Re: Increasing Unloading Rate Of Pebble Lime??
Road tankers are normally rated at 2 barg you are off loading at 1 bar hence it is taking long time. Ask the tanker man to try to convey at close to 2 barg. This will increase the conveying rate. Conveying at higher pressures is very much dependent on the type of tanker and valve arrangement, I cant comment on it ! as I don’t have the details
Putting secondary air into the convening line is not advisable. ■
Re: Increasing Unloading Rate Of Pebble Lime??
The truck is not an ASME pressure vessel therefore it is limited to 14.9 psig. The conveying line is then run at 13 psig to convey the lime. ■
Re: Increasing Unloading Rate Of Pebble Lime??
Well you are already working at max pressure. So not much can be done.
any word on the blower size? ■
Re: Increasing Unloading Rate Of Pebble Lime??
Dear Kevinc,
Increasing capacity, using a booster compressor is a commonly used method.
In combination with a booster, the tank outlet, pipeline diameter and the silo filter have to be checked and most likely, to be adapted.
Conveying ” particles through a 4” pipeline (dimension ratio 4/(3/4) = 5.3)could be difficult indeed.
If more info is given, a calculation is possible.
best regards
teus ■
Teus
Re: Increasing Unloading Rate Of Pebble Lime??
Teus
The system in place consists of a 75' high silo with a 4" impact elbow at the entrance of the silo. The 4" line to the truck is standard sch 40 to the ground level and from there, about 40-50 feet of rubber concrete hose to the truck connection.
The truck blower is rated at ~750 cfm @ 15psig. There is a bin vent filter on the silo with an exhuast fan rated at 1250 cfm with 508 ft^2 of filter media.
The air to cloth ratio is ~1.5 which is acceptable (I'm told by mfg). The filters are pleated cartridges that do plug up unreasonably quickly but even when new, the best the trucks can do is 3 hours. Typical unload times at other plants are on the order of 1.5-1.75 hours. ■
Re: Increasing Unloading Rate Of Pebble Lime??
Dear Kevinc,
Some quick, orientation calculations give the following results
(converted from your English units)
particle size 19000 micron
suspension velocity 19 m/sec in atmospheric air
compressor volume 0354 m3/sec
pipe line diameter 0.100 m
pressure 9200 mmWC
capacity 8.5 tons/hr
Based on these data I calculate a product loss factor of 0.85717 , which is used in the further calculations.
If the compressor volume is increased to 0.405 m3/sec, then the capacity increases to 11.8 tons/hr. The reason for this increase is that the sedimentation in the pipe disappears, due to the higher velocity.
Maintaining the air velocity of 33.8 m/sec at the beginning of the pipeline and approx 63 m/sec at the end of the pipeline, the pipeline diameter is increased to 0.15 m (5”)
The blower volume is then increased to 1 m3/sec (Booster volume 0.646 m3/sec)
Probably a lot of the pebble lime is crushed to smaller sizes in the pipeline due to the high velocities, making accurate calculations very difficult.
I have experienced this size detoriation with pebble lime in the past.
The resulting calculated capacity is then approx. 33 tons/hr at 9200 mmWC
Disregarding all other possible reasons for your low present capacity, this calculation should only be regarded as indication only.
The system capacity seems to be very depending on particle size(distribution) and chosen velocities.
Thorough investigation of the existing installations and related field data are very important for further knowledge building.
have a nice day
teus ■
Teus
Re: Increasing Unloading Rate Of Pebble Lime??
Teus,
That confirms my hunch about adding air flow although I thought it would have to be at a higher pressure. This will be much simpler to test out as a possible solution to our problem.
One clarification; you suggest going from 4 to 5 inch line. Is that for the entire line or only a portion of it to allow for expansion of the compressed air.
Thank you
Kevin ■
Re: Increasing Unloading Rate Of Pebble Lime??
Dear Kevin,
Firstly I have to correct an error in my previous post.
A pipeline diameter of 0.15 m is equal to 6” (NOT 5”)
Sorry for that.
The booster air should be injected in the pipeline right after the hose connection to the pipeline.
From that location on, the pipeline must be changed to 6”.
This is, of course, to keep the velocities at the designed values.
As far as I understand, a higher pressure than 13 psi (# 9200 mmWC) is not possible, because of the fact that your pressure vessel is not ASME.
Another issue is the pressure vessel outlet.
If the pipeline is replaced by a 6” pipe and a booster of 0.646 m3/sec at 1 bar is installed, it is not certain that the vessel outlet (4") will be able to feed sufficient pebble lime into the system.
An adaption might be necessary there to or even the booster should be connected to the outlet of the tank.
