A method for intelligent dust removal control of large air volume in a hot rolling production line

Abstract

This invention discloses a high-volume intelligent dust removal control method for hot rolling production lines, relating to the field of environmental protection technology in the metallurgical industry. The method comprises six steps: on-site condition survey and equipment reuse assessment, air volume adaptation design, dust source collection mechanism layout, main dust removal equipment debugging, system pipeline optimization and intelligent control system construction, phased implementation, and system calibration. This invention achieves efficient dust source control through adaptive high-volume design and near-source side suction collection. Combined with weather-resistant purification equipment and intelligent frequency conversion control linked to hot rolling conditions, it achieves deep purification of dust-laden flue gas and low-energy system operation. This solves the problems of low collection efficiency, high energy consumption, high maintenance costs, and poor stability in existing hot rolling dust removal systems, ensuring environmental compliance and continuous stable operation of the hot rolling production line.

Description

Technical Field

[0001] This invention relates to the field of environmental protection technology in the metallurgical industry, specifically to a method for intelligent dust removal control of large air volume in hot rolling production lines. It is applicable to the purification and treatment of flue gas dust in various hot-rolled strip steel production lines, and is particularly suitable for hot rolling production lines that do not have an existing dust removal system or require upgrades to the dust removal system. Background Technology

[0002] Hot-rolled strip steel production lines are core equipment in the production of sheet metal in the steel industry. During the production process, a large amount of oily fumes and dust are generated. The unorganized diffusion of such pollutants not only pollutes the factory working environment but also affects the operational stability of precision equipment on the production line. At the same time, there are environmental compliance risks. Therefore, a high-efficiency and stable dust removal system is a necessary guarantee for the safe and compliant operation of hot-rolled production lines.

[0003] The existing technology has the following problems:

[0004] 1. Existing dust removal systems in hot rolling production lines generally suffer from insufficient adaptability of air volume design to dust-generating conditions, poor dust source capture efficiency, and inability to achieve effective dust control under all operating conditions, making it difficult to meet the standards for environmental remediation.

[0005] 2. The existing dust removal system lacks linkage control with the hot rolling production process, resulting in high system energy consumption, easy clogging and wear of filter elements, high equipment maintenance frequency, high maintenance costs, and insufficient operational stability. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned shortcomings in the prior art and provide a high-volume intelligent dust removal control method for hot rolling production lines. Through adaptive air volume design, efficient source dust collection, weather-resistant purification treatment, and intelligent control linked with production conditions, this invention solves the problems of insufficient collection efficiency, high operating energy consumption, high maintenance costs, and poor stability of existing hot rolling production line dust removal systems, thereby achieving efficient dust purification and low-consumption, stable operation of the dust removal system in hot rolling production lines.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for intelligent dust removal control of large air volume in a hot rolling production line includes the following steps:

[0009] The first step is on-site working condition survey and equipment reuse assessment: a comprehensive survey of all dust-generating points on the target hot rolling production line is conducted to collect the dust generation patterns, flue gas characteristics, and on-site spatial layout parameters of each dust-generating point. At the same time, a comprehensive reusability assessment is conducted on the existing supporting equipment that can be used for the dust removal system, including induced draft equipment, dust collector housings, and conveying pipelines, to identify components that can be directly reused or modified for reuse, and to formulate a suitable reuse plan.

[0010] The second step is the design of the dust removal system's air volume adaptation: Based on the dust-generating parameters obtained from the on-site survey and combined with the maximum dust-generating conditions of the hot rolling production line, the core air volume of the dust removal system is designed to adapt to the dust. At the same time, air volume redundancy is reserved to cover the dust generation fluctuations of the entire production line, ensuring that the dust at the dust-generating points can be fully captured during the full-load operation of the production line, and avoiding unorganized spillover.

[0011] The third step is to optimize the layout of the dust source collection mechanism: a special side-suction gas collection mechanism adapted to the hot rolling mill stand is adopted, and the gas collection mechanism is precisely placed at the corresponding position of each dust-generating point on the production line, so that the suction port of the gas collection mechanism is precisely aligned with the dust-generating point. At the same time, a flow guiding and equalizing component is set inside the gas collection mechanism to optimize the airflow distribution, realize efficient source collection of dust at the dust-generating point, and reduce the processing load of the subsequent dust removal system.

