Procedures for handling bags
Options for receiving bulk at a bag-handling port
Procedures for handling bulk
Low volume bulk
Small general cargo vessels can be used to carry bagged grain, but bag handling is not common in major grain exporting countries and attracts additional costs because of slow loading and lower density stowage compared to mechanically handled bulk. Preslung pallets and on-board forklift trucks reduce loading time.
Sampling and analysis - can take place from exposed bags before and during discharge. The objective of the analysis will be to ensure that the shipment meets contract specifications and to detect damage or live insect infestations. (Refer Chapter 4).
Shipboard fumigation - fumigants penetrate bagged cargo more evenly than bulk. Ventilation after fumigation is a problem unless the vessel is fitted with a forced draught ventilation system. (Refer Chapter 3.3)
Cargo discharge - a labour-intensive operation using slings and ship derricks or dockside cranes. Spillage is a major problem. Added costs are incurred because of slow ship turn-round time and long wharf occupancy. Vessels standing off may unload into lighters when no berth is available or the draught of the loaded vessel is greater than the depth of water alongside the quay.
Port storage - general transit sheds in the port area and outdoor stacks are used for temporary storage. This operation will require local transport and an adequate supply of experienced labour. Facilities must be available for direct loading to road and rail vehicles for transport up-country or to storage facilities outside the port area.
Fumigation in the port area - fumigation, especially with phosphine, may be a problem because of interference with general store working. Properly prepared outdoor stacks can be fumigated. (Refer Chapter 3.2)
Primary and secondary storage - bagged commodities can be moved directly to wholesalers or retail outlets. Mills can receive stocks from stores or directly from the port.
(a) Bag off on board ship.(b) Discharge by cranes fitted with clam shell grabs, by pneumatic conveyors or elevators directly onto wharf. Bags are then filled manually or by using a bagging plant incorporating a weighing machine to give standardized bags.
(c) Specialized plant is available mounted on barges for bulk discharge.
Operations of this type are highly labour intensive (an advantage in areas where employment opportunities are limited); produce excessive quantities of spillage, dust loss and pollution; and result in port congestion.
Regular high volume imports or exports justify provision of high-speed handling equipment. Purpose-built bulk carriers are used which are compatible with loading machinery at the port of origin. However, the draught of such vessels when loaded may present difficulties at the port of discharge.
It is essential that all components of the system are compatible. For example, poor forward planning causes delays and payment of demurrage on vessels; unreliable electricity supplies will disrupt grain movement; complete stoppage of the system may be prolonged if repair and maintenance facilities are inadequate.
Sampling and analysis - samples can be taken from the exposed surface of the grain. Where this has been loaded as one grade it will be more homogeneously mixed than with a bagged cargo. However, over-stowage of an interior quality of grain will not be detected.
Shipboard fumigation - bulk vessels can be fitted with equipment for fumigating the entire cargo with phosphine. The absence of this equipment means that only insects infesting the upper levels of the cargo will be controlled, because of slow dispersal of fumigant. (Refer TDS # 15).
Port grain terminal - silos should be constructed on the quayside to avoid long distance conveying which is expensive to maintain and operate. Unloading rates can be up to 1000 tonnes/hour allowing vessels a quick turn-round. Commodities can be loaded directly to block trains and bulk road transport. Any excess of discharge over despatch can be held in the silos. Moisture and mould problems occur when low-temperature grain is off-loaded at hot, humid ports. Driers may be needed at port terminals to reduce grain moisture content to a safe level.
Fumigation - port silos can be fitted with a fumigation system so that insect-infested cargoes can be dealt with on shore rather than on board ship.
Portside mills - must have sufficient silo capacity to accommodate different grades of grain which will be blended to give an optimum quality product.
Where bag handling facilities are inadequate a modified bulk system may be employed to handle smaller or intermittent imports of bulk grain. This may be a scaled down version of a full bulk system with a slower rate of grain handling and longer periods of storage in silos. Occasional arrivals of bulk grain may be handled with improvised equipment such as port side cranes fitted with clam shell grabs and bag stores converted for on-floor bulk. However, this system is time consuming and may involve considerable spillage.
