Development of a microbalance suitable for space application

The tapered element oscillating microbalance (TEOM), an ultrasensitive mass measurement device which is suitable for both particulate and vapor deposition measurements is described. The device can be used in contamination measurements, surface reaction studies, particulate monitoring systems or any microweighing activity where either laboratory or field monitoring capability is desired. The active element of the TEOM consists of a tube or reed constructed of a material with high mechanical quality factor and having a special taper. The element is firmly mounted at the wide end while the other end supports a substrate surface which can be composed of virtually any material. The tapered element with the substrate at the free (narrow) end is set into oscillation in a clamped free mode. A feedback system maintains the oscillation whose natural frequency will change in relation to the mass deposited on the substrate

Investigation of biomass alkali release in a dual circulating fluidized bed chemical looping combustion system

Chemical looping combustion (CLC) of biomass is a promising technology for power generation with integrated carbon capture. In CLC, alkali content of biomass poses potential issues of bed agglomeration, as well as heat exchanger fouling and corrosion. The fate of biomass alkalis was investigated in a dual-interconnected circulating fluidized bed CLC system. Experiments were conducted in oxygen carrier aided combustion (OCAC) and CLC modes. Ilmenite and braunite oxygen carriers and three biomass fuels (wood pellets, wood char, straw pellets) were tested. Flue gas alkali emissions in the air reactor (AR) and fuel reactor (FR) were measured with a surface ionization detector (SID). Results showed that CLC operation yields gas-phase alkali emissions that are up to 15 times higher than in comparable OCAC operation. Results analysis concluded that increased alkali emissions in CLC arise from the steam atmosphere in the FR, whereby steam accelerates the decomposition of alkali compounds in the biomass. Retention of alkalis in the condensed phase was found to be >97% for ilmenite and >92% for braunite CLC operation. Up to 60?80% of the retention was attributed to fuel ash formation. The residual retention was attributed to absorption of alkalis by the oxygen carriers. Absorption likely occurred mainly through formation of alkali manganates and silicates in braunite, and formation of alkali silicates, aluminosilicates, manganates, and titanates in ilmenite. Gas-phase alkali emissions in the AR, although less than in the FR, were found to occur due to combustion of unconverted fuel carried over from the FR to the AR

The Release, Distribution, and Implications of Alkalis in Chemical Looping Combustion of Biomass

Chemical looping combustion (CLC) of biomass is a promising technology for power generation with a potential net negative CO2 footprint. Like other fluidized bed biomass conversion technologies, biomass CLC may be susceptible to alkali-induced \ua0agglomeration, fouling, and corrosion. The mechanisms, distribution, and implications of alkali release in CLC systems presents a significant knowledge gap that is critical for upscaling and commercialization of biomass CLC. To investigate gas-phase alkali release in CLC, a CLC-specific surface ionization detector (SID) measurement system was developed. This system was validated in Papers V and VI against two independent alkali measurement techniques. Alkali emissions were measured in four experimental campaigns using three different CLC pilots, four oxygen carriers (OC), and nine different biomass fuels. The SID-based emissions measurements showed that up to 17% of the fuel alkalis are released to the gas phase of the fuel reactor (FR), and up to 7% to the air reactor (AR). Thermodynamic modelling of alkali release, and chemical analysis of flue gas alkalis indicated that gaseous FR alkalis are dominated by KOH(g) and KCl(g). FR alkali emissions levels were found to rise with temperature and steam concentration. Two key alkali release processes were identified: 1) sublimation of KCl(s) to KCl(g), and 2) decomposition of alkali salts, such as K2CO3, to yield KOH(g). It was determined that higher temperature accelerates both of these processes, while steam enables and accelerates the second path. AR emissions were independent of temperature and other operating parameters within the performed tests. Experimental evidence suggests that AR emissions occur via carryover of char from the FR to AR. Ash-bound and OC-bound carryover mechanisms were also proposed, but could not be experimentally validated. Modelling of alkali release and AR fly ash chemical analyses suggest that AR emissions are essentially KCl-free. Alkali retention in condensed phases was found to be >77%, with OC alkali uptake accounting for approx. 30%. A balance on potassium in the 10 kW pilot indicated that up to 60% of fuel alkalis can be elutriated from the FR as solid ash particles, while AR fly ash accounted for up to 3% of fuel alkalis. Biomass CLC experiments indicate that alkali release behavior does not constrain the fuel conversion and carbon capture performance of CLC systems. Furthermore, CLC technology offers inherent advantages for conversion of high alkali biomass. The key advantage is that the low corrosion potential of the AR flue gases should allow for higher steam temperatures, and thus more efficient operation of the main process heat exchangers in the AR. Further work is needed to evaluate long-term effects of alkali release on OC performance

