Oily wastewater treatment process for thermal power plant

Abstract

The invention belongs to the technical field of thermal power plant oily wastewater treatment, and particularly relates to a thermal power plant oily wastewater treatment process. The method comprises the following steps: firstly, enabling oil-containing wastewater to flow from a collecting tank to a regulating tank, pumping floating oil at the upper part of the regulating tank by a pump, pumping clear liquid in the middle of the regulating tank to a rotational flow dissolved air flotation device to remove oil and suspended matters, enabling air flotation effluent to enter a modified active filter material filter to remove oil and suspended matters, and discharging after reaching the standard; the invention solves the problems of high treatment cost, large occupied area, more corollary equipment and long process flow of a double-medium filter in the conventional processes of a regulating tank, an oil separator, an air floatation tank and a coagulative precipitation tank; the oil content of effluent of the process is stably reduced to below 10mg / L, the oily wastewater discharge index of a thermal power plant in the IFC thermal power plant occupational health and safety guide standard is met, the operation cost is reduced by two thirds, the occupied area is reduced by one half, a sludge treatment device is not needed, and sump oil is recycled.

Description

Technical Field

[0001] The invention belongs to the technical field of treatment of oily wastewater from thermal power plants, and in particular relates to a treatment process for oily wastewater from thermal power plants. Background Art

[0002] During operation, thermal power plants generate oily wastewater, which will pollute the surrounding environment if discharged directly. Therefore, the oily wastewater needs to be treated until it meets the standards before being discharged or used for irrigation of green areas in the park. The oily wastewater includes: (1) drainage in the machine room: the pollutants are mainly lubricating oil and dust carried out by the equipment flushing water; (2) drainage in the engine area: the pollutants are mainly lubricating oil and dust carried out by the flushing water of turbines, pumps, etc.; (3) drainage in the auxiliary system area: the pollutants are mainly rust residue flushed out of the pipes by the circulating water of the power plant and fuel oil leaked from the equipment; (4) drainage in the workshop and cleaning room: the main pollutants are oil and suspended matter in the cleaning water; (5) drainage in the oil tank area: the main pollutants are fuel oil and bottom residue carried out by the drainage at the bottom of the oil tank; (6) drainage in the fuel processing area: the main pollutants are fuel oil and suspended matter leaked during transportation by tank trucks carried out by surface water; (7) drainage in the transformer area: the main pollutants are oil products leaked into the underground pool during transformer maintenance. Rain washes pollutants from this wastewater to the ground and into the regulating pond. Consequently, the treatment capacity varies significantly between the dry and rainy seasons. During the heavy rainy season, oily wastewater exhibits high flow and good quality. During the light dry season, oily wastewater exhibits low flow and poor quality. The highest concentration of pollutants comes from the bottom drainage of the oil tank area. Due to the uncertainty of the incoming oil from thermal power plants, which can range from crude oil to fuel oil to residual oil, the water content in the oil fluctuates. Irregular drainage from the tank area results in high instantaneous water volumes and high pollutant concentrations. Consequently, thermal power plant oily wastewater suffers from significant fluctuations in both incoming water quality and volume, making maintenance difficult.

[0003] Traditional oil removal processes face problems such as unstable dosing control, drug waste, or substandard water quality when water quality fluctuates. Therefore, how to ensure the stability of the effluent quality after wastewater treatment in thermal power plants under different water quality and water volume fluctuations is a technical problem that needs to be solved urgently. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the present invention provides a process for treating oily wastewater from thermal power plants. This process, specifically designed for treating oily wastewater discharged from different areas of a thermal power plant, effectively removes oil and suspended solids from wastewater during fluctuations in incoming water flow, reducing the oil content to less than 10 mg / L, meeting requirements for greening irrigation or external discharge in industrial parks.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] The first aspect of the present invention provides a process for treating oily wastewater from a thermal power plant, the flow chart of which is as follows:Figure 1 As shown, the treatment process includes the following steps:

[0007] (1) The oily wastewater flows from the plant collection pool to the regulating pool by gravity, and the floating oil on the upper part of the regulating pool is pumped away;

[0008] (2) The clear liquid in the middle of the regulating tank is pumped to the cyclone dissolved air flotation device to remove oil and suspended solids;

[0009] (3) The flotation effluent enters the modified active filter media filter to remove oil and suspended solids;

[0010] (4) Meet emission standards.

