Online condenser cleaning technology resolves issues such as decreased vacuum level, increased exhaust temperature, and greater terminal difference in power plant condensers within 10 hours

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Online cleaning technology for condensers without shutting down down resolves issues such as reduced vacuum level, increased exhaust temperature, and larger terminal difference in power plant condensers within 10 hours. Abstract: The shift supervisor in a thermal power plant observed various abnormalities in the condensers of the generator sets in the control room, including low vacuum levels, high exhaust temperatures, large terminal differences, decreased efficiency of the generator sets, and reduced thermal economy. After examining and ruling out possible causes for these abnormal conditions, it was determined that scaling on the condenser cooling tubes was responsible for the abnormalities in the related data. By analyzing the impact of scaling on the economic efficiency of the generator sets and by comparing existing cleaning methods used in the thermal power industry, it was decided to adopt an online chemical cleaning method for the condensers. A comparison of the performance data of the condensers before and after cleaning showed that this online chemical cleaning technique is useful for adoption in the thermal power industry. Keywords: condenser scaling ； Online condenser cleaning ； High condenser exhaust temperature ； Decrease in condenser vacuum ； Application of Energy-Saving Technologies 1. Introduction The role of the condenser in thermal power turbine units is to create and maintain a vacuum at the outlet of the turbine, as well as to condense the turbine exhaust into water for reuse in the boiler. Improving and maintaining the condenser vacuum, as well as reducing the turbine exhaust pressure and exhaust temperature, can enhance the cyclic thermal efficiency of the turbine unit. Typically, after one to two years of operation, in steam power plant turbine units, corrosive substances, dust and impurities, microbial sludge, carbonate scale, and silicate scale present in the cooling water circulating around the turbine condenser accumulate on the inner walls of the stainless steel, copper, or titanium tubes used for heat exchange in the condenser. This results in the formation of scale, which increases the thermal resistance of the condenser’s cooling tubes and reduces the volume of cooling water circulating. Under a certain steam load, the temperature of the cooling water rises above normal levels, leading to a decrease in the condenser’s vacuum level, an increase in the exhaust steam temperature, an increase in the temperature difference, a reduction in the turbine’s power generation efficiency, and an increase in the standard coal consumption per kilowatt-hour, expressed in g/KWh. Severe scaling in the condenser can also cause vibrations in the turbine unit, affecting the safe operation of the equipment. Figure 1 shows that scaling on the condenser of a power plant leads to a decrease in vacuum level, an increase in exhaust temperature, an increase in the temperature difference, and a reduction in power generation. The thermal conductivity of brass heat exchange tubes is approximately 109–125 W/(m·K), while that of stainless steel heat exchange tubes is about 15–30 W/(m·K). The thermal conductivity of titanium heat exchange tubes is also around 15–30 W/(m·K). The thermal conductivity of mixed-type scale is approximately 0.4 W/(m·K). Tests have shown that 1 mm of scale can reduce the heat transfer coefficient of condenser heat exchange tubes by around 50%. In the condenser, the cooling water carries away less heat due to scale formation, which leads to an increase in the temperature of the heat exchange tubes in the condenser. This results in a decrease in the vacuum level of the condenser, an increase in the terminal difference, a reduction in the thermal efficiency of the turbine unit, and an increase in the standard coal consumption for power generation. Scaling in the condensers of thermal power plants reduces the service life of these equipment as well as their operational capacity. Severe scaling can affect the operation of the units and compromise production safety. For example, in a 300MW thermal power turbine generator unit, for every 1 kPa increase in the vacuum level of the turbine generator, the average standard coal consumption for power generation decreases by 2.2 grams per kilowatt-hour, or 2.2 g/KWh. If such a power plant generates 5 billion kWh of electricity per year, it can save 11,000 tons of standard coal, reduce production costs by over 5.48 million yuan, and cut carbon dioxide emissions by more than 29,000 tons. This not only contributes to energy conservation and emission reduction but also brings significant economic benefits. 2. Overview: The Tongshan biomass cogeneration project in Xuzhou is equipped with 35MW high-temperature, ultra-high-pressure reheated steam turbine generators, along with a 130t/h high-temperature, ultra-high-pressure reheated circulating fluidized bed biomass boiler. Using agricultural straws and forestry waste as primary raw materials, the project processes over 600,000 tons of straws per year and generates approximately 300 million kWh of electricity annually. It provides enterprises in the equipment manufacturing industrial park with combined supply of cooling, heating, electricity, and compressed air. Figure 2: Scaling on the power plant’s condenser leads to a decrease in vacuum level, an increase in exhaust temperature, an increase in the terminal difference, and a reduction in power generation. 