Flue Gas Measurement Research Articles

Flame and emission characteristics from NH3/CH4 combustion under ultrasonic excitation

As a high energy density hydrogen-rich carrier, ammonia (NH3) is a highly promising carbon-free fuel. The large-scale industrial application of NH3 is limited by its low reactivity and high NOx emission. In this work, the flame and emission characteristics of ammonia/methane (NH3/CH4) non-premixed combustion were investigated under ultrasonic excitation. An experimental system was designed and built, including non-premixed combustion system, loading ultrasonic system, deflectionmography temperature measurement system and flue gas measurement system. Combustion and measurement experiments at different ultrasonic frequencies and NH3/CH4 blending ratios were carried out. Flame images and flue gas species concentrations under ultrasonic excitation were acquired. The 3-D temperature field was reconstructed. The influence of ultrasonic excitation at different frequencies on flame characteristics, flame temperature field and emission characteristics of the combustion process was analysed. The mechanism of NH3/CH4 combustion enhancement and emission reduction was revealed when the flame was ex-cited by ultrasonic waves. Results showed that part of the hydrocarbon fuels was replaced by NH3 to reduce CO2 emission. The height and color of the NH3/CH4 flame were changed and the high temperature area of the flame gradually expanded as ultrasonic acted on the flame. As ultrasonic frequency increased, the emission concentrations of unburned CH4, unburned NH3, and NO decreased significantly. The flame was ex-cited by ultrasonic waves, which reduced its local equivalent ratio, improved combustion efficiency and suppressed NOx generation.

Investigation of Heat Recovery Potential According to Flue Gas Field Measurements in Solid Fuel-Fired Buildings with District and Central Heating Systems

In this study, flue gas heat recovery potential was determined by using the flue gas measurements from boilers of buildings with solid fuel-fired district and central heating systems in Balikesir, Turkey. Potential flue gas heat recovery potential in terms of energy savings were examined. The potential of heating the preheated water and combustion air supplied to the boiler was analyzed. Thus, the efficiency of the heating system was increased, and energy savings were achieved by providing fuel savings. In order to reduce the flue gas temperature in solid fuel-fired boilers, the acidification temperature, fuel properties and excess air coefficient should be known. Below the acidification temperature, corrosion and other adverse effects may occur in the flue and in the heat exchanger. In this study, acidification temperature and fuel and combustion characteristics of coal were taken into account. Generally, seven types of coal are used for heating purposes in Balikesir province. Thus, flue gas heat recovery potential was determined for these seven types of coal. In terms of energy savings, the recovery potential in Balikesir province was calculated to be between 287,706 and 152,780 kW.

Experimental and Kinetic Investigation of Stoichiometric to Rich NH3/H2/Air Flames in a Swirl and Bluff-Body Stabilized Burner

Ammonia (NH3) is an inorganic substance considered as a promising fuel for power sector decarbonization. As a result of the absence of carbon in its structure, ammonia is capable of producing energy with zero CO2 emissions when burned. However, the combustion of NH3 presents several challenges as a result of its low reactivity and low flame speed as well as the formation of large quantities of nitrogen oxides (NOx) and frequent ammonia slip. A suggested solution for gas turbines is the use of rich-to-lean approaches, with a fuel-rich first-stage combustion, which mitigates NOx formation, followed by a lean phase for the oxidation of the remaining reactants, improving combustion efficiency. To help assess this concept, the present work investigates experimentally and computationally the combustion of ammonia/air mixtures, enriched by hydrogen (H2) for enhanced burning characteristics, in a swirl and bluff-body stabilized burner, at stoichiometric to fuel-rich conditions. Stability tests were performed for a fixed thermal input (2.8 kW), and flames of fuel/air equivalence ratios of 1.0, 1.1, and 1.2, with molar fractions of ammonia in fuel of 0.7 and 0.8, were studied. Temperature profiles along the combustor axis were measured, and flue gas measurements for NOx emissions and unburned NH3 and H2 concentrations were performed for the six studied flames. Computational simulations were performed using a chemical reactor network coupled with recent kinetic mechanisms to compare species trends and further understand the NOx formation and NH3 conversion into hydrogen, through rate of production analyses. It was found that the present laboratory combustor performed well in terms of flame stability, also generating low levels of NOx emissions in all fuel-rich conditions. H2 was detected in high concentrations in the flue gas, partially originated from ammonia dissociation, and is followed by high unburned ammonia emissions. Both H2 and NH3 emissions increase with the equivalence ratio. A secondary, spontaneous diffusion flame was observed above the combustor, proving that the flue gas may subsequently be burned. Higher fractions of hydrogen in the fuel generate more unburned ammonia but also higher H2 concentrations in the flue gas. The predictions based on a reactor network model coupled with the evaluated kinetic mechanisms presented good agreement with the experimentally observed species trends and fair agreement with species values.

