Non-isokinetic Sampling Research Articles

Development of a sampling probe with a small non-isokinetic sampling error in variable flow velocity environments

The flow velocity of exhaust gas from an industrial stack varies from facility to facility and can easily change over time, even in a stack. To accurately measure the concentration of fine particles such as PM10 or PM2.5 emitted in such environments, the conditions for isokinetic sampling must be satisfied. In this study, a novel sampling probe that generates a small error in particle concentration in variable flow velocity environments was developed, even though isokinetic sampling was not performed. The mass distributions obtained by isokinetic sampling using a conventional sampling probe at a flow velocity of 0–6 m/s were compared with those measured using the developed probe to verify the performance of the proposed probe. It was confirmed that the two mass distributions are similar within an error of 5% under all flow velocity conditions. The mass concentrations estimated through theoretical correction considering sampling loss or gain in non-isokinetic environments were also compared, and the distributions were quite similar within approximately 5%. This verifies that the proposed sampling probe can perform nearly perfect sampling of fine particles without changing the sampling flow rates, with minimal particle under- or overestimation caused by non-isokinetic sampling for variable flow velocity conditions.Copyright © 2022 American Association for Aerosol Research

Development of a Sampling Probe with a Small Non-Isokinetic Sampling Error in Variable Flow Velocity Environments

Development of a Sampling Probe with a Small Non-Isokinetic Sampling Error in Variable Flow Velocity Environments

Performance Evaluation of Throatless Gasifier Using Pine Needles as a Feedstock for Power Generation

This paper deals with the performance evaluation of a throatless gasifier TG-SI-10E. Evaluation of the throatless gasifier was done in three streams, which were the thermal, design and economic aspects. It was tested with pine needles, derived from the Himalayan chir pine (Pinus roxburghii). A non-isokinetic sampling technique was used for measuring the tar and dust contents. The carbon dioxide and carbon monoxide emission at the exhaust of engine was in the range of 12.8% and 0.1-0.5% respectively. The maximum temperature of producer gas measured at the outlet of the gasifier was 505 °C. The specific biomass consumption rate of pine needles was calculated to be 1.595 kg/kWh (electrical). Specific gasification rate for the given design was found to be 107 kg/m2h. Economic evaluation was based on direct tax incidence.

Comparison of real time suspended sediment transport measurements in river environment by LISST instruments in stationary and moving operation mode

Suspended sediment and particle size measurements were in this study performed with two instruments based on laser diffraction. The measurements were conducted in the river Danube during a 1-year flood, which enabled measurements in a large scale and under conditions with high sediment load. The aim of this study was to compare LISST-SL stationary measurements with LISST-SL moving measurements to gain knowledge for extensive field surveys of large areas. The moving measurements were performed in four different depths along a transect and compared with stationary measurements in five verticals in the same depths. The results showed that the measured suspended sediment concentrations are smaller for the moving measurements compared to the stationary measurements. In addition thus the d50 was smaller for the moving measurements, which is an indicator for the phenomena of non-isokinetic sampling. A comparison of the pump speed of the two operation modes proofed that during LISST-SL moving measurements a non-isokinetic sampling effect occurred. Hence, a suction effect happened, resulting in an underestimation of particles >63µm. Beside the LISST-SL simultaneously a LISST-STX was used during the field survey to investigate the behavior and the results of the instrument under conditions where it is originally not designed for. However, the predominant suspended sediment concentrations in the river influenced the measurements and thus multiple scattering occurred. As a consequence the measurements of the suspended sediment concentrations showed lower values for the measured suspended sediment concentrations compared to the LISST-SL stationary measurements. It could also be seen that due to the high amount of fine particles, which were transported during the flood event, a re-scattering of light occurred also in case of measurements where the value for the optical transmission was with 0.38 above the standardized used limit of 0.3.

