Systems and methods for determining minimum ignition energies of dust clouds

Abstract

A small-scale minimum ignition energy (MIE) testing system for estimating the MIE of a dust cloud includes a small-scale testing chamber, a supply conduit in fluid communication with a supply of test gas and defining an enclosable supply chamber having a target volume, a dispersion nozzle fluidically connected between the supply conduit and the small-scale testing chamber for receiving a sample dust, a control valve positioned along the supply conduit between the enclosable supply chamber and the dispersion nozzle, the control valve having a closed state that restricts fluid communication between the supply chamber and the small-scale testing chamber and an open state providing fluid communication between the supply chamber and the small-scale testing chamber, and a pair of electrodes coupled to the small-scale testing chamber.

Description

2238-23901SYSTEMS AND METHODS FOR DETERMINING MINIMUM IGNITION ENERGIES OF DUST CLOUDSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a non-provisional application claiming priority to U.S. provisional patent application No. 63 / 717,581 filed November 7, 2024, and entitled “Small Scale Apparatus and Methods for Determining the Minimum Ignition Energy of Dust Clouds,” which is hereby incorporated herein by reference in its entirety for all purposes.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not applicable.BACKGROUND

[0003] Fires and explosions in the process industries pose an ongoing threat to worker safety and material assets. Dust cloud explosions are a subset of such incidents and are a considerable safety threat in many solids manufacturing processes. Common examples of flammable dusts include food products (powdered sugar, flour, cornstarch, etc.), pharmaceutical ingredients (amino acids, vitamins, protein powders, etc.), cosmetic products (inks, dyes, paints, etc.) and metallurgical byproducts (aluminum powder, coal dust, coke, etc.). Hazardous dust clouds exist in many industries, and explosions of such dust clouds can occur anytime there is a confined accumulation of dust that experiences a sufficient ignition energy. Generally, dust cloud explosions typically require each of fuel (suspended dust particles), an ignition source, oxidizer (air), confinement, and dispersion.

[0004] When it comes to fires and explosions, thorough risk assessment usually requires the consideration of experimental flammability data. Risk assessment considers the likelihood and consequence of a hypothetical event, and in practice, is generally applicable to many industries. While the consequence of a dust cloud explosion is often self-explanatory, the relative likelihood of such an event is more difficult to quantify. Useful experimental metrics for such quantification include, among others, minimum ignition energy (MIE). Accurate experimental data describing these2238-23901 metrics is critical for proper risk assessment of the explosion hazard of different applications.BRIEF SUMMARY

[0005] An embodiment of a small-scale MIE testing system for estimating the MIE of a dust cloud comprises a small-scale testing chamber having an internal volume between 25 cubic centimeters and 100 cubic centimeters, a supply conduit in fluid communication with a supply of test gas and defining an enclosable supply chamber having a target volume, a dispersion nozzle fluidically connected between the supply conduit and the small-scale testing chamber for receiving a sample dust, a control valve positioned along the supply conduit between the enclosable supply chamber and the dispersion nozzle, the control valve having a closed state that restricts fluid communication between the supply chamber and the small-scale testing chamber and an open state providing fluid communication between the supply chamber and the small-scale testing chamber, a pair of electrodes coupled to the small-scale testing chamber, and a computer system comprising one or more processors and one or more memory devices containing instructions that, when executed by the one or more processors, cause the one or more processors to initiate an activation of the pair of electrodes, shift the control valve from the closed state to the open state in response to the initiation of the activation of the pair of electrodes and following a controlled delay period whereby the target volume of test gas from the enclosable supply chamber is provided to the dispersion nozzle to produce a dust cloud of the sample dust in the internal volume of the small- scale testing chamber, and generate, following a controlled delay period triggered by the shifting of the control valve from the closed state to the open state, an electrical spark by the pair of electrodes in the internal volume of the small-scale testing chamber. In some embodiments, the delay period is user-selected. In some embodiments, the instructions, when executed by the one or more processors, cause the one or more processors to control a pressure of the in the enclosable supply chamber. In certain embodiments, the system comprises an endcap sealingly coupled to an end of the small-scale supply chamber opposite the dispersion nozzle. In certain embodiments, a purge fluid conduit coupled to the endcap and configured to deliver a test gas purge through a port of the endcap to the internal volume of the small-scale testing chamber. In some embodiments, the system comprises a heating element controllable by the2238-23901 computer system and coupled to the small-scale testing chamber for heating the internal chamber of the small-scale testing chamber.

[0006] An embodiment of a small-scale MIE testing system for estimating the MIE of a dust cloud comprises a small-scale testing chamber having an internal volume between 25 cubic centimeters and 100 cubic centimeters, a supply conduit in fluid communication with a supply of test gas, a dispersion nozzle fluidically connected between the supply conduit and the small-scale testing chamber for receiving a sample dust, the dispersion nozzle having an inner parabolic surface defining a parabolic volume that is open to the internal volume of the small-scale testing chamber, a control valve positioned along the supply conduit having a closed state that restricts fluid communication between the supply of test gas and the small-scale testing chamber and an open state providing fluid communication between the supply of test gas and the small-scale testing chamber, a pair of electrodes coupled to the small-scale testing chamber, and a computer system comprising one or more processors and one or more memory devices containing instructions that, when executed by the one or more processors, cause the one or more processors to initiate an activation of the pair of electrodes, and shift the control valve from the closed state to the open state in response to the initiation of the activation of the pair of electrodes whereby the target volume of test gas from the enclosable supply chamber is provided to the dispersion nozzle to produce a dust cloud of the sample dust in the internal volume of the small-scale testing chamber, and through which an electrical spark between the pair of electrodes extending following the activation of the pair of electrodes. In some embodiments, a distal end of the dispersion nozzle from which the parabolic volume extends is entirely open to the internal volume of the small- scale testing chamber. In certain embodiments, the dispersion nozzle comprises a dispersion manifold positioned in the parabolic volume, the dispersion manifold defining a plurality of circumferentially spaced dispersion ports. In certain embodiments, the dispersion nozzle comprises polytetrafluoroethylene (PTFE).

[0007] An embodiment of a method for estimating a minimum ignition energy (MIE) of a dust cloud comprises (a) conducting a MIE test of a sample dust, the test comprising (a1 ) generating a dust cloud comprising the sample dust in an internal volume of a small- scale testing chamber, (a2) generating, following (a1 ), an electrical spark in the internal volume of the small-scale testing chamber and in contact with dust cloud, (b) repeatedly conducting (a) and counting, for each instance of (a), a go for each full ignition of the dust cloud, and a no-go each non-ignition or partial ignition of the dust cloud, and (c)2238-23901 estimating a MIE of the dust cloud based on (b). In some embodiments, the method comprises (d) cleaning an inner surface of the small-scale testing chamber following each instance of (a). In some embodiments, (d) comprises brushing the inner surface using an electrically insulative brush. In certain embodiments, the estimated MIE of the dust cloud is based on fewerthan ten different instances of (a). In certain embodiments, an electrical energy of the electrical spark and a mass of the sample dust is the same for each of the ten different instances of (a). In some embodiments, the method comprises (d) pre-purging with test gas the internal volume of the small-scale testing chamber following each instance of (a). In some embodiments, (a) comprises (a3) applying heat from a heating element to the small-scale testing chamber to maintain the internal volume at an elevated setpoint temperature. In certain embodiments, the internal volume of the small-scale testing chamber is between 25 cubic centimeters and 100 cubic centimeters. In certain embodiments, (a1 ) comprises selectably controlling at least one of a pressure or a quantity of test gas delivered to the internal volume of the small-scale testing chamber. In some embodiments, (a) comprises selectably applying a delay period between the execution of (a1 ) and (a2).BRIEF DESCRIPTION OF THE DRAWINGS

[0008] For a detailed description of disclosed embodiments, reference will now be made to the accompanying drawings in which:

[0009] FIG. 1 is a schematic view of a small-scale MIE testing system according to some embodiments;

[0010] FIG. 2 is a schematic view of another small-scale MIE testing system according to some embodiments;

[0011] FIG. 3 is a perspective view of a small-scale testing chamber according to some embodiments;

[0012] FIG. 4 is a schematic view of a dispersion nozzle according to some embodiments;

[0013] FIG. 5 is a schematic view of another dispersion nozzle according to some embodiments;

[0014] FIGS. 6-9 are schematic views of another small-scale MIE testing system according to some embodiments;

[0015] FIG. 10 is a schematic view a small-scale MIE testing system according to some embodiments;2238-23901

[0016] FIG. 11 is a block diagram of a computer system according to some embodiments;

[0017] FIG. 12 is a flowchart for estimating a MIE of a dust cloud according to some embodiments;

[0018] FIG. 13 is a graph illustrating dispersion velocity as a function of spark delay according to some embodiments;

[0019] FIG. 14 is a graph illustrating dispersion velocity as a function of dispersion pressure according to some embodiments; and

[0020] FIGS. 15-17 are graphs illustrating spark energy as a function of mass loading according to some embodiments.DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS

[0021] The following discussion is directed to various embodiments. However, one skilled in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness.

