An apparatus and method for in-situ detection of internal products of combustion in a porous medium

Abstract

The application discloses a kind of porous medium combustion internal product in-situ detection device and method, including porous medium combustor, is equipped with combustion chamber, the combustion chamber is filled with ordered structure porous medium material, the two side walls of the combustion chamber are equipped with first penetration layer and second penetration layer, the two outer sides of the first penetration layer and second penetration layer are respectively equipped with first collimating lens and second collimating lens, first lens group between the first collimating lens and first penetration layer is arranged to make that light beam converges into the light beam of extremely small diameter and passes through first penetration layer, second lens group between the second collimating lens and second penetration layer is arranged to make that light beam converges into the light beam of extremely small diameter and is shot into first collimating lens;Light source;Spectrometer, computer.By adjusting the structure design of porous medium, in-situ detection of internal components of porous medium is realized in combination with ultraviolet differential absorption spectrometry.Compared with traditional extraction type, it is faster, lower in cost and stronger in real-time performance.

Description

Technical Field

[0001] This invention relates to the field of burner technology, and in particular to an in-situ detection device and method for internal products of porous media combustion. Background Technology

[0002] Porous media combustion technology is a novel combustion technology that, compared to traditional combustion technologies, utilizes the heat conduction and storage properties of porous media to significantly improve combustion efficiency, save energy, and reduce CO and NO emissions. X The emission of pollutants such as NO. X The emission levels of pollutants such as NO are one of the indicators for evaluating the quality of porous media burners, so studying their NO emissions is important. X The formation process and emission characteristics of pollutants are crucial.

[0003] For the detection of pollutant concentrations produced by combustion, methods are generally divided into chemical detection and spectroscopic detection. While gas sensors based on traditional chemical detection methods have low detection limits, small size, and low cost, they suffer from low accuracy, require frequent calibration, are susceptible to environmental interference, and have significant errors. Therefore, spectroscopic methods are often chosen for certain scenarios due to their advantages such as high sensitivity, fast response, large measurement range, good stability, and the ability to perform rapid and continuous detection, enabling real-time, high-precision online measurements. However, most spectroscopic methods suffer from complex system structures, low cost-effectiveness, weak anti-interference capabilities, and significant susceptibility to environmental factors such as moisture.

[0004] Furthermore, due to the structural characteristics of porous media, it is difficult to achieve in-situ online detection of the internal combustion process and pollutant generation process through spectroscopic methods, which brings difficulties to revealing the reaction process and pollutant generation mechanism. Summary of the Invention

[0005] The purpose of this invention is to provide an in-situ detection device and method for internal products of combustion in porous media, so as to solve one or more technical problems existing in the prior art, and at least provide a beneficial option or create conditions.

[0006] The technical solution adopted to solve the above-mentioned technical problems is as follows:

[0007] This invention provides an in-situ detection device for internal products of combustion in porous media, comprising:

[0008] The porous medium burner is provided with a combustion chamber filled with ordered porous medium material, and first and second penetrating layers are arranged on the two side walls of the combustion chamber, and first and second collimating lenses are arranged on the two outer sides of the first and second penetrating layers, respectively, and a first lens group is arranged between the first collimating lens and the first penetrating layer to make the light beam converge into a light beam with extremely small diameter and pass through the first penetrating layer, and a second lens group is arranged between the second collimating lens and the second penetrating layer to make the light beam converge into a light beam and enter the first collimating lens, and the first and second penetrating layers, the first and second collimating lenses, the first and second lens groups and the ordered porous medium material are arranged on the same straight line.

[0009] The light source is connected with the first collimating lens through a first optical fiber, and the wavelength range of the light source is 190-2500 nm.

[0010] The spectrometer is connected with the second collimating lens through a second optical fiber.

[0011] The computer is connected with the spectrometer.

[0012] The porous medium burner is provided with a combustion chamber filled with ordered porous medium material, and first and second penetrating layers are arranged on the two side walls of the combustion chamber, and first and second collimating lenses are arranged on the two outer sides of the first and second penetrating layers, respectively, and a first lens group is arranged between the first collimating lens and the first penetrating layer to make the light beam converge into a light beam with extremely small diameter and pass through the first penetrating layer, and a second lens group is arranged between the second collimating lens and the second penetrating layer to make the light beam converge into a light beam and enter the first collimating lens, and the first and second penetrating layers, the first and second collimating lenses, the first and second lens groups and the ordered porous medium material are arranged on the same straight line.

