Ash and Bed Material in Circulating Fluidized Bed Boilers

[hassanfadil]

I am doing a study to compare two options of fuel a Sugar refinery, the fuels are petroleum coke and South African coal, in terms of quantities needed and handling equipment.
Though I am not very familiar with the CFB boilers, but my main concerns right now are the amount of bed material needed and the amount of ashes discharged from the boiler for the two fuels; so my questions right now are:

1. The amount of bed material required as a ratio of the boiler MCR or the consumption of fuel
2. The amount of ashes discharged (correct me if I am wrong but I think the ashes are bed ash and fly ash) as a ratio of the boiler MCR or the consumption of fuel.

I am aware that it depends on the amount of ash in the fuel and the amount of bed material.
As I searched I decided to use the figures of 1% ash in pet-coke and 15% ash in coal.
The boiler characteristics is:
Pressure: 31 bar (a)
Temperature: 400 ⁰C
MCR: 60 t/h

Required amounts of fuels are:
Pet-Coke: 5.97 t/h
Coal: 7.81 t/h

I appreciate if you also suggest me any further materials to read
Thank you in advance...

 

[dougarthur42]

I will try to answer to the best of my ability. I am familiar with cfb's and co firing coal and petcoke.
A lot of CFB operation is difficult to understand. First of all your fuel mix looks about right, you don't want any more petcoke to coal ratio than what you have. Yes the amount of bed is somewhat proportional to fuel compsumption (load on boiler) but not always.
the amount of ash removed is the amount of ash content put into the boiler. Example petcoke 6 t/h @ 1% ash content = .06 t/h. coal 7.8t/h @ 15% ash content = 1.17 t/h. 1.17+.06 = 1.23t\ h of ash needs to be removed or your boiler (bed) will fill up. How much bed is needed?? good question. your boiler manufacturer should be able to tell you the boiler fire box (bed)capacity. Once a certain level of bed is in the boiler you just need to keep it there, as fuel ash is added some needs to be removed. fly ash and bottom ash will exist. approx. 15% will be fly ash and the other 85% will be heavy bottom ash. I have more info if needed.
By for now Doug