1、 What is precision aeration?
Precision aeration is the product of the sewage treatment plant from the early extensive manual control mode to the modern fine automatic control mode.
The traditional activated sludge process has been applied worldwide for hundreds of years. Many authoritative experts at home and abroad have repeatedly proposed and stressed the need to deeply excavate the century old activated sludge process to realize the optimal control and efficient operation of biochemical treatment process.
The primary goal of precision aeration is to ensure the stable operation of biochemical treatment process and the stable standard of effluent, so as to save energy and reduce consumption of blast aeration system and reduce the operation cost of sewage treatment plant.
Automation and fine management and control of sewage treatment plants have long been advocated internationally. Precision aeration is an effective tool for the fine management of sewage plants, which requires the joint efforts of blowers, aeration equipment, precision aeration system and other parties.
Precise aeration system can realize various complex gas supply schemes, such as intermittent aeration, micro aeration, normal aeration, dissolved oxygen distribution control, etc; It can help the sewage treatment plant to realize the fine adjustment of the process, adapt to various processes, and adjust with the change of the process; It can also notify the main control of the blower to adjust the air volume according to the current required aeration volume, so as to prevent abnormal conditions such as surge and vibration and save the power consumption of the blower.
2、 Why accurate aeration?
In the biological treatment process of sewage treatment plant, if the aeration volume is insufficient, it will lead to the deterioration of process operation and the discharge of effluent quality exceeding the standard; Excessive aeration will lead to high energy consumption and increase the operation cost of sewage treatment plant. Therefore, only by reasonably distributing and accurately adjusting the aeration volume of each area according to the actual demand can we ensure the efficient and economic operation of the sewage treatment plant.
A good automatic control system of sewage treatment process can not only ensure the continuous and stable operation of sewage treatment plant equipment, but also save energy and reduce consumption. It has been paid attention to and applied in process upgrading and transformation. Precision aeration control system is a set of energy-saving technology developed in recent years to better control blast aeration.
The energy consumption of sewage treatment plants in China is mainly power consumption. The power consumption per ton of sewage treatment is about 0.2-0.3 kwh, and the electricity charge accounts for about 50% - 70% of the sewage treatment cost. Based on the construction of sewage treatment plants in China, through the optimal operation of existing facilities, there is a huge space to improve effluent quality and reduce energy and material consumption. By the end of June 2019, more than 5000 urban sewage treatment plants (excluding township sewage treatment plants and industries) have been built in cities across the country, with a sewage treatment capacity of 210 million m3 / day.
According to the calculation of 50 billion tons of sewage treated by China's sewage treatment plants every year, if the energy consumption can be saved by 20%, it can save about 3 billion kwh of electricity for the country. Under the background that the state vigorously advocates energy conservation and consumption reduction, the energy conservation and consumption reduction of sewage treatment plant is of great significance.
About half of China's sewage treatment plants use oxidation ditch and AAO Process, and more and more AAO deformation processes show an upward trend. The energy consumption of blast aeration accounts for about 51% of the total energy consumption of sewage treatment plant. Therefore, the realization of energy-saving operation of aeration system is the key to energy-saving of sewage plant.
Excessive aeration directly wastes electric energy, and dissolved oxygen is brought to the anoxic area through internal reflux to affect the effect of denitrification, while dissolved oxygen is brought to the anaerobic area through external reflux to affect the process of anaerobic phosphorus release.
Insufficient aeration affects the microbial activity in the biochemical tank and may affect the effluent quality; It may also cause denitrification in the secondary sedimentation tank, and the sludge floats up, affecting the effluent.
Precision aeration system can not only ensure the continuous and stable operation of sewage treatment plant equipment, but also save energy and reduce consumption. Our company perfectly combines international top equipment such as blower, aerator, electric valve and on-line monitoring instrument with good automatic control system, and truly realizes the reliable and stable operation of the whole system.
The aeration process involves two steps: one is the diffusion and dissolution of oxygen. In the blast aeration system, it is mainly reflected in the transfer of oxygen in the air from the gas phase to the liquid phase after the air is released from the aeration head at the bottom of the aeration tank. The second is the utilization and consumption of dissolved oxygen. This process integrates the organic carbon removal process, biological nitrogen removal and biological phosphorus removal of aerobic treatment process, and is the result of the comprehensive action of multiple processes.
The aeration process of activated sludge process is to provide appropriate dissolved oxygen for the removal of organic carbon, nitrification and phosphorus absorption, so as to promote the normal progress of three biochemical reactions. The goal of aeration flow control is to form stable dissolved oxygen conditions and establish a dynamic balance and reliable living environment for microbial growth and pollutant degradation. The essence of this dynamic equilibrium process is to make the total oxygen transfer rate approximately equal to the total oxygen consumption rate. As the inlet water quality and quantity of the sewage plant change, the oxygen consumption also changes in a specific period of time. Only by making the oxygen supply and oxygen consumption in this period balanced, can we ensure the stability of the treatment environment and the outlet water quality.
