HIGH MP CARGOES
High MP Cargoes are heated to reduce unpumpables and to reduce load on the ships centrifugal pumps. They should be washed with a temperature above MP, with cold interface removed.
Chemicals have different thermal properties. Some will heat up very quickly, whereas others, will require substantial heating, before any temperature gain is noticed. Similarly, those cargoes that heat quickly, tend to cool down quickly, whereas the cargoes which heat slowly have far better heat retention properties.
The colour too matters –white is a bad absorber and a bad radiator, while black is a good absorber and good radiator. These individual cargo properties should be recognised when heating cargoes on the loaded voyage. The length of the voyage must also be considered when deciding on heating schedules to avoid waste of fuel.
Unless instructions are given to the contrary, any “solidifying substance” should be maintained and discharged at a temperature of at least 10° above its melting point, to avoid pre-washing.
Stowage of cargoes with MP > 55 C must NOT be adjacent to cold interface lest the whole bulkhead gets a solidified thick film.
Should the cargo require it, heating coils can be opened to the tank, when the liquid is at a level of approximately one metre. This can off set cumulative list at berth –as for cargoes like Tallow.
If a cargo requiring heating is deemed dangerous/toxic leaks back to the engine room then “Dangerous/Toxic” return tank is required by BCH/IBC Code.
When loading solidifying cargoes, due regard must be made to ensure that lines do not become frozen. In any case, should stress and list/ trim conditions allow it, the tanks furthest away from the manifold should be completed first, using a sequence of working towards the shortest pipe length. In manifolds with connections both port and starboard, the opposite side to loading generally gets frozen. This must be unblocked at sea before discharge port.
Company policy requires that no tank is loaded to a volume of greater than 98% at any time. For cargoes like wine, take the permission of the chemical operator.
After loading high MP cargoes leave the pipelines open till the contents are drained properly. If proper written heating instructions are not received Master must Note Protest and inform the chemical operator.
If the tank is not blanketed with Nitrogen the sedimentation or build up at the tank bottom must be ascertained with sounding rod.
Charterers heating instructions must be obeyed and in any case heating increase must not exceed 5°C in a period of 24 hrs.
During cold weather the functioning of p/v relief valves should be checked regularly . It is possible that humid air vented from a cargo tank may condense and freeze thus inhibiting ventilation. This is also possible for cargoes with high melting point, such as Phenol, where cargo vapours could solidify in vent line .
For sedimented / high MP cargoes ensure that the deepwell impeller is not frozen by running the pump before arrival port with delivery valve shut.
When discharging a homogeneous heated cargo, the wing tanks should, as far as possible, be emptied before the centre tanks.
During the discharge, several tanks may be emptied simultaneously, however when the cargo sounding becomes around 1 meter discharge of such tank must be ceased temporarily. Final emptying, stripping and sweeping of the tanks must then happen one tank at a time.
The temperature in the tanks must be monitored and the heating must be adjusted in the tanks accordingly.
Never leave high MP cargoes inside the pipeline even for short periods like shifting barges etc. Check out if the common collector line will get frozen.
When vessels are carrying solidifying products it is important that the products are at the maximum discharge temperature (or slightly above) at least one week prior to arrival at the discharge berth. Also during this period once the product is up to required temperature, soundings must be made in each tank using a rod and line to determine if there are any solid products on the tank bottom.
In addition, any ballast in double bottom tanks beneath the cargo tanks MUST be lowered so that there is no direct contact between the ballast and the cargo in adjacent tanks.
Be aware of the slope of the pump delivery deck pipes towards the manifold. Some shipyards deliberately tilt the aft of manifold pipelines to avoid fitting superstrip lines. When loading high MP cargoes in winter from barges , any delay in between two barges can freeze cargo inside pipelines .
If the cargo goes below the steam coils and the surveyor makes a remark that there is unpumpable then the tank must be filled up again to cover the steam coils, reheated and then discharged again. Get tank dry certificate promptly—give notice to surveyor in writing in the pre-discharge CCR meeting.
