Influence of mixed fuels combustion on boiler operation

The aim of this work is to study the effect of different fuel mixtures on the operation of circulating fluidized bed (CFB) boiler. The applicability of heat balance modeling software IPSEpro to simulate CFB boiler operation is also investigated. The work discusses various types of boilers and methods of boiler operation. The fuel properties and the possible fuel influence on the boiler efficiency are described. Various biofuel types that are possible to use in combination with other fuels are presented. Some examples of the fuel mixtures use are given. A CFB boiler model has been constructed using IPSEpro and applied to analyze boiler operation outside design conditions. In the simulations, the effect of different load levels and moisture contents for the fuel mixture has been studied.

A study of combustion phenomena in circulating fluidized beds by developing and applying experimental and modelling methods for laboratory-scale reactors

The results shown in this thesis are based on selected publications of the 2000s decade. The work was carried out in several national and EC funded public research projects and in close cooperation with industrial partners. The main objective of the thesis was to study and quantify the most important phenomena of circulating fluidized bed combustors by developing and applying proper experimental and modelling methods using laboratory scale equipments. An understanding of the phenomena plays an essential role in the development of combustion and emission performance, and the availability and controls of CFB boilers. Experimental procedures to study fuel combustion behaviour under CFB conditions are presented in the thesis. Steady state and dynamic measurements under well controlled conditions were carried out to produce the data needed for the development of high efficiency, utility scale CFB technology. The importance of combustion control and furnace dynamics is emphasized when CFB boilers are scaled up with a once through steam cycle. Qualitative information on fuel combustion characteristics was obtained directly by comparing flue gas oxygen responses during the impulse change experiments with fuel feed. A one-dimensional, time dependent model was developed to analyse the measurement data Emission formation was studied combined with fuel combustion behaviour. Correlations were developed for NO, N2O, CO and char loading, as a function of temperature and oxygen concentration in the bed area. An online method to characterize char loading under CFB conditions was developed and validated with the pilot scale CFB tests. Finally, a new method to control air and fuel feeds in CFB combustion was introduced. The method is based on models and an analysis of the fluctuation of the flue gas oxygen concentration. The effect of high oxygen concentrations on fuel combustion behaviour was also studied to evaluate the potential of CFB boilers to apply oxygenfiring technology to CCS. In future studies, it will be necessary to go through the whole scale up chain from laboratory phenomena devices through pilot scale test rigs to large scale, commercial boilers in order to validate the applicability and scalability of the, results. This thesis shows the chain between the laboratory scale phenomena test rig (bench scale) and the CFB process test rig (pilot). CFB technology has been scaled up successfully from an industrial scale to a utility scale during the last decade. The work shown in the thesis, for its part, has supported the development by producing new detailed information on combustion under CFB conditions.

Model development for circulating fluidized bed boiler operation

Comprehensive understanding of the heat transfer processes that take place during circulating fluidized bed (CFB) combustion is one of the most important issues in CFB technology development. This leads to possibility of predicting, evaluation and proper design of combustion and heat transfer mechanisms. The aim of this thesis is to develop a model for circulating fluidized bed boiler operation. Empirical correlations are used for determining heat transfer coefficients in each part of the furnace. The proposed model is used both in design and offdesign conditions. During off-design simulations fuel moisture content and boiler load effects on boiler operation have been investigated. In theoretical part of the thesis, fuel properties of most typical classes of biomass are widely reviewed. Various schemes of biomass utilization are presented and, especially, concerning circulating fluidized bed boilers. In addition, possible negative effects of biomass usage in boilers are briefly discussed.

