Incineration systems, heat-recovering

Incineration System (Option 1). The system flow diagram is shown in Figure 1. About 70.5 percent of the heat of the municipal refuse is recovered in the form of steam (265°C). A portion of the steam is used in the auxiliary equipment in the incineration system such as the air heater. The efficiency of the low pressure turbine generator is about 0.21. Utilities for the operation of the system and operating costs are listed in Table IV. The caustic soda solution costs to meet the air pollution standards are high. 

Clearly, the proper way to dispose of plastic materials in garbage is to bum them in an incineration system equipped to use the heat of combustion either to generate electricity or to provide steam for municipal heating. In this way, one can consider that the use of a plastic container is simply borrowing a barrel of petroleum to make the plastic, using it once or twice as a container, and then recovering about the same amount of heat from it as if the barrel of petroleum had been burned in the first place. Such applications obviously represent a considerable conservation of energy and raw materials. 

Contaminated feedstock is heated in an indirectly fired rotary dryer. The vapors are then transported to a gas treatment system via an inert gas such as nitrogen where they are scrubbed and cooled to condense the organics. The carrier gas is reheated and recycled to the dryer. The recovered organics can be reclaimed, used on-site or off-site as fuel, or incinerated. The technology is available in laboratory-, pilot-, and full-scale systems. 

The successful operation of this system demonstrated the potential for heat recovery from incineration of cotton gin trash. At a 30% recovery ratio, enough heat can be recovered from the incineration process to supply most of the energy required for seed cotton drying, even in low-capacity gins (Table IX). Only the size and volume of the ginning operation will dictate whether such recovery will be economically feasible. 

Thermal. Combustion techniques bum waste for the recovery of heat energy, Waterwall combustors are the most technically developed energy recovery systems and employ special grates to bum "as received urban waste and recover steam either at saturated or superheated conditions. Over 250 plants are operating worldwide seven of them in the United States. Three of the seven were originally built as incinerators. Worldwide there have been a number of technical problems, with the control of corrosion and erosion being the most serious. The most recent European designs have solved these problems but at an increased capital cost. 

For estimating purposes, about 3 to 4 poimds of steam can be recovered for each pound of typical institutional type sohd waste incinerated. However, the economic feasibility of providing a waste heat recovery system usually depends upon the abUity to use the recovered energy. If orily half of recovered steam can be used because of low seasonal steam demands, heat recovery may not be cost effective. 

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