Advanced Optical Diagnostic Techniques for Detection of Alkali Vapors in High-Temperature Gases

Two advanced optical techniques for the detection of alkali vapors in high-temperature gases are introduced in this Thesis. Alkali vapors are released in solid fuel combustion and increase the maintenance costs of the power plant boilers. Especially, biomass and waste are challenging fuels for contemporary technology. Alkali related problems are controlled with proper fuel mixture ratios and additives that are mixed to fuels or sprayed into the boiler. However, the controlling increases the cost of the produced energy and the additives increase SO2 concentration. In order to study the alkali formation mechanisms and to control alkali concentrations in power plant boilers, fast, accurate and highly sensitive detection techniques are needed. This Thesis presents the fundamental absorption properties of the K, KCl and KOH vapors, reviews previously applied techniques for the detection of alkalis, and introduces two novel detection methods. The first method is based on the Photoacoustic Spectroscopy (PAS), that utilizes two branches of physics, namely optics and acoustics. A high-temperature PAS cell is introduced and applied to detect KCl and NaCl. Moreover, the possibility to apply the PAS cell to high-temperature salt-induced metal oxidation is discussed. The second method, which was fully developed during this work, is called Collinear Photofragmentation and Atomic Absorption Spectroscopy (CPFAAS). CPFAAS provides the limit of detection below parts per billion and the dynamic range of eight orders of magnitude in the detection of alkali chlorides. Moreover, the detection time of the CPFAAS measurement is in the order of micro second, which enables the diagnostics of the fast changing processes, such as combustion. The technique is calibration free and is integrable to "see-through" applications. In this Thesis, CPFAAS is applied to determine potassium vapor concentrations from a laboratory cell, flue gases emanated from 10 mg fuel samples, and flue gases in intermediate and large scale combustion boilers. The presented applications, modeling and comparison with previously applied detection methods show that CPFAAS enables new detection and monitoring capabilities from corrosive high temperature gases

Gas phase potassium release from a single particle of biomass during high temperature combustion

A notable characteristic of solid biomass fuels as compared to coal is their significantly higher potassium content. Potassium influences ash deposition and corrosion mechanisms in furnaces and boilers, the effects of which may differ depending on phase transformations of potassium species in the gas phase and condensed phase. An understanding of how potassium is released from biomass fuels during the combustion process is therefore useful for plant designers and operators assessing means of avoiding or mitigating these potential problems. An experimental method is used to measure release patterns from single particles of biomass fuels using flame emission spectroscopy and a single-particle combustion rig. The experimental arrangement also allowed simultaneous thermal imaging of the combusting particle in order to determine the surface temperature. A model of the single particle combustion is presented. Using experimental data on devolatilisation and burnout times for different sized particles and the measured surface temperature profiles, the thermal and kinetic sub-models are verified. A model for potassium release is described and this is integrated to the single particle combustion model to allow prediction of the temporal patterns of release of gas-phase potassium. The modelled release patterns were compared with those observed. Good agreement between modelled and measured potassium release patterns was attained confirming that the proposed mechanisms affecting potassium release are valid

Transversely Excited Multipass Photoacoustic Cell Using Electromechanical Film as Microphone

A novel multipass photoacoustic cell with five stacked electromechanical films as a microphone has been constructed, tested and characterized. The photoacoustic cell is an open rectangular structure with two steel plates facing each other. The longitudinal acoustic resonances are excited transversely in an optical multipass configuration. A detection limit of 22 ppb (10−9) was achieved for flowing NO2 in N2 at normal pressure by using the maximum of 70 laser beams between the resonator plates. The corresponding minimum detectable absorption and the normalized noise-equivalent absorption coefficients were 2.2 × 10−7 cm−1 and 3.2 × 10−9 cm−1WHz−1/2, respectively

Observations on the release of gas-phase potassium during the combustion of single particles of biomass