Sources of unburned carbon in the fly ash produced from low-NOx pulverized coal combustion

Journal ArticleThe unburned carbon in the fly ash produced from low-NOx pulverized coal combustion is shown to consist of a mixture of soot and coal char. The soot was identified by the presence of chains or aggregates of 10-50-nm-diameter primary particles in electron microscope images of both laboratory samples and a sample of fly ash from a power plant operating low-NOx burners. Laboratory samples showed increasing carbon content with decreasing nitrogen oxide (NOx) concentration. The experiments included a high-NOx base case and four low-NOx cases consisting of (1) staged combustion with short (0.5 s) residence time, (2) staged combustion with long (1.5 s) residence time, (3) a low-NOx burner with slow mixing, and (4) reburning using coal as the reburning fuel. Comparison of the base case that used premixed coal and air with the long-residence-time staged combustion case shows a decrease in the NOx from over 900 ppm to below 200 ppm and an increase in the carbon in the ash from 4% to over 30%. The fly ash from staged combustion was a mixture of large soot aggregates, porous char, and spherical particles of mineral ash, whereas the ash from reburning lacked the large aggregates. For all laboratory conditions, the carbon content in the particle fraction with an aerodynamic diameter over 10 lm was higher than in the 1-2.5- lm-diameter fraction. Both soot aggregates and char contributed to the high carbon in the large particle fraction. The difference in carbon burnout between the two staging conditions was consistent with published soot oxidation rates. Both char burnout and soot formation need to be considered in studies of the carbon content of pulverized coal fly ash

Determining the Fate and Operational Implications of Alkalis in Chemical Looping Combustion of Biomass

Chemical looping combustion (CLC) of biomass is a promising thermal conversion technology with integrated carbon capture. As with other fluidized bed fuel conversion processes, biomass CLC may be susceptible to issues of agglomeration, fouling and corrosion stemming from the release of alkalis during fuel conversion. How alkalis are released and what implications they have on CLC operation is currently largely unknown. The experimental studies presented in Papers I - III of this thesis aimed at addressing this knowledge gap.Measurement of gas-phase alkali release in CLC was addressed through the design and construction of a modular and transportable surface ionization detector (SID) system, customized for alkali emissions measurement from the fuel reactor (FR) and the air reactor (AR) of CLC pilots. Gas-phase alkali emissions measurement showed that approximately 1-10% of fuel alkalis are released to the gas phase in CLC. The FR alkali emissions were found to rise with the fuel’s alkali content, while no definitive correlation was established for AR emissions. With respect to emissions distribution, AR emissions were found to be generally lower than that of the FR. Surprisingly, in several cases, AR emissions were equal or marginally higher than in the FR. Analysis presented in Paper III led to a preliminary conclusion that AR gas-phase alkali emissions likely occur due to char or ash carryover from the FR, whereby the transported alkali compounds release to the gas phase at the higher temperatures of the AR.Papers I-III also established that >97% of fuel alkalis are retained in solid form. Although a major part of the alkali retention originates from fuel ash formation, significant retention likely occurs due to oxygen carrier interaction with the fuel’s inorganic content. In Paper III it was also found that in CLC, the steam-rich FR atmosphere enhances the gas-phase release of alkalis from decomposition of alkali carbonates and sulphates. This was established in tests comparing CLC operation with oxygen carrier aided combustion (OCAC).Development of biomass CLC technology was also addressed in this thesis. Paper I demonstrated that gas conversion efficiencies of >96% can be achieved with mixed synthetic and natural oxygen carriers. Experiments in Paper II commissioned a new 10 kW CLC pilot and demonstrated that the implementation of a volatiles distributor in the FR can improve fuel gas conversion efficiency by up to 10 percentage points. Papers I and II also evaluated the interdependencies of the CLC system’s control parameters with gas-phase alkali release. It was concluded that CLC system control parameters, other than temperature, likely do not significantly influence and are not constrained by alkali release behavior

Ultrasonic atomisers for reducing pollution from petrol engines

This thesis opens with a review of present knowledge about pollution from internal combustion engine exhaust, covering the formation of pollutants in the engine, some of the effects of emission on man, and the influence of various engine parameters on exhaust emission. The thesis describes the development and application of ultrasonic atomisers operating at approximately 100 kHz, the investigation of the formation of droplets in a liquid layer on a vibrating surface and the measurement of droplet size using liquid wax and microphotography. Chapter 4.3 presents the results of calculations of eigenvalues and vibration amplitudes in an ultrasonic atomiser, using a three dimensional finite element programme. Chapter 6.2 and 6.3 describes experiments on a two-stroke and a four-stroke engine which demonstrate the improvement in engine emissions which can be achieved using ultrasonic atomisers, particularly at low load. Experiments were carried out with ultrasonic atomisers mounted in a novel carburettor unit, and the result were compared with the engine performance using a normal carburettor. A special manifold intended to achieve the best possible utilisation of the atomiser was designed and tested

