<p></p><p>In the grain handling and processing industry, dust emission and accumulation are major concerns for the safety of workers and for explosion risks. Dust emission and accumulation locations highly depend on the facility design and equipment used for handling and processing. To prevent an explosive atmosphere, monitoring the amount of dust accumulated or dispersed is extremely important. However, methods of measuring the dust concentration require the installation of equipment. The Occupational Safety and Health Administration (OSHA) regulations and National Fire Protection Association (NFPA) standards restrict the thickness of dust layers on floors for fine powder materials such as starch. The objective of this dissertation was to better understand the rate of dust layer accumulation, dust suspension patterns, and the optical properties of suspended dust. For this purpose, The Discrete Phase Model (DPM) was combined with a Computational Fluid Dynamics Model (CFD) and the hybrid model was used to model dust dispersion. Dust dispersion patterns under pressure, such as primary explosions or leakage from equipment, were simulated using the unsteady CFD-DPM approach. The particle-wall interaction based on energy conservation was also introduced in this model. Both one-time and continuous dust dispersion in an enclosed chamber were simulated to mimic secondary explosions and the dust emission from processing equipment. In addition, the light extinction property of suspended dust was studied as a method of measuring suspended dust concentration. </p> <p>For a one-time dust dispersion incident, the predicted dust concentration agreed with the simulation result for the trial conducted at a dust injection velocity of 2 m/s with injection rates of 0.05 and 0.10 kg/m³ and at a dust injection velocity of 10 m/s with an injection rate of 0.05 kg/m³. The dust concentration in the entire chamber increased with dust injection velocity and the mass of injected dust. As dust injection velocity increased, dust spread out and formed a larger explosive dust cloud. However, the dust concentration inside the chamber was non-uniform. Considering the minimum explosive concentration, the largest explosive cloud was created at a dust injection velocity of 10 m/s with an injection rate of 0.10 kg/m³. Explosive concentrations of dust were found somewhere in the chamber for all dispersion rates. At an injection velocity of 10 m/s with an injection rate of 0.10 kg/m³, the predicted dust concentration was 10% more than the measured dust concentration. Thus, this model is suitable for dilute dust particle dispersion flows, where the volume fraction of particles is less and only a single particle layer settles.</p> <p>Continuous dispersion was simulated to determine the suspended dust concentration and particle deposition patterns. Dust was dispersed for 30 s at dispersion rates of 2, 4 and 6 g/min at a dust injection velocity of 2 m/s. The dust concentration increased at a constant rate after a few seconds of dispersion, regardless of the dust dispersion rate. Most dust particles were deposited near the dust dispersion nozzle. Large particles were more affected by gravitational force and inertia compared with small particles, which traveled with airflow and settled behind the nozzle. The dust accumulated close to the dispersion nozzle faster than behind the nozzle location. However, specific attention must be paid to small particles, because they are more likely to cause an explosion, as their minimum explosive concentration is lower than that of large particles.</p> <p>The light extinction coefficients of cornstarch, grain dust, and sawdust were measured using a two-target method. The suspended dust concentration was measured using a calibrated laser instrument. The light extinction coefficient was linearly related to the suspended dust concentration. The correlation coefficient between the light extinction coefficient and suspended dust concentration depended on particle size, particle shape, and chemical properties. </p> <p>Controlling dust cloud generation and minimizing the concentration and volume of dust clouds are some key measures to prevent dust explosions. The mathematical models developed in this study to predict dust dispersion, suspension, and rate of settling will help solve a few of the challenges in the particulate material handling and processing industry. This method of measuring the light extinction coefficient can be applied development of a dust safety monitoring system. The result presented in this dissertation will help the industry prevent the formation of an explosive atmosphere.</p><br><p></p>