Experimental tests on co-firing coal and biomass waste fuels in a fluidised bed under oxy-fuel combustion

The co-firing of coal and biomass waste in oxy-fuel fluidised beds is an important oxy-fuel combustion technology for CO2 capture and waste disposal. However, practical experience regarding co-firing in an oxy-fuel fluidised bed is still limited. In this study, a 10 kWth oxy-fuel fluidised bed with continuous fuel-feeding and real-time flue gas measurements was developed. The combustion stability and dynamic response during the switch in combustion states were examined. The effect of the combustion atmosphere (air or oxy-fuel combustion), inlet O2 concentration (V0o2), combustion temperature, fuel type, and biomass blending mass ratio (Mb) on the combustor temperature distribution, CO2 enrichment, carbon conversion, and combustion residues were systematically investigated. The results indicated that the combustion state can switch quickly during the co-firing process (similar to the rapid switch in combustion states during oxy-coal or oxy-biomass combustion), and stable combustion in the fluidised bed can be maintained when V0o2 is increased to 30% or more. The optimal range of Mb, which is directly related to the fuel type and combustion mode, contributes to a highly uniform temperature distribution, increased CO2 generation, and decreased amount of unburnt carbon in the fly ash. The bottom slag had a honeycomb structure, which became larger than quartz sand (bed material) after 120 h of combustion. Furthermore, no agglomeration of bottom slag, quartz sand, and fly ash was detected during the tests.

Chemical-looping combustion in a 100 kW unit using a mixture of synthetic and natural oxygen carriers – Operational results and fate of biomass fuel alkali

Biomass fuel use in chemical looping combustion enables negative CO2 emissions through BECCS (Bio-Energy Carbon Capture and Storage). Effective biomass utilization in CLC requires an economical and effective oxygen carrier to achieve high fuel conversion, effective CO2 capture, and management of the harmful effects of biomass alkali release (bed agglomeration, oxygen carrier deactivation, fouling and corrosion). These issues were addressed in 100 kW CLC pilot experiments.Building on previous work, a mixture of a synthetic calcium manganite perovskite and natural ilmenite was used as the oxygen carrier. Four biomass fuels of varied alkali content were tested: black pellets of steam-exploded stem wood (BP), BP impregnated with K2CO3, a mixture of 50% BP with 50% straw pellets, and wood char. Experiments showed high fuel conversion and very high CO2 capture, with overall performance exceeding that of ilmenite and manganese ore. More than 95% gas conversion was achieved with black pellets at around 950 °C.The fate of biomass alkali, previously virtually unknown in CLC research, was explored by implementing online surface-ionization-based measurement of alkali released in the flue gases of the fuel reactor (FR) and air reactor (AR). Release levels were found to correlate with the fuel alkali content. The flue gas measurements and bed material elemental analyses suggest that most of the fuel alkali are accumulated in the oxygen carrier. Unexpectedly, it was found that flue gas alkali release occurs in both the FR and AR, with AR exhibiting an equal or higher rate of release vs. the FR.

Online Corrosion Measurements in Combination with Deposit and Aerosol Analysis during the Co-firing of Straw with Coal in Electrically Heated, Small-Scale Pulverized Fuel and Circulating Fluidized Bed Systems

