to fully cool the tanks when they have to be

converted back to propane carriage, indeed it is preferable to vent the Propane / Butane mix at the interface rather than save it Once all the Propane has been consolidated in the remaining Propane tank, transfer the available Propane liquid to the pressure vessel by pump Finally the tanks are to be cooled ready to load

 It is important that if the pressure vessel does not have sufficient capacity for the quantity of Propane that is recoverable from the tanks, then the excess Propane is retained in the Propane cargo tank If there is a large excess of Propane remaining then the Charterer should be informed of the amount that can be added to the Bill of Lading, but the ship must retain

sufficient to convert the two tanks back to Propane and cool them after the completion of the Turkish voyage

Changing Butane tanks to Propane

 On departure from the discharge port, the heel in the butane tanks to be changed should be puddle heated and the resulting vapour reliquified back to the remaining Butane cargo tank If there is a large amount of Butane recovered, the Charterer should be informed so that they can add the excess to the Bill of Lading

 Propane from the pressure vessel is to be passed through the tank to be changed, the Butane is to be removed from the bottom of the tanks, reliquefied and returned to the designated Butane cargo tank, the interface between the Butane and Propane is readily detectable by

observing the condensing pressure on the reliquifaction plant or the temperature after the

expansion valve If there is insufficient propane in the pressure vessel to fully change the

atmosphere of the tanks, then liquid or vapour can be taken from the designated propane cargo tank

 When the atmosphere in the tanks has been changed to Propane then Propane liquid, from the reliquifaction plant or by cargo pump is to be sprayed into the top of the tank until it is fully cooled ready for loading

 If there is insufficient Propane retained after discharge, either to fully change the atmosphere in the cargo tanks or to fully cool them ready for loading, then the Charterer is to be informed that the ship will require coolant at the load port and that it will have to go off the berth

 It must be stressed that if, for any reason, the Master believes that the ship will be

unable to fully achieve the required arrival temperatures and pressures, the Ship Managers and Charterer must be informed as early as possible, in order to either arrange coolant or an

indemnity against delays due to high tank pressures during loading

Preamble

Butadiene and Crude C4 containing Butadiene are very reactive chemicals which during transport may react with itself and form polymers (dimers) and/or react with any oxygen in the cargo system and form highly explosive peroxides Refer to form "Notice Butadiene"

Objective

To minimise the risk of any unwanted chemical reaction when transporting Butadiene and Crude C4 containing Butadiene

Inerting of Cargo Tanks with Nitrogen

In order to avoid the formation of peroxides, which besides being highly explosive also acts as a catalyst for polymerisation, the cargo tanks, piping and refrigeration system shall be inerted with nitrogen until the oxygen in the cargo system is reduced to the level required by the shippers

Regardless of the requirements by the shippers Butadiene shall not be loaded into a tank containing more than 0.2% oxygen

Before leaving the loading port a certificate shall be delivered on board stating the following:

The name and quantity of the inhibitor added;

The date inhibitor was added and the normally expected duration of its effectiveness;The action to be taken should the length of the voyage exceed the effective lifetime of the inhibitor;

Any temperature limitations affecting the inhibitor.

If a certificate is not received prior to departure, the Gas tanker Department shall be contacted immediately

Transportation Temperature

As polymerisation increases with heat, it is important that the cargo is cooled until fully refrigerated

as soon as possible, and maintained fully refrigerated during the entire voyage regardless of the discharge temperature

Draining Water

Depending on the specification Butadiene may contain up to 0.5 per cent water, which besides the risk of freezing the pumps also absorbs the inhibitor, with subsequent risk of polymerisation

When the cargo has settled, the cargo tanks are checked for free water by opening the puddle

heating/stripping line If no or only a little water is present the tanks are left until the temperature in the sump is close to +1 C Any water contained in the cargo will emerge during cooling and the

cargo tanks shall again be checked for water when the temperature in the sump is close to +1 C.