[0011] Furthermore, the specific process of step (1) is as follows: oily wastewater from different sources is collected and mixed in a plant collection pool, and then flows to a regulating pool together. In the regulating pool, the oily wastewater is divided into three compartments. The first compartment is an oil collection area that receives oily wastewater and dirty oil discharged from a dissolved air flotation device. The dirty oil and part of the dirty oil in the oily wastewater float to the oil collection compartment. The oil pump is controlled by an oil-water level gauge to regularly pump the dirty oil to a dirty oil tank, and then to an incinerator for treatment. The clear liquid flows from the lower part of the oil collection area to the second compartment, which is a buffer zone. The wastewater overflows from the upper part of the buffer zone to the third compartment, which is a water outlet area. The wastewater in the water outlet area is pumped to a cyclone dissolved air flotation device by a pump.

[0012] Furthermore, the specific process of step (2) is as follows: after the wastewater in the outlet area of ​​the regulating tank reaches the cyclone dissolved air flotation device, it enters the flotation tank, the outlet water of the flotation tank partially flows back, the reflux wastewater is pressurized and dissolved by the dissolved air pump, the dissolved air water enters the dissolved air tank, the steam-water mixture in the dissolved air tank enters the flotation tank, and the suspended matter and dirty oil in the wastewater are removed by the action of cyclone and flotation. The dirty oil is regularly discharged from the upper part of the flotation tank and sent to the oil collection area of ​​the regulating tank, and the outlet water enters the modified active filter material filter.

[0013] Furthermore, the air source of the cyclonic dissolved air flotation device is compressed air, and the waste gas is discharged into a waste gas treatment device for unified treatment.

[0014] Furthermore, the specific process of step (3) is as follows: the flotation effluent enters the modified active filter media filter through the filter lift pump, and the dirty oil and suspended solids are reduced to meet the emission indicators through the interception of the filter, and are discharged to the external drainage pool for reuse or external discharge.

[0015] Furthermore, the modified active filter media filter is regularly backwashed with water from an external drainage pool, with a backwash frequency of once a day for 1 minute each time. The backwash water contains oil and suspended matter and is pumped back to the regulating pool through a backwash pump.

[0016] Furthermore, the modified active filter material is a quartz sand filter material with a SiO2 content greater than 99.9%.

[0017] The second aspect of the present application provides a power plant oily wastewater treatment system for the above-mentioned treatment process, the treatment system comprising a plant area collection tank, a conditioning tank device, a cyclone dissolved air flotation device, a modified active filter and an external discharge tank connected in sequence.

[0018] Further, the external discharge tank is provided with a backwash pump for pumping water in the external discharge tank to the modified active filter for backwashing, and the backwashed water is sent to the conditioning tank.

[0019] Further, the conditioning tank device comprises a conditioning tank, a submersible pump, a first sludge oil pump, a second sludge oil pump, a sludge oil tank and an incinerator in the conditioning tank, the submersible pump being used to pump the effluent in the conditioning tank to the cyclone dissolved air flotation device, the first sludge oil pump being used to pump the sludge oil floating in the conditioning tank to the sludge oil tank, and the second sludge oil pump being used to pump the sludge oil in the sludge oil tank to the incinerator for incineration.

[0020] Further, the conditioning tank is composed of a first compartment, a second compartment and a third compartment, the first compartment being an oil collection zone for receiving the oily wastewater and the sludge oil discharged from the dissolved air flotation device, the sludge oil and most of the sludge oil in the oily wastewater floating to the oil collection zone, and the sludge oil being pumped to the sludge oil tank by the sludge oil pump at regular intervals through an oil-water level meter; the clear liquid flowing from the lower part of the oil collection zone to the second compartment, the second compartment being a buffer zone, the wastewater overflowing from the upper part of the buffer zone to the third compartment, and the third compartment being an effluent zone, the wastewater in the effluent zone being pumped to the cyclone dissolved air flotation device by the submersible pump, and most of the sludge oil being removed through the preliminary separation in the conditioning tank.