Modelling of combustion and sorbent reactions in three-dimensional flow environment of a circulating fluidized bed furnace

This thesis presents a three-dimensional, semi-empirical, steady state model for simulating the combustion, gasification, and formation of emissions in circulating fluidized bed (CFB) processes. In a large-scale CFB furnace, the local feeding of fuel, air, and other input materials, as well as the limited mixing rate of different reactants produce inhomogeneous process conditions. To simulate the real conditions, the furnace should be modelled three-dimensionally or the three-dimensional effects should be taken into account. The only available methods for simulating the large CFB furnaces three-dimensionally are semi-empirical models, which apply a relatively coarse calculation mesh and a combination of fundamental conservation equations, theoretical models and empirical correlations. The number of such models is extremely small. The main objective of this work was to achieve a model which can be applied to calculating industrial scale CFB boilers and which can simulate all the essential sub-phenomena: fluid dynamics, reactions, the attrition of particles, and heat transfer. The core of the work was to develop the model frame and the required sub-models for determining the combustion and sorbent reactions. The objective was reached, and the developed model was successfully used for studying various industrial scale CFB boilers combusting different types of fuel. The model for sorbent reactions, which includes the main reactions for calcitic limestones, was applied for studying the new possible phenomena occurring in the oxygen-fired combustion. The presented combustion and sorbent models and principles can be utilized in other model approaches as well, including other empirical and semi-empirical model approaches, and CFD based simulations. The main achievement is the overall model frame which can be utilized for the further development and testing of new sub-models and theories, and for concentrating the knowledge gathered from the experimental work carried out at bench scale, pilot scale and industrial scale apparatus, and from the computational work performed by other modelling methods.

Kaukolämpöverkon paluuveden hyödyntäminen lämmityksessä

Tässä diplomityössä on määritetty paluuvesilämmityksen mahdollisuudet Savon Voima Oyj:n kaukolämpöpaikkakunnilla. Työssä tarkasteltiin paluuvesilämmityksen tuoman paremman kaukolämpöveden jäähtymän vaikutuksia kaukolämpöverkkoon ja energiantuotantoon sekä laskettiin esimerkkipaikkakunnilla kaukolämmön paluuveden lämpötilan alentumisen tuomat rahalliset hyödyt. Lisäksi tarkasteltiin paluuvesilämmityksen taloudellisuutta esimerkkipaikkakunnilla. Laskennassa saatiin paluuvesilämmityksen tuomaksi jäähtymähyödyksi pumppauskustannuksissa 0,7 – 0,8 €/MWh ja lämpöhäviöissä 1,5 – 2,9 €/MWh. Iisalmessa sähköntuotannon lisääntymisestä saadaan hyötyä 0,7 €/MWh. Suurin hyöty saadaan Pielaveden ja Suonenjoen biolämpökeskusten lämmöntalteenotolla varustetuista savukaasupesureista. Pielavedellä tämä hyöty on 6,4 €/MWh ja Suonenjoella 6,1 €/MWh. Paluuvesilämmityksen kannattavuus asuinkiinteistöissä vaatii lämmöntuotannon yhteydessä olevan savukaasupesurin tuoman rahallisen hyödyn. Esimerkiksi Iisalmessa asiakkaalle myönnettävissä oleva jäähtymähyvitys paluuvesilämmöstä ei riitä kattamaan paluuvesilämmityksen suurempia investointikuluja. Myös pesuripaikkakunnilla kannattavuus vaatii suuren vuosittaisen lämmönkäytön. Tavoiteltaessa 8 vuoden korollista takaisinmaksuaikaa vaatii kannattavuus kohteelta Pielavedellä 250 MWh:n ja Suonejoella 300 MWh:n vuosittaisen lämmönkäytön. Myös asiakkaan sijainnin sopivuus kaukolämpöverkossa paluuvesilämmitykseen täytyy tarkastella tapauskohtaisesti. Paluuvesilämmitys ei tule työn tulosten perusteella tulevaisuudessa yleisesti käyttöön, mutta yksittäisiä asiakkaita siihen voidaan liittää.

