Unloading
Umarye,
What are you unloading? A railcar, a ship? And what material are you unloading? Grain, iron ore? And which machine are you using? A grab unloader, a bucket wheel unloader?
Please be more specific if you want an answer.
Reinhard Wohlbier ■
Capacity Of Unloader
We are unloading iron ore from river barges in capacity range of 1000 to 3000 Tons.
We are using rail mounted gantry type four rope Grab Barge Unloaders. ■
Capacity Of Unloader
The answer to your question is dependent upon the style of barge - open, single source or multiple hatch design.
I'm assuming that as you have stated fairly small cargoes of 1kt-3kt that it is a single source, open barge. In this case the free or "cream" digging rate will increase the average throughput of the grab unloader as there is less time required for clean up of the remnants in the hold compared with the percentage of cream digging time.
You need to calculate the amount of the material able to be accessed by the grab without external intervention (FEL's, bobcats, manpower, etc) in the first instance, thus the time taken for this operation can be calculated.
The amount of time taken for the clean up of the remnants will depend on what method you're using and how clean the barge needs to be before casting off.
Happy to provide any further advice if required. ■
Re: Capacity Of Unloader
Ours is a single hold open barge without hatch covers of 1Kt - 3Kt
95% of the material is accessible through the grab without any external intervention. Any external intervention if any will be only through manual means.
5 % of the cargo is left back in the barges and through clean up is not carried out.
Kindly advise whether the average rate that can be achieved by the unloader can be reasonably considered to be 85% of the free digging capacity. ■
Capacity Of Unloader
If you're only leaving 5% of the material in the barge (50 - 150t) this is pretty clean and will mean that you will be part loading the grab a fair amount of the time when close the the hold extremities.
The best way to estimate the theoretical through hold rate is to use free digging cut off as the top 1/3 to 1/2 of the pile (based on the rill angle) where the grab is full 100%. The remainder is to be taken at reduced capacity (down to say 75% full for the next 1/3 height and 35% for the remainder).
This is a rough "rule of thumb" but will give you a guide. It really all depends on the barge dimensions and the cargo geometry you are employing. Another variable is whether you can rotate your grab for the best orientation.
I would have thought that 85% would be a little optimistic and would expect to see a figure closer to 72-78%. ■
Capacity Of Unloader
The cargo hold of the Barge is rectangular shape of size 13 mtrs. wide x 40 mtrs length and the cargo is stacked in 2-4 heaps which are conical in shape. Since the unloader is Gantry type, the Grab cannot be rotated.
In the event of having to select the party from following data which should be the best option to deliver the avarage capacity of 750 TPH.
Parameters I II III IV V VI
Cycle time (secs) 46 38 52 48 52 42
No. of Cycles
/Hour 77 95 69 75 69 86
Grab volume
(m3) 5.36 6.0 -- 6.9 6.3 4.5
Payload (Tons)12.6 14.5 -- 15.2 15 10
Average rate
(TPH) 750 750 750 750 750 750
Free digging capacity
(TPH) 913 1250 -- 1125 --- ---
Since the above data cannot be displayed in the tabulated form, each figure in the row to be considered as the parameter of the party indicated under roman numbers ■
Re: Capacity Of Unloader
Dear Sir.
There are no any international standards which defines the “kinds” of ship loader/unloader capacity, though many organizations or institutes provide such definitions due to different reasons. Anyway, the capacity of uloader is a parameter more suitable for continuous type machines where capacity slightly depends on type and locations of cargo source and receiver. For this kind of unloaders the capacity is one of the main parameters, it can be given in m3/h or in TPH but last is only for some “specific” cargo.
In case of cyclic type loading/unloading machines, like cranes or grab (un)loaders, the definition “capacity” like “productivity” is not exactly applicable to single machine. The main parameters are: grab capacity, safe working load (SWL), lifting and lowering velocity, trolley velocity etc. Here we can talk about capacity only if we have a certain technological chain, like “barge – grab unloader – stock pile” or “barge – grab unloader – receiving hopper – belt conveyor – stocker – pile”. So here, you are free to go. You can use phrase “average capacity” when you want to describe capacity what you usually have. “Maximum capacity” can be capacity reached under the best conditions: shortest distance, mild weather, best operator, usage of anti-swinging controller, etc. Nominal capacity I’d rather live for continuous unloaders.
I think it would be much easier to answer to your question if you explained the reason of your question, i.e. what you want to do with these parameters.
Best regards,
Vladimir. ■
Re: Capacity Of Unloader
We have a barge- grab barge unloader-receiving hopper- belt conveyer- stacker-pile arrangement.
We want to assess the design that has been submitted by our client who have erected our barge unloaders and the average capacity as per their offer is not being realised by these machines.
The machines are to deliver 750TPH on the average but what we realise is only 500 TPH. ■
Re: Capacity Of Unloader
Now your question seems more clear. In your case the free digging or maximum capacity is capacity of barge unloader which stays in one position, and takes the cargo from the heap (i.e. always having full grab in first attempt). Taking in consideration figures shown in your previous message, it is about 1200 TPH.
The average capacity – it is not exactly capacity of your unloader, but it is a capacity of barge discharging by given unloader. Here you lose the time working with partly filled grab while cleaning the barge and, most probably, while changing the position of unloader. Usually such kind of (un)loaders has a small traveling velocity.
If I understood you clear, you were wondered to know what normal/usual ratio in % between these “maximum” and “average” capacities. I wouldn’t like distress you, but hardly someone will give you certain answer to your question. The average capacity on half depends on many local factors. The main factors affecting average capacity are: “free digging unloader capacity” + traveling velocity, barge discharging plan (depends on hydrostatic and strength barges properties), weather conditions, qualification of operators, and many other factors. ■
Re: Capacity Of Unloader
Dear Shri Umarye,
Possibly, you are looking for a straight answer that is average capacity with respect to peak capacity. It would be difficult for the respondents to give any meaningful answer because it depends upon actual installation, degree of automation in various movements, control logic, and so on. This information is not known to the respondents.
As a general rule, whether it is stacker cum reclaimer machine or whether it is ship unloader etc., the average capacity and peak capacity can be decided as below.
1) The values as a design projection : For peak capacity, calculating the value would be quite easy using the machine parameters and assuming the most favourable situation. As for the average capacity, one has to fix the numerous operational movements and their timing. During each of this operational movement one calculates the quantity of material being handled. This type of calculation is a routine feature for machine designers because they have to always project the final performance of the machine. If the projections are done correctly by the concerned experts, then the result will match with the actual, with certain safety margins.
2) The another method is to decide the actual average after installation. The average would be certain quantity unloaded divided by the time taken. The quantity unloading to be done in a defined manner. In this case, one can use theoretically calculated peak capacity if it is convenient for a particular calculation model. Or one can find out peak capacity in a specific situation during short time interval.
Regards,
Ishwar G Mulani.
Author of Book : Engineering Science and Application Design for Belt Conveyors.
Author of Book : Belt Feeder Design and Hopper Bin Silo
Advisor / Consultant for Bulk Material Handling System & Issues.
Pune, India.
Tel.: 0091 (0)20 25871916 ■
Capacity of unloader
how is average unloading capacity determined with respect to free digging capacity in % terms ■