Slurry circulating pump dynamic operation control method based on load segmentation

Abstract

The invention discloses a dynamic operation control method for a slurry circulating pump based on load segmentation. The method comprises the following steps: collecting unit load, SO2 concentration of inlet flue gas, pH value of slurry in an absorption tower, slurry density and vibration value of the slurry circulating pump in real time; the unit load is divided into a low load section (450-600MW), a medium load section (600-800MW) and a high load section (800-1030MW), and the SO2 concentration of inlet flue gas is divided into three grades of less than or equal to 1800mg / m < 3 >, 1800mg / m < 3 >-2000mg / m < 3 > and more than 2000mg / m < 3 >; according to the method, outlet SO2 < = 35 mg / m < 3 > is taken as a core hard constraint, and the problem of short-time standard exceeding caused by response lag in the traditional technology is thoroughly solved through a 15-second feed-forward pre-control mechanism (for example, a pump is started in advance when the load change rate is larger than 8% / min) of load segmentation and SO2 concentration grading and emergency logic of strengthening adjustment after the standard exceeds 30 seconds. In practical application, the standard reaching rate of export SO2 is increased to 99.8% or above from 90%-95% in the prior art, and the latest environmental protection standard requirements are completely met.

Description

Technical Field

[0001] The present invention provides a dynamic operation control method for a circulating pump, in particular a dynamic operation control method for a slurry circulating pump based on load segmentation. Background Art

[0002] In wet flue gas desulfurization systems in thermal power plants, the slurry circulation pump is a core component for maintaining desulfurization efficiency. Its operating status directly impacts SO2 removal from flue gas, system energy consumption, and equipment life. Currently, control methods for slurry circulation pumps primarily focus on achieving desulfurization efficiency targets. However, significant technical deficiencies exist in adaptability to complex operating conditions, multi-parameter coordinated optimization, and energy efficiency, making it difficult to meet increasingly stringent environmental standards and economic requirements.

[0003] In the existing technology, the control of the slurry circulation pump mostly relies on a single liquid-gas ratio adjustment, and a linkage mechanism between the load, flue gas SO2 concentration and the core parameters of the absorption tower (such as pH value and slurry density) has not been established. For example, the traditional method simply reduces the number of pump operations when the unit load decreases, but does not synchronously adjust the pH value of the slurry circulation pump dynamic operation control method based on load segmentation (usually controlled within the range of 5.2-5.8). This results in a decrease in the desulfurization reaction efficiency due to changes in mass transfer conditions, and even instantaneous excess of SO2 at the outlet. At the same time, the real-time correction of the slurry density (18% to 20%) is insufficient, which can easily cause pipeline scaling, poor gypsum crystallization, and other problems due to the slurry being too concentrated or too thin. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is that the control strategy of the variable frequency slurry circulation pump has obvious adaptability defects.

[0005] The above technical problem is solved by the following technical solution: The present invention proposes a dynamic operation control method of a slurry circulation pump based on load segmentation, comprising the following steps:

[0006] Real-time collection of unit load, inlet flue gas SO2 concentration, absorber slurry pH value, slurry density and slurry circulation pump vibration value;

[0007] The unit load is divided into low load section (450-600MW), medium load section (600-800MW), and high load section (800-1030MW), and the inlet flue gas SO2 concentration is divided into ≤1800mg / m3 1800~2000mg / m 3 、>2000mg / m 3 Three levels;

[0008] Based on the segmentation and classification results, combined with the slurry pH value (5.2-5.8) and slurry density (18% to 20%), the number and speed of slurry circulation pumps are dynamically adjusted to form a "load-SO2 concentration-pH-slurry density" closed-loop control;

[0009] Ensure that the SO2 concentration of the outlet flue gas is stable at ≤35mg / m3. If it exceeds the standard, the enhanced regulation mechanism will be triggered.

[0010] In a preferred embodiment of the load-segmented dynamic operation control method of the slurry circulation pump of the present invention: the pH control range corresponding to the low load segment (450-600MW) is 5.5-5.6, the pH control range corresponding to the medium load segment (600-800MW) is 5.4-5.5, and the pH control range corresponding to the high load segment (800-1030MW) is 5.2-5.4.