[0012] The fourth step is the installation and commissioning of the main dust removal equipment: Select temperature-resistant, oil-resistant, and moisture-resistant filter elements that are compatible with the characteristics of hot-rolled oily flue gas as the core purification components, build the main dust removal equipment, and install self-cleaning and anti-clogging bag components to meet the purification requirements of hot-rolled oily dust. After the installation of the main dust removal equipment is completed, the equipment is commissioned according to the flue gas characteristics of the hot-rolling production line to ensure stable equipment operating resistance and good dust removal effect.

[0013] The fifth step is to optimize the system pipeline and establish intelligent control: optimize the low-resistance layout of the dust removal system's conveying pipeline, carry out air leakage control of the entire pipeline, and reduce system airflow loss and operating resistance; perform frequency conversion adaptation of the dust removal system's induced draft mechanism, and build an intelligent linkage control module between the dust removal system and the hot rolling production line to realize the dynamic adjustment of the induced draft mechanism's operating parameters according to the dust generation conditions of the production line; at the same time, configure an integrated ash unloading and conveying mechanism to realize the automatic cleaning and conveying of purified and collected dust, reducing the need for manual intervention.

[0014] Step 6, phased implementation and full-condition system calibration: Following the phased implementation process of first installing the source collection mechanism, then debugging the main dust removal equipment and the dust removal system, and finally optimizing the pipeline and building the intelligent control system, the dust removal system is installed and debugged in a step-by-step manner to avoid interfering with the normal and continuous operation of the hot rolling production line. After the system is installed, the control link is connected, and system calibration is carried out covering no-load and full-load conditions of the production line to ensure that the purification efficiency and operational stability of the dust removal system meet the standards.

[0015] Due to the adoption of the above technical solution, the technical progress achieved by this invention compared to the prior art is as follows:

[0016] 1. This invention, through its adaptable airflow design and efficient source collection mechanism, can achieve effective dust collection and deep purification under all operating conditions of the hot rolling production line, fully meeting environmental control requirements and completely avoiding environmental compliance risks.

[0017] 2. Through comprehensive on-site surveys and equipment reuse assessments in the early stages, this invention can fully reuse existing supporting equipment on-site, significantly reducing the investment cost of technical upgrades to the dust removal system, while also being adaptable to hot rolling production line scenarios of different specifications.

[0018] 3. This invention, through intelligent frequency conversion control linked to hot rolling production conditions, enables dynamic adjustment of the dust removal system's operating parameters according to dust generation conditions, avoiding ineffective energy consumption and significantly reducing the long-term operating electricity costs of the dust removal system.

[0019] 4. This invention uses a weather-resistant filter element and a self-cleaning anti-clogging bag structure that are compatible with hot-rolled oily flue gas. This can effectively avoid the problems of filter element clogging and excessive wear, reduce the frequency of equipment maintenance and spare parts replacement costs, and reduce the labor input for operation and maintenance.

[0020] 5. This invention, through optimized low-resistance pipeline layout and leakage control, can significantly reduce the overall operating resistance of the dust removal system, reduce wear during equipment operation, and significantly extend the mechanical service life of the core equipment of the dust removal system.

[0021] 6. The present invention adopts a phased implementation process, which can complete the installation and commissioning of the dust removal system under the premise of normal and continuous operation of the hot rolling production line, thus avoiding production stoppage losses caused by the technical transformation process.

[0022] 7. Through system calibration under all working conditions and stable purification design, this invention can effectively avoid the pollution and blockage of precision equipment on the production line caused by the unorganized diffusion of dust, ensure the stable operation of the core equipment of the hot rolling production line, and improve the continuous production efficiency of the production line. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the overall layout of the high-volume intelligent dust removal system for the hot rolling production line described in this invention.

[0025] Figure 2 This is a schematic diagram of the structure of the rolling mill-specific side-suction gas collecting mechanism described in this invention;

[0026] Figure 3 This is a schematic diagram showing the connection between the dust removal main equipment and the intelligent linkage control module described in this invention. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art will understand that the present invention covers all alternatives, improvements, and equivalents that may be included within the scope of the claims.

