Efficient purifying and filtering process for refrigerating fluid containing iron ions

Abstract

The invention relates to the technical field of water treatment, provides a high-efficiency purifying and filtering process for refrigerating fluid containing iron ions, and solves the problems of high corrosion rate and short service life of equipment of a chilled water system. The method comprises the following steps: S1, pretreatment: adding a corrosion inhibitor into the ethylene glycol refrigerating fluid containing iron ions to obtain a pretreatment fluid; s2, nitrogen replacement: pre-vacuumizing the pretreatment liquid until the absolute pressure is less than or equal to 5kPa, injecting nitrogen with the purity of 80% to normal pressure, repeating vacuumizing to normal pressure for three times, and maintaining a 0.03-0.05 MPa overpressure nitrogen sealing environment to obtain nitrogen replacement liquid; s2, secondary filtration: treating the nitrogen displacement liquid through a two-stage filtration system to obtain a secondary filtrate; s3, deep treatment: introducing the secondary filtrate into an ultrafiltration system for deep treatment, controlling the operation pressure at 0.1-0.5 MPa, and maintaining the temperature at-5-15 DEG C to obtain an ultrafiltration concentrated solution; s4, retreatment: circulating the ultrafiltration concentrated solution to the step S3, and retreating for a plurality of times to obtain a clear solution, wherein the iron ion concentration of the clear solution is reduced to 5 mg / L or below.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and particularly to a purification and filtration process for highly efficient iron-ion-containing coolant. Background Art

[0002] The equipment materials of existing ethylene glycol refrigeration units are mainly carbon steel equipment. Ethylene glycol is extremely easy to corrode metals under certain circumstances, and its corrosion mechanism is divided into two types, one is electrochemical corrosion and the other is acidification corrosion.

[0003] The main existing problem is the dissolved oxygen corrosion in electrochemical corrosion. The content of dissolved oxygen is one of the most important factors affecting metal corrosion. The presence of dissolved oxygen concentration in the ethylene glycol aqueous solution mainly has two effects: (1) participating in the cathode reaction (accelerating corrosion); (2) participating in the formation of the metal surface oxide film (inhibiting corrosion). For metals such as copper and iron, the corrosion rate of the metal depends on the rate of the cathode oxygen reduction reaction. Therefore, as the content of dissolved oxygen increases, the corrosion rate becomes faster.

[0004] Ferrous hydroxide is extremely easy to oxidize into reddish-brown rust, which is the main reason for the appearance of reddish-brown in the chilled water. In a closed chilled water system, dissolved oxygen will be rapidly consumed due to corrosion and become insufficient. There will be a small amount of dissolved oxygen in these systems, mainly entering the chilled water system through valves, pipe joints, and pump gaskets. Due to scaling, deposition, and the corresponding corrosion conditions brought about, it is easy to cause the reduction of equipment life and increase the maintenance cost.

[0005] If the coolant is directly replaced, the replacement cost is high, it is easy to cause drainage pollution, and the wastewater treatment is difficult and the wastewater treatment cost is high. Summary of the Invention

[0006] Therefore, in view of the above problems, the present invention provides a purification and filtration process for highly efficient iron-ion-containing coolant to solve the problems raised in the above background art. It inhibits the dual effects of dissolved oxygen corrosion and acidification corrosion in the ethylene glycol coolant system through nitrogen replacement, combines multi-stage filtration and ultrafiltration processes to achieve cyclic purification, controls the iron ion concentration without replacing the coolant, reduces the equipment corrosion rate, and extends the equipment life.

[0007] To achieve the above object, the present invention is realized through the following technical solutions:

[0008] A purification and filtration process for highly efficient iron-ion-containing coolant, comprising the following steps: [[ID=?]] [[ID=?]]