[0013] By adjusting the structure design of the porous medium and combining the ultraviolet differential absorption spectrum method, in-situ detection of the internal components of the porous medium is realized. Compared with the traditional extraction type, the response is faster, the cost is lower, the real-time performance is stronger, and the instrument does not need to be directly contacted with the flue gas, thereby reducing the influence of the flue gas environment on the service life of the instrument. Moreover, the detection is of the internal products of the burner, which is in a semi-closed space, so the online calibration is relatively simple. Moreover, the diameter of the light beam generated by the light source can be reduced from 20 mm to about 4 mm by using different lens combinations, thereby improving the spatial resolution of the detection system.

[0014] As a further improvement of the above technical solution, a three-dimensional moving platform is further arranged, and the porous medium burner is arranged on the three-dimensional moving platform, so that the position of the porous medium burner can be adjusted conveniently, and the measurement of the spatial distribution of the gas concentration in the burner can be realized conveniently.

[0015] As a further improvement of the above technical solution, the three-dimensional moving platform comprises a horizontal moving block, a vertical moving block, a front-back moving block and a base, the horizontal moving block is arranged on the base and can be adjusted left and right, the vertical moving block is arranged on the horizontal moving block and can be adjusted up and down, and the front-back moving block is arranged on the horizontal moving block and can be adjusted front and back.

[0016] As a further improvement of the above technical solution, the first lens group comprises a first plano-convex lens and a second plano-convex lens arranged on the light beam of the light source in sequence.

[0017] As a further improvement of the above technical solution, the second lens group comprises a third plano-convex lens.

[0018] As a further improvement of the above technical solution, the light source comprises a UV deuterium lamp. The device uses in-situ testing of the gas concentration generated inside the combustor, so the optical path is short, and therefore a UV light is used as the light source, which has large energy, and the NO X The strong absorption of gas in the UV band makes up for the low signal-to-noise ratio caused by the short optical path.

[0019] As a further improvement of the above technical solution, the first and second penetration layers are both far-UV optical quartz glass, and the application band is 185-2500nm.

[0020] As a further improvement of the above technical solution, the working band of the spectrometer is 190-415nm, the resolution is 0.16nm, and the signal-to-noise ratio is 250:1.

[0021] The application also provides an in-situ detection method for internal products of porous medium combustion, which is applied to the in-situ detection device for internal products of porous medium combustion.

[0022] When the porous medium combustor is working, the UV light beam emitted by the light source is aggregated into the spectrometer after passing through the porous medium material after aggregation;

[0023] The computer can calculate the absorbance of the to-be-detected gas by comparing the background spectrum data obtained before the combustor is running, which does not carry the gas absorbance information, with the absorption spectrum data carrying the gas absorbance information;

[0024] After a certain mathematical method is processed, the differential absorbance is obtained, the differential absorption cross-section data of the to-be-detected gas is obtained by consulting a database or measuring a gas with a known concentration, and the concentration information of the to-be-detected gas can be inversely calculated through the corrected Lambert-Beer law.

[0025] The method realizes in-situ detection of internal components of the porous medium by adjusting the structure design of the porous medium and combining the UV differential absorption spectrum method. Compared with the traditional extraction type, the response is faster, the cost is lower, the real-time performance is stronger, and the instrument does not need to be directly contacted with the flue gas, thereby reducing the influence of the flue gas environment on the service life of the instrument. Moreover, the detection is for internal products of the combustor, which is in a semi-closed space, so the online calibration is relatively simple.

[0026] Moreover, a UV deuterium lamp is used as the light source, which has large energy, and the NO X The strong absorption of gas in the UV band makes up for the low signal-to-noise ratio caused by the short optical path.

[0027] As a further improvement of the above technical solution, the combustion adjuster is placed on a three-dimensional moving platform, and the position of the combustion adjuster is adjusted by the three-dimensional moving platform, and the measurement step is repeated multiple times. The combustion adjuster is installed on the three-dimensional moving platform, and the distribution information of the combustion internal product at different spatial positions can be obtained by adjusting the height position of the combustion adjuster, and the spatial representation of the measurement data is better. BRIEF DESCRIPTION OF DRAWINGS

[0028] The present application will be further described below in conjunction with the drawings and examples.

