ONLINE DEVICE AND METHOD FOR OPTICALLY MEASURING FLY ASH PARTICULATE IN INDUSTRIAL STACK EMISSIONS INDEPENDENT OF MOISTURE TECHNICAL FIELD

[0001] The present invention generally relates to opacity monitoring devices and methods. The present invention is additionally related to devices for measuring industrial stack emissions. The present invention also relates to optical opacity monitoring devices and methods. The present invention in particular relates to an online device and method for optically measuring fly ash particulate in industrial stack emissions independent of moisture.

BACKGROUND OF THE INVENTION [0002] Opacity monitors based on optical extinction and other scattering based instruments are well known in the art for stack dust monitoring. Typically, extinction-based measurements are preferred for high dust loading applications and scattering based instruments are preferred for low dust loading applications. Both extinction and scattering are particularly advantageous as measured intensities at the detector are insensitive to the surface morphology or the type of aerosol. [0003] Majority of conventional dust-monitoring instruments deployed in-situ are insensitive to the type of aerosol measured, enabling it to be applied across industries. However, the output of the optical monitoring systems for stacks downstream of wet-scrubbers are influenced by the moisture. Mist eliminators are employed to eliminate the mist/moisture, to limit the carryover of moisture, droplet carryover ranging from 0.02 to 3.0 g/acf (0.7 to 106 g/m3) (Marot, 1982). In such systems, even for a well-designed system with high removal efficiency, the carry-over is of the order of 50 to 100 mg/m .

[0004] With the standards for PM emission limitations across the world require the value to be maintained above 50 to 100 mg/m ³ , water carryover has not yet been considered as a problem in monitoring the dust. However, with the growing importance to health and climate, new standards requiring lower dust limits are introduced across the world.

[0005] With the implementation of new standards and regulations for emission limits, there is a high need for devices and methods for regulating and maintaining the lower dust limits across the industries. The prior art continuous emission monitoring systems (CEMS) are unable to indicate and measure the true value of emissions due to the interference of the droplets/water aerosol along with other PM emissions. For example, an optical measurement system, both extinction and forward scattering are unable to register the moisture carryover as reportable PM emission. Also, sensors using the triboelectric principle report error data due to changes in the dielectric constant of water aerosol as opposed to fly ash.

[0006] In one embodiment of the prior art, Durag (Model No. DR820F) has proposed an extractive solution, where a flue gas sample is extracted and heated before using optical extinction for measurement. Such a prior art solution is prone to errors due to sampling and dilution. Currently, there are no in-situ real time measurement techniques that can measure the fly ash concentration insensitive of water carryover. In-situ measurements are preferred due to lower cost and avoidance of isokinetic sampling requirements; however, the prior art solutions are error some and are not accurate, particularly at stack velocities > 15 m/s. Light scattering offers a viable option to develop an in-situ dust monitor for wet stacks, provided it has the ability to be insensitive to the presence of carryover moisture. [0007] Based on the foregoing a need therefore exists for an improved opacity monitor for measuring the emission levels which is insensitive to the carryover moisture. Also, a need exists for an online device and method for optically measuring fly ash particulate in industrial stack emissions independent of carryover moisture, as discussed in greater detail herein.

SUMMARY OF THE INVENTION

[0008] The following summary is provided to facilitate an understanding of some of the innovative features unique to the disclosed embodiment and is not intended to be a full description. A full appreciation of the various aspects of the embodiments disclosed herein can be gained by taking the entire specification, claims, drawings, and abstract as a whole.

[0009] Therefore, one aspect of the disclosed embodiment is to provide for an improved opacity monitor for measuring industrial stack emissions.

[00010] It is another aspect of the disclosed embodiment to provide for an improved device and method for measuring the fly ash particulate in industrial emissions independent of carryover moisture. [00011] It is further aspect of the disclosed embodiment to provide for an improved an online device and method for optically measuring fly ash particulate in industrial stack emissions independent of carryover moisture, as discussed in greater detail herein.