A measurement campaign has been conducted both in a pilot-scale pulverized fuel and in a pilot-scale circulating fluidized bed test rig to evaluate the behavior of two different online corrosion sensors during the co-combustion of straw with bituminous coal. The online corrosion sensors based on the linear polarization method were equipped with material rings of the alloy10CrMo9-10 and air-cooled to a material temperature of 530 °C (PF) and 560 °C (CFB). They were implemented at a flue gas temperature of approximately 750−800 °C in both test rigs to simulate superheater tubes. The derived signals were compared with flue gas measurements (O2, CO2, SO2, and HCl) as well as selected fine particle measurements and deposit sampling during co-firing tests of 0, 10, 25, 40, 60, and 100% straw with coal on an energy basis. Slight deviations between the fuels tested in the different test rigs were observed. Main differences were measured in the coal ash composition and chlorine content of the straw. Online corrosion sensors reacted quickly to changes in the blend composition. While no enhanced corrosion was detected during the co-combustion of 10% and 25% straw, both sensors identified possible corrosive processes on the metal surface during the 60% straw case. The detected signal change could be correlated to an increased share of chlorine in the fine particles (in the PF and the CFB test rigs) and deposits (only in the CFB tests). Interestingly, a smaller signal change was detected during the 40% straw case in the PF combustion, in contrast to a larger signal gradient during the 40% case in the CFB tests. Two reasons could be identified for this behavior: On the one hand, the sensor used in the PF tests showed a lower sensitivity due to a different design of the sensor head. On the other hand, a significant amount of chlorine was detected in the aerosolic particles in the CFB tests in contrast to no chlorine in the PF experiments during this case. The known interaction mechanisms of alkali mitigation during combustion of difficult fuels (sulfation and embedding in alumino-silicates), which lead to a chlorine reduction in the fine particles, were investigated thoroughly. It was found that sulfation might be more pronounced under conditions typical of CFB systems.

Combustion characteristics of straw stored with CaCO3 in bubbling fluidized bed using quartz and olivine as bed materials

The addition of Ca-containing compounds can reduce mass loss from agricultural biomass during storage. The resulting alkaline environment is detrimental to microorganisms present in the material. Theoretical analysis of Ca-containing biomass suggests that combustion properties are improved with respect to slagging. To validate the theoretical calculations, barley straw was utilized as a typical model agricultural biomass and combustion characteristics of straw pre-treated with 2 and 4 w/w% CaCO3 for combined improvement of storage and combustion properties were determined through combustion at 700 °C in a bench-scale bubbling fluidized-bed reactor (5 kW) using quartz and olivine sand as bed materials. The combustion characteristics were determined in terms of elemental composition and compound identification in bed ash and bed material including agglomerates, fly ash, particulate matter as well as flue gas measurements. The addition of CaCO3 to straw had both positive and negative effects on its combustion characteristics. Both additive levels raised the total defluidization temperature for both quartz and olivine, and olivine proved to be less susceptible than quartz to reactions with alkali. With Ca-additives, the composition of deposits and fine particulate matter changed to include higher amounts of KCl potentially leading to higher risk for alkali chloride-induced corrosion. Flue gas composition was heavily influenced by CaCO3 additives by significantly elevated CO concentrations likely related to increased levels of gaseous alkali compounds. The results suggest that it is necessary to reduce gaseous alkali compounds, e.g. through kaolin or sulphur addition, if alkali-rich straw is to be co-combusted with Ca-rich biomass or large amounts of Ca-additives.

Sulfation of alkali halides in a bench-scale bubbling fluidized bed reactor

During biomass and waste combustion, high levels of alkali halides in the flue gas often lead to increased deposit formation and accelerated superheater corrosion. These problems can be reduced either by co-combustion or by the use of sulfur-containing additives. A measurement campaign was carried out in a 20kWth bubbling fluidized bed (BFB) bench-scale reactor to characterize the sulfation behaviors of alkali chloride and alkali bromide. Spruce bark was used as the base fuel – serving as a source of alkali metals (mainly K). HCl and HBr gases were fed with the fluidization air to simulate co-firing of a halide-rich fuel with bark. SO2 and elemental S powder were used as additives to convert the alkali halide aerosols to less corrosive alkali sulfates. The sulfation behavior of alkali halides was evaluated by means of several measurements including: FTIR (flue gas measurement), a low-pressure impactor (particle size distribution and chemical composition of extracted aerosol particles) and deposit probe sampling (deposit growth rate and chemical composition of the windward, 90° side and leeward deposits). The results indicated a higher tendency for sulfation of alkali chloride than of alkali bromide.

Comparing CO2 Emission Factors Estimated Using Stack Flue Gas Measurement Data for Two Types of Ceramic Kiln: A Case Study in Hanoi City, Vietnam

In Vietnam, the ceramic industry is one of the construction material production sectors that has large emission of CO2 - the major greenhouse gas, since it consumes a large amount of fossil fuels. This research aims at preliminarily estimating the CO2 emission factors for two major kiln technologies currently used in ceramic production sector in Vietnam, namely the traditional kiln and tunnel kiln. For this purpose, field measurements of CO2 concentration in stack flue gases of two ceramic factories in Hanoi City, Vietnam were conducted. The results of data analysis have shown that the traditional kiln has higher CO2 emission factors compared to those of tunnel kiln. The low energy efficiency and high energy consumption of the traditional kiln are the major causes for its higher CO2 emission factors.

