Incineration improving efficiency

It has been estimated that roughly 25% of incineration systems installed within the last 10 years either do not operate properly or do not satisfy user performance objectives. A 1981 University of Maryland survey of medical and academic institutions incinerating low-level radioactive wastes indicated that only about 50% of the institutions surveyed (23 total) reported no problems, and about 47% of the institutions (20 total) reported problems ranging from mechanical difficulties to combustion difficulties. A survey conducted by the U.S. Army Corps of Engineers Research Laboratory in 1985 at 52 incineration facilities reported that 17% of the users were very pleased with their systems, 71% were generally satisfied with the performance of their systems (but indicated that minor changes were needed to reduce maintenance and improve efficiency), and 12% were not happy with their systems (reporting severe problems). Results of this Army survey are summarized in Table 4.26. 

The major products of combustion are CO2, water, SO, and NO. The products of combustion are clearly beshminimized by making the process efficient in its use of energy through improved heat recovery and avoiding unnecessary incineration through minimization of process waste. 

The Bndgeport HESGO power plant mixes garbage to facilitate the drying process which improves the efficiency of energy generation by incineration (Gorbis Corporation)... 

Since 1974, the USEPA has conducted many incineration tests for pesticide destruction. Most pesticides tested were capable of being destroyed to an efficiency of more than 99.99%. The only exception was Mirex, with 98-99% destruction. However, investigators felt that destruction could be improved to the 99.99% level with a somewhat more effective incinerator design. Incineration has become very controversial in recent years because of the potential to generate dioxin under high temperature conditions. 

To improve energy efficiency, refractories with superior K factors are used in lining the kiln, thus reducing radiant heat losses. Moreover, kiln mounted blowers now inject combustion air into the kilns in the zone where the volatiles evolve from the coke, thus permitting utilization of the Btu content in these previously wasted gases. In modern calciners, most of the energy required is obtained by burning the coke volatiles and fine particulate matter in the kiln. In some instances, rotary kilns equipped with kiln mounted blowers actually operate without external fuel (except for start-up). When these units are also equipped with incinerators (to combust the unburned volatiles and emitted coke fines) and waste... 

A number of benefits of using OEC in MSW incinerators have been cited.8 The economic incentives include increased waste-processing capacity, greater thermal efficiency, increased production in a waste-to-energy facility, reduced demand on the exhaust system, and a smaller air pollution control system. Increased capacity may be particularly important for many waste processors which are at their maximum capacity, since it is usually difficult to obtain permits to build new facilities. The environmental incentives include improved ash burnout, lower hydrocarbon emissions, lower CO, greater flexibility and control, and the ability to bum low-heating-value wastes such as dewatered sludge. 

In the 1980 s the opportunity for using hydrated lime to remove acid gases from processes such as incinerators and small boilers was recognised. However, trials showed that relatively large excess of commercially available hydrate had to be added to reduce the acid gas concentrations to the required levels. It was postulated that increasing the effective surface area would increase absorption efficiencies. The challenge was how to produce a hydrate with significantly improved properties. 

When a metal-catalyzed reaction is so fast that external mass transfer controls, several layers of fine wire screen can be used as the catalyst bed. The catalytic oxidation of ammonia to nitric oxide, which is the first step in nitric acid production, is carried out with screens (called gauzes) of Pt/Rh alloy, and very high ammonia conversions are obtained. Similar gauzes are used in the Andrussov process for manufacture of HCN from CH4, NH3, and O2. Wire screens are also used for catalytic incineration of pollutants and in improving combustion efficiency in gas burners. 

---