3、 Composition of precision aeration system
It is mainly composed of the following six equipment: (1) blower, (2) valve, (3) flowmeter, (4) aeration panel / pipe, (5) do and other field instruments, (6) precise aeration control cabinet. 1. Blower
The blower is the air supply equipment of the precision aeration system, which is responsible for providing compressed air with appropriate pressure and flow. It is the key equipment of the whole precision aeration system. Without a stable air source, there will be no stability of the whole system, not to mention controlling the aeration volume of each corridor and maintaining the stability of parameters and processes. Therefore, selecting a blower suitable for the aeration system is the key to realize the precision aeration system.
1. Control mode of blower
Most of the regulation modes of blowers in the market are divided into three modes: frequency regulation, air volume regulation and pressure regulation. It is the most efficient aeration system to adjust the pressure. The blower with constant pressure mode is recommended as a special blower for precise aeration system to achieve efficient control.
2. Surge risk of blower
At the same time, when selecting the blower, we should not only consider the control mode of the blower, but also consider the air volume operation range of the blower. Due to the change of water quality and quantity, the aeration volume required by the process changes at the most time. If the air volume required by the process is less than the minimum air volume that the blower can provide, the blower may have the risk of surge. For example, now there are two blowers in constant pressure control mode to supply air to the process. The air volume range of a single blower is 6000-10000m3 / h. The two blowers on site operate in linkage. If the air demand required by the process is 1100m3 / h, the air volume of one blower is not enough, and two blowers need to be opened, but the air volume is too large, resulting in the valve at the minimum valve position, the pipeline pressure of the whole aeration system is getting higher and higher, and finally leading to the surge of the blower.
There are two ways to avoid blower surge. Size formula: when selecting the type, considering the size distribution of the blower, that is, selecting a 4000-8000m3 / h blower and a 5000-10000m3 / h blower can realize the continuous flow gas supply of 4000-18000m3 / h, avoid the risk of blower surge, greatly increase the range of adjustable air volume of the blower, and well solve the risk of surge. If it is a new project, the blower size formula is recommended. If it is a reconstruction project, the minimum gas method is recommended. Optional. 2. The valve is the main control equipment of the whole aeration system. According to the set parameters, the system adjusts the flow of the pipeline by adjusting the opening of the valve, so as to achieve the purpose of adjusting the process parameters. This has higher requirements for the valve, and the selection of its working characteristic curve is also very important. It is best to select the regulating valve with good linearity, such as prismatic valve, and take into account the reducing size of the valve, pressure loss and other factors. Some manufacturers use butterfly valve to replace the regulating valve. Due to the limitation of its regulating curve, the pressure loss is high, the regulation linearity is not good, and the effect is very bad.
3. Do field process instrument
Field instruments mainly include do instruments, ammonia nitrogen instruments, pH value instruments, etc. there are many brands of instruments in the market that can meet the requirements. The convenience of normal maintenance is mainly considered, because most instruments need regular maintenance and calibration, which requires high requirements for the operators of the sewage treatment plant. If the field instrument cannot accurately measure the process value (such as instrument sensor blocking, etc.), the whole accurate aeration system will control in the wrong direction and affect the quality of effluent.
4. Flow meter
The flowmeter is used to measure the flow of the pipeline and is the measuring equipment of the whole aeration system. The mass flowmeter shall be selected as the flowmeter, which is not affected by temperature and pressure. Select flowmeter with high precision and good repeatability. At the same time, the installation requirements of flowmeter and valve shall be considered. There are special requirements for the installation of flowmeter, such as the distance between straight pipe section, reducing and expanding diameter and flowmeter, the distance between valve and flowmeter, and the influence of elbow on the measurement of flowmeter.
5. Aeration tray / pipe
The installation of aeration tray / pipe shall be qualified without air leakage and installation level. The installation process shall be strictly followed to prevent air leakage, and the level test shall be conducted to ensure the uniform distribution of air volume.
6. Precision aeration system control cabinet
The precise aeration system can be compared to an experienced process worker. If the blower is the heart and the instruments such as valves, flow meters and do are hands and feet, the control cabinet of the precise aeration system is the brain. The accuracy of its control directly affects the accuracy of the system and the stability of the effluent quality.
Four、 Ideal precision aeration system
The ideal precise aeration system should consider the influence of valves, flow meters, do instruments, blowers and other equipment, and be able to adapt to the working characteristics of these equipment. It should have parameter settings for different process loads, as well as control mode and alarm output in case of emergency (such as do instrument failure, blower surge and other adverse factors)
There are many manufacturers of precision aeration system in the market, and their control is also different, but in general, a perfect precision aeration system should have the following characteristics:
The ideal precise aeration system should be able to adapt to different water quality requirements and various supporting process equipment. For other equipment (such as blower), it can well adapt to its control mode, such as flow and pressure control mode.
The ideal precision aeration system should have independent control ability. Just put the system in automatic mode, the system can operate according to the set process parameters without interference from other communication circuit breakers. And in case of emergency, there are alternative control methods and alarm output to ensure the stability of parameters.
The ideal precision aeration system should refine the control range, because the curves of different valves and flow meters are different, the parameters of different valves and flow meters can be introduced into the precision aeration system, and even the butterfly valve can achieve good results.
4. Parameter selectability:
The parameters of the ideal precision aeration system should be optional, such as setting control mode (flow control, valve position control, do control, etc.), control location (remote / local), control parameters,
(some articles on this website are collected from the Internet, such as infringement contact deletion)