3. Problems with the condenser: The steam turbine generator set in this cogeneration project is equipped with a double-flow, surface-type condenser; this condenser features separate water chambers to allow it to operate while half of it is under maintenance. The original design of the condenser featured gel ball cleaning systems installed in each of the two separate water chambers, to carry out online cleaning of the condenser tube bundles. The recovery rate of rubber balls in the condenser of this thermal power plant is low, and it remains unstable. During shutdowns for maintenance of the steam turbine generator set, inspections revealed severe scaling on the heat exchange tubes of the condenser as well as blockages in the ball collection nets, preventing timely cleaning of the condenser. Severe scaling in the condenser leads to an increase in the temperature difference at the turbine side of the condenser, resulting in a deterioration of the vacuum. The decrease in vacuum level raises the exhaust pressure, reduces the available heat for the turbine, lowers the turbine’s output, and diminishes the power generation efficiency ； The exhaust temperature of the condenser increases, causing components such as the exhaust cylinder and bearing housings to expand due to heat, which leads to a change in the bearing’s position and results in vibration in the turbine ； An increase in exhaust temperature can also cause the flanges of the heat exchange tubes in the condenser, such as those made of copper, stainless steel, or titanium, to become loose, thereby compromising the seal integrity of the condenser ； Furthermore, a decrease in the condenser vacuum leads to a reduction in the volumetric flow rate of the exhaust steam, causing flow separation and swirls on the last stage blades of the turbine. At the same time, significant excitation forces are generated at certain parts of these blades, which can easily damage them and lead to safety incidents during operation. 4. Eight common condenser cleaning techniques for addressing the problem of scaling in the condensers of steam turbine generators; currently, these eight techniques are divided into two categories: shutdown cleaning and online cleaning. Common techniques for cleaning condenser fouling that causes shutdowns in steam turbine generator sets include traditional chemical cleaning during shutdown, high-pressure water cleaning, and shot blasting ； Common online cleaning methods for fouling in the condensers of steam turbine generators include gel ball cleaning, ultrasonic cleaning, robotic cleaning, spiral ribbon cleaning, and online chemical cleaning. 4.1 Condenser scaling removal techniques – Traditional chemical cleaning of condensers: With traditional chemical cleaning, the cleaning efficiency of the tube walls in the condenser’s heat exchange tubes is high, ensuring thorough cleaning. Traditional chemical cleaning of condenser fouling in copper tubes, stainless steel tubes, and titanium tubes requires shutting down the unit; the cleaning process takes a long time, which affects the normal operation of the unit ； Traditional chemical cleaning for condenser scaling requires the use of effective corrosion inhibition techniques, as well as manual operation, monitoring, and maintenance, in order to prevent corrosion and leakage in the copper, stainless steel, and titanium tubes used for heat exchange, which could otherwise lead to the failure and disposal of these tubes. 4.2 Condenser scaling cleaning technology – High-pressure water cleaning of condenser scaling. High-pressure water cleaning is a mechanical method that uses power tools and other equipment to clean the condenser. The disadvantages of this cleaning method include the need to shut down the unit, which affects its normal operation; it can also damage the inner surfaces of copper tubes, stainless steel tubes, and titanium tubes. In addition, mechanical scratches appear to varying degrees on the inner surfaces of these heat exchange tubes, and corrosion can occur at these spots, forming crack nuclei that continue to spread inward, leading to damage to the copper tubes, stainless steel tubes, and titanium tubes in the condenser. 4.3 Condenser scaling cleaning technology – Bullet cleaning for condenser scaling. The advantages and disadvantages of bullet cleaning are similar to those of high-pressure water cleaning; both are mechanical methods that use tools and equipment to clean the condenser. Sometimes, in order to thoroughly clean the walls of the condenser’s heat exchange tubes, both bullet cleaning and high-pressure water cleaning are used alternately. 4.4 Condenser scaling cleaning technology – Online rubber ball cleaning without shutting down the plant. There are various types of cleaning rubber balls, including ordinary rubber balls, peeled rubber balls, and silicone balls. This method of cleaning with rubber balls is widely used in many thermal power plants; however, the effectiveness of such cleaning devices is limited. Issues such as uneven distribution of rubber balls, low recovery rates, loss of balls, blockages in the heat exchange tubes caused by balls, and high water resistance in the secondary filters mean that shutdown for cleaning is necessary to ensure a high cleanliness level of the condenser. 