Small amounts of water are drained overboard by use of an ejector During the draining the

soundings shall

be closely monitored to avoid any excessive loss of cargo

If a large amount of water (more than 100 litres per tank) is either suspected or detected, the Gas tanker

Department and the Nautical Department shall be contacted before any draining is commenced

Circulating the Cargo during Voyage

The inhibitor used in Butadiene and Crude C4 containing Butadiene is normally Catechol (TBC)

Tertiary-Butyl-If too much inhibitor has been added in the loading port, it may be difficult to remove the surplus inhibitor during the subsequent tank cleaning

Circulation of the cargo for a few hours each day during the laden voyage reduces the risk of surplusinhibitor sticking to the tank surface Circulation shall be through the upper spray line and filling line

Before circulation is performed the precautions mentioned in Section B3 of these Guidelines shall

be taken

Circulating the Cargo during Discharge

During discharge some of the cargo shall be recirculated through the start-up line When the

sounding is at about 1.5 metres some of the cargo shall also be circulated through the lower spray lines If performing Nitrogen Displacement Discharge according to Section E13 in these Guidelines,

no circulation of cargo shall be performed during discharge

Product Washing in the H-class

During discharge product washing according to Section E12 in these Guidelines shall be performed Product washing is not to be performed if the vessel is discharging by use of Nitrogen Displacement Discharge according to Section E13 in these Guidelines, in which case a complete methanol wash shall be performed when tank cleaning

As the inhibitor does not boil off and the vapour therefore is uninhibited, the risk of polymerisation

or formation of peroxides in the refrigeration system is present

Cooling of Butadiene

Normal Cooling Operation

During normal cooling operation the flow of uninhibited liquid through the refrigeration system is constant and the risk of polymerisation or formation of peroxides is therefore minimal

Compressor Discharge Temperature

The Chemical reaction increases when Butadiene is heated and pressurised and it is therefore

important that the compressor discharge temperature and the suction pressure do not exceed the values prescribed by the manufacturer, i.e 600C and 2.0 Bar Gauge The Temperature Selector Switch shall be set accordingly before cooling of Butadiene or Crude C4 containing Butadiene is initiated

Disconnection of the Refrigeration Plant

If the refrigeration plant or a part thereof is taken out of operation and blanked off from the cargo system for a prolonged period, the system in question must be drained and cleaned in a systematic manner in order to positively remove all Butadiene

Gas Freeing after Discharge

After discharge of Butadiene or Crude C4 containing Butadiene all pipes, compressors, condensers, intermediate coolers, auxiliary manifolds and drain system used for loading and discharging must bedrained and cleaned in a systematic manner in order to positively remove all Butadiene thus

preventing the formation of peroxides

Anhydrous (water free) Ammonia (NH)is a gas at ordinary temperatures and pressures It may

be liquefied by reducing its temperature to minus 330C, or by moderately increasing thepressure above it Anhydrous Ammonia should not be confused with Aqueous Ammonia,which is a solution of Ammonia in water Often Anhydrous Ammonia is simply referred to asAmmonia Ammonia is a common feedstock in the fertiliser industry

Properties of Ammonia

All persons on board should be familiar with the properties of Ammonia At normal

temperature and atmospheric pressure Ammonia is a pungent colourless vapour Under low temperature conditions it may appear as a dense white vapour Ammonia vapour serves as its own warning agent At concentrations of 10 ppm the odour will be detectable by most

persons The TLV of Ammonia is 25 ppm Any uncontrolled leakage of Ammonia, especially

of li4uid, will release large amounts of harmful vapour which may cause varying degrees of damage to the skin, eyes and respiratory tract Skin contact with liquid will cause skin bums.Warm Ammonia vapour at ambient temperature is lighter than air and in the open will

disperse by virtue, of its own buoyancy Vapour produced from cold liquid may mix with air however and produce heavier than air mixtures which will stay close to the ground dispersing only when it warms to ambient temperature A concentration of 2500 ppm is rapidly fatal to life

The main physical constants of Ammonia are as follows:

1) Atmospheric boiling point -33.30C

5) Latent heat (1 atm, minus 330C) 1370.76 J/kg

6) Flammable limits(% by vol in air) 16 – 28 %

7) Auto ignition temperature 6510C

At ordinary temperatures and atmospheric pressure Ammonia is a vapour, /~, but by reducing

its temperature to its atmospheric boiling point of minus 33.3 50C, it may be stored as a refrigerated liquid

The vapours of Ammonia are flammable and bum with a yellow flame forming water vapour

and Nitrogen, however, the vapour in air requires a high concentration (16 - 25%) to be

flammable and has a high ignition energy requirement (600 times that for propane) and bums

with a low combustion energy For these reasons the IMO codes (1994), while requiring full

attention to the avoidance of ignition sources, do not require flammable gas' detection in the

hold or other spaces of ships carrying Ammonia However, Ammonia must be regarded as a

flamn4able cargo All electrical equipment used in the cargo area must be electrically safe

Health Hazards

At low concentrations in air, Ammonia vapour irritates the eyes, nose and throat Inhalation ofhigh concentrations produces a sensation of suffocation, quickly causes burning of respiratorytracts and may result in death