[0022] In the following discussion and in the claims, the terms "including" and "comprising" are used in an open-ended fashion, and thus should be interpreted to mean "including, but not limited to..." Also, the term "couple" or "couples" is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection as accomplished via other devices, components, and connections. In addition, as used herein, the terms "axial" and "axially" generally mean along or parallel to a central axis (for example, central axis of a body or a port), while the terms "radial" and "radially" generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis.

[0023] As described previously, conventionally, MIE is a critical parameter for proper risk assessment of the explosion hazard of different applications. The minimum ignition energy for a dust cloud is generally regarded as the minimum spark energy which has2238-23901 been observed to ignite a cloud of the dust suspended in air. There are many factors that affect this measurement, some of which are inherent to the dust under study, such as dust chemistry, particle shape, particle size, moisture content, etc. Alternatively, some factors affecting dust cloud MIEs are artifacts of the experimental method, such as spark generation technique, dust cloud method and vessel size. For these reasons, the MIE of a dust cloud is not an intrinsic property, but rather an empirical consensus that is useful in determining relative ignitability.

[0024] Typically, Hartmann tube-style systems (or simply “conventional MIE testing systems’’) are utilized for quantifying dust clouds ignitability using MIEs. Generally, such systems include a vertical glass tube containing a dust cloud, which can be ignited by sparks generated therein to satisfy each of the requirements for creating a dust cloud explosion under controlled circumstances. Additionally, such conventional MIE testing systems serve as a basis for international standards for testing MIEs of dust clouds such as, for example, the ASTM E2019 standard. Conventional MIE testing systems suspend dust within the tube as a dust cloud using a compressed air pulse that is applied to a controlled amount of dust. Following the injection of the air pulse to the tube to generate the dust cloud therein, one or more electrodes of the system activate to generate a spark in the midst of the dust cloud such that, if the ignition or “spark” energy is sufficient, the dust cloud will ignite. A controlled delay period may be used between the injection of the air pulse and the activation of the one or more electrodes to ensure the dust cloud has had sufficient time to enter into contact or cover the one or more electrodes.

[0025] Experiments that result in ignition of the dust cloud are colloquially referred to as “Go” experiments whereas experiments that fail to result in ignition of the dust cloud are referred to as “Go-Go” experiments. Generally, with conventional Hartmann tube-style systems, ten successively repeated (under the same conditions) no Go experiments are typically required to determine that the tested conditions are not ignitable. Additionally, given that the electrodes of conventional MIE testing systems have limited spark energy resolution (e.g., may only create sparks having spark energies of 10 millijoules (mJ), 30 mJ, 100 mJ, 300 mJ, and the like), conventional MIE testing system may only bracket the MIE of a given dust cloud instead of determining the precise MIE of the dust cloud. Not intending to be bound by any particular theory, this concept may be expressed in accordance with Equation (1) below where Ei represents the highest spark energy that2238-23901 fails to ignite the dust cloud, E2 represents the lowest spark energy that ignites the dust cloud, and MIE represents the true MIE of the dust cloud:Ex< MiE < E2(1 )

[0026] Repeated MIE tests run on a selected dust may be used to populate an MIE response curve of the dust which may then be ultimately used to estimate the MIE of a dust cloud containing the selected dust. Not intending to be bound by any particular theory, as represented in Equation (2) below, an estimated MIE may be determined from E1 , E2, along with l2which represents the number of tests at E2 that resulted in ignition, and T2 which represents the total number of tests at E2:

[0027] While conventional MIE testing systems as described above have proliferated in use among dust cloud MIE testers, such systems, due to their relatively large size, can be slow and dangerous to operate while requiring a substantial amount of sample dust to operate as intended. In at least some applications, the dust tested by MIE testing systems can be expensive, toxic, and / or radioactive. In addition, such dusts may require labor and / or capital-intensive preparation (e.g., drying, milling, sieving) before they may be tested. Using relatively large amounts of dust, the explosive energies generated by go experiments with conventional MIE testing systems may be relatively large, increasing the possibility of equipment failure during the testing such as damaging of the testing system or failing to contain the deflagration generated within the tube of the testing system. Moreover, using relatively large amounts of dust also requires more extensive clean up following operation, reducing the speed at which these repetitive experiments must be individually carried out, which may compound substantially with each repeated experiment.

[0028] Accordingly, embodiments of small-scale MIE testing systems are disclosed herein which address at least some of the limitations of conventional MIE testing systems outlined above. Particularly, embodiments of small-scale MIE testing systems disclosed herein include a testing chamber having a volume that is significantly (e.g., ten times less, twenty times less) smaller than the volume of the Hartmann tube of conventional MIE testing systems. By reducing the volume of the testing chamber, embodiments of small-scale MIE testing systems disclosed herein reduce the energy of the deflagration formed in the testing chamber, thereby increasing the operational safety2238-23901 of the small-scale MIE testing system by reducing the risk of damaging testing equipment or failing to contain the deflagration within the testing chamber.

[0029] Additionally, by substantially reducing the volume of the testing chamber, embodiments of small-scale MIE testing systems disclosed herein also substantially reduce the amount of sample dust required for each MIE test conducted by the small- scale MIE testing system. Additionally, the small-scale MIE testing system may significantly reduce the overall volume of sample dust required to populate the MIE response curve of the dust and determine an estimated MIE of a dust cloud containing the dust. This may further improve the safety of the small-scale MIE testing system when toxic, radioactive, or otherwise dangerous dusts are being tested by the small- scale MIE testing system. Moreover, substantially reducing the volume of required sample dust may also substantially reduce the amount of time and effort required for preparing the sample dust and / or cleaning or otherwise preparing the small-scale MIE testing system between repeated MIE tests, thereby increasing the operational speed of the small-scale MIE testing system relative to conventional MIE testing systems.

[0030] In addition to the above, embodiments of small-scale MIE testing systems disclosed herein are modular such that the small-scale MIE testing system may be integrated into or with pre-existing testing equipment of conventional MIE testing systems. In this manner, embodiments of small-scale MIE testing systems may be quickly and conveniently integrated into conventional MIE testing systems with minimal time, effort, and expense. This may be particularly advantageous when it is desired to switch between small-scale MIE testing system and the conventional MIE testing system depending on the requirements of the given testing application.

[0031] Referring to FIG. 1 , an embodiment of a small-scale MIE testing system 10 is shown. As will be described further herein, small-scale MIE testing system 10 may be utilized to estimate the MIE of dust clouds containing a variety of types of dusts (e.g., flammable dusts) through generating a dispersion of the dust (a dust cloud) and applying an ignition or spark energy to the dust cloud. By running repeated MIE tests on a selected dust using the small-scale MIE testing system 10 a MIE response curve of the selected dust may be populated from which an estimated MIE of the selected dust may be determined.

[0032] In this exemplary embodiment, small-scale MIE testing system 10 generally includes a small-scale testing chamber 12, chamber testing equipment 16, a supply of test gas 20 (or simply test gas supply 20), a supply control valve 44, a working fluid2238-23901 source 48, a computer system 56, a system controller 60, a data acquisition device 64, an electrical ignition circuit 68, and a delay mechanism 72. In some embodiments, the test gas comprises ambient air. In other embodiments, the test gas comprises varying amounts of oxygen (e.g., 20% O2, 18% O2) to act as an oxidizer along with other gasses such as Nitrogen and the like. Additionally, in some embodiments, the working fluid comprises ambient air and / or other gasses such as cylinder air, nitrogen, and the like.

[0033] The small-scale testing chamber 12 is configured to contain the dispersion or dust cloud produced by the application of a pulse of air from the test gas supply 20 to the small-scale testing chamber 12. In some embodiments, small-scale testing chamber 12 comprises a tubular structure defining a generally cylindrical internal volume. In other embodiments, the shape or geometry of small-scale testing chamber 12 may vary. Additionally, the small-scale testing chamber 12 may comprise a transparent material (e.g., glass, transparent plastics) to permit an operator of small- scale testing system 10 visually determine whether a given MIE test conducted using the small-scale MIE testing system 10 results in the ignition of the dust cloud contained in the small-scale testing chamber 12 (corresponding to a “go” experiment). In other embodiments, the small-scale testing chamber 12 may not be transparent to permit visual confirmation of the result of the MIE test and, instead, other mechanisms may be used to determine whether a given MIE test has resulted in ignition of the dust cloud contained in the small-scale testing chamber 12 such as, for example, one or more sensors (e.g., pressure, temperature, acceleration, optical, and the like) that may be internal or external the small-scale testing chamber 12.

[0034] The chamber testing equipment 16 of small-scale MIE testing system 10 facilitates the creation of a dust cloud within the small-scale testing chamber 12 along with the potential ignition of the dust cloud therein. In this exemplary embodiment, chamber testing equipment 16 includes a dispersion nozzle 17, a stationary electrode 18, a moving electrode 19, and an electrode actuator 21. In other embodiments, chamber testing equipment 16 may include additional equipment such as, for example, a support structure for physically supporting the small-scale testing chamber 12.

