Steam Heating Aggregate in a Concrete Plant

[esermakine]

Hello,

I am asked to estimate the capacity of the boiler that will be used for our concrete plant, I don't know how to approach the problem. The properties are as follows:

Aggregate : 100 m^3/h
Will be heated from -20 C to + 30

Aggregate will be heated in 50 m^3 cells.

Given data is not enough I know, but we can make some assumptions and provide a estimate result.

Some suppliers tell us a capacity of 800 000 cal/h steam will be enough. But I am expected to give the basic steps.

Also where can I get the basics for such a aggregate heating system, I have some other questions such as How much should aggregate wait in a cell to fully develop its temperature.

Any insight and help would be appreciated.

 

[btrueblood]

You will need to estimate the heat capacity of the stones (look up values of kJ/kg-C for various minerals?) and estimate the mass in each cell.

 

[esermakine]

Is it that simple? No need to consider anything else?
What about transient effects for fully thermal development of aggregate in the cell?

 

[btrueblood]

Transient problem will fall out with the above data, you will need to assume a few things. Grab your heat transfer book and start figuring.

 

[esermakine]

I know where to find the necessary info, this is kind of urgent that is why I asked a specific resource for aggregate drying systems.
Anyway thanks a lot for the help.

 

[rmw]

What does "thermal development of the aggregate" mean?

You also have to consider whether or not your aggregate is wet (or contains ice) when you put it in the cell and if it is, account for the amount of heat needed to dry the moisture present.

That would be in addition to simply heating the mass of the rock.

rmw

 

[chicopee]

Instead of steam heating the aggregate, why don't you warm up the water that is mixed with the concrete batch. That's what we were doing, of course you'll have to base the boiler size on the normal batching cycle.

 

[som1973]

Hi esermakine,
I can help you to calculate the
amount of steam required but I need the following
info.
1. Weight of material to be heated in lbs/hr or
kg/hr.
2.Operating steam pressure in PSIG or bar.
3.Heat-up Time in minutes.
4.Specific heat of material( if you have)
in Btu/lb F

 

[esermakine]

rmw by thermal development I was trying to point at transient effects, e.g. center of the aggregate to reach the desired temp

chicopee heating the water is a good point to consider. Thank you for that tip.

som1973 with some approximations and assumptions we figured out the amount of steam and capacity of boiler needed. Thank you very much anyway.

Thanks for all your efforts. We solved the issue. We calculated the boiler capacity and decided to handle transient effects by trial and error since modeling the system is a very hard problem.