Combustion properties of biomass residues rich in phosphorus

Tillgången på traditionella biobränslen är begränsad och därför behöver man ta fram nya, tidigare outnyttjade biobränslen för att möta de uppställda CO2 emissionsmålen av EU och det ständigt ökande energibehovet. Under de senare åren har intresset riktats mot termisk energiutvinning ur olika restfraktioner och avfall. Vid produktion av fordonsbränsle ur biomassa är den fasta restprodukten ofta den största procesströmmen i produktionsanläggningen. En riktig hantering av restprodukterna skulle göra produktionen mera lönsam och mer ekologiskt hållbar. Ett alternativ är att genom förbränning producera elektricitet och/eller värme eftersom dessa restprodukter anses som CO2-neutrala. Målsättningen med den här avhandlingen var att studera förbränningsegenskaperna hos några fasta restprodukter som uppstår vid framställning av förnybara fordonsbränslen. De fyra undersökta materialen är rapskaka, palmkärnskaka, torkad drank och stabiliserat rötslam. I studien används ett stort urval av undersökningsmetoder, från laboratorieskala till fullskalig förbränning, för att identifiera de huvudsakliga utmaningarna förknippade med förbränning av restprodukterna i pannor med fluidiserad bäddteknik. Med hjälp av detaljerad bränslekarakterisering kunde restprodukterna konstateras vara en värdefull källa för värme- och elproduktion. Den kemiska sammansättningen av restprodukterna varierar stort jämfört med mera traditionellt använda biobränslen. En gemensam faktor för alla de studerade restprodukterna är en hög fosforhalt. På grund av de låga fosforkoncentrationerna i de traditionella biobränslena har grundämnet hittills inte ansetts spela någon större roll i askkemin. Experimenten visade nu att fosfor inte mera kan försummas då man studerar kemin i förbränningsprocesser, då allt flera fosforrika bränslen tränger in på energimarknaden.

Sellutehtaan vedenkäytön vähentäminen

Työn tarkoituksena oli etsiä mahdollisia kohteita sellutehtaan veden käytön vähen-tämiseksi. Analyysien avulla selvitettiin voidaanko havaittujen kohteiden tällä hetkellä menetettyjä vesivirtoja käyttää uudelleen. Lopuksi arvioitiin miten kierrä-tettävät vedet vaikuttaisivat raakaveden laatuun, mikäli ne yhdistettäisiin tämän joukkoon. Veden käytön vähentämiskohteita etsittiin tutkimalla tehtaan prosessi-kaavioita osastokohtaisesti sekä selvittämällä näin havaittuja kohteita osastoilla. Työn kokeellinen osa koostui vesianalyyseistä. Vesianalyyseissä määritettiin seu-raavat arvot sellutehtaalle tulevasta vedestä: sameus (FTU), kiintoaine, sähkönjoh-tavuus, pH, CODCr, BOD7ATU, kokonaisfosfori P, Mn, Cl, K, Ca, Mg ja AOX. Nämä tehtiin valituista kohteista havaituista tällä hetkellä tehtaalta pois johdetuista mutta mahdollisesti kierrätettävistä vesistä. Työn tuloksien perusteella havaittiin, että seuraavissa tarkasteluun valituissa koh-teissa vedet olivat hyvin puhtaita ja talteen otettavia kierrätykseen. Näitä olivat savukaasupesurin vedet, sekundäärilauhdesäiliön vedet sekä tiivistevedet. Haih-duttamon lämminvesisäiliön sekä kuivauskone 4 kiertovesitornin vedet olivat hieman likaantuneet mutta hyvin kierrätettävissä. Koivulinjan D0-vaiheen, havu-linjan D1-vaiheen sekä kuivauskone 4 lajittamon vesivirtoja ei likaantumisen vuoksi kannattanut kerätä hyötykäyttöön.