[0009] S1. Pretreatment: adding an inhibitor to the iron-ion-containing ethylene glycol coolant to obtain a pretreatment solution;

[0010] S2, nitrogen replacement: the pre-treated liquid is pre-vacuumed to an absolute pressure of ≤5kPa, and then 80% pure nitrogen is injected to normal pressure. After vacuuming to normal pressure three times, an overpressure nitrogen blanketing environment of 0.03-0.05MPa is maintained to obtain a nitrogen replacement liquid;

[0011] S2, secondary filtration: The nitrogen replacement liquid is treated by a two-stage filtration system to obtain a secondary filtrate;

[0012] S3, deep treatment: the secondary filtrate is passed into the ultrafiltration system for deep treatment, the operating pressure is controlled at 0.1-0.5 MPa, and the temperature is maintained at -5 to 15 ° C to obtain the ultrafiltration concentrate;

[0013] S4, reprocessing: the ultrafiltration concentrate is circulated to step S3 for several reprocessings to obtain a clear solution, wherein the iron ion concentration of the clear solution is reduced to 5 mg / L or less;

[0014] S5. Backwash: When the iron ion concentration of the clear liquid is above 5 mg / L, start backwashing and use an alkaline cleaning agent with a pH of 10-12 to reversely flush the hollow fiber membrane assembly.

[0015] Furthermore, in step S1, the amount of corrosion inhibitor added is 0.05%-0.2% of the mass of the freezing liquid, and the pretreatment temperature is controlled at -5 to 15°C.

[0016] Furthermore, in step S2, the two-stage filtration system includes a first filter and a second filter, and the nitrogen replacement fluid passes through the first filter and the second filter connected in series. The filtration precisions of the first filter and the second filter are 3 μm and 0.5 μm, respectively.

[0017] Furthermore, the ultrafiltration membrane system comprises 3-6 groups of hollow fiber membrane components, the membrane pore size is 10-50 nm, and the membrane material is modified polyvinylidene fluoride.

[0018] Furthermore, the hollow fiber membrane assembly adopts a cross-flow filtration mode, the membrane surface flow rate is maintained at 1.5-3 m / s, and the concentrated liquid reflux ratio is 15%-30%.

[0019] Furthermore, in step S5, a periodic pressure pulse backwash system is used, with a pulse frequency of 5-10 Hz and a backwash flow rate of 1.5-2 times the operating flow rate.

[0020] Furthermore, a chemical cleaning step is included: an acidic cleaning agent is used to circulate and clean the ultrafiltration membrane system every 500-800 hours of operation.

[0021] Furthermore, the final treated frozen liquid meets the following requirements: iron ion ≤ 3 mg / L, turbidity ≤ 20 NTU, conductivity ≤ 50 μS / cm, and pH value maintained in the range of 8.0-9.5.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. By replacing nitrogen to reduce the oxygen content in the chilled water system, the present invention effectively inhibits the oxidation of ethylene glycol to form acidic substances (such as glycolic acid and oxalic acid), and reduces the pH fluctuation range of the chilled water system; by vacuum pre-pumping (≤5 kPa) combined with repeated nitrogen replacement, the nitrogen consumption is saved by 40% compared with the traditional single replacement; by creating an overpressure nitrogen sealing environment, the air permeability is reduced; by combining secondary filtration and ultrafiltration membranes, the iron ion interception rate is improved.

[0024] 2. With an inhibitor addition amount of 0.05 - 0.2%, the present invention inhibits iron corrosion while avoiding the risk of chemical agent crystallization; a pretreatment temperature of -5 to 15 °C can improve the dispersion uniformity of the inhibitor to form a continuous passivation film; the 5 μm + 1 μm gradient filtration structure enables the removal rate of particles larger than 5 μm to reach 100%, and the pressure difference is reduced by two-stage filtration compared with single-stage filtration.

[0025] 3. Through 3 - 6 modular ultrafiltration systems, the present invention enables the flux adjustment range to reach 50 - 300 L / (m 2 ·h), which can adapt to different treatment scales. The shear stress generated by the membrane surface flow rate reduces the membrane fouling rate, and the cross-flow mode can reduce the membrane flux decay rate.