Liquid Ammonia causes severe burns on contact with the skin, while its effect on being

swallowed would be to cause severe corrosive action on the mouth, throat and stomach

Severe eye damage can be caused by exposure to high gas concentrations or direct contact

with liquid

Advice on emergency medical treatment for Ammonia is also contained in the IMO Medical

First Aid Guide (MFAG), Table 725 A copy of the guide must be available in the medical

locker / dispensary

Safety Equipment

A set of respiratory and eye protection shall be provided for each person on board The

number of sets on board must take into account any supernumeraries carried in addition to thearticled crew The number of sets on board should not be less than the number of person who

are likely to sail on the ship In addition to the foregoing, a further two sets must be located onthe bridge for the use of pilots or other persons temporarily on board

The respiratory protection must be of a self contained type and have a working duration of at least

15 minutes Filter type respiratory protection is not permitted Emergency escape respiratory

protection will normally be stored in the same location as a person's lifejacket Emergency escape respiratory protection shall not be used for fire-fighting or cargo handling purposes Each piece of respiratory equipment shall be marked with this requirement

A separate set of tight fitting goggles shall be provided with each emergency escape respiratory protection set unless the design of the 'respiratory equipment face mask also provides suitable eye protection

All persons on deck or in the vicinity of the cargo area shall at all times wear, or have immediatelyavailable on their person a set of tight fitting eye goggles Goggles shall be worn over the eyesduring all high risk operations such as sampling, disconnection of cargo hoses / arms or when thereare any leaks or suspected leaks of cargo liquid or vapour

At least two decontamination showers and an eye wash shall be maintained in an operationalcondition at all times Ammonia liquid or vapour are on board The showers and eyewash are to be

prominently marked such that there location can easily be identified from all areas on the cargodeck The showers and eyewash shall be constructed and maintained such that they can operated inall ambient temperatures Isolation valves in the showers or eyewash supply line shall be kept open

at all times When due to maintenance or other requirements the water supply to the showers oreyewash must be isolated, alternative arrangements for the supply of water to temporary showersand eyewash must be made

All persons on deck or in the vicinity of the cargo area shall wear suitable clothing, which willprovide them with protection against the effects of a release of Ammonia

All protective equipment required by the IMO Gas Code shall be maintained in good operatingcondition at all times The location of all equipment is to be clearly marked The equipment shall belocated in areas where personnel can retrieve and don the equipment in the minimum of time.Equipment should not be stored in the vicinity of areas which could be considered at high risk in theevent of a leak or spill i.e the manifold area

Toxic Gas and Moisture Detection Equipment

All instrumentation for monitoring the level of Ammonia in spaces must be maintained in goodcondition and be operating at all times Ammonia liquid or vapours are on board It should also bepossible to monitor the pressure in all hold spaces These items form part of the operationalchecks detailed in Section 8

All detection equipment calibration shall be checked and all audible I visual alarms and any

other systems shall be tested at least monthly A record of all calibration checks and system tests shall be maintained In the event of a toxic gas detection system deficiency, the Master shall be informed

All equipment shall be maintained in accordance with the manufacturer's instructions A copy of the instructions shall be maintained on board

At least two sets of portable detection equipment shall be maintained in good condition on board

A sufficient supply of Ammonia detector tubes shall be available The tubes carried shall all be within their expiry date The portable detection equipment shall be fitted with sample lines of suitable length to enable sampling of remote spaces

Solubility

Ammonia vapour is extremely soluble in water and will be absorbed rapidly with heat liberated during the solution process, to produce a strong alkaline solution of Ammonium Hydroxide One volume of water may absorb 1000 volumes of Ammonia vapour The introduction of water into tanks containing high concentrations of Ammonia may immediately cause dangerous vacuum conditions unless unrestricted access of air is provided Similarly, the air within the hold spaces around cargo tanks should be maintained in a dry condition, so as to prevent a vacuum forming

in the event of a leakage of Ammonia into the space

Ammonia is alkaline and Ammonia vapour/air mixtures may cause stress corrosion cracking in any part of the cargo containment system made of Carbon-manganese steel or Nickel steel Whenany changes are made to any part of the cargo system on board, then any replacement or

additional parts must conform to the requirements of the applicable IMO codes and Flag or Classrequirements.

