Spark detectors for conveyor systems of flammable materials

Abstract

The invention relates to a spark detector for extraction and conveying systems of combustible materials. Such spark detectors serve for the early detection of incipient fires and have a detector element 2, which is designed as an optical sensor. The small-area detector element is protected against contamination by the transported materials by a flat protective glass pane. According to the invention, the flat protective glass pane is replaced by an optical arrangement for generating a focal point, in particular by a converging lens, which causes the electromagnetic radiation 3 to be detected to be focused directly onto a focal point, or in its vicinity, on the surface of the detector element 2. This significantly increases the sensitivity of spark detector 1.

Description

[0001] The present invention relates to a spark detector for fire suppression in pneumatic extraction or conveying systems in which flammable materials are transported.

[0002] In pneumatic extraction and conveying systems, drop chutes, or mechanical conveying systems transporting flammable materials such as pellets or wood shavings, the generation of sparks and flying sparks can often lead to extensive and dangerous fires. Even when flammable materials and dusts are transported via airflow, for example, in connected filter systems, flying sparks can cause fires or explosions and damage the equipment. The generation of such ignition points in conveyed materials is usually caused by the machinery used or by material contamination. Production downtime, significant property damage, and risks to the life and health of employees can result from delayed fire suppression measures. To eliminate this fire risk, extraction systems must be effectively monitored for sparks using spark detectors and protected by spark extinguishing systems.Optical sensors used as spark detectors are designed to reliably detect the infrared radiation emitted by sparks or ignition points and to send an alarm signal to a fire suppression control center to initiate a fire suppression process.

[0003] The term "spark detector" refers to any type of optical sensor with an optical window for detecting any type of electromagnetic radiation emanating from fires or incipient fires, such as sparks, flames or embers (ignition initials).

[0004] For reliable signal detection, the spark detectors must be positioned as close as possible and directly within the monitoring area of ​​a conveyor system. The sensitive sensors (detector elements) are protected by optical, i.e., radiation-transmitting, flat optical windows.

[0005] Furthermore, the use of fiber optic rods instead of flat glass discs as a protective mechanism for the detector elements is also known.

[0006] When arranging glass panes designed as optical windows to protect detector elements (optical sensors), usually either flat-ground or curved glass panes without further optical functions are used.

[0007] The surface area of ​​the protective glass pane is much larger than that of the optical sensors designed as detector elements that are to be protected.

[0008] As a result, only a small portion of the infrared radiation emanating from a spark or embers reaches the surface of the optical sensor of the detector element installed in the spark detector.

[0009] Most of the electromagnetic radiation penetrating the glass pane does not reach the detector element and passes through the housing of the spark detector without generating a signal, and therefore cannot be used for the necessary early detection of fires.

[0010] A similar technical problem of focusing electromagnetic radiation to monitor flames using optical sensors is known, for example, from heating technology.

[0011] German patent DE102021114278A1 describes a flame monitoring device comprising a hollow mirror that reflects the ultraviolet radiation emitted by the gas flames of a heating appliance onto a lens, which then directs the UV radiation to an optical sensor for flame monitoring. However, the beam focusing technique described here is not suitable for detecting rapidly moving ignition sources, such as sparks, in conveyed materials in conveyor systems. Even the arrangement of hollow mirrors in suitable pipelines for beam focusing is hardly feasible.

[0012] The object of the present invention is therefore to propose improved detection of ignition initiations in a moving material stream consisting of combustible particles using spark detectors with optical sensors. Furthermore, the protection of the surface of the optical detectors and their signal stability in the harsh measuring environment of extraction and conveying lines are also to be improved.

[0013] These problems are essentially solved by the inventive features of the first and sixth patent claims in conjunction with the preamble.

[0014] Further advantageous embodiments of the invention are specified in the dependent claims.

[0015] According to the invention, the protective glass pane on the head of a spark detector, which is usually ground flat on both sides, is replaced by an optical arrangement in the form of a converging lens for generating a focal point.

[0016] The distances between the converging lens and the light-sensitive surface of the optical sensor on the optical axis, as well as the curvature and shape of the converging lens, are chosen such that the focal point for signal generation is located on or near the optical sensor.

[0017] This causes the electromagnetic radiation to be detected to be focused onto a focal point directly on or near the surface of the detector element, thus generating a signal.

[0018] Depending on the radiation spectrum to be captured, different types of glass can be used for the converging lens, which have a correspondingly high transmission at the IR wavelengths to be captured.

[0019] According to the invention, various optical sensors, each with different detection spectra and usable as detector elements for the spark detector, are arranged behind the converging lens.

[0020] Depending on the various flammable materials transported in pneumatic extraction and conveying systems, the spark detectors can also be designed with material-specific detection spectra.

[0021] The spark detector according to the invention, whose optical system, consisting of a detector element and collecting lens, which is directly exposed to the detection of ignition initials in the transport lines, can be monitored for impurities on the optical surface by means of an automatic contamination detection system.

