Slagging propensities of blended coals

This paper presents the experimental results on the slagging propensity of three pairs of blended coals tested in the Australian Coal Industry Research Laboratory furnace. The results showed that none of the coals or blends produced strongly molten deposit. At worst, the deposits contained some moderately sintered material. Most of the blends have (slightly) worse slagging behavior than the component coals. In order to rank the slagging propensity numerically, we defined the minimum heat flux ratio and total heat flux ratio based on the heat flux profiles. They are better in ranking the slagging propensities than other measures such as the build-up rate and visual physical characteristics. The Fe2O3/CaO molar ratio correlates the slagging propensity for five coals and six blends of this study. The worst slagging occurs when the ratio approaches 1.0. This ratio provides explanation of why the blends had worse slagging than the component coals for the pairs of blends: A-B and C-D. However, we note that there are causes of slagging other than the Fe2O3/CaO molar ratio. (C) 2001 Elsevier Science Ltd. All rights reserved.

A comparison of thermal condition between pilot- and full-scale furnaces for studying slagging and fouling propensity in PF boilers

The Australian Coal Industry Research Laboratory (ACIRL) furnace is scaled to simulate slagging and fouling in operating boilers. This requires that the gas and target temperatures, the heat flux, and the flow pattern be the same as those in real boilers. The gas and target temperatures are maintained by insulating the wall and cooling the target respectively. The flow pattern of a small burner cannot be the same as a large furnace. However, this flow pattern is partially compensated for by placing the slagging panels in three vertical locations. The paper develops the models of radiant heat transfer from the flame to the deposits both in pilot-scale and full-scale furnaces. They are used to compare the effective radiant heat transfer of the pilot- and full-scale furnaces. The experimental data both from the pilot- and full-scale furnaces are used to verify the incident heat flux and temperature profiles in the pilot- and full-scale furnaces. The results showed that the thermal condition in the pilot-scale furnace meets the requirements for studying the slagging regarding the gas temperature and the incident heat flux, particularly for the panel #1. The gas temperature in the convective section also meets the requirement for studying the fouling.

Biomass Utilization in PFC Co-firing System with the Slagging and Fouling Analysis

Master’s thesis Biomass Utilization in PFC Co-firing System with the Slagging and Fouling Analysis is the study of the modern technologies of different coal-firing systems: PFC system, FB system and GF system. The biomass co-fired with coal is represented by the research of the company Alstom Power Plant. Based on the back ground of the air pollution, greenhouse effect problems and the national fuel security today, the bioenergy utilization is more and more popular. However, the biomass is promoted to burn to decrease the emission amount of carbon dioxide and other air pollutions, new problems form like slagging and fouling, hot corrosion in the firing systems. Thesis represent the brief overview of different coal-firing systems utilized in the world, and focus on the biomass-coal co-firing in the PFC system. The biomass supply and how the PFC system is running are represented in the thesis. Additionally, the new problems of hot corrosion, slagging and fouling are mentioned. The slagging and fouling problem is simulated by using the software HSC Chemistry 6.1, and the emissions comparison between coal-firing and co-firing are simulated as well.

Estudo da formação de depósitos e aglomeração de cinzas durante a combustão de biomassa em leito fluidizado e co-combustão com carvão para minimizar a sua ocorrência

Dissertação para obtenção do Grau de Doutor em Energia e Bioenergia

Combustion of alternative biomass fuels in a domestic boiler and in a large-scale furnace

Programa Doutoral em Engenharia Mecânica.

Biopolttoaineseoksen poltosta aiheutuvien ongelmien arviointityökalu.

