Incinerator Design Research Articles

Trash, Heat, and Ash

This article highlights about process of incineration that offers French municipalities a number of advantages. First, it reduces the volume of solid waste to a fraction of its bulk. A metric ton of household waste leaves about 250 kg of bottom ashes and 30 to 50 kg of fly ash. This is an important consideration in France, which has much less landfill space than New World giants such as the United States or Canada. Combustion also sanitizes by destroying any microbes present, and the heat produced by the waste furnace can generate steam or hot water to heat residences, supply factories, or generate electricity in a turbine. Two popular French waste incinerator designs are rolling hearth and inclined grate furnaces. The former type contains a sloping series of rollers turned continuously by motor. As fuel slides down the rollers from top to bottom, solid residues drop out. Electricite de France is researching several ways of reducing the costs of vitrification. In laboratories near Fontainebleau, fly ash is fed into an electric arc furnace equipped with a graphite electrode.

Fundamental Principles of Incinerator Design

AbstractWaste management has become a major concern world‐wide and incineration is now being increasingly used to treat waste which cannot be economically recycled. The combustion of conventional well specified fossil fuels is a very complex process since it involves two‐phase turbulent reacting flow including radiant heat transfer. Incineration is even more complex since the waste is poorly specified and its composition varies from moment to moment. In the past, the design of incinerators has not been based on fundamental understanding and modelling of the process, and empirical rules have had to be used.Over the last few years, computational fluid dynamics (CFD) has provided a means to model the freeboard region in a conventional municipal solid waste incinerator but the open literature contains no rigorous fundamentally based model of the bed region. The prediction of the flow composition emerging from this region is particularly important since it provides the “upstream” boundary condition for the flow calculations in the freeboard. For example, the calculation of the subsequent history of heavy metals requires knowledge of their emission rate from the burning bed.The processes in the bed include drying, pyrolysis, oxidative burning, and gasification of the char. Furthermore, the movement of the grate is designed to mix the waste as it burns. Indeed, the existence of a rigorous bed model would also permit the grate design to be optimised, and, if immediate data on the feed were available, a rational combustion control strategy could be devised. A preliminary model of combustion in the bed is proposed herein based on governing equations for the burning of individual “regions” of waste in the upward gas flow, their motion, and radiant heat transfer within the bed. The emissions of gases from the surface of the bed is very non‐uniform with oxygen emitted from either end of the bed, organic compounds from the one‐third region, and carbon monoxide from the centre. The surface layer of this central part of the bed consists of char with gases coming up from the oxidising layer below containing NOx derived from the fuel nitrogen. The char region therefore acts as an important reburn zone and it is suggested that this reduces some of the NOx to nitrogen. This is important since the minimisation of NOx by optimising the basic combustion process is likely to be environmentally preferable to subsequent control of NOx by the injection ofreactants such as ammonia.The calculation of flow and combustion in the freeboard using CFD can quantify the consequences of design concepts, however guidelines are needed to devise specific design concepts which are worthy of investigation. Thus the computer cannot “invent” a design but it can quantify the results of ideas.Incinerator design thus requires a judicious combination of fundamental combustion science, ingenious engineering guided by an understanding of the mixing process, and last but not least, practical experience of previous failures and successes.

A Series Reaction Approach to VOC Incineration

Thermal incineration of VOCs has been evaluated by means of a two step series reaction approach, VOC → CO → CO 2 , so that the rates of VOC and CO oxidation may both be considered. Temperature and concentration profiles have been obtained for oxidation of several VOCs as functions of space time τ. Appropriate conditions for 99.99% removal of VOC and 99.5% oxidation of intermediate CO appear to be 930 to 980 K inlet temperature, 0.05 to 0.06kmol auxiliary fuel per kmol dry waste air and 90 to 130 % excess air for auxiliary fuel, without heat recovery. These conditions yield approximately 0.4 seconds space time and an L/d i ratio for the oxidation section of the incinerator of approximately 2 to 3. Heat loss from the incinerator should be less than 2% of the total heat from auxiliary fuel and VOC combustion and incinerator design should therefore be optimized with respect to fuel and insulation costs. The approach outlined in this work can easily be adapted to estimate auxiliary fuel savings via heat recovery.