Reactivity

Ammonia is highly reactive with Copper Alloys, Aluminium Alloys, Galvanised surfaces, Phenolic Resins, Polyvinyl Chloride,~ Polyesters and Viton Rubbers These are unsuitable for any part of machinery or instrumentation which may be exposed to Ammonia liquid or vapour, even if due to accidental release

It can form explosive compounds with Chlorine, Iodine, Bromine, Calcium, Silver Oxide and Silver Hypochlorite and Mercury It is for this reason that instruments containing mercury must not used if Ammonia can come into contact with the Mercury either by design or by accidental release

Mild steel, stainless steel, neoprene rubber and polythene are generally suitable

Preparing to Load Ammonia

When preparing a tank in a gas free condition for the carriage of Ammonia, inert gas from a combustion type inert gas generator must never be used, due to the reaction of Ammonia vapour with the CO2 content of the inert gas The reaction will form carbamates which will cover tank walls and may block sensors and lines also seize pumps The formation of carbamates is to be avoided

Inerting prior to the carriage of Ammonia is not required by international conventions, however many terminals may require tanks to be inert prior to loading Ammonia When inerting is

required, Nitrogen must be used

If loading into a gas free tank, liquid Ammonia should never be sprayed into the tank containing air as there is a risk of creating a static charge which could produce a source of ignition and also the conditions for stress corrosion cracking due to the presence of oxygen

In order to minimise the risk of Ammonia stress corrosion cracking in tanks constructed of

Garbo-manganese or Nickel steel it is advisable to keep the dissolved oxygen content below 2.5

ppm w/w This can best be achieved by reducing the average oxygen content in the tanks prior tothe introduction of liquid Ammonia to less than the values given as a function of the carriage temperature in Table below

+100C 0.10

Ammonia is usually purged with fresh air and this is swept through the cargo system once tank temperatures have increased above the dew point of the air so as to avoid condensation and contamination of tank surfaces

Water Washing

Water washing with fresh water to remove the final traces of Ammonia may be carried out andthis is a very quick and effective method for certain types of tank since Ammonia is extremelysoluble in water The high solubility of Ammonia could lead to vacuum conditions being createdwithin a tank depending on vapour concentration prior to washing It is very important to ensure

an adequate air supply into any tank during the washing process

Water washing is best used only on cargo containment systems which are completely clean, rustfree and have minimum interior structure

If water washing, the following precautions are to be observed:

 Low Ammonia concentrations must be ensured before water is introduced to the tank The concentration should be measured by means of suitable detector tubes

 Fresh water must be used Salt water will leave deposits which are difficult to remove and will increase rust formation in steel tanks

Tanks should not be washed if they contain submersible pumps unsuitable for water immersion

After washing it is essential to remove all water residues using either the tank's cargo pump, aportable pump or eductor system Prior to the use of a cargo pump to discharge water from atank, the manufacturers operating instructions should be consulted to ensure the pump is capable

of pumping water (density 1000 kg/in3), without over-loading the pump motor

The tanks and pipework system must be thoroughly dry before proceeding with preparations to load, not only to avoid ice formation, but also to remove all water which will otherwise hold Ammonia contamination for many voyages

In order to achieve maximum dryness after purging it is important to:

I) Ventilate the tanks with air having a dew point lower than the tank temperature so as toavoid condensation on the tank surfaces In conditions of high humidity ventilation with warm air may be necessary

2) Ventilate the tanks and cargo system at the highest practicable temperature to

encourage release of Ammonia from rusty or other surfaces Ammonia is released 10 times faster

at 450C than at 00C

If Ammonia washings are to be discharge overside, the requirements of MARPOL Annex II must

be observed Aqueous Ammonia is classed as a category C substance under Annex II In some areas, the discharge of Ammonia overside may be prohibited

If Ammonia is discharged overboard in accordance with the requirements of MARPOL 73/78, Ammonia contaminated washings should not be allowed to enter the ship's sea water intakes to the engine room due to the fact that Ammonia will be corrosive to copper-based alloys in the

Objective

To ensure that the cargo intake at Rafnes is optimised by initiating cooling of the cargo as soon aspossible

1 Inerting with Nitrogen

Prior to commencing loading in a cargo tank, the cargo tank shall be inerted with nitrogen deliveredfrom shore until the requested oxygen level has been reached The inerting with nitrogen shall beperformed according to Section A 2 in these Guidelines except the lining up which shall be asdescribed below

1.1 Lining Up

In order to commence loading and cooling cargo as soon as possible tanks 2 and 4 are purged inparallel and in series with tanks 1 and 3, thereby making it possible to load tanks 2 and 4 whilecompleting the purging of tanks 1 and 3

1.1.1 Shore Tanks Full on Arrival

If the shore tanks are full on arrival the shore installation may require the vessel to start loading assoon as possible, in which case cargo tank no I should be inerted with nitrogen and loaded first