[0021] Further, the cyclone dissolved air flotation device comprises a cyclone dissolved air flotation equipment, an air compressor and a waste gas treatment device, the air compressor generating air into the cyclone dissolved air flotation equipment, the waste gas in the cyclone dissolved air flotation equipment entering the waste gas treatment device, the cyclone dissolved air flotation equipment comprising a flotation tank, a dissolved air pump and a dissolved air tank, the dissolved air pump pressurizing the backflow wastewater in the flotation tank to dissolve air, and then entering the dissolved air tank, the suspended solids and sludge oil in the wastewater being removed through the cyclone and air flotation effects, the sludge oil being periodically discharged from the upper part of the flotation tank to the oil collection zone of the conditioning tank, and the effluent entering the modified active filter.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] The present application provides an oil removal treatment method for power plant oily wastewater, which is technically feasible and economically reasonable, can effectively remove the sludge oil and suspended solids in the oily wastewater, and can stabilize the oil content in the effluent within 10 mg / L. The present application does not need to add any chemical agent, the sludge oil can be recycled, the generation of oily sludge is reduced, secondary pollution is avoided, no sludge treatment device is needed, the air consumption of the cyclone dissolved air flotation device is 10%, the energy consumption of the air compressor is reduced, and the operation cost is greatly reduced. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The process flow chart for treating the oil-containing wastewater of the power plant according to the present application.

[0025] Figure 2 The process flow chart for treating the oil-containing wastewater of the power plant according to the present application. DETAILED DESCRIPTION

[0026] The specific embodiments of the present application are further described below. It is to be understood that the description of these embodiments is intended to help understand the present application and does not constitute a limitation of the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as there is no conflict.

[0027] The experimental methods in the following examples are all conventional methods unless otherwise specified. The experimental materials used in the following examples are all commercially available unless otherwise specified.

[0028] Example: Treatment of oil-containing wastewater of a 120 MW dual-fuel power plant abroad

[0029] The oil-containing wastewater of the power plant is treated by using the process for treating the oil-containing wastewater of the power plant according to the present application, and the process flow chart is shown in Figure 2 The oil-containing wastewater treatment system of the power plant according to the present application comprises the following components:

[0030] The system comprises, in sequence, a plant area collection tank, a regulating tank device, a cyclone dissolved air flotation device, a modified active filter, and an effluent tank.

[0031] The effluent tank is provided with a backwashing pump, which is used to pump the water in the effluent tank to the modified active filter for backwashing, and the backwashed water is sent to the regulating tank.

[0032] The regulating tank device comprises a regulating tank, a submersible pump, a first sludge oil pump, a second sludge oil pump, a sludge oil tank, and an incinerator, which are arranged in the regulating tank. The submersible pump is used to pump the effluent in the regulating tank to the cyclone dissolved air flotation device. The first sludge oil pump is used to pump the sludge oil floating in the regulating tank to the sludge oil tank. The second sludge oil pump is used to pump the sludge oil in the sludge oil tank to the incinerator for incineration.

[0033] The adjusting tank is composed of a first compartment, a second compartment and a third compartment. The first compartment is an oil collection area for receiving oil-containing wastewater and waste oil discharged from the dissolved air flotation device. Most of the waste oil in the oil-containing wastewater floats to the oil collection compartment, and the waste oil is pumped to a waste oil tank by a waste oil pump controlled by an oil-water level meter at regular intervals. The clear liquid flows from the lower part of the oil collection area to the second compartment. The second compartment is a buffer area. The wastewater overflows from the upper part of the buffer area to the third compartment. The third compartment is a water outlet area. The wastewater in the water outlet area is pumped to a cyclone dissolved air flotation device by a submersible pump. After the wastewater is preliminarily separated in the adjusting tank, most of the floating oil is removed.

[0034] The cyclone dissolved air flotation device includes a cyclone dissolved air flotation equipment, an air compressor and a waste gas treatment device. The air compressor generates air into the cyclone dissolved air flotation equipment. The waste gas in the cyclone dissolved air flotation equipment enters the waste gas treatment device. The cyclone dissolved air flotation equipment includes a flotation tank, a dissolved air pump and a dissolved air tank. The dissolved air pump pressurizes the backflow wastewater in the flotation tank to dissolve air, and then the wastewater enters the dissolved air tank. Through the effects of cyclone and air flotation, the suspended matter and waste oil in the wastewater are removed. The waste oil in the upper part of the flotation tank is discharged to the oil collection area of the adjusting tank at regular intervals, and the water outlet enters a modified active filter material filter.

