Dear Sir

We noted your inquiry for a cement unloader, and are pleased to offer the following Surplus package.

It is a self containced Barge Mounted unit. Capacity is 400tph. Year 1995. Excellent condition.

Please feel free to contact us for additional information.

Sincerely,

Al Goodmundson

Phone Canada (306)-664-7260

Email norsequip@sasktel.net ■

Your required unloading rate would probably help others reading this thread. ■

Dear Mr Sulaiman,

I presume that this question is also referring to your thread –Cement Silo- under

-Silos, Hoppers, Bins and Domes- .

The silos you mention there will have a storage capacity of approx 11000 tons each (inverse cone type), making a total of aprox. 22000 tons maximum storage capacity of your terminal.

(For this volume a dome or a flat storage is also an option to consider)

As the (I think) only feasible way to load a silo of that height is pneumatic, you at least require a pneumatic pressure system after your ship unloader.

In that case, the comparison of the ship unoading part is between pneumatic unloading and mechanical unloading plus a transfer system to the pneumatic silo loading system.

The investment difference is the complete mechanical unloader versus the vacuum unloading part of a pneumatic unloader.

The operational differences are listed below.

Comparison pneumatic- versus mechanical unloading and transport

Pneumatic transport for unloading cement uses suction systems

and is always in dilute phase.

For pneumatic transport of cement by pressure systems,

dense phase and dilute phase are both possible.

For long distances and high capacities the dilute phase

system is preferred, while plugging can be avoided easily.

Mechanical unloading is done in various ways, of which

the grab-unloader and the screw-unloader are commonly used.

The grab-unloader is considered non-continuously ,

while pneumatic- and screw-unloaders are considered continuously.

The main properties of grab-unloaders are :

==========================================

- high flexibility

- acceptable reach in holds

- acceptable energy consumption per ton

- clean-up capabilities under normal conditions sufficient.

- dust emission caused by leaking grab shell

- dust emission when opening grab shell by air displacement.

- Receiving hopper with dust extraction filters around the circumference.

- Receiving hopper with rain cover when not operating.

- The hopper can also be filled through a pneumatic

conveying pipeline, using the filters for dedusting

the convey-air and with closed rain cover.

- risk of damage to the ship

- wearing by cement on rope wires and grabs

- subsequent transport also mechanical by means of

belt conveyors, screw conveyors, trucks, screw feeders, etc.

The main properties of screw-unloaders are:

==========================================

- low flexibility.

different types of commodities do mix with

remaining products in dead spaces in the system.

- insufficient reach in holds due to rigid construction

- lower energy consumption.

- clean-up capabilities are poor due to the principle

of the vertical screw, whereby the screw section must

be completely filled to transport (use of additional devices)

- system is sensible for blocking in case of overfeeding

(use of additional control system)

- dust emissions in the holds by avalanches and during

clean-up because of product falling back from the

screw in case of insufficient filling.

risk of damage to the screw by foreign matter in the cement.

(In such an event the screw can even get stuck)

- wearing by cement on screws, screw pipes and shaft seals

- subsequent transport also mechanical by means of

belt conveyors, screw conveyors, trucks, etc.

- a pneumatic subsequent pressure-transport is also an option with the related

properties.

The main properties of dilute phase pneumatic transport are :

============================================================

- high flexibility

Easy reduction of dead spaces in the system internally

makes the system suitable for handling different types

of commodities because of simple and minimum cleaning

procedures

- reach in holds improved by manoeuvrable nozzle into

two perpendicular directions

- Because of the principle of pneumatic dilute transport

(higher velocities) a higher energy consumption.

- clean-up capabilities are good, due to the

feeding independent function and movability of the

suction nozzle into two perpendicular directions

- vacuum system is not sensible for blocking (or

plugging) because of operating principle with

application of positive displacement pumps.

- pressure system is almost insensible for blocking

due to regulating system for continuous maximum

performance.

- dust emission in the holds is reduced to a minimum

by "skimming off" movement of nozzle and downwards

flowing covey-air. This also applies for the

clean-up situation.

Proper operation of shovels is then required.

- limited risk of damage to the system by foreign matter

in the cement. Too big lumps are left behind in the

hold. Smaller lumps can pass the system freely.

Butterfly valves can be affected by foreign matters in

the cement.(mainly ropes).

- little wearing by cement (only on butterfly valves)

- Subsequent transport is generally also pneumatic,

especially where long distances and difficult routings are involved.

Combination of mechanical- and pneumatic convey system

using a screw feeder.

=============================================

A screw-feeder consists of a screw with a reducing

pitch along the screw in the transport direction whereby the

screw fits exactly into a tube.

The feeding of the screw is then higher than the output.

This causes the material to be compacted and forming a plug in the tube. This plug can be stable and strong enough to withstand and seal against the high pressure in the pipeline.

As the screw feeder in a pneumatic pressure convey system has to

push the compacted bulk volume against the pressure under

considerable friction between the tube wall and the

screw flights, this type of feeder consumes a high energy per

conveyed ton, depending on backpressure.

(f.e. 110 kW for 150 tons/hr at 1.7 bar(o) # 0.73 kWh/ton)

Higher pressure requires higher power, also due to increased friction.

A to high pressure will cause the drive motor of a screw feeder

to stall and choke the screw tube.

The screw feeder/pneumatic convey system is continuous.

Systems using a screw unloading, with the inherit properties,

that dump the product into a screw feeder for subsequent

pneumatic pressure conveying, will therefore consume this

extra amount of energy compared to a double pressure vessel system.

This additional energy consumption is a considerable

disadvantage.

As a terminal design is depending on many parameters, s.a. maximum ship size, annual throughput, local labour cost, dock structure, etc. these variables may influence the decisions.

