Directional sensitivity of differential pressure sensors of gas velocity used in manual gravimetric measurements of dust emissions from stationary sources / Czułość kierunkowa różnicowo-ciśnieniowych czujników prędkości gazu stosowanych w manualnych pomiarach grawimetrycznych emisji zanieczyszczeń pyłowych ze źródeł stacjonarnych

Abstract

Measurements of the amount of dust emitted to the atmosphere together with fl ue gases (after cleaning them) are brought to the determination of the emission mass concentration of dust in the gas s and/or the so-called dust emission rate E (being the fl ux of dust mass) -in the fl ow conduit (duct or stack) at the outlet to the atmosphere. Both of these parameters are the basis for assessment -in various aspects -of noxiousness of the source of dust pollutant emissions.The key concentration of dust s is determined by the measurement. The emission rate is calculated according to the formula E = sV · , where V · denotes the volumetric gas fl ow rate in the conduit. This fl ow rate is calculated according to the relationship V · = w -A, in which A is the area of the conduit cross--section and w -is the average gas velocity in the direction of the duct axis. The latter -by means of a suitable averaging -is determined on the basis of the point profi le of a x i a l velocity w 0 , which is found by measuring. A frequent method and at the same time a reference method of measuring the dust concentration s is the manual gravimetric method based on collecting a dust carrying gas sample at representative points in the duct cross-section and determining the concentration of dust in it. Measurements of distribution of gas axial velocity in the duct accompanying this method are often performed with differential pressure sensors (EN 2001, PN-EN 2007, PN 1994. The classical in use are independent anemometric systems which in the manual version contain Pitot tubes. There are also cases in which gravimetric dust samplers are provided with Pitot tubes mounted on the dust sampling probe near to the aspiration nozzle. In some other -rarer -solutions, gravimetric dust samplers contain a special so-called zero dust sampling probe with the function of a velocity sensor.Known from the rules of fl uid mechanics, the principles of independent measurement of gas point velocity with use of a differential pressure sensor are provided e.g. in the ISO standard (2013) and its counterparts EN ISO (2013) and PN-EN ISO (2013), and also in another ISO standard (1994). They mention the necessity of keeping the practical alignment of a sensor with a direction of gas fl ow. The ideal situation occurs when the gas fl ow at the measuring point inside the Keywords: directional sensitivity, differential pressure sensors of gas velocity, fl ue gas velocity measurements, dust emission measurements, Pitot tubes, zero pressure dust sampling probe.Abstract: Manual measurements of distribution of gas velocity in conduits of fl ue gas installations using systems with differential pressure sensors of velocity are often performed for the requirements of determining emissions of dust pollutants from industrial process plants to the atmosphere. The aim is to determine an axial velocity profi le. Flows in measuring sections are not always coaxial along the run of the duct; they are characterized by different directions of the velocity vector at various measuring poin...

Metrology and Measurement Systems

“…1d), because of large diameters of measuring holes, which are practically the same size as the inner diameters of pressure tubes transmitting a pressure signal to the measuring device. This feature makes these probes the most commonly employed in measurements of dust emissions [9]. Although the manufacturing technology of these probes is very simple, their aerodynamic characteristics are very sensitive to technological nuances [7].…”

Estimation of uncertainty of mean velocity of flue gas in a conduit as determined by the traverse method within the gravimetric measurement of particulate concentration

“…A method has been developed to take account of the characteristic profile decay in the vicinity of a wall and in corners during the measurement of mean velocity [14][15][16]6]. There are descriptions of point velocity measurements carried out by means of a zeropressure dust probe with an anemometric function [17], as well as the estimation of error of axial velocity measured with the use of pressure-type probes for actual local gas flow deviations in a conduit [18]. The quantitative assessment of some other types of distinctive errors in point velocity measurements might be adopted from the standard [19] concerned with the independent, accurate measurement of volumetric gas flow rates in uniform flows.…”