Influence of dust particles on the characteristics of premixed methane-air flames has been studied in this dissertation. Experiments are performed in a Bunsen burner type experimental set-up called Hybrid Flame Analyzer (HFA), which can be used to measure the burning velocity of gas, dust, and hybrid (gas and dust) premixed flames at constant pressure operating conditions. In the current study, analysis of particle-gas-air system of different types of dust particles (at particle size, dp = 75-90 µm) in premixed methane-air (ϕg = 0.8, 1.0 and 1.2) flames. Coal, sand, and sodium bicarbonate particles are fed along with a premixed methane-air mixture at different concentrations (λp = 0-75 g/m3) in both laminar and turbulent conditions. First, the variation of laminar burning velocity with respect to the concentration of dust particles, and type of dusts are investigated for different equivalence ratios. Second, the laminar premixed flame extinction with inert and chemical suppressant particles are studied. Third, the variation of turbulent burning velocity of these hybrid mixtures are investigated against different turbulent intensities apart from the different concentrations and types of dusts. Fourth, the radiative fraction of heat released from turbulent gas-dust premixed flames are also presented against the operating parameters considered. Combustible dust deflagration hazard is normally quantified using the deflagration index (Kst) measured using a constant volume explosion sphere, which typically is a sealed 20-liter metal sphere where a premixed mixture is ignited at the center and the progression of the resulting deflagration wave is recorded using the pressure measured at the vessel wall. It has been verified from prior studies that the quantification of the turbulence by this method is questionable and there is a need to analyze the controlling parameters of particle-gas-air premixed system accurately through a near constant pressure operated experimental platform. Thus, the main objective of this study is to analyze the influence of dust particles on premixed methane-air flames at near constant pressure conditions. The turbulent burning velocity is calculated by averaging the measured flame heights and the laminar burning velocity is calculated through the premixed cone angle measurements from several high-speed shadowgraph images obtained from the experiments. The turbulent intensity and length scale of turbulence generated by a perforated plate in the burner is quantified from the hot-wire anemometer measurements. Radiative heat flux is also measured for each of the turbulent test conditions. The outcomes from these experiments are: 1. An understanding of the variation of turbulent burning velocity of gas-dust premixed flames as a function of dust type, turbulent intensity, integral length scale, dust concentration and gas phase mixture ratio. 2. An understanding of the flame extinction characteristics and variation of laminar burning velocity of gas-dust premixed flames as a function of dust concentration and gas phase mixture ratio. 3. Quantify the radiative heat flux and radiative fraction of heat released from gas-dust turbulent premixed flames as a function of dust type, turbulent intensity, dust concentration and gas phase mixture ratio. Dust type and concentration play an important role in deciding the trend in the variation of both laminar (SL) and turbulent burning velocity (ST). Coal particles, with the release of volatile (methane), tend to increase burning velocities except for fuel rich conditions and at higher coal concentrations at larger turbulent intensities. At a higher turbulent intensity and larger concentrations, higher ST values are observed with the addition of sand. Sodium bicarbonate addition, with the release of CO2 and H2O, decreased the burning velocity at all the concentrations, turbulent intensities and equivalence ratios. Laminar flame extinction was observed with the addition of sand and sodium bicarbonate particles at conditions exceeding certain critical dust concentrations. These critical concentrations varied with the equivalence ratios of gaseous premixed flames. The turbulence modulation exhibited by particles and particle concentration is evident in these observations. The independent characteristic time scale analysis performed using the experimental data provided further insights to the results. The chemical and convective times in gas phase confirm the broadened preheat thin reaction zone regime in the current test cases, which has an effect of attenuating turbulence and thereby the resulting turbulent burning velocity. The particle time scale analysis (Stokes number) show that the effect of particles and particle concentration is to slightly enhance the turbulence and increase the turbulent burning velocity at lower concentrations. However, the time scale analysis of particle vaporization (vaporization Damköhler number) indicate an increase in the vaporization rate for particles (coal and sodium bicarbonate) resulting in a decrease in their turbulent burning velocities at higher concentrations and turbulent intensities. Sodium bicarbonate has higher evaporation rate than coal at same level of turbulence and the absence of this effect for inert (sand) results in higher turbulent burning velocities at higher concentrations. An increase in the turbulent intensity increases the vaporization rate of particles. The investigation on radiative fraction of heat released by methane-air-dust turbulent premixed flames identified that, the addition of dust particles increases the radiative fraction irrespective of the dust type due to the radial and axial extension of flame. A unified approach to couple this multiple complex phenomenon of turbulence, particle interaction, particle vaporization and combustion in particle laden premixed gaseous flames is the direction for future research.

