Heated Sampling Line Research Articles

Quantification of PAH concentrations in premixed turbulent flames crossing the soot inception limit

Soot formation in combustors is a complex process comprising highly intermittent interactions between physical and chemical processes across a wide range of time-scales and the influence of turbulence on the soot inception process remains substantially conjectural. The current study quantifies the impact of flame temperature, equivalence ratio, and strain rate on PAH concentrations in premixed turbulent ethylene flames crossing the soot inception limit using a back–to–burnt opposed jet configuration that provides accurate control of flow parameters. The upper nozzle features fractal grid generated turbulence and provides premixed ethylene/air mixtures with equivalence ratios 1.7 ≤ ϕ ≤ 2.2 with flames stabilised against well-defined lower nozzle hot combustion products (HCP) from N2 diluted H2 flames. The flame structures are initially analysed using PAH/CH2O/PLIF and elastic light scattering with gas chromatography–mass spectrometry (GC–MS) subsequently used to quantify PAH samples from inside the turbulent flame brush. A combination of hot nitrogen dilution and a heated sampling line is used to minimise PAH and particle losses during sample extraction. The work quantifies the growth in PAH concentrations across the soot inception limit and shows that the rate of strain exerts a dominant influence. It is further shown, through centrifuging of samples, that soot particles contain large amounts of PAHs (e.g. benzo[a]pyrene) with EDX used to quantify the growth in carbon deposition.

A Test Stand Study on the Volatile Emissions of a Passenger Car Brake Assembly

Brake-related airborne particulate matter contributes to urban emissions in the transport sector. Recent research demonstrated a clear dependence of the number of ultra-fine particles on the disc brake temperature. Above the so-called transition temperature, the number of ultra-fine particles increases dramatically (several magnitudes). As for exhaust emissions, part of the emissions released during braking can be in the volatile fraction. For this reason, a disc brake test stand specifically designed for aerosol research was equipped with three different aerosol sampling instruments: (i) a standard cascade impactor, (ii) a cascade impactor operating at high temperature with a heated sampling line, and (iii) a standard cascade impactor with a thermodenuder. Tests with a brake assembly representative of European passenger vehicles were executed, and the concentration of released airborne particles was determined. The results showed a decrease by several magnitudes in the concentration (in the size range of below 200 nm) using the cascade impactor operating at 180 °C with the sampling line heated to 200 °C. A further decrease in the concentration of airborne particles with size fractions below 200 nm was measured using a standard cascade impactor with a thermodenuder heated to 300 °C.

Rich biomass combustion: Gaseous and particle number emissions

The cone calorimeter is a standard test method for material behaviour in fires. The principle of the cone calorimeter is to use an electric radiant heater to raise the temperature of the combustion zone and ignite the fuel. 35 kW/m2 was used in the present work, as this has been previously shown to be sufficient to establish fully developed combustion of biomass materials such as wood. As one of the main fire loads is wood and wood is the dominant biomass for energy generation, it is reasonable to use the cone calorimeter to characterize the combustion of biomass on a small scale and pine was used in the present work. The cone calorimeter was used in the controlled atmosphere mode with an enclosure around the test biomass that enabled the air flow for biomass combustion to be controlled at 19.2 g/m2s, which corresponds to a combustion heat release rate HRR of 57 kW/m2, assuming all the oxygen in the air is consumed. This air flow will be shown to generate rich combustion at a metered equivalence ratio, Ø, of about 2, which is comparable with the first gasification stage of biomass two stage burning in log burners and pellet burners, where air is added downstream of the gasification stage of biomass combustion. Soot emissions are generated in this rich gasification stage burning and potentially oxidized in the oxidation second stage burning. The rich burning gasification zone particulate emissions were analysed for number size distribution using the Cambustion DMS 500 particle size analyser. The exit from the controlled combustion zone was extended in a 75 mm diameter chimney where a mean gas sample was taken. A heated Gasmet FTIR was used for gas composition analysis, using a heated sample line, filter and pump from the sample point to the analyser. The particles emitted were sampled after the second stage combustion from entrained air into the chimney discharge gases into a dilution tunnel with a fixed gas flow rate of 24 l/s, which gave a dilution ratio of the primary combustion gases of 150/1 which is required for nano-particle size analysis. A Cambustion DMS500 electrical mobility particle number and size instrument was used with size resolution from 5 to 1000 nm. The present results show that in the rich burning first stage chimney sample there were very high levels of 20 nm nanoparticles, 1 × 1010/cc, and an accumulation mode peak at 200 nm. The presence of the 20 nm particles makes the particulate emissions extremely toxic.