[0035] In some embodiments, the dispersion nozzle 17 defines a receptacle for receiving a sample dust prior to creation of the dust cloud within the small-scale testing chamber 12. Additionally, the dispersion nozzle 17 may receive a target quantity of test gas as a test gas pulse from the test gas supply 20 provided at a target pressure which may encounter the sample dust located in or on the dispersion nozzle 17 to thereby2238-23901 form a dust cloud within the small-scale testing chamber 12, the dust cloud comprising the sample dust suspended within the test gas pulse.

[0036] The electrodes 18 and 19 may generate or provide the spark or ignition energy (user-selectable at different energy increments, e.g., 1 mJ, 3 mJ, 10 mJ, 30 mJ, 100 mJ, 300 mJ, 1 ,000 mJ) to the small-scale testing chamber 12. Electrodes 18 and 19 are each in signal communication with the electrical ignition circuit 68 of small-scale MIE testing system 10 whereby electrical energy may be selectably communicated from the electrical ignition circuit 68 to the electrodes 18 and 19 for generating an electrical spark extending between the electrodes 18 and 19 and across an internal volume of the small- scale MIE testing system 10 at a controlled, target spark energy. The operation of electrical ignition circuit 68 may be controlled by computer system 56 and / or system controller 60.

[0037] In this exemplary embodiment, during a MIE test conducted by the small-scale MIE testing system 10, the electrode actuator 21 is activated to physically displace the moving electrode 19 along an electrode axis towards the stationary electrode 18 to gradually reduce a linear spark gap extending between the electrodes 18 and 19. The electrode actuator 21 may comprise a linear actuator that, in this exemplary embodiment, is pneumatically driven by working fluid supplied by working fluid source 48. However, the configuration of electrode actuator 21 may vary in other embodiments. For instance, in other embodiments, electrode actuator 21 may instead comprise an electromechanical actuator.

[0038] The ignition energy may be applied to electrodes 18 and 19 as moving electrode 18 is displaced from a first position defining a first or maximum spark gap towards a second position defining a second or minimum spark gap. The generation of the electrical spark across the spark gap as the moving electrode 18 travels towards the stationary electrode may minimize parasitic capacitance, reducing variance between the target spark energy intended to be delivered by an operator of the small-scale MIE testing system 10 and the amount of spark energy actually delivered by the electrodes 18 and 19 during the performance of a MIE test. However, in other embodiments, both of the electrodes 18 and 19 may be stationary relative to the small-scale testing chamber 12 with a fixed spark gap extending between electrodes 18 and 19.

[0039] Test gas supply 20 may comprise a pressure vessel (e.g., one or more canisters) containing a desired quantity of test gas. The composition and / or other parameters of the test gas supplied by test gas supply 20 may be controlled as desired by an operator2238-23901 of small-scale MIE testing system 10. In some embodiments, small-scale MIE testing system 10 includes a pressure regulator 24 in fluid communication with the test gas supply 20 to regulate the pressure of the test gas supplied by test gas supply 20. For example, the pressure regulator 24 may comprise a compressor and / or a release valve for maintaining the test gas supplied by test gas supply 20 at a setpoint pressure. The setpoint pressure may be controlled manually by an operator of small-scale MIE testing system 10 or automatically by a computer system (e.g., computer system 56, system controller 60).

[0040] An inlet or test gas conduit 36 extends between the test gas supply 20 and the supply control valve 44. Additionally, a supply isolation valve 40 is positioned along the test gas conduit 36 between the test gas supply 20 and the supply control valve 44. In this arrangement, an enclosable supply volume or chamber 41 of the test gas conduit 36 extends between the supply isolation valve 40 and the supply control valve 44. The size or volume of the enclosable supply chamber 41 may be precisely controlled by an operator of the small-scale MIE testing system 10 to control the configuration of the test gas pulse applied to the small-scale testing chamber 12. In this exemplary embodiment, a pressure sensor 42 is in fluid communication with the enclosable supply chamber 41 for monitoring a pressure thereof. For instance, in some embodiments, pressure sensor 42 may be in signal communication with computer system 56 and / or system controller 60 for monitoring pressure in the enclosable supply chamber 41 .

[0041] A controlled volume of test gas supplied by test gas supply 20 may be captured within the enclosable supply chamber 41 by shifting supply isolation valve 40 from an open state to a closed state with supply control valve 44 remaining in a closed state. Additionally, the quantity of test gas captured in the enclosable supply chamber 41 is contingent on the pressure within the enclosable supply chamber 41 as monitored by pressure sensor 42. Thus, by controlling the volume of enclosable supply chamber 41 and the pressure of test gas therein (via pressure regulator 24, for example), a target quantity of test gas at a target pressure may be delivered to the small-scale MIE testing chamber 12, minimizing variances in testing conditions between different MIE tests such that the repeatability of small-scale MIE testing system 10 may be desirably increased.

[0042] To further aid in minimizing variances in testing conditions to increase repeatability of small-scale MIE testing system 10, in this exemplary embodiment, small- scale MIE testing system 10 comprises a purge fluid conduit 28 extending in parallel with the test gas conduit 36 between the test gas supply 20 and the small-scale testing2238-23901 chamber 12. A purge isolation valve 32 is positioned along the purge fluid conduit 28 between the test gas supply 20 and the small-scale testing chamber 12 to selectably restrict fluid communication between the test gas supply 20 and small-scale testing chamber 12 along the purge fluid conduit 28. Purge isolation valve 32 may be manually controlled by an operator of small-scale MIE testing system 10 and / or controlled (e.g., automatically controlled) by the computer system 56 and / or system controller 60. As will be discussed further herein, purge fluid conduit 28 may be used to purge (e.g., flood) the internal volume of small-scale testing chamber 12 with test gas from test gas supply 20 prior to conducting a MIE test. By purging the small-scale testing chamber 12 with test gas, it may be ensured that the small-scale testing chamber 12 is free of materials that may reduce the repeatability or accuracy of the small-scale MIE testing system 10. In addition, in some embodiments, the small-scale testing chamber 12 may be cleaned (e.g., via brushing and the like) between MIE tests to ensure the environment within the small-scale testing chamber 12 is as consistent as possible between MIE tests, further maximizing the repeatability and accuracy of the small-scale MIE testing system 10. In certain embodiments, given that only a small volume of sample dust is required by the small-scale MIE testing system 10, the sample dust may be advantageously replaced (rather than being reused) following each MIE test to further enhance the repeatability of the small-scale MIE testing system 10.

[0043] Small-scale MIE testing system 10 illustrates the modularity thereof as small- scale testing system 10 may utilize components of conventional MIE testing systems. For example, at least some of the chamber testing equipment 16 (e.g., a support structure thereof), electrodes 18 and 19, electrode actuator 21 , test gas supply 20, computer system 56, data acquisition device 64, electrical ignition circuit 68 and / or other equipment may comprise equipment of a conventional MIE testing system whereas, for example, the dispersion nozzle 17, small-scale testing chamber 12, system controller 60, and delay mechanism 72 may comprise equipment unique to the small-scale MIE testing system 10 integratable with equipment of the conventional MIE testing system such as, for example, equipment of a MIKE3 MIE testing apparatus provided by Adolf Kuhner AG, Birsfelden, Switzerland. By working with pre-existing equipment of conventional MIE testing systems, the small-scale MIE testing system 10 may increase the flexibility and applicability of system 10 such that operators may utilize both conventional MIE testing systems and the small-scale MIE testing system 10 with minimal inventory requirements.2238-23901

[0044] The delay mechanism 72 (which may be computer-implemented) may particularly facilitate integration of small-scale MIE testing system 10 with conventional MIE testing systems such as the MIKE3 by allowing a user of small-scale MIE testing system 10 to adjust a spark timing that is triggered by the shifting of supply control valve 44 from the closed state to the open state and, upon the conclusion of the delay period defined by the spark timing, immediately results in the creation of an electrical spark by the pair of electrodes 18 and 19 to potentially trigger a dust cloud ignition within the small-scale testing chamber 12. By allowing the spark timing to be adjusted to account for the substantially smaller volume of small-scale testing chamber 12, the delay mechanism 72 allows the control algorithm for a conventional MIE testing system to be adapted or tuned for use with the small-scale testing chamber 12 which may be significantly smaller than the conventional testing chamber of the conventional MIE testing system. In some embodiments, the spark timing of small-scale MIE testing system 10 is less than 100 milliseconds (ms). In some embodiments, the spark timing of small-scale MIE testing system 10 ranges approximately between 40 ms and 70 ms.

[0045] Referring to FIG. 2, another embodiment of a small-scale MIE testing system 100 is shown. In some embodiments, corresponding equipment of the small-scale MIE testing system 10 shown in FIG. 1 may be configured similarly as the small-scale MIE testing system 100; however, in other embodiments, equipment of small-scale MIE testing system 10 may vary in configuration from similar equipment of the small-scale MIE testing system 100.