[0022] For this purpose, a microcontroller-controlled TOF sensor is additionally arranged in the head of the spark detector.

[0023] The invention will now be explained in more detail with reference to two figures and several exemplary embodiments.

[0024] They show: Fig. 1: the cross-section of the spark detector, 1 with a converging lens 5, Fig. 2: how Fig. 1. Curvature of the converging lens towards the detector element 2.

[0025] The spark detector 1 designed according to the invention for detecting electromagnetic radiation in the infrared range has an optical sensor designed as a detector element 2 on its head section 10. The detector element 2 is connected to evaluation electronics 7, known per se, for evaluating and forwarding the electrical signals of the received IR radiation converted in the detector element 2 via the connecting line 8.

[0026] Since early detection of ignition points in a volume flow of rapidly moving combustible particles plays a crucial role in initiating fire protection measures, high optical sensitivity of the detector element (2), particularly for the wavelength ranges of IR radiation, is of great importance. The often low IR emission of moving ignition points, such as a spark, is focused by the arrangement of a converging lens 5 in front of the small-area detector element 2, which is positioned at or near the focal point of the ignition point, according to the invention. With the previously used, significantly larger flat glass plate in front of the detector element 2, a large proportion of the incoming IR radiation is not utilized for signal processing.

[0027] With conventional systems, up to 80% of the IR radiation to be detected is lost when using glass panes that are flat on both sides.

[0028] According to the invention, the infrared radiation components are focused by the converging lens 5, and the detector element 2, located at or near its focal point, is used to generate a stronger signal. This significantly increases the signal strength and sensitivity of the spark detector 1, enabling a much earlier alarm trigger for firefighting measures.

[0029] Any type of converging lens or convex lens or other arrangement for generating a focal point on the detector element 2 can be used, regardless of its shape, number and arrangement. The lens shape can vary depending on the application or required beam focusing.

[0030] More complex optical arrangements in front of detector element 2 are also conceivable for generating a focal point.

[0031] In a particularly preferred embodiment, the converging lens 5 is ground flat on one side, while the other side is curved and shaped as a spherical segment, focusing the incoming radiation to a focal point.

[0032] In Fig. 1 and Fig. 2 are differently shaped and oriented converging lenses 5 in the head part 10 of the spark detector 1 to generate a focal point.

[0033] Since aberrations such as spherical aberration occur in every optical system for generating a focal point, the detector element 2 is not always positioned exactly at the focal point of the convex lens 5. The generated focal point is not point-like, but has a certain length.

[0034] However, even focused IR rays deviating from the focal point generate a much higher radiation intensity and thus a higher signal strength on the detector surface 2. This significantly improves the sensitivity of the entire novel spark detector system 1 compared to the previously known conventional spark detector with a flat glass pane on both sides as sensor protection.

[0035] In further special embodiments, depending on the transport material, types of glass are used for the relevant wavelength ranges for ignition initials which have a high transmittance for the emission spectra of the expected sparks and other ignition initials.

[0036] For example, for classic sparks in pneumatic extraction and transport systems, borosilicate glasses with a 90% transmission in the visible and infrared spectrum or sapphire glass with a high transmission in the near infrared range are used for the detection of embers and hot particles that do not glow but can be responsible as possible ignition sources for the start of a fire.

[0037] Table 1 below shows examples of different types of glass whose transmission in the visible and infrared spectrum is ≥ 90% for different spectral ranges. Table 1: Examples of glass types Glass Transmission > 90% Borosilicate from approximately 0.31µm to approximately 2.2µm Quartz glass from approximately 0.17µm to approximately 5µm Sapphire glass from approximately 0.15µm to approximately 6µm

[0038] According to the invention, the type of glass for the collecting lens 5 and for the construction of the spark detector 1 according to the invention is selected according to the expected detection spectrum of the material to be monitored in the extraction or transport line.

[0039] Depending on the fire protection monitoring task, suitable types of glass can also be selected and used, as well as different sensor types or detector elements 2.

[0040] Therefore, in further advantageous embodiments of the invention, detector elements 2 with different detection spectra can also be used for a spark detector 1 with a converging lens 5 according to the invention.

[0041] The following table lists IR detectors for various wavelength ranges within the IR spectral range. The appropriate detector with the corresponding detection spectrum must be selected according to the ignition initiations to be monitored. Table 2: Examples of IR detectors Detector element (IR detector) Detection spectrum in µm Silicon (Si) from approximately 0.4 µm to approximately 1.1 µm Germanium (Ge) from approximately 0.8 µm to approximately 2.1 µm Indium arsenide (InAs) from approximately 0.9 µm to approximately 3.5 µm Indium gallium arsenide (InGaAs) from approximately 1.1 µm to approximately 1.7 µm Lead(II) sulfide (PbS) from approximately 1 µm to approximately 3.3 µm Lead selenide (PbSe) from approximately 1 µm to approximately 5.2 µm Indium antimonide (InSb) from approximately 1 µm to approximately 5.5 µm

[0042] The detector elements 2 listed in Table 2 are only examples, as other detector elements with different compositions and configurations are also suitable for detecting electromagnetic radiation in the desired spectral ranges.