1.2 Swing Elbows

The ship arrives with the systems connected to one system except elbows 1C910 A and 1C929 A onthe condensate line, which shall be out Before arrival valve 1C071 aft of the port booster pump onthe liquid line below the heat exchanger shall be blanked off between the valve and System I (tanks

1 and 3) to ensure that any possible leakage will not cause VCM liquid to mix with nitrogen duringinerting of tanks 1 and 3 simultaneously with loading tanks 2 and 4

1.3 Manifold Connections

The nitrogen hose is connected on the vapour manifold Main System I, the loading arm is connected

on the liquid manifold Main System II and the vapour return on the vapour-manifold Main SystemII

1.4 Flow Direction

The nitrogen is led through the vapour stations aft of the compressor house to the top of tanks 2 and

4 in parallel via the vapour line Initially the air is vented off from the liquid line and the lower sprayline to vent stacks 2 and/or 4 When nitrogen is detected in the bottom of tanks 2 and 4, vent stacks 2and/or 4 are closed and the corresponding elbows connecting the liquid line to the vent stacks areremoved The air/nitrogen is directed to tanks 1 and 3 via the condensate line

When the required oxygen concentration has been reached in tanks 2 and 4, the flow of nitrogen isaltered to complete nitrogen purging of tanks 1 and 3 directly from the manifold via the vapour line,and elbows 1C930 on the condensate-line and 1C928 A on the Vapour-line are removed

The air from tanks 1 and 3 is vented off via vent stacks I and/or 3 When the required oxygen

concentration has been reached in tanks I and 3, the elbows to the vent stacks are removed

2 Loading of cargo tanks 2 and 4

As soon as inerting tanks 2 and 4 is completed and elbows 1C930 and 1C928 A have been removedthe loading is commenced in tank 2

2.1 Loading via Cargo Heater

If the sea water is colder than the product in the shore tanks, loading via the cargo heater should beused in order to cool the cargo The cargo heater must be pressure tested well in advance of arrival

by means of hand pump to about 5 bars overpressure

2.2 Removing Nitrogen from Cargo Tanks

Compressor nos 2 and 3 are used for transferring nitrogen/VCM-mixture to tank 4 Thecompressors are used one by one as the compressors shall be stopped before the maximum alloweddischarge temperature of +900C is reached The minimum interval between the start of eachcompressor shall be in accordance with manufacturer's instructions, i.e 20 minutes

pressure in the shore tanks.

2.4 Vapour Return to Shore

When the pressure in tank 4 is well above the pressure in the shore tanks the cooling of tank 2 isstopped and all vapour and condensate valves to tank 2 are closed Loading is continued in tank 4

The vapour return to shore is then opened and the pressure in tank 4 is reduced until slightly abovethe pressure in the shore tanks

When the pressure is reduced, the vapour return and all vapour valves on tank 4 are closed, andcooling of tank 2 is continued

Above procedure is continued until the vapour in tank 4 is pure VCM, upon which cooling of thetank is initiated Cooling of tanks 2 and 4 is continued throughout the remaining loading operation

3 Loading of Cargo Tanks 1 and 3

When the atmosphere in cargo tanks 2 and 4 is pure VCM, the blank at valve 1C071 is removed, provided that tanks I and 3 are inerted to the required oxygen level, and the vapour return is changed

to the vapour-manifold Main System I Before the vapour return is changed the hose must be purgedwith nitrogen

Loading is then commenced in tank no 3

3.1 Removing Nitrogen from Cargo Tanks

Compressor no 1 is used for transferring nitrogen/VCM-mixture to tank 1 The compressors shall bestopped before the maximum allowed discharge temperature of +9OoC is reached Minimuminterval between each start of the compressor shall be in accordance with manufacturer'sinstructions, i.e 20 minutes

3.2 Vapour Return to Shore

When the pressure in tank 1 is well above the pressure in the shore tanks the transferring ofnitrogen/VCM mixture from tank 3 is stopped and all vapour and condensate valves to tank 3 areclosed The loading is continued in tank 3

Vapour from tank I is returned to shore via the vapour return until the tank pressure is slightly abovethe pressure in the shore tanks

When the pressure is reduced, the vapour return and all vapour valves on tank I are closed, andtransferring of air/VCM mixture from tank 3 is continued

The above procedure is continued until the vapour in tank 3 is pure VCM, upon which thecondensate is returned to tank 3 and cooling of tank 3 is commenced Tank I is then loaded until the