Comparative Assessment of Co2 Emission Factors Estimated Using Stack Flue Gas Measurement Data for Two Types of Brick Kiln: A Case Study in Phu Tho Province, Vietnam

In Vietnam, the brick production sector is one of the construction material production sectors that has large emission of CO2 – the major greenhouse gas, since it consumes a large amount of fossil fuels. This research aims at preliminarily estimating the CO2 emission factors for two major kiln technologies used in brick production sector in Vietnam, namely tunnel and vertical shaft brick kiln (VSBK). For this purpose, field measurement of CO2 concentration in stack flue gases of two brick factories in Phu Tho province – one of the largest brick production areas in the North of Vietnam were conducted. The results of data analysis have shown that the tunnel kiln has higher CO2 emission factors compared to those of VSBK. The lower specific energy consumption and lower heat losses are the major causes for lower CO2 emission factors of VSBK.

Fate of bromine and chlorine in bubbling fluidized bed combustion – Formation of alkali halide aerosols

In solid substances used as fuels, bromine originates mainly from flame retarded plastics and textiles, as well as from wastewater sludge. It has been indicated that bromine behaves in a similar way as chlorine with respect to ash forming matter, aerosol formation and high temperature corrosion in biomass and waste fired boilers. In this work, a measurement campaign was carried out in a 20kWth bubbling fluidized bed (BFB) bench scale reactor to characterize the fate of Cl and Br in BFB combustion conditions. Spruce bark was used as the base fuel – serving as a source of alkali metals (mainly K, little Na). The gases HCl and HBr were fed with the fluidization air at different proportions into the BFB unit. In total, six experiments were done. The fate of bromine and chlorine was evaluated by means of several measurements including: FTIR (flue gas measurement), a low-pressure impactor (size distribution and chemical composition of aerosol particles) and deposit probe sampling (deposit growth rate and chemical composition of the windward, 90° side and leeward deposits). It was shown that the addition of HBr or HCl greatly increased the release of alkali metals (K, Na) from the original fuel (spruce bark) during combustion. The promoting effect of HBr was more obvious than that of HCl. HBr was found more reactive towards alkali metals than HCl.

Deposit chemistry and initial corrosion during biomass combustion – The influence of excess O2 and sulphate injection

Corrosion of superheater tubes is a serious problem during combustion of fuels with a high content of chlorine, such as waste and certain biomasses. The alkali chlorides are released to the flue gas and may condense on the heat exchanger tubes forming corrosive, chloride‐rich deposits. In this work the effect of ammonium sulphate ((NH4)2SO4) injection on gaseous alkali chlorides, deposit chemistry and initial corrosion attack of superheater tubes during biomass combustion have been investigated. The investigation was carried out at three different sulphate injection rates (reference, low and high) and at three air excess ratios (λ = 1.1, 1.2 and 1.4). Short‐term exposures of Sanicro 28 specimens, using temperature controlled probes, were used for deposit collection and to study the initial corrosion attack.The results showed reduced concentrations of potassium chloride in the flue gas when injecting ammonium sulphate and in particular in combination with high air excess ratios. A decrease of chlorine was also observed in the deposit, but the concentrations did not always correlate to the flue gas measurements. In particular, it was evident that a subsequent sulphation occurred on the tube surface at low air excess ratios. Metallography revealed that sulphation reactions on the tube surface, rather than in the flue gas, had a detrimental effect on the initial corrosion attack. As a consequence, the corrosion attack correlated more clearly to the KCl(g) concentration in the flue gas than the chlorine content in the deposit.

Effects on a 50 MWth Circulating Fluidized-Bed Boiler Co-firing Animal Waste, Sludge, Residue Wood, Peat, and Forest Fuels