[0028] Implementation Plan

[0029] This implementation plan provides a high-volume intelligent dust removal control method for hot rolling production lines, applied to a 1780 hot-rolled strip steel production line in a steel enterprise. This production line is a conventional hot continuous rolling line, including a roughing mill, a finishing mill, laminar flow cooling, and a coiling area. The entire line lacks an existing dust removal system. The roughing and finishing mill areas are the core dust-generating areas during production, producing oily, high-temperature, and dusty flue gas, requiring a dedicated dust removal system to achieve environmentally compliant emissions. The specific implementation steps of this plan are as follows:

[0030] Step 1: On-site working condition survey and equipment reuse assessment: A survey was conducted on the entire 1780 hot rolling production line to identify the roughing mill and finishing mill as the core dust-generating areas. The spatial dimensions and dust generation patterns of the dust-generating points were measured, and the total dust generation, flue gas temperature, and oil content were determined when the production line was running at full load. At the same time, the existing equipment on site was investigated. There were no usable induced draft fans, dust collector shells, or main pipelines on site, and no usable reused parts. Therefore, a completely new construction plan was adopted.

[0031] Step 2, Dust Removal System Airflow Adaptation Design: Based on the surveyed dust generation data, the core processing airflow of the dust removal system is designed to be 350,000 m³ / h, while reserving 10% airflow redundancy, that is, the maximum processing airflow can reach 385,000 m³ / h, covering dust generation fluctuations under all operating conditions of the production line.

[0032] Step 3: Optimization of Dust Source Collection Mechanism Layout: A special side-suction type dust collection hood adapted to the 1780 hot rolling mill stand is adopted. Dust collection hoods are deployed at each dust-generating point in the roughing mill and finishing mill. The installation position and angle of the dust collection hoods are adjusted to ensure that the dust inlet is precisely aligned with the dust-generating point. A flow guide plate is installed inside the dust collection hood to optimize the airflow distribution. According to on-site testing, the dust collection efficiency can reach 96%.

[0033] Step 4: Layout and commissioning of main dust removal equipment: sintered plastic plates are selected as the core filter element to build a large-volume dust removal main equipment, equipped with a pulse self-cleaning system, which has anti-clogging and self-cleaning functions to meet the purification needs of hot-rolled oily fumes; after the equipment is installed, the cleaning cycle and cleaning pressure are adjusted according to the characteristics of hot-rolled fumes. After the adjustment, the equipment operating resistance is stable within 1500Pa, and the cleaning effect is good.

[0034] Step 5: System Piping Optimization and Intelligent Control Setup: The dust removal pipeline is designed with a low-resistance layout. The main pipeline adopts smooth elbows and diameter transitions to reduce local resistance. At the same time, the entire pipeline is sealed to control the air leakage rate to within 5%. The main induced draft fan is upgraded with frequency conversion, and an intelligent PLC control unit is built to achieve interlocking and linkage with the hot rolling production line. The fan speed can be dynamically adjusted according to the mill's operating load and dust generation. At the same time, an integrated dust collection and conveying device consisting of a ash discharge valve and a scraper conveyor is installed to achieve automatic dust collection and conveying.

[0035] Step 6, Phased Implementation and Full-Condition System Calibration: The system was implemented in phases: "Fuel hood installation → dust removal main equipment installation and cleaning system commissioning → pipeline optimization and intelligent control system construction." The entire process utilized the production line's scheduled maintenance window, ensuring uninterrupted normal operation of the production line. After system installation, system calibration was performed under no-load, 70% production line load, and full-load conditions. After calibration, dust emission concentration stabilized below 8 mg / m³, system operating resistance was reduced by 22% compared to conventional design, equipment lifespan is expected to reach 6 years, and annual maintenance costs can be reduced by 180,000 yuan, fully meeting environmental protection and production operation requirements.

[0036] In this implementation plan, it should be noted that, firstly, through a comprehensive on-site survey, the dust generation patterns and flue gas characteristics of each dust-generating point in the hot rolling production line are accurately grasped. At the same time, the reuse assessment of existing equipment is completed, providing a basis for the adaptability design of the dust removal system, ensuring that the system design is fully matched with the on-site working conditions, and maximizing the control of technical transformation investment costs.