4.5 Condenser scaling cleaning technology – Online ultrasonic cleaning without shutting down the system. Online ultrasonic cleaning is a method commonly used to clean the copper tubes in condensers; it utilizes ultrasonic vibrations generated by high-frequency sound waves to clean and remove surface dirt. Online ultrasonic cleaning cannot remove severe fouling from condensers without shutting down the system; it is suitable for removing mild to moderate levels of fouling. However, for severe fouling or deposits inside the copper tubes of the condenser, ultrasonic cleaning may not be effective enough, and other more powerful cleaning methods are required ； Online ultrasonic cleaning of the condenser to remove scaling without shutting down the system may cause mechanical damage; the impact force generated by ultrasonic vibrations is considerable. Careful operation is required when using ultrasonic cleaning, and it is essential to select the appropriate frequency and power level. Improper handling can lead to scratches, corrosion, or damage on the surface of the condenser’s copper tubes ； Online ultrasonic cleaning of condenser fouling without shutting down the system takes a long time; compared to traditional cleaning methods, ultrasonic cleaning usually requires more time to achieve an optimal level of cleanliness ； It requires high costs and energy consumption, and its cleaning effect on the latter part of the pipeline is poor. 4.6 Condenser scaling cleaning technology – Non-stop online robotic cleaning of condenser scaling. The online robotic cleaning system is installed within the condenser water chamber; servo motors and reducers are used to control the arms, enabling precise injection of high-pressure water streams to clean the tube bundles. It can be combined with various cleaning methods to achieve better cleaning results. However, it has issues such as long cleaning cycles, low efficiency, rapid decay of high-pressure water kinetic energy, poor cleaning performance in the rear section of the tube bundle, a complex system, a high potential failure rate, high investment costs, and high maintenance expenses. 4.7 Condenser scaling cleaning technology – Non-stop online spiral ribbon cleaning for condenser scaling. In this method, a spiral ribbon that can rotate around an axis is placed inside the cooling tubes; the cooling water flowing through these tubes causes the ribbon to rotate and swing, thereby removing dirt. Additionally, this movement improves the heat exchange efficiency within the tubes. This system has advantages such as simple equipment and the ability to operate continuously. However, the connectors increase the frictional loss along the pipeline, raising the power consumption of the circulation pump and thus increasing production costs. Moreover, these connectors can cause wear on the pipe bundle or lead to their own breakage, which in turn may result in blockages and damage to the pipe bundle. 4.8 Condenser scaling cleaning technology — Online chemical cleaning without shutting down the plant. The advantage of traditional shutdown-based chemical cleaning for condenser scaling is thorough cleaning and a high cleaning efficiency. The disadvantage is the need to shut down the system for cleaning, which results in a loss in power generation efficiency ； Cleaning processes that take a long time, and require manual operation, monitoring, and maintenance ； High cost investment and significant losses in the economic efficiency of power generation. Online chemical cleaning of condenser fouling without shutting down is a cleaning technology that has evolved from the traditional shutdown-based chemical cleaning methods. The online chemical cleaning for removing scale from condensers is carried out without shutting down the system, which means a short processing time and no loss of power generation due to shutdowns. The HS-186 multi-functional agent, which includes properties for sterilization, removal of sludge, cleaning of scale, and metal passivation, is used; this results in low cleaning costs and short processing times. Online cleaning can be conducted for around 10 hours without shutting down the system, during which moss and other microorganisms, as well as dust, are removed. Meanwhile, scale inside the tubes is cleared away, and corrosion of metal components is prevented ； Online chemical cleaning to remove scaling from the condenser can be carried out at any time, without the need to wait for major or minor maintenance of the unit. Online chemical cleaning without shutting down the plant is employed to remove scale from the condenser and ensure a high cleanliness level. After such cleaning, the key performance indicators of the condenser reach the following values: A. Vacuum level increases by ≥1.0–2.0 kPa; B. The temperature difference decreases by ≤3.0 degrees Celsius; C. The exhaust gas temperature decreases by ≤2.0°C; D. Power generation increases by ≥2% under the same air supply conditions as before. While there are advantages and disadvantages associated with scale removal techniques for condensers, the online chemical cleaning method developed based on traditional shutdown-based cleaning processes allows for better results in terms of operation, safety, and cost-efficiency, with minimal modifications to existing equipment. Colleagues and students, aside from these 8 condenser cleaning techniques – traditional chemical cleaning, high-pressure water cleaning, projectile cleaning, online gel ball cleaning without shutting down the system, online ultrasonic cleaning without shutting down the system, online robotic cleaning without shutting down the system, online spiral ribbon cleaning without shutting down the system, and online chemical cleaning without shutting down the system – what other condenser cleaning techniques are you aware of? Which condenser cleaning technology do you think offers the best overall performance at present? Regarding issues such as corrosion and scaling in condensers, red-colored boiler drainage water, adjustment of the pH value of boiler feedwater, red-colored boiler water, hardness in steam condensation water, tube failures due to corrosion and scaling in boilers, corrosion in steam systems, excessive iron content in steam condensation water, yellow-colored steam condensation water, as well as online cleaning and descaling techniques that allow operations to