Method for treating silicon-containing wastewater in molecular sieve preparation

Abstract

The invention relates to the technical field of sewage treatment, in particular to a method for treating silicon-containing wastewater in molecular sieve preparation, which comprises the following steps: (1) introducing the silicon-containing wastewater into a first reaction tank, adding an agent A into the first reaction tank, stirring and mixing, standing and settling, and controlling the pH value of the mixed wastewater to be 11.0-13.0; (2) overflowing supernate in the first reaction tank into a second reaction tank, adding an agent B and an agent C into the second reaction tank, stirring and mixing, standing and settling, and controlling the pH value of the mixed wastewater to be 7.0-9.5; and (3) overflowing the supernate in the second reaction tank to a third reaction tank, adding an agent D into the third reaction tank, stirring and mixing, standing and settling, and overflowing to a clarification tank after the third reaction tank is full. According to the method, lime calcium and magnesium are not introduced into a sewage treatment system during silica removal, so that the sludge amount is reduced, the technical problems of blockage and scaling of the sewage treatment system are solved, meanwhile, sodium carbonate for removing lime calcium is saved, and the use amount of alkali liquor is also greatly reduced.

Description

Technical Field

[0001] The invention relates to the technical field of sewage treatment, and in particular to a method for treating silicon-containing wastewater in the preparation of molecular sieves. Background Art

[0002] During the production of catalytic cracking catalysts, the molecular sieve unit gel unit will produce wastewater with a high silicon content of 200-1200 mg / L. Before entering the wastewater membrane treatment system, the silicon content must be reduced to below 60 mg / L, the lower the better. Otherwise, dense silicon scale will form on the surface of the permeable membrane and react with Al in the wastewater. 3+ The reaction forms silica-alumina gel, both of which will block the permeation membrane channel and reduce the permeability of the membrane, seriously affecting the long-term operation of the permeation membrane. The membrane column operating pressure will increase, and it must be cleaned when it reaches a certain pressure. The membrane cleaning water needs to be returned to the front system for reprocessing. The increase in the number of cleaning times will increase the load on the sewage system and increase the treatment cost.

[0003] At present, silicon in industrial wastewater is mainly removed by the following methods: coagulation desiliconization, electrocoagulation desiliconization, ion exchange desiliconization, flotation removal of colloidal silicon, ultrafiltration removal of colloidal silicon, etc. The most commonly used is coagulation, which mainly removes silicon from sewage by adding lime, magnesium agent and flocculant. Lime and magnesium agent introduce calcium and magnesium ions into the sewage system. To remove lime, calcium and magnesium, it is necessary to use alkali solution to adjust the pH value to a higher level, and then add soda solution to remove calcium and magnesium. For example, CN 105000642 A discloses a method for treating silicon-containing wastewater generated during the preparation of molecular sieves. A lime emulsion with a solute mass percentage concentration of 3%-10% is added to the silicon wastewater, stirred for a period of time, and then allowed to stand for separation. The silicon content of the supernatant will be reduced, and the bottom sludge will be discharged. The gel impurities in the gel wastewater can be well treated, and the turbidity of the treated wastewater is significantly reduced. Its technical defects are low silicon removal efficiency, only about 50%; the main component of lime is calcium oxide, and the main component of magnesium agent is magnesium oxide, which has low solubility, and the prepared solution is easy to settle and block the delivery pumps and pipelines; calcium and magnesium are introduced into the sewage treatment system, which are easy to scale and block the pipelines, and adhere to the walls of the reaction vessel, the stirring shaft, the stirring blades, the heat exchange plates of the post-system heat exchanger, the pump cavity and the impeller of the pump, affecting the normal operation of the reactor, heat exchanger and pump, and need to be cleaned regularly. Summary of the invention

[0004] In view of the technical problems that the desiliconization method using lime and magnesium agents and flocculants is prone to cause blockage and scaling of sewage treatment systems, the present invention provides a method for treating silicon-containing wastewater in the preparation of molecular sieves. During desiliconization, lime, calcium and magnesium are not introduced into the sewage treatment system, which reduces the amount of sludge and solves the technical problem of blockage and scaling of the sewage treatment system. At the same time, soda ash used for removing lime and calcium is saved, and the amount of alkali solution used is also greatly reduced.

[0005] The present invention provides a method for treating silicon-containing wastewater in the preparation of molecular sieves, comprising the following steps: (1) Silicon-containing wastewater is passed into the first reaction tank, and agent A is added into the first reaction tank for stirring and mixing, and the mixture is allowed to settle, and the pH value of the mixed wastewater is controlled to be 11.0-13.0. Agent A includes Al2O3 and Na2O; (2) The supernatant in the first reaction tank overflows to the second reaction tank, and Agent B and Agent C are added to the second reaction tank, stirred and mixed, and allowed to settle. The pH value of the mixed wastewater is controlled to be 7.0-9.5. Agent B is sulfuric acid, and Agent C is polyferric sulfate; (3) The supernatant in the second reaction tank overflows into the third reaction tank, and agent D is added into the third reaction tank, stirred and mixed, and allowed to settle. After the third reaction tank is full, it overflows into the clarification tank. Agent D is polyacrylamide.