Current status of the waste-to-energy chain in the County of North Savo, Finland

The aim of this report is to describe the current status of the waste-to-energy chain in the province of Northern Savonia in Finland. This work is part of the Baltic Sea Region Programme project Remowe-Regional Mobilizing of Sustainable Waste-to-Energy Production (2009-2012). Partnering regions across Baltic Sea countries have parallelly investigated the current status, bottle-necks and needs for development in their regions. Information about the current status is crucial for the further work within the Remowe project, e.g. in investigating the possible future status in target regions. Ultimate result from the Northern Savonia point of view will be a regional model which utilizes all available information and facilitates decision-making concerning energy utilization of waste. The report contains information on among others: - waste management system (sources, amounts, infrastructure) - energy system (use, supply, infrastructure) - administrative structure and legislation - actors and stakeholders in the waste-to-energy field, including interest and development ideas The current status of the regions will be compared in a separate Remowe report, with the focus on finding best practices that could be transferred among the regions. In this report, the current status has been defined as 2006-2009. In 2009, the municipal waste amount per capita was 479 kg/inhabitant in Finland. Industrial waste amounted 3550 kg/inhabitant, respectively. The potential bioenergy from biodegradable waste amounts 1 MWh/inhabitant in Northern Savonia. This figure includes animal manure, crops that would be suitable for energy use, sludge from municipal sewage treatment plants and separately collected biowaste. A key strategy influencing also to Remowe work is the waste plan for Eastern Finland. Currently there operate two digestion plants in Northern Savonia: Lehtoniemi municipal sewage treatment sludge digestion plant of Kuopion Vesi and the farm-scale research biogas plant of Agrifood Research Finland in Maaninka. Moreover, landfill gas is collected to energy use from Heinälamminrinne waste management centre and Silmäsuo closed landfill site, both belonging to Jätekukko Oy. Currently there is no thermal utilization of waste in Northern Savonia region. However, Jätekukko Oy is pretreating mixed waste and delivering refuse derived fuel (RDF) to Southern Finland to combustion. There is a strong willingness among seven regional waste management companies in Eastern Finland to build a waste incineration plant to Riikinneva waste management centre near city of Varkaus. The plant would use circulating fluidized bed (CFB) boiler. This would been a clear boost in waste-to-energy utilization in Northern Savonia and in many surrounding regions.

Limestone Reactions in a Fluidized Bed Heat Exchanger of an Oxy-fuel Circulating Fluidized Bed Boiler

Oxy-fuel combustion in a circulating fluidized bed (CFB) boiler appears to be a promising option for capturing CO2 in power plants. Oxy-fuel combustion is based on burning of fuel in the mixture of oxygen and re-circulated flue gas instead of air. Limestone (CaCO3) is typically used for capturing of SO2 in CFB boilers where limestone calcines to calcium oxide (CaO). Because of high CO2 concentration in oxy-fuel combustion, calcination reaction may be hindered or carbonation, the reverse reaction of calcination, may occur. Carbonation of CaO particles can cause problems especially in the circulation loop of a CFB boiler where temperature level is lower than in the furnace. The aim of the thesis was to examine carbonation of CaO in a fluidized bed heat exchanger of a CFB boiler featuring oxy-fuel combustion. The calculations and analyzing were based on measurement data from an oxy-fuel pilot plant and on 0-dimensional (0D) gas balance of a fluidized bed heat exchanger. Additionally, the objective was to develop a 1-dimensional (1D) model of a fluidized bed heat exchanger by searching a suitable pre-exponential factor for a carbonation rate constant. On the basis of gas measurement data and the 0D gas balance, it was found that the amount of fluidization gas decreased as it flew through the fluidized bed heat exchanger. Most likely the reason for this was carbonation of CaO. It was discovered that temperature has a promoting effect on the reaction rate of carbonation. With the 1D model, a suitable pre-exponential factor for the equation of carbonation rate constant was found. However, during measurements there were several uncertainties, and in the calculations plenty of assumptions were made. Besides, the temperature level in the fluidized bed heat exchanger was relatively low during the measurements. Carbonation should be considered when fluidized bed heat exchangers and the capacity of related fans are designed for a CFB boiler with oxy-fuel combustion.