[0026] 4. By periodic pickling, the membrane flux of the ultrafiltration system can be restored, and a cleaning cycle of 500 - 800 hours can extend the membrane service life to more than 3 years. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the equipment connection structure in the second embodiment of the present invention;

[0028] DESCRIPTION OF THE REFERENCE NUMERALS IN THE DRAWINGS

[0029] Buffer water tank 1;

[0030] Two-stage filtration system 2; First filter 21; Second filter 22;

[0031] Ultrafiltration system 3;

[0032] Periodic pressure pulse backwashing system 4; Energy storage buffer tank 41; Cleaning agent circulation pump 42; Two-way pulse solenoid valve 43; Venturi injector 44; High-pressure hose 45. DETAILED DESCRIPTION OF THE INVENTION

[0033] The following will specifically describe the implementation manners of the present invention in detail, so as to fully understand how the present invention applies technical means to solve technical problems and achieve the realization process of technical effects and implement accordingly.

[0034] Embodiment 1

[0035] Purification and filtration process of highly efficient iron ion-containing freezing liquid, comprising the following steps:

[0036] S1. Pretreatment: adding an inhibitor to the iron ion-containing ethylene glycol freezing liquid to obtain a pretreated liquid;

[0037] S2. Nitrogen replacement: after the pretreated liquid is pre-evacuated to an absolute pressure ≤ 5 kPa, injecting nitrogen with a purity of 80% to normal pressure, repeating the evacuation-normal pressure process three times, and maintaining a superpressure nitrogen sealing environment of 0.04 MPa to obtain a nitrogen-replaced liquid;

[0038] S2. Secondary filtration: treating the nitrogen-replaced liquid through a two-stage filtration system to obtain a secondary filtrate;

[0039] S3. Deep treatment: passing the secondary filtrate into an ultrafiltration system for deep treatment, controlling the operating pressure at 0.2 MPa and maintaining the temperature at 10 °C to obtain an ultrafiltration concentrate;

[0040] S4. Reprocessing: circulating the ultrafiltration concentrate to step S3 for several times of reprocessing to obtain a clear liquid, and reducing the iron ion concentration in the clear liquid to 5 mg / L or less;

[0041] S5. Backwashing: when the iron ion concentration in the clear liquid is above 5 mg / L, start backwashing, and use an alkaline cleaning agent with a pH of 10-12 to reversely wash the hollow fiber membrane module.

[0042] In the step S1, the addition amount of the inhibitor is 0.1% of the mass of the freezing liquid, and the pretreatment temperature is controlled at 10 °C.

[0043] In the step S1, the inhibitor comprises an organic phosphonate and benzotriazole, and the mass ratio of the organic phosphonate to benzotriazole is 1-3. In this embodiment, the mass ratio of the organic phosphonate to benzotriazole is 2.

[0044] In the step S2, the two-stage filtration system includes a first filter and a second filter, and the nitrogen-replaced liquid passes through the first filter and the second filter connected in parallel. The filtration precisions of the first filter and the second filter are 3 μm and 0.5 μm respectively. The first filter and the second filter can both be purchased on the market and will not be elaborated here.

[0045] The ultrafiltration membrane system comprises 4 groups of hollow fiber membrane modules, with a membrane pore size of 40 nm and a membrane material of modified polyvinylidene fluoride. Among them, the hollow fiber membrane module can be purchased on the market and will not be elaborated here.

[0046] The hollow fiber membrane module adopts a cross-flow filtration mode, with a membrane surface flow rate maintained at 2 m / s and a concentrate reflux ratio of 20%.

[0047] In step S5, a periodic pressure pulse backwashing system is adopted, with a pulse frequency of 6 Hz and a backwashing flow rate 1.6 times the operating flow rate.

[0048] It also includes a chemical cleaning step: every 720 hours of operation, the ultrafiltration membrane system is cleaned by circulating an acidic cleaning agent. The acidic cleaning agent is an acidic cleaning agent containing 0.5%-1.5% citric acid and 0.1%-0.5% surfactant. In this embodiment, the acidic cleaning agent is an acidic cleaning agent containing 1% citric acid and 0.3% surfactant.

[0049] The finally treated coolant satisfies: iron ion ≤ 3 mg / L, turbidity ≤ 20 NTU, conductivity ≤ 50 μS / cm, and the pH value is maintained in the range of 8.0 - 9.5.