Mercury capture by boiler modifications with sub-bituminous coals

The extent of mercury (Hg) emissions at a particular coal-fired boiler is unit-specific and determined by factors that include the type of coal fired, boiler operating conditions, and the amount of Hg removed at the boiler back-end by the pollution control devices. Mercury speciation, adsorption and removal in the boiler are affected by parameters such as the flue gas and fly ash characteristics, and back-end boiler configuration/operation. Various studies have reported that boiler operating conditions can be optimized to enhance the “naturally” occurring Hg capture in coal-fired boilers.A study was carried out to investigate the impact of boiler operating conditions on Hg emissions at a full-scale coal-fired power plant. Testing was performed at a 810MW coal-fired power plant firing a Northern Powder River Basin (PRB) coal, and equipped with a low-NOx system and a wet flue gas desulfurization (FGD) system for particulate and sulfur dioxide (SO2) control. Speciated (total and elemental, Hg0) Hg measurements and analytical procedures were performed according to the Ontario Hydro Method (OHM)/ASTM D6784-02 Method. OHM measurements were conducted at the air preheater (APH) inlet and the stack. Mercury emissions were also continuously monitored using single-point, non-isokinetic sampling with semi-continuous emissions monitors (SCEM). Readings from these analyzers were used for guidance during boiler control setting manipulations. Individual semi-continuous sampling modules were installed at four single-point locations along the convective pass: APH inlet, FGD inlet, FGD outlet and the stack.The test results obtained in this study showed the benefit of boiler modifications for Hg control and the extent to which the “natural” Hg control could be influenced. Parametric testing indicated a modest, but inconsistent improvement in the stack Hg (HgT) emissions at reduced excess oxygen. This was probably due to the fact that the fly ash unburned carbon levels were very low (less than 1.0%). Modifications to the low-NOx system over-fire registers, burner tilt and FGD liquid-to-gas (L/G) ratio resulted in stack HgT reductions in excess of 25%. The FGD L/G ratio manipulations also resulted in an improvement in oxidized mercury removal across the FGD. However, none of the test data suggested any reduction in Hg0 across the FGD. The combination of optimal boiler control settings for reduced Hg emission operation resulted in a 34.5% reduction in HgT at the stack.

Sediment Monitoring Bias by Automatic Sampler in Comparison with Large Volume Sampling for Parking Lot Runoff

A field study was conducted to assess biases of suspended sediment concentration (SSC) analyses (ASTM Standard D3977-97) performed on discrete samples obtained by automatic sampler in comparison with actual sediment concentrations from large volume sampling. Research results indicate that the biases attributed to the monitoring of sediment event mean concentration (EMC) and median particle size in parking lot runoff by automated samplers (nonisokinetic) were minimal. Large volume samples (∼15,000 L) of the first-flush event runoff were taken from a storm-water sewer system for eighteen storm events over two years. The intent was to obtain a complete portion of a storm to accurately determine EMCs and particle size distributions (PSDs). Concurrently, flow-weighted discrete samples were obtained by automatic samplers for the same portion of the events. Thus, characteristics of sediments from a whole-storm sample were compared with those of subsamples obtained by an automatic sampler using nonisokinetic sampling. SSCs and PSDs were compared for the two respective field sampling methods. The two methods showed a strong correlation for median sediment EMCs (R2=0.98, n=18). Biases to particle size distributions were found to be both for the large particles (>75–150 μm) and smaller fines (<25 μm). Specific sediment size fractions captured by the large volume sampling and automatic sampler were not significantly different (α=0.05) for D50, which = 58 and 46 μm, respectively.

Effect of sampling in the evaluation of particle size distribution in nanoaerosols

The isokinetic sampling procedure is adopted to avoid errors in important parameters (particle concentration, collection efficiency, etc.) in aerosol studies. To attain isokinecity in a given sampling can be costly or difficult to control. This study aims at evaluating the behavior of nanometric particles in the laminar aerosol flow for various conditions of non-isokinetic sampling. Polydispersed sodium chloride (NaCl) particles dispersed in an extra pure air current were used as a test aerosol. The analysis was based on comparisons of size distribution measurements of the particles collected using different sampling nozzles and v 1/ v 2 ratios (i.e. between the velocity in the main duct, v 1, and at the nozzle, v 2). The results show that the size distribution was an independent ratio, for a given sampling nozzle. Also, the sampling size distribution did not depend on the ratio between the diameter of the sampling nozzle and that of the main flow duct in the system. Based on these findings, it can be concluded that, within the particle size range of 12.0–130.0 nm, duct Re < 600, duct/sampling velocity ratio ( v 1/ v 2) ranging from 0.28 to 6.25 and small particle Stokes number (St') ranging from 2.7 × 10 − 7 to 1.1 × 10 − 5, the effects of non-isokinetic sampling at the particle size distribution are negligible.