This work is a part of an effort to maximize the operational safety of a 50 MWth circulating fluidized-bed (CFB) boiler located in Perstorp, Sweden, co-firing animal waste, peat, waste wood, forest residues, and industrial sludge. An increase in the CFB boiler availability reduces the use of expensive fossil fuel (oil) in backup boilers during operational problems of the CFB boiler. The work includes a thorough mapping and analysis of the failure and preventive maintenance statistics, together with elemental analysis of boiler ash and deposits, flue gas, and fuel fractions. Correlations between boiler parameters and boiler availability are sought, and recommendations regarding boiler design and operation are made. An explicit description of the boiler is made to allow for the use of presented material as future reference material. It was observed that the failure frequency is especially high where (1) rapid chloride-rich windward deposit buildup is combined with (2) high construction material temperature and (3) windward soot blowing. In areas where one of these factors was absent, a more moderate material loss could be seen. The flue gas average elemental composition can be regarded as close to constant as it flows through the series of heat exchangers. Thus, the significant differences in deposit buildup of different flue gas cross-sections cannot be a result of changed average flue gas composition. The areas of the steam tubes suffering from rapid material loss are also exposed to high deposit rates. Downstream of a well-defined temperature threshold in the secondary superheater, neither material loss nor substantial deposit buildup could be seen. Tube deposits are dominated by Na, S, Ca, K, and P, but only Na, K, and S are enriched in the windward tube deposits relative to the fly ash bulk composition. The temperature of the flue gas is the major parameter governing the rate of deposit buildup in the boiler heat exchangers. Of the fuel nitrogen, 95 wt % leaves the process as N2(g). Fuel mix ash content analysis via a separate ashing of different fuel fractions by heating to 550°C does not reflect the ash content of the fuel mix correctly. The soot blowing angle of attack on the deposits should be regarded in areas with rapid deposit growth when boilers and soot blowers are designed to allow for efficient tube cleaning. The use of heterogeneous fuel in the boiler creates strong variations in fuel, flue gas, and particle composition and makes it increasingly important to have online measurements to be able to understand and control the furnace chemistry. The filter ash in the flue gas baghouse filter effectively sorbs HCl(g) and NH3(g) from the flue gas already without the addition of sorbents. Online flue gas measurement to control the furnace chemistry must therefore be installed upstream of the filter to enable accurate control. Also, a significantly larger filtration area can be installed in the baghouse filters with a slight increase in cost, to allow for efficient use of the ash as free of cost sorbent and lowered emission levels. Scanning electron microscopy analysis of the flue gas deposits shows that no pieces of ground bone, sand particles, or other relatively large flue gas particles contribute directly to the deposit buildup. White crystals rich in N and Cl, most likely ammonium chloride, precipitate downstream of the flue gas filter. The precipitation interferes with the dust emission measurement and forces a reduced usage of waste-derived fuels because of the exceedance of environmental limits. More expensive forest fuels are used to replace waste-derived fuels, resulting in a higher fuel cost.

Solar and pellet combisystem for apartment buildings: Heat losses and efficiency improvements of the pellet boiler

This paper is based on the analysis of the solar combisystem installed in a 4-storey apartment building in Sigulda, Latvia. The combisystem consists of: 42m2 of flat plate solar collectors, a 2.35m3 accumulation tank and a 100kW pellet boiler as the auxiliary heater. This paper focuses on the optimisation of the thermal performance of the pellet boiler.During laboratory tests on the 25kW pellet boiler, the influence of the supply ratio of the combustion air, the chemical and heat losses in the flue gases on the performance of the boiler was established. The results demonstrate the optimum thermal performance, CO emissions, chemical and heat losses, which are related to the amount of free oxygen (O2) in the flue gases.The results of the laboratory tests were then applied to optimise the operation of the 100kW pellet boiler. The flue gas measurements for the 100kW boiler were performed in order to identify the O2 concentration, CO emissions and flue gas temperature. The results showed that what is required to optimise performance is to reduce the amount of air supplied to the boiler’s combustion chamber. Changes were made to the boiler’s control algorithms to achieve the desired result.Additionally, boiler performance was improved by changing the location of the air intake point. Decreasing temperatures in the heat accumulation tank were achieved by making modifications to the boiler’s control algorithms.

Optimization Strategy of Boiler Send-Guide-Air Automatic Control Scheme

In this paper, we present an optimization control strategy for problems in conventional boilers send-guide-air automatic control system of power plant. We meet optimization of boiler send-guide-air automatic control scheme by means of improving air flow and oxygen content in flue gas measurement, revising control system structure, adopting fuzzy control algorithm, adding protection and other measures.

Research on ash-free sampling device and its application in the mercury testing of coal-fired flue gas

In this paper, an ash-free sampling device of coal-fired flue gas has been developed, including the U-shaped sampling probe, electric heating element and thermostat, sampling ports, porous ceramic filter, which can not only be used for low-ash flue gas sampling and measurement, but also be able to achieve high-ash flue gas measurement. The developed ash-free sampling device can work at a wide temperature range from 120 ∼ 650°C. It is adopted to conduct the field-testing at a coal-fired power station to measure mercury in the coal-fired derived flue gas, and the attained date are satisfactory and can reflect the actual power plant flue gas emissions level and speciation of mercury. The developed ash-free sampling device is with simple configuration and efficient function, providing an effective method and tool for mercury and other pollution emission measurement and their control.