Application of Acoustic and Design Enhancement to Onboard Naval Waste Thermal Treatment Facilities

ABSTRACT Incineration or, more politicallY, waste thermal treatment is a preferred method for waste handling on board naval platforms. It can accomplish several goals of at-sea treatment of shipboard wastes, including volume reduction, sterilization, and detoxification. It is also considered to be the most cost-effective approach available and among the safest, requiring little specialized personnel training. Unfortunately, existing seaworthy incinerator designs that meet the naval requirements of compactness and minimal weight are not expected to meet the higher throughput demands of planned shipboard operations. This has lead to the exploration of novel approaches, such as the use of forced acoustics to improve heat transfer, turbulent mixing, and firing density in order to reduce the size and increase the throughput of incineration systems. Energy and Environmental Research Corporation (EER) has designed and constructed an experimental facility to study the application of forced acoustics for the impro...

96/06330 Comparative evaluation of municipal solid waste incinerator designs by flow simulation

96/06330 Comparative evaluation of municipal solid waste incinerator designs by flow simulation

Comparative evaluation of municipal solid waste incinerator designs by flow simulation

Flow simulations have been carried out to evaluate the effects of combustion chamber design and air/combustion gas flow configuration on the overall performance of municipal solid waste incinerators. Computational results show velocity and temperature fields in the entire region of flow passage. Local recirculations and uneven distributions of flow velocity and temperature should be minimized and mixing is to be enhanced. Two parameters are proposed to help quantify the overall flow condition. The degree of mixing of different species, which enter the incinerator from the air and combustion gas inlets, is represented by the mixing parameter α. Here, α is calculated on the nodal points. The probability distribution of α in the entire computational domain is used for comparative evaluation of incinerator designs. The thermal decomposition parameter β is calculated by integrating the kinetic rates along the trajectory of a fluid element. This parameter represents the portion of the unreacted materials among the total pollutants released from the bed. By employing these parameters, various incinerator design alternatives can be quantitatively analyzed from two principal viewpoints, i.e., the effectiveness in mixing and the thermal decomposition of pollutants.

Design of a small-scale incinerator with low PCDD/PCDF emissions

Attempts were made to achieve complete combustion by improving secondary combustion for the purpose of reducing PCDDs/PCDFs in a small-scale incinerator. Particular emphasis was placed on improving gas turbulence in the chamber. First, the gas flow in the chamber was analyzed by the flow visualization technique, using laboratory scale equipment. Then, the combustibility was evaluated using a model gas containing standard carbon monoxide. Finally, the reduction of PCDDs/PCDFs was confirmed with an actual plant. A resultant finding was that PCDDs/PCDFs emissions at the incinerator outlet can be significantly reduced by changing the gas flow pattern in the secondary combustion chamber.

Guidelines for the design, installation and operation of incinerators

Incineration of hazardous and medical (clinical) waste crepates an air pollution problem which s at the moment controlled in terms of the Atmospheric Pollution Prevention Act of 1965. It is exercised by officials from local authorities in accordance with part 3 of the Act and is very specialized. Consequently, officials from local authorities are not always trained to do this, especially at the smaller municipalities. Therefore, this function is dealt with in the wrong manner, or not dealt with at all. Incinirators are to be classified into three categories, namely incinirators where the refuse that is being burnt is also used as fuel or as supplementary fuel, incinerators which are not used for medical and hazardous waste destruction. If halogens like chlorine are present in teh waste, then there is a difinite possibility that dioxins and furans will be emitted during the incineration process. With a halogen content of more than 1% in the waste a minimum tempature of 1100 degree celsius for 2 senconds at the inner wall of the secondary chamber is imperative. For cytotoxic waste teh temperature must be at least 1000 degree celsius.

Analytical survey of elements in veterinary college incinerator ashes

While appreciable attention has been given to the elemental composition of ashes from municipal solid waste incinerators, relatively little information is available on the elemental content of incinerators burning animal carcasses and medical wastes. In the work reported here, an analytical survey was conducted of the concentration of 22 elements in the ashes of incinerators located at veterinary colleges or animal disease diagnostic laboratories in seven states. With the exception of Zn, the concentrations of most elements were well below those found in ashes from municipal solid waste incinerators. Conversely, Ca, P and K were much higher in concentration probably deriving largely from bones, teeth and other organs of animals. There was an indication that burned plastic wastes were a source of Pb in the ashes. The concentrations of several toxic elements varied widely probably due to variations in initial waste composition, incinerator design and operating parameters. The concentrations of soluble salts in the ashes were appreciable. Organic matter in the ashes was low to nondetectable indicating the completeness of incineration.

