This Master´s thesis deals with the verification calculation of boiler which burns brown coal for the application of the selective catalytic reduction method. The thesis is divided into several parts. In the first of all is performed the calculation of the furnace chamber which involves stoichiometrics calculations and enthalpy calculations of air and flue gas. In the second part the heat balance of the boiler, the boiler losses and the thermal efficiency are determined. After all the heating surfaces are calculed for the verify the dimensions. In the conclusion of the thesis we looked for the temperature range which is used for the SCR application. Then the improvements for the appropriate temperature range are designed.

My master´s thesis deals with the problems of NOx abatement that are included in flue gas. The accent is put on flue gases treatment throug cloth filter or ceramic candles, where the deposited catalyst enables NOx reduction throug the method of selective cytalytic reduction. In thesis is also describe experimental unit which current remove gaseous pollutants (dioxin, VOC and NOX) and ash on catalytic cloth filter or catalytic ceramic candles. For experimental unit has been calculated pressure drop. Pressure drop has been calculated for nominal and maximal conditions for cloth filter and ceramic candle. Last part of thesis deals with compile a experimental schemes for different concentration of NO, flow and temperature of combustion.

This thesis deals with the reduction of oxides of nitrogen (NOx) which are part of the exhaust gas combustion devices. The focus is on reduction of NOx by selective catalytic reduction (SCR) and catalyst filtration. The first part of this work deals with the formation of NOx, their hazards and related legislation. The following is an overview of the available technologies to reduce NOx in the flue gas and comparison of this methods. The following section describes the experimental catalytic filtration unit INTEQ II, where the first real experiment selective catalytic reduction of NOx with ammonia was realized. We have verified the operability of the experimental units and achieve up to 80% efficiency SCR. The final section describes the progress of the experiment and its results. It is recommended a few minor adjustments to improve stabile operation of unit INTEQ II.

V současnosti musí velké energetické podniky k dodržení emisních předpisů, zejména pak vyžadovaných limitů NOx, uplatňovat denitrifikační metody. Tématem předkládané diplomové práce jsou moderních denitrifikační metody a jejich praktické uplatnění v lokálních poměrech uhelného kotle s parním výkonem 640 t.h-1 v elektrárně Počerady. Práce obsahuje rešerši moderních denitrifikačních metod používaných velkými uhelnými kotli se zaměřením zejména na sekundární denitrifikační metody. Jsou uvažovány dvě možné varianty denitrifikace – varianta 1 využívá selektivní katalytickou redukci (SCR) a varianta 2 selektivní nekatalytickou redukci (SNCR) společně s nízkoemisními hořáky a stupňovaným přívodem spalovacího vzduchu. Pro výběr vhodné denitrifikační metody jsou studovány investiční náklady jednotlivých variant – nižší investiční náklady (o 19.4%) slibuje varianta 2. Při srovnávání SCR se SNCR vyšlo najevo, že investiční náklady metody SNCR jsou 5krát nižší než metody SCR. V souladu s investičními náklady, s dispozicí kotle a se složitostí jeho instalace je pro navazující studium problematiky využita varianta 2. Stěžejní část práce se zabývá stanovením optimálního tzv. teplotního okna pro konkrétní metodu SNCR. Těžištěm práce je tepelný výpočet ohniště a části deskového přehříváku pro stanovený rozsah paliv a výkon kotle v rozmezí 60-100%. S uvažováním výsledků z výpočtu jsou navrženy dvě vstřikovací roviny, které mají zaručit vysokou efektivitu denitrifikačního procesu při uvažovaných provozních podmínkách kotle. Diplomová práce rovněž diskutuje obecnou vhodnost instalace SNCR a SCR ve stávajících uhelných kotlích.