Waste-to-Energy Scenarios in the China Context

Waste incineration plants are increasingly established in China. A low heating value and high moisture content, due to a large proportion of biowaste in the municipal solid waste (MSW), can be regarded as typical characteristics of Chinese MSW. Two incineration technologies have been mainly established in China: stoker grate and circular fluidized bed (CFB). Both of them are designed to incinerate mixed MSW. However, there have been difficulties to reach the sufficient temperature in the combustion process due to the low heating value of the MSW. That is contributed to the usage of an auxiliary fossil fuel, which is often used during the whole incineration process. The objective of this study was to design alternative Waste-to-energy (WTE) scenarios for existing WTE plants with the aim to improve the material and energy efficiency as well as the feasibility of the plants. Moreover, the aim of this thesis was to find the key factors that affect to the feasibility of the scenarios. Five different WTE plants were selected as study targets. The necessary data for calculation was gained from literature as well as received from the operators of the target WTE plants. The created scenarios were based on mechanical-biological treatment (MBT) technologies, in which the produced solid recovered fuel (SRF) was fed as an auxiliary fuel into a WTE plant replacing the fossil fuel. The mechanically separated biowaste was treated either in an anaerobic digestion (AD) plant, a biodrying plant, a thermal drying plant, or a combined AD plant + thermal drying plant. An interactive excel spreadsheet based computation tool was designed to estimate the viability of the scenarios in different WTE cases. The key figures of the improved material and energy efficiency, such as additional electricity generated and avoided waste for landfill, were got as results. Furthermore, economic indicators such as annual profits (or costs), payback period, and internal rate of return (IRR) were gained as results. The results show that the AD scenario was the most profitable in most of the cases. The current heating value of MSW and the tipping fee for the received MSW appeared as the most important factor in terms of feasibility.

Fluid dynamic modelling and simulation of circulating fluidized bed reactors: importance of the interface turbulence transfer

The main objective of this work is to analyze the importance of the gas-solid interface transfer of the kinetic energy of the turbulent motion on the accuracy of prediction of the fluid dynamic of Circulating Fluidized Bed (CFB) reactors. CFB reactors are used in a variety of industrial applications related to combustion, incineration and catalytic cracking. In this work a two-dimensional fluid dynamic model for gas-particle flow has been used to compute the porosity, the pressure, and the velocity fields of both phases in 2-D axisymmetrical cylindrical co-ordinates. The fluid dynamic model is based on the two fluid model approach in which both phases are considered to be continuous and fully interpenetrating. CFB processes are essentially turbulent. The model of effective stress on each phase is that of a Newtonian fluid, where the effective gas viscosity was calculated from the standard k-epsilon turbulence model and the transport coefficients of the particulate phase were calculated from the kinetic theory of granular flow (KTGF). This work shows that the turbulence transfer between the phases is very important for a better representation of the fluid dynamics of CFB reactors, especially for systems with internal recirculation and high gradients of particle concentration. Two systems with different characteristics were analyzed. The results were compared with experimental data available in the literature. The results were obtained by using a computer code developed by the authors. The finite volume method with collocated grid, the hybrid interpolation scheme, the false time step strategy and SIMPLEC (Semi-Implicit Method for Pressure Linked Equations - Consistent) algorithm were used to obtain the numerical solution.

Particle model for simulating limestone reactions in novel fluidised bed energy applications

The development of carbon capture and storage (CCS) has raised interest towards novel fluidised bed (FB) energy applications. In these applications, limestone can be utilized for S02 and/or CO2 capture. The conditions in the new applications differ from the traditional atmospheric and pressurised circulating fluidised bed (CFB) combustion conditions in which the limestone is successfully used for SO2 capture. In this work, a detailed physical single particle model with a description of the mass and energy transfer inside the particle for limestone was developed. The novelty of this model was to take into account the simultaneous reactions, changing conditions, and the effect of advection. Especially, the capability to study the cyclic behaviour of limestone on both sides of the calcination-carbonation equilibrium curve is important in the novel conditions. The significances of including advection or assuming diffusion control were studied in calcination. Especially, the effect of advection in calcination reaction in the novel combustion atmosphere was shown. The model was tested against experimental data; sulphur capture was studied in a laboratory reactor in different fluidised bed conditions. Different Conversion levels and sulphation patterns were examined in different atmospheres for one limestone type. The Conversion curves were well predicted with the model, and the mechanisms leading to the Conversion patterns were explained with the model simulations. In this work, it was also evaluated whether the transient environment has an effect on the limestone behaviour compared to the averaged conditions and in which conditions the effect is the largest. The difference between the averaged and transient conditions was notable only in the conditions which were close to the calcination-carbonation equilibrium curve. The results of this study suggest that the development of a simplified particle model requires a proper understanding of physical and chemical processes taking place in the particle during the reactions. The results of the study will be required when analysing complex limestone reaction phenomena or when developing the description of limestone behaviour in comprehensive 3D process models. In order to transfer the experimental observations to furnace conditions, the relevant mechanisms that take place need to be understood before the important ones can be selected for 3D process model. This study revealed the sulphur capture behaviour under transient oxy-fuel conditions, which is important when the oxy-fuel CFB process and process model are developed.

