A Modern Flue-gas Cleaning System For Waste Incineration .
WASTEINCINERAA modern flue-gascleaning system forwaste incinerationplantsTIONthat in practice the waste remaining aftersorting has to be disposed of by incineration.The shortage of suitable landfills makesincineration – within the framework of totalwaste management – the only practicablesolution. Nevertheless, a common criticismof this solution is that a third of the wastestill remains afterwards, mainly in the form ofslag. This is only half the truth. While it istrue that incineration reduces the waste tojust a third of its mass, it reduces it at thesame time to one tenth of its volume, andSince 1990, waste incineration plants in Germany have had to comply withthis is what matters most in the context ofEurope’s strictest emissions legislation – a clean-air decree known aslandfilling.the ‘17th BImSchV’. Building on the clean-air limits contained in the 1986German decree ‘TA-Luft’, it also forms the core of the European Union’sNew legislation is more rigorousguideline for the thermal treatment of hazardous waste that took effectLegislation and regulations applying toin 1993. Total Cleaning and Recycling (TCR) is a process, developed bywaste incineration plants have become farABB, which ensures compliance with the ‘17th BImSchV’, in some casesmore stringent in recent years. The Germanguaranteeing results well below the limits given in it. Because TCRclean-air decree ‘TA-Luft’ was passed insystems are of modular design, they can be easily retrofitted to older1986, and in 1990 the emission limits wereincineration plants. Results from a full-scale demonstration system inreduced once more through a furtheroperation in Hobro, Denmark, confirm the good performance of the newdecree known as the ‘17th BImSchV’. TheABB technology.European Union guideline for the thermaltreatment of hazardous waste that hasPthe impact this pollutant has on the environ-the stipulations contained in the ‘17thation plants is low mainly as a result of thement.BImSchV’. Table 1 shows how the limits forublic approval of municipal waste inciner-existed since 1993 is also largely based onpollutants emitted by facilities that were builtMore recently, a general rethinking of theback in the 1970s and early 1980s. This hassituation has become apparent. The con-emissionsandpollutantshavebeenled, understandably, to criticism of thermalsensus is that the thermal treatment of theBesides fulfilling these requirements,disposal as such and fuelled an ongoingwaste after sorting – and its avoidance,plant operators are also making a strongdebate about the best way to change thewhere possible, in the first place – should beeffort to utilize the energy produced by thepublic’s ‘use and throw-away’ mentality. Fortied into a total waste management pro-thermal process and to recover and recyclesome time now, society has perceivedgramme. A new German decree regulatingthe residual materials. The extremely lowwaste incineration as a mainstay of this atti-the disposal of domestic waste (‘TA Sied-emission levels have a political goal, namelytude.lungsabfall’) points the way. This makes itto gain public acceptance of thermal wasteIn Germany even new, stricter legislation,unlawful to dump materials with an organicdisposal. Although they should not be seencalling for a drastic two-stage reduction incontent of more than 5 percent, meaningas a solution to the overall emissions situ-reduced since the 1986 decree.flue-gas emissions from waste incinerationation as it applies in Germany, they areplants and upgrading of older plants in theinevitably providing new benchmarks forshort term has not been able to change thisindustry as a whole.perception.Waste incineration plants equipped withmodern flue-gas cleaning technology emitDr. Jürgen GottschalkDr. Peter ButtmannModern flue-gas cleaning with TCRABB Umwelttechnik GmbHThe more stringent regulations have led thepractically no dioxins into the atmosphere.environmental control industry to step up itsOn the contrary, they act as dioxin sinks,Torgny Johanssondevelopment programmes in a dramaticdestroying the dioxins which are naturallyABB Fläkt Industri ABway.present in the waste and actually lesseningABB has developed its own advancedABBReview1/199629