Biopolttoaineiden erityispiirteitä ovat alhainen lämpöarvo, korkea kosteuspitoisuus ja suuri haihtuvien aineiden määrä. Lisäksi biopolttoaineiden tuhkat sisältävät runsaasti alkaleja. Näistä ominaisuuksista seuraa ongelmia, jotka on otettava huomioon biopolttoainetta polttavan voimalaitoksen suunnittelussa ja käytössä. Diplomityössä selvitetään biopolttoaineiden poltosta aiheutuvat ongelmat ja niiden syyt sekä kehitetään työkalu, jonka avulla voidaan arvioida biopolttoaineseoksen polton ongelmien syntymistä. Arviointi tapahtuu biopolttoaineseoksen ominaisuuksien perusteella. Kattilassa vallitsevien, polton aikaisten olosuhteiden vaikutusta syntyviin ongelmiin ei tässä työssä tarkastella. Kun lähtötiedoista lasketut, ongelmien synnyn kannalta olennaiset polttoaineseoksen ja sen tuhkan ominaisuudet tunnetaan, verrataan niitä työssä koottuihin raja-arvoihin. Jos laskettu arvo on suurempi kuin rajaksi asetettu arvo, on todennäköistä, että kattilassa esiintyy ongelmia. Suurimmat ongelmat biopolttoaineiden leijupoltossa ovat likakerrostumien muodostuminen lämpöpinnoille, leijukerroksen sintraantuminen ja agglomeroituminen sekä lämpöpintojen korkealämpötilakorroosio. Raja-arvoina käytetään sekä tutkimustuloksina saatuja että käytännön kokemuksiin perustuvia arvoja. Raja-arvoja määritettäessä on huomioitu niiden soveltuvuus tarkastelun kohteena olevalle voimalaitokselle, jonka tyyppi ja kokoluokka vaikuttavat käytettäviin raja-arvoihin. Työkalu tukee keskikokoisen biovoimalaitoksen, jossa palaminen tapahtuu kerrosleijukattilassa, tuotteistusprosessia. Työkalua käytetään voimalaitoksen tuotteistuksessa optimaalisen polttoaineseoksen etsimiseen, riskienhallintaan sekä konseptikehitykseen. Lisäksi työkalua tullaan käyttämään valmiin tuotteen myyntiin ja markkinointiin.

Sähkön ja lämmön yhteistuotanto haasteellisilla polttoaineilla

Maailman energian kulutuksen lisääntymisen ja ilmastonmuutoksen myötä energiantuotannossa joudutaan jatkuvasti sopeutumaan muuttuviin tilanteisiin ja haasteisiin. Polttoteknillisiä haasteita aiheuttavat pelto- ja kierrätyspolttoaineet ovat lisäämässä osuuttaan uusiutuvien polttoaineiden joukossa. Jotta kyseisiä haasteellisia polttoaineita pystytään hyödyntämään, täytyy niiden aiheuttamat ongelmat tuntea ja laitevalmistajien kehittää niiden hyödyntämiseen sopivaa tekniikkaa. Tässä diplomityössä käydään läpi tulevaisuudessa käytettävät polttoaineet, nykyiset päästörajat, kiinteiden polttoaineiden poltto- ja kaasutustekniikat sekä likaantumis-, kuonaantumis- ja korroosiomekanismit voimalaitoskattiloissa. Työssä tutkitaan, onko haasteellisten polttoaineiden käyttöön investoiminen järkevää ja mikä nykypäivän tekniikoista on kannattavin. Myös välitulistuksen, lauhdeperän ja apujäähdyttimen kannattavuuksia vertaillaan sähkön ja lämmön yhteistuotannossa. Tuloksiksi saatiin, että edullisten peltobiomassojen ja kierrätyspolttoaineiden käyttäminen, joko perinteisten polttoaineiden seassa tai pääpolttoaineena, on nykyhinnoilla perinteisiin polttoaineisiin verrattuna kannattavaa. Investoiminen kierrätyspolttoaineiden valmistuslaitteisiin maksimoi kierrätyspolttoaineista saatavaa hyötyä. Välitulistuksen todettiin soveltuvan huonosti vastapaineprosessiin, sillä siitä saatava sähköntuotannon lisäys on hyvin pieni. Lauhdeperän ja apujäähdyttimen vertailuissa huomattiin, että lauhdeperä on kannattava investointi, jos sähkön ja lämmön hintaero pysyy tarpeeksi suurena. Haasteellisilla polttoaineilla pystytään pienentämään kasvihuonepäästöjä ja korvaamaan fossiilisten polttoaineiden käyttöä.

