Two sets of oily sewage treatment devices are designed and arranged, each with a treatment capacity of 1.5m 3/h, and each system can operate independently as a backup. The oily wastewater is directly discharged after being treated by this set of equipment, and the separated waste oil is collected in the waste oil tank and cleaned regularly.
Sources and characteristics of oily wastewater
1. 1 source of oily wastewater
Sources of oily wastewater in this project are: (1) oil systems of steam turbines, generators and makeup pumps, and oil systems of condensate pump rooms in steam turbine rooms; (2) Diesel generator set, fuel oil and lubricating oil system; (3) Ground drainage of rooms where oil spills and oil spills may occur; (4) Emergency oil drainage and rainwater from outdoor transformer rainwater pit; (5) The cable room and cable trench of flame retardant cable shall be drained after fire extinguishing.
1.2 characteristics of oily wastewater
(1) There are many kinds of oils, including lubricating oil, various types of engine oil and endless oil (such as transformer oil and cable oil).
(2) The water quality and quantity change greatly: when the power station is running, the oil concentration is not high, that is, the oil is ≤100 mg/L; Suspended substance SS ≤ 200mg/l; During maintenance, the mass concentration of oil is higher, reaching above 1000mg/L, and the concentration of suspended solids is also higher. Under normal working conditions, the maximum daily discharge of oily wastewater is100m3; In extreme cases (fire in electrical workshop), the maximum daily discharge of oily wastewater is 160m3, and the maximum hourly discharge is 50m3.
2. Process flow and sewage discharge standard
2. 1 process flow
See figure 1 for the design process flow of oily sewage treatment system.
The wastewater first enters the grid to remove the floating objects in the wastewater, and then it is collected into the regulating tank to regulate the water quantity and homogenize the water quality. Then it is lifted by submersible sewage pump to the parallel-flow oil separation tank to remove the dispersed oil in the wastewater, and then it is lifted by booster pump to the high-efficiency oil-water separator for deep oil removal. The separated oil enters the dirty oil tank, and the effluent reaches the standard and is discharged.
2.2 sewage discharge standard
The effluent quality meets the first-class standard of national comprehensive wastewater treatment standard (GB 8978- 1996): SS≤30mg/L, oil ≤ 5 mg/L. ..
3, the main equipment and structures
3. 1 regulating pool
Mainly used for regulating water quantity and homogeneous water quality. It is a steel-concrete structure with an effective volume of 160m3 and a designed hydraulic retention time of 24h. The pool has built-in lift pumps and reflux facilities, and a single system is equipped with two lift pumps (1 standby, Q= 17m3/h, H=8.0m, n = 60).
3.2 Downstream grease trap
It is mainly used to remove dispersed oil from wastewater. The principle is that during the upward flow of oil and water in the inclined plate, due to the difference of oil-water density, the oil floats on the water surface, near the bottom of the inclined plate, and the water is below, so that the water below flows out of the device, and the oil floats on the device through a series of water collection devices. Oil flows into the concentration tank through the oil collecting pipe and is discharged after concentration, thus achieving the purpose of oil-water separation.
This set of equipment is provided by Jiangsu Yao Peng Group Co., Ltd., the model is GYT-15 (* * 2 sets), the specification size is 1.7m×l.05m×l.6m, and the material is Q235 steel.
Features: high treatment efficiency (when the oil concentration of oily wastewater is high, that is, the treatment effect is better when the oil concentration is ≥ 1000mg/L), large treatment capacity, no energy consumption, no operation cost, automatic operation, simple maintenance, small floor space, etc.
3.3 Efficient oil-water separator
The wastewater enters the oil-water separator after being pressurized by the screw pump. Firstly, the wastewater is filtered by a pre-filtration device to reduce the suspended solids in the wastewater, and then it is subjected to coarse granulation treatment and adsorption coagulation treatment. The treatment device organically combines the treatment processes of enhanced gravity separation, coarse granulation and adsorption agglomeration into a steel cylindrical integral structure, and is combined with an infusion pump and a filter to form a treatment device. Oily wastewater Oily wastewater is filtered by an oleophilic filter element, and oil particles are adsorbed and gathered on the filter element to form large oil droplets, which float to the oil collection cavity and are discharged regularly, while the effluent is discharged.