[0043] In a further advantageous embodiment of the invention, in addition to its optical system 6, consisting of detector 2 and collecting lens 5, an automatic contamination detection system is arranged for contaminants on the surface of the collecting lens 5.

[0044] This makes it possible, and particularly advantageous, to detect and eliminate certain changes in signal strength caused by contamination particles adhering to the collecting lens 5 at an early stage. This is especially important because the spark detectors 1 must be positioned in a harsh environment with rapidly moving particles.

[0045] Such systems for detecting contamination of optical surfaces are known and are described, for example, in DE102020100837 A1.

[0046] The hardware of this contamination detection system for spark detectors comprises a contamination sensor designed as a TOF sensor, which is signal-linked to the spark detector. The TOF (Time-Of-Flight) sensor, also located in the head section 10 of the spark detector 1, is equipped with a microcontroller and connected to the spark detector 1.

[0047] However, it is also conceivable to adapt and use other known methods for detecting contamination of optical surfaces and to integrate their sensors into the spark detector 1 according to the invention.

[0048] Additional monitoring for contaminants on the outer surface of the collecting lens 5 ensures a permanently increased sensitivity of the detection of ignition initiations in the pneumatic extraction and conveying systems in question.

[0049] The arrangement of a focal point-generating converging lens 5 makes it possible to focus the radiation to be detected from monitored objects onto or near the required detection surface, to detect ignition initials that could lead to fires even earlier and to take extinguishing measures.

[0050] The spark detector 1 according to the invention allows an improvement in the detection of electromagnetic radiation taking into account the detection angle of the radiation, such as the angle of incidence of the radiation into the converging lens 5.

[0051] However, other detection parameters such as the detection distance, i.e. the distance of the ignition initial to the detector element 2, as well as the size of the ignition initial as an effective radiation area or the temperature of the ignition initial are also significantly improved by the spark detector 1 according to the invention compared to the prior art. Reference symbol list 1 spark detector 2 Detector element, optical sensor (infrared radiation) 3 Electromagnetic radiation 4 spark detector housings 5 Converging lens, convex lens (optical lens), (Optical arrangement for creating a focal point) 6 optical system (2, 5) 7 Evaluation electronics 8 Connection line for signal transmission 9 flat surface of 5 10 Head of the spark detector 1 QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 102021114278A1

[0011] DE 102020100837 A1

[0045]

Claims

[1] Spark detector (1) for detecting electromagnetic radiation (3) emitted by sparks, flames and other ignition sources which may occur in pneumatic extraction and conveying systems, drop chutes or mechanical conveying systems of combustible materials, comprising at least one optical sensor designed as a detector element (2) which is arranged in a spark detector housing (4) and is protected against contamination by the transported materials by a flat protective glass pane, characterized by , that the flat protective glass pane is replaced by an optical arrangement for generating a focal point (5), which causes the electromagnetic radiation (3) to be detected to be focused onto a focal point directly on, or in the vicinity of, the surface of the detector element (2). [2] Spark detector (1) according to claim 1, characterized by, that the optical arrangement for generating a focal point (5) is designed as a converging lens (5) which is formed in a convex shape on one side or on both sides of the optical axis to generate a focal point on or near the surface of the detector element (2), wherein the shape of the converging lens (5) can vary depending on the application of the EM radiation to be detected or the required radiation focusing. [3] Spark detector (1) according to claim 2, characterized by , that the converging lens (5) and the detector element (2) form the optical system (6) which is designed for the detection of EM radiation in the infrared range and the converging lens (5) consists of a glass transparent to IR radiation which has sufficient transmission for the entire detection spectrum to be detected. [4] Spark detector (1) according to claim 3, characterized by , that the converging lens (5) is made of borosilicate glass, quartz glass or sapphire glass. [5] Spark detector (1) according to claim 4 characterized by , that the optical sensor (2) designed as a detector element (2) based on silicon or germanium or indium arsenide or indium gallium arsenide or lead (II) sulfide or lead selenide or indium antimonide with correspondingly different sensitivities of their detection spectra can be installed in the spark detector (1) depending on the application. [6] Spark detector (1) according to any one of the preceding claims, characterized by , that the collecting lens (5) of the optical system (6) is equipped with a system for automatic contamination detection which monitors the spark detector (1) for contamination. [7] Spark detector (1) according to claim 6, characterized by, that the automatic contamination detection on the collecting lens (5) has a TOF sensor (Time-Of-Flight) designed as a contamination sensor and a microcontroller, which are connected to the evaluation electronics (7) of the spark detector (1) and the fire alarm control panel via signal technology.

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