[0029] Fig. 1 is a schematic structural diagram of an embodiment of a porous medium combustion internal product in-situ detection device provided by the present application.

[0030] Fig. 2 is a front view schematic diagram of a three-dimensional moving platform of an embodiment of a porous medium combustion internal product in-situ detection device provided by the present application, wherein the four arrows respectively represent forward, backward, upward and downward.

[0031] REFERENCE NUMERALS:

[0032] Light source 1, first optical fiber 2, first collimating lens 3, first plano-convex lens 4, second plano-convex lens 5, first penetration layer 6, porous medium combustor 7, second penetration layer 8, ordered structure porous medium material 9, third plano-convex lens 10, second collimating lens 11, second optical fiber 12, spectrometer 13, computer 14, three-dimensional moving platform 15, transverse moving block 16, longitudinal moving block 17, third fixed block 171, third adjusting screw 172, forward-backward moving block 18, second fixed block 181, second adjusting screw 182, base 19, first fixed block 191, first adjusting screw 192. DETAILED DESCRIPTION

[0033] This part will describe the specific embodiments of the present application in detail, and the preferred embodiments of the present application are shown in the drawings. The drawings serve to supplement the description in the text part of the specification, so that one can intuitively and visually understand each technical feature and the overall technical solution of the present application. However, it cannot be understood as a limitation on the protection scope of the present application.

[0034] In the description of the present application, it should be understood that the orientation description, such as the orientation or position relationship indicated by up, down, front, back, left, right, etc. is based on the orientation or position relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0035] In the description of the present application, if the word such as "several" is described, its meaning is one or more, the meaning of more than two is more than two, greater than, less than, more than, etc. Understand as not including the number, above, below, within, etc. Understand as including the number.

[0036] In the description of the present application, unless otherwise explicitly limited, the words such as setting, installation, connection, etc. Should be understood broadly, and those skilled in the art can reasonably determine the specific meaning of the above words in the present application in combination with the specific content of the technical scheme.

[0037] Porous medium combustion technology is a new type of combustion technology, NO X The emission of pollutants such as NO X The generation process and emission characteristics of pollutants such as NO

[0038] UV differential absorption spectroscopy is a gas concentration spectral detection technology, compared with other spectral methods, it has the advantages of simple system structure, high cost performance, strong anti-interference ability, less affected by environmental moisture, etc. It can be used for multi-component simultaneous measurement. Its unique spectral absorption characteristics of different gas molecules are used to identify gas types, and based on Lambert-Beer law, the gas concentration is further inverted by certain mathematical means.

[0039] In the measurement method of pollutants generated by combustion, it is generally divided into extraction and direct measurement. The extraction method is to collect sample gas by probe, and then measure after a certain pretreatment into the gas cell. However, this method has the problems of long measurement response time, poor real-time performance, easy to appear system error caused by different temperature and pressure, etc. Direct measurement, also known as in-situ measurement, is that the probe directly contacts the flue gas under the actual flue gas temperature, pressure and humidity environment, which can more accurately and truly reflect the concentration information of the flue gas. Compared with the extraction method, its structure is simpler, the response time is faster, and the data results are more representative.

[0040] However, due to the structural characteristics of the porous medium itself, the internal combustion process and the pollutant generation process are difficult to realize in-situ online detection by spectral method, which brings difficulties to reveal the reaction process and pollutant generation mechanism.

[0041] Therefore, with reference to Figs. 1-2 The present application provides a porous medium combustion internal product in-situ detection device and method, and makes the following embodiments:

[0042] In some embodiments, a porous medium combustion internal product in-situ detection device comprises a light source 1, a first optical fiber 2, a first collimating lens 3, a first lens group, a porous medium combustor 7, a second lens group, a second collimating lens 11, a second optical fiber 12, a spectrometer 13, a computer 14, and a three-dimensional moving platform 15.