[0035] The steps of the oil-containing wastewater treatment process of the thermal power plant are as follows:

[0036] In the first section, the oil-containing wastewater from various areas in the plant is collected in a plant collection tank, mixed and then discharged into the adjusting tank. The adjusting tank is designed to have a residence time of 8 hours. In the adjusting tank, the floating oil of the wastewater and the waste oil discharged from the air flotation tank are pumped to a waste oil tank by a first waste oil pump. The waste oil in the waste oil tank is pumped to a incinerator by a second waste oil pump for incineration. The suspended matter in the water settles at the bottom of the adjusting tank. In the dry season without precipitation, the bottom of the adjusting tank is cleaned during maintenance. The water outlet of the adjusting tank is pumped to the air flotation tank by a submersible pump. The oil-containing wastewater preliminarily removes the floating oil and the large particle suspended matter with a fast settling velocity in the adjusting tank.

[0037] In the second section, the water outlet of the adjusting tank is pumped into the air flotation tank by a submersible pump. The air flotation process adopts a cyclone dissolved air flotation. The incoming water enters the air flotation tank tangentially to generate a cyclone effect, which accelerates the collision and aggregation of bubbles and pollutants and the floating of the pollutants. The residence time is 5 minutes. The air flotation tank adopts an external air source injection method. A part of the water outlet of the air flotation tank enters a dissolved air tank after being mixed with compressed air by a dissolved air pump. The compressed air is generated by an air compressor. The gas-liquid mixture enters the dissolved air tank, and the dissolved air water is mixed with the water inlet of the air flotation tank to enter the air flotation tank. At this time, the dissolved bubbles in the water are released by decompression, and dense bubbles are formed in the water. These bubbles accelerate the collision and aggregation of pollutants through cyclone and float up, carrying away the oil and suspended matter in the wastewater. The waste oil in the air flotation tank is discharged from the upper part back to the adjusting tank, and the waste gas in the air flotation tank is pumped to a waste gas treatment device. The oil content in the water outlet of the air flotation tank is less than 50 mg / L, and the suspended matter is less than 30 mg / L, meeting the water quality requirements for entering the filter.

[0038] Step three: the air floatation effluent enters the modified active filter, the residence time is 20 minutes, the oil content in the water is reduced to below 10 mg / L by the interception of the modified active filter, the suspended matter is reduced to below 10 mg / L, the filter effluent is discharged into the external discharge pool, and is externally discharged or reused after being analyzed by the on-line detector, the water in the external discharge pool can be backwashed by the backwash pump to modify the active filter, the filter material is quartz sand filter material with SiO2 content > 99.9%, the filter material is modified by super-hydrophilic comb oil and is not easy to be blocked, the backwash does not need chemical agents, the backwash is performed once a day, the backwash time is 1 minute, the backwash effluent containing oil and suspended matter returns to the adjusting pool.

[0039] The treatment effects of each treatment unit in the above process are shown in Table 1.

[0040] Table 1

[0041] Processing Unit Oil content suspended matter PH Collection pool 2000mg / L 500mg / L 6～9 regulating pond 1000mg / L 300mg / L 6～9 Cyclone dissolved air flotation 50mg / L 30mg / L 6～9 Modified active filter media filter 10mg / L 10mg / L 6～9 Drainage indicators 10mg / L 10mg / L 6～9

[0042] It can be seen that the oil content in the effluent of the above process is reduced to below 10 mg / L, the suspended matter is reduced to below 10 mg / L, and the process is a pure physical treatment process, so the water quality pH does not change, and the discharge requirements are met.

[0043] The above process is controlled by DCS automatically, is connected to the plant control room, and needs two people for regular inspection.

[0044] The overall operation cost of the above process is two-thirds less than that of the traditional dosing air floatation, the equipment investment is reduced by one-third, and the equipment occupation area is reduced by one-half.

[0045] The embodiments of the application are described in detail above, but the application is not limited to the described embodiments. For those skilled in the art, various changes, modifications, replacements and variations of the embodiments can be made without departing from the principles and spirits of the application, and still fall within the protection scope of the application.

Claims

1. A process for treating oily wastewater from a thermal power plant, characterized in that: The treatment process comprises the following steps: (1) The oily wastewater flows from the plant collection pool to the regulating pool by gravity, and the floating oil on the upper part of the regulating pool is pumped away; (2) The clear liquid in the middle of the regulating tank is pumped to the cyclone dissolved air flotation device to remove oil and suspended solids; (3) The flotation effluent enters the modified active filter media filter to remove oil and suspended solids; (4) Meet emission standards.