[0011] In a preferred embodiment of the load-segmented slurry circulation pump dynamic operation control method of the present invention: when the load is low and the inlet SO2 concentration is ≤1800mg / m3, the control strategy is: start a single slurry circulation pump (pump A is preferred), change the frequency to 55% to 75% of the speed, and maintain the liquid-gas ratio at 8 to 10L / m 3 If the inlet SO2 concentration rises to 1800-2000 mg / m 3 , increase the pump speed to 75% and adjust the pH to 5.6.

[0012] In a preferred embodiment of the load-segmented slurry circulation pump dynamic operation control method of the present invention: when the load segment is medium and the inlet SO2 concentration is ≤2000mg / m3, the control strategy is: start two slurry circulation pumps (pump A at 55% to 75% frequency conversion and pump B at 60% to 80% frequency conversion), maintain the liquid-gas ratio at 10 to 12L / m 3 ; If the inlet SO2 concentration is greater than 2000mg / m 3 , add a power frequency pump (C pump), liquid-gas ratio ≥12L / m 3 .

[0013] In a preferred embodiment of the load-segmented dynamic operation control method of the slurry circulation pump of the present invention: when the high load section and the inlet SO2 concentration is greater than 2000 mg / m3 and lasts for more than 5 minutes, the control strategy is: start three variable frequency pumps (B pump 70% to 90% and C pump 75% to 95% and D pump) and one power frequency pump (E pump), and the liquid-gas ratio is increased to 14L / m 3If the slurry density is greater than 20%, the upper limit of the variable frequency pump speed will be locked to 90%, and the slurry will be diluted to 19.5%.

[0014] In a preferred embodiment of the load segmentation-based dynamic operation control method of the slurry circulation pump of the present invention: when the unit load change rate is greater than 8% / min, the speed of the slurry circulation pump is adjusted 15 seconds in advance or the standby pump is pre-started, and the response time is ≤15 seconds.

[0015] In a preferred embodiment of the load-segmented dynamic operation control method for a slurry circulation pump according to the present invention, the frequency conversion range of the slurry circulation pump is 55% to 105% (wherein the rated power of the E pump is 1250kW, and the frequency conversion range is 55% to 105%), and when a single pump is operated at a low load stage with a variable frequency, power saving is ≥30% compared to the fixed frequency mode.

[0016] In a preferred embodiment of the load-segmented dynamic operation control method of the slurry circulation pump described in the present invention: the vibration value of the slurry circulation pump is monitored in real time. If the vibration is greater than 4.2 mm / s, the pump speed is automatically reduced by 10%; if the vibration continues to be greater than 5.0 mm / s, an emergency shutdown is triggered and switching to the standby pump is performed.

[0017] In a preferred embodiment of the load-segmented dynamic operation control method for slurry circulation pumps of the present invention: when the slurry density is greater than 20%, the upper limit of the speed of all variable frequency pumps is limited to 90%; when the slurry density is less than 18%, the number of power frequency pumps is reduced first, and the variable frequency pumps are retained to maintain the minimum liquid-gas ratio of 8L / m 3 .

[0018] In a preferred embodiment of the load-segmented dynamic operation control method for a slurry circulation pump according to the present invention, a pump group rotation mechanism is also included: pump A is started and stopped first in the low-load section, and pump E is started and stopped first in the high-load section. The deviation of the operating time of each pump in a single day is ≤2 hours, and the main pump is automatically rotated every 72 hours, so that the mean time between failures (MTBF) of the equipment is increased from 6,000 hours to more than 8,500 hours.

[0019] The beneficial effects of this invention lie in its core hard constraint of outlet SO₂ ≤ 35mg / m₃. Through a 15-second feedforward control mechanism based on "load segmentation and SO₂ concentration grading" (e.g., early pump activation when the load change rate exceeds 8% / min), and emergency logic that implements enhanced regulation after exceeding the standard for 30 seconds, this technology completely resolves the short-term overshooting caused by the response lag of traditional technologies. In practice, the outlet SO₂ compliance rate has increased from 90% to 95% with existing technologies to over 99.8%, fully meeting the latest environmental standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings of the embodiments of the present invention. Obviously, the drawings described below only relate to some embodiments of the present invention and are not intended to limit the present invention. Among them:

[0021] Figure 1 shows a flow chart of the control method of the present invention; DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to better understand the present invention, the present invention is further described in detail below with reference to specific embodiments and the accompanying drawings.