WIncinerationASTEINBag filterCINERATScrubberIONFilsorptionSCR denoxAmmoniaNaturalgasH2OActivatedcokeMilk of limeMixture ofactivatedcoke andlime 2To incineratorHg-bearingactivated carbonHeavy-metalcondensate 3Glassgranules 30Gypsum 6Quantity in kg per tonne of wasteHydrochloric acid 15VitrificationLime sludgeHCl productionGypsum production1TCR process, with resource recovery, for flue-gas cleaning in waste incineration plantsprocess, which it calls Total Cleaning andbag filter, where the dust is removed. Thecontaining heavy metals is also removedRecycling, or TCR.high efficiency of the bag filter has a verywith the dust.As the process schematic 1 of thepositive effect on the performance of theIn the first scrubber, quenching is fol-modular TCR facility shows, the flue gasscrubbing stages, and especially on thelowed by wash-out of the hydrochloric acidfirst passes from the incineration graterecovery of resources from the scrubbing(HCl) under acidic conditions. The secondto the heat-recovery boiler and then to aliquids. The majority of the particulatescrubber absorbs the sulfur dioxide. Thissolves the initial problem of removing theprincipal acidic constituents of the flueTable 1:Allowed pollutant emissions for waste incineration plants(in mg/Nm3, dry, 11 % O2) – average daily values and mean valueduring samplingPollutantsTA Luft ’86 17th BlmSchVEU Guidelinegas. In addition, the first scrubber dissolvesand separates the gaseous heavy metals(eg, mercury) and the residual heavy metalparticles.The scrubbing stages are followed bya second bag filter in which a processDust30Carbon monoxide100Organic materials (C tot)20100Sulfur oxides as SO2Gaseous anorg. comp. of chloride as HCl 50Gaseous anorg. comp. of fluorine as HF 5Nitrogen oxides as NO2500Cd, TlY 0.2HgSb, As, Pb, Cr, Co, Cu, Mn, Ni, V, Sn–Dibenzodioxins/-furans–in ng/Nm3, dry, 11 % O2(Toxic equivalent (TE) in accordance with 050.050.50.10.1known as filsorption – a name taken fromfiltration and adsorption – takes place. Thefilsorption filter uses a mixture of activatedcoke and lime hydrate, and is largelyresponsible for the exceptionally goodclean-gas data. It is especially good atadsorbing dioxins and furans as well as anyresidual mercury left after scrubbing, while italso removes any harmful acids, dust andheavy metals still present. As a result, cleangas values even lower than the detectionlimits are achieved.30ABBReview1/1996
WATE The sorbent material used in the filsorp-Further developmentferred alternative to coke bed filters. Withtion process is led directly back to theof the dual-alkali processreactors containing several hundred cubicfurnace in order to destroy the dioxinsABB has developed a particularly interestingmeters of activated coke, the latter repre-and furans contained in it. Alternatively,variation of the TCR process for washingsent a genuine fire hazard. Both processesthe material can be vitrified together without the harmful acidic gases. It combinesemploy the highly efficient technologythe dust collected in the first filter.the ABB spray scrubber 2 with the dual-Filsorption is offered by ABB as its pre-known generically as adsorption.SINCINERATIONThe TCR concept is so new that all thealkali process developed by ABB especiallyA direct comparison shows the filsorp-modules making up the facility could not yetfor waste incineration plants.tion process to be better not only in terms ofbe installed and used together in the sameThe state of the art is to separate thesafety but also with regard to dust, heavyincineration plant. However, each individualacidic gases hydrogen chloride (HCl) andmetal and carbon monoxide emissions.module has been tested in the field on asulfur dioxide (SO2) in consecutive scrub-With regard to all the other components, thelarge scale. The flue-gas cleaning system,bing stages. Prior to the absorption (ie, dur-two processes perform at similar levels.for example, is operating in several plants,ing quenching) the flue gas is cooled to itsand reliable emission data with this systemwet-bulb temperature by co-current spray-is now readily available.ing of a liquid into the flue-gas flow. In theThe denox stage, which employs selective catalytic reduction (SCR), is usuallypositioned by ABB at the end of the fluegas cleaning process. The filsorption filterupstream provides optimum protection forthe catalyst. Since the denox process cantake place at a temperature of 200 C or2ABB spray scrubber