One of the more significant characteristics of solid biomass fuels as compared to coal is the quantity of potassium that they contain. Potassium content influences ash deposition and corrosion mechanisms in furnaces, the effects of which may differ depending on phase transformations of potassium species in the gas phase and condensed phase. The fate of potassium from the fuel during the combustion process is therefore an important concern. To investigate this, an experimental method is presented in which the release patterns from single particles of various biomass fuels are measured by use of flame emission spectroscopy implemented using a custom-built photo-detector device. Single particles of fuel are combusted in a methane flame with a gas temperature of ∼1800 K. The observed potassium release patterns for thirteen solid biomass materials are presented. The data are analyzed to examine the relationships between: the level of potassium in the fuel particle; the fraction of potassium released at each stage of combustion and the peak rate of release of potassium to gas-phase during combustion. Correlations between these quantities are identified with key trends, patterns and differences highlighted. The analyses provide useful information for the development and validation of modelling of potassium release during combustion of biomass

Advanced Optical Diagnostic Techniques for Detection of Alkali Vapors in High-Temperature Gases

Two advanced optical techniques for the detection of alkali vapors in high-temperature gases are introduced in this Thesis. Alkali vapors are released in solid fuel combustion and increase the maintenance costs of the power plant boilers. Especially, biomass and waste are challenging fuels for contemporary technology. Alkali related problems are controlled with proper fuel mixture ratios and additives that are mixed to fuels or sprayed into the boiler. However, the controlling increases the cost of the produced energy and the additives increase SO2 concentration. In order to study the alkali formation mechanisms and to control alkali concentrations in power plant boilers, fast, accurate and highly sensitive detection techniques are needed. This Thesis presents the fundamental absorption properties of the K, KCl and KOH vapors, reviews previously applied techniques for the detection of alkalis, and introduces two novel detection methods. The first method is based on the Photoacoustic Spectroscopy (PAS), that utilizes two branches of physics, namely optics and acoustics. A high-temperature PAS cell is introduced and applied to detect KCl and NaCl. Moreover, the possibility to apply the PAS cell to high-temperature salt-induced metal oxidation is discussed. The second method, which was fully developed during this work, is called Collinear Photofragmentation and Atomic Absorption Spectroscopy (CPFAAS). CPFAAS provides the limit of detection below parts per billion and the dynamic range of eight orders of magnitude in the detection of alkali chlorides. Moreover, the detection time of the CPFAAS measurement is in the order of micro second, which enables the diagnostics of the fast changing processes, such as combustion. The technique is calibration free and is integrable to "see-through" applications. In this Thesis, CPFAAS is applied to determine potassium vapor concentrations from a laboratory cell, flue gases emanated from 10 mg fuel samples, and flue gases in intermediate and large scale combustion boilers. The presented applications, modeling and comparison with previously applied detection methods show that CPFAAS enables new detection and monitoring capabilities from corrosive high temperature gases