I och med nuvarande och kommande lagkrav för utsläpp från tunga lastbilar finns en efterfrågan på utvecklade strategier för utsläppsminskning. För att kontrollera utsläppen av kväveoxider (NOx) används katalytisk omvandling med AdBlue (vätskeblandning av urea och vatten).  AdBlue-dropparna förångas av avgaserna eller på en förångningsyta där en väggfilm kan skapas som i sin tur kan öka risken för utfällningar av urea. Därför finns ett behov av ett reglersystem för att minimera risken för utfällning,  Målet med detta examensarbete var att skapa en bättre förståelse för hur risken för utfällning av urea kan relateras till den nuvarande kalibreringen på Scania och föreslå hur det nuvarande reglersystemet kan förbättras. Tester uppdelat i två delar genomfördes i en provcell. Först testades ureadoseringen i pulser där doseringsmängden, förångningstiden och pulsfrekvensen varierades. Därefter testades varierat avgasflöde mellan två flöden genom att ändra ramptiden.  Genom visuella inspektioner visade det sig att pulserna med urea behöver längre förångningstid än vad den aktuella kalibreringen anger. Detta för att minska risken av utfällningar. Vid dosering av urea över den stationära förångningskapaciteten skapades väggfilmen längre bort från doseringsenheten. Detta leder till mindre effektiv användning av den doserade urean. För varierat avgasflöde med de valda ramptidena förändrades inte risken för utfällning. Därför skulle det nuvarande styrsystemet kunna förbättras genom att inkludera en längre tid för förångning mellan ureadoseringspulserna. / With current and upcoming emission legislation for heavy-duty transport, there is a demand for improved emission abatement strategies. To control nitrogen oxide (NOx) emissions, catalytic conversion with AdBlue (a liquid mixture of urea and water) is used. Droplets of AdBlue are evaporated by the exhaust gas or on an evaporation surface where a wall film can be created. A wall film increases the urea deposit risk which in turn causes problems. Consequently, there is a need for a control system to minimize the risk of urea deposits. The target of this thesis was to create a better understanding of how the urea deposit risk can be related to the current control calibration at Scania and to suggest how the current control system could be improved. Tests were performed in an engine testbed, in two parts. Firstly, varying of urea dosing was tested in pulses where the dosing amount, evaporation time and pulse frequency were varied. Secondly, the exhaust flow rate was varied between two flows by changing the ramp time. Through visual inspections, it was shown that the urea dosing pulses need longer evaporation time than the current control calibration states, to reduce the build-up of urea deposits. Furthermore, when dosing urea above the stationary evaporation capacity, the wall film was created further away from the dosing unit, thus, leading to less efficient use of the injected urea. For varying exhaust flow rate, the chosen ramp times did not change the urea deposit risk. Therefore, the current control system could be improved by including longer time for evaporation between the urea injection pulses.

No description available.

The reaction mechanism for the selective catalytic reduction (SCR) of nitric oxide by ammonia on (010) V2O5 surface represented by a V2O9H8 cluster was simulated by density functional theory (DFT) calculations. The computations indicated that SCR reaction consisted of three main parts. In the first part ammonia activation on Br&oslash / nsted acidic V-OH site as NH4+ species by a nonactivated process takes place. The second part includes the interaction of NO with pre-adsorbed NH4 + species to eventually form nitrosamide (NH2NO). The rate limiting step for this part as well as for the total SCR reaction is identified as NH3NHO formation reaction. The last part consists of the decomposition of NH2NO on the cluster which takes advantage of a hydrogen transfer mechanism between the active V=O and V-OH groups. Water and ammonia adsorption and dissociation are investigated on (101) and (001) anatase surfaces both represented by totally fixed and partially relaxed Ti2O9H10 clusters. Adsorption of H2O and NH3 by H-bonding on previously H2O and NH3 dissociated systems are also considered. By use of a (001) relaxed Ti2O9H10 cluster, the role of anatase support on SCR reaction is investigated. Since NH2NO formation on Ti2O9H10 cluster requires lower activation barriers than on V2O5 surface, it is proposed that the role of titanium dioxide on SCR reaction could be forming NH2NO. The role of vanadium oxide is crucial in terms of dissociating this product into H2O and N2. Finally, NH3 adsorption is studied on a V2TiO14H14 cluster which represents a model for vanadia/titania surface.