[00012] The aforementioned aspects and other objectives and advantages can now be achieved as described herein. An online device and method for optically measuring fly ash particulate in industrial stack emissions independent of carryover moisture, is disclosed herein. A light source (e.g., a green laser (l = 532nm)) is used for measuring the polarization resolved intensity of fly ash and water aerosol in an industrial stack wherein the scattered light signal is detected using a photo multiplier tube. The laser is rated at 555.2 mW maximum rated power, with output power ranging from 60 mW to 555.2 mW and the measurement is made at approximately 350 mW. The collimated light beam is sent through a 50:50 beam splitter and polarized with reference to the scattering plane wherein a first half of the beam passes through the measurement section and a second half of the beam passes onto a monitor photo diode to provide baseline reference for laser power output. [00013] The beam going towards the measurement section is passed through an

IRIS with an aperture of diameter 0.5 mm to reduce intensity variations. The optical measurement device comprises 16 apertures for detection and 2 apertures for laser to pass through the aerosol medium and then to light trap. A condensing lens (f = 12 mm) for collecting the scattered signal that passes through a polarizer and coupled to a photo multiplier tube (PMT) using an optical fiber. The detection optics can be rotated around the scattering chamber at discrete scattering angles. As an exemplary embodiment, the device disclosed herein involves measurement at 10 ^° , 30 ^° forward scatter and 170 ^° back scatter angles which are also considered for polarization measurement.

BRIEF DESCRIPTION OF DRAWINGS

[00014] The drawings shown here are for illustration purpose and the actual system will not be limited by the size, shape, and arrangement of components or number of components represented in the drawings.

[00015] FIG. 1 illustrates a graphical representation of the online device 100 for optically measuring fly ash particulate in industrial stack emissions independent of carryover moisture, in accordance with the disclosed embodiments; [00016] FIG. 2 illustrates a graphical representation illustrating the optical configuration in the online device online for optically measuring fly ash particulate in industrial stack emissions independent of carryover moisture, in accordance with the disclosed embodiments; and

[00017] FIG. 3 illustrates a graph illustrating the intensity ratio vs. loading rate ration (fly ash: water droplets) depicting the importance of the 170 ^° back-scatter angle in resolving, in accordance with the disclosed embodiments.

DETAILED DESCRIPTION

[00018] The particular values and configurations discussed in these non limiting examples can be varied and are cited merely to illustrate at least one embodiment and are not intended to limit the scope thereof.

[00019] FIG. 1 illustrates a graphical representation of the online device 100 for optically measuring fly ash particulate in industrial stack emissions independent of carryover moisture, in accordance with the disclosed embodiments. FIG. 1 illustrates the stack and systems for optical measurement, gravimetric sampling, aerosol feeding and data acquisition respectively. Note that the stake (6m high and 20cm circular cross-section) is operated in once through mode, where the stack velocity and aerosol feed rate are varied to change the concentration of the aerosol.

[00020] The device 100 comprises a rotating table 1, laser power source 2, optical fiber 3, laser polarizer 4, beam splitter 5, monitor photo-diode 6, IRIS 7, polycarbonate filter holder 8, flow controller 9, a vacuum pump 10, analyzing polarizer 11, condenser lens 12, photo detector 13, oscilloscope 14, beam dump 15, honey comb flow straighter 16, turn table dust feeder 17, dust feeder outlet 18, isokinetic sampling probe 19, photo detector mount 20, beam collimator 21, and acrylic chamber.

[00021] The light source (e.g., a green laser (l = 532nm)) 2 is used for measuring the polarization resolved intensity of fly ash and water aerosol in an industrial stack wherein the scattered light signal is detected using a photo multiplier tube. The laser 2 is rated at 555.2 mW maximum rated power, with output power ranging from 60 mW to 555.2 mW and the measurement is made at approximately 350 mW. The collimated light beam is sent through a 50:50 beam splitter 5 and polarized with reference to the scattering plane wherein a first half of the beam passes through the measurement section and a second half of the beam passes onto the monitor photo diode 6 to provide baseline reference for laser power output.

[00022] The beam going towards the measurement section is passed through the IRIS 7 with an aperture of diameter 0.5 mm to reduce intensity variations. The optical measurement device 100 comprises 16 apertures for detection and 2 apertures for laser to pass through the aerosol medium and then to light trap. The condensing lens (f = 12 mm) 12 for collecting the scattered signal that passes through the polarizer 4 and coupled to a photo multiplier tube (PMT) using the optical fiber 3. The detection optics can be rotated around the scattering chamber at discrete scattering angles. As an exemplary embodiment, the device disclosed herein involves measurement at 10 ^° , 30 ^° forward scatter and 170 ^° back scatter angles which are also considered for polarization measurement.

