Summary:
With the continuous development of network technology and multimedia technology, the traditional industrial control model also needs to continuously introduce these new technologies to meet the new requirements of control and management in today's society. This article focuses on the monitoring system for the oilfield sewage treatment station of Xinjiang Xingang Company. Optimization and upgrade. Among them, an integrated control concept was adopted, and a controller that integrates PLC control, network communication, video monitoring, and data storage was selected, and the function of the control system was enhanced. The system has been put into operation for more than two years, stable and reliable, with good application and promotion value.
Keywords: sewage treatment station; integrated controller; automatic control system upgrade
Oil Field Sewage Disposal Station Automatic Control System
YANG Xianli
Xingang company in Sinopec in Kelamayi province in China
Abstract:Along with the development of networking and multi-media technology , the traditional industry control mode need to introduce these technology to meet both requirements of the control and management from the nowadays' society.This article mainly introduces the upgrade of oil fieldaus Station automatic control system in Xin Jiang Xin Gang company. We use All-in-One control idea and the controller which integrated the PLC control, the network communication, video monitoring and datalog in the upgrade which enhanced the function of the system. Has been put into run steadily and reliable for two years. It offers valuable reference for the using and popularization.
Key words:sewage disposal station; All-in-One controller;upgrade of auto control system
Oilfield sewage mainly includes crude oil stripped water (also known as oilfield produced water), drilling effluent, and other types of oily wastewater in the station. Treatment of oilfield sewage can be done in a variety of ways depending on factors such as oilfield production and environment. When the oilfield needs water injection, the oilfield sewage is treated and injected back into the stratum. At this time, many indicators such as suspended solids and oil in the water must be strictly controlled to prevent damage to the stratum. If it is used as a steam generator or boiler feed water, it is necessary to strictly control the calcium, magnesium and other easily scaleable ion content in the water, the total salinity and the oil content in the water. If discharged after treatment, treat the wastewater to discharge standards according to local environmental requirements. In recent years, with the gradual aging of the domestic sewage treatment station monitoring system, how to monitor and control the entire wastewater treatment process safely and efficiently puts forward new requirements for the monitoring system.
1. Process flow
The purpose of the oilfield sewage treatment is to remove oil, suspended solids, additives and other unfavorable components that hinder water injection and cause corrosion and scaling of the water injection system. The technologies used include dozens of methods such as gravity separation, coarse granulation, flotation, filtration, membrane separation, and biological methods. [1] The water quality components of various oilfields or blocks are complex and the differences are large. The water quality requirements for the reinjection water after treatment are also different, so the treatment process should be selected. The following describes the main treatment processes and control schemes involved in this sewage treatment plant. Judging from the current situation of heavy oil wastewater treatment and application at home and abroad, the heavy oil wastewater treatment and reuse boiler is the ultimate solution to solve the heavy oil wastewater generated during the development and production of heavy oil. The heavy oil effluent quality at No.91 station in Xinjiang Xingang Company is much better than that in Shengli Oilfield and Liaohe Oilfield. The salinity is below 3000mg/l, the hardness is within 100mg/l, SiO2 is less than 50mg/l, and other oilfield heavy oil wastewater The minimum mineralization is 7000mg/l and the hardness is above 200mg/l. Gravity degreasing - coagulation sedimentation - filtration process, treated water and then softened to achieve the "heavy oil gathering and steam injection system design specifications" SYJ0027-94 reuse standard heat recovery boiler, in Processing technology is already mature. That is: incoming water → regulation → coagulation sedimentation process → filtration
The incoming water enters two 5000m3 regulating storage tanks for homogenizing even treatment, so that the oil content in the water reaches <70mg/L, and the suspended matter is <100mg/L; after the three medicaments are continuously added in a certain sequence and time interval on the outlet pipeline, Re-entry into four reactors and two 2000m3 coagulation sedimentation tanks to react and precipitate, and treat most oil slicks and suspended solids to make the oil in the water reach <5mg/L, suspended solids <15mg/L, and then undergo two-stage filtration. The oil content in the water is up to <2 mg/L, and the suspended solids are <2 mg/L. The oil is sent to a demineralized water station for softening and used in oilfield steam injection boilers.
The site's hardware system consists of three HORNER OCS integrated controllers, remote IO modules, main control room server, sewage station duty room monitoring computer, fiber optic switches, cameras, field instruments, inverters and other components. The upper computer configuration software selected Schneider's Citect configuration software. The following brief description of the main hardware:
(1) OCS integrated controller: The system uses three integrated controllers from the United States HORNER. The controller integrates the functions of the PLC, touch screen, and network module into one, and supports functions such as Ethernet, serial port, Cscan bus, memory card, and video.
(2) Citect Configuration Software: The system has selected Citect's configuration software from Schneider Electric. The software's IO point expansion ability is relatively strong, and the data refresh time is less than 1 second. In the product, the software system required for various hardware communication devices is directly packaged and has good compatibility. At the same time support WEB release and other functions, the same local area network computer can monitor the scene operation.
(3) All communication with the inverter using bus communication (Modbus RTU protocol)
(4) Field instrument: It mainly includes various temperature, pressure sensors, combustible gas detectors, flow meters and power meters. The power meter selects the products that support Modbus RTU function, and the rest of the meters use 4-20mA analog signals for monitoring.
3. System network structure
The system network structure is shown in Figure 2.