used in combination with the dual-alkali processfor washing out harmful acidic gases1Quenching stage2HCl stage3SO2 stagelower, long residence times are possible.Reasons can also be given, however, forinstalling the catalyst immediately after thescrubbers. In this case, a combined catalystis used. It first reduces the nitrogen oxides(NOx) and then oxidizes the organic substances, in particular the dioxins and furans.3The operating temperature with this configuration is about 300 C. Its advantage isthat the dust collected in the filter is practically free of dioxins.The residues produced by flue-gas cleaning are treated in different process stages: The fly ash from the incinerator and thedust collected in the first bag filter are2passed through the DEGLOR process[1], in which an electrically heated fur-1nace melts them into a harmless glassyslag suitable for use in, eg, sand-blastingor road construction, plus a ‘heavy metalconcentrate’ which can be processed inspecialized metallurgical plants. The draw-off from the scrubbing processcan be treated in different stages (distillation, evaporation, crystallization, filtration, etc) to recover valuable resources.Some possible products are hydrochloricacid,sodiumchlorideforchlorine-alkali electrolysis, and gypsum (eg, foruse in manufacturing wall-board).ABBReview1/199631
asinletLimemixingtankSpray scrubberSO2 stageGypsumsedimentation tankGypsumdewatering stageSodamixingtankLimestonesedimentation tankGypsum3Flow chart of the dual-alkali system developed by ABB. Gypsum is precipitated by this patented process.first scrubber the HCl in the flue gas isuses limestone rather than a caustic sodaImportant benefits in respect of the SO2absorbed by an acidic solution comprisingsolution. Another reason for this preferenceseparation are:HCl and water. At the top of the HCl stageis that many operators prefer gypsum very fine droplets of the scrubbing agent are(CaSO42 H2O) to sodium sulfate as antance to mass transfer during the ab-sprayed into the gas flow in the counter-cur-end-product, since the former has moresorption process and oxidation to sulfaterent direction. The diluted hydrochloric acidcommercial uses.is very low.that is produced collects at the bottom of Althoughtheaboveconsiderations Since a clear solution is used, the resis-The ratio of the liquid to flue gas in thethe tank and is pumped back to the nozzleweigh heavily, scrubbers using a causticlevel in the circuit. The scrubbing liquid issoda solution have several clear technologi-drawn off and replaced by fresh watercal advantages over those which use lime-according to the acid concentration. Thestone, particularly in the areas of operationTo be able to take advantage of the bene-drawn-off liquid can be processed to obtainand reliability. These benefits can be sum-fits of a scrubber that uses a causticmarized as follows:soda solution and produce gypsum at All feed material and reaction productsthe same time, ABB has further develo-dioxide is absorbed by mixing caustic sodaare in the form of aqueous solutions; noped the so-called dilute mode dual-or lime hydrate (calcium hydroxide) with thesolids are involved.alkali process, modifying it for flue-gasNo protection against erosion has to becleaning in waste incineration plants. Inprovided.this processSince there are no sediments, the liquidented, the solution drawn off from thedoes not have to be circulated to preventneutral SO2 stage of the scrubber hasconcentrated hydrochloric acid, etc.In the second scrubbing stage the sulfurscrubbing agent to keep it neutral. Use of crushed limestone (CaCO3) as a neutralizing agent is also possible. Continuous measurement of the pH value is necessaryin this stage.sedimentation.The type of neutralizing agent chosen will generally depend on the overall costs. Calcium hydroxide and limestone being much terchange,gypsum is precipitated and the causticsoda solution is regenerated:space as well as costs.1/1996hydrateThrough3 , which has been pat-The alkaline stage can be installed simplyplant operators often prefer a scrubber thatReviewresidence time is short.demister is required.on top of the acid stage, saving floorABBThere is only a small pressure drop; thelimemaintenancecheaper than caustic soda, incineration32scrubber is small. Na2SO4 Ca(OH)2 –– CaSO4 2NaOH