Most companies that have any type of combustion or other pollution process via emission to air needs to measure their emissions to ensure they are within legal boundaries. Among the different types of pollution measurements, one of the most common is dust concentration, also known as particle concentration. An important factor in dust concentration measurements is to ensure that the concentration of the measured dust is representative to the dust concentration in the emissions. This is measured in isokinetic deviation, defined as (vn 􀀀 vd)=vd, where vn is the velocity in the entry nozzle and vd the velocity in the duct. Methods of dust concentration measurements used today are dependent on manual tuning and sensor readings, and the isokinetic deviation is calculated after a test. The focus of this project was therefore to investigate how the process of dust concentration measurements using standard reference methods could be automated in the way that isokinetic sampling is controlled and regulated by an automated control system in real time. Pressures, temperatures and sampled gas volume were quantized. A PIDcontroller was designed, implemented and tested. The PID-controller took the differential pressure between the inside of the entry nozzle and the duct, called zero pressure, as input. The system was tested in a laboratory environment by letting a radial fan create a flow, and thus create a zero pressure of -60 Pa, meaning that the pressure in the duct was 60 Pa greater than the pressure inside the entry nozzle. The PID-controller was then enabled and ran for five minutes. The result showed that the PID-controller managed to control the system to the reference point in less than 50 seconds for entry nozzles of diameters 6 mm, 8 mm, 10 mm and 12 mm. The results of the isokinetic deviations were -12 %, -5 %, -6 % and -4 % for entry nozzles with diameters 6 mm, 8 mm, 10 mm and 12 mm respectively. This is higher than the accepted values according to the European standard, which allows deviations in the interval -5%to 15%. However, these tests ran for relatively short time periods and started with large deviations which made it difficult to reach an isokinetic deviaiton in the accepted interval. Possible improvements could be to include the real time isokinetic deviation in the PID-controller, this would make it possible to change the reference value of the zero pressure in real time and guarantee isokinetic deviations in the accepted interval, even in extraordinary situations. / EU-regler ställer krav på anläggningar att kontrollera och begränsa sina utsläpp av stoft enligt EU standard 13284-1:2017. Vid en stoftmätning måste det tas hänsyn till många parametrar, där en av de viktigaste parametrarna är att provtagningen ska utföras isokinetiskt. Isokinetisk provtagning innebär att hastigheten i kanalen (skorstenen) är samma som i sonden där provgasen sugs ut. Dagens metoder för stoftmätning förlitar sig på manuella inställningar och den isokinetiska avvikelsen beräknas efter ett test. Det resulterade i frågeställnigen hur en automatiserad metod för bestämning av masskoncentration av stoft kan utformas så att den isokinetiska avvikelsen beräknas i realtid. Tryck, temperatur och gasvolym kvantiserades från analoga sensorer och kommunicerades till en mikrokontroller med det seriella protokollet I2C. En PID-reglator designades, implementerades och testades. PID-regulatorn tog tryckskillnaden mellan kanal och sond som insignal. Utsignalen från PID-regulatorn var en spänning som via en motordriven ventil kontrollerade inflödet i munstycket. Systemet testades i laborativ miljö genom att låta en fläkt skapa ett flöde tills den uppmätta tryckskillnaden mellan sond och kanal var -60 Pa. Därefter aktiverades PID-regulatorn och testet pågick sedan i fem minuter. Testet utfördes för munstycken med diameterna 6 mm, 8 mm, 10 mm och 12 mm. Resultatet visade att PID-regulatorn styrde systemet till referenspunkten på mindre än 50 sekunder för samtliga diametrar på munstyckena. De isokinetiska avvikelserna (skillnaden i hastighet mellan munstycke och kanal) beräknades till -12 %, -5 %, -6 % och -4 % för munstyckena 6 mm, 8 mm, 10 mm och 12 mm. I två av fallen var det högre än det accepterade värdet enligt EU standarden som tillåter avvikelser inom intervallet -5 % till 15 %. Det kan förklaras av att testen utfördes under en relativ kort tidsperiod och startades med stora avvikelser. Regulatorn skulle dock kunna förbättras genom att använda testets aktuella isokinetiska avvikelse och med den informationen bestämma systemets referenspunkt. Det skulle göra det möjligt att kompensera för tidigare avvikelser och på det sättet uppnå isokinetiska avvikelser inom tillåtet intervall även för extremfall.