The development of seasonal emission factors from a Canadian commercial laying hen facility

Pollutants emitted from poultry housing facilities are a concern from a human health, bird welfare, and environmental perspective. Development of emission factors for these aerial pollutants is difficult due to variable climatic conditions, the number and type of poultry, and the wide range of management practices used. To address these concerns, a study was conducted to develop emission factors for ammonia and particulate matter over a period of one year from a commercial poultry laying hen facility in Wellington County, Ontario, Canada.Instruments housed inside an on-site mobile trailer were used to monitor in-house concentrations of ammonia and size fractionated particulate matter via a heated sample line. Along with a ventilation profile, emission factors were developed for the facility. Average emissions of 19.53 ± 19.97, 2.55 ± 2.10, and 1.10 ± 1.52 g day−1 AU−1 (where AU is defined as an animal unit equivalent to 500 kg live mass) for ammonia, PM10, PM2.5, respectively, were observed. All emissions peaked during the winter months, with the exception of PM2.5 which increased in the summer.

Implementation of proton transfer reaction‐mass spectrometry (PTR‐MS) for advanced bioprocess monitoring

We report on the implementation of proton transfer reaction-mass spectrometry (PTR-MS) technology for on-line monitoring of volatile organic compounds (VOCs) in the off-gas of bioreactors. The main part of the work was focused on the development of an interface between the bioreactor and an analyzer suitable for continuous sampling of VOCs emanating from the bioprocess. The permanently heated sampling line with an inert surface avoids condensation and interaction of volatiles during transfer to the PTR-MS. The interface is equipped with a sterile sinter filter unit directly connected to the bioreactor headspace, a condensate trap, and a series of valves allowing for dilution of the headspace gas, in-process calibration, and multiport operation. To assess the aptitude of the entire system, a case study was conducted comprising three identical cultivations with a recombinant E. coli strain, and the volatiles produced in the course of the experiments were monitored with the PTR-MS. The high reproducibility of the measurements proved that the established sampling interface allows for reproducible transfer of volatiles from the headspace to the PTR-MS analyzer. The set of volatile compounds monitored comprises metabolites of different pathways with diverse functions in cell physiology but also volatiles from the process matrix. The trends of individual compounds showed diverse patterns. The recorded signal levels covered a dynamic range of more than five orders of magnitude. It was possible to assign specific volatile compounds to distinctive events in the bioprocess. The presented results clearly show that PTR-MS was successfully implemented as a powerful bioprocess-monitoring tool and that access to volatiles emitted by the cells opens promising perspectives in terms of advanced process control.

Characterizing a Quantum Cascade Tunable Infrared Laser Differential Absorption Spectrometer (QC-TILDAS) for measurements of atmospheric ammonia

Abstract. A compact, fast-response Quantum Cascade Tunable Infrared Laser Differential Absorption Spectrometer (QC-TILDAS) for measurements of ammonia (NH3) has been evaluated under both laboratory and field conditions. Absorption of radiation from a pulsed, thermoelectrically cooled QC laser occurs at reduced pressure in a 0.5 L multiple pass absorption cell with an effective path length of 76 m. Detection is achieved using a thermoelectrically-cooled Mercury Cadmium Telluride (HgCdTe) infrared detector. A novel sampling inlet was used, consisting of a short, heated, quartz tube with a hydrophobic coating to minimize the adsorption of NH3 to surfaces. The inlet contains a critical orifice that reduces the pressure, a virtual impactor for separation of particles, and additional ports for delivering NH3-free background air and calibration gas standards. The level of noise in this instrument has been found to be 0.23 ppb at 1 Hz. The sampling technique has been compared to the results of a conventional lead salt Tunable Diode Laser Absorption Spectrometer (TDLAS) during a laboratory intercomparison. The effect of humidity and heat on the surface interaction of NH3 with sample tubing was investigated at mixing ratios ranging from 30–1000 ppb. Humidity was seen to worsen the NH3 time response and considerable improvement was observed when using a heated sampling line. A field intercomparison of the QC-TILDAS with a modified Thermo 42CTL chemiluminescence-based analyzer was also performed at Environment Canada's Centre for Atmospheric Research Experiments (CARE) in the rural town of Egbert, ON between May–July 2008. Background tests and calibrations using two different permeation tube sources and an NH3 gas cylinder were regularly carried out throughout the study. Results indicate a very good correlation at 1 min time resolution (R2 = 0.93) between the two instruments at the beginning of the study, when regular background subtraction was applied to the QC-TILDAS. An overall good correlation of R2 = 0.85 was obtained over the entire two month data set, where the majority of the spread can be attributed to differences in inlet design and background subtraction methods.