After completion discharge of high MP pour point cargoes better to wash back lines using hot FW if feasible – compressed air is no use. In case of planned stop of high MP cargo in freezing weather keep the cargo recirculated. For recirculation of shore lines which can freeze discuss in the preloading meeting and agree in writing. Or you may have a condition where ship is blamed for cargo frozen in unlagged or non-thermal jacketed portions of shore lines.
In order to make the tank cleaning faster and more efficient, the Master should always try to get the Dry Tank Certificate as the tanks get empty one by one —especially for drying veg oils and solidifying cargoes which jam the impeller and freeze the valves.. Washing as soon as possible after receiving tank dry cert—and if the terminal allows it-- will prevent some solidification and save time.
During discharge the temperature of the cargo must be at least 10 degrees C higher than the pour point of the relevant cargo.
If vsl is discharging high MP cargoes the surveyor must be present at stripping/ sweeping time. If the discharge of high MP cargoes is stopped for any reason (shore tank change over/ barge change over/ shore leak ), the connecting hoses and lines on deck must immediately be drained back into the tank in order to avoid the system being blocked by coagulated cargo.
Any ROB noted on the certificate is clearly marked and considered by all parties as “unpumpable and unreachable, non free-flowing sediments / sludge”.
After dischg of vegetable oils / palm oils to prevent them from drying on the bulkheads, the bulkheads must be kept moist until the tank cleaning begins. In warm weather the drying process is fast and in cold / wet weather much slower. Hot cargo in adjacent tanks will make the residues dry very fast on the bulkheads.
Substances with a reasonable solubility (down to 0.2 %) will be removed with water. Be aware that the solubility of some chemicals increases with temperature. The wash water should be at least 150C higher than the melting point of the cargo.
For Caustic potash crystallizing point is 9C while for Caustic soda it is 12 to 15C. As per the IBC code prewash for substances which have a viscosity equal to or greater than 50 mPa.s at 20°C shall be washed with hot water (temperature at least 60°C), unless the properties of such substances make the washing less effective.
MP of a few cargoes in deg C:--
Coconut oil/ 14-28 C
Hydrogenated corn oil/ 28-35
Hydrogenated rapeseed oil/ 28-38
Palm oil/ 23-50
Peanut butter/ 23-45
Fatty alcohol/ 3 -40
Paraffin wax/ 55-60
Polyisobutylene PIB/ 90
Undecyl alcohol/ 15
Some cargo residues have very high MP which makes them difficult to emulsify. To clean such residues it may be necessary to use a solvent like toluene.
The cleaning of PV vent lines is best done with live steam.
Pre-cleaning non-drying fats with hot water is best done after first steaming the tanks
When Graco injecting using degreasers use only one machine. Graco injection is usually 0.1% or one litre per ton of water. But for very dirty tanks 0.5% is ok.
Washing pressures and temperatures must be maintained together and must not be adjusted to compensate for either a loss in temperature by reducing the pressure and/or the number of machines. If a problem is experienced with a loss of heat, then washing may be continued, but the washing time should NOT count until the required temperature has been reached again..
In the pre-planning stage, a proposed time scale ( bar chart ) must be formulated, to provide fore warning for the engine room. The Chief officer must also try to ensure that once pressures and temperatures have been reached, they should be kept as constant as possible, without undue fluctuations. This will avoid major fluctuations and associated problems in the engine room.
Temperature of the cleaning solution must be 20 C > MP of the cargo. Temperature of the cleaning solution must be 20 C > MP of the cargo.
Avoid rapid changes of temperature especially in cold weather will adversely stress the ship's structure.
When cargoes with a high wax content are carried, care must be taken that temperatures are not allowed to drop below flocculation/wax precipitation temperature as wax will not revert back into solution no matter how much the temperature is increased.
Hence if the actual loading temperature is considerably different from the specified loading temperature the Master must protest in writing . In cases of extreme temperature difference the Master may at his discretion, cease all loading operations until the matter is resolved. Keep the Chemical operator informed.
When calculating the bunkers required for cargo heating a reserve quantity of bunkers shall be included in the total to guard against voyage delays due to adverse weather or unforeseen climatic conditions.
-------CAPT AJIT VADAKAYIL