I. Enterprise Overview
The Chengbei Water Plant was built in 1997. It is an advanced automated water plant built with loans from the Spanish government. Most of the plant's equipment is imported from abroad. It is one of the ten key projects in Nanjing that year.
The North City Waterworks has a design capacity of 500,000 tons per day. In 2000, the first phase of the project was completed. It can supply 250,000 tons of tap water per day, accounting for about one-fifth of the total water supply in Nanjing. It mainly supplies the east part of Nanjing City, including Yadong New District, Qixia, Yanziji, Maigao Bridge, and Suojin Village.
Source water (river water) is pumped by a pump house to the water purification plant through oblique flow. It first enters the water distribution well and is equipped with a static mixer behind the well. The mixed water is evenly distributed to the reaction pools on both sides of the folding plate ( The sides are divided into three groups, each of which is parallel to the five grids. Along the flow, the wave folding plate, the wave folding plate, and the flat plate technology are used in this order.
The water in the reaction chamber is rectified into the sedimentation tank through the perforated wall. The sedimentation tank uses an advection precipitation process. The sedimentation tanks are divided into two sides of the gallery, two on each side, and each is divided into two parallel grids with diversion walls.
The precipitated water is collected in a stainless steel finger-shaped perforated catch basin and then enters the filter tank. The filter tank uses a V-filter process. There are 14 grids in each filter, symmetrically distributed on both sides of the gallery.
The filtered water enters a clear water tank with a capacity of 25,000 m3 (a total of two, one for each phase) through a DN1800mm clean water pipe, and is chlorinated before entering the clean water tank. The water in the clear water tank flows through the DN2000mm pipeline to the second pump house suction well. The second pump room is designed with five horizontal centrifugal pump unit foundations. There are two sets of frequency control devices; one for three sets, (an additional one in 2003) and two sets of two for full load. Pressurized water enters the urban pipe network through two pipes of DN1500mm and DN1200mm.
The whole process of water production is like a pipeline, and the water with an average annual turbidity of 140NTU is treated as a factory water of 0.2NTU or less. At present, the company's factory water turbidity standard is below 0.2NTU.
The power supply is designed as two 35kV lines. The capacity of the two main transformers is 8000kVA respectively. The substation control system adopts a microcomputer protection device from the State Power South, which realizes the unattended and remote operation of the substation.
The control system adopts the distributed control system of American AB Company. A total of six PLC substations are located in a pump room, a twisting room, a chlorination room, a recoil pump room, a pump room, and a sludge pumping station. Seven SLC substations are dedicated to the filter. A pump room pump is automatically adjusted according to the water level of the clear water tank, and the automatic single-factor control method is adopted for the automatic twisting. The chlorination, filtration and backwashing also adopt international advanced control methods. The pump of the second pump room is automatically adjusted according to the pressure of the pipe network. . As a highly automated water plant, staffing has been greatly simplified compared to water plants of the same scale, and only 4 people are required to maintain normal operation. This reflects the advantages of advanced technology.
Due to the improvement of the automation level, the equipment and instrument configuration have reached a relatively advanced level. Most of the process control instruments are directly imported and imported. For example, an on-line turbidity meter, residual chlorine analyzer, PH meter, and flow galvanometer are used for water quality testing in our factory. The data collected by the control instrument is passed to each PLC substation and uploaded to the central control room so that the on-duty personnel can understand the real-time dynamic data at any time. With the help of advanced detection equipment, our factory's automated production level has embarked on a new level.
Second, automated instruments have an important position in the water treatment system
In a modern water purification plant, every production process always appears and exists with the corresponding instrumentation and automation technology. The instrument can detect various process parameters, and can be manually or automatically controlled according to these data, so as to coordinate the relationship between supply and demand, between the various components of the system, and the respective water treatment processes so as to make the various devices and facilities more accessible. Fully more reasonable use. At the same time, the value measured by the measuring instrument can be continuously compared with the given value. When deviation occurs, the adjustment is performed immediately to ensure the quality of the water treatment. According to the parameters detected by the instrument, it can further automatically adjust and control the dosage of the pharmaceutical and the reasonable operation of the pump unit, making the management more scientific. Because the instrument has the function of continuous detection and over-limit alarm, it is convenient to deal with the accident in time, and the instrument is still the precondition of computer control. Therefore, in the advanced water treatment system, it is inseparable from the automation instrument. It can be said that automated instruments are the "eyes" of automated control systems.
