Many companies, central governments, and local governments have looked for a practical environmental management technique of more efficient and responsible care for the Environmentally Sound and Sustainable Development (ESSD). As one of practical method, the Eco-Eco(economy-ecology) Balance approach which considers both economy and environment is tried for the possible applications to the public sector problem of infectious medical waste and municipal solid waste management systems in Korea. In environmental and economical aspect, the incineration system with heat recovery turns out to be the one of best alternative in the management of both hazardous and general wastes.
But solid waste incinerator emits various air pollutants such as dust, acidic gases, toxic organic gases(eg. dioxins), and trace metal vapors in addition to the ashes. The concentration and distribution properties of air pollutants are functions of solid wastes composition, plant design ＆ operation parameters, and etc. Therefore, the optimal ＆ environmentally aound design and operations of incinerator are very important.
Currently in Korea and Japan, the portion of small and medium size incinerator is higher due to the regulation in which each municipal government and generators have the responsibility for the treatment of their general solid waste. In Korea, in spite of the minor portion$(23%_w in 1998)$ of annual incineration capacity, the small and medium size incinerators have emitted more pollutants(approximately 2 times) than that of the large incinerators. For the ESSD, more efforts have to be focused on the medium size incineration.
Thus in this research, the objectives are to find the ecological and optimal operation parameters of medium size solid waste incinerator to minimize emissions of poly chlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), to reduce the effective toxicity from incineration by studying the distribution of PCDD/Fs 2,3,7,8-substitute isomers at inlets and outlets, and to increase the efficiency of semi-dry scrubber(SDS) by evaluating simultaneous removal of PCDD/Fs, heavy metals and acidic gaseous pollutants of air pollution control device.
For the scale up of SDS and the verification of pollutants removal mechanism, an equilibria analysis from laboratory experiment for hydrophilic $(SO_2)$ and hydrophobic($CH_2CHCL$, vinyl chloride) pollutants removal, and the pilot test with 50S㎥/min flow rate of high temperature flue gas for heat and mass transfers of $SO_2$ has been performed and compared. From this confidence, the full scale incineration plants is designed for the verification. It is the stoker moving bed type of 20 ton/day capacity for municipal solid waste and the SDS system consisted of SDS, injection system for powdered activated carbon(PAC) and membrane bag filter(B/F).
The specific gravity and the lower calorific value of waste are 0.132ton/㎥ and 2,031Kcal/kg, and it`s physical composition is 36%w paper, 18%w wood, 14%w textile, 17%w plastic, 5%w rubber, 5%w food waste, and 5%w non- combustibles. The design and operation parameters of APCD systems are; 120mg/S㎥ feeding concentration of PAC; 0.025L/㎥ lime slurry feeding rate; 0.5m/sec specific line velocity and 14.75sec retention time in SDS; 0.77m/min air-to-clothe ratio; and 0.4m/sec lifting velocity of bag filter.
For the study of ecologically optimal operations 18 samples of PCDD/Fs have been collected and evaluated with statistics tools. The conventional parameters, e.g. flue gas temperature$(r^2=0.21)$, gas residence time$(r^2=0.17) and CO concentration$(r^2=0.05) of secondary combustion chamber are turn out to be insufficient to minimize PCDD/Fs in medium size incineration systems as shown in parentheses with very low correlation coefficients.
Thus new parameters from the field experience are created, screened, and suggested, and show the satisfactory result as the followings in the order of higher correlation: input calorific value per feed$(r^2=0.96)$, dust concentration of outlet flue gas at bag filter$(r^2=0.86)$, number of CO haunting per hour$(r^2=0.75)$, feeding rate of powdered activate carbon$(r^2=0.71)$, and etc. These are also normalized for the extended applications to other incineration plant.
For the study of PCDD/Fs` finger print, 4 types of medium size incinerators have been investigated, sampled, and analyzed. Regardless of incineration types, Furans dominate the toxicity equivalent with more than 70% of Total Dioxins and Furans at the stack emissions.
Also interesting result are found that the type of heat exchanger after incinerator has profound effect on the finger print. While the boiler type exchanger in which indirect heat exchange occurs does not change the finger print (PCDDFs: PCDDs = 70:30), but the water spray type in which direct heat exchanger occurs between flue gas and water the finger print changes from the Furans dominance (PCDDFs:PCDDs = 90:10) to the pseudo equivalence (PCDDFs:PCDDs = 60:40).
Further researches on the cause of this phenomena is required by the investigation of the both physical(solid and gas forms of PCDD/Fs) and chemical (water solubilities of PCDD/Fs) aspects, and the improvement of SDS design methodology by adopting CFD(computational fluid dynamics), chemical partitioning, and etc. has to be achieved in addition to the endless development of incineration system for the ESSD of medium size incinerator.