Figure 2 System Network Structure
Fig.2Structure of System Networking
From Figure 2, we can see that the field network can be divided into two levels: The CsCAN network is selected between the integrated controller and the remote IO module; the Modbus TCP network is used between the host computer and the controller, the smart meter, and the frequency converter. The following brief description of these two kinds of networks:
(1) CsCAN network [2]: The CsCAN protocol is a CAN bus-based fieldbus protocol standard developed by the American HORNER Corporation. The CsCAN network device supports point-to-point communication while supporting master-slave mode network configuration. The maximum data transmission rate of the CsCAN network can reach 1Mbps, the maximum transmission distance of the network is 2000 meters, and the maximum number of nodes is 253.
(2) Modbus TCP Network: Modbus is a derivative of a simple, neutral vendor's Modbus serial communication protocol for managing and controlling automation equipment. Since the Modbus protocol appeared earlier and is an open protocol, it has a large number of equipment support groups, which is conducive to the expansion of the system.
In the field network selection, taking into account the number of on-site IO modules are more, and some modules are far away, and there is a certain requirement on the communication speed, so the CsCAN network is used for communication between the IO module and the OCS controller. When selecting the upper computer to monitor the network, because the host computer is far from the field device, and considering the problem of system upgrade and capacity expansion later, the Modbus TCP network based on industrial Ethernet is selected.
4 automatic control system design
The following is divided into three parts to introduce the PLC control part
(1) Automatic Dosing Control of Oily Sewage
In the sewage treatment process, the accuracy and stability of the dosing are crucial. As the waste water comes from the oilfield production fluid, the water quality is relatively stable. Therefore, automatic dosing is mainly based on the "ratio" of the amount of sewage in the reaction tank and the amount of each agent. Through the upper or touch screen operation, the “ratio†of the amount of oily wastewater in each reaction tank and the number of doses (constant concentration) is set, to control the adding amount of the three agents A, B and C; when entering the reaction tank When the amount of water changes, the amount of oil (A, B, and C) that tracks the amount of oil in the reaction tank (frequency control) is proportionally adjusted to control the amount of dosing.
A liquid flowmeter is installed on the on-site tap water pipeline, and the information on the incoming water from each reaction tank is transmitted to the controller. After the controller processes the above information, the PID function (see Figure 3) is used to control the pump frequency converter, and the adjustment is added. The flow rate of the drug pump, thus completing the control of the “ratioâ€, realizing the automatic control of the dosing system, avoiding overdosing and underdosing of the dosing system; not only reducing the sewage treatment costs but also ensuring the water quality indicators of the sewage treatment process. In the automatic dosing system, the video function is cited. When someone finds out that they are operating the screen, they automatically capture the photos of the operating area and store them in the CF card, which improves the security of the system.
(2) Filter outlet pressure control
When the backwash or operating load of the softener unit of the primary and secondary sewage filters and the demineralized water station changes, the regeneration effect will be affected. [1] The backwash pressure signal is integrated into the program control of the filter and becomes a prerequisite in the regeneration process, which solves the effect on the regeneration effect due to the non-compliance of the backwash pressure and improves the regeneration efficiency. Through frequency conversion control, the pump speed of the lift pump ensures that the pressure of the purified water at the outlet of the secondary filter is always controlled at the set value target, so that the primary and secondary sewage filters have a stable biochemical ring; and the smooth operation of the downstream softener equipment is also ensured. ; And through the process of transformation using its outlet of purified water pressure to complete its own backwash process.
The flushing time can be stored in the TF card, and the time record data [3],
(3) Sludge treatment system control
A time interval is set on the upper position or the touch screen of the controller to periodically control the electric valve on the low level and high level sewage pipelines of the reaction tank to achieve automatic drainage; since the reaction lift pump needs regular maintenance, the system will accumulate pumps The operating time, when it reaches the set time, will remind the operator to perform maintenance, as shown in Figure 6.
Sewage tanks mainly receive the discharge of reaction tanks and settling tanks. If the amount of sewage discharged suddenly increases, it is very easy to cause the risk of pool discharge. Here, the single-flange intelligent liquid level transmitter with damping is used to monitor the liquid level of the sewage tank. After the data is sent to the controller, alarm indications are set on the controller screen and the upper system.
Set the time interval on the upper position or the touch screen of the controller, start and stop the sludge centrifuge and the sludge pump equipment of the drainage tank at regular intervals, and realize the automatic technical treatment of the sludge: under the action of centrifugal force, make the solid in the sludge. The particles are compacted and separated from the moisture in the sludge to avoid contamination of the environment.
At the same time, multiple hydrogen sulfide gas and flammable gas sensors are installed in the system, and the gas monitoring information is transmitted to the upper system in real time.
5 Conclusion
The new sewage treatment station self-control system consisting of an integrated controller and upper computer meets the standard Client/Server architecture and uses the Modbus TCP, a common fieldbus protocol. The system has good compatibility and scalability. Through the optimization and upgrading of the automatic control system of the sewage treatment station, not only the control function of the system itself has been improved, but also the management level of the equipment has been improved. Now managers, operators, and related departments that need the production data later can use the network. These data can be used to monitor the entire production process, historical data, and statements in real time, which lays a good foundation for the construction of digital oil fields.
references:
[1] Liu Dexu. Oilfield sewage treatment project [M]. Petroleum Industry Press, 2001:43-45.
[2] Ken Jannott. CsCAN Protocol Summary, First Edition: 12-13, 2001.
[3] Andy Swales. Open MODBUS TCP Specification (Chinese version), Rev. 1.0: 2-3, 1999.
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