[0037] Secondly, the air volume is designed to be adaptable based on the survey data, matching the air volume requirements of the production line under the maximum dust generation conditions, while reserving air volume redundancy for fluctuations in operating conditions. This ensures that dust can be completely captured from the source, preventing unorganized spillover. Through a side-suction air collection mechanism adapted to the rolling mill stand, dust-generating points can be captured near the dust source. Combined with internal flow guiding and equalization components to optimize airflow distribution, the dust collection efficiency is greatly improved, and the processing load of subsequent systems is reduced.

[0038] Then, the captured dust-laden flue gas is deeply purified by using weather-resistant filter elements adapted to the characteristics of hot-rolled oily flue gas. A self-cleaning and anti-clogging bag structure is provided to prevent filter element blockage and ensure long-term stable operation of the dust removal equipment. Through low-resistance pipeline design and air leakage control, the system operating resistance and air volume loss are reduced, and equipment wear is reduced.

[0039] Finally, through the intelligent linkage control module, the dust removal system and the hot rolling production line are interlocked. The operating parameters of the induced draft mechanism are dynamically adjusted according to the rolling mill's operating load and dust generation, avoiding ineffective system operation and significantly reducing operating energy consumption. At the same time, a step-by-step implementation process is adopted to complete the system construction and transformation without affecting the normal operation of the production line. With the integrated ash unloading and conveying mechanism, the manual input of system operation and maintenance is reduced, and the long-term low-consumption and stable operation of the dust removal system is achieved.

[0040] The present invention will be further described in detail below with reference to embodiments:

[0041] Example 1

[0042] This embodiment, based on the above implementation plan, is applied to a newly built 1780 hot rolling production line in a steel company. The entire line lacks an existing dust removal system. The specific implementation steps are as follows:

[0043] (1) On-site survey and reuse assessment: The dust generation points in the roughing, finishing and coiling areas of the production line were surveyed. The total dust generation under full load was measured to be 1200 kg / h, the highest flue gas temperature was 120℃, and the oil content was 8%. There was no usable reuse equipment on site, so a new construction plan was determined.

[0044] (2) Air volume design: The core design air volume is 350,000 m³ / h, with a 10% air volume redundancy reserved, and the maximum processing air volume is 385,000 m³ / h.

[0045] (3) Layout of gas collection mechanism: The rolling mill-specific side suction gas collection hoods are evenly distributed at all dust-generating points along the line. The gas collection hoods have built-in flow guide plates and the alignment deviation between the suction inlet and the dust-generating point is controlled within 50mm. After testing, the dust source collection efficiency is 96.2%.

[0046] (4) Main dust removal equipment: a plastic sintered plate dust collector is adopted, with a filtration velocity of 0.8 m / min and a pulse self-cleaning system. The cleaning pressure is 0.4 MPa and the cleaning cycle is 15 min. After debugging, the equipment operating resistance is stable at 1450 Pa.

[0047] (5) System optimization and intelligent control: The main pipeline adopts a low-resistance design with a total pipeline air leakage rate of 4.2%; the main induced draft fan is equipped with a frequency conversion control system, which is interlocked with the mill operation and can dynamically adjust the fan speed according to the mill load, with an operating frequency range of 20-50Hz; it is equipped with an integrated ash unloading and conveying device to realize the automatic conveying of dust to the ash silo.

[0048] (6) Phased implementation and calibration: The phased implementation was carried out during the equipment installation window of the production line, without affecting the commissioning and production progress of the production line; after full-condition calibration, the dust emission concentration was stabilized at 7.2mg / m³, the system operating resistance was reduced by 23% compared with the conventional design, the equipment is expected to have a service life of 6.5 years, and the annual operation and maintenance cost was reduced by RMB 190,000 compared with the conventional solution.

[0049] This embodiment achieves efficient and stable operation of the dust removal system in the newly built hot rolling production line. The dust collection efficiency and emission concentration both meet the most stringent environmental protection standards. The system energy consumption and operation and maintenance costs are significantly reduced, and it is fully adapted to the continuous production needs of the production line.