Matkapuhelinverkkojen analysointi : Case: JoikuSpot

Internetin käyttötarpeet ovat muuttuneet työelämän vaatimusten ja ihmisten muuttuneiden tarpeiden myötä. Internetiin halutaan päästä myös kodin ja työpaikan ulkopuolella, jolloin kiinteätä tai langatonta Internet-yhteyttä ei ole saatavilla. Matkapuhelimeen asennettava Joikusoft Oy:n kehittämä JoikuSpot-sovellus muuntaa matkapuhelimen langattomaksi tukiasemaksi, joka hyödyntää matkapuhelimen 3G-yhteyttä ja muodostaa Internet-yhteyden langattomien laitteiden käytettäväksi. JoikuSpotin muodostaman Internet-yhteyden aikana sovellus kerää tietokantaan dataa muun muassa käytössä olevasta yhteysnopeudesta. Opinnäytetyön tavoitteena oli selvittää, millaista dataa tietokantaan kertyy ja miten sitä voidaan hyödyntää. Tarkoituksena oli tutkia, missä maissa ja minkä operaattoreiden verkoissa on eniten JoikuSpot-käyttäjiä. Työ rajattiin koskemaan kymmentä maata, joissa käyttäjiä on eniten, ja näistä maista kolmea käytetyintä operaattoria. Maista ja operaattoreista oli tarkoitus selvittää, millä puhelinmalleilla ja mihin tarkoituksiin JoikuSpotia käytetään. Lisäksi tarkoituksena oli tutkia tietokantaan tallentuneita yhteysmääriä ja niiden kestoja sekä yhteyksien aikana siirrettyjä datamääriä ja tiedonsiirtonopeuksia. Työ toteutettiin QlikView business intelligence -sovelluksen ja SQL-kyselykielen avulla. Työn tuloksena selvisi, että tarkastelujakson aikana 1.7.–31.12.2010 Joiku¬Spotia käytettiin eniten Kiinassa ja käytetyin puhelinmalli oli Nokian 5800 XpressMusic. JoikuSpotia käytettiin keskimäärin 67,5 minuutin mittaisissa yhteyksissä ja yhden yhteyden aikana dataa siirrettiin keskimäärin 26 megabittiä. Selvitystyö osoitti myös, että suurimmalla osalla JoikuSpotia käyttävistä henkilöistä on puhelimessaan vähintään 1 Mb/s Internet-yhteys palveluntarjoajaltaan, ja eri verkkojen läpimenoajat ovat yleisimmin alle sekunnin. Opinnäytetyö antaa vertailupohjan seuraaville mahdollisille selvitystöille, joita voitaisiin tehdä puolivuosittain. Vertailemalla nyt saatuja tuloksia tulevien selvitysten kanssa nähtäisiin, miten matkapuhelinmallien käyttömäärät muuttuvat ja miten nopeudet kehittyvät.Business requirements and people's changed needs have modified the use of the Internet. It is important to get online even outside the workplace and home, from places where a fixed or wireless Internet connection is not available. Joikusoft has developed an application called JoikuSpot that turns a mobile phone into a wireless base station. It shares the 3G connection of the phone creating an Internet connection for wireless devices. When JoikuSpot is used, the application collects data into a database. The data includes, for example, information on the speed of the connection used. The purpose of this thesis was to find out what kind of information about mobile networks is received by analyzing the collected data. The examined countries were chosen according to their number of JoikuSpot users and ten countries with the most users were chosen. Further, three most used mobile operators from each country were examined. The purpose was to investigate with which phone models and for what kind of purposes JoikuSpot is used. In addition, the purpose was to examine the amounts and durations of sessions stored into the database as well as the transferred megabytes and data transfer speeds. QlikView Business Intelligence application and SQL were used for data processing. The results showed that during the period 1st July – 31st December in year 2010, JoikuSpot was used the most in China. The most popular phone model among JoikuSpot users was Nokia 5800 XpressMusic. The results revealed that the average JoikuSpot session lasted for 67,5 minutes at a time and the transferred amount of data was 26 megabytes during a session. The investigation also indicated that a JoikuSpot user has at least 1 Mb/s mobile broadband on his or her phone and the round trip times on different networks are typically less than a second. In the future, it could be possible to repeat the research semi-annually, for example. By comparing the results to this thesis, the change of mobile phone model usage and developed speeds could be observed

In situ laser measurement of oxygen concentration and flue gas temperature utilizing chemical reaction kinetics

Combustion research requires detailed localized information on the dynamic combustion conditions to improve the accuracy of the simulations and, hence, improve the performance of the combustion processes. We have applied chemical reaction kinetics of potassium to measure the local temperature and O2 concentration in flue gas. An excess of free atomic potassium is created in the measurement volume by a photofragmenting precursor molecule such as potassium chloride or KOH which are widely released from solid fuels. The decay of the induced potassium concentration is followed with an absorption measurement using a narrow-linewidth diode laser. The temperature and O2 concentration are solved from the decay curve features using equations obtained from calibration measurements in a temperature range of 800°C–1000°C and in O2 concentrations of 0.1%–21%. The local flue gas temperature and O2 concentration were recorded in real time during devolatilization, char burning, and ash cooking phases of combustion in a single-particle reactor with a 5 Hz repetition rate. The method can be further extended to other target species and applications where the chemical dynamics can be disturbed with photofragmentation.acceptedVersionPeer reviewe