In this blog post, we’ll delve into the intricacies of desulfurization and absorption towers within the context of dust collector baghouse operations. These are critical components in the process of converting pollutants generated during coal combustion into secondary energy sources like electricity.
1. What is the principle and process of desulfurization?
Answer: Desulfurization is the process of removing sulfur dioxide (SO2) from flue gas emitted during coal combustion in power plants. This is achieved through a wet flue gas desulfurization (FGD) system. In this process, a slurry of limestone and water, known as absorption slurry, is used. Inside the absorption tower, SO2 in the flue gas reacts with calcium carbonate (CaCO3) in the slurry and oxygen to form calcium sulfite (CaSO3) and water. This calcium sulfite is further oxidized to calcium sulfate (CaSO4), commonly known as gypsum. The cleaned flue gas is then discharged into the atmosphere.
2. What are the main equipment components of a desulfurization system?
Answer: The main equipment components of a wet FGD system include limestone slurry preparation system, flue gas system, SO2 absorption system, dewatering system, wastewater treatment system, and process water system. Key equipment includes wet ball mills, booster fans, flue gas dampers, gas-to-gas heat exchangers (GGH), absorption towers, demisters, spray layers, oxidation blowers, slurry circulation pumps, mixers, limestone hydrocyclones, gypsum hydrocyclones, vacuum belt dewatering machines, vacuum pumps, pipelines, and valves.
3. What is the structure and function of an absorption tower?
Answer: The absorption tower is the core component of the absorption system in FGD equipment. It facilitates the absorption of harmful gases such as SO2 and SO3 from flue gas. The tower consists of a shell, packing material, packing support, liquid distributor, intermediate support and redistributor, gas and liquid inlet/outlet connections, among other components. The tower shell is typically constructed from metal materials.
4. What are the prerequisites for commissioning a desulfurization unit?
Answer: Before commissioning a desulfurization unit, several conditions must be met: all maintenance and testing work related to desulfurization must be completed, lubrication and cooling systems of equipment must be in good condition, actuators of dampers and gates must function properly, seal water for slurry pumps must flow smoothly, limestone slurry system must be operational, gypsum dewatering system must pass trial operation, absorption tower must be filled with water, and the desulfurization system must meet startup criteria.
5. Under what conditions would a desulfurization system undergo emergency shutdown?
Answer: A desulfurization system may undergo emergency shutdown due to various reasons such as high inlet flue gas temperature, failure of booster fan, GGH malfunction, complete stoppage of absorption tower circulation pumps, interruption in 6V power supply, boiler trip or malfunction of oil/electrostatic precipitator, power failure in the desulfurization system, among others.
6. How is the pH value of absorption slurry adjusted in the absorption tower?
Answer: The pH value of limestone slurry significantly affects the desulfurization efficiency. Proper adjustment of slurry flow rate is crucial to meet desulfurization requirements. During normal operation, the slurry flow rate can be adjusted based on pH value, inlet SO2 concentration, desulfurization efficiency, and slurry concentration. Increasing slurry flow rate is recommended when pH value decreases and outlet SO2 concentration increases, and vice versa. If desulfurization efficiency is low, increasing slurry flow rate along with the number of recirculation pumps can be considered.
7. How is the density of absorption slurry regulated?
Answer: The absorption tower is designed to operate with a slurry concentration of 15%-20% and gypsum content above 90%. Slurry density is primarily adjusted through gypsum dewatering. High slurry concentration can lead to equipment wear, corrosion, and scaling, while low concentration affects gypsum crystallization and desulfurization efficiency. To regulate slurry density, intensify gypsum dewatering and increase demister flushing frequency for high slurry concentration, and halt gypsum dewatering for low slurry concentration.
8. What are the causes and remedies for decreased circulation pump flow rate in the absorption tower?
Answer: Decreased circulation pump flow rate in the absorption tower may result from pipeline blockage, nozzle blockage, improper valve positioning, or decreased pump output. Remedial actions include pipeline and nozzle cleaning, valve position inspection and correction, and pump maintenance.
9. What are the reasons and solutions for abnormal liquid level in the absorption tower?
Answer: Abnormal liquid level in the absorption tower may stem from faulty level indicators, circulating pipe leakage, internal leakage of flushing valves, or tower leakage. Solutions involve checking and correcting level indicators, repairing circulating pipelines, replacing valves, and inspecting tower and bottom blowdown valves.
