CTM 9.10 A4	Chemical Tanker Manual CTM Handling and carriage of Molasses	Doc No.: CTM 9.10 A4 Revision: 01 Date: 15 Oct 2024 Issued by: DPA Approved by: MD

1. GENERAL

Molasses is the thick dark brown syrupy liquid left after sucrose has been removed from the mother liquid in sugar manufacture. There are two types of molasses – cane molasses and beet molasses. Blackstrap molasses is the syrup from which no more sugar can be obtained economically.

2. Viscosity

The viscosity of both beet and cane molasses is influenced by constituents other than sugar. Beet molasses is usually of lower viscosity, particularly at ambient temperatures, than cane molasses, but in both cases, it is affected by the dry matter content. Molasses exhibits the phenomenon called critical viscosity, which means that above a certain dry matter content, the viscosity increases at a greater rate than might be expected from the increased dry matter content. The critical viscosity for cane molasses lies between 81 and 85º hydrometer brix. The viscosity of molasses is affected both by dry matter and temperature. For example, a rise in temperature of 10 ºC may reduce the viscosity to half or less, and a reduction in the dry matter content will also decrease viscosity.

Molasses is not a Newtonian fluid, and pumpability does not only depend on viscosity but also on factors like where it is coming from, storage time, fermentation process, brix value, and temperature during the period the fluid is onboard the ship.

Pumpability depends on brix value, its place of origin, storage time, fermentation process, and temperature during the period the cargo is on board the ship. BRIX indicates pumpability of the product.

SG = 400 / (400 - brix) in degrees.

3. Fermentation of Molasses

The visual effect of fermentation in molasses is an increase in volume and the creation of a layer of foam in and especially on top of the molasses. Besides the development of foam, the temperature sharply increases by a couple of ºC per 24 hours, and an alcoholic odor can always be observed, sometimes in combination with the odor of acetic acid. Fermentation can be stopped by blowing air into the molasses; the available oxygen will destroy the anaerobic bacteria and help to slow down the fermentation process.

Molasses fermentation occurs when molasses is diluted with salt or fresh water and is accelerated by heat. During fermentation, CO2 (with possible traces of ethanol and higher alcohol vapors) is given off, which will produce inhalation hazards in compartments containing molasses residue.

4. Prior Loading

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

The only accurate means of calculating cargo quantity is by means of a Draft Survey, although the vessel's radar ullaging system will produce a result sufficiently accurate for checks during cargo operations. However, be aware that ‘foaming’ may affect the radar readings. It is extremely important to obtain as accurate a 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. 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 possible, should either have their tanks pressed up or emptied.

The ship's 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 is not recommended (Please refer to the below note) 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.

5. During 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 the vessel's 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 minimize 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 revert to manual ullaging, ensuring that such tapes are available should such a problem occur.

6. During Loaded 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 41°C. The maximum increase per day must not exceed 5°C. 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 should be controlled by the return valve.

It is important to check p/v valves daily for good operation to avoid tank overpressure.

7. Heating of Molasses

Obtain heating instructions and full specifications from the shipper; otherwise, a letter of protest should be issued. At a temperature of 40°C, molasses is relatively stable, but as the temperature rises, sugar may be lost due to thermal decomposition. At temperatures above 60°C, there is always the possibility of thermal decomposition and complete destruction of the cargo.

Heating instructions must be strictly followed, and a heating log should be completed. It is important to maintain accurate temperature records. Note that temperature should be measured at several places and levels within the tank, as different temperatures can be experienced.

When ballasting, if possible, keep tanks slack to avoid the tank top cooling down too quickly.

8. Discharging Molasses

On arrival at the discharge berth, the shore terminal should take samples from each ship's 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 is made easier. However, ensure that the heating coils are turned off well before completion of discharge to avoid caramelization of the molasses onto the coils.

If permitted by the Charter Party/Operator/Terminal or by an attending Superintendent (as relevant), 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, along with authorization for this procedure, may be handed to the Master (should be requested).

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.

9 TANK CLEANING AFTER MOLASSES

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. Then hammer coils vigorously with wooden mallets. Remove balance powder with scotch brite pads, especially underneath. Don’t try to remove with Kew Machine—the caramel will become like sticky chocolate.