[0023] The terms used in the present invention are those commonly used in the art in view of the functions of the present invention, but these terms may vary according to the intentions of those skilled in the art, precedents, or new technologies in the art. In addition, specific terms may be selected by the applicant, and in such cases, their detailed meanings will be described in the detailed description of the present invention. Therefore, the terms used in the specification should not be understood as simple names, but rather as the meanings of the terms and the overall description of the present invention.

[0024] Reference Figure 1The dynamic operation control method of the slurry circulation pump based on load segmentation and flue gas SO2 emission limit disclosed in the present invention is mainly used in the wet desulfurization system of thermal power plants, and is particularly suitable for the operation control of the five slurry circulation pumps (A / B / C / D / E pumps) equipped with a 2×1030MW unit. Its core is to achieve coordinated optimization of desulfurization efficiency, energy consumption and equipment safety by constructing a dual constraint system of "load segmentation and SO2 concentration classification" and combining multi-parameter linkage and dynamic adjustment. The implementation of this method starts with parameter collection. The key parameters such as unit load, inlet flue gas SO2 concentration, absorption tower slurry pH value, slurry density and slurry circulation pump vibration value are obtained in real time through the distributed control system (DCS). The unit load is collected by both the turbine speed sensor and the generator power transmitter, and the weighted average value (weight 7:3) is taken as the judgment basis. When the deviation between the two exceeds 5MW, the data abnormality alarm is triggered, and the instantaneous fluctuation is eliminated by a 3-second sliding average filter to ensure the accuracy of the load data; the inlet flue gas SO2 concentration is collected by three laser gas analyzers (range 0-3000mg / m3) arranged in the inlet flue of the desulfurization tower, and the median value is taken as the measurement value. If the deviation of a single instrument from the median value is greater than 50mg / m3, it is marked as a fault and automatically removed to ensure that the concentration measurement error does not exceed The pH value of the slurry is monitored by two pH electrodes (insertion depth 1.5m) arranged at different heights in the absorption tower. They are automatically cleaned and calibrated every 10 minutes. When the deviation of the measured values ​​of the two electrodes is greater than 0.1, the backup electrode is started to ensure that the pH control accuracy reaches ±0.05; the slurry density is measured jointly by a differential pressure density meter (installed in the circulation pipeline at the bottom of the absorption tower) and a gamma-ray density meter (installed in the slurry discharge pipe). When the deviation between the two exceeds 0.5%, the density correction program is started, and dynamic calibration is performed by adjusting the amount of filtrate water added; the vibration value of the slurry circulation pump is measured by installing a vibration sensor (range 0-10mm / s) at the motor bearing and pump casing of each pump, and the maximum value is taken as the representative vibration value of the pump. The sampling frequency is 10Hz, and the high-frequency interference signal is filtered out by Fourier transform to ensure the reliability of vibration monitoring.

[0025] Based on parameter collection, this method divides the unit load into three sections, namely low load section (450-600MW), medium load section (600-800MW), and high load section (800-1030MW). At the same time, the inlet flue gas SO2 concentration is divided into three levels, namely ≤1800mg / m 3 1800~2000mg / m 3 、>2000mg / m 3This classification method directly matches the actual operating range of the power plant and provides a basis for subsequent precise control. For the low load section (450-600MW), its core control goal is to give priority to energy saving under the premise of ensuring desulfurization efficiency. When the load is in this range and the inlet SO2 concentration is ≤1800mg / m 3 When the load is 450MW and the inlet SO2 concentration is 1500mg / m3, the control strategy is to start a single slurry circulation pump (pump A is preferred), change its frequency to 55% to 75% speed, maintain the liquid-gas ratio at 8 to 10L / m3, and control the pH value at 5.5-5.6. By increasing the limestone slurry feed rate to increase the dissociation degree of calcium carbonate, the mass transfer loss caused by the reduction of the liquid-gas ratio is compensated. For example, when the load is 450MW and the inlet SO2 concentration is 1500mg / m 3 When the slurry density is 18.5%, pump A runs at 55% speed (about 990r / min), the power drops from 900kW to 270kW, and the outlet SO2 is stabilized at 30mg / m3, saving 40% of electricity compared with the traditional method. If the inlet SO2 concentration of the low load section rises to 1800-2000mg / m 3 , the pump speed is increased to 75% and the pH is adjusted to 5.6 to ensure that the desulfurization efficiency is not affected by the increase in concentration. At the same time, the slurry density is monitored in real time. If the density exceeds 20%, the upper limit of the variable frequency pump speed is limited to 90% to avoid pump wear caused by excessive slurry concentration.