As an unloader has to handle ALL the cement through your installation, a failure will stop your operations immediately. Therefore apply a well designed unloader of high quality and maintainability and lowest possible energy demand.

We are ready for more information, if required.

Success

teus ■

Dear Mr Sulaiman,

The annual throughput is also very important to know, as it determines the number of ships per year and thereby the available unloading time per ship.

A 400 tons/hr designed pneumatic unloader will perform approx 250 – 300 tons/hr through the ship capacity (depending on the efficiency of the ship and operators)

This means that a 20000 dwt ship will be unloaded in about 40 to 45 hrs

For a 20000 dwt ship, the required unloading rate per day is approx. 3900 tons per day.

This means at least 13 to 16 hrs working per day (2 shifts)

The pipeline diameter should be 18”/22” (stepped) (first estimate) and an air volume of 170 m3/min at 2.5 bar (Divided between a compressor and a booster, 2 x Aerzen VM85)

(The dynamic force at the outlet will be approx. 7900 N)

To reach that capacity, 40 m3 pressure tanks are needed.

Detail decisions on your total terminal are related to your future use pattern and therefore it is difficult to advise you in detail.

F.i.

Are you outloading into bulk trucks, trains, other ships, to a nearby concrete factory, bagging station or mill or a combination of these?

Are you also planning to use cement self unloaders ?

Is your quay length sufficient for shifting the sea going vessel or do you have to move the unloader?

Consult experienced experts with proven knowledge of these installations and contact

terminal operators with similar installations.

success

teus ■

Cement or alumina unloaders etc should always be vacuum machines in the interests of respiratory health & general environmental well-being.

Suction unloading involves collecting the material first. What happens afterwards is optional & a straightforward fued between pneumatic & tube conveying proponents.

It would seem obvious to limit the lift height during the suction process but nobody seems interested & you will initially be offered machines demanding about 0.6MW which will lift the powder out of the hold & up to a receiver some 12m aloft, at least, on the quay.

A smaller receiver located in the hold, by a standard dockside crane would seriously reduce the lift height for the powder. Under the receiver would be a vane valve pair, one on standby, to admit powder into a blow tank & thence propel it over the ship's rail.

You could afford 2 or 3 of these machines & then your utilisation would be very high, absolutely fully continuous even, because you would not need to take time out to position an obscenely ponderous special purpose track mounted gadget in sympathy with vessel hogging & hatch coaming considerations.

In rememberance of some previous cement importing fiascos, Nigeria springs to mind, there is always the probability that you will have to unload bagged, or IBC, consignments someday. For that reason large suction unloaders carry an auxilliary general purpose dockside crane anyway.

There are also companies making compact tyre mounted suction unloaders which are fondly used to unload Rhine barges & similar applications. Have a look for them in the e-directory. ■

dear mr Sulaiman,

I compared your silos ot 18 m dia x 60 m height with 6 inverse silos, I installed in 1994.

The maximum content of the silos is even about 18800 tons each. (Totally 37900 tons)

The lifting height of a pneumatic unloader is firstly given by the height of the hatch coaming of the ballasted, unloaded ship above the dock level.

Whether the receiving vessel of the vacuum unloader has to be necessarily higher than this, depends on the ship size and the distance between the water level and the dock height.

The unloading of Rhine barges require always a considerable lifting height, because the Rhine can have level differences of 6m to 7m and then the dock height has to be overcome.

Big sea ships do not have that problem when they are close to the sea.

In estuaries or on tidal rivers (as the Tames) this problem does exist.

To unload a 20000 dwt ship the unloader would need approx 300 m3/min of air displacement (2 x Aerzen GM 150 Sm), requiring approx. 350 kW.

best regards

teus ■

In the August 1991 issue of "Bulk Solids Handling" there was an article on this topic. 800 tonne/h of cement to be transferred from ships on the River Thames to four 10,000 tonne silos 500 m away. A pneumatic conveying system was chosen for the application.

A single vacuum nozzle was used for off-loading and twin pipelines with a positive pressure blowing system was used for the transfer to the silos. The single unloader on the jetty included two sets of twin blow tanks for the onward conveying.

With the ship off-loading line being relatively short and operating at 85% vacuum I suspect that this equates to dense phase conveying. Vacuum conveying does not preclude dense phase conveying; it is determined entirely by pressure gradient, as is positive pressure conveying.

It was stated that 2400 kW was required for the duty of 800 tonne/h, although the total installed power was 3200 kW.

A pneumatic conveying system was chosen in preference to alternative mechanical systems for the duty for cost, maintenance and environmental reasons. Although the pneumatic ship off-loading section of the plant would have been more expensive than the equivalent mechanical equipment, it was stated that the twin pipelines for the onward transfer to the silos were much chaper than the mechanical equivalent. ■

Dear mr Mills,

I know the cement unloader you refer to, because I was the project manager of that machine and I commissioned it in 1991 with my colleagues in 1991.

Installed are :

8 vacuum pumps Aerzen VM410-VE at 132 kW motor

2 compressors Aerzen VM410 at 240 kW motor

2 booster compressors VM 537 at 520 kW motor

Totaling at 2570 kW installed motor power.

We managed to reach 750 tons/hr over one hour on the first ship, just limited by the discharge side of the installation. So we might have reached a somewhat higher capacity on the suction side.

The off loading length is approx 44.2 mtrs.

The vacuum unloading was running at approx 65% to 70% vacuum at a solid loading ratio of approx 61.

The other 800 tons/hr pneumatic cement unloader is in Los Angeles.

Good old memories

best regards

teus ■

Dear Mr Sulaiman,

You can send me a message through this forum.

Just click on my name and my profile pops up.

Then you can choose to send me an e-mail

best regards

teus ■