[0050] Example 2

[0051] This embodiment, based on the above implementation plan, is applied to a 1780 hot rolling production line of a steel company that has been in operation for 5 years. The original dust removal system has a designed air volume of 280,000 m³ / h, and suffers from insufficient collection efficiency, excessive emissions, and high energy consumption. This is an upgrade and renovation project, and the specific implementation steps are as follows:

[0052] (1) On-site survey and reuse assessment: The dust generation conditions of the production line were surveyed and the total dust generation under full load was measured to be 1150 kg / h. The original dust collection system had a collection efficiency of only 82% and an emission concentration of 28 mg / m³. The existing equipment was repurposed. The original dust collector shell and main pipeline could be modified and reused. The original fan, filter material and dust removal system needed to be replaced. The reuse rate could reach 42%, which greatly reduced the modification cost.

[0053] (2) Air volume design: The core design air volume is 350,000 m³ / h, with a 10% air volume redundancy reserved. The original main pipeline is expanded to meet the air volume requirements.

[0054] (3) Layout of the gas collection mechanism: The original inefficient gas collection hood was removed and replaced with a side-suction gas collection hood for rolling mills. It has a built-in flow guide plate and accurately aligns with the dust generation point. After testing, the dust source collection efficiency was increased to 95.7%.

[0055] (4) Main dust removal equipment: The original dust collector shell is reused and replaced with a high-efficiency oil-resistant filter cartridge as the core filter element. The pulse self-cleaning system is upgraded and the cleaning parameters are optimized. After debugging, the equipment operating resistance is stable at 1520Pa.

[0056] (5) System optimization and intelligent control: The original pipeline was sealed and made low-resistance, and the leakage rate of the entire pipeline was controlled within 4.8%; the original fan was replaced with a variable frequency induced draft fan, and an intelligent linkage control module was built to interlock with the operation of the rolling mill and dynamically adjust the fan operating parameters; the original ash unloading system was upgraded to an integrated ash unloading and conveying device to realize automatic ash unloading and conveying.

[0057] (6) Step-by-step implementation and calibration: The monthly maintenance window of the production line was used for step-by-step implementation, and the production line was not shut down throughout the process; after full-condition calibration, the dust emission concentration was stabilized at 8.5mg / m³, the system operating resistance was reduced by 20% compared with before the modification, the equipment is expected to have a service life of 5.5 years, the annual operation and maintenance cost was reduced by RMB 160,000 compared with before the modification, and the annual electricity saving benefit reached RMB 220,000.

[0058] This embodiment solves various defects of the original dust removal system by reusing and upgrading the existing system and core technologies, achieving environmentally compliant emissions. At the same time, it significantly reduces the system's energy consumption and maintenance costs, making the technical upgrade investment controllable and ensuring that the implementation process does not affect the normal operation of the production line.

[0059] Comparative Example

[0060] This comparative example uses existing conventional hot rolling production line dust removal technology, applied to a 1780 hot rolling production line of the same specifications as Example 1. The specific scheme is as follows:

[0061] (1) Conventional design scheme: a conventional top suction type air collection hood is adopted, with a design air volume of 280,000 m³ / h. There is no air volume redundancy. A common bag dust collector is used, equipped with a fixed frequency induced draft fan. There is no intelligent linkage control. The ash is unloaded manually.

[0062] (2) Implementation and testing: After the system is installed, a full-load test is conducted. The test results are as follows: the dust source collection efficiency is 81%, the dust emission concentration is 32mg / m³, the equipment operating resistance is 2100Pa, the fan operating power is constant, there is no energy saving effect, the average service life of the filter bag is 1.5 years, the annual maintenance cost is 350,000 yuan, the filter bag clogging and smearing problems occur frequently during operation, and the machine needs to be shut down for maintenance once a month.

[0063] The conventional dust removal technology used in this comparative example cannot meet the latest environmental protection standards in terms of dust collection efficiency and emission concentration. The system has high operating resistance, high energy consumption, short equipment lifespan, high operation and maintenance costs, and frequent maintenance will affect the continuous operation of the hot rolling production line, posing significant environmental compliance risks and production operation risks.