[0043] The light source 1 is connected with the first collimating lens 3 through the first optical fiber 2, and the combination forms an emission end. The spectrometer 13 is connected with the second collimating lens 11 through the second optical fiber 12, and forms a receiving end. The wavelength range of the light source 1 is 190-2500 nm, wherein an ultraviolet deuterium lamp can be used as the light source 1. The device uses an in-situ method to test the gas concentration generated inside the combustor, so the optical path is short. Therefore, ultraviolet light is used as the light source 1, which has the advantages of large energy, high NO X The strong absorption of gas in the ultraviolet band makes up for the low signal-to-noise ratio caused by the short optical path;

[0044] The first optical fiber 2 and the second optical fiber 12 both use ultraviolet aging-resistant optical fibers. The first lens group comprises a first plano-convex lens 4 and a second plano-convex lens 5 arranged in sequence on the light beam of the light source 1. The second lens group comprises a third plano-convex lens 10. The number of lenses in the first lens group and the second lens group is related to the focal length of the lenses, and is specifically set according to actual needs, as long as the light beam can be converged into a very small light beam.

[0045] The working wavelength range of the spectrometer 13 is 190-415 nm, the resolution is 0.16 nm, and the signal-to-noise ratio is 250:1.

[0046] The three-dimensional moving platform 15 is provided with the porous medium combustor 7, so that the porous medium combustor 7 can be adjusted in the lateral direction, the longitudinal direction, and the front-back direction.

[0047] Specifically, the three-dimensional moving platform 15 comprises a base 19, a lateral moving block 16, a longitudinal moving block 17, and a front-back moving block 18. The lateral moving block 16 is slidably arranged on the base 19. The base 19 is provided with a first fixing block 191. The first fixing block 191 is threadedly connected with a first adjusting screw 192. The first adjusting screw 192 is rotationally connected with the lateral moving block 16. Rotating the first adjusting screw 192 drives the lateral moving block 16 to slide left and right. A screw micrometer can be used to replace the first adjusting screw 192, which can accurately obtain the adjustment displacement.

[0048] The front and rear moving block 18 is arranged to slide forward and backward on the transverse moving block 16, the transverse moving block 16 is provided with a second fixed block 181, the second fixed block 181 is threadedly connected with a second adjusting screw 182, the second adjusting screw 182 is rotationally connected with the front and rear moving block 18, rotating the second adjusting screw 182 drives the front and rear moving block 18 to slide forward and backward, and a screw micrometer can be used to replace the second adjusting screw 182 to accurately obtain the adjustment displacement.

[0049] The longitudinal moving block 17 is arranged to slide up and down on the front and rear moving block 18, the front and rear moving block 18 is provided with a third fixed block 171, the third fixed block 171 is threadedly connected with a third adjusting screw 172 arranged to extend upward and downward, the third adjusting screw 172 is rotationally connected with the longitudinal moving block 17, rotating the third adjusting screw 172 drives the longitudinal moving block 17 to slide up and down, and a screw micrometer can be used to replace the second adjusting screw 182 to accurately obtain the adjustment displacement. The porous medium burner 7 is arranged on the longitudinal moving block 17, in order to avoid the third adjusting screw 172 interfering with the measurement of the porous medium burner 7, an adjusting knob of the third adjusting screw 172 is arranged below the third fixed block 171. The base 19, the transverse moving block 16 and the front and rear moving block 18 are all provided with sliding rails to improve the sliding stability. The sliding rails can be linear guides, rolling guides, etc.

[0050] In other embodiments, the adjustable arrangement of the transverse moving block 16, the longitudinal moving block 17 and the front and rear moving block 18 can also be driven by electric push rods, motors, air cylinders or hydraulic cylinders, etc. to automatically control the movement of the porous medium burner 7. A control system is arranged to control the movement of the three-dimensional moving platform 15 in each direction, responsible for receiving input signals, processing control algorithms and outputting control instructions. The control system usually uses PLC, single-chip microcomputer or industrial computer as the control core.

[0051] The porous medium burner 7 is provided with a combustion chamber, the combustion chamber is filled with ordered structure porous medium material 9, both side walls of the combustion chamber are provided with a first penetrating layer 6 and a second penetrating layer 8, a light source 1 is arranged on an optical path in sequence, including a first collimating lens 3, a first plano-convex lens 4, a second plano-convex lens 5, the first penetrating layer 6, the ordered structure porous medium material 9, the second penetrating layer 8, a third plano-convex lens 10 and a second collimating lens 11; wherein the first penetrating layer 6 and the second penetrating layer 8 are both far ultraviolet optical quartz glass, the application wavelength range is 185-2500nm, and other materials with a wavelength range of 185-2500nm can also be used.

