| # | Topic :: High un-burnt in Fly ash and Bottom ash in coal fired boilers | Post / Comment | View Comments |
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Topic Initiated By : Administrator
Jan 21, 2019
Category : Administrator Organization : India Boiler Dot Com
The loss of un-burnt carbon with Fly ash and Bottom ash of any solid fuelled boilers is undesirable as it leads to huge wastage of fuel and thus revenue loss. Un-burnt in the fly ash in particular should be critically controlled. This community invites the members to share their experiences in this regard.
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Post By : Ansuman SenSharma(Expert) (Profile)
Feb 08, 2019
Category : Technology Partners Organization : India Boiler Dot Com
This is one of those problems where the measurement scale doesn’t really imply the actual magnitude of the problem. For example, let us assume that the un-burnt in the fly ash in a 300 MW Pulverized coal fired boiler has increased from 0.7% to 1.2%.
So far as the increase in percentage un-burnt is concerned, it has increased by a marginal 0.5%. Apparently this doesn’t look so serious! But when you consider this boiler is firing around 180 TPH coal with a CV of 3600 kcal/ kg and 35% ash and costing around Rs.3.50 per kg. Assuming 80% of the ash is collected as fly ash and 320 days of operation per annum; this seemingly marginal increase of 0.5% in the fly ash un-burnt is causing an additional expenditure of a little more than Rs. 1.5 crores in fuel cost, then it starts looking very serious!! And this is one of the controllable losses in Boiler. One needs to carefully adjust the PA/ SA ratio, vertical bias in SADC, Mill fines, burner tilt to control this loss. Changing the fines as well as SADC according to elevation is one innovative practice, which have given me good results in various systems. I have seen systems operating with < 0.5% un-burnt in Fly Ash. In FBC boilers this particular problem can defeat one of the biggest advantages of this system, which is higher combustion efficiency using a wide range of fuels. The root of the problem actually lies in the very fact that everyone knows about this advantage and use different grades of fuels with varied characteristics when it suits them. This is perfectly alright so long you also change the combustion conditions accordingly. I have seen CFBC system producing 21% un-burnt in Fly Ash. This ash can actually be used in another FBC boiler as fuel!! | Post | --- |
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Post By : Harish Patel (Profile)
Apr 26, 2019
Category : Industry Member Organization : Jesons Industries Limited
We have one 170 TPH cold cyclone CFBC boiler. We are firing Petcoke blended with Indonesian coal in 70:30 proportions. Fuel size is 6 – 8 mm. But we are getting LOI of 10 – 11% in the fly ash, which I feel is too high. Bed temperature is maintained around 830 – 840oC. Since about a year, we are operating with reduced the bed height of 800 mmwc (design 850 mmwc) and achieved significant APC reduction.
I have a doubt that the reduced bed height may be causing the unusually high un-burnt in the fly ash. I will appreciate if the experienced members of this community can help me to control this loss. | Post | --- |