주거용 화목난로의 대기오염 배출량 추정에 관한 연구

Recently the Korean government has tried to cut down the concentration by the Special Law for Air Quality Improvement. But the concentrations of have exceeded the air quality standard at most monitoring stations. Primary emitted from various sources and emission data have large uncertainty. The biomass burning is one of the major sources of emission. The biomass burning is composed of wood stove usage, meat cooking and agricultural combustion etc.. Activity data and emission factors for the biomass burning are limited, and it is hard to calculate the air pollution emissions from these sources. In this study, we tried to estimate the air pollution emission from residential wood stove usage. The number of total wood stoves is estimated by the survey of wood stove manufacturer. And air pollution emission factors for the wood stove are investigated using the flue gas measurement by U.S. EPA particulate test method (Method 5G). As the results, the and CO emission factors of wood stove are estimated as 7.7 g/kg-wood and 78.8 g/kg-wood respectively. The annual and CO emissions from wood stove are calculated as 1,200~3,600 ton/year and 12,600~36,400 ton/year in Korea. It is confirmed that wood stove is the one of major sources of biomass burning, and the survey for activity data and the measurement for emission factors are needed for reducing the uncertainty of these emission data.

Temporal variation and impact of wood smoke pollution on a residential area in southern Germany

This paper is a continuation of our previous publication (Bari, M.A., Baumbach, G., Kuch, B., Scheffknecht, G., 2009. Wood smoke as a source of particle-phase organic compounds in residential areas. Atmospheric Environment 43, 4722–4732) and describes a detailed characterisation of different particle-phase wood smoke tracer compounds in order to find out the impact of wood-fired heating on ambient PM 10 pollution in a residential area near Stuttgart in southern Germany. The results from previous flue gas measurements help distinguishing different tracer compounds in ambient PM 10 samples. In the residential area, significant amounts of hardwood markers (syringaldehyde, acetosyringone, propionylsyringol, sinapylaldehyde) and low concentrations of softwood markers (vanillin, acetovanillone, coniferyldehyde, dehydroabietic acid, retene) were found in the ambient air. The general wood combustion markers Levoglucosan, mannosan and galactosan were detected in high concentrations in all particle-phase PM 10 samples. To find out the size distribution of ambient particles, cascade impactor measurements were carried out. It was found that more than 70% of particulate matter was in the particle diameter of less than 1 μm. Using emission ratio of levoglucosan to PM 10, it can be demonstrated that during winter months 59% of ambient PM 10 pollution could be attributed to residential wood-fired heating.

Evaluation of the potential air pollution from fuel combustion in industrial boilers in Kocaeli, Turkey

The potential air pollution from the fuel combustion in the uncontrolled industrial boilers in Kocaeli, the most industrialized area in Turkey, was evaluated by using the emission factors determined based on the flue gas measurements conducted at over 100 industrial plants in the area. The emissions were modeled for conventional combustion pollutants by a Gaussian dispersion model to determine the possible contribution of these emissions to the background air pollution. Results show that the emission factors calculated for the pollutants including CO, SO 2, NO 2, PM and formaldehyde are comparable with those given in literature for other countries. On the other hand, the emission factors are laid in a wide range due to the presence of many factors affecting the emission of the pollutants, including the characteristics of fuel, boiler and combustion practice. The Gaussian air dispersion model applied by using the emission factors indicated that the effect of the industrial fuel combustion on the background air pollution was low for the conventional combustion pollutants despite the high number of industrial boilers in the area, suggesting the significant contribution of other sources, i.e. residential heating and mobile sources.

Evaluation of on-line flue gas measurements by MISiCFET and metal-oxide sensors in boilers

Metal insulator silicon carbide field-effect transistor sensors, metal-oxide sensors, and a linear Lambda sensor in an electronic nose was used to measure on-line in hot flue gases from a boiler. Flue gas from a 100-MW pellets-fuelled boiler has been used to feed the experimental setup. Several reference instruments, which measure the flue gases in parallel to the sensor array, are connected to the electronic nose. Data was collected during six weeks and then evaluated. Using principal component analysis as the data evaluation method, different operating modes for the boiler have been identified in the data set. The different modes could be described in terms of high or low O/sub 2/ and CO concentration. Furthermore, we have shown that it seems possible to use a sensor array to determine the operating mode of the boiler and, by partial least-squares models, measure the CO concentration when the boiler operates in its optimum mode.