I'm trying to solve the same problem. We store corn in concrete walls circular silos. The vertical height is about 22 m, with 8 m of diameter and a 54º (with the vertical) hopper. The main problem we have is that there are important changes of the bulk density influenced by humidity, temperature, etc. This means that we store 1200 tons of grain but then we just have 1100 tons (mass loss). We are trying to actually estimate this difference accurately so we can design a proper ventilation system next.

As "lrey" said, any suggestion will be welcomed.

Best. ■

Perhaps you shuld take the easy way: measure the height, calculate the volume, then multiply by density.

Continuous level measuring could be done by radar (not recomended), suspended wire, or a Yo-Yo.

If yur density changes with umidity, you may measure misture content as well ■

My experience shows that the best way to get an accurate weight measurement of any material stored in a bin or a silo is to use load cells. For this, bins and silos would need installation on load cells. This technology is well known in the industry.

Regards,

Amrit Agarwal

Consulting Engineer

Pneumatic Conveying Consulting

Email: polypcc@aol.com

Ph and Fax: 304 346 5125 ■

Load cells on silos proved itself very unoccurate. The reason is the high dead weigh of the silo itself (tare), compared to the net weigh of the product.

This technolgy was very popular during the ninteen nineties, but almost vanished by now. ■

Load cells are widely used these days. They are not the 90's technology.

The tare weight of the bins/silos does not change, it is subtracted from the total weight measured by the load cells to determine the weight of the stored material.

I beg to differ from the post given above.

Regards,

Amrit Agarwal

Consulting Engineer

Pneumatic Conveying Consulting

Email: polypcc@aol.com

Ph and Fax: 304 346 5125 ■

Appreciating that you cannot now comfortably utilise the otherwise totally admirable & technologicaly acceptable load cells I would suggest radiometric sensors to measure the moisture & radar sensors to measure the height. The original question seeks an estimate not a spot on weight. Endress & Hauser will sort you out in a jiffy.

How was your predicament overlooked at the design stage?

By the way 1990's technology is not to be derided under any circumstances. In bulk handling affairs it is in its infancy, like some of its critics. ■

we install some pressure sensors (at the hopper walls) we have here and we try to estimate the mass weight based on the pressure measures. One of the biggest problem we are facing now is related to the aireation. Once a day we inject air for a couple of hours and the sensor measurements are highly non stationay (they have long time constants and they reach different states, even when the mass of corn is remained constant) ■

The best way to know the quantity it's use the wheightscale before loading and after discharging. But if you don't have this possibility, you may measure a height of the cargo by any known methods, calculate the volume that grain ocupied in silos, and divide this volume on stowagefactor.

That's all seems easy to be done, but here is one problem exist: how to calculate volume of the top layer of the cargo, because after loading and after partly discharging it has irregular form.

The scientists and engineers traying to solve this question a long time. But all methods still give a roughly results, because to much factors acting when the cargo surface forms.

We are work with the wheat, barley, and corn and store it in silos and domes. Each our silo is 9m wide and 32m height. Some times we are use these methods for operative control, but it gives about 5-7 percent difference from real figure. ■

I agree with Vladimir. Using multiple level sensors might help calculate the volume of the top layer.

If feeding is done vertically to the center, than a symetric cone is created. Emptying cone could also considered as symmetric.

If you place one level sensor in the center (make sure incoming product would not hit it!) & one or more near silo's wall, you can easyly calculate good astimation of the volume. Calculation is simple enough to be done on Excell.

I still dont think load cells can work well on concrete silo. ■

Now, measuring with manually,I CAN SAY 60'S technology. ■

All brilliance is very simply. The silo was designed too much earlier than 60'S but we still consider it as one of modern storage for wide range of cargoes.

Same manual measuring, it's a cheap, fast, most suitable, accurate and widespread industrial measuring methods today.

When you just started with new silo, you have to try some different methotd and select one, which is more suitable for you. On this step, i think, only manual measuring can be applicable.

Just then, when measuring method was determinated, you can install some modern electronic measuring device.

As I know (but it's just my knowledge):

- ultrasound devices work no properly on distance over 12 meters;

- optical (laser) distance measuring devices are cheap and very accurate, but they doesn't work with the dust;

- new radio wave radars working on high frequency, as i know, gives good result (only 0.1% mistake) and work in any air condition. But their price is abt 5000 USD per unit. ■

This thread takes a deserving place on this forum.

By overall majority we can make a conclusion that the first step that we have to do to make Mass Estimation in Silo it measure a height of the cargo in silo and calculate occupied volume. But it's only cargo volume estimation.

On next step we must multiply this volume on cargo density. This is the next question that I’d like to discuss on this forum: How to check density of the cargo?

My company works with grain. We have good equipped and modern laboratory where we make a measuring of grain density, we call it natural density, but this is not enough. There is stowage density or stowage factor (index which is opposite to density, shows how much space occupied 1 ton of the cargo) have to be used for mass calculation. This magnitude depends on many factors: fraction of the cargo, percent of dust, height of storage etc. We use weight scales before silos loading and after their discharging, so every time we know exactly how much cargo we have in each silo at the present moment. But we don’t know exactly how many grain we can arrange in one silo to avoid a broken stowage (space loss) or silo overloading. This happens because of stowage density changes. Per 5000 MT can be 200 MT difference.

We had look through a lot of literature, tried to find out transferring coefficient for convert natural density to stowage density but it all gives a not satisfied result (of course it work but not properly). And every time when silo becomes to full we check manually distance from top of the silo to grain surface.

Of course, one way to solve this problem is install an approach sensor on top of the silo. But maybe some one has experience and can give advice how to find out stowage density of cargo before its loading into a silo or other compartment? ■