[Akuma2636]

Why do some wheat silos explode?
I read a few articles where wheat silos have mysteriously exploded, and now I'm interested to why they do this.

[Jiro]

hmmmm... after i drank some orange juice one hot day, finishing what was left in the 2 litre carton, I closed the lid and just sat back in my chair relaxing. The juice was nice and cold, fresh from the fridge and the carton jug i guessed would be around the same cool temperture. Then I left the kitchen leaving the carton on the table. Next thing i heard was a bang and came back to the kitchen and found the carton on the floor. haha, my little brother thought it was a ghost!

As i observed the scene the carton looked bloated like how you blow air into one of those 250ml apple juice cartons with the straw when you were a kid. The carton was already almost off the edge to begin with but in the end I hypothesised that because the gas inside the carton was cooler than the big outside it caused the temperture to change inside the carton so it would equal the temperture outside the carton. This resulted in a change of volume for the gas. In this case volume increased (PV=nRT)... this change was enough to disrupt the carton object to alter its position in potential energy.

I think this maybe why wheat silos explode.

[Borek]

Mot probably when the wheat catches some humidity it's volume grow. Pressure in such situations can be enormous (in ancient Egypt it was used to burst rocks used then for buildings and sculptures - small holes were drilled first, then they were filled with some grain and water was poured on).

[Donaldson Tan]

what's a wheat silo?

[Borek]

Silo is a large tank (cylindrical in shape). Wheat is the rice of western civilisation

Have you ever seen a Pole teaching Chinese English before?

[billnotgatez]

Spontaneous combustion and dust explosions have been the bane of barns, granaries and silos throughout history.

[Borek]

the bane of barns, granaries and silos

You forgot mills.

[Garneck]

Have you ever seen a Pole teaching Chinese English before?

No, but now I've seen everything

[Garneck]

BTW, have you ever tried to burn flour? It gives a flamethrower-like flame. Just needs a little fire. A match maybe. How many people in the world smoke cigarettes? Now you can think about exploding silos.

[mike]

It has a lot to do with the surface are of the dispersed dust.

Maybe ask your teacher to show you the lycopodium dust explosion demonstration.

[billnotgatez]

http://www.angelo.edu/faculty/kboudrea/demos/lycopodium/lycopodium.htm
Burning Lycopodium Powder: Simulating a Grain Elevator Explosion

[constant thinker]

I agree with the dust. Quite a few things won't ordinarily burn, but if you crush them up into a fine powder they burn quite rapidly. Wheat is one of these or some of those investigators say.

Saw mills have to worry about the saw dust exploding.

[Oldtimer]

.
Unless the grain is some oil grain like Sunflower seeds the grains are pretty safe. Confectioner {edible} sunflower seeds aren't the same as oil sunflowers. They'll burst into flame while harvesting them in the field if they come into contact with a hot piece of metal on the machinery.

 The volume of these bins is enormous, and they are not vented well so the atmosphere is dry. The dust can cake up in them over years and gets a foot thick or better. That's a dangerous thing. Generally only poorly cared for bins will ever have a problem.

Smoking a cigarette inside a bin isn't enough to cause it to blowup. You need an electrical spark from the bin fans or monitoring equipment. Sometimes even an outright fire inside the things before anything catches. Except for the oil grains, most of it is pretty  safe.

Refined sugar is also kept in large concrete bins before it is bagged or shipped. That sugar dust and oil grain dust is highly flammable, like natural gas.

Andy

[jdurg]

As has been mentioned before, ANY substance will become highly flammable if it is in a small enough form.  What usually prevents a substance from burning tends to not be a factor when the particle size is as tiny as can be.  (See aluminum powder.  You cannot get aluminum metal to burn unless you have a VERY high temperature and a very high oxygen concentration.  Take some aluminum powder and disperse it into a fine dust, however, and it will ignite very easily).

[Oldtimer]

Harvesting isn't a really clean operation, chaff and dirt aren't seperated well from most grains in favor of speed rather than cleaning. All that extra plant material is flammable.

i used to burn sugar by pouring it from those little packets in restaurants. But sugar dust is like lint, it just floats in the air forever.

The chaff grinds up when being transfered from place to place with the grain. Grain itself cracks and is pulverized into small dust particles. A very dry atmosphere and the fumes from insectides in these bins make it the  explosive problem.

We used to actually add vegetable oil to grain to keep the dust from floating everywhere. If the stuff doesn't float in air it doesn't get lit.

Like anything else, operator failure is the prime cause for these explosions. The conveyors, screw augers, bin fans, etc. will get a bad bearing at some point. If they get hot enough they'll ignite the contents of their surroundings.

Andy