[0052] The light beam emitted by the light source 1 is converged into a light beam with extremely small diameter after passing through the plano-convex lenses 4 and 5, penetrates the quartz glass windows 7 and 8, passes through the ordered holes of the porous medium material 9, and is converged again after passing through the burner 6 through the plano-convex lens 10, then enters the collimating lens 11 and the spectrometer 13, and the computer 14 is connected to the spectrometer 13.

[0053] When the porous medium burner 7 is not started, the original background spectrum I0(λ) without gas absorption information can be obtained from the computer 14. During the combustion operation of the burner 6, the above operation is repeated, the ultraviolet light passes through the porous medium inside the burner, the absorption information of the internal products generated by combustion is obtained, then enters the spectrometer 13, and the gas absorption spectrum I(λ) can be obtained from the computer 14.

[0054] After the original spectrum and the absorption spectrum are preprocessed in a certain manner, the absorbance OD is obtained by dividing and taking the logarithm:

[0055]

[0056] The part of the absorbance OD that changes rapidly with wavelength is extracted by mathematical means, that is, the differential absorbance OD´, the gas differential absorption cross section σ´(λ) data can be obtained through a database or by self-testing of a known concentration gas, and after the optical path L, that is, the width of the porous medium burner 7, is measured, the concentration c can be calculated by the modified Lambert-Beer law through mathematical inversion.

[0057]

[0058] By adjusting the position of the porous medium burner 7 through the three-dimensional moving platform 15, the above measurement steps are repeated, and the distribution information of the internal products of the burner at different spatial positions can be measured.

[0059] The application also provides a porous medium combustion internal product in-situ detection method embodiment, which is applied to the porous medium combustion internal product in-situ detection device.

[0060] The light beam emitted by the light source 1 forms a parallel light with a diameter of about 20 mm after passing through the first collimating lens 3. To ensure that the light beam can smoothly pass through the ordered holes in the porous medium material with as little energy loss as possible, a first plano-convex lens 4 with a large focal length is placed about 20 cm away from the first collimating lens 3, and the light beam is converged. At this time, the diameter of the light beam at the focal point is still not small enough, so a second plano-convex lens 5 with a small focal length is placed about 60 cm away from the first plano-convex lens 4 to further converge the light beam, so that it can smoothly pass through the porous medium burner 7. The distance between the porous medium burner 7 and the second plano-convex lens 5 is about 7 cm. The windows made of ultraviolet optical quartz glass are installed on both sides of the porous medium burner 7, so that the light beam can pass through the ordered holes of the ordered structure porous medium material 9 without attenuation of the light intensity in the measurement waveband. A third plano-convex lens 10 with a small focal length is placed about 25 cm away from the porous medium burner 7. The light beam passing through the porous medium burner 7 is converged by the third plano-convex lens 10. A second collimating lens 11 is placed about 25 cm away from the third plano-convex lens 10. After the light beam enters the second collimating lens 11, it enters the spectrometer 13 through the second optical fiber 12.

[0061] The computer 14 can calculate the absorbance of the gas to be measured by comparing the background spectrum data obtained before the burner is operated with the absorbance information of the carried gas obtained by the absorption spectrum data.

[0062] After a certain mathematical method is used, the differential absorbance is obtained. According to the known differential absorption cross section and optical path data, the concentration information of the gas to be measured can be obtained by the corrected Lambert-Beer law. For specific calculation process, refer to the description of an embodiment of the in-situ detection device for internal products of a porous medium combustion. The burner is placed on the three-dimensional moving platform 15, and the position of the burner is adjusted by the three-dimensional moving platform 15, and the measurement steps are repeated multiple times. The distribution information of the internal products of the combustion at different spatial positions can be obtained, and the spatial representativeness of the measurement data is better.

[0063] This method realizes the in-situ detection of the internal components of the porous medium by adjusting the structure design of the porous medium and combining the ultraviolet differential absorption spectrum method. Compared with the traditional detection system, it has faster response, lower cost, stronger real-time performance, less influence of flue gas environment on the service life of the instrument, and relatively simple online calibration.