10. What are the reasons and remedies for decreased circulation pump flow rate?
Answer: Similar to question 8, decreased circulation pump flow rate can be attributed to pipeline and nozzle blockages, improper valve positioning, or decreased pump output. Remedial measures include cleaning pipelines and nozzles, inspecting and adjusting valve positions, and conducting pump maintenance.
11. What are the causes and solutions for increased SO2 concentration at the flue gas outlet?
Answer: Increased SO2 concentration at the flue gas outlet may result from inaccurate SO2 measurement, low absorption tower pH value, decreased circulation pump outlet pressure and flow rate, high inlet flue gas dust content, decreased gypsum discharge pump outlet pressure and flow rate, or insufficient dewatering system capacity. Solutions involve verifying SO2 measurement accuracy, checking circulation pump outlet pressure and flow rate, increasing limestone feed rate, adjusting boiler combustion, inspecting gypsum discharge pump, and enhancing dewatering system performance.
12. What are the reasons for and remedies to low desulfurization efficiency in the absorption tower?
Answer: Low desulfurization efficiency in the absorption tower may arise from inaccurate SO2 and pH measurements, low pH value of absorption slurry, reduced circulation slurry flow rate, excessive flue gas flow rate, or increased SO2 concentration in flue gas. Remedies include calibrating SO2 and pH meters, adjusting limestone feed rate, increasing circulation pump operation, and inspecting pump output.
13. What are the causes and solutions for poor gypsum quality?
Answer: Poor gypsum quality may stem from insufficient slurry feed, inadequate vacuum seal water flow, belt misalignment, high dust concentration, vacuum belt machine malfunction, insufficient oxidation reaction in the tower, defective hydrocyclones, or other operational issues. Remedies involve adjusting valve openings, increasing feed rates, checking vacuum pumps, correcting belt alignment, adjusting oxidation fan output, inspecting hydrocyclones, and optimizing pH and slurry density.
14. How should FGD accidents be handled?
Answer: In case of FGD accidents, steps include ensuring closure of inlet and outlet flue gas dampers, adjusting and reducing slurry pool and absorption tower slurry concentration and liquid level, maintaining normal operation of mixers, flushing areas with stagnant slurry, addressing GGH failure if applicable, and following protocols for power interruption.
15. What are the reasons for and measures to handle FGD system tripping?
Answer: FGD system tripping may occur due to flue gas system malfunction resulting in closure of inlet/outlet dampers, flue gas temperature exceeding 180°C, boiler trip or oil injection, inlet flue gas pressure exceeding maximum value, high flue gas dust concentration, or desulfurization system power failure. Measures include notification of relevant personnel, adjusting slurry pool and absorption tower slurry concentration and liquid level after tripping, maintaining mixer operation, flushing areas with stagnant slurry, and preparing for system restart.
16. What are the general steps for starting a desulfurization system?
Answer: The general steps for starting a desulfurization system involve comprehensive inspection and testing of the entire system, including mechanical, electrical, thermal, and instrumentation components. This includes startup tests for FGD pressure air system, process water system, cooling water system, limestone slurry system, flue gas system, gypsum dewatering system, wastewater treatment system, and completion of system startup to normal operation.
17. What are the approximate steps for shutting down a desulfurization system?
Answer: Shutdown of a desulfurization system involves steps such as stopping limestone slurry preparation, shutting down flue gas system, stopping absorption tower operation, halting dewatering system operation, stopping wastewater treatment system operation, draining residual slurry, and stopping FGD pressure air system.
18. What precautions should be taken in the event of a power outage in the desulfurization system?
Answer: In the event of a power outage in the desulfurization system, immediate actions include ensuring closure of flue gas system dampers, confirming UPS and DC system power supply, isolating electrical loads, stopping limestone feed if interlocked, monitoring flue gas system temperatures, and preparing for system restart.
This comprehensive guide explores various aspects of desulfurization and absorption tower operation in dust collector baghouse systems. From understanding the principles and processes to addressing common issues and implementing effective solutions, this knowledge equips stakeholders with the tools needed to optimize system performance and ensure environmental compliance.
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