[0046] In this exemplary embodiment, small-scale MIE testing system 100 generally includes a support structure or base 102, a dispersion nozzle 110, a small-scale testing chamber 120, a stationary electrode 130, a moving electrode 134, an electrode actuator 140, and an endcap 150. The support base 102 may be positioned on an external support surface 95 (e.g., a tabletop and the like) and physically supports the dispersion nozzle 110, small-scale testing chamber 120, and / or other equipment of small-scale MIE testing system 100. The dispersion nozzle 110 is physically supported on the support base 102 and comprises a test gas inlet 111 and a dust receptacle 112 for receiving a user-selected quantity of a sample dust to be tested by the small-scale MIE testing system 100.

[0047] The small-scale testing chamber 120 is generally cylindrical in this exemplary embodiment and extends between a first or vertically lower end 121 and a longitudinally opposed second or vertically upper end 123. An internal testing volume 122 is defined2238-23901 by the small-scale testing chamber 120 which extends between the ends 121 and 123 thereof. The small-scale testing chamber 120 is positioned atop the dispersion nozzle 110 with the lower end 121 thereof supported by the dispersion nozzle 110 in this exemplary embodiment. Additionally, the internal testing volume 122 is in fluid communication with the sample receptacle 112 of the dispersion nozzle 110 such that dust contained therein may flow into the internal testing volume 122 as a dispersion or dust cloud upon the application of a suitable test gas pulse to the test gas inlet 111 of dispersion nozzle 110. In some embodiments, dispersion nozzle 110 may comprise a metallic material (e.g., aluminum, stainless-steel), a plastic material such as polytetrafluoroethylene (PTFE) and the like selected for chemical inertness (e.g., corrosion resistance), machinability, cleanability, and the like. However, the material of dispersion nozzle 110 may vary in other embodiments.

[0048] The electrodes 130 and 134 are each coupled to and supported by the small- scale testing chamber 120 at a location spaced between the ends 121 and 123 thereof. Electrodes 130 and 134 may both be positioned along an electrode axis that extends orthogonally relative to a longitudinal or central axis of small-scale testing chamber 120. In this arrangement, an electrical spark may be selectably generated within the internal testing volume 122 of small-scale testing chamber 120, along a spark gap extending between the electrodes 130 and 134. In some embodiments, electrodes 130 and 134 and electrode actuator 140 may be configured or function similarly as the electrodes 18 and 19 and electrode actuator 21 shown in FIG. 1.

[0049] Endcap 150 may selectably enclose or seal the upper end 123 of small-scale testing chamber 120. In this exemplary embodiment, endcap includes an annular or disc-shaped lip 152 that extends into the internal testing volume 122 of small-scale testing chamber 120 to seal against an inner surface thereof when the endcap 150 is coupled to the upper end 123 of small-scale testing chamber 120. The endcap 150 is also provided with a port 154 that may be fluidically connected to a purge fluid conduit (e.g., purge fluid conduit 28 shown in FIG. 1) for pre-purging the interior testing volume 122 with test gas from a common test gas supply used to similarly supply the test gas inlet 111 of dispersion nozzle 110 with test gas.

[0050] Instead of being permanently coupled or threadably coupled and the like, lip 152 of endcap 150 slides into the internal testing volume 122 of small-scale testing chamber 120 with a friction fit to seal the upper end 123 of small-scale testing chamber 120. In this manner, endcap 150 may automatically release or “pop off” of the upper end 123 of2238-23901 small-scale testing chamber 120 in response to a threshold pressure being achieved in the internal testing volume 122 thereof. For instance, the endcap 150 may release automatically from the upper end 123 of small-scale testing chamber 120 in response to an ignition of a dust cloud present in the internal testing volume 122 thereof with the ignition increasing pressure in the internal testing volume 122 to that equalling or exceeding the threshold pressure.

[0051] Referring to FIG. 3, another embodiment of a small-scale testing chamber 200 is shown. In some embodiments, the small-scale testing chambers 12 and / or 120 shown in FIGS. 1 and 2 may be configured similarly as the small-scale testing chamber 200; however, in other embodiments, small-scale testing chambers 12 and / or 120 may vary in configuration from the small-scale testing chamber 200. In this exemplary embodiment, small-scale testing chamber 200 extends between a first end 201 and a longitudinally opposed second end 203. A central passage or internal testing volume 204 is defined by a generally cylindrical inner surface 206 of small-scale testing chamber 200 that extends between ends 201 and 203. Additionally, small-scale testing chamber200 includes a generally cylindrical outer surface 208 similarly extending between ends201 and 203.

[0052] In some embodiments, a longitudinal length 205 of the small-scale testing chamber 200 ranges approximately between 100 millimeters (mm) and 110 mm. In certain embodiments, an outer diameter (OD) 207 of the small-scale testing chamber 200 ranges approximately between 30 mm and 35 mm. In certain embodiments, an internal diameter (ID) of the small-scale testing chamber 200 ranges approximately between 20 mm and 25 mm. In some embodiments, a radial thickness of the small- scale testing chamber 200 (extending radially between surfaces 206 and 208 thereof) ranges approximately between 2.5 mm and 7.5 mm. In some embodiments, the internal testing volume 204 ranges approximately between 25 cubic centimeters (cm3) and 100 cm3. However, the values of these parameters of small-scale testing chamber 200 may vary in other embodiments.

[0053] In this exemplary embodiment, small-scale testing chamber 200 additionally includes a pair of electrode bores 210 each extending radially entirely between the inner surface 206 and outer surface 208 of small-scale testing chamber 200. Electrode bores 210 may sealingly receive a pair of electrodes that may extend through the electrode bores 210 into the internal testing volume 204 of small-scale testing chamber 200. Additionally, electrode bores 210 are circumferentially spaced 180 degrees apart about2238-23901 a central axis of small-scale testing chamber 200 such that the electrode bores 210 each extend along a shared electrode axis 213 that extends orthogonally to the central axis of small-scale testing chamber 200. In some embodiments, the longitudinal length 215 between the first end 201 of small-scale testing chamber 200 and the electrode bores 210 ranges approximately between 33 mm and 38 mm. In certain embodiments, an ID of both electrode bores 210 ranges approximately between 1 mm and 3 mm.

[0054] Referring to FIG. 4, another embodiment of a dispersion nozzle 250 is shown. In some embodiments, the dispersion nozzles 17 and / or 110 shown in FIGS. 1 and 2 may be configured similarly as the dispersion nozzle 250; however, in other embodiments, dispersion nozzles 17 and / or 110 may vary in configuration from the dispersion nozzle 250. In this exemplary embodiment, dispersion nozzle comprises a first or proximal end 251 and an opposing second or distal end 253. The distal end 253 may be receivable into an internal testing volume of a small-scale testing chamber such as the internal testing volumes 122 and 204 of small-scale testing chambers 120 and 200 shown in FIGS. 2 and 3.

[0055] In this exemplary embodiment, the distal end 253 of dispersion nozzle 250 is defined by a generally cylindrical outer surface 256 that extends from the distal end 253 and terminates at a radially extending outer shoulder 254. The outer surface 256 may sealingly engage an inner surface of a corresponding small-scale testing chamber. Additionally, the distal end 253 of dispersion nozzle 250 is defined by a generally parabolic inner surface 260 that defines a parabolic volume 261. In some embodiments, a sample dust may be positioned along the inner surface 260 within the parabolic volume 261 with the parabolic volume 261 defining a receptacle for the sample dust. Additionally, in this exemplary embodiment, the parabolic volume 261 may be entirely open or exposed to the internal testing volume of the small-scale testing chamber such that no obstructions project radially inwards from, for example, the distal end 253 to partially cover the parabolic volume 261 .

[0056] Dispersion nozzle 250 additionally includes a test gas supply passage 258 extending between an exterior of the dispersion nozzle 250 and an opening 262 formed in the parabolic surface 260 which may be located at a terminal end of the parabolic surface such that a central axis 255 of the dispersion nozzle 250 extends through the opening 262. The parabolic inner surface 260 and corresponding parabolic volume may, as will be discussed further herein, facilitate the consistent generation of a parabolic or parabolic front of an expanding dust cloud within the internal testing volume2238-23901 of the small-scale testing chamber, increasing the repeatability and accuracy of small- scale MIE testing systems incorporating the dispersion nozzle 250.

[0057] Referring to FIG. 5, another embodiment of a dispersion nozzle 300 is shown. In some embodiments, the dispersion nozzles 17 and / or 110 shown in FIGS. 1 and 2 may be configured similarly as the dispersion nozzle 300; however, in other embodiments, dispersion nozzles 17 and / or 110 may vary in configuration from the dispersion nozzle 300. Particularly, dispersion nozzle 300 is similar to the dispersion nozzle 250 shown in FIG. 4 except that dispersion nozzle 300 includes a manifold 302 positioned on the parabolic surface 260 and located or extending centrally with respect to a central axis 305 of the dispersion nozzle 305. Manifold 302 includes a plurality of dispersion ports 304 circumferentially spaced about the central axis 305 to evenly distribute the test gas pulse circumferentially about the central axis 305 during the operation of dispersion nozzle 300. However, no restrictions or obstructions are positioned downstream of dispersion manifold 302 and the internal testing volume of the small-scale testing chamber to which the dispersion nozzle 300 is connected.