continue without shutdown, there is also online descaling technology for boiler scaling that enables continued operation without stopping the boiler. Yan Hui from Beijing University of Chemical Technology at I86OO475З86 welcomes colleagues to discuss these issues and exchange experiences and insights at any time. Students are also welcome to share new technologies related to condenser cleaning, while colleagues can share their experience in managing and using boiler equipment, so as to learn from each other in addressing various practical problems associated with boilers. The online cleaning technology for condensers without shutting down the plant can resolve issues such as a decrease in vacuum level, an increase in exhaust temperature, and an enlarged terminal difference in power plant condensers within 10 hours. Figure 3 shows a comparison before and after online chemical cleaning of the heat exchange tubes in the condensers of steam turbine generators in thermal power plants. 5. Application example of the online chemical cleaning technology for removing scale from condensers without shutting down the plant in the Xuzhou Tongshan biomass co-generation project. 5.1 Operating conditions before online chemical cleaning of condenser scale without shutdown. At 2:58 p.m. on April 14, 2023, the control room of the thermal power plant in the Xuzhou Tongshan biomass co-generation project displayed a screenshot showing the condition of the condenser prior to online cleaning, as shown in Figure 4. The boiler’s gas supply rate is 114.5 t/h, the vacuum level is -87.4 kPa, the exhaust steam temperature is 51.6°C, and the terminal difference is 17.1 degrees Celsius. The power generation capacity is 30.69 MW/H. Scaling on the condenser clearly leads to a low vacuum level in the condenser as well as a large terminal difference; this reduces the thermal efficiency of the turbine unit, increases the standard coal consumption for power generation, and results in a significant decrease in power output. Figure 4: Operation status of the turbine generator set’s condenser in the power plant’s control room prior to online chemical cleaning without shutting down the system. 5.2: Operation status after online partial chemical cleaning of the condenser without shutting down the system due to scaling. At 5:01 a.m. on April 23, 2023, in the control room of the biomass cogeneration project’s power plant in Tongshan, Xuzhou, a screenshot was taken of the condition of one half of the condenser after approximately 5 hours of online chemical cleaning without shutting down the system, as shown in Figure 5. The boiler’s steam output is 118 t/h; the vacuum level increases to -96.0 kPa, the exhaust steam temperature drops to 36.2°C, and the terminal difference decreases from 17.1°C to 6.5°C, returning to normal levels. The power generation capacity rises to 33.71 MW/H, with a net increase of 3.020 MW per hour – representing a 10% increase in power generation. This results in an additional About 72,000 kWh of electricity generated per day. At a cost of 0.7 yuan per kWh, this translates to an additional profit of about 50,000 yuan per day. All operational parameters of the condenser have returned to normal. Figure 5: Operation status of the condenser in the turbine generator set in the power plant’s control room after online partial chemical cleaning without shutting down the system. 5.3: Operation status after online full-sided chemical cleaning of the condenser to remove scaling, also without shutting down the system. At 4:21 a.m. on April 24, 2003, in the control room of the biomass cogeneration power plant in Tongshan, Xuzhou, a screenshot was taken of the condition of the other half of the condenser after approximately 5 hours of online chemical cleaning without shutting down the system, as shown in Figure 6. The steam supply rate of the boiler is 115.4 t/h, the vacuum level increased to -97.6 kPa, the exhaust steam temperature dropped to 31.8°C, and the terminal difference narrowed to 3.7 degrees Celsius. It became necessary to stop one of the circulation pumps; otherwise, overcooling would also affect power generation efficiency. As a result, the power generation capacity increased only to 32.75 MW per hour. Figure 6 shows the operational conditions of the turbine generator set’s condenser in the power plant’s control room after chemical cleaning on both sides without shutting down the unit. 6. Conclusion: The application of online cleaning technology for condensers without shutting down the unit in 35MW high-temperature, ultra-high-pressure reheated turbine generator sets shows that scaling in the circulating water used in the condenser’s heat exchange tubes has a significant impact on power generation. This online cleaning technology can resolve issues such as increased exhaust temperature, reduced vacuum level, and increased terminal difference in the plant’s condenser within 10 hours. Compared to the chemical or mechanical/physical cleaning methods that require shutting down the traditional condenser due to scaling, the online chemical cleaning technique that can be applied while the condenser is still in operation ensures a high cleanliness level of the condenser. It allows for good results in terms of operation, safety, and cost-effectiveness, with minimal modifications to the existing equipment, within a relatively short period of time. It is proven that the online chemical cleaning technology for condensers without shutdown has practical significance for adoption and promotion in the thermal power industry. Online cleaning technology for condensers without shutting down down – solving issues such as reduced vacuum level, increased exhaust temperature, and greater terminal difference in power plant condensers within 10 hours (Yan Hui)