An Induced Environment Contamination Monitor for the Space Shuttle

The Induced Environment Contamination Monitor (IECM), a set of ten instruments integrated into a self-contained unit and scheduled to fly on shuttle Orbital Flight Tests 1 through 6 and on Spacelabs 1 and 2, is described. The IECM is designed to measure the actual environment to determine whether the strict controls placed on the shuttle system have solved the contamination problem. Measurements are taken during prelaunch, ascent, on-orbit, descent, and postlanding. The on-orbit measurements are molecular return flux, background spectral intensity, molecular deposition, and optical surface effects. During the other mission phases dew point, humidity, aerosol content, and trace gas are measured as well as optical surface effects and molecular deposition. The IECM systems and thermal design are discussed. Preflight and ground operations are presented together with associated ground support equipment. Flight operations and data reduction plans are given

Modeling and Simulation of Components in an Integrated Gasification Combined Cycle Plant for Developing Sensor Networks to Detect Faults

The goal of this work is to help synthesize a sensor network to detect and diagnose faults and to monitor conditions of the key equipment items. The desired algorithm for sensor network design would provide information about the number, type and location of sensors that should be deployed for fault diagnosis and condition monitoring of a plant. In this work, the focus was on the integrated gasification combined cycle (IGCC) power plant where the faults at the equipment level and the plant level are considered separately. At the plant level, the objective is to observe whether a fault has occurred or not and identify the specific fault. For component-level faults, the objective is to obtain quantitative information about the extent of a particular fault. For the model-based sensor network design, high-fidelity process model of the IGCC plant is the key requirement.;For component level sensor placement, high-fidelity partial differential algebraic equation (PDAE)-based models are developed. Mechanistic models for faults are developed and included in the PDAE-based models. For system-level sensor placement, faults are simulated in the IGCC plant and the dynamic response of the process is captured. Both the steady-state and dynamic information are used to generate markers that are then utilized for sensor network design.;Whether faults in a particular equipment item should be considered at the unit level or system level depend on the criticality of the equipment item, its likelihood to failure, and the resolution desired for specific faults. In this work, the sour water gas shift reactor (SWGSR) and the gasifier are considered at the unit level. Fly ash may get deposited on the SWGSR catalyst and in the voids in the SWGSR resulting in decreased conversion of carbon monoxide. A MATLAB-based PDAE model of the SWGSR has been developed that considers key faults such as changes in the porosity, surface area, and catalyst activity. In a slagging gasifier, the molten slag that flows along the inner wall can penetrate into the refractory layer, and due to chemical corrosion and thermal and mechanical stress eventually result in thinning or spalling of the refractory. Extent of penetration of slag into the refractory wall and the spalling of the refractory are considered to be important variables for condition monitoring of the gasifier. In addition, as an increasing slag layer thickness can eventually lead to shutdown of the gasifier yet the slag layer thickness cannot be directly measured using the current measurement technology, slag layer thickness is also considered to be an important variable for condition monitoring. For capturing the slag formation, and detachment phenomena accurately, a novel hybrid shrinking core-shrinking particle (HSCSP) model is developed. For tracking the detached slag droplets and the char particles along the gasifier, a particle model is developed and integrated with the HSCSP model. A slag model is developed that captures the process of the detachment of the slag droplets from the char surface, transport of the droplets towards the wall, deposition of a fraction of the droplets on the wall and formation of a slag layer on the wall. Finally, a refractory degradation model is developed for calculating the penetration of the slag inside the wall and the size and time for a spall to occur due to the combined effects of volume change as a result of slag penetration as well as thermal and mechanical stresses.;System-level models are enhanced and faults are simulated spanning across various sections of the IGCC plant. For example, in the SELEXOL-based acid gas removal unit the available area in the trays of distillation columns may get reduced due to deposition of solids. This can result in loss of efficiency. Leakages in heat exchangers in this unit can result in the loss of expensive solvent or hazardous gases. In the combined cycle section, faults such as leakages and fouling in the heat exchangers, increased loss of heat through the combustor insulation that can result in loss of efficiency are simulated.;Sensor placement using a two-tier approach is also performed by developing a sensor network for a combined system that includes unit level as well as system level faults. A model of the gasification island is developed by integrating the SWGSR model developed in MATLAB with the model of the rest of the plant developed in Aspen Plus Dynamics. Since the two models are developed using different software platforms, an integration framework is developed that couples and synchronizes the two dynamic models. The sensor network obtained using the models developed in this work is found to be effective in observing and resolving faults both at the unit level as well as the plant level. (Abstract shortened by UMI.)