2. A thermal power plant oily wastewater treatment process according to claim 1, characterized in that: The specific process of step (1) is as follows: oily wastewater from different sources is collected and mixed in a plant collection pool, and then flows to a regulating pool by gravity. The regulating pool is divided into three compartments. The first compartment is an oil collection area for receiving oily wastewater and dirty oil discharged from a dissolved air flotation device. The dirty oil and part of the dirty oil in the oily wastewater float to the oil collection compartment. The dirty oil is regularly pumped to a dirty oil tank by a dirty oil pump controlled by an oil-water level gauge, and then sent to an incinerator for treatment. The clear liquid flows from the lower part of the oil collection area to the second compartment, which is a buffer zone. The wastewater overflows from the upper part of the buffer zone to the third compartment, which is a water outlet area. The wastewater in the water outlet area is pumped to a cyclonic dissolved air flotation device by a submersible pump.

3. A process for treating oily wastewater from a thermal power plant according to claim 1, characterized in that: The specific process of step (2) is as follows: after the wastewater in the outlet area of ​​the regulating tank reaches the cyclone dissolved air flotation device, it enters the flotation tank, the outlet water of the flotation tank partially flows back, the reflux wastewater is pressurized and dissolved by the dissolved air pump, the dissolved air water enters the dissolved air tank, the steam-water mixture in the dissolved air tank enters the flotation tank, the suspended matter and dirty oil in the wastewater are removed by the action of cyclone and flotation, the dirty oil is regularly discharged from the upper part of the flotation tank and sent to the oil collection area of ​​the regulating tank, and the outlet water enters the modified active filter material filter.

4. A process for treating oily wastewater from a thermal power plant according to claim 3, characterized in that: The air source of the cyclonic dissolved air flotation device is compressed air, and the waste gas is discharged into the waste gas treatment device for unified treatment.

5. A thermal power plant oily wastewater treatment process according to claim 1, characterized in that: The specific process of step (3) is as follows: the flotation effluent enters the modified active filter media filter through the filter lift pump, and the waste oil and suspended solids are reduced to meet the emission indicators through the interception of the filter, and are discharged to the external drainage pool for reuse or external discharge.

6. A thermal power plant oily wastewater treatment process according to claim 5, characterized in that: The modified active filter media filter is backwashed regularly with water from an external drainage pool, with a backwash frequency of once a day for 1 minute each time. The backwash water contains oil and suspended solids and is pumped back to the regulating pool through a backwash pump.

7. A process for treating oily wastewater from a thermal power plant according to claim 5, characterized in that: The modified active filter material is a quartz sand filter material with a SiO2 content greater than 99.9%.

8. A thermal power plant oily wastewater treatment system used in the treatment process according to any one of claims 1 to 7, characterized in that: The treatment system comprises a plant collection tank, a regulating tank device, a cyclone dissolved air flotation device, a modified active filter material filter and an external drainage tank which are connected in sequence.

9. The oily wastewater treatment system of a thermal power plant according to claim 8, characterized in that: The regulating tank device includes a regulating tank, a submersible pump located in the regulating tank, a first sewage oil pump, a second sewage oil pump, a sewage oil tank, and an incinerator. The submersible pump is used to pump the effluent from the regulating tank to the cyclone dissolved air flotation device, the first sewage oil pump is used to pump the sewage oil floating in the regulating tank to the sewage oil tank, and the second sewage oil pump is used to pump the sewage oil in the sewage oil tank to the incinerator for incineration.

10. The oily wastewater treatment system of a thermal power plant according to claim 8, characterized in that: The cyclone dissolved air flotation device includes a cyclone dissolved air flotation device, an air compressor and a waste gas treatment device. The air generated by the air compressor enters the cyclone dissolved air flotation device, and the waste gas in the cyclone dissolved air flotation device enters the waste gas treatment device. The cyclone dissolved air flotation device includes a flotation tank, an air dissolving pump and an air dissolving tank. The air dissolving pump pressurizes and dissolves the reflux wastewater in the flotation tank, and then the reflux wastewater enters the air dissolving tank, and the suspended matter and dirty oil in the wastewater are removed through the cyclone and flotation effects.

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