WASTEINCINERATIONAlthough it is usual for the lime hydrate totation of the sulfate). One of the main goalsplant. In addition, the theoretical risk of thebe added in the dry state, lime milk or evenof the development work was to ensure thatgypsum quality varying was far greater, dueslaked quicklime can also be used.the process has only a minimal effect on themainly to the operating conditions in aIn a second stage, a very small quantityavailability and operation of the scrubber.waste incineration plant fluctuating moreof soda (Na2CO3) is added to the solutionThis is often the key to reliable operation ofstrongly than in a power station, where theregenerated with lime hydrate in order tothe incineration plant. The separate processquality of the coal remains relatively con-replace the Na ions lost during the pro-stages also provide numerous possibilitiesstant. The recovery of products from wastecess. The use of soda, which is relativelyfor optimizing plant operation, for exampleincineration is also a political issue, sincecheap, also has the effect of softening thethrough the installation of intermediate stor-they are automatically considered to beregenerated solution according toage tanks or the use of parallel or common‘dirtier’ than the same material originatingsystems for more than one incineration line.from other sources. The goal was toThe scrubber may also be operated withachieve a gypsum quality that would allowjust fresh caustic soda solution if required.disposal in Class I landfills as per theNa2CO3 Ca2 –– CaCO3 2Na before it passes back to the scrubber, thusAn installation of the type described hasGerman ‘TA Siedlungsabfall’ decree. Thisreducing the risk of sedimentation in thebeen built in the Hobro waste incinerationreduces the cost of landfilling substantially,scrubber cycle.plant in Denmark, allowing full-scale fieldcompared with the alternative of gypsumexperience to be gained for the first timedisposal in Class II landfills, as is usuallywith this technology.necessary when the calcium salts comeThe calcium carbonate which is produced is precipitated, separated from theclear regenerated solution and re-used inInitially, the quality of the gypsum pro-from a treatment plant in which the waste-duced in the Hobro plant was evaluatedwater is still contaminated with heavyThe regeneration process for recoveringunder the assumption that it would probablymetals.the caustic soda solution takes place in abe disposed of in landfills. This assumptionThe results from the Hobro demonstra-separate plant and therefore has no in-was made on the basis of the quantity pro-tion plant were promising from the begin-fluence on the availability of the scrubberduced in a waste incineration plant usuallyning, and gypsum suitable for Class I landfil-and the chemical reactions. Oxidation of thebeing much smaller than the amount pro-ling could be produced immediately andremaining sulfite to sulfate takes place in aduced, for example, in a coal-fired powerwithout problems. The requirements forthe effluent treatment plant.separate oxidation tank located in the outletof the scrubber’s SO2 stage. Completeoxidation is easily achieved since both thesulfite and the sulfate are present in thedissolved state.4Separation of sulfur dioxide with the ABB spray scrubber(N.tr. standard condition, dry gas)Green SO2, inletRedSO2, outletBlue SO2, theoretical equilibrium2Na2SO3 O2 –– 2Na2SO4mg/m3, N.tr.Control of this process is also easy. The6001500dose rate for the regenerated NaOH sol-500ppm,tr.ution passed back to the scrubber is controlled via the pH value in the scrubber cir-400cuit, while the amount to be drawn off is1000regulated according to the level of the liquid300in the system. Control of the lime feed rateis also relatively simple, regulation takingSO2200place in direct proportion to the amount ofSO2 separated. This is possible due to thestoichiometric ratio being close to unity.500100In terms of operating reliability, the combination of NaOH scrubber and dualalkali system offers good flexibility due toseparate stages being used for scrubbing,06.16.36.56.7pHoxidation and NaOH recovery (with precipi-ABBReview1/199633
