Nitric Oxide Removal from Flue Gases by Carbon-enriched Coal Fly Ash
Keywords:fly ash, activated carbon, nitric oxide, selective catalytic reduction
The aim of this work is to evaluate the characteristics of activated and non-activated carbon obtained from carbon-enriched coal fly ashes (CECFA) from two different power stations to be used in the low temperature reduction of NO from stack gases. Carbon-rich fractions were obtained by mechanical sieving of fly ashes and by oil agglomeration. Activation of some samples was carried out in steam at 900ºC in order to develop porosity onto the samples. The obtained activated and non-activated samples were characterised by several techniques and their nitric oxide removal capacity at a low temperature using ammonia as a reducing agent was evaluated (gas conditions: 150 ºC, 1000 µL/L NO, 1200 µL/L NH3 , 60 mL/L O2, Ar as balance).
CECFA obtained only by sieving had carbon content varying from 1 % to 47 %, and NO reduction levels varying from 3 % to 29%. CECFA L2A and E2A, obtained by sieving, agglomeration and further activation, contained 66 % and 57 % of carbon respectively, and their NO conversion was 36 % and 48%. BET surface areas of CECFA samples before activation were in all cases below 20 m2/g. In the case of activated samples, L2A and E2A the surface area increased to 217 and 395 m2/g respectively.
In all cases, and comparing samples with the same carbon content, CECFA coming from Escucha demonstrated higher NO conversion capacity.The obtained results show that carbon content, surface area and parent coal type are the main parameters that influence the NO removal capacity of the obtained CECFA.
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