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Weighbridge used to measure bagasse flow on conveyor belt

Weighbridge used to measure bagasse flow on conveyor belt

Weighbridge used to measure bagasse flow on conveyor belt

(OP)
Hi
Bagasse coming from the sugar mill passes over several conveyor belts before entering our 2 boilers to be burnt as fuel. The flow is controlled by a PLC and is measured by Precia Molen weighbridge installed on the conveyor using load cells.
Every Sunday when the sugar mill stops, a calibration of the weighbridges can be done. From Monday to Sunday morning, the plant operates 24/24 and no calibration can be done.
We notice that the weighbridge measurement drifts quickly after 1-2 days of calibration. Someone from Precia Molen came on site to check but problem still the same.
On the conveyor belts, there are belts on either side to prevent spillage of bagasse. When these side belts wear, the force they exert on the conveyor belt decreases and this affects the reading of the weighbridge.

Are there are technologies that can be used to measure flow of bagasse on conveyor belts accurately?

RE: Weighbridge used to measure bagasse flow on conveyor belt

For the rest of us:

Source: Oxford Languages
ba·gasse
/bəˈɡas/

noun: bagasse
the dry pulpy residue left after the extraction of juice from sugar cane, used as fuel for electricity generators, etc.

The question implies that the conveyor system cannot be changed. Otherwise a wider/v-belt conveyor could be used. It looks like https://www.preciamolen.com/product/modular-belt-w... has styles for conveyors that would not require independently supported side belts. Is the material pile too large to fit the largest units?

Without a photograph of the installation it's not clear what could be done more cheaply. I would guess and likely be wrong that a guide be added to prevent the side belts from ever touching the weighing belt so the tare would not change.

RE: Weighbridge used to measure bagasse flow on conveyor belt


Link

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Weighbridge used to measure bagasse flow on conveyor belt

That radiometric sensor uses a radioactive gamma ray source. From the manual: "In radiometric measurement, a Caesium-137 or Cobalt-60 isotope emits focussed gamma rays."

I'm not sure how they are focusing gamma rays; I suspect they shield the rest of the universe from the gamma rays and only allow a narrow view of the radioactive material that impinges on the scintillation detector.

Cobalt 60 has a 5.7 year half-life and Caesium-137 is 30 years

https://en.wikipedia.org/wiki/Cobalt-60
https://en.wikipedia.org/wiki/Caesium-137

Interesting.

RE: Weighbridge used to measure bagasse flow on conveyor belt

(OP)
Thanks Waross for the info

RE: Weighbridge used to measure bagasse flow on conveyor belt

(OP)
Has someone use the radiometric sensor to measure sugar cane bagasse flow on conveyor belt? Are you satisfied with the equipment over a long period of time?

Bagasse has 45-55% of humidity and the density may vary between June to December, maturity of cane, adjustment of mills at the Milling, etc.

How frequently should a calibration or zero be done?

RE: Weighbridge used to measure bagasse flow on conveyor belt

I understand that samples may be taken "on the fly" and that density corrections may be made to the controller, "on the fly".
Confirm with the manufacturer.
I have been involved in the installation of a couple of these but not in the final calibration.
One measured the consistency of black liquor in a pulp and paper mill.
One measured the through-put of potash on a conveyor belt.
I have avoided the vicinity of a couple of others in petro-chemical plants.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Weighbridge used to measure bagasse flow on conveyor belt

In systems that I have seen the side belts did not put any pressure on the main belt, this could be an alignment issue.
Also there should not be constant material against the side belts. If there is constant load against the side belts then you have overloaded the belt or undersized the system.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Weighbridge used to measure bagasse flow on conveyor belt

SA07,
Where are you located?It is sometimes very complicated to import radioactive sensor. Check with your local authorities.
Esperantes.