This set of equipment is provided by Jiangsu Yao Peng Group Co., Ltd., and the model is GJSZ- 15B (* * * 2 sets). Equipped with four screw pumps (model1g58-1-Ⅱ, power 7.5kW), two water inlet pumps, two backwashing pumps and an electric heating device with power of 6.0kW.
Features: This set of equipment has the advantages of compact structure, less land occupation, simple installation and debugging, fully automatic operation, simple maintenance and management, high separation efficiency and low energy consumption. At the same time, because its treatment process makes full use of the characteristics of gravity separation, it is difficult to treat all kinds of oily wastewater.
3.4 Operation control
The control of this oily sewage treatment system adopts PLC as the central controller, which mainly controls the automatic operation of lifting pump, inlet pump of high-efficiency oil-water separator, backwashing pump and high-efficiency oil-water separator. The lift pumps automatically switch to each other and run alternately within 12h.
4. Discussion on problems in operation.
4. 1 improvement of energy saving scheme
The actual operation shows that because of the low oil content in the raw water of oily wastewater, the treatment effect of parallel-flow grease trap is not obvious, and oily wastewater is pumped to the oil-water separator twice, which increases the power consumption and is uneconomical. Therefore, it is decided to add a set of auxiliary piping system of vacuum water baffle between the regulating tank and the booster pump. The water inlet pipe of the system is led out from the water outlet pipe of the regulating tank and then connected to the water inlet pipe of the booster pump, that is, the system is a bypass supplement to the original process and has no influence on the original process. See Figure 2 for process flow changes.
When the oil content of oily wastewater is low, auxiliary pipeline system can be used, that is, oily wastewater can be directly sent to the pre-filter through the system with pressurized pump to reduce the lift of the primary pump and achieve the purpose of energy saving in operation; When the mass concentration of oil in oily wastewater is >: 1000mg/L, the original design process can be adopted.
4.2 The running noise and vibration of screw pump are too large.
When the equipment is running, the running noise and vibration of the high-efficiency oil-water separator screw pump are too large, which seriously affects the operation of the equipment and the surrounding working environment.
(1) Analysis reason: There are some defects in the installation of water pump, such as the pump foundation is not independent, there is no damping pad, and the inlet and outlet pipes of water pump are hard connected, which will inevitably lead to excessive noise and vibration of water pump. After the corresponding technical transformation of the above defects, the running noise and vibration of the pump have been improved to some extent. However, after running for a period of time, the noise and vibration of the pump are too large, indicating that the pump itself must have quality problems.
(2) Measures: The manufacturer decides to replace the water pump after on-site inspection and startup. After the water pump is replaced, start the water pump again, and the noise and vibration are normal. After running for a period of time, the noise and vibration are still normal.
5. Conclusion
(1) This system adopts physical and chemical methods ("oil separation+coarse particle separation process") to treat nuclear power plant. The oily wastewater in nuclear power plant adopts high-efficiency oil-water separator as the final means of oil treatment, in which the co-current oil separation tank device is used for oil separation and the high-efficiency oil-water separator device is used for coarse particle separation. The actual operation shows that it completely meets the emission standard of oil products.
(2) Economic analysis. The running cost of this system is low, and the main cost is power consumption. See table 1 for the power consumption of the analysis equipment.
Note: When the booster pump and the lift pump are closed, the backwash pump is started, and vice versa; Usually, electric heating is basically not turned on, so it is not considered.
Considering that 1 set of equipment runs continuously for 24 hours, the water treatment capacity is 360m3, and the power consumption per m3 of wastewater treatment is 0.6 1KW? H, press 0.52 yuan /(KW? H) The power consumption is 0.32 yuan/m3. If the scheme after energy-saving transformation is adopted (the lifting pump and grease trap are not running), the power consumption per cubic meter of wastewater treatment is 0.5 1KW? H, press 0.52 yuan /(KW? H), the power consumption is 0.27 yuan m3.
(3) Since the system was put into operation in August 2003, after necessary technical transformation, the equipment has been in good working condition, and the daily average treatment of oily wastewater reaches 100m3. The oil and suspended solids in wastewater are effectively removed in the oil-water separator (the removal rate is stable at 85%-95%), and the effluent quality of the system meets the national comprehensive wastewater discharge standard (GB 8978-).