[0026] For the medium load section (600-800MW), the control target is to balance the desulfurization efficiency and energy consumption. When the inlet SO2 concentration is ≤2000mg / m 3 When the load is 700MW and the inlet SO2 concentration is 1900mg / m3, the liquid-gas ratio is maintained at 10-12L / m3 and the pH value is controlled at 5.4-5.5. 3 When the slurry density is 19%, the frequency of pump A is increased to 70%, and that of pump B is increased to 75%. The outlet SO2 is stabilized at 28mg / m3, saving 25% of electricity compared to the traditional dual-pump power frequency operation. If the SO2 concentration at the inlet of the medium load section is greater than 2000mg / m3, the power frequency operation of pump C is increased to form a combination of "two variable frequencies and one power frequency", with a liquid-gas ratio of ≥12L / m3, ensuring a desulfurization efficiency of ≥98.4%. In addition, when the load change rate of the unit in the medium load section is greater than 8% / min (for example, it is expected to increase from 600MW to 750MW within 15 seconds), this method will trigger the feedforward pre-control mechanism, increasing the frequency of pump A to 75% and pump B to 80% 15 seconds in advance. The response time is less than 15 seconds, avoiding excessive outlet SO2 due to a sudden increase in load.

[0027] The core control target of the high load section (800-1030MW) is to prioritize environmental protection standards. When the inlet SO2 concentration is greater than 2000mg / m 3If the frequency conversion rate lasts for more than 5 minutes, pump B (70% to 90%), pump C (75% to 95%), and pump D will be started at the power frequency. Pump E will be automatically frequency-converted to 80% to 105%, forming a full-load configuration of "three frequency conversions and two power frequencies". The liquid-gas ratio is increased to 14L / m3, and the pH value is controlled at 5.2-5.4. For example, when the load is 1030MW and the inlet SO2 concentration is 2142mg / m 3 When the slurry density is 20%, the outlet SO2 is stabilized at 28-32 mg / m3 through this configuration, meeting the ultra-low emission standard (≤35 mg / m 3 ), saving 30% more electricity than traditional fixed pump sets. If the slurry density in the high-load section exceeds 20%, the upper frequency limit of all variable-frequency pumps is locked to 90%, and the slurry is diluted to 19.5% with filtrate water to maintain mass transfer efficiency and prevent pipeline deposits. If the slurry density is less than 18%, the number of mains-frequency pumps is prioritized, while the variable-frequency pumps are retained to maintain a minimum liquid-to-gas ratio of 8L / m³ to prevent poor gypsum crystallization caused by low density.

[0028] In the implementation of the variable frequency speed regulation strategy, this method makes full use of the variable frequency characteristics of the five slurry circulation pumps (for example, the rated power of pump E is 1250kW, and the variable frequency range is 55% to 105%), and designs differentiated speed regulation schemes for different load sections. The low-load section adopts the single-pump variable frequency mode. When the load is 500MW and the inlet SO2 concentration is 1600mg / m 3 When pump A runs at 55% speed (990r / min) and power is 270kW, if the SO2 concentration rises to 1800mg / m 3 , automatically raising the upper limit of the frequency conversion to 75% (1350r / min), while the pH value rises from 5.5 to 5.6, saving 630kWh of electricity per hour compared with the fixed frequency operation, saving more than RMB 380,000 in electricity bills per year. The medium load section adopts the dual pump coordinated frequency conversion mode. When the load is 700MW and the inlet SO2 concentration is 1900mg / m 3 The total power of pumps A and B is 1200kW (405kW for pump A and 795kW for pump B), which saves 33% of electricity compared with the dual-pump power frequency operation (1800kW), and the outlet SO2 fluctuation is less than 5mg / m 3 The high load section adopts multi-pump coordinated frequency conversion and power frequency standby mode. When the load is 1030MW and the inlet SO2 concentration is 2142mg / m 3 At this time, the total power of pumps B, C and D is 3150kW, which saves 49% of electricity compared with full-frequency operation (total power of 5 pumps is 6150kW), effectively avoiding wear caused by long-term high-load operation of a single pump.

