Molasses

Molasses

Molasses is an easy product to carry and handle, however if problems occur the often create some spectacular results. The items below may then be of help.

Prior to loading

Tanks should be free of traces of any previous cargo, odour free and dry. Open lines and valves check for water. Check and test heating coils and log test results.

This is the only accurate means of calculating cargo quantity is by means of a Draft Survey, although the vessels radar ullaging system will produce a result sufficiently accurate for checks during cargo operations, but be aware that ‘foaming’ may affect the radar readings. It is extremely important to obtain as accurate draft survey as possible, both before and after loading.

Measurements of ullage and volume are merely a check, and must never be considered as a means of establishing the weight of the cargo. Arrival trim should not exceed two meters by the stern, and there must be a positive draft forward. It will be necessary to check the ballast carefully, and specific gravity will need to be obtained. Vessels that have a double bottom ballast system, if at all possible, should either have their tanks pressed up or empty. It is usual to make a check of fresh water on board; but fuel figures are taken as given by the Chief Engineer.

The ships tanks to be loaded will clearly depend on draft, trim, list and stability requirements. Obviously the number of tanks utilized should be minimized, to save draining time and tank cleaning.

However, 98% capacity should be treated with some caution as problems can arise due to foaming when air is released from the molasses during passage. On vessels with large cargo tanks, there can also be problems with heat distribution and the ability to obtain an even temperature throughout the tank on passage.

Ensure that all vessel small bore lines are blinded off to prevent molasses entering these systems.

Loading

The loading of molasses is a relatively simple operation, though sometimes a slow procedure. It may be through the ship’s manifold, direct to the drop lines, or over the tank top, all of which are acceptable subject to local regulations. Samples should be taken from the pipeline during loading, and from the ship’s tanks on completion.

A further draft survey is taken on completion of loading, to establish the loaded weight. Any apparent shortages should be protested by the Master to the shipper.

If loading was through vessel cargo lines, then ensure that all lines are well drained immediately after loading.

Loading of molasses is preferred through the drop lines as this will minimise the chance of ‘foaming’.

Foaming may well cause a radar ullaging system to cease working, resulting in the CCR screens to ‘white-out’. The only short term solution is to resort back to manual ullaging, Ensure that such tapes are available should such a problem occur.

On passage

Heating instructions will be issued to the Master prior to departure. In general, heating should commence about five days from the first discharge port, to obtain a discharge temperature of 41C. Maximum increase per day must not exceed 5C. Careful checks of temperature and records must be maintained during heating. Heating of molasses is not uniform, and erratic changes can occur. Regular checks must be made of heating coil returns, and ideally the steam supply controlled by the return valve.

Discharging

On arrival at the discharge berth, the shore terminal should take samples from each ship tank for analysis. A check will be made of ullages, temperature and refractometer brix (to check water content). A further draft survey will be carried out to verify the quantity of cargo on board.

Any vessel discharging molasses can only discharge as fast as her ability to drain tanks. It is strongly advised against pumping the bulk ashore and leaving the draining to near completion. This will result in long delays that are of no benefit to the Owner or the Charterers. It is quite acceptable to reduce the bulk discharge rate, to facilitate keeping the draining program up to date.

During discharge, monitor the cargo temperature. It is important that the temperature is maintained as the viscosity is reduced and pumping hence made easier, however ensure that the heating coils are turned off well before completion of discharge to avoid caramelisation of the molasses onto the coils.

If permitted by the Charter Party or by an attending Molasses Superintendent as each ship’s tank comes to draining level (about 6″), live steam should be injected into the tank by whatever means available. A letter stating the amount and time and authorization for this procedure may be handed to the Master (on request). NEVER, inject steam directly into the molasses, unless directed to do so by a Molasses Superintendent under exceptional circumstances.

Foaming can occur on the surface of the molasses as air is released from the cargo. This may be reduced by directly injecting air into the cargo, causing movement, and the foam being taken into the molasses. This however remains a temporary solution and should only be carried out under supervision.

If a multi berth discharge is involved, terminal personnel are likely to request that all draining be delayed to the last berth. This is not recommended, except where there is sufficient time to drain tanks during sea passage to the next port.

Using deepwell cargo pumps

For hydraulically driven pumps, consider the use of food-grade oil. Hydraulic oil leakage into molasses has, and will, result in rejection of the cargo, although the seal arrangement in Framo pumps should prevent this.

Vessels with large, deep cargo tanks may find difficulty in discharging and require provision of portable screw and booster pumps.

These portable pumps are not constructed with a cofferdam in way of the seals, so any leakage will result in hydraulic oil contamination of the cargo. As these pumps are often connected to the vessels own hydraulic line connections, it is strongly advised that food-grade hydraulic oil is used in the ship’s systems.

Should portable power-packs be provided, food-grade hydraulic oil should be specified.

For deepwell pumps, the lower pump speed setting is often best for molasses discharge to prevent any cavitation or foaming.

Filling of the deepwell cargo pump cofferdams with fresh water or even continuous flushing of the pump cofferdam with fresh water during the entire period that the molasses is onboard is recommended so that burning of the cargo pump seals is avoided.

The FRAMO Bulletin No. 18 provides useful guidance.

Tank Cleaning

Provided that steaming of the cargo tank during discharge has been carried out, then a good hot wash is all that is required for cleaning.

Diluted solutions of Molasses should be removed from the cargo tank within 24 hours, or when acidic, should be neutralised by an alkaline tank cleaning product to a pH of between 5 and 9.

If caramelisation has occurred on the heating coils, then when the tank is completely clean and dry, crack live steam onto the coils. This will cause the caramel to drop off the coils where it may then be swept up. Any remaining caramel may be wiped off the coils with a dry cloth.

Comments are closed.