WASTEINCINERATIONAdditional optimization of the scrubberwas not necessary. The principal lessonHobro has taught is therefore that scrubberoperation is not affected at all by the operation of the dual-alkali system. From this itcan be concluded that all sodium-basedABB scrubbers can be retrofitted with adual-alkali system. As a rule, other, nonABB scrubbers using a caustic soda solution can also be brought up to the standard required for retrofitting with an ABBdual-alkali system.The demister flushing system in theHobro plant was shut down completely forseveral weeks, during which time no traceof sedimentation could be detected. Likewise, there were no signs of incrustation inthe scrubber. This shows how effective thesoda is at softening the regenerated causticsoda solution.Dual-alkali systemThe experience gained in the Hobro incineration plant mainly concerns the dual-alkali system, in which the entire liquid flow fromthe scrubber is treated. The tests haveshown that the scrubber and regenerationsystem can handle all the operating conditions that could arise in practice. Full-scaleoperation was especially important for theway it helped with the design and fine-tuning of the control system.Operation on this scale is also necessaryFilsorption stage with scrubber using a sodium hydroxide solution,as retrofitted recently in the waste incineration plant at Zirndorf in Germany5to obtain reliable mass balances for thecombinedscrubberandregenerationsystem. Tests were carried out both with dryconstruction-quality gypsum could also beOperating experience infulfilled from the start. At about the samethe Hobro waste incineration plantslaked lime and lime milk.Full-scale trials are also important as theyprovide experience with operation of the in-time, several countries began to requirewaste incineration plants to produce recy-Scrubberdividual components. The only componentclable end-products only. In view of this,The scrubber, which uses a caustic sodathat has had to be replaced during the pro-special emphasis was placed on demon-solution, is a proven ABB design with moregramme is the gypsum dewatering system.strating the Hobro plant’s capability for pro-than 65 modules; 15 of these are part of theBecause the gypsum crystals obtained withducing construction-quality gypsum (eg, forwaste incineration flue-gas cleaning pro-the new system are considerably larger thanwall-board).cess. Since the scrubber was optimized forthose obtained with similar systems andTables 2 and 3 compare the achievedthis application from the start, emissionwith the pilot installation in the ABB re-gypsum quality with the requirements forvalues are very low 4
HCl and water. At the top of the HCl stage very fine droplets of the scrubbing agent are sprayed into the gas flow in the counter-cur-rent direction. The diluted hydrochloric acid that is produced collects at the bottom of the tank and is pumped back to the nozzle level in the circuit. The scrubbing liquid is drawn off and replaced by fresh water
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The Club HE 18 can be installed to a number of different concentric flue systems. The different flue applications as shown in Figure 2 are available as kits usually comprising the connecting 2.5 CONCENTRIC AIR / FLUE DUCT SPECIFICATIONS 82 FLUE OPTIONS Vertical flue kit - Part no. 956081 with flat roof flashing plate Vertical flue kit - Part no .
IEA Clean Coal Centre – Microalgae removal of CO 2 from flue gas 10 1 Introduction Burning fossil fuels to generate electricity produces flue gas. Flue gas emitted from coal combustion mostly contains carbon dioxide (CO 2), nitroge
These systems can be adjusted using the flue gas analyzer and checked for compliance with the applicable limit values. The following tasks can also be carried out with the flue gas analyzer: Regulating the O2, CO and CO2 values in combustion plants for the purpose of ensuring optimal operation. Draught measurement.
Figure 3. Typical tail gas incinerator burner Corrosion Due to the presence of SOx in the flue gas, care must be taken to prevent the steel shell of the oxidizer from getting below the dew point of the acid gas. Sulfuric acid can condense at very high temperature in flue gas. The acid gas dew point in the flue gas from a sulfur
Standard horizontal flue kit at 100 mm outside diameter for flues up to 4 m in length. Flue duct kits for horizontal (125 mm outside diameter) for flue lengths up to 13 m and vertical flue systems for flue lengths up to 13.7 m. Fitting instruc-ti
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