[0058] Referring to FIGS. 6-9, another embodiment of a small-scale MIE testing system 350 is shown. Small-scale MIE testing system 350 may include features in common with embodiments shown in FIGS. 2-5, and shared features are labeled similarly. In this exemplary embodiment, small-scale MIE testing system 350 generally includes small- scale testing chamber 120, electrodes 130 and 134, and dispersion nozzle 300. Dispersion nozzle 300 is coupled to the lower end 121 of small-scale testing chamber 120 with the lower end 121 of small-scale testing chamber 120 landed against outer shoulder 254 of dispersion nozzle 300 and an inner surface of small-scale testing chamber 120 sealingly contacting the outer surface 256 of dispersion nozzle 300.

[0059] FIGS. 6-9 illustrate an exemplary operation or MIE test of a sample dust 352 conducted using the small-scale MIE testing system 350. Initially, sample dust 352 may be loaded into the parabolic volume 261 of dispersion nozzle 300 such as along the parabolic surface 260. An electrical ignition circuit electrically connected to electrodes 130 and 134 may be initiated (e.g., whereby one or more capacitors of he electrical ignition circuit are charged to a target electrical energy) along with an electrode actuator responsible for gradually reducing a spark gap extending between electrodes 130 and 134. Additionally, a user-selected quantity of test gas is supplied to the test gas supply passage 258 of dispersion nozzle 300 which is dispersed through the dispersion ports 304 and into the parabolic volume 261. The application of the test gas pulse to the2238-23901 dispersion nozzle 300 may trigger a user-selectable delay period of the small-scale MIE testing system incorporating the dispersion nozzle 300. The dispersed test gas mixes with the sample dust to form a dust cloud 354 having a parabolic cloud front 356 that travels towards the upper end 123 of small-scale testing chamber 120 at a gradually decaying dispersion velocity (indicated by arrow 355 in FIGS. 7-9). With the terminal ends of electrodes 130 and 134 enveloped in the dust cloud 354, initiation of the electrical ignition circuit is completed marking the completion of the spark timing resulting in the activation of electrodes 130 and 134 and the generation of an electrical spark 357 that extends through the dust cloud 354 along the spark gap formed between electrodes 350 and 354.

[0060] As compared to conventional MIE testing systems, small-scale testing systems such as small-scale MIE testing system 350 may have a significantly smaller spark timing where the magnitude of the spark timing is inversely correlated with dispersion velocity 355. Thus, the dispersion velocity at the point of activation of electrodes 130 and 134 for embodiments of small-scale MIE testing systems disclosed herein may be significantly less than that of conventional MIE testing systems. This reduced dispersion velocity 355 results in a less turbulent dust cloud 354 and, concomitantly, a significantly more accurate and repeatable MIE test conducted by the small-scale MIE testing system (e.g., small-scale MIE testing system 350). In certain embodiments, the dispersion velocity 355 of dust cloud 354 at the point of activation of electrodes 130 and 134 ranges approximately between 30 centimeters per second (cm / s) and 70 cm / s.

[0061] In some instances, the activation of electrodes 130 and 134 will result in either no ignition of the dust cloud 354 in the presence of the electrical spark 357 bridging the spark gap between electrodes 130 and 134, as shown particularly in FIG. 7. In other instances, as shown particularly in FIG. 8, the activation of electrodes 130 and 134 results in a partial ignition 358 of the dust cloud 354. In still other instances, as shown particularly in FIG. 9, the activation of electrodes 130 and 134 results in a full ignition 360 of the dust cloud 354. As used herein, the term “partial ignition” of a dust cloud (e.g., dust cloud 354) refers to an ignition of the dust cloud that does not span the entire ID of the small-scale testing chamber (e.g., the ID of small-scale testing chamber 120) in which the dust cloud is located. In other words, in a partial ignition, a flame front of the partial ignition does not extend entirely across the ID of the small-scale testing chamber.2238-23901

[0062] Conversely, as used herein, the term “full ignition” of a dust cloud (e.g., dust cloud 354) refers to an ignition of the dust cloud that spans at least the entire ID of the small- scale testing chamber (e.g., the ID of small-scale testing chamber 120) in which the dust cloud is located. In other words, in a full ignition, a flame front of the full ignition extends entirely across the ID of the small-scale testing chamber. As will be discussed further herein, in some embodiments, and in the interest of maximizing the repeatability of MIE tests conducted using a small-scale MIE testing system, a MIE test resulting in either no ignition or only a partial ignition of the dust cloud is counted as a “no go” MIE test whereas only MIE tests resulting in full ignition are counted as “go” MIE tests.

[0063] Referring to FIG. 10, another embodiment of a small-scale MIE testing system 400 is shown. In some embodiments, corresponding equipment of the small-scale MIE testing system 10 shown in FIG. 1 may be configured similarly as the small-scale MIE testing system 400; however, in other embodiments, equipment of small-scale MIE testing system 10 may vary in configuration from similar equipment of the small-scale MIE testing system 400.

[0064] In this exemplary embodiment, small-scale MIE testing system 400 generally includes, among other equipment, small-scale testing chamber 120, dispersion nozzle 300, a heating element, 402, a heating element power supply 410, an electrical relay 420, a heating element controller 430, and a temperature sensor 440. Heating element 402 is generally configured to apply a selectable amount of heat to the small-scale testing chamber 120 to control an internal temperature (e.g., a temperature of the internal testing volume) of the small-scale testing chamber 120. In this exemplary embodiment, heating element 402 comprises an electrically powered heat tape configured to generate a given amount of heat based on amount of electrical power supplied to the heat tape by the heating element power supply 410. In this exemplary embodiment, the heat tape may be conveniently wound helically about an outer surface of the small-scale testing chamber 120 to uniformly apply heat thereto. However, the configuration of heating element 402 may vary in other embodiments.

[0065] The temperature sensor 440 monitors the internal temperature of the small-scale testing chamber 120 (or of the small-scale testing chamber 120 itself from which internal temperature may correlate with or be inferred from) and provides temperature feedback data 442 to the heating element controller 430. In some embodiments, temperature sensor 440 comprises a thermocouple. However, the configuration of temperature sensor 440 may vary in other embodiments.2238-23901

[0066] The heating element controller 430 is electrically connected to the heating element 402 through the electrical relay 420 (e.g., a solid state relay) whereby the heating element controller 430 may control the amount of electrical power supplied to the heating element 402 and, in-turn, the amount of heat generated by heating element 402 and applied to the small-scale testing chamber 120). For example, the heating element controller 430 may be configured to maintain the internal temperature of small- scale testing chamber 120 at an elevated desired or setpoint temperature whereby heating element controller 430 controls the amount of heat generated by heating element 402 to minimize the difference between the internal temperature of small-scale testing chamber 120 (as monitored by temperature sensor 440) and the setpoint temperature. Thus, by “maintaining” the internal temperature at the elevated setpoint temperature the heating element controller 430 may minimize (but not necessarily eliminate) differences between the internal temperature and the elevated setpoint temperature. In some embodiments, the heating element controller 430 comprises a proportional-integral-derivative controller; however, the configuration of heating element controller 430 may vary in other embodiments.

[0067] By heating the internal volume of small-scale testing chamber 120, the conditions of actual industrial applications may be better replicated given that such industrial operations often involve elevated temperatures. Moreover, replicating the temperatures of actual industrial operations may be important in testing MIE of sample dusts given that MIE may vary as a function of temperature, with the MIE of at least some dusts decreasing with temperature.

[0068] Any of the systems and methods disclosed herein can be carried out (e.g., entirely or partially) on a computer or other device comprising a processor (e.g., a desktop computer, a laptop computer, a tablet, a server, a smartphone, or some combination thereof). Referring now to FIG. 11 , a computer system 500 suitable for implementing one or more embodiments disclosed herein (e.g., computer system 56 and system controller 60 shown in FIG. 1 , heating element controller 430 shown in FIG. 10) is shown. The computer system 500 includes a processor 501 (which may be referred to as a central processor unit or CPU) that is in communication with memory devices including secondary storage 502, read only memory (ROM) 503, random access memory (RAM) 504, input / output (I / O) devices 505, and network connectivity devices 506. The processor 501 may be implemented as one or more CPU chips.2238-23901

[0069] It is understood that by programming and / or loading executable instructions onto the computer system 500, at least one of the CPUs 501 , the RAM 504, and the ROM 503 are changed, transforming the computer system 500 in part into a particular machine or apparatus having the novel functionality taught by the present disclosure. Thus, the RAM 504 and / or the ROM 503 may comprise a non-transitory machine- readable (or computer-readable) medium that may include instructions (which may be referred to herein as machine-readable instructions) that are executable by CPU 501 to provide functionality to computer system 500. Thus, in some embodiments, a machine-readable instructions stored on a memory may be executed on a processor, so as to configured the processor to carry out some or all of the features of the methods described herein.