Le problème étudié dans cette thèse est la commande en boucle fermée d'un système SCR (Réduction Sélective Catalytique) par l'urée tel qu'utilisé dans les systèmes de dépollution des gaz d'échappement des moteurs diesel automobiles. Une première contribution du manuscrit est en un modèle détaillé de la SCR, soulignant de la nature distribuée (1D) du système considéré, et plusieurs réductions successives de ce modèle de simulation conduisant à un modèle plus simple, utilisable à des fins de synthèse de contrôleur. Une seconde contribution consiste à prendre en compte la sensibilité au NH3 du capteur de NOx utilisé pour la rétroaction lors du développement d'algorithmes de commande (observateur d'état, boucle de rétroaction, séquencement de gain, interprétation du signal capteur). L'observateur-contrôleur présenté possède plusieurs points d'équilibre dues à la sensibilité du capteur de sortie. On montre que seul le point d'intérêt pratique est asymptotiquement stable, les autres étant instables naturellement, rendus instables par une implémentation spécifique ou aisémentdétectés comme indésirables. Ces deux contributions ont été testées expérimentalement et validées. En résumé, la méthode de contrôle proposée dans cette thèse permet, à partir d'un moteur conforme aux exigences Euro 5 et avec une procédure de pré-conditionnement du catalyseur, de satisfaire la norme Euro 6. / The problem studied in this thesis is the closed-loop control of a urea-SCR (urea Selective Catalytic Reduction) as used in aftertreatment systems of diesel vehicles. A first contribution of the thesis is a detailed model for the SCR, highlighting the distributed (1D) nature of the considered system, and several successive reductions of this simulation model leading to a simpler one, better-suited for control design purposes. A second contribution consists in considering the sensitivity to NH3 of the NOx sensor used in a feedback loop, in the development of the control algorithms (state observer, feedback, gain scheduling, measurement interpretation). The ambiguity of the output measurement could be detrimental to the closed loop response, as it generates multiple equilibrium points (artefacts), besides the point of practical interest. A study of the closed-loop dynamics is performed in the vicinity of each point, which shows that the closed loop system naturally converges to the point of interest not to the artefacts. Both contributions have been tested and validated experimentally. In summary, the method proposed in this thesis might allow an engine equipped with Euro 5 hardware to satisfy Euro 6 standard using a preconditioning procedure of the catalyst.

This master‘s thesis deals with denitrification of brown coal-fired boiler of electric power plant. First chapters describe technical characteristics of the boiler and possible measurements which would lead to lowering NOx emissions. In order for boiler to meet emission standards valid from 1.1.2016 flue gas treatment by selective catalytic reduction is proposed. Main part of the thesis is thermal calculation of the boiler with modifications necessary in order to apply SCR. The aim of calculation is to determine flue gas exit temperature and temperature at catalyst area in order to assess the suitability of proposed modifications.

The effect of soot on the catalytic properties of a diesel particulate filter coated with a catalyst for the selective catalytic reduction of NOx with ammonia (SDPF) was studied by means of model-gas experiments. After loading of the SDPF with model soot from 0 to 10 g l-1, the NH3 storage as well as the catalytic DeNOx behavior of the standard SCR reaction was investigated. The model soot present in the filter was shown to have an NH3 storage capacity. The soot deposit inside the SDPF filter wall lead to a decreased NO conversion in SCR experiments of up to 20 %. The NH3 breakthrough was found to be shifted towards earlier time-on-stream during NH3 adsorption on soot loaded SDPF samples. Both effects could be attributed to a diffusive mass transport limitation of the gas species through the soot to reach at the chemically active sites inside SDPF filter wall. The self-diffusion coefficient of NH3 probe molecules within a soot layer could be measured using Pulsed Field Gradient-NMR technique. The unit collector model is capable of describing the backpressure upon soot loading with a depth filtered (inside filter wall) soot amount of 1 g l-1 and 0.36 g l-1, respectively, for both SDPF types under investigation. Based on Scanning Electron Microscopy (SEM) investigation a 1-D microscopic soot filter wall-model was set up. The model implies soot as diffusion barrier for mass transport. It was calibrated based on experimental observations and allows to conclude on the distribution of the soot within the filter wall. Thus, a high soot-coverage of the porous filter wall close to the inlet channel, a slightly covered middle part and a soot free zone close to the outlet explains the observed reduction in NO conversion as well as the NH3 breakthrough at earlier time-on-stream during NH3 adsorption experiments for SDPF samples loaded with soot. A modelled homogeneous soot distribution (0.6 µm soot layer on top of washcoat) within the whole SDPF was shown to result in NO conversion drop up to 45 %.