Third, the classification of commonly used instruments of water treatment system
The instruments used in water supply engineering can be roughly divided into two categories: one is the instruments that monitor the physical parameters of the production process, such as temperature, pressure, liquid level, and flow rate. Another category is instruments that test water quality analysis, such as water turbidity, pH, residual chlorine, SCD, dissolved oxygen, and COD. These special instruments have developed relatively late in China. Therefore, the monitoring of water quality analysis instruments using advanced foreign equipment is more economical and plausible in the long run. The quality of the instrumentation is directly related to the effect of water supply automation. The instruments used by our factory for testing water quality analysis (including laboratory instruments for laboratory use) are imported instruments. Such as the United States HACH company's 1720D, 1720E, SS6, 2100N, 2100P turbidity meter, CL17 chlorine analyzer; US Milton's SC5200 flow current detector and so on.
Fourth, the water plant automatic control system composition and monitoring parameters
1. Make up pattern
The water plant automatic control system adopts the distributed control system of American AB Corporation, which consists of the water plant central control room and on-site monitoring two-level system. There are six PLC substations in the whole plant, which are located in a pump room, plus room, and chlorination room. The recoil pump house, the second pump house and the sludge pump house are monitored in accordance with the principles of centralized management and decentralized control. The monitoring data of each substation instrument is sent to the computer system, which can record, display, print, and alarm on the central control room computer. Some data must also be transmitted to the head office dispatch center.
2. Monitoring parameters
A pump house substation monitoring parameters
Water quality parameters: source water turbidity, pH value, water temperature, dissolved oxygen, COD, etc.
Operating parameters: pressure, suction well water level, source water flow, etc.
Inter-station monitoring parameters
Water quality parameters: sediment effluent turbidity, SCD value.
Operating parameters: sedimentation tank water level, flow, drug tank level, concentration
Chlorination intermediate station monitoring parameters
Operating parameters: filter outlet flow, pressure, chlorine volume
Recoil pump house substation monitoring parameters
Water quality parameters: filtered water turbidity, residual chlorine
Operating parameters: filter water level, head loss, backwash water flow, rinse strength
Second pump house substation monitoring parameters
Water quality parameters: water turbidity, residual chlorine
Operating parameters: factory water pressure, flow, clear water level, suction well water level, etc.
V. Work status of major water quality analysis instruments
1720D, 1720E, SS6 Scatter Turbidimeter from Hach Company
The water is clear and transparent in the light, without any suspended impurities or colloidal impurities, the turbidity is zero, (in reality there is no zero water is about 0.01 or 0.012 NTU) and vice versa is muddy. Turbidity is a measure of the degree of turbidity of a body of water, ie, the presence of finely dispersed suspended particles in the body of water to make water less transparent. The turbidimeter is an instrument for measuring the degree of turbidity in a water body. It is mainly used for the monitoring of water quality.
Turbidity is a crucial water quality indicator for water supply and industrial water treatment. Reducing turbidity also reduces bacteria, coliforms, viruses, cryptosporidium, iron, and manganese in water. Studies have shown that when the water has a turbidity of 2.5 NTU, organic matter in the water is removed by 27.3%; when the turbidity is reduced to 0.5 NTU, organic matter is removed by 79.6%, and when the turbidity is 0.1 NTU, most organic substances are removed, and pathogenic microorganisms are eliminated. The content is also greatly reduced. Especially for the tap water industry, the turbidity index is critical. In 2007, the tap water standard was promulgated to require drinking water to reach 0.5NTU or less; Nanjing Water Supply Co. had water turbidity below 0.2NTU, precipitation water turbidity about 3NTU, and filtered water below 0.1.
In the water plant before filtration, after filtration, precipitation and factory water monitoring, the continuous monitoring using an on-line turbidity meter is mainly used, and the SS6, 1720E, and 1720D on-line turbidity meters manufactured by HACH need to be used for automatic control. Automatic feeding system information feedback.
The water plant is responsible for supplying residential water and industrial water. The quality of water supply directly involves the people's health and safety and the normal production and product quality of food, brewing, medicine, textile, printing and dyeing, electricity and other industries. Turbidity is a very important water quality indicator. Therefore, the choice of turbidimeter is particularly important. Turbidity meter can be divided into two categories: visual turbidity meter and photoelectric turbidity meter. Optoelectronic turbidimeter can be divided into process monitoring (continuous measurement) turbidity meter and laboratory (including portable) turbidity meter for its use. Based on its design principle, opto-electronic turbidity meter can be divided into transmission turbidity meter and Scattering light turbidity meter.