[0070] It is fundamental to the electrical engineering and software engineering arts that functionality that can be implemented by loading executable software into a computer can be converted to a hardware implementation by well-known design rules. Decisions between implementing a concept in software versus hardware typically hinge on considerations of stability of the design and numbers of units to be produced rather than any issues involved in translating from the software domain to the hardware domain. Generally, a design that is still subject to frequent change may be preferred to be implemented in software, because re-spinning a hardware implementation is more expensive than re-spinning a software design. Generally, a design that is stable that will be produced in large volume may be preferred to be implemented in hardware (for example in an application specific integrated circuit (ASIC), or field-programmable gate arrays (FPGA)) because for large production runs the hardware implementation may be less expensive than the software implementation. Often a design may be developed and tested in a software form and later transformed, by well-known design rules, to an equivalent hardware implementation in an application specific integrated circuit that hardwires the instructions of the software. In the same manner as a machine controlled by a new ASIC is a particular machine or apparatus, likewise a computer that has been programmed and / or loaded with executable instructions may be viewed as a particular machine or apparatus.

[0071] Additionally, after the computer system 500 is turned on or booted, the CPU 501 may execute a computer program or application. For example, the CPU 501 may execute software or firmware stored in the ROM 503 or stored in the RAM 504. In some cases, on boot and / or when the application is initiated, the CPU 501 may copy2238-23901 the application or portions of the application from the secondary storage 502 to the RAM 504 or to memory space within the CPU 501 itself, and the CPU 501 may then execute instructions of which the application is comprised. In some cases, the CPU 501 may copy the application or portions of the application from memory accessed via the network connectivity devices 506 or via the I / O devices 505 to the RAM 504 or to memory space within the CPU 501 , and the CPU 501 may then execute instructions of which the application is comprised. During execution, an application may load instructions into the CPU 501 , for example load some of the instructions of the application into a cache of the CPU 501. In some contexts, an application that is executed may be said to configure the CPU 501 to do something, e.g., to configure the CPU 501 to perform the function or functions promoted by the subject application. When the CPU 501 is configured in this way by the application, the CPU 501 becomes a specific purpose computer or a specific purpose machine.

[0072] The secondary storage 502 is typically comprised of one or more disk drives or tape drives and is used for non-volatile storage of data and as an over-flow data storage device if RAM 504 is not large enough to hold all working data. Secondary storage 502 may be used to store programs which are loaded into RAM 504 when such programs are selected for execution. The ROM 503 is used to store instructions and perhaps data which are read during program execution. ROM 503 is a non-volatile memory device which typically has a small memory capacity relative to the larger memory capacity of secondary storage 502. The RAM 504 is used to store volatile data and perhaps to store instructions. Access to both ROM 503 and RAM 504 is typically faster than to secondary storage 502. The secondary storage 502, the RAM 504, and / or the ROM 503 may be referred to in some contexts as computer readable storage media and / or non-transitory computer readable media.

[0073] I / O devices 505 may include printers, video monitors, electronic displays (e.g., liquid crystal displays (LCDs), plasma displays, organic light emitting diode displays (OLED), touch sensitive displays, etc.), keyboards, keypads, switches, dials, mice, track balls, voice recognizers, card readers, paper tape readers, or other well-known input devices.

[0074] The network connectivity devices 506 may take the form of modems, modem banks, Ethernet cards, Omni-Path Architecture (OPA), InfiniBand (IB), universal serial bus (USB) interface cards, serial interfaces, token ring cards, fiber distributed data interface (FDDI) cards, wireless local area network (WLAN) cards, radio transceiver2238-23901 cards that promote radio communications using protocols such as code division multiple access (CDMA), global system for mobile communications (GSM), long-term evolution (LTE), worldwide interoperability for microwave access (WiMAX), near field communications (NFC), radio frequency identity (RFID), and / or other air interface protocol radio transceiver cards, and other well-known network devices. These network connectivity devices 506 may enable the processor 501 to communicate with the Internet or one or more intranets. With such a network connection, it is contemplated that the processor 501 might receive information from the network, or might output information to the network (e.g., to an event database) in the course of performing the methods described herein. Such information, which is often represented as a sequence of instructions to be executed using processor 501 , may be received from and outputted to the network, for example, in the form of a computer data signal embodied in a carrier wave.

[0075] Such information, which may include data or instructions to be executed using processor 501 for example, may be received from and outputted to the network, for example, in the form of a computer data baseband signal or signal embodied in a carrier wave. The baseband signal or signal embedded in the carrier wave, or other types of signals currently used or hereafter developed, may be generated according to several known methods. The baseband signal and / or signal embedded in the carrier wave may be referred to in some contexts as a transitory signal.

[0076] The processor 501 executes instructions, codes, computer programs, scripts which it accesses from hard disk, floppy disk, optical disk, solid state drives (SSD) (these various disk-based systems may all be considered secondary storage 502), flash drive, ROM 503, RAM 504, or the network connectivity devices 506. While only one processor 501 is shown, multiple processors may be present. Thus, while instructions may be discussed as executed by a processor, the instructions may be executed simultaneously, serially, or otherwise executed by one or multiple processors. Instructions, codes, computer programs, scripts, and / or data that may be accessed from the secondary storage 502, for example, hard drives, floppy disks, optical disks, and / or other device, the ROM 503, and / or the RAM 504 may be referred to in some contexts as non-transitory instructions and / or non-transitory information.

[0077] In an embodiment, the computer system 500 may comprise two or more computers in communication with each other that collaborate to perform a task. For example, but not by way of limitation, an application may be partitioned in such a way2238-23901 as to permit concurrent and / or parallel processing of the instructions of the application. Alternatively, the data processed by the application may be partitioned in such a way as to permit concurrent and / or parallel processing of different portions of a data set by the two or more computers. In an embodiment, virtualization software may be employed by the computer system 500 to provide the functionality of a number of servers that is not directly bound to the number of computers in the computer system 500. For example, virtualization software may provide twenty virtual servers on four physical computers. In an embodiment, the functionality disclosed above may be provided by executing the application and / or applications in a cloud computing environment. Cloud computing may comprise providing computing services via a network connection using dynamically scalable computing resources. Cloud computing may be supported, at least in part, by virtualization software. A cloud computing environment may be established by an enterprise and / or may be hired on an as-needed basis from a third-party provider. Some cloud computing environments may comprise cloud computing resources owned and operated by the enterprise as well as cloud computing resources hired and / or leased from a third-party provider.

[0078] In an embodiment, some or all of the functionality disclosed above may be provided as a computer program product. The computer program product may comprise one or more computer readable storage medium having computer usable program code embodied therein to implement the functionality disclosed above. The computer program product may comprise data structures, executable instructions, and other computer usable program code. The computer program product may be embodied in removable computer storage media and / or non-removable computer storage media. The removable computer readable storage medium may comprise, without limitation, a paper tape, a magnetic tape, magnetic disk, an optical disk, a solid-state memory chip, for example analog magnetic tape, compact disk read only memory (CD-ROM) disks, floppy disks, jump drives, digital cards, multimedia cards, and others. The computer program product may be suitable for loading, by the computer system 500, at least portions of the contents of the computer program product to the secondary storage 502, to the ROM 503, to the RAM 504, and / or to other non-volatile memory and volatile memory of the computer system 500. The processor 501 may process the executable instructions and / or data structures in part by directly accessing the computer program product, for example by reading from a CD-ROM disk inserted into a disk drive peripheral of the computer system 500.2238-23901Alternatively, the processor 501 may process the executable instructions and / or data structures by remotely accessing the computer program product, for example by downloading the executable instructions and / or data structures from a remote server through the network connectivity devices 506. The computer program product may comprise instructions that promote the loading and / or copying of data, data structures, files, and / or executable instructions to the secondary storage 502, to the ROM 503, to the RAM 504, and / or to other non-volatile memory and volatile memory of the computer system 500.

[0079] In some contexts, the secondary storage 502, the ROM 503, and the RAM 504 may be referred to as a non-transitory computer readable medium or a computer readable storage media. A dynamic RAM embodiment of the RAM 504, likewise, may be referred to as a non-transitory computer readable medium in that while the dynamic RAM receives electrical power and is operated in accordance with its design, for example during a period of time during which the computer system 500 is turned on and operational, the dynamic RAM stores information that is written to it. Similarly, the processor 501 may comprise an internal RAM, an internal ROM, a cache memory, and / or other internal non-transitory storage blocks, sections, or components that may be referred to in some contexts as non-transitory computer readable media or computer readable storage media.