[0064] The data from Examples 1 and 2 are compared with those from the comparative examples in the table below:

[0065]

[0066] The present invention has been described in detail above. However, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, any modifications or improvements that do not depart from the spirit of the present invention are within the scope of protection of the present invention.

Claims

1. A method for intelligent dust removal control of large air volume in a hot rolling production line, characterized in that, Includes the following steps: S1. Conduct a comprehensive survey of the dust generation conditions and on-site layout of the target hot rolling production line, and at the same time conduct a reusability assessment of the existing dust removal equipment on site to determine the reusable supporting components. S2. Based on the dust-generating operating parameters obtained from the survey, design the adaptability of the dust removal system's air volume, while reserving air volume redundancy to adapt to fluctuations in operating conditions. S3. Install suitable side-suction gas collection mechanisms at each dust-generating point in the hot rolling production line to complete the dust source capture at the dust-generating points. S4. Install weather-resistant dust removal main equipment connected to the gas collection mechanism to purify the collected dust-laden flue gas and complete the working condition adaptation and debugging of the dust removal main equipment. S5. Modify the induced draft mechanism of the dust removal system to adapt to frequency conversion, optimize the dust removal pipeline layout and configure an integrated ash unloading and conveying mechanism, and build an intelligent linkage control module between the dust removal system and the hot rolling production line. S6. Complete the installation and commissioning of the dust removal system according to the preset step-by-step implementation process, complete the system calibration under all working conditions, and ensure that the dust removal system operates stably and meets the standards.

2. The intelligent dust removal control method for large air volume in a hot rolling production line according to claim 1, characterized in that, In step S1, the survey of dust-generating conditions includes the comprehensive collection of dust generation patterns, flue gas characteristics, and on-site spatial constraints at each dust-generating point on the production line.

3. The intelligent dust removal control method for large air volume in a hot rolling production line according to claim 1, characterized in that, In step S2, the air volume adaptation design is matched based on the maximum dust generation condition of the production line, and the reserved air volume redundancy can cover the dust generation fluctuations of the entire production line under all operating conditions.

4. The intelligent dust removal control method for large air volume in a hot rolling production line according to claim 1, characterized in that, In step S3, the side-suction gas collection mechanism adopts a special structure adapted to the hot rolling mill stand, and the suction port of the gas collection mechanism is precisely aligned with the dust generation point.

5. The intelligent dust removal control method for large air volume in a hot rolling production line according to claim 1, characterized in that, In step S3, the side-suction gas collection mechanism is equipped with a flow guiding and equalizing component to optimize the gas collection airflow distribution and improve dust collection efficiency.

6. The intelligent dust removal control method for large air volume in a hot rolling production line according to claim 1, characterized in that, In step S4, the dust removal main equipment uses a temperature-resistant, oil-resistant, and moisture-resistant filter element as the core purification component, and is equipped with a self-cleaning and anti-clogging bag component to meet the purification requirements of hot-rolled oily fumes.

7. The intelligent dust removal control method for large air volume in a hot rolling production line according to claim 1, characterized in that, In step S5, the intelligent linkage control module can collect the operating conditions and dust generation data of the hot rolling production line, dynamically adjust the operating parameters of the induced draft mechanism, and realize the follow-up energy-saving control of the dust removal system.

8. The intelligent dust removal control method for large air volume in a hot rolling production line according to claim 1, characterized in that, In step S5, the optimization of the dust removal pipeline includes low-resistance design of the pipeline layout and leakage control of the entire pipeline, thereby reducing the air volume loss and operating resistance of the dust removal system.

9. The intelligent dust removal control method for large air volume in a hot rolling production line according to claim 1, characterized in that, In step S6, the step-by-step implementation process proceeds in the following order: first, the source collection mechanism is installed; then, the purification main body is debugged; and finally, the control and pipeline are optimized, so as to avoid interfering with the normal operation of the hot rolling production line.

10. The intelligent dust removal control method for large air volume in a hot rolling production line according to claim 1, characterized in that, In step S6, the system calibration covers the entire operating range of the dust removal system under no-load and full-load conditions of the hot rolling production line. After calibration, the purification efficiency and operational stability of the dust removal system are guaranteed.

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