For the calculation of loads, frictions and speeds etc., it is advisable, to use dimensionless factors, like Reynold or Nusselt numbers.

To this it is necessary, to make a dimension analysis.

Thanks ■

From the mass flows involved & the duct dimensions you can easily determine the internal velocities for assessing the pipe friction forces from reference to the Moody Diagram. Then there is a bit of Bernoulli to quantify the dynamic (total) head acting on the bends. Wind load procedure is stated in your local building design code: there is also the Universal Building Code to fall back on. Don't forget Seismic & Thermal influences.

Much dust in the pipeline will settle out on evey shut down. Some will get picked up in the next rush of air but not all.

If you allow for a 50 mm coating inside the fairly flat parts you won't be far off target. That will be around the situation when bits of debris that become dislodged into the airstream will be noticed. Foreign Object Damage (FOD) is the notification that there is severe deposition. Assume that maintenance is lax & this 50mm becomes a realistic accumulated figure. Overnight condensation along a stationary duct, out of service, will make a mortar which bakes set next day. So it builds up.

Flue dust recirculates in chimneys & the accumulation can be very thick, heavy & dangerous. I have seen a 1.2m thick x 35m high, at least, dust lining in a smelter stack. If that had become dislodged, eg by seismic disturbance from rogue mine blasting, the stack would have collapsed. You will have daily quarry blasts so the chimney deposits might be limited. Without established company standards, which you might be able to solicit from eg Lafarge, you can examine the experiences mentioned above as they relate to your equipment.

Another issue to consider is the maintenance load. It takes a bigger crane lift to break out a pipe section that is lined with crud & cemented into the line than it did to place it in the line first time round. That crane tugs & tugs at the surprised extra load; suddenly the cement shears and the crane stability is critically compromised. Almost as important is the lift imposed on the duct mountings which are generally designed for down & wind loads etc only.

I know the bigger firms have acceptable accretion levels in their design standards but its so long since I was involved that I'm afraid I can't help further. Any of those firms should be willing to help you along the way because in this age of mergers & aquisitions it is better to buy a plant that is safe & repairable if that day dawns.

Re & Nu might fit in there somewhere.

Standard/norm velocities for the ducts you mention just might exist. Without knowing them you cannot know the duct dead loads because you don't know the duct sizes; if you intend to use those, as yet unknown, velocities that is. Just a point of order.

Very good luck with the rest of us. ■

Hi sir,

very glad to meet you,

In one of my project am dealing with bagfilter vent ducts & process ducts design, as per my knowledge i designed the duct sizing and dead load of same.

Now i want to know the Live load calculation for my sturcture design. Please guide me the general norms for calculating the live loads for vertical, horizontal and inclined ducts in cement industry and if you have any velocity norms for material flow inside the ducts please share for my reference.

Thanks.

Damu ■

Originally Posted by Rajendra Patel

Ducting Load Data Calculation For Using The Cement Plant

Let me know how calculationthe load data of ducting for structure design. Like Dust load, Live load, friction load, Wind load. ect. I know the deadload of ducting.

Also standard velocity ducting for 1. Rawmill to cyclong ducting, 2. ESP duct, Velocity inside the chimany. Ect.

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

You have to contact a mechanical engineer that specialises in cement plants for that type of information

as you hav eonly asked questions and not provided any type of detail. ■

In a cement plant the duct from the raw mill to the cyclones can become plugged as can pretty much any pneumatic transport duct. Civil design should account for the duct fully plugged. Has it ever happened? Yes, Lafarge Sugar Creek Plant. It took them 3 weeks to jack hammer out the material. The duct diameters are typically sized by the OEM equipment supplier as this becomes all part of their process guarantees. This is not dust collection this is pneumatic transport on an extremely large scale. There are so many factors including the distance travelled, are the separators located on top of the silo or at ground level are they high efficiency, what type of mill are you using VRM or Ball.... and so on.

You need to worry less about duct size and more about duct expansion and how to control duct expansion without damaging the equipment on each end. This is typically where OEM make mistakes and supply cheap expansion joint that fail quite rapidly. What temp air are you using through the mill? Process ducts should not be horizontal. In cement even nuisance dust collection duct are rarely horizontal as low velocity dust collection is preferred due to the very abrasive nature of cement and clinker dust with vertical ducting. You need to review on a case by case basis what is the possibility of plugging or blocking the designed duct. In most cases they can become plugged or very close to being plugged.

Good Luck with your project ■