[0080] Referring to FIG. 12, a method 550 is shown for estimating a MIE of a dust cloud. Beginning at block 552, method 550 includes conducting a MIE test of a sample dust. In this exemplary embodiment, block 552 includes subblocks 554 and 556. At subblock 554, block 552 includes generating a dust cloud comprising the sample dust in an internal volume of a small-scale testing chamber. At subblock 556, block 552 includes generating, following the generation of the dust cloud, an electrical spark in the internal volume of the small-scale testing chamber and in contact with dust cloud. At block 558, method 550 includes repeatedly conducting the MIE test and counting, for each instance of the MIE test, a go for each full ignition of the dust cloud, and a no- go each non-ignition or partial ignition of the dust cloud. At block 560, method 550 includes estimating a MIE of the sample dust based on each counted go and no-go.EXAMPLES

[0081] The subject matter having been generally described, the following examples are given as particular aspects of the disclosure and are included to demonstrate the2238-23901 practice and advantages thereof, as well as aspects and features of the presently disclosed subject matter. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventors to function well in the practice of the present subject matter, and thus can be considered to constitute exemplary modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific aspects which are disclosed and still obtain a like or similar result without departing from the scope of the instant disclosure. It is understood that the examples are given by way of illustration and are not intended to limit the specification of the claims to follow in any manner.

[0082] An experimental small-scale testing system was designed and subsequently tested to compare the performance of the experimental system with that of conventional MIE testing systems and particularly with respect to the MIKE3. The design of a small-scale device of the experimental system was proposed to be a Hartmann tube-style apparatus which would utilize the electrodes and ignition circuit of the MIKE3. As such, it was of interest to design a device which could easily be implemented into the MIKE3 hardware, such that the device would be modular and user-friendly. Furthermore, it was decided to fabricate a glass tube from a commonly available stock tube as a proportional scale down of the IKE3 tube, with the dimensions of the available stock tube being such that the small-scale tube ended up being a roughly 20x volumetric reduction from the MIKE3. Holes were drilled into the small-scale tube such that the electrodes of the MIKE3 could pass through them, and were positioned such that the relative height of the electrodes with respect to the tube dimensions matched those of the MIKE3. To ensure that the sparks would generate properly, it was decided to use the same 6 mm electrode gap that was used in previous MIKE3 testing. A Teflon® nozzle was fabricated to facilitate the dispersion of dust within the small-scale tube. The small-scale tube was mounted on the small-scale nozzle and then mounted on an aluminum base plate. A small threaded hole was machined into the MIKE3 nozzle base to allow easy mounting of the small-scale assembly. A Teflon cap which was machined to loosely fit the glass tube, and which carried an air-line that allowed for purging of the volume within the glass tube prior to testing.

[0083] With the physical design of the experimental small-scale device resolved, it was necessary to implement additional equipment to facilitate the air pulse which would2238-23901 disperse the dust for ignition testing. In this experimental study, it was necessary to implement supporting equipment in addition to the nozzle, tube, base assembly, and purging cap. This included gas handling and electronic integration with the MIKE3. It was known that there would be two purposes of the supporting equipment. The first purpose was to allow for a metered pulse of compressed air to be sent to the small- scale nozzle, facilitating the dispersion of dust within the small-scale tube. The second purpose was to time the small-scale dust cloud with respect to the MIKE3 electrodes’ timing, such that the spark would occur during the instant in which the dust is suspended within the small-scale tube.

[0084] To address these two needs, a system was designed with a solenoid valve connected to a data acquisition card which was set up to respond to a signal from the MIKE3. To save on costs of certified air, the pneumatically driven electrodes of the MIKE3 were connected to a tank of nitrogen, which was connected through lines in the MIKE3 hardware to moving electrodes. In normal operation, the MIKE3 is controlled by software on an external computer and is connected via USB cable. However, it was necessary to devise a system that could control the timing of the small-scale dispersion with respect to the actuation of the MIKE3 electrodes, which is initiated by a command from the MIKE3 software. To coordinate this control, a LabVIEW® program was developed. A data acquisition card read the signal from the MIKE3 software and, on a LabVIEW®-programmed delay, actuated the solenoid valve, causing the dispersion in the small-scale device.

[0085] This experimental small-scale device included three possible operational parameters of the small-scale air dispersion: The LabVIEW®-programmed delay determined the elapsed time between the actuation of the MIKE3 and the initiation of the small-scale dispersion valve and was termed as the small-scale spark timing (to). The duration of the small-scale dispersion pulse was dictated by the time period over which the solenoid valve was opened (Zlf), which was also a LabVIEW®-adjustable parameter. It was discovered that the solenoid valve was not fast enough to perform consistently at low dispersion durations. Therefore, it was decided that this parameter would be dropped from the analysis and would be set to a constant 200 ms allowing the entire contents of a supply chamber or interstitial volume to impart the dispersion. This was considered to be a justifiable decision, as evidence suggested that the dispersion pressure alone was sufficient to parameterize the intensity of the small- scale dispersion. Finally, the quantity of air in the small-scale dispersion is related to2238-23901 the pressure of compressed air within the interstitial volume (Po). These two variables (spark timing and dispersion pressure) came to be the operational parameters which affect the dynamics of the experimental small-scale dispersion.

[0086] In summary, the experimental small-scale device was designed to control the timing of the dispersion with respect to the spark, and to deliver the compressed air that would facilitate the dispersion. The nature of the supporting equipment was such that the dispersion dynamics would be controlled by only two operator-defined parameters (t0and Po). The investigation of the dispersion, including the effects of these parameters, and the means by which the small-scale dispersion was optimized to match that of the MIKE3.

[0087] Previous efforts to characterize the MIKE3 dispersion examined the velocity of the dust cloud as it was propelled upwards by the compressed air pulse. To match the MIKE3 dispersion dynamics in the small-scale, it was anticipated that spark timing (time between dispersion and spark) would also need to be considered, as the ideal spark timing for the small-scale would be less than the 120 ms used in the MIKE3. Therefore, it became necessary to propose a second dispersion characteristic that could be retroactively identified using the videos of the previous MIKE3 dispersions, and which would help identify the proper spark timing for the small-scale dispersion. To fulfill this requirement, a modified version of the Stokes number from fluid dynamics was used. The Stokes number is usually used to describe particle behavior entrained in fluid flow. The proposed modified stokes number is shown below in Equation (3), where tsrepresents the time elapsed from the beginning of the dispersion to the spark, vsrepresents the velocity of the dispersion at the moment of the spark, and Herepresents the distance from the nozzle to the electrodes:

[0088] The tsterm is analogous to the 120 ms delay used in previous MIKE3 experiments. Although this modified Stokes number was proposed for use in evaluating the dispersion dynamics, it was unknown whether or not this figure would be a useful dispersion characteristic. Since the idea of matching dispersion dynamics in a novel, scaled-down device was unprecedented in the literature, it was decided to proceed with an attempt to match the small-scale dispersion velocity and modified Stokes numbers to those which were previously observed in the MIKE3 dispersions.2238-23901

[0089] Now that the two dispersion characteristics of interest had been identified, it was necessary to explore how the two small-scale dispersion parameters affected the small-scale dispersion dynamics. The adjustable parameters for the experimental small-scale dispersion included the spark timing and dispersion pressure. It was believed that parameterization of these variables would result in visible changes to the dispersion dynamics, which could be captured and quantified by an iPhone® camera. An arrangement was set up with a ruler next to the small-scale tube, such that the dispersion velocity could be easily calculated. In the case of each dispersion, it was possible to calculate the velocity and modified Stokes number by comparing the images from frame to frame.

[0090] To get a better understanding of the effects of changing each small-scale dispersion parameter, several conditions were tried using 50 milligram (mg) mass loadings of Pittsburgh pulverized coal (PPC), and each condition was recorded with the iPhone® camera. 50 mg mass loadings were chosen because they are a 20x scaledown of 1200 mg mass loadings that were observed to behave well in the MIKE3. Trial and error led the operators to a coarse set of values for the two dispersion parameters, which resulted in a reasonable dispersion. From there, variation of each parameter was performed to see the effects on the dispersion.

[0091] Referring to FIGS. 13 and 14, graphs 600 and 610 are shown illustrating dispersion velocity 602 as a function of spark delay (graph 600) and dispersion velocity 612 as a function of dispersion pressure (graph 610), which illustrate the results of parameterizing Po and to. Each point on graphs 600 and 610 shows the average of five repeated tests recorded using the high-speed video function of the iPhone®. It was clear from the data shown in graphs 600 and 610 that the dispersion velocity (at the moment of the spark) is directly related to the backpressure, Po, and inversely related to the spark timing, to. Both of these results make logical sense: greater backpressure will cause greater velocities, and a greater spark delay will cause more velocity decay leading up to the spark.

