Incineration systems with heat

ESTIMATED INVESTMENT COSTS FOR LARGE MODULAR REFUSE INCINERATION SYSTEMS WITH HEAT RECOVERY... 

Option 1 is a conventional stoker incineration system with heat recovery. Electric power will be generated with the steam from the waste heat boiler. To meet the air pollution standards, exhaust gas has to be cleaned by an electrostatic precipitator and... 

R Fraunfelker. Small Modular Incinerator Systems with Heat Recovery. A Technical Environmental and Economic Evaluation. Executive Summary, Report SW-797, US Environmental Protection Agency, 1979. 

A number of environmental applications [3] have been performed in order to size characterize colloids collected in rivers (riverbome particles, SPM, and sediments), clay samples and ground limestone (from soils), coal particles, diesel soot particles (from combustion processes), or airborne particles in urban areas (from waste incinerators, vehicles, household-heating systems, and manufacturing). In many of these cases, not only the size but also the particle size distribution was important and thus, in conjunction with the traditional UV detector, specific detectors such as ETAAS, ICP-MS, ICP-AES were used [40] in order to obtain more detailed, more specific compositional information. 

Incineration systems are based on the principle that all volatile organic compounds are combustible and can, in principle, be eliminated simply by being burned. Combustion can be achieved without catalysts (thermal systems) or with catalysts (catalytic systems). In either case, flue gases are passed into a chamber where they are heated in an excess of air, resulting in the oxidation of VOCs. Thermal systems operate at temperatures of 750°C-1,000°C, while catalytic systems operate at temperatures of about 350°C-500°C. 

Another development is due to the interest in polychlorodibenzofurans, spurred by their occurrence as environmental contaminants. Polychloro-phenols are manufactured in large amounts (150,000 tons per annum) and find a wide range of uses. The usual method of manufacture involves the hydrolysis of chlorobenzenes, and side reactions, favored by high temperature, can lead to the production of polychlorodibenzofurans and poly-chlorodibenzo-p-dioxins. The Seveso incident is well known." Polychloro-biphenyls are also widely used industrial chemicals, particularly in heat exchange systems, and their pyrolysis leads to the formation of polychloro-dibenzofurans. Polychlorodibenzofurans have also been detected in the fly ash and flue gases of incinerators and industrial heating plants. The most toxic of the polychlorodibenzofurans are 2,3,7,8-tetra-, 1,2,3,7,8-penta-, and 2,3,4,7,8-pentachlorodibenzofuran, and an extensive literature exists on the environmental pollution and the results of human exposure to these substances. A particularly tragic example of the latter occurred in 1968 in the Fukuoka prefecture of Japan after consumption of rice oil contaminated with a commercial polychlorobiphenyl. 

The only available small-scale system is a packaged two chamber incinerator with waste heat recovery. This technique is practical at the 25 to 100 tons per day (TPD) scale. In these units, partial oxidation occurs in the first section of the unit and causes a portion of the waste material to degrade and give off combustible gases. These gases, as well as products of combustion and particulate from the first chamber, flow to a second chamber where they are combusted with excess air and a natural gas or oil pilot flame. The combustion products then flow through appropriate heat transfer equipment to produce steam, hot water, or hot air. Today, four small cities and more than sixty industrial plants use the technique with heat recovery equipment. 

Table III summarizes the basic plant operating requirements in terms of utilities, manpower, and ash disposal. Electric power consumption figures are provided for three different system designs simple incineration without heat recovery or an air pollution control device, incineration with heat recovery but no air pollution control device, and incineration with both heat recovery and air pollution control (stack gases filtered through a baghouse).

Destruction of dioxins and dibenzofurans in contaminated soils and wastes is best achieved by high-temperature pyrolysis. Treatment of soils contaminated with polychlorinated di-benzo-p-dioxins at 2200°C (3992°F) in an electrically heated pyrolyzer reduced levels of tetra-, penta-, and hexachlorinated dibenzo-p-dioxins and dibenzofurans to <0.12 ppb (Boyd et al. 1987). Waterland et al. (1987) reported destruction and removal efficiencies greater than 99.9999% for TCDD in still-bottom wastes with initial concentration of 37 ppm TCDD using a rotary kiln incineration system. Portable infrared incinerators having removal efficiencies greater than 99.9999% have been reported (Daily 1987). 

One manufacturer uses single-drum, watertube type waste heat boilers on incineration systems. Watertube bodets are also used by other manufacturers in installations where high steam pressures and flow rates are required. Another manufacturer offers heat recovery systems with water wall or radiant sections in the primary chamber. These water wall sections, which are usually installed in series with a convective type waste heat boiler, can increase overall heat recovery efficiencies by as much as 10 to 15%. 

Process Description. An incineration system eonsists of three main units feed preparation and handling, primary combustion unit, and off-gas treatment. Feed preparation usually includes screening to remove oversized particles that could clog or jam the combustion unit. Oversized waste may be shredded so that it can be incinerated, or treated or landfilled separately. Sludge is usually dewatered to make the material easier to feed to the incinerator and to limit the fuel cost associated with heating, volatilizing, and treating the water in the incinerator. 

The most suitable disposal systems for polymers in collected mixed plastics waste are pyrolysis with recovery of useful chemicals or incineration with heat energy. Degradable plastics will not interfere with these processes. 

Furnace systems must have effective flue gas cleaning units in order to eliminate harmful substances such as SO2, HCl, HF, NOx, arsenic trioxide and dust produced during incineration. Together with the waste heat utilization units, these plant components are often of a much larger size than the incineration unit itself. 

The policy for waste heat recovery from the flue gas varies between incinerator operators. Incinerators located on the waste producer s site tend to be fitted with waste heat recovery systems, usually steam generation, which is fed into the site steam mains. Merchant incinerator operators, who incinerate other people s waste and... 

Condensation Equipment There are two basic types of condensers used for control contact and surface. In contact condensers, the gaseous stream is brought into direct contact with a cooling medium so that the vapors condense and mix with the coolant (see Fig. 25-15). The more widely used system, however, is the surface condenser (or heat exchanger), in which the vapor and the cooling medium are separated by a wall (see Fig. 25-16). Since high removal efficiencies cannot be obtained with low-condensable vapor concentrations, condensers are typically used for pretreatment prior to some other more efficient control device such as an incinerator, absorber, or adsorber. 

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