An international perspective on the characterisation and management of residues from MSW incinerators

Fully integrated municipal solid waste (MSW) management strategies around the globe include the use of incineration, either with or without energy recovery. During the late 1970's and early 1980's, the practice of incineration was subjected to increased scrutiny due to concerns over air emissions. As a result, the industry quickly moved to improve the design, operation and air pollution control systems of MSW incinerators to the point where emissions from modern, well operated and well maintained incinerator systems are no longer considered a threat to human health or the environment. This has resulted in a shift of concerns from air emissions to the incinerator residues. Many of the concerns regarding the disposal of MSW incinerator residues have become controversial in nature, mostly due to the broad scope of the factors influencing ash characteristics (such as MSW composition, incinerators technologies and operation), the fragmented database, the heterogeneity of the residues, and uncertainty over the long-term behaviour of the residue in the environment. Recognising there was a need to compile and evaluate the available information, the International Ash Working Group (IAWG) was established to conduct an in-depth review of the existing scientific data and develop a state-of-knowledge treatise on MSW incinerator residue characterisation, disposal, treatment and utilisation.

Effects of high speed jets and internal baffles on the gas residence times in large municipal incinerators

AbstractThe value of knowing the gas residence times in large municipal incinerators and the serious error imposed by the traditional use of gas volume flow rate based average residence time with regard to these incinerators are recognized. There is increasing public awareness and concern over emissions from municipal solid waste incinerators. Modelling studies of particle trajectories using computational fluid dynamics shows the utility of simulation for the determination of residence time distribution in incinerators. These studies indicate that residence time distributions contain valuable information, important to the understanding and evaluation of mixing processes in the incinerator overfire region. A number of design modifications and changes in operational conditions (which have a major influence on the mean gas residence times and overall performance of two large municipal incinerator plants (35 MW and 65 MW) are proposed. Specifically, the effect of high speed jets and different internal baffle configurations have been investigated using mathematical modelling, in an attempt to obtain optimum combustion conditions. This would increase the mean gas residence times, minimize the emission of pollutants and improve the temperature profile throughout the system. The utility of having detailed RTD information for the incinerator overfire region is demonstrated by estimating the residence times using numerical simulation of tracer injection into the 3‐dimensional reacting flow field of two typical municipal incinerator configurations. The modelling results not only underscore the critical role played by jets in achieving desirable states of mixing in the overfire region but also point to the significance of the geometry effects.This modelling work has yielded important results, all of which clearly could not be experimentally verified at the industrial scale due to practical and cost limitations. Nevertheless, the results guide specific modifications to the design and operation and this new approach will be of considerable use to the incinerator design community.

Development of an Environmentally Acceptable Thermal Treatment Alternative for Energetic Material

Alternatives to the open burn/open detonation (OB/OD) disposal of energetic materials are being actively investigated by both the government and industry because of increasing restrictions being imposed by the various air quality districts and governmental agencies. Aerojet has developed a system that can dispose of these types of materials in a three-step process that meets all environmental regulatory requirements. Step 1 is the removal of the energetic material from its container, if required, using high pressure water. Step 2 involves macerating the material in water to facilitate desensitization of Class 1.1 and Class 1.3 energetic materials prior to incineration (Step 3) which is structured around a dual chamber, fixed hearth incinerator designed to operate under negative pressure to eliminate fugitive emissions. This incinerator is a two-stage, controlled-air unit equipped with tandem liquid scrubbers capable of limiting particulates to less than 1.0 micron with a 95% efficiency at 0.5 micron, a design requirement imposed by its originally intended use in the nuclear industry where high efficiency particulate adsorber (HEPA) filters were required on the output to ensure the capture of radioactive particles. Adapting the basic design to handling energetic materials principally involved the selection of different refractory materials; the original design produced a clean burning, low emissions incinerator capable of handling a variety of combustible solid and liquid feed streams. Additional improvements in emissions levels were made possible by using orthogonal experimental arrays and analyses based on Taguchi Methods®. This approach provided the needed insight into the effects of controllable factors on emissions to permit optimization of the operating parameters for the incinerator. Combustion efficiencies of 99.98+%, destruction and removal efficiencies (DRE) of 99.99+%, and emissions levels well below regulatory limits have been consistently observed which demonstrates the efficacy of this incinerator design and of the experimental approach used for operational optimization.