Due to the scattered light turbidity meter, it has high sensitivity to low turbidity of water, high accuracy, small relative error, good repeatability, water turbidity does not show turbidity, and the ratio of scattered light to incident light intensity can be presented. Linear relationship. Therefore, in September 1992, the World Health Organization published the "Guidelines for Drinking Water Quality" that stipulates a scattered light turbidity meter as a measuring instrument. At the same time, the “Water Supply Industry 2000 Technology Development and Development Plan†has clearly specified that the water turbidity index of the Type I water network is 1 NTU.
Hach's 1720D, 1720E, and SS6 turbidimeters commonly used in water plants are scattered light turbidity meters. The 1720D and 1720E turbidimeters were used in the measurement of sedimentation water, filtered water and factory water. In use, the water sample continuously flows into the turbidimeter and flows through the deaerator to drain air bubbles in the water stream. The water sample then enters the middle column of the turbidimeter and rises into the measuring chamber. The photocells immersed in the water sample are measured. Scattered light in the direction of 90 degrees of suspended solids in water, the amount of scattered light is proportional to the turbidity in the water sample. Moreover, the 1720 series does not use a sample cell, which can reduce the scattered light and improve the measurement accuracy. We control the sampling water flow rate between 250 and 750ml in routine maintenance and measure it with a stopwatch and a graduated cylinder. A small flow rate will affect the accuracy of the instrument. Periodically clean the sampling part of the turbidimeter, including sampling tubes, defoamers, photocells, light bulbs, lenses, etc. to ensure that the sampled water is not contaminated. Regular calibration, do a good job of instrument inspection and calibration record tracking instrumentation.
The SS6 series surface scattering turbidity meter is used to measure the high turbidity water of source water. It measures the scattered light from the liquid surface by irradiating the light beam on the liquid surface, avoiding the contact between the optical system and the water sample, and eliminating the cleaning flow cell. Loss of signal. The measurement range of SS6 is 0-9999NTU, and the source water turbidity of general surface water plants is within this range. The flow rate of the sampled water flowing into the instrument is important because of the high turbidity of the water. When the flow rate is low, the sediment in the water is likely to precipitate and block the water pipe. We generally control the water volume at 1-2 L/min. This overflows the water at the top of the sampling tank. A smooth liquid surface is formed with no bubbles, no fluctuations, accurate meter values, and normal operation.
American HACH CL17 chlorine analyzer
The CL17 residual chlorine analyzer collects a portion of the liquid from the sample every 2.5 minutes for analysis. When the sampled water enters the meter cuvette for measurement of the blank absorbance, the meter can compensate for any interference or color of the sampled water and provide an automatic zero reference point. The reagent is added at this reference point and gradually appears magenta, and the meter will measure it and compare it with the zero reference point. The residual chlorine in the water (hypochlorous acid and hypochlorite) oxidizes the DPD indicator to a fuchsia compound at a pH of between 6.3-6.6. The depth of coloration is directly proportional to the amount of residual chlorine in the sample. The buffer solution for residual chlorine can maintain a proper pH. The instrument works like this. Instrument manufacturers provide detailed installation instructions. After the instrument is installed, parameters must be set. Selecting the range and adding reagents can work normally. Normal maintenance is not large, regular replacement of reagents and pipes, regular cleaning of the colorimeter room, to maintain the normal operation of the instrument.
Sixth, summary
1. To realize the modern management of the water plant, automation instruments must be used.
2. When selecting the instrument, it should be: stable, easy to operate, easy to install, capable of continuous measurement, responsive, and easy to maintain.
3. In the daily inspection of the meter, it is necessary to check the sampling water flow rate, the amount of buffer used, and whether the alarm light of the instrument is on, and whether there is any abnormal sound when the instrument works.
4. Management personnel should always pay attention to the collection and organization of technical data so as to absorb and digest it.
5. After the water plant is completed and the water is turned on, the instrument is put into use normally. The management personnel should conduct follow-up investigation on the use of the instrument, understand the working condition of the instrument, and sum up experience in a timely manner so as to facilitate the improvement of the work in the future.