Think before you do
You are welcome
Teus ■
Teus
Re: Increasing Unloading Rate Of Pebble Lime??
Teus,
If we are to change the line to 6", we would change the inlet as well. Increasing the velocity at that point would be foolish in my opinion being that close to the bin vent filter whether it would work or not.
As far as the pressure is concerned, that applies only to the tanker, the piping can be at any pressure it is designed for. The issue I will have either way is how to introduce the added air without impeding the flow from the tanker. That was originally my concern as to whether an inductor is used or how it is done.
This has been an very informative conversation.
Thank you again
Kevin ■
Re: Increasing Unloading Rate Of Pebble Lime??
Kevin,
The highest pressure is in the tanker.
If the pressure in the pipeline is higher than in the tanker, then the air would blow back into the tank.
The booster pressure is always lower than the tankpressure.
When you mention the inlet, is that the silo inlet or the pipe inlet
and how about the tanker outlet?
If you can mail me some installation data (drawings ) I will have a look at it.
It would be a pity that a misunderstanding causes unforseen problems.
use the forum messaging system.
have a nice day
teus ■
Teus
Re: Increasing Unloading Rate Of Pebble Lime??
Dear Sir Teus,
Don't you think that a velocity of 30m/sec and above is going to create maintainance problems ?????
Regards
Sachin Kr. Arora ■
Re: Increasing Unloading Rate Of Pebble Lime??
Dear Sachin,
Higher velocities cause more wear on the pipelines than lower velocities.
But the rate of wear can be economically acceptable.
Pebble lime is a rather soft material ( that is why I mentioned breakage before) and the steel pipeing will last for a reasonable period of time.
The rubber hose between the tanker and the pipeline will suffer more.
best reggards
teus ■
Teus
Re: Increasing Unloading Rate Of Pebble Lime??
Dear Sir,
I do agree but as per Indian Standards the allowable velocities even for air is much lesser.
Regards
Sachin ■
Re: Increasing Unloading Rate Of Pebble Lime??
You can't get any more out of the truck. Are your lines clean?
Why not consider 2 intermediate pots & give the truck blower a fighting chance before the stuff gets well blasted, by a new blower, up the silo feed pipe? You would be/are paying 2 hours demurrage every 4 hours; i.e. half life demurrage costs. In Europe that would amount to about Euros 35,000 p.a.; still not a lot. Is it worth the cost of modifying the system? Does your plant demand more feed? ■
John Gateley johngateley@hotmail.com www.the-credible-bulk.com
Re: Increasing Unloading Rate Of Pebble Lime??
We are currently receiving trucks 7 days a week and will be getting the demurrage charges. Unloading faster would allow for 2 truckloads/day, 3-4 times/week.
The unload time is non-typical and needs to be improved. It is an inefficient job taking this long to unload 1 truck.
The truck has always been slow to unload so I would say yes the lines are clean. We haven't seen any indication of plugged or restricted lines. ■
Re: Increasing Unloading Rate Of Pebble Lime??
Your four inch line and the bin vent set up are seemingly the Archilles heel in the current set up. Adding a booster blower or compressor will certainly add to your material degradation and therfore to a higher dust load I would imagine.
An out of the box idea (I must concede I am hanging out to the ankles) is to use a live bottom or bottom dump trailers that would allow material transfer into either a double pressurized kettle, or a rotary feeder Fuller Kinyon pump type set up that you could pressurize with 30-45PSIG at the proper airflow with an oil free rotary screw compressor. It would mean that you would have to invest quite a bit of capital as you would also have to upgrade to a ligher conveyig line and vent bin.
ASME VIII allows up to 14.9PSI pressure rise, but high pressure trailers can be built as well. They would be a bit expensive and much heavier though and thus reduce the payload. Interesting pickle that you are in. If you need to tinker around with your current system and need a temporary air source, I think I can possibly help you out with that. Knowing Tuis a bit, I would trust him to recommend a further course of action before you take drastic measures. ■
Increasing unloading rate of pebble lime??
We currently are unloading pebble lime from pneumatic trucks. It takes a minimum of 4 hours to unload 34 tons and the trucking company is not happy with this rate nor are we. I would like to increase the unloading rate in order to cut down on the time.
I have seen an article where the line going to the silo is charged with another blower after the truck blows it into the line initially.
The lime is 3/4"-, the truck unloads at about 13 psig. Our system is about 100' of 4" steel line and a 1750 acfm filter @ 7" H20 on the silo. I am checking to see what the blower on the truck is rated at.
I don't know what is necessary to do this...any ideas would be appreciated. ■