RE: Weighbridge used to measure bagasse flow on conveyor belt

(OP)
Yes this type of weighbridge.
We can see the flow of bagasse measured is drifting quickly 1-2 days after calibration is done on Sunday.
There is a direct supply of bagasse from milling to our boilers and other conveyors which will top up from our bagasse store. Since weighbridge values are drifting, there is a high risk of creating bagasse jamming in conveyor chutes/ductings. This has happened several times in the past.

RE: Weighbridge used to measure bagasse flow on conveyor belt

(OP)
We are having difficulty with this type of weighbridge since 2007. We have used new models of cards from Precia Molen but still the same.

RE: Weighbridge used to measure bagasse flow on conveyor belt

I think you might have a never solved initial installation problem. Look beyond the weighbridge to things that might affect it's measuring. Bagasse is not an easy material to handle.

Is material sticking to the speed measuring wheel, or the belt?
Is the scale too close to the loading point?
Is the belt tension constant?
Is the weighbridge inclined? Is the incline steep? Can the incline change?
Is the conveyor curved near the scale?

Could there be a problem with the conveyor loader?

If your conveyor uses side belts rather than a single belt folded into a V shape, do they stay synchronized?

There is also a fit to task issue - are you using the weighbridge as part of an air / fuel boiler control system (tight control requires accurate weights)? Or is this control just attempting to keep the conveyor feeding such that the system does not get overfill / stopped up (accuracy requirements are less)?

RE: Weighbridge used to measure bagasse flow on conveyor belt

Have you considered an automated system to take regular samples and test and monitor the moisture content and make frequent and automatic updates to the weighing system.
In the black liquor application, the flow rate was known. The radiometric device was used to determine the constituency or moisture content.
Given the high capacitive constant of water, measuring the capacity between two conducting plates, one above and one below the bagasse may be used to quite accurately measure the water content of the passing bagasse.
The technique has been used to measure the moisture content of lumber in lumber drying kilns.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Weighbridge used to measure bagasse flow on conveyor belt

Waiting for a photograph or a diagram of what causes the problem ... at least this makes it a fun guessing game.

Colonel Mustard with the Wrench in the Kitchen.

RE: Weighbridge used to measure bagasse flow on conveyor belt

A radiometric system will measure the total mass passing the measuring point.
A capacitive moisture detection system will measure the total water passing the measuring point.
A simple subtraction will give the mass of bone dry bagasse passing the measuring point.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Weighbridge used to measure bagasse flow on conveyor belt

When you consider that each pound of water may rob your fuel of over 1000 BTU, a variation in moisture content may be affecting your end results more than weight calibrations.
Wagner meters has been in the moisture measuring business for around 50 years.
Even if they do not have a system specifically for bagasse, they may be interested in working with you on a moisture monitoring system.
Wagner Meters

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Weighbridge used to measure bagasse flow on conveyor belt

Quote (Science Direct dot Com)

The Calorific Value of Bagasse
The gross calorific value (GCV) of dry bagasse has a mean value of 19605 kJ/kg......
Water has no calorific value and it also absorbs heat being vaporized during combustion.The net calorific value of bagasse, with around 48% moisture content is about 7670 KJ/kg
Science Direct

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Weighbridge used to measure bagasse flow on conveyor belt

(OP)
No bagasse is sticking to the drum or speed sensor
Scale is not close to loading point. They are in the middle of conveyor belts.
3 conveyor belts are inclined and 1 is horizontal. Precia Molen was aware of all specs at construction stage.
I will be working from home for several weeks. After I resume work on site I will take pictures and share.

What do you mean side belts stay synchronized?

The weighbridge on 3 conveyor belts are used to determine how much bagasse must be fed from the bagasse store; to top up missing bagasse going to boilers from the sugar Mill. The main problem is that a higher set point must be used for a chain conveyor. This have caused bagasse jam in chutes or conveyors, stoppage time.

The weighbridge problem has no direct effect on boiler regulation/operation.