Effect of Biofuels on Nanoparticle Emissions from Spark- and Compression-ignited Single-cylinder Engines with Same Exhaust Displacement Volume

Nanosized particles emitted from automotive engines continue to attract concern because of their adverse health effects and their impact on the environment. Automotive engines are a major source of fine and ultrafine particles emitted into the atmosphere. Through stricter emission regulations and the introduction of advanced technologies, the specific particulate mass emissions (in g/km and g/kWh) from internal combustion engines have decreased by about 1 order of magnitude since the 1980s. However, the number concentration of nanoparticles (No./m3) emitted from internal combustion engines may continue to increase considerably and has recently attracted the attention of the Particle Measurement Programme (PMP). This program is intended to evaluate engine nanoparticle measurement systems for use in future emission regulations. In the study reported in this paper, two latest-generation engines, one spark-ignited and the other compression-ignited, were used for a comparison of the particulate emission characteristics, including number density. Both engines were single-cylinder with the same displacement volume of 500 cm3, and neither included after-treatment traps or catalytic converters. Test fuels used for the study were: gasoline and E85 (mixture of 85% ethanol and 15% gasoline, sometimes called gasohol) for the spark-ignited engine having a compression ratio of 10; and ultralow sulfur diesel (ULSD) and BD100 (100% biodiesel, i.e. soybean methyl ester) for the compression-ignited engine having a compression ratio of 15. A fast-response particle spectrometer (DMS500) with heated sample line was used for continuous measurement of the particle size and number distribution in the size range of 5−1000 nm (aerodynamic diameter). The experimental results showed that particle number peaked within the range of 10−300 nm under all engine operating conditions, regardless of engine combustion type. An observed shift toward larger particle size with increasing engine load could be explained by particle coagulation. The effect of the different fuels on nanoparticle size distributions was dependent on the engine type (spark-ignition or compression-ignition).

Volatile metal species in coal combustion flue gas.

Metals are released in effluents of most of combustion processes and are under intensive regulations. To improve our knowledge of combustion process and their resulting emission of metal to the atmosphere, we have developed an approach allowing usto distinguish between gaseous and particulate state of the elements emitted. This study was conducted on the emission of volatile metallic species emitted from a coal combustion plant where low/medium volatile coal (high-grade ash) was burnt. The occurrence of volatile metal species emission was investigated by cryofocusing sampling procedure and detection using low-temperature packed-column gas chromatography coupled with inductively coupled plasma-mass spectrometry as multielement detector (LT-GC/ICP-MS). Samples were collected in the stack through the routine heated sampling line of the plant downstream from the electrostatic precipitator. The gaseous samples were trapped with a cryogenic device and analyzed by LT-GC/ICP-MS. During the combustion process, seven volatile metal species were detected: three for Se, one for Sn, two for Hg, and one for Cu. Thermodynamic calculations and experimental metal species spiking experiments suggest that the following volatile metal species are present in the flue gas during the combustion process: COSe, CSSe, CSe2, SeCl2, Hg0, HgCl2, CuO-CuSO4 or CuSO4 x H2O, and SnO2 or SnCl2. The quantification of volatile species was compared to results traditionally obtained by standardized impinger-based sampling and analysis techniques recommended for flue gas combustion characterization. Results showed that concentrations obtained with the standard impinger approach are at least 10 times higher than obtained with cryogenic sampling, suggesting the trapping microaerosols in the traditional methods. Total metal concentrations in particles are also reported and discussed.

Continuous Monitoring of Toxic Metals in Gas Flows Using Direct-Current Plasma Excited Atomic Absorption Spectroscopy

A measurement apparatus employing direct current (dc) plasma excited atomic absorption spectroscopy was developed and demonstrated for continuous measurement of toxic metals in process gases. Process gas is continuously sampled along a heated sample line. Metal compounds contained in the gas are thermally decomposed by mixing the gas with a plasma jet produced with a dc nitrogen plasma torch. Transmission of monochromatic light is measured through the gas jet, and absorbance caused by metal atoms is distinguished from the background by means of the Zeeman effect. The metal concentration in the sample gas is calculated from the measured absorbance with the known dilution and decomposition factors taken into account. The detection limits of the current prototype are 0.04 mg/m3 for cadmium and 0.4 mg/m3 for lead. The measurement accuracy is better than 20%, and the maximum measurement rate is about 100 values per minute. The instrument was designed to withstand wet, corrosive, and particulate-laden flue gases at temperatures up to 1100 °C. The instrument can also be used, after minor modification, for measurements at pressurized conditions. The performance of the instrument was demonstrated in connection with a real fluidized bed combustor.

An innovative carbon-atom-balance-based method for diesel particulate measurement

This paper describes an innovative carbon-atom-balance-based method for diesel particulate measurement using a single non-dispersive infrared CO2 sensor. The diesel particulate sampler (DPS) uses two integrated steps of operation, i.e. collection and analysis of diesel particulate. In the collection operation, the diesel exhaust is channelled through a heated sampling line to a quartz filter where soot particulates, unburned hydrocarbons, water vapour, etc are trapped. Upon completion of particulate collection, the DPS system is isolated from the surroundings. This is followed by an analysis of the diesel-particulate sample by either one of two analysis modes, namely, the regular and ramp modes. In the regular mode, the quartz filter is heated at a constant temperature for a defined dwelling period. Multiple sessions of heating at constant temperatures with individual dwelling periods are allowed for each analysis. In the ramp mode, the temperature controller is programmed to achieve a specified heating rate. The lowest possible rate is 2 °C min-1. Some preliminary results, in terms of mass concentrations of particulates, were obtained from engine emission sampling using this DPS system.