[0064] This method uses ultraviolet light as the light source, which has large energy, and the NO X The gas has large absorption intensity in the ultraviolet waveband and is less affected by the main combustion products (H2O, CO2) and other interference, which makes up for the low signal-to-noise ratio caused by the short optical path during in-situ detection.

[0065] The method uses a light beam with a minimum diameter as measuring light, adjusts the position of the burner through a three-dimensional moving platform, and can realize the measurement of the spatial distribution of the gas concentration in the burner, and improves the spatial resolution of the detection system.

[0066] The above describes the preferred embodiments of the present application, but the present application is not limited to the embodiments, and those skilled in the art can make various equivalent modifications or replacements without departing from the spirit of the present application, and these equivalent modifications or replacements are all included in the scope defined by the claims of the present application.

Claims

1. An in-situ detection device for internal products of combustion in porous media, characterized in that, include: A porous media burner includes a combustion chamber filled with an ordered porous media material. The combustion chamber has a first penetrating layer and a second penetrating layer on its two side walls. A first collimating lens and a second collimating lens are respectively disposed on the outer sides of the first and second penetrating layers. A first lens group is disposed between the first collimating lens and the first penetrating layer, allowing the light beam to be focused into a beam with an extremely small diameter and pass through the first penetrating layer. A second lens group is disposed between the second collimating lens and the second penetrating layer, allowing the light beam to be focused into a beam with an extremely small diameter and enter the first collimating lens. The first penetrating layer, the second penetrating layer, the first collimating lens, the second collimating lens, the first lens group, the second lens group, and the ordered porous media material are all arranged on the same straight line. The first lens group includes a first plano-convex lens and a second plano-convex lens sequentially disposed on the light beam of the light source. The light source is connected to the first collimating lens via a first optical fiber, and the wavelength range of the light source is 190-2500nm; The spectrometer is connected to the second collimating lens via a second optical fiber. A computer connected to a spectrometer.

2. The in-situ detection device for internal products of combustion in porous media according to claim 1, characterized in that: It also includes a three-dimensional moving platform that makes the porous media burner adjustable in the three directions of transverse, longitudinal and forward and backward, wherein the porous media burner is disposed on the three-dimensional moving platform.

3. The in-situ detection device for internal products of combustion in porous media according to claim 2, characterized in that: The three-dimensional moving platform includes a horizontal moving block, a vertical moving block, a front-back moving block, and a base. The horizontal moving block is adjustable left and right on the base, the vertical moving block is adjustable up and down on the horizontal moving block, and the front-back moving block is adjustable front and back on the horizontal moving block.

4. The in-situ detection device for internal products of combustion in porous media according to claim 3, characterized in that: The second lens group includes a third plano-convex lens.

5. The in-situ detection device for internal products of combustion in porous media according to claim 1, characterized in that: The light source includes an ultraviolet deuterium lamp.

6. The in-situ detection device for internal products of combustion in porous media according to claim 1, characterized in that: Both the first and second penetrating layers are far-ultraviolet optical quartz glass, with an application wavelength of 185-2500nm.

7. The in-situ detection device for internal products of combustion in porous media according to claim 1, characterized in that: The spectrometer operates in the 190-415nm wavelength range, has a resolution of 0.16nm, and a signal-to-noise ratio of 250:

1.

8. A method for in-situ detection of internal products during combustion in porous media, characterized in that, It is applied to the in-situ detection device for internal combustion products of porous media as described in any one of claims 1 to 7, comprising: When the porous media burner is working, the ultraviolet beam emitted by the light source is polymerized, passes through the porous media material, and then converges into the spectrometer. The computer can calculate the absorbance of the gas to be tested by comparing the absorption spectrum data carrying gas absorbance information with the background spectrum data that does not carry gas absorbance information obtained before the burner is running. After processing with certain mathematical methods, the differential absorbance is obtained. By consulting a database or measuring a gas of known concentration, the differential absorption cross-section data of the gas to be tested is obtained. Then, by applying the modified Lambert-Beer law, the concentration information of the gas to be tested can be deduced.

9. The method for in-situ detection of internal products of combustion in porous media according to claim 8, characterized in that: The burner is positioned on a three-dimensional moving platform, and its position is adjusted using the platform. This measurement process is repeated multiple times.

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