At present, environmental problems are one of the main social problems facing China, and the discharge of industrial enterprises is one of the main sources of environmental pollution in China. In order to better monitor the discharge of enterprises, many regions have adopted online monitoring. CNOOC Petrochemical Company is a key chemical enterprise in Hainan Province and an advanced unit for sewage treatment in Hainan Province. In the past, the Hainan Provincial Environmental Protection Department's monitoring of the company's emissions was mainly conducted through regular or irregular spot checks, which was time-consuming, laborious, and difficult to be accurate. Therefore, CNOOC Limited proposed a set of online monitoring system for sewage discharge so that the environmental protection department can monitor the company's sewage.
CNOOC Petrochemical's main products are urea and methanol, and its monitoring scope includes three indicators of ammonia nitrogen, COD and emissions. Therefore, the sewage monitoring system of China Shipping Chemical Company mainly realizes the real-time transmission of the three online detection data of ammonia nitrogen, COD and emissions to the main system of the Hainan Environmental Protection Monitoring Station to meet the environmental protection department's monitoring of the company's sewage.
1. Design of online monitoring system for sewage discharge
1.1. Construction objectives, design basis and functional requirements of the online sewage monitoring system
Attaching importance to environmental protection construction, consciously accepting the online monitoring of the company's sewage discharge by the national environmental protection monitoring department, which embodies CNOOC's attitude towards national and social responsibility, and is also a requirement for the company's sustainable and healthy development. The main target of the online sewage discharge monitoring system implemented this time is the production and domestic sewage discharge of the Hainan production plant area of ​​China Shipping Chemical Company. The Hainan production plant area is the main production area of ​​CNOOC Chemical Company, accounting for more than 70% of the production capacity of the chemical company, and is also the main production sewage production place.
The design basis of the sewage monitoring system of China Shipping Chemical Company is as follows:
Technical requirements for environmental protection product certification for chemical oxygen demand (CODcr) on-line monitoring instruments (HBC6-2001)
Technical requirements of ammonia nitrogen water quality automatic analyzer (HJ / T101-? 2003)
"Water Quality Chemical Oxygen Demand Potassium Dichromate Method" (GB1194-89)
"Determination of Water Quality Ammonium? Nessler's Reagent Colorimetry" (GB7974-87)
Comprehensive Wastewater Discharge Standard (GB8978-1996)
The main functions of China Shipping Chemical's online sewage discharge monitoring system shall include:
On-line detection of NH4-N and COD indicators of discharged water after treatment in a sewage treatment plant;
Online measurement of discharge water flow after treatment in the sewage treatment plant;
The NH4-N and COD detection data and flow measurement data of the discharged water after treatment by the sewage treatment plant are uploaded:
Display function of various monitoring indicators, alarm function exceeding standard, power failure protection function, etc.
1.2. System Integration Design Overview
The sewage online monitoring system is composed of sampling unit, pretreatment unit, analysis monitoring unit, system control unit, communication unit, remote monitoring center, etc. The sampling unit and pretreatment unit complete the sampling control process such as water sample collection and water sample pretreatment for automatic water quality monitoring; the analysis and monitoring unit completes the analysis process of water quality monitoring parameters; the system control unit completes the system's monitoring operations and various data collection, etc. The communication unit realizes the uplink and downlink transmission process of data and control instructions; the remote monitoring center as the central station of the system, receives data in real time and performs remote monitoring operations and data analysis. The system is based on the principles of reasonableness, practicability, economy, reliability, and simple operation and maintenance, and is strictly designed with reference to relevant national technical standards, specifications and technical standards of relevant departments. Meet user requirements for real-time monitoring and remote monitoring of water quality.
The sewage online monitoring system integration is composed of water sample collection device, pretreatment, online monitoring sub-instrument equipment, local monitoring device equipment, communication equipment and monitoring center station. The monitoring center station combined with the corresponding monitoring and analysis software can remotely monitor the operation of the system to realize the unattended and manned mode of system operation.
Water sample collection:
The discharge pond (clear water pond) of the sewage treatment plant of the chemical company is in a low position, and the sampling analysis of the self-flow method cannot be realized. Therefore, it is necessary to sample the discharged sewage through sampling equipment.
Water sample pretreatment:
Water sample pretreatment mainly controls the filtration of water samples. The sampling unit of the COD of HACH and the ammonia nitrogen analyzer have a pretreatment function, which can reasonably process the collected water samples according to the measurement requirements of the instrument, and also has a self-cleaning function.
Monitoring and analysis:
According to the specific requirements of the environmental protection department, parameters such as ammonia nitrogen and COD can be monitored. Various instruments can meet the requirements of local water quality monitoring and flow monitoring.
Data collection and transmission:
According to the specific requirements of the environmental protection department, parameters such as ammonia nitrogen and COD can be monitored. Various instruments can meet the requirements of local water quality monitoring and flow monitoring.
Data collection and transmission:
The selected instruments are equipped with 4 ~ 20mA output and MODBUS, RS485 communication output functions, which can realize remote data communication and two-way control.
1.3. Selection of main instruments and equipment
The instrument selection of the sewage online monitoring system must first meet the requirements of the relevant national regulations, especially the requirements of the Comprehensive Wastewater Discharge Standard (GB8978-1996), as well as the requirements of system performance stability and reliability. .
The on-line sewage monitoring system should be able to operate under severe working conditions and environmental conditions. At the same time, it needs to meet the requirements of simple and simple on-site operation, easy operation and maintenance, and wrong judgment. Therefore, the design of the system should always give priority to the reliability of the system. position. Fully consider the specific conditions of each monitoring point, in the system design and future implementation, comprehensive consideration of local water quality, flow, operating environment and other factors. Therefore, in terms of system design and instrument selection, high-quality, high-reliability, and mature monitoring equipment are required as much as possible. In terms of equipment selection, the most important thing is the selection of analytical instruments. The selection of analytical instruments with good stability, accurate and reliable measurement data, strong resistance to harsh environments, and satisfactory measurement range is the prerequisite for the stability and reliability of the entire monitoring system, otherwise the quality of the monitored data is difficult to guarantee. The technical aspects of flow measurement instruments are relatively mature, and the quality of many manufacturers is relatively guaranteed, and it is easier to select models.
After various comparisons, CNOOC decided to choose the most widely used, stable and reliable HACH CODmax COD analyzer and Amtaxcompact ammonia nitrogen analyzer in the final selection of COD and ammonia nitrogen analysis. The monitoring signal transmitter uses the KSJK series environmental protection wireless monitoring system designated by the Hainan Environmental Protection Bureau.
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