Solid Flux in a Circulating Fluidized Bed Riser

This work is aimed at exploring the flow structure of a gas–solid suspension in a circulating fluidized bed (CFB) riser. A cold model of a CFB 6.2 m high and 0.152 m diameter was used, with sand particles of 200 μm volume mean diameter and of density 2646 kg m−3 (i.e. Geldart B particle). A non-isokinetic sampling technique was used to explore the flow structure at five angular and three axial positions along the riser. Although a good symmetric profile of solid flux around the riser was found over a wide range of operating conditions, non-symmetric profiles were also observed. Some distinctive features of the radial profile of solid i.e. the existence of the peaks located around radial positions r/RT = ± 0.6 were found. Although some researchers attributed this peculiarity to the behaviour of Geldart A powder, in this work as well as in some others in the literature, this feature was found for sand particles belonging to Geldart B class.

Correction of non-isokinetic sampling of wetness measurement for wet steam flow

A mathematical model for predicting the behavior of wet steam flow in the vicinity of the intake head of the sampling probe is presented. The vapor flow field and droplet trajectory in the calculated region have been obtained. The errors caused by non-isokinetic sampling for different conditions have been analyzed and the analytical results would provide useful data for the design and application of a heating method-based wetness measurement probe in practice.

On-line Measurement of Fog Droplets in Wet Scrubbing Processes

For formation can cause severe corrosion and emission problems in industrial wet scrubbing processes, such as flue gas cleaning plants. Detailed knowledge on fog characteristics supports the technical solution of emerging problems. As liquid droplets react sensitivively to changes in temperature and pressure most particle size measurement techniques are not applicable. The three-wavelength extinction technique is a non-interfering optical method which allows in situ measurements. However, it needs intermediate reference measurements without droplets which makes it difficult to use it in most industrial cases. For this reason, an optical access in a bypass has been developed and tested. The bypass measurements show good agreement to parallely made in situ measurements. The effects of non-isokinetic and non-isothermal sampling have been studied. It was found that the orientation of the bypass with respect to gravity has an unexpected impact on the results. The system can measure within a range of particle concentrations from 10 5 to 10 8 droplets per cm 3 and droplet diameters from 0.2 to 4 μm.

A preliminary study into the local solids fluxes in a downer reactor

A non-isokinetic sampling method was used to study the effects of gas velocity, solids circulation rate and axial and radial positions on the local solids flux in a gas–solids downer fluidized bed. The radial profiles of solids flux are highly dependent on the axial position. The local solids flux is also dependent on the overall solids circulation rate but not dependent on the gas velocity. The solids flux profiles in the downer were also found to be quite different from those reported in the riser.

Comparative study of non-isokinetic sampling probes for solids flux measurement in circulating fluidized beds

Non-isokinetic sampling probes are used to study the solids flux profiles in circulating fluidized beds (CFB). The circulating solid flowrate (and its distribution) is one of the most important parameters of industrial units. However, little work has been done on the comparison of sampling probes. Three different types of non-isokinetic sampling probes (90° bend, small radius with circular opening and large radius with square opening) were studied and compared in a rectangular cross-section pilotscale CFB column. The net solids flux profiles are obtained from the difference between upward and downward fluxes and averaged over the cross-section of the column. The mean net solid flux is then compared to the overall circulating solids flowrate. The results obtained show that the non-isokinetic probe yields accurate solids circulation values. Best results were obtained using the ‘large radius’ probe.

Horizontal Elutriator Preliminary Test Results under Nonstill Air Conditions

Recently, a high-volume horizontal elutriator with a flared inlet was developed to monitor inhalable particulates in the ambient air. Preliminary results of a study to evaluate the performance of the horizontal elutriator under nonstill air conditions are presented. Collection efficiency data were obtained for monodisperse aerosols with particle sizes of 4.0, 9.25, 20.0, and 30.7 um aerodynamic diam. Experimental results indicate that the device does not meet the established performance criteria. The main cause of nonperformance is prrobably a combination of exterior turbulent propagation into the initial part of the elutriator, nonisokinetic sampling conditions and particle diffusion.

Portable Sampler for Microorganisms in Incinerator Stack Emissions

To obtain reliable information on viable microbial cells in incinerator stack emissions, a new sampling device has been developed that will concentrate microorganisms from large quantities of stack emissions into a small quantity of 0.067 m phosphate buffer. The simple, portable sampler provides a method for qualitative, nonisokinetic sampling, adjustable to isokinetic conditions that will yield quantitative results.

Portable sampler for microorganisms in incinerator stack emissions.

To obtain reliable information on viable microbial cells in incinerator stack emissions, a new sampling device has been developed that will concentrate microorganisms from large quantities of stack emissions into a small quantity of 0.067 m phosphate buffer. The simple, portable sampler provides a method for qualitative, nonisokinetic sampling, adjustable to isokinetic conditions that will yield quantitative results.