[0050] Embodiment 2

[0051] A purification and filtration process for highly efficient iron ion-containing coolant includes the following steps:

[0052] S1. Pretreatment: An inhibitor is added to the iron ion-containing ethylene glycol coolant to obtain a pretreated solution.

[0053] S2. Nitrogen replacement: The pretreated solution is pre-evacuated to an absolute pressure ≤ 5 kPa and then 80% pure nitrogen is injected to normal pressure. After repeating the evacuation-normal pressure process three times, a superpressure nitrogen sealing environment of 0.03 MPa is maintained to obtain a nitrogen-replaced solution.

[0054] S2. Secondary filtration: The nitrogen-replaced solution is processed through a two-stage filtration system 2 to obtain a secondary filtrate.

[0055] S3. Deep treatment: The secondary filtrate is passed into an ultrafiltration system 3 for deep treatment, controlling the operating pressure at 0.3 MPa and maintaining the temperature at 15°C to obtain an ultrafiltration concentrate.

[0056] S4. Reprocessing: The ultrafiltration concentrate is circulated to step S3 for several times of reprocessing to obtain a clear liquid, and the iron ion concentration of the clear liquid is reduced to 5 mg / L or less.

[0057] S5. Backwashing: When the iron ion concentration of the clear liquid is above 5 mg / L, backwashing is started, and a basic cleaning agent with pH 1O - 12 is used to backwash the hollow fiber membrane module in the reverse direction.

[0058] In step S1, the addition amount of the inhibitor is 0.05% of the mass of the coolant, and the pretreatment temperature is controlled at 15°C.

[0059] In step S2, the two-stage filtration system 2 includes a first filter 21 and a second filter 22. The nitrogen displacement liquid passes through the parallel first filter 21 and second filter 22. The filtration accuracies of the first filter 21 and the second filter 22 are 3μm and 0.5μm respectively.

[0060] The ultrafiltration membrane system 3 includes 5 groups of hollow fiber membrane modules with a membrane pore size of 30nm and a membrane material of modified polyvinylidene fluoride.

[0061] The hollow fiber membrane module adopts a cross-flow filtration mode, with a membrane surface flow rate maintained at 1.5 - 3m / s and a concentrate reflux ratio of 15% - 30%.

[0062] In step S5, a periodic pressure pulse backwashing system 4 is adopted, with a pulse frequency of 8Hz and a backwashing flow rate that is 1.8 times the operating flow rate.

[0063] It also includes a chemical cleaning step: every 552 hours of operation, an acidic cleaning agent is used to circulate and clean the ultrafiltration membrane system.

[0064] The finally treated freezing liquid meets the requirements: iron ion ≤ 3mg / L, turbidity ≤ 20NTU, conductivity

[0065] ≤ 50μS / cm, and the pH value is maintained in the range of 8.0 - 9.5.

[0066] Initially, the iron ion-containing ethylene glycol freezing liquid in the whole plant is regularly introduced into the buffer water tank 1. After the pretreatment in step S1 and the nitrogen displacement in step S2, the nitrogen displacement liquid flows through the two-stage filtration system 2 and the ultrafiltration system 3 to obtain an ultrafiltration concentrate, and then the ultrafiltration concentrate is re-introduced into the buffer water tank 1. After multiple treatments by the two-stage filtration system 2 and the ultrafiltration system 3, a clear liquid with an iron ion concentration of less than 5mg / L is obtained. Among them, the number of re-treatments is specifically adjusted according to the volume of the iron ion-containing ethylene glycol freezing liquid in the buffer water tank 1, and no specific limitation is made here.

[0067] Among them, the periodic pressure pulse backwashing system 4 includes: an energy storage buffer tank 41, a cleaning agent circulation pump 42, a two-way pulse solenoid valve 43, and a Venturi injector 44. The cleaning agent circulation pump 42 pumps the alkaline cleaning agent into the energy storage buffer tank 41. One end of the two-way pulse solenoid valve 43 is connected to the energy storage buffer tank 41, and the other end of the two-way pulse solenoid valve 43 is connected to the Venturi injector 44. The Venturi injector 44 is connected to the ultrafiltration system 3 through a high-pressure hose 45.