Simulation and optimization of IGCC technique for power generation and hydrogen production by using lignite Thar coal and cotton stalk

The purpose of this study was to simulate and to optimize integrated gasification for combine cycle (IGCC) for power generation and hydrogen (H2) production by using low grade Thar lignite coal and cotton stalk. Lignite coal is abundant of moisture and ash content, the idea of addition of cotton stalk is to increase the mass of combustible material per mass of feed use for the process, to reduce the consumption of coal and to increase the cotton stalk efficiently for IGCC process. Aspen plus software is used to simulate the process with different mass ratios of coal to cotton stalk and for optimization: process efficiencies, net power generation and H2 production etc. are considered while environmental hazard emissions are optimized to acceptance level. With the addition of cotton stalk in feed, process efficiencies started to decline along with the net power production. But for H2 production, it gave positive result at start but after 40% cotton stalk addition, H2 production also started to decline. It also affects negatively on environmental hazard emissions and mass of emissions/ net power production increases linearly with the addition of cotton stalk in feed mixture. In summation with the addition of cotton stalk, overall affects seemed to negative. But the effect is more negative after 40% cotton stalk addition so it is concluded that to get maximum process efficiencies and high production less amount of cotton stalk addition in feed is preferable and the maximum level of addition is estimated to 40%. Gasification temperature should keep lower around 1140 °C and prefer technique for studied feed in IGCC is fluidized bed (ash in dry form) rather than ash slagging gasifier

Modeling of fireside deposit formation in two industrial furnaces

Fireside deposits can be found in many types of utility and industrial furnaces. The deposits in furnaces are problematic because they can reduce heat transfer, block gas paths and cause corrosion. To tackle these problems, it is vital to estimate the influence of deposits on heat transfer, to minimize deposit formation and to optimize deposit removal. It is beneficial to have a good understanding of the mechanisms of fireside deposit formation. Numerical modeling is a powerful tool for investigating the heat transfer in furnaces, and it can provide valuable information for understanding the mechanisms of deposit formation. In addition, a sub-model of deposit formation is generally an essential part of a comprehensive furnace model. This work investigates two specific processes of fireside deposit formation in two industrial furnaces. The first process is the slagging wall found in furnaces with molten deposits running on the wall. A slagging wall model is developed to take into account the two-layer structure of the deposits. With the slagging wall model, the thickness and the surface temperature of the molten deposit layer can be calculated. The slagging wall model is used to predict the surface temperature and the heat transfer to a specific section of a super-heater tube panel with the boundary condition obtained from a Kraft recovery furnace model. The slagging wall model is also incorporated into the computational fluid dynamics (CFD)-based Kraft recovery furnace model and applied on the lower furnace walls. The implementation of the slagging wall model includes a grid simplification scheme. The wall surface temperature calculated with the slagging wall model is used as the heat transfer boundary condition. Simulation of a Kraft recovery furnace is performed, and it is compared with two other cases and measurements. In the two other cases, a uniform wall surface temperature and a wall surface temperature calculated with a char bed burning model are used as the heat transfer boundary conditions. In this particular furnace, the wall surface temperatures from the three cases are similar and are in the correct range of the measurements. Nevertheless, the wall surface temperature profiles with the slagging wall model and the char bed burning model are different because the deposits are represented differently in the two models. In addition, the slagging wall model is proven to be computationally efficient. The second process is deposit formation due to thermophoresis of fine particles to the heat transfer surface. This process is considered in the simulation of a heat recovery boiler of the flash smelting process. In order to determine if the small dust particles stay on the wall, a criterion based on the analysis of forces acting on the particle is applied. Time-dependent simulation of deposit formation in the heat recovery boiler is carried out and the influence of deposits on heat transfer is investigated. The locations prone to deposit formation are also identified in the heat recovery boiler. Modeling of the two processes in the two industrial furnaces enhances the overall understanding of the processes. The sub-models developed in this work can be applied in other similar deposit formation processes with carefully-defined boundary conditions.