[0029] In order to meet the real-time requirements of operating condition fluctuations, this method establishes a 15-second feedforward pre-control mechanism. In the load surge scenario, when the load surges from 600MW to 750MW (change rate 10% / min) and the inlet SO2 concentration is 1850mg / m3 When the feedforward calculation (load change × 0.8 and SO2 increment × 0.5) is used, the preset amount is 235, and the C pump is started at the power frequency 15 seconds in advance. At the same time, the frequency of the B pump is increased from 60% to 75%, and the liquid-gas ratio is increased from 10L / m 3 Increased to 12L / m 3 , shortening the duration of SO2 exceeding the standard at the outlet from 120 seconds to less than 30 seconds. In the scenario of sudden increase in SO2 concentration, when the inlet SO2 concentration suddenly increases from 1800mg / m3 to 2200mg / m 3 , when the load is 800MW, the trigger is >2000mg / m 3 Logic is used, pump E automatically changes frequency to 80%, pump B frequency increases from 70% to 85%, pH drops from 5.4 to 5.2, and at the same time limits the upper limit of the variable frequency pump speed to 90% and dilutes the slurry to 19.5%, reducing outlet SO2 from 40mg / m3 to 28mg / m3 within 15 seconds, thus avoiding environmental penalties.

[0030] In terms of equipment safety and life management, this method integrates vibration protection logic and a pump group rotation mechanism. The vibration protection logic monitors the vibration value of the pump group in real time. When the vibration is greater than 4.2mm / s, the pump speed is automatically reduced by 10%. If the vibration continues to be greater than 5.0mm / s, an emergency shutdown is triggered and the backup pump is switched to. For example, when the vibration of pump C rises to 4.5mm / s, the frequency drops from 80% to 70%, and the vibration value drops to 3.8mm / s, avoiding accidents such as impeller breakage and reducing annual maintenance costs by 50%. The pump group rotation mechanism sets the start and stop priority (low load prioritizes starting and stopping pump A, high load prioritizes starting and stopping pump E), controls the running time deviation of each pump in the control unit to ≤2 hours, and automatically rotates the main pump every 72 hours, thereby increasing the mean time between failures (MTBF) of the equipment from 6000 hours to more than 8500 hours, and extending the replacement cycle of a single pump by 40%.

[0031] This method uses the configuration of pump B (90% variable frequency) and pump C (95% variable frequency) and pump D and pump E at the working frequency under the conditions of load 1030MW and inlet SO2 2142mg / m3, pH 5.2, liquid-gas ratio 14L / m 3 , the outlet SO2 level stabilized at 28mg / m3, with power consumption of 4800kW, a 30% energy saving compared to traditional methods, and the vibration values ​​of the pump units were all less than 4.0mm / s. When a single pump was operating at 55% variable frequency in the low-load range, power consumption dropped from 1250kW to 410kW, resulting in annual electricity savings exceeding 6 million kWh, a comprehensive energy saving rate of 30%, and an annual electricity bill savings of approximately 1.8 million yuan for a single unit. Compared with existing technologies, this method does not require complex algorithm modeling, and all control logic can be directly embedded in the DCS system. While ensuring the outlet SO2 compliance rate (above 99.8%), it significantly reduces energy consumption and maintenance costs, demonstrating strong practicality and widespread promotion value.

[0032] Finally, it should be pointed out that the methods and devices described in detail above are merely embodiments, and those skilled in the art can modify these embodiments in different ways without departing from the scope of the present invention.

Claims

1. A dynamic operation control method for a slurry circulation pump based on load segmentation, characterized in that: The following steps are involved: Real-time collection of unit load, inlet flue gas SO2 concentration, absorber slurry pH value, slurry density and slurry circulation pump vibration value; The unit load is divided into low load section (450-600MW), medium load section (600-800MW), and high load section (800-1030MW), and the inlet flue gas SO2 concentration is divided into ≤1800mg / m 3 1800~2000mg / m 3 、>2000mg / m 3 Three levels; Based on the segmentation and classification results, combined with the slurry pH value (5.2-5.8) and slurry density (18% to 20%), the number and speed of slurry circulation pumps are dynamically adjusted to form a "load-SO2 concentration-pH-slurry density" closed-loop control; Ensure that the SO2 concentration of the outlet flue gas is stable at ≤35mg / m3. If it exceeds the standard, the enhanced regulation mechanism will be triggered.