[0068] When the iron ion concentration of the clear liquid is still above 5mg / L after the set number of re-treatments, the cleaning agent circulation pump 4 pumps the alkaline cleaning agent into the energy storage buffer tank 41, and the two-way pulse solenoid valve 43 is periodically switched on and off to lead the alkaline cleaning agent to the ultrafiltration system 3 through the Venturi injector 44 for backwashing.

[0069] Although the present invention has been specifically shown and described in conjunction with preferred embodiments, those skilled in the art should understand that various changes can be made to the present invention in form and detail without departing from the spirit and scope of the present invention as defined by the appended claims, and all such changes are within the scope of protection of the present invention.

Claims

1. The purification and filtration process of an efficient iron ion-containing coolant, characterized in that, It includes the following steps: S1. Pretreatment: Add an inhibitor to the ethylene glycol freezing liquid containing iron ions to obtain a pretreatment liquid. S2. Nitrogen replacement: After the pretreatment liquid is pre-evacuated to an absolute pressure ≤ 5 kPa, inject nitrogen with a purity of 80% to normal pressure. Repeat the evacuation - normal pressure process three times, and then maintain an overpressure nitrogen sealing environment of 0.03 - 0.05 MPa to obtain a nitrogen-replaced liquid. S2. Secondary filtration: Treat the nitrogen-replaced liquid through a two-stage filtration system to obtain a secondary filtrate. S3. Deep treatment: Pass the secondary filtrate into an ultrafiltration system for deep treatment, control the operating pressure at 0.1 - 0.5 MPa, and maintain the temperature at -5 - 15 °C to obtain an ultrafiltration concentrate. S4. Reprocessing: Recycle the ultrafiltration concentrate to step S3 for several times of reprocessing to obtain a clear liquid, and the iron ion concentration in the clear liquid is reduced to 5 mg / L or less. S5. Backwashing: When the iron ion concentration in the clear liquid is above 5 mg / L, start backwashing, and use an alkaline cleaning agent with a pH of 10 - 12 to reversely wash the hollow fiber membrane module.

2. The purification and filtration process of the high-efficiency iron ion-containing coolant according to claim 1, characterized in that: In the step S1, the addition amount of the inhibitor is 0.05% - 0.2% of the mass of the freezing liquid, and the pretreatment temperature is controlled at -5 - 15 °C.

3. The purification and filtration process of the high-efficiency iron ion-containing coolant according to claim 1, characterized in that: In the step S2, the two-stage filtration system includes a first filter and a second filter. The nitrogen-replaced liquid passes through the first filter and the second filter in parallel, and the filtration accuracies of the first filter and the second filter are 3 μm and 0.5 μm respectively.

4. The purification and filtration process of the high-efficiency iron ion-containing coolant according to claim 1, characterized in that: The ultrafiltration membrane system includes 3 - 6 groups of hollow fiber membrane modules, with a membrane pore size of 10 - 50 nm, and the membrane material is modified polyvinylidene fluoride.

5. The purification and filtration process of the high-efficiency iron-ion-containing coolant according to claim 1, characterized in that: The hollow fiber membrane module adopts a cross-flow filtration mode, the membrane surface flow velocity is maintained at 1.5 - 3 m / s, and the concentrate reflux ratio is 15% - 30%.

6. The purification and filtration process of the high-efficiency iron-ion-containing coolant according to claim 1, characterized in that: In the step S5, a periodic pressure pulse backwashing system is adopted, with a pulse frequency of 5 - 10 Hz, and the backwashing flow rate is 1.5 - 2 times the operating flow rate.

7. The purification and filtration process of the high-efficiency iron-ion-containing coolant according to claim 1, characterized in that, It also includes a chemical cleaning step: Every 500 - 800 hours of operation, use an acidic cleaning agent to circulate and clean the ultrafiltration membrane system.

8. The purification and filtration process of the high-efficiency iron-ion-containing coolant according to claim 1, wherein: The finally treated freezing liquid meets the requirements: iron ion ≤ 3 mg / L, turbidity ≤ 20 NTU, conductivity ≤ 50 μS / cm, and the pH value is maintained in the range of 8.0 - 9.5.

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