OCR Text |
Show (1) In the case of low-level control of dioxins by combustion, CO is most influential correlation~of all continuously measurable operation data at present of a Waste-to-Energy Plant. Therefore, ?t11)sf. CO can be considered as one of the~important factors as dioxin levels cannot be continuously measured at present by a Waste-toEnergy Plant for dioxins control. (2) As mentioned in the previous chapter, it is important to have a dry zone in the incinerator generating reduction gas to control NOx as part of other air pollution controls than of dioxins. To control dioxins while satisfying these requirements, it is necessary for the furnace to have a shape that ensures re-combustion more steadily ov~r under a high temperature, "ithin a range of 850 to 900t, for example. Fig. 2-3 shows the relationship between 02 (% of oxygen) and CO (P.P.II.). It shows that CO greatly depends on the performance of mixing. which ift=t~ depends on the furnace shape. In a double flue gas type furnace with better mixing performance and shown in Fig. 2-4. CO falls ~hor·t of ~pproximntp.ly 20 p.p.m. if O ~ cortr.('ntr~ti()n is 7% or more. which represents a normal operation condition. (3) Fig. 2-5 compares a refractory type incinerator with a water spraying system with a water wall type incinerator in terms of their relations between 02 concentration and temperature at the furance outlet. As a result of our long experience in the operation of Waste-toEnergy Platns, 800 to 95018 is currently used as an optimum tellPerature range at the furnace outlet· to ensure st~ble operation of the incinerator, although it depends on the calorific value of waste. From the viewpoint of dioxins control. however. a temperature range between 850 and 100018 is considered appropriate. In this case, the level of 02 ranges from 6.5 to 11%. From Fig. 2-3, this range of 02 sufficiently satisfies re-combustion conditions and is considered to have sufficient efficiency of combustion to maintain CO at a low level. On the other hand, if the temperature at the furnace outlet is raised above 100018. it not only causes troubles including slagging due to combustion, but also 6 ·5 reduces the 02 concentration to less than~. Therefore, the level of CO goes UP higher as shown in Fig. 2-3, which on the contrary is |