Study of the Formation Mechanism and Control Technology for PCDD/Fs onto the Fly Ash

• Main Authors: Lee Yen Fen, 李彥芬
• Other Authors: Lin Chieh
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/19541549171882395221

碩士 === 國立屏東科技大學 === 環境工程與科學系 === 92 === The secondary formation of dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the flue gas and ash from the incineration system draw a lot of attention to public about this state-of-art technology. Studies showed the favored temperature range and high surface area in the particulate matter play the important roles. The high removal efficiency of particulate active carbon injection was to apply for most of incineration systems to reduce the heavy metal compounds and PCDD/Fs. The adsorption carbon residue in the fly ash stream is still a controversial issue for the final disposal treatment. The comparison between the raw fly ashes as received from the different units of incinerator was investigated in this research project. Inducing precursors experiments take place in a laboratory scales reactor. The preliminary results show that PCDD/Fs onto the ashes from superheater and electric state precipitater (ESP) is positive related to the chlorinated precursor (i.e. chlorobenzene) induced concentration. The ratio of PCDDs/PCDFs is between 1.2 and 3.31. Ash collected from bag filter shows the similar trend as the ashes from superheater and ESP. However, the ratio of PCDDs/PCDFs is less than 1 and de novo formation is dominant. The ash collected from electric arc furnace (EAF) after chlorobenzene pass through shows the similar distribution of PCDD/Fs congeners profile as the raw fly ash as received. The formation rate of PCDD/Fs is positive related to the precursor concentration (i.e. chlorobenzene). Dibenzofurans and copper chloride was added to the fly ash matrix to stimulate the formation of PCDD/Fs. Results revealed that copper chloride can enhance the PCDD/Fs formation from 86.92ng/g to 5307.78ng/g. Since dibenzofurans is the primary precursor of PCDFs, the formation rate of PCDDs was significantly lower than the PCDFs. Ash collected from the bag filter was added particulate active carbon to simulate the reformation effect of PCDD/Fs. Under such conditions higher concentrations of PCDD/Fs can be formed. The fly ash was heated to remove PCDD/Fs. The residue concentration is 2.28ng/g and the removal efficiency is between 80% and 99%. It suggests that the characteristics of fly ash may be changed due to the particulate active carbon injection and thermal treatment is effective to destruct PCDD/Fs onto the fly ash matrix.