Concentrations of metals in grasses in the vicinity of a municipal refuse incinerator

There is currently much public opposition to the construction of municipal refuse incinerators in the United States owing to health concerns about emitted toxicants. In this study, 19 elements and polychlorinated biphenyls (PCBs) were determined in grasses sampled upwind and downwind from a municipal refuse incinerator which had no emission control devices. Concentrations of Cd, Mo, Hg, Zn, Fe, and Pb were generally highest immediately adjacent to the incinerator. Foliar concentration of the metals, Cd, Mo, Zn, Fe, and Pb was inversely related to the logarithm of the distance downwind from the incinerator. Foliar concentration of Hg decreased linearly with distance downwind. Polychlorinated biphenyls were not detectable in any of the grass samples possibly due to their thermal destruction during incineration or greater dispersion because of their higher vapor pressure. The metal concentration in plants in the vicinity of such incinerators will be affected by the composition of the refuse, incinerator design and stack height, combustion operating conditions, emission control devices, the nature of the plant surface, the water solubility of deposited metal-containing particulates, prevailing weather conditions and root uptake of such metals by plants.

The existence of second threshold for combustion and its implications to incineration

This paper reports a set of experiments examining the oxidation kinetics of CH 3 Cl, C 6 H 6 and C 6 H 5 Cl. These compounds were chosen because they are typical of the most difficult to incinerate materials encountered in hazardous waste incineration. The specific rate at which these compounds oxidize was measured as a function of the initial concentration of the compound and found to decrease with decreasing initial concentration. At low initial concentrations of CH 3 Cl, C 6 H 6 and C 6 H 5 Cl the specific rates of oxidation found were very low and may represent a previously unrecognized problem in the design and operation of hazardous waste incinerators. Adding CO, however, greatly increased the specific rate at which the organics oxidized and improvements in their extent of oxidation of up to a factor of 10,000 were achieved. The author believes that these experiments demonstrate the existence of a second threshold for lean fuel combustion/oxidation. Gas phase combustion/oxidation reactions are rapid for two reasons: because they are exothermic and because they occur by chain branching mechanisms. The former consideration means that combustion systems can be self-heating. This implies existence of the first threshold of combustion, the familiar flammability limit, i.e., to be flammable a mixture must contain enough fuel to be able to heat itself to flame temperature. Similarly the fact that combustion, oxidation reactions occur by chain branching mechanisms means that combustion/oxidation reactions can generate much higher concentrations of free radical chain carriers than equilibrium would provide. This, then, implies a second threshold, i.e., if a reaction is to occur with the high rate that a superequilibrium free radical concentration can provide, then the initial concentration of the fuel must be high enough to generate that superequilibrium concentration. This second threshold for combustion/oxidation may limit the effectiveness with which incinerators destroy toxic organic materials and it may be possible to improve that effectiveness by injecting some clean fuel to bring the total fuel concentration above this threshold and thus restore a rapid rate of oxidation.

Design optimization of a large municipal solid waste incinerator

This paper discusses a number of design modifications and changes in operational conditions which have a major influence on the overall performance of the large Sheffield municipal solid waste incinerator plant (30 MW) which incorporates a heat recovery system for district heating. The effect of installing four different baffle configurations inside the radiation shaft and various primary and secondary air distribution patterns have been investigated using mathematical modelling, in attempt to eliminate the existing recirculation zone inside the shaft and at the same time obtain optimum combustion conditions which would minimize the emission of pollutants and reduce maintenance costs at the plant. A mathematical model of the finite difference type was employed to predict the three dimensional reacting flows within these modified incinerator designs. The κ - ε submodel has been employed for turbulence, together with a combustion model of the Magnussen type. A Lagrangian model was used to estimate the residence times for different cases. The results obtained from the modelling work demonstrate that the suggested modified design produces longer residence times in the incinerator, improves the temperature profile at the exit, reduces the concentration of products of incomplete combustion and increases the overall boiler efficiency by nearly 8%. Using these modelling results a preliminary economic assessment of the potential benefits of the suggested modified incinerator design compared to the original design has been made assuming the energy recovered is sold as steam. The calculation indicated that because of significant savings in running and maintenance costs, an 18% reduction in net waste disposal cost may be achieved.

