Pneumatic Systems for Bulk Grain Unloading
Mr. Tomas Kisslinger, NEUERO Industrietechnik Germany
Mr. Jack Fox, NEUERO Corporation USA
With the opening of new flour mills, especially in the Far East, which depend heavily on the supply of grain by ships, shipunloading systems have become an important cost factor in today's competitive market. In this article we will present studies of the three main systems which are used to unload bulk grain carriers:
- Mobile systems
- Self-supporting equipment (Single line ship unloaders)
- Customised towers
When choosing a particular system each solution depends on many local conditions and variables, such as:
- The kind and size of ships
- Ownership of the facility
- Proximity of storage
- Quantity of grain to be unloaded per year
- Cost of labour
- Environmental protection etc.
Use of mobile systems
Mobile unloading systems are used when the available space has to be shared with other port activities and where the point of grain discharge may change according to port decisions. This system works well when dealing with almost any ship size and shape.
The new generation of NEUERO mobile unloaders - type GSD 280 - has brought a new dimension to the use of mobile equipment.
In realising a good unloading rate, capacity is the main factor - but this should be achieved at all equipment positions, and not only at one point. The working range at the same capacity and the span between the unloading and discharging points are fundamental to the operation.
Figures 1 and 2 show the working range of the GSD 280.
The booms on both the sucion and pressure sides of the unloading process are held by the machine. A swivelling capability of more than 310° results in a greater working range, allowing the mobile system to be positioned easily into small hatches. The use of a rotating cyclone instead of a flexible pipe allows the GSD 280 to achieve the maximum capacity in each position. Because of the equipment's turning range, interruptions caused by rain - which require the closure of the cargo hatch - are easier and quicker to handle.
|Figure 3 shows the GSD 280 working on a ship where its high capacity of 180 tons per hour (t/h) changes the work procedures. Instead of three to five machines being required to unload each hatch, only one is now needed. .... The high capacity of this system can dramatically cut shipping costs with a low capital investment cost.|
Single line ship unloaders
The use of mobile systems requires the availability of cranes to move the equipment into position. Also, the need to add the vertical pipes to the system requires a labour force to be in position 24 hours a day. In order to get a better overall performance with less operational expense, shipunloading systems such as the Multiport are used. These unloaders normally have a peak capacity of up to 500 t/h. They can be powered via electrical cable or by diesel generators and can be fixed or self-propelled on rails or rubber tyres.
The use of horizontal and vertical telescopic pipes allows a big area of the unloading hatch to be reached. With an auxiliary winch attached to the boom, a payloader (bobcat) can help the clean up operation in the ship's holds.
Figure 4 shows five Multiport type unloaders discharging a ship into quayside trucks and rail wagons. One of them is used as a "floater" i.e. it can be moved around easily, because it is mounted on rubber tyres. This rubber tyred "floater" can move to any location to help in the discharging as required. It is a 4-wheel steerable unloader and can avoid dead time by travelling quickly in curves. Characteristic of this type of equipment developed in the last few years include:
The Multiports, for example, are equipped with filters which capture the dust from the products being handled. One special type of filter cleaning system has shown to be the most adequate is the reverse flow generated by a blower. It uses the same air of the filter (same temperature and density), thus avoiding water condensation and blockage of the filter bags. Also, filter bags can be cleande by air blasts generated by an air compressor with an air dryer needed to avoid the mentioned water condensation. Today, the sound insulation in this equipment is standard and its use in ports close to residential areas is becoming more and more acceptable.
Short delivery time - standardisation
The Multiport unloader has a short delivery time because all swivelling parts are standardised, even the gantry if a rubber wheel type is required. With the use of rails, the design and necessary engineering takes some more time. A rail unloader will normally require a six-month delivery time and, if in stock, rubber tyred with generating set unloader will be available.
Maintenance and protection
Multiport unloaders offer electrical and mechanical protections such as:
- Electrical panel with PLC and troubleshooting lamps
- Limit switches
- Over and underload protection
- Protection of rotating parts
- Easy access to checking points
The possibility of lowering the boom to the ground offers a considerable advantage because inspection and substitution of parts - wearing plates of the elbow, winches and cable pulleys etc. - are made on the ground, making careful inspection very easy, and any dangerous work high above the ground is eliminated.
Use of customized towers
Heavier than Multiports, these towers are railbound and have a longer delivery time. The towers offer design advantages which allow other functions, like ship-loading and weigher-units, to be incorporated into the structures, combined or separately.
Figure 5, photograph taken at the Bogasari Flour Mill in Jakarta, shows two unloaders rated at 1000 t/h each one of them equipped with a loading boom. The units have a seven-ton x 20 m crane in each structure so that the lifting of "bobcat" payloaders can be made without interruption to the grain unloading/loading operation. This addition is often very useful in handling general cargo.
Access to each component of the tower is made easy by the availability of space in this type of equipment. The towers are ideal for grain terminals with a very high handling rate. Direct connection to a conveying system optimises material flow.
To clarify points that are always found confusing with bulk discharging systems we will define peak capacity, average capacity, and design and nominal capacity:
- Peak capacity is achieved at the shortest distance and this is the maximum that the system can handle
- Average capacity is the mass unloaded divided by the time elapsed between arrival and departure of a ship
- Design capacity (under ideal conditions) should be calculated at ten per cent over nominal capacity
- Nominal capacity is the capacity at a point of the system. In pneumatic systems normally mid way of telescopic pipes or an imaginary point in the ship's hold
There are also many variables beyond the control of the manufacturer, such as:
- Ship size and shape
- Skill of operation personnel
- Weather (rain, wind etc)
- Unloading sequence - depends on ship design
- Clean up tools
- Availability of payloaders
- Conveying equipment after unloading
Special attention should be given to the clean-up operation. The use of two bobcats increases the efficiency considerably by keeping the suction-nozzle in the product.
NEUERO started in pneumatic grain conveying 80 years ago with the manufacture of small agricultural machines. Since then the company has delivered equipment in the 20 t/h to 1000 t/h range to many installations around the world. NEUERO has two companies with sales, engineering, manufacturing and service facilities in Germany and in the USA.
(This article was publised in Port Technology International - Issue No. 6)