[0092] Further trial and error resulted in an optimized combination of Po and to that was suspected to be sufficient, despite the fact that no ignition tests had yet been carried out. When these parameters were applied to a 50 mg mass loading in the small-scale, a similar dispersion to that which was seen in the MIKE3 was achieved. The specific values of the ideal Po and to parameters were referred to qualitatively as the “standard parent” conditions. These conditions resulted in a small-scale dispersion featuring a2238-23901 modified Stokes number of about 0.71 , which is close to the average modified Stokes numbers of 0.62 and 0.74 which were previously observed in the MIKE3 for the 1200 mg mass loadings. The small-scale dispersion velocity resulting from the standard parent conditions was determined to be about 50 cm / s. This was about half of the velocity of previous the ~1 m / s MIKE3 dispersion, representing less turbulence. It was qualitatively observed that dispersion velocities higher than ~50 cm / s resulted in the Teflon® cap being blown off of the small-scale tube, resulting in a loss of containment of the dispersion. For this reason, the standard parent conditions were optimized to result in dispersion velocities of no more than 50 cm / s for 50 mg mass loadings. Since the standard parent conditions matched the modified Stokes numbers between the small-scale and the MIKE3, it was decided to go forward evaluating these conditions with ignition tests.

[0093] Three separate control batches were tested in the small-scale, using the previously identified standard parent dispersion. Successful ignitions were readily observed using this dispersion. To characterize the ignition behavior of the control batches, the mass of the dust and the energy of the spark was parameterized over many experiments, such that the MIE response curve could be characterized for each dust in the small-scale device. These efforts started with 50 mg mass loadings, since this is the mass that was used for the dispersion development. From there, the dust mass and spark energy of the small-scale experiments could be changed so as to parse out the entire MIE response curve. Referring to FIGS. 15-17, graphs 620 (including Gos 622 and No-Gos 624), 630 (including Gos 632 and No-Gos 634), and 640 (including Gos 642 and No-Gos 644) are shown, respectively, indicating small- scale MIE response curves for the three control batches.

[0094] It was quickly observed that the MIE response curves obtained in the MIKE3 and in the small-scale were of different shapes with respect to mass loading. However, the MIEs for each control batch were bracketed at the same energy level as they were in the MIKE3. Equation (2) was used to calculate estimated MIE values (Es) which were similar between the MIKE3 and the experimental small-scale device.

[0095] An observation of interest was encountered during the completion of this experimental study. 10 tests of the same mass / spark combination are necessary to disprove ignitability at that condition using the MIKE3. With the small-scale, however, it was found that the MIEs were properly bracketed with only five repeat tests, cutting down on experimental overhead. To be sure of positive ignition, high-speed videos2238-23901 were taken of each ignition test in the small-scale. Some tests were shown to feature only shortlived, non-propagating ignitions, and these were colloquially called partial or “micro ignitions.”

[0096] The occurrence of micro ignitions highlights the subjectivity of ignition. Some micro ignitions were later identified in the footage of the PPC MIKE3 experiments. Although combustion was clearly occurring in the event of a micro ignition, it was not necessarily the case that all operators would qualify a micro ignition as a Go rather than a No-Go without the aid of highspeed video. Furthermore, the process safety case for dust cloud ignition research would be mostly interested in ordinary ignitions, although questions regarding the manner of dust cloud ignition propagation have received due attention.

[0097] To circumvent this subjectivity, it was concluded that some objective criteria was necessary for qualifying a Go in the small-scale. It was decided that an experiment would qualify as a Go if the length of the flame were equal to or greater than the inner diameter of the tube. This is the qualification that was used in parsing out the MIE response curves shown in graphs 620, 630, and 640, and was deemed an adequate criterion for all test results.

[0098] While disclosed embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the disclosure. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1 ), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simplify subsequent reference to such steps.

Claims

2238-23901CLAIMSWhat is claimed is:

1. A small-scale minimum ignition energy (MIE) testing system for estimating the MIE of a dust cloud, the system comprising: a small-scale testing chamber having an internal volume between 25 cubic centimeters (cm3) and 100 cm3; a supply conduit in fluid communication with a supply of test gas and defining an enclosable supply chamber having a target volume; a dispersion nozzle fluidically connected between the supply conduit and the small-scale testing chamber for receiving a sample dust; a control valve positioned along the supply conduit between the enclosable supply chamber and the dispersion nozzle, the control valve having a closed state that restricts fluid communication between the supply chamber and the small-scale testing chamber and an open state providing fluid communication between the supply chamber and the small-scale testing chamber; a pair of electrodes coupled to the small-scale testing chamber; and a computer system comprising one or more processors and one or more memory devices containing instructions that, when executed by the one or more processors, cause the one or more processors to: initiate an activation of the pair of electrodes; shift the control valve from the closed state to the open state in response to the initiation of the activation of the pair of electrodes and following a controlled delay period whereby the target volume of test gas from the enclosable supply chamber is provided to the dispersion nozzle to produce a dust cloud of the sample dust in the internal volume of the small-scale testing chamber; and generate, following a controlled delay period triggered by the shifting of the control valve from the closed state to the open state, an electrical spark by the pair of electrodes in the internal volume of the small-scale testing chamber.

2. The system of claim 1 , wherein the delay period is user-selected.2238-239013. The system of claim 1 , wherein the instructions, when executed by the one or more processors, cause the one or more processors to: control a pressure of the in the enclosable supply chamber.

4. The system of claim 1 , further comprising an endcap sealingly coupled to an end of the small-scale supply chamber opposite the dispersion nozzle.

5. The system of claim 4, a purge fluid conduit coupled to the endcap and configured to deliver a test gas purge through a port of the endcap to the internal volume of the small-scale testing chamber.

6. The system of claim 1 , further comprising a heating element controllable by the computer system and coupled to the small-scale testing chamber for heating the internal chamber of the small-scale testing chamber.

7. A small-scale minimum ignition energy (MIE) testing system for estimating the MIE of a dust cloud, the system comprising: a small-scale testing chamber having an internal volume between 25 cubic centimeters (cm3) and 100 cm3; a supply conduit in fluid communication with a supply of test gas; a dispersion nozzle fluidically connected between the supply conduit and the small-scale testing chamber for receiving a sample dust, the dispersion nozzle having an inner parabolic surface defining a parabolic volume that is open to the internal volume of the small-scale testing chamber; a control valve positioned along the supply conduit having a closed state that restricts fluid communication between the supply of test gas and the small-scale testing chamber and an open state providing fluid communication between the supply of test gas and the small-scale testing chamber; a pair of electrodes coupled to the small-scale testing chamber; and a computer system comprising one or more processors and one or more memory devices containing instructions that, when executed by the one or more processors, cause the one or more processors to: initiate an activation of the pair of electrodes;2238-23901 shift the control valve from the closed state to the open state in response to the initiation of the activation of the pair of electrodes whereby the target volume of test gas from the enclosable supply chamber is provided to the dispersion nozzle to produce a dust cloud of the sample dust in the internal volume of the small-scale testing chamber, and through which an electrical spark between the pair of electrodes extending following the activation of the pair of electrodes.

8. The system of claim 7, wherein a distal end of the dispersion nozzle from which the parabolic volume extends is entirely open to the internal volume of the small-scale testing chamber.

9. The system of claim 7, wherein the dispersion nozzle comprises a dispersion manifold positioned in the parabolic volume, the dispersion manifold defining a plurality of circumferentially spaced dispersion ports.

10. The system of claim 7, wherein the dispersion nozzle comprises polytetrafluoroethylene (PTFE).

11. A method for estimating a minimum ignition energy (MIE) of a dust cloud, the method comprising:(a) conducting a MIE test of a sample dust, the test comprising:(a1) generating a dust cloud comprising the sample dust in an internal volume of a small-scale testing chamber;(a2) generating, following (a1 ), an electrical spark in the internal volume of the small-scale testing chamber and in contact with dust cloud;(b) repeatedly conducting (a) and counting, for each instance of (a), a go for each full ignition of the dust cloud, and a no-go each non-ignition or partial ignition of the dust cloud; and(c) estimating a MIE of the dust cloud based on (b).

12. The method of claim 1 1 , further comprising:(d) cleaning an inner surface of the small-scale testing chamber following each instance of (a).2238-2390113. The method of claim 12, wherein (d) comprises brushing the inner surface using an electrically insulative brush.

14. The method of claim 11 , wherein the estimated MIE of the dust cloud is based on fewer than ten different instances of (a).

15. The method of claim 14, wherein an electrical energy of the electrical spark and a mass of the sample dust is the same for each of the ten different instances of (a).

16. The method of claim 11 , further comprising:(d) pre-purging with test gas the internal volume of the small-scale testing chamber following each instance of (a).

17. The method of claim 11 , wherein (a) comprises:(a3) applying heat from a heating element to the small-scale testing chamber to maintain the internal volume at an elevated setpoint temperature.

18. The method of claim 11 , wherein the internal volume of the small-scale testing chamber is between 25 cubic centimeters (cm3) and 100 cm3.

19. The method of claim 11 , wherein (a1) comprises selectably controlling at least one of a pressure or a quantity of test gas delivered to the internal volume of the small- scale testing chamber.

20. The method of claim 11 , wherein (a) comprises selectably applying a delay period between the execution of (a1 ) and (a2).

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