Solids Pyrolysis and Volatiles Secondary Reactions in Hazardous Waste Incineration: Implications for Toxicants Destruction and PIC's Generation

Solids are important contributers to the United States hazardous wastes problem. Hazardous solids include several million tons yearly of residues from industrial processing and treatment of other wastes, and millions to billions of tons of contaminated soils found in numerous, and widely distributed abandoned dump sites. Incineration is an attractive technology for decontaminating hazardous solids, but realization of its potential requires improved public acceptance which can come from better technical understanding. Organic solids fed to an incinerator are thermally decomposed (pyrolyzed, devolatilized) into three products requiring burnout: gases and liquids (volatiles) and a solid residue (char). This paper describes how solids pyrolysis and further, so-called secondary reactions of newly formed volatiles (e.g. cracking, partial oxidation) can contribute to desired and undesired effects within incineration chambers, e.g. high destruction efficiencies for targetted wastes, or generation of undesired by-products. It is shown that incinerator design, operation, and performance monitoring will benefit from better quantitative understanding of devolatilization-related phenomena. Important issues are how solids pyrolysis and volatiles secondary reactions are affected by properties of the raw waste, and by incinerator operating conditions (e.g. temperature, heating rate, treatment time, local oxygen partial pressure). Research methods for obtaining this information are discussed, typical results are illustrated, and research challenges and opportunities in solid wastes pyrolysis are noted.

Incineration of solid waste

AbstractThe concern over solid waste disposal and dump‐site clean‐up resulted in the passage of three major U.S. environmental laws. They are the Resource Conservation and Recovery Act (RCRA) of 1976, Public Law 94–580, the Toxic Substances Control Act (TSCA) of 1976, Public Law 94–469, and the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) of 1980, Public Law 96–510. The implementation of these three laws has intensified incineration research, because incineration represents the highest degree of destruction and environmental control possible for various waste types. This paper reviews the fundamentals of incineration and provides an incinerator design example to show how combustion fundamentals are applied to an incineration system.

Continuous recovery of heavy metals from MSW incinerator ashes

AbstractThe leachable concentrations of heavy metals from ash residues from the incineration of municipal solid waste (MSW) often exceeds the Extraction Procedure Toxicity Test (EP Tox) limits, requiring these materials to be considered as a potential hazardous waste. The kinetics of Pb, Cd, and Cr extraction were determined through a series of batch extraction studies. The specific incinerator design and the equilibrium conditions strongly influenced the ash matrix and subsequently the extraction kinetics. Recovery of the metals from the extractant solution was accomplished utilizing electrochemical plating techniques.

Incineration of Sewage Sludge ‐ A Reappraisal

ABSTRACTThe paper briefly reviews the history of incineration in the UK. The need for an integrated flow sheet concept in the design and operation of modern incinerators is stressed. Each element of the flow sheet (dewatering, predrying, the incinerator, waste heat recovery, flue gas cleaning, ash disposal) is reviewed. The economics of the process are discussed and the importance of autogenous combustion and need to avoid the inclusion of spare capacity is emphasised.

Emissions of polychlorinated dibenzo-p-dioxins from municipal incinerators

Polychlorinated dibenzo-p-dioxins (PCDDs) in flue gases, slag and fly ashes from 7 incinerators in Kyoto Prefecture were measured as the total amounts of T4-O8CDDs by packed-column GC/MS analysis.The results showed that various amounts of T4-O8CDDs were present in many samples and that their main component was O8CDD. Although there was no correspondence between the distributions of concentration of any congeners in different species of samples, a similarity was found in the case of the distribution of concentration of each isomer in different incinerators and samples. A tendency for the concentrations of congeners to increase was observed in proportion to the number of chlorine atoms in the ashes of the electrostatic precipitators and gases.Estimations of the emission amounts of each congener per day and per refuse by each incinerator were also carried out. The emission amounts of each congener per day were from 1.1 to 5800mg/d. The emission ratio from each sample varied according to the incinerator and congener.The range of emission amounts of each congener per 1 ton of refuse was from 0.013 to 64mg/t, with T4CDDs and P5CDDs being 0.013-2.1mg/t and 0.022-4.4mg/t, respectively.Therefore, it was suggested that the formation and decomposition of PCDDs depends on the different incinerator designs and operating conditions.