Incinerators operating considerations

Operational Considerations. The performance of catalytic incinerators (28) is affected by catalyst inlet temperature, space velocity, superficial gas velocity (at the catalyst inlet), bed geometry, species present and concentration, mixture composition, and waste contaminants. Catalyst inlet temperatures strongly affect destmction efficiency. Mixture compositions, air-to-gas (fuel) ratio, space velocity, and inlet concentration all show marginal or statistically insignificant effects (30). 

Considerable time is sometimes required to obtain approval and proceed to full-rate incinerator operations after submission of trial burn results. Because of the size and complexity of the task for trial burn report review and approval, increased resources and specific trial burn and regulatory skills could greatly speed the process. It is an accepted practice to provide funding to a regulatory agency so that it can hire a third party to support regulatory reviews.13... 

Heavy Metals Table 2 shows the behaviour of chromium VI (Cr+6T in pyrolytic operation. The behaviour of Cr+° in incinerating operation on cake E is algo shown in the table. The ratio of Cr+o to total chromium (Cr+°/T-Cr) is an indicator of the behaviour of chromium compounds in thermal processings. As indicated in the table, a part of chromium HE (Cr 3) in fed cake is oxidized into Cr+6 during incinerating operation, whereas a considerable portion of Cr 6 in fed cake is reduced during pyrolytic operation. 

Doucet, L.G., Incineration State-of-the-Ait Design, Procurement and Operational Considerations, Technical Document No. 055872, American Society for Hospital Engineering, Environmental Management File, Chicago, 1988. 

There has been considerable concern throughout Europe about the incineration of wastes, yet in Japan about 70% of all MSW is incinerated, and plans are that this should increase to 90% by the year 2000 [33]. Incinerators that are poorly operated may run at temperatures too low to burn potentially hazardous intermediates of the combustion process such as the products from pyrolysis which are believed to be the precursors in the combustion processes [34]. Of particular concern has been the discovery of extremely toxic materials such as dioxins (chlorinated dibenzo-/ -dioxins and benzofuran dioxins), in the flue gases of some incinerators. Such is the level of concern that many European countries have increased the legislative and environmental controls on incinerator operators, and some are moving to ban the incineration of plastics [35], and particularly PVC. In incinerators where the temperature is below about 1400 K, dehydrochlorination of PVC occurs, accompanied by the formation of polyenes. The polyenes can then cyclise and be oxidised, and then be attacked by chlorine-containing species to produce dioxins, the most toxic of which is 2,3,7,8-tetra-chlorodibenzo-/7-dioxin (TCDD), the material at the centre of the disaster at Sveso, Northern Italy, in 1979. More than 70 dioxins are known to exist (Figure 13.11). 

ILLUSTRATIVE EXAMPLE 21.1 In order to meet recently updated environmental regulations for discharging hydrocarbons to the atmosphere, a gas stream must be reduced by 99.5% of its present hydrocarbon concentration. Due to economic considerations, it is proposed to meet the above requirement by combusting the hydrocarbons in an incinerator operating at 1500°F. The gas and methane (fuel) are to be fed to the incinerator at 80°F and 1 atm. Design the proposed incinerator using kinetic principles. 

Design considerations and costs of the catalyst, hardware, and a fume control system are direcdy proportional to the oven exhaust volume. The size of the catalyst bed often ranges from 1.0 m at 0°C and 101 kPa per 1000 m /min of exhaust, to 2 m for 1000 m /min of exhaust. Catalyst performance at a number of can plant installations has been enhanced by proper maintenance. Annual analytical measurements show reduction of solvent hydrocarbons to be in excess of 90% for 3—6 years, the equivalent of 12,000 to 30,000 operating hours. When propane was the only available fuel, the catalyst cost was recovered by fuel savings (vs thermal incineration prior to the catalyst retrofit) in two to three months. In numerous cases the fuel savings paid for the catalyst in 6 to 12 months. 

Operating Temperature and Pressure Arresters are certified subject to maximum operating temperatures and absolute pressures normally seen at the arrester location. Arrester placement in relation to heat sources, such as incinerators, must be selected so that the allowable temperature is not exceeded, with due consideration for the detonation potential as run-up distance is increased. 

Thermal and catalytic incinerators, condensers, and adsorbers are the most common methods of abatement used, due to their ability to deal with a wide variety of emissions of organic compounds. The selection between destruction and recovery equipment is normally based on the feasibility of recovery, which relates directly to the cost and the concentration of organic compounds in the gas stream. The selection of a suitable technology depends on environmental and economical aspects, energy demand, and ease of installation as well as considerations of operating and maintenance. 7 he selection criteria may vary with companies or with individual process units however, the fundamental approach is the same. 

Some considerations relevant to public health concerns about modern and effective incineration systems have been described. However, local health officials and citizens of communities with hazardous waste incinerators have expressed to ATSDR their concern that they may not be able to judge a good operation, or that, once the initial trial burns and inspections are completed, the system may not be operated in the same manner as during the testing phase. Citizens have also expressed concern that burning rates will be exceeded or monitoring systems will be overridden. 

Worldwide, there are numerous plasma system designs for treatment of all types of wastes. Economical considerations limit their commercial applications to the most profitable actions. Presently they commercially operate in Switzerland and Germany for low level nuclear waste vitrification, in France and the USA for asbestos waste vitrification, in the USA and Australia for hazardous waste treatment, in Japan and France for municipal fly ash vitrification. The most of installations is working in Japan because there 70% of municipal waste is incinerated and the ash can not be used as landfill. EU Regulations banning the disposal to landfill of toxic and hazardous wastes after year 2002 may cause wider use of plasma waste destruction technology in Europe. 

All projects involving any significant quantity of LNAPL product recovery require the consideration of economic factors. Careful planning to optimize each project phase can lead to the lowest cost of operation and can occasionally generate positive cash flow, while currently accomplishing aquifer restoration. A basic premise in this discussion is that the recovered LNAPL is suitable for reuse (i.e., as refinery feed stock or fuel for incinerators). Products unsuitable for resale only add to the debit side of the economic equation. 

The SCWO process is able to achieve destruction efficiencies for organic waste comparable with those attained by incineration technology, without the requirement of expensive dewatering equipment. The key to a successful SCWO process is a design that integrates various unit operations. Important design considerations include ... 

Examples of commonly used bioseparations include sedimentation, coagulation, and filtration. The scale of operation for such bioseparation processes is considerable, because of the volumes of effluent which are processed and the throughputs required. Proprietary aerobic digesters such as the Deep Shaft process may use centrifugation to recover biomass from the treated effluent for recycle as an inoculum for the digester or to reduce the quantity of water before sending the solid material either to incineration or land fill. 

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