2. The method for dynamic operation control of a slurry circulation pump based on load segmentation according to claim 1, characterized in that: The pH control range corresponding to the low load section (450-600MW) is 5.5-5.6, the pH control range corresponding to the medium load section (600-800MW) is 5.4-5.5, and the pH control range corresponding to the high load section (800-1030MW) is 5.2-5.

4.

3. The method for dynamic operation control of a slurry circulation pump based on load segmentation according to claim 1, characterized in that: In the low load section and when the inlet SO2 concentration is ≤1800mg / m3, the control strategy is: start a single slurry circulation pump (pump A is preferred), change the frequency to 55% to 75% of the speed, and maintain the liquid-gas ratio at 8 to 10L / m 3 If the inlet SO2 concentration rises to 1800-2000 mg / m 3 , increase the pump speed to 75% and adjust the pH to 5.

6.

4. The method for dynamic operation control of a slurry circulation pump based on load segmentation according to claim 1 is characterized in that: In the medium load section and when the inlet SO2 concentration is ≤2000mg / m3, the control strategy is: start two slurry circulation pumps (pump A 55% to 75% frequency conversion and pump B 60% to 80% frequency conversion), maintain the liquid-gas ratio at 10 to 12L / m 3 ; If the inlet SO2 concentration is greater than 2000mg / m 3 , add a power frequency pump (C pump), liquid-gas ratio ≥12L / m 3 .

5. The method for dynamic operation control of a slurry circulation pump based on load segmentation according to claim 1, characterized in that: When the inlet SO2 concentration is greater than 2000mg / m3 and lasts for more than 5 minutes in the high load section, the control strategy is to start three variable frequency pumps (B pump 70% to 90% and C pump 75% to 95% and D pump) and one power frequency pump (E pump), and the liquid-gas ratio is increased to 14L / m 3 If the slurry density is greater than 20%, the upper limit of the variable frequency pump speed will be locked to 90%, and the slurry will be diluted to 19.5%.

6. The method for dynamic operation control of a slurry circulation pump based on load segmentation according to claim X is characterized in that: When the unit load change rate is greater than 8% / min, adjust the speed of the slurry circulation pump 15 seconds in advance or pre-start the standby pump, and the response time is ≤15 seconds.

7. The method for dynamic operation control of a slurry circulation pump based on load segmentation according to claim 1, characterized in that: The variable frequency range of the slurry circulation pump is 55% to 105% (the rated power of the E pump is 1250kW, and the variable frequency range is 55% to 105%). When a single pump is operated in variable frequency mode in the low load section, the power saving is ≥30% compared with the fixed frequency mode.

8. The method for dynamic operation control of a slurry circulation pump based on load segmentation according to claim 1, characterized in that: Monitor the vibration value of the slurry circulation pump in real time. If the vibration is greater than 4.2 mm / s, the pump speed will be automatically reduced by 10%. If the vibration continues to be greater than 5.0 mm / s, an emergency shutdown will be triggered and the standby pump will be switched.

9. The method for dynamic operation control of a slurry circulation pump based on load segmentation according to claim 1, characterized in that: When the slurry density is greater than 20%, the upper limit of the speed of all variable frequency pumps is limited to 90%; when the slurry density is less than 18%, the number of power frequency pumps is reduced first, and the variable frequency pumps are retained to maintain the minimum liquid-gas ratio of 8L / m 3 .

10. The method for dynamic operation control of a slurry circulation pump based on load segmentation according to claim 1, characterized in that: It also includes a pump rotation mechanism: pump A is started and stopped first in low-load sections, and pump E is started and stopped first in high-load sections. The deviation in the operating time of each pump per day is ≤2 hours, and the main pump is automatically rotated every 72 hours, increasing the equipment's mean time between failures (MTBF) from 6,000 hours to more than 8,500 hours.

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