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# Ash Run Off

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### #1 Rey Aryana

Rey Aryana

Brand New Member

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Posted 08 February 2012 - 05:51 AM

Hello sir, i want to ask several question about ash run off. (Power Plant Industry)

1. How to design ash run off, there are any standard calculation for it???

2. How many time that bottom ash need to settle in the ash run off??

3. Please tell me the simplest way, How to seperated bettwen water and ash in ash run off??

Thank you.

Regards,

Rey

### #2 kkala

kkala

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Posted 11 February 2012 - 06:44 AM

I do not have design experience on the subject, but probably following notes are useful and hopefully answering the query to some extent.
1. Please explain the reported ash runoff. Runoff is probably rain water collected from an area (water shed), so it may be the rainwater of the plant mixed with ashes laying on the ground. A trench is supposed around the plant to collect external run off and guide it to a river or to sea.
2. Assumed ash run off can go to a settling pond for the ash particles to settle down. Overhead liquid may or may not need treatment (depending on its chemical analysis) before disposal.
3. Volume of settling pond should cover max rainfall (that is rain water falling on the site), so that the pond shall not overflow during a storm. Suppose a site of 10000 m2 and a maximum rainfall of 250 mm. The water to be collected into the pond is 10000*0.25*φ = 2500*φ m3, where φ= percentage of rainwater absorbed by soil. If the soil is covered with asphalt / concrete φ=1.0, if there are trees it can be down to (say) 0.6, according to books on hydraulics.
4. Suppose φ=0.8, then water during max rainfall shall be 2000 m3, so volume above minimum level of settling pond is 2000 m3. That max rainfall total quantity is usually estimated to be higher (ie pond to overflow) once every 15 or 20 years. Meteorological data are needed to estimate max rainfall. If I remember well, (Porter?) theory of extreme values is useful to estimate the max runoff out of 15 - 20 years.
5. Granulometry and (not bulk) density of ash is needed to estimate settling velocity of ash.

Above is what I can remember from a settling pond of an alumina plant project (1987) to separate water run off from entrained bauxite dust (height of the pond about 3 - 4 m). An hydraulics engineer (branch of civil engineering here) is the pertinent person for more precise information on the above matters. Look for such a professional in your organization.
For other options beside the settling pond, look at Perry, Chemical Engineer's Handbook, McGraw-Hill, Gravity Sedimentation Operations.

Edited by kkala, 11 February 2012 - 06:48 AM.