Leijukerroslämmönsiirtimien tukkeutuminen biovoimalaitoksessa

Leijukerroslämmönsiirtimien, eli hiekanpalautuspolvessa sijaitsevien tulistimien tukkeutuminen on ollut Kaukaan Voima Oy:n biovoimalaitoksen suunnittelemattomien seisokkien suurin syy vuodesta 2012 lähtien. Tulistimet tukkeutuvat kahdella tavalla. Nopeassa tukkeutumisessa tulistinkammion seinien kuonakerrostumat romahtavat yhtäkkiä tulistimen päälle tukkien sen. Tämä johtaa aina koko laitoksen alasajoon. Hitaassa tukkeutumisessa tulistinputkien pinnalle muodostuu vähitellen kerrostuma sekä tulistinputkien väliin jää suurempia kappaleita, jotka tukkivat tulistinta. Nopea tukkeutuminen johtuu tuhkassa olevien alkali-, eli kalium- ja natriumyhdisteiden synnyttämistä kerrostumista lämmönsiirrinkammion seinille. Hidas tukkeutuminen johtuu osittain myös alkaliyhdisteistä, mutta merkittävämpi aine tulistinputkien pinnalla olevassa kerrostumissa näyttää olevan kalsiumsulfaatti, joka tukkii tulistinta. Palavan aineen pääsy tulistinkammioon ilmanjakoasetuksista ja tulistinkammion rakenteesta johtuen aiheuttaa kerrostumien syntymisen. Kerrostumien syntymiseen johtavat syyt johtuvat monesta tekijästä ja yksiselitteistä aiheuttajaa on vaikea määritellä. Selvin yhteys on lietteen epätasaisessa poltossa ja turpeen käytössä. Nykyisillä lietteenkäsittelylaitteilla lietteen tasainen syöttö on vaikeaa ja se aiheuttaa ongelmia. Turpeen poltto biopolttoaineiden rinnalla pitää tulistimet puhtaampina. Muita todennäköisiä kerrostumia lisääviä syitä ovat puhtaan hiekan vähäinen syöttömäärä ja usean huonomman polttoaineen yhtäaikainen poltto.

Effects of plant diversity on bioenergy parameters in grassland biomass

Extensive grassland biomass for bioenergy production has long been subject of scientific research. The possibility of combining nature conservation goals with a profitable management while reducing competition with food production has created a strong interest in this topic. However, the botanical composition will play a key role for solid fuel quality of grassland biomass and will have effects on the combustion process by potentially causing corrosion, emission and slagging. On the other hand, botanical composition will affect anaerobic digestibility and thereby the biogas potential. In this thesis aboveground biomass from the Jena-Experiment plots was harvested in 2008 and 2009 and analysed for the most relevant chemical constituents effecting fuel quality and anaerobic digestibility. Regarding combustion, the following parameters were of main focus: higher heating value (HHV), gross energy yield (GE), ash content, ash softening temperature (AST), K, Ca, Mg, N, Cl and S content. For biogas production the following parameters were investigated: substrate specific methane yield (CH4 sub), area specific methane yield (CH4 area), crude fibre (CF), crude protein (CP), crude lipid (CL) and nitrogen-free extract (NfE). Furthermore, an improvement of the fuel quality was investigated through applying the Integrated generation of solid Fuel and Biogas from Biomass (IFBB) procedure. Through the specific setup of the Jena-Experiment it was possible to outline the changes of these parameters along two diversity gradients: (i) species richness (SR; 1 to 60 species) and (ii) functional group (grasses, legumes, small herbs and tall herbs) presence. This was a novel approach on investigating the bioenergy characteristic of extensive grassland biomass and gave detailed insight in the sward-composition¬ - bioenergy relations such as: (i) the most relevant SR effect was the increase of energy yield for both combustion (annual GE increased by 26% from SR8→16 and by 65% from SR8→60) and anaerobic digestion (annual CH4 area increased by 22% from SR8→16 and by 49% from SR8→60) through a strong interaction of SR with biomass yield; (ii) legumes play a key role for the utilization of grassland biomass for energy production as they increase the energy content of the substrate (HHV and CH4 sub) and the energy yield (GE and CH4 area); (iii) combustion is the conversion technique that will yield the highest energy output but requires an improvement of the solid fuel quality in order to reduce the risk of corrosion, emission and slagging related problems. This was achieved through applying the IFBB-procedure, with reductions in ash (by 23%), N (28%), K (85%), Cl (56%) and S (59%) and equal levels of concentrations along the SR gradient.

The prediction and representation of phase equilibria and physicochemical properties in complex slag systems

The development of new experimental techniques for the determination of phase equilibria in complex slag systems, chemical thermodynamic, and viscosity models is reported. The new experimental data, and new thermodynamic and viscosity models, have been combined in a custom-designed computer software package to produce limiting operability diagrams for slag systems. These diagrams are used to describe phase equilibria and physicochemical properties in complex slag systems. The approach is illustrated with calculations on the system FeO-Fe2O3-CaO-SiO-Al2O3 at metallic iron saturation, slags produced in coal slagging gasifiers, and in the reprocessing of nonferrous smelting slags. This article was presented at the Mills Symposium Molten Metals, Slags and Glasses-Characterisation of Properties and Phenomena held in London in August 2000.