For the time being the humidity content is not the issue. Main issue is weighbridge measurement is drifting quickly 1-2 days after calibration. We must wait next Sunday to do calibration. We cannot stop process to do the calibration or zero. May be a zero may also help to correct the drifting. In the manual it is recommended to do a zero every 24 hrs. This is not possible for us.
One possible cause may be the side belts which prevent spillage. They wear and affect the force exerted on the load cells. So measurement drifts.

When we do the calibration, everything seems ok. We can leave the test weight on the weighbridge and run the conveyor belt to check the cumulative weight for 1 hr. This is also correct.

Plz see attached doc with some info.

RE: Weighbridge used to measure bagasse flow on conveyor belt

What you show should not have side belts. Is there a picture showing where the side belts are?

RE: Weighbridge used to measure bagasse flow on conveyor belt

Quote (What do you mean side belts stay synchronized?)

All of the belts (side belts and main belt) must run at exactly the same speed or there could be slippage of load material. This would result in the average speed of material on the conveyor being different than the measured speed of the conveyor.

RE: Weighbridge used to measure bagasse flow on conveyor belt

(OP)
Plz see a picture of side belts on the conveyor to prevent spillage of bagasse. These are fixed and not moving.


RE: Weighbridge used to measure bagasse flow on conveyor belt

The picture above shows what I would have considered these to be sideboards, rather than sidebelts, as they do not move with the belt.
I see lots of possibilities for force to develop between the conveyor and the sideboard. If you are attempting to get close to the published accuracy of the weigh bridge (class 2 of better) the interaction of the sideboards and the belt can be significant.
Not sure if this would fix the problem or make it worse. I would try setting the bottom of the sideboard so that it does not rest on the conveyor belt (a bit more clearance than 1 sheet of paper). Too much gap might create a problem with fibers getting stuck in the gap.

RE: Weighbridge used to measure bagasse flow on conveyor belt

>The main problem is that a higher set point must be used for a chain conveyor. This have caused bagasse jam in chutes or conveyors, stoppage time.

What action does raising the setpoint activate? Does raising the setpoint increase the belt speed in order to deliver more product in a given time interval? If so, it appears that a step increase in setpoint/beltspeed causes the product jam in chutes or conveyors, correct? The higher delivery rate at the increased setpoint chokes the mechanics of the system, right?

Hence there is a maximum limit for the setpoint, otherwise the system chokes. Is setpoint limit known? Would it make it sense to determine that SP limit value and limit the setpoint range of the controller?

How much is the setpoint increased to make up for low delivery 1/2%, 1%? 5%? 10%? Is the operation ignored until lunch time and then an operator makes a guesswork setpoint bump to make up for low delivery?

It seems that the initial setpoint on day 2 and day 3 when the so-called drift is occurring that the system is not providing an adequate flowrate, right? Is it possible to increase the initial setpoint on day 2 or day 3 or day 4 by some minor amount to compensate for the drift? A minor increase in the initial setpoint might provide sufficient delivery over time as opposed to a large step change in delivery rate to try to make up for the shortage, which then chokes the system.

Has anyone documented what the maximum delivery rate is, with this product, that the system mechanics can tolerate before the system chokes?

Is there a flow totalizer that indicates the total product delivery mass over time?

RE: Weighbridge used to measure bagasse flow on conveyor belt

(OP)
All is controlled by a PLC.
Increasing set point on the chain conveyor increases its speed. It is controlled by a VSD.
Correction should be done within minutes else the boiler will lack bagasse as fuel. It cannot be increased gradually over a few days.
In the weighbridge there are totalizers also on the scada.

It seems the radiometric sensor may be a solution for us. As wear on the side belts will not affect it contrary to the load cells of the Precia Molen. We have requested quote and we will inform you of the outcome.

RE: Weighbridge used to measure bagasse flow on conveyor belt

Quote (SA07)

No bagasse is sticking to the drum or speed sensor
How about bagasse sticking on to the belt itself?

Best Regards A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

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