[00023] FIG. 2 illustrates a graphical representation 200 illustrating the optical configuration in the online device online for optically measuring fly ash particulate in industrial stack emissions independent of carryover moisture, in accordance with the disclosed embodiments. FIG. 2 illustrates the optical components configuration while at 10 ^° , 30 ^° forward scatter angle and 170 ^° back scatter angle. It shows position of the light source or laser and the detector used for scattered light measurement at different angles.

[00024] The optical fiber 3, coupling the scattered signal to the PMT, was connected to Wave Runner 6100A oscilloscope. The scattered signal from the particles was sampled at 1 MHz per channel and the amplitude was averaged over the duration of pulse (Is) to reduce the effect of random noise. The measurements were conducted for 1 MHz, 10 MHz and 25 MHz sampling rates and an acceptable signal to noise ratio (SNR) was obtained above 1 MHz sampling rate. Hence, 10 million data points were recorded for each experimental run and the PMT output was averaged over the entire signal pulse above the threshold (where the threshold was defined as m + 3s of the reference signal recorded with the flow but without the aerosol).

[00025] The beam size at the source was maintained to 0.5 mm diameter using an aperture. Factoring in 20 percent of beam size to be containing scattering information amounts to 100 pm beam diameter. The velocity maintained in the stack was of the order of 10 m/sec which is equivalent to 10 pm/psec, thereby providing a 10 psec residence time for particles in the laser beam. To resolve the velocity, sampling rate should be the inverse of residence time. For one particle in the beam, it is 100 kHz. Ten particles can be accommodated in the beam, as the particle size is of the order of 10 pm leading to a minimum required sampling rate of 1 MHz. However, there are more particles than geometrically considered here. Hence, a minimum sampling rate of 1 MHz was considered factoring in concentration and velocity effects. The measured signal was the average of total energy scattered by particles, which was then related to the concentration of particles in the scattering volume through isokinetic gravimetric sampling.

[00026] The invention disclosed herein uses a polarization resolved measurement technique to monitor PM emissions in wet industrial stacks. Depolarization of horizontally polarized incident light was observed and quantified for fly ash and water aerosol for various azimuthal scattering angles. Complete depolarization was observed for fly ash at the 170 ^° back-scatter angle, while water droplets retained the incident state. FIG. 3 illustrates a graph 300 illustrating the intensity ratio vs. loading rate ration (fly ash: water droplets) depicting the importance of the 170 ^° back-scatter angle in resolving, in accordance with the disclosed embodiments.

[00027] The cross-polarization measurement in this angle, where the scattering energy from the mixed flow could directly represent the fly ash concentration, could present the best possible measurement configuration for minimizing the impact of interference from water carryover in industrial emission stacks. Further, the change in depolarization ratio of the mixture (5m) when compared to fly ash (5a) alone is proportional to the scattering intensity ratios of ash and water respectively and could be used to estimate the individual mass concentrations.

[00028] The phase function (F11(0)/F11(1O ^° )) and depolarization parameter (F22/F11) was estimated from scattering matrix elements (evaluated from the measured intensities) was validated against previous studies performed in small scale and semi-quiescent test rigs to ensure that the light scattering behaviour remained similar in the scaled up testing facilities.

[00029] Further, based on partitioning of scattering energies in the back-scatter direction, a procedure for quantifying the mass concentrations of both water and fly ash aerosol has been evolved. While there are many depolarization studies with regards to atmospheric aerosol measurement, to our knowledge, this is the first study to present measurement of depolarization in an industrial stack, along with intensity calibration against concentration. The cross -polarization configuration identified here presents a method that is suitable for measuring fly-ash aerosol in the presence of moisture carryover, thereby providing an alternative to heated probe design, which is currently being used for wet stacks. It is possible to estimate the individual mass concentrations of fly ash and water aerosol by measuring depolarization by the mixture and comparing it against depolarization by ash.

[00030] It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.