Epífitos vasculares em fragmentos de Floresta Ombrófila Mista, Curitiba, Paraná, Brasil

Este estudo foi realizado em 14 áreas de floresta com Araucária, sob clima Cfb, com valores médios anuais de precipitação de 1.450 mm e de temperatura 16,7 ºC. Foram registradas 106 espécies epifíticas (10 exóticas) distribuídas em 21 famílias. Orchidaceae (35 espécies), Polypodiaceae (14 spp.) e Bromeliaceae (12 spp.) apresentaram maior riqueza específica. O número de espécies nativas por fragmento variou entre 10 e 64. A riqueza dos epífitos vasculares em Floresta Ombrófila Mista é menor que em Floresta Ombrófila Densa, e maior que em florestas estacionais brasileiras. As variações climáticas, o tipo de cobertura vegetacional, o grau e intensidade de perturbação nos fragmentos são determinantes na manutenção e incremento das comunidades epifíticas.

Promoting Cleantech in Emerging Markets: Business Model for Waste Pre-treatment Equipment in China

Waste incineration is becoming increasingly widespread method of waste disposal in China. Incineration plants mostly use grate and circular fluidized bed (CFB) technology. Waste combustion in cement production is also beginning to gradually increase. However, Chinese waste composition is causing problems for the energy utilization. Mechanical waste pre-treatment optimizes the combustion process and facilitates the energy recovery. The objective of this study is to identify how Western waste pre-treatment manufacturer could operate in Chinese markets. Chinese waste management industry is reviewed via PESTEL analysis. The current state and future predictions of grate and CFB incineration as well as cement manufacturing are monitored. Grate combustion, which requires lesser waste pre-treatment, is becoming more common at the expense of CFB incineration in China. The most promising future for waste treatment is in cement production industry. Waste treatment equipment manufacturer should try to create pilot projects with biggest cement producers with a view of growing co-operation in the future.

Reduction of nitrogen oxide emissions in lime kiln

Different nitrogen oxide removal technologies for rotary lime kiln are studied in this thesis, the main focus being in commercial technologies. Post-combustion methods are investigated in more detail as potential possible NOx removal with combustion methods in rotary lime kiln is more limited or primary methods are already in use. However, secondary methods as NOx scrubber, SNCR or SCR technologies are not listed as the Best Available Technologies defined by European Union. BAT technologies for NOx removal in lime kiln are (1) Optimised combustion and combustion control, (2) Good mixing of fuel and air, (3) Low-NOx burner and (4) Fuel selection/low-N fuel. SNCR method is the most suitable technique for NOx removal in lime kiln when NOx removal from 50 % to 70 % is required in case primary methods are already in use or cannot be applied. In higher removal cases ammonia slip is an issue in SNCR. By using SCR better NOx reduction can be achieved but issues with catalyst materials are expected to arise because of the dust and sulphur dioxide which leads to catalyst poison formation in lower flue gas temperatures. NOx scrubbing has potential when simultaneous NOx and SO2 removal is required. The challenge is that NO cannot be scrubbed directly, but once it is oxidized to NO2 or further scrubbing can be performed as the solubility of NO2 is higher. Commercial installations have not been made regarding SNCR, SCR or NOx scrubbing regarding rotary lime kiln. For SNCR and SCR the closest references come from cement industry.