How and where are the Hoppers unloaded at a Cement Plant?

[Anonymous]

Yes the powder flows very well under air pressure... dont EVER have water anywhere in the system. We sometimes sprayed a regular garden hose on a leaking fitting that is blowing a cloud of powder all over the place to create a bond that will seal off the leak.

A bulk tanker needs to unload cement and it can be done one of two ways.

Option one... a Exhaust driven turbine blower mounted behind the tractor cab to feed air into the trailer. It is basically a minature Jet and will pressurize a tanker to about 16 pounds max.. although 11-13 PSI is where I want it at.

Advantage... if it screams constantly without change in the sound pitch and your tank pressure is constant everything is going well.

If it =goes "Cough cough cough" (literally... with a metallic clank) you are on the way to backing up the entire unloading system and need to shut off the product flow and increase the air flow before you hit total "lock up"

The second option would be to have the customer use thier own air pressure to unload you. This enables you to shut off your engine and unload the product very very fast. If you drive the tank air with your engine it can take you about 1.5 hours. IF the customer's powerful air system sucks the product out of your tank you could be empty in about 40 minutes.

Lehigh Cement on the Baltimore Harbor depends on trucks to recieve portland cement from Lime Kiln Maryland at the old Essoroc (Name spelling? or new name change?) facility. They can create enough pressure to unload about 30 trucks at a time.

However you need to watch every truck that is unloading, if one should go empty and left unattended.. it becomes a drain on the customer's air system that will rob all the other trucks of pressure and possibly threaten lock up of the material in the system.

I did this work for a period of time, it is very "easy" to do while you really have to monitor the gauges to prevent blockage or loss of product/pressure the rest of the day it is a matter of staying awake as you made several trips to and from the cement supplier.

You would see drivers hitting the bottoms of the pots with rubber mallets. A dull thunk thunk thunk means there is still product in the bottom pot. A musical ringing "CLANG!!" that echoes means that your pot is empty and it's time to open the next one.

Never ever ever use a regular hammer on a bulk tank under pressure. It stands a real danger of actually going thru the metal skin of the tank and releasing the pressure with lethal results to YOU and damaging problems to all nearby objects.

Railroad cars are unloaded with air driven shakers to ensure that the product is shaken out of the cars without wearing out the elbows of the personel that needs to determine if the pots are empty.

Hatches are very simple affairs that literally "Clip" into place to create a sealed hatch capable of holding pressure. The tanks usually have some kind of pressure blowdown that relieves ALL pressure inside the tank. That is the very first valve you will open before you ever go to the top to open the hatch to load the product from above.

Once a year or so.. someone forgets and opens a tank under pressure. The hatch will throw the driver's body for 50-100 feet up and away from the rig's 12'6" deck with very damaging injury or lethal results.

To me opening hatches and connecting hoses are the two most dangerous moments in cement hauling. I am not sure about covered hoppers but they probably share the same problems.

[Anonymous]

I believe most of the cement materials would be unloaded pneumatically. At least anything in powder form or small granules. The filler materials or aggregate would be dumped from the bottom and most likely screw conveyed or belt conveyed to storage. If you see what looks like a small house on top of a silo, with piping coming from it, that is a sign of pneumatic conveying as the "house" is a filtering media for the system. We use this to convey plastic pellets where i work and they are very economical and very fast at moving material. It is not uncommon for us to move 30,000 pounds per hour of plastic pellets. The drivers that deliver to us have told me cement is about the same to transfer as it flows rather well.

[leighant]

You might be interested in another hopper shipment connected with Portland cement plants...coal. In 1980s, Centex Cement in Corpus Christi began using coal to fire the refractor that cooks lime etc to produce cement. The heart of a cement plant is a big horizontal tube heated red hot on the side and rotating. At the Centex plant, the tube was hundreds of feet long, 8 feet around and rotating. On the outside, you just see this long tube thing with wheel bearings under it so it can turn and some kind of enclosures over each end of the tube. I once got to see on the inside, looking down the inside of this slowly-turning red hot tube going a city block into the distance-- awe-inspiring.

Back in the 1950s, the cement plant used cheap natural gas, oysters dredged from the bay and left a white plume of white dust-filled smoke that could be seen for dozens of miles up and down the coast. Boaters used it as a beacon. Of course, the environmental concerns of the 1960s got the oyster reef dredging curtailed and the smoke effluent minimized. The plant went to producing cement from lime clinkers (whatever those are) imported by ship.

Then the rising price of natural gas came into play. Coal was cheaper than natural gas to make heat for the process, but it many industries, coal put out black smoke that cost $$$ to abate. However, in the concrete manfuacturing process, the black particles from buring coal would be absorbed into the Portland cement without affecting its quality. That make coal cost-efficient. So the cement plant had coal shipped by hopper cars into an area which had historically shipped fuel out-- oil and natural gas. I remember seeing three or four coal hoppers on a time on their spur... not the big shipment that goes to large coal-fired electric power plants.

Centex had an elevator at the port to load bulk Portland cement onto ships-- much smaller than the big export grain elevators. Five or six upright silos. Made of concrete of course.

[Anonymous]

They simply take the covered hoppers deliver them as a "train" to the cement facility that would ship by truck to support the ready mix plants.

The facility would use a very small electric motorman type vehicle to "pull" one hopper onto the unloading track. A air driven hammer is attached to the "pot" which is the actual bottom of the hopper, the hatches are opened and the cement "shaken" out of the car into a grate where it then is sent up to the silo for storage.

It does not take long to unload one of these. The Cement facility at Hope Arkansas where I used to take cement out to a ready mix plant by truck in little rock would recieve about 120 covered hoppers (2 bay) twice a week (or once a week not sure)

In Union Bridge at Lehigh Cement, the covered hoppers are switched directly into the silo building where they simply "pull" the cement out of the cars into underground carriers where the cement is sent "UP" to the silo above. This was big time railroading as nighly cement trains came in from the Maryland Midland. (I dont know where they came from)

Now there is a major facility that made portland cement in Virginia (I think either winchester or martinsburg) and they basically drive most if the supply of cememt for a large area of the midatlantic.

Another facility was in Baltimore near Curtis Bay and they would pull cement off the ship by air pressure and put it into the silos above for transloading into trucks. It only took a few minutes to "feed" a bulk tanker. The Canton Railroad also switches this area as well. I think it was either "Blue circle" or "Blue star" cement but dont remember.

"Cement" is the word for the material which when mixed with water, rock, sand, additives etc at a ready mix plant becomes "Concrete"

[Anonymous]

I'm building a Cement Plant (Walters Valley Cement Kit). I was wondering how the hoppers filled with raw materials (silica, lime, sand, etc.), at a real facility, were unloaded and transfered to the bulk storage building? Which is later mixed and made into cement.

Thanks for the info,

26115 [:)]