The sewage (wastewater) discharged from the pollution source cannot meet the discharge standard requirements or meet the environmental capacity requirements due to the high total amount or concentration of pollutants.
In order to reduce the quality and functional goals of the water environment, the place that must be artificially strengthened is the sewage treatment plant, also known as sewage
Processing station.
The general process flow of the sewage treatment plant is:
Sewage pumping room - aeration settling tank - primary sedimentation tank - aeration tank - secondary sedimentation tank - contact tank - sludge concentration
Tank - sludge digester - dewatering machine room - gas cabinet - biogas generator
The unique underground pipe gallery of the sewage treatment plant occupies a very large area and has complex terrain, and the ventilation is very poor, so toxic gas and methane leakage or oxygen concentration
No one knows about it, and once the staff enters, it is extremely life-threatening. Especially in the sewage treatment plant, there are many underground pipe galleries, once someone is there
Danger occurs in the pipe gallery, but no one finds it in time, and it will be death.
The mud area is a high-risk area, and the concentration of hydrogen sulfide is higher than 50ppm when the dewatering pump room and drying room equipment are operating normally.
Therefore, the gas detector and gas alarm control system used in the wastewater treatment plant should have the following characteristics:
※ The equipment and system are fast and have a high level of safety
※ The equipment works stably, has a long service life and low maintenance
※ Dense distribution points and wide coverage
※ There are many types of gases to be detected
In different processes of sewage treatment, a large amount of flammable gas and toxic gas will be generated in different plant areas. The main gases to be detected are:
※ hydrogen sulfide ※ sulfur dioxide ※ carbon monoxide ※ methane ※ ammonia ※ oxygen
In wastewater treatment plants, the detector should consider the following locations where leaks are likely to occur:
※ Grille room ※ Inlet pump room ※ Air sedimentation room ※ Sand washing room ※ Mud collection well
※ Concentration tank ※ Dewatering machine room ※ Drying room ※ Pipe gallery
When determining the specific location of a detector, it should be noted that some detectors are sensitive to location and airflow. Depending on whether the density of the leaking gas is greater than that of air,
And combine the air flow trend to comprehensively complete the detector arrangement. According to the dominant wind direction of the place, the possible circulation phenomenon and rise of the air flow
trends, and the habitual channels where air flows naturally in the underground pipe gallery, etc., and judges the leakage direction of gas when a large number of leaks occur, detectors should usually be installed in the downwind direction.
According to whether the density of the leaking gas is greater than that of air, combined with the air flow trend, the detector arrangement is comprehensively completed. For suspected gas leaks
For places with heavy and airy conditions, the detector should be arranged close to the operating surface; For places that are lighter than air, the detector head should be arranged in
Above the protected device or area. At the same time, if conditions permit, the detector should be arranged higher than the structural steel that will change the air flow mode,
Where the pipelines and equipment are located.
Study whether the leak state of the leak point is microleak or jet. If it is a slight leak, the position of the point should be closer to the leakage point; If yes
For jet leaks, it should be slightly further away from the leak point.
For sites where area coverage is required, it should be done in relation to the floor and operating surface, depending on the heating and ventilation system and the potential release gas characteristics
The maximum spacing of the detector is 13~15m. For areas with a large outdoor area, key leakage points can be arranged separately
The method of combining uniform arrangement and design.
When evenly arranged, the distance between each monitoring point should be 10~20m, and the density of its installation can be according to the safety requirements of the production process
Come and add or subtract appropriately.
For indoor ventilation pipe galleries, places where gas is easy to accumulate in underground trenches, underground cable trenches, thermal ditches and sewage with sealed covers
In places where gas buildup is likely to accumulate regularly, such as trenches or under abnormal production conditions, the detector should usually be fixed in those areas where there may be gas leakage
Blind spots.
The following figure is a simple diagram and introduction of a typical wastewater treatment plant gas monitoring system:
The complete system consists of a gas monitoring system and a video system, all of which are components of Honeywell
Composition. The function of the whole system is: oxygen, hydrogen sulfide, carbon monoxide, sulfur dioxide, methane gas detector when installed in different areas
If the detector detects that the relevant gas concentration is exceeding the standard, the detector itself will generate an alarm through an external sound and light alarm, if there is one next to it
People can get a warning and evacuate in time, and at the same time, the alarm signal is uploaded to the server, and the server will command the video surveillance system to switch the main screen to
The speaker installed in the alarm area will broadcast relevant alarm information and remind relevant staff to pay attention and take relevant measures.
In addition, the system is also equipped with a monitoring computer, which monitors the detection value and working status of each detector in the system in real time through the configuration software.
All data and status are recorded and stored at the same time, so that operators can understand the on-site situation at any time, or query alarm/fault records.
The on-site detector uses XCD type gas detector. XCD is a universal gas detection platform developed by Honeywell and equipped with catalysis
Various sensors with three working principles: combustion, electrochemical, and infrared absorption compensation, can detect more than 20 kinds of gases, including the above gases
Flammable, explosive and toxic and harmful gases.
A branch of the water area
System57
controller
and alarm video linkage
cabinet
The second branch of the mud area
System57
controller
and alarm video linkage
cabinet
In the sewage industry, the location where the detector is installed is often underground, such as pipe galleries and other poorly ventilated places. Therefore, flammable gas detection
It is advisable to use a detector with infrared absorption compensation detection principle.
The XCD standard comes with 3 relays, which can be rooted
Output high alarm (A1) and high alarm according to user needs
(A2) and Fault (Fault) 3 relay signals.
The relay has a contact capacity of up to5A@250VAC，
Enough to drive any control device.
In addition, XCD has a unique 3-color backlight display: normally, LCD screen green backlight, when a fault occurs, LCD LCD screen yellow backlight, LCD LCD screen red backlight when alarm occurs. This is especially convenient for maintenance personnel to observe from a distance in low-light underground. Since the detector is the same model, the user's future spare parts requirements are simple, and only a few spare parts need to be selected to cope with a large number of detector maintenance needs.
The gas alarm controller uses the System57 gas alarm controller. The System57 gas alarm controller adopts an independent board structure, and each channel works completely independently. Depending on the user's needs, the System57 gas alarm controller can output three relay signals: High Alarm (A1), High High Alarm (A2) and Fault for each detector in the field. To configure a large gas detection system, the System57 controller can also output an RS-485 Modbus signal to a higher-level system or a SCADA monitoring computer. As an important security system, the security of the system itself must also be guaranteed. The power supply of all detectors on the entire system site is centrally provided by the gas alarm control cabinet. The alarm system control cabinet is equipped with 1 set of UPS system. When the external power supply is suddenly cut off, the UPS system can support the normal operation of the system for another 2 hours, and at the same time send a power loss alarm to the upper system.
For small sewage plants, one independent gas alarm system is sufficient. For large sewage plants, due to the wide distribution of detectors and the large number of points, the branch plant is generally divided into several systems, and then several small systems are integrated into a large system through Modbus communication or SCADA system.
In addition to gas detection and alarm, data collection and recording are also a very important link. The more detailed the data collected and recorded, the more beneficial it is for the analysis of the cause of alarm failure.
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Sensepoint XCD type gas detector
System57 Gas Alarm Controller