[0006] Furthermore, in step (1), the mass ratio of Al2O3 to Na2O is 3.5~11:13~29.

[0007] Furthermore, in step (1), every 1m 3 The volume dosage of Agent A corresponding to silicon-containing wastewater is 2~29L.

[0008] Furthermore, in step (2), the concentration of sulfuric acid is 30% to 98%.

[0009] Furthermore, in step (2), based on the maximum volume of the mixed wastewater that can be stored in the second reaction tank, the amount of polyferric sulfate used is 20-80 mg / L.

[0010] Furthermore, in step (2), based on the maximum volume of the mixed wastewater that can be stored in the third reaction tank, the amount of polyacrylamide used is 2-7 mg / L.

[0011] Furthermore, in step (3), the sludge settled at the bottom of the clarifier is discharged to the sludge thickening tank through a sludge pump. After further clarification, the supernatant overflows into the water collection tank, and the water in the water collection tank is returned to the third reaction tank for reuse.

[0012] Furthermore, the concentrated sludge in the sludge thickening tank is sent to a plate and frame filter press for filtration, and the clear liquid after filtration is sent to a collection tank.

[0013] The beneficial effects of the present invention are as follows: the present invention abandons the traditional lime-magnesium flocculant and soda precipitation method, the silicon-containing gel wastewater is first mixed with agent A in proportion and stirred evenly to adjust the pH value to 11.0-13.0, then agent B and agent C are added, the pH value is adjusted to 7.0-9.5 by acid, and a flocculant is added, and then the silicon content in the wastewater is reduced from the original 200-800 mg / L to below 40 mg / L after flocculation and clarification, the turbidity is ≤60NTU, the amount of alkali used in wastewater treatment is greatly reduced, the amount of sludge in the system is reduced, and the amount of flocculant used is also greatly reduced, thereby solving the technical problem that the removal of silicon by lime-magnesium agent in the prior art easily causes clogging and scaling of the wastewater treatment system. DETAILED DESCRIPTION

[0014] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0015] In the following examples, overflow in the reaction pool can be achieved through an overflow port or overflow pipe disposed between two adjacent reaction pools, and the overflow port or overflow pipe can be opened or closed.

[0016] Example 1 A method for treating silicon-containing wastewater in molecular sieve preparation comprises the following steps: (1) Silicon-containing wastewater is generated during the preparation of catalytic cracking catalyst molecular sieves. The silicon content in the silicon-containing wastewater is 538 mg / L. The silicon-containing wastewater is introduced into the first reaction tank at the top of the tank. Agent A is added to the first reaction tank and stirred. Agent A includes Al2O3 and Na2O. The Al2O3 content in Agent A is 99.7 g / L, the Na2O content is 149.6 g / L, and the density of Agent A is 1.2~1.4 g / cm 3 , every 1m 3 The volume dosage of Agent A corresponding to the silicon-containing wastewater is 29L, the flow rate of Agent A is 83L / h, and the pH value of the mixed wastewater is controlled to be 12.9 after static sedimentation.

[0017] (2) The supernatant in the first reaction tank overflows into the second reaction tank, and Agent B and Agent C are added into the second reaction tank, stirred and mixed, and allowed to settle. Agent B is sulfuric acid with a concentration of 98%, and Agent C is polyferric sulfate. Based on the maximum volume of mixed wastewater that can be stored in the second reaction tank, the amount of polyferric sulfate is 50 mg / L, and the pH value of the mixed wastewater is controlled to be 7.5.

[0018] (3) The supernatant in the second reaction tank overflows into the third reaction tank, into which agent D is added for stirring and mixing. Agent D is polyacrylamide (PAM). Based on the maximum volume of mixed wastewater that can be stored in the third reaction tank, the amount of polyacrylamide is 4.5 mg / L, and the flow rate of PAM addition is 87 g / h. The supernatant overflows into the clarification tank after being allowed to settle.

[0019] (4) When the third reaction tank is full, the overflow flows into the clarification tank. At the same time, the scraper and the sludge pump are turned on. The scraper scrapes the sludge at the bottom of the clarification tank to the inverted cone bottom of the clarification tank. The settled sludge slurry is discharged to the sludge thickening tank through the sludge pump. After settling, it is pumped to the plate and frame filter press. The filter sludge is collected and transported out. The clean water after the filter press flows into the collection tank by gravity. When the clarification tank is full, the overflow flows into the feed tank of the deammonification nitrogen removal device. At the same time, the supernatant of the sludge thickening tank flows into the collection tank by gravity through the valves of the overflow port with different liquid level heights. The clean water in the collection tank is automatically controlled by the liquid level and the pump linkage, and the sewage in the collection tank is sent to the third reaction tank for reuse.

[0020] The silicon content, turbidity and sludge discharge of the supernatant in each treatment step of Example 1 were tested, and the obtained data are shown in Table 1.

[0021] Table 1 Sewage treatment effect data of each treatment process Processing facilities Settling time, h Silicon content in supernatant, mg / L Supernatant turbidity, NTU Mud discharge The first reaction tank 0.34 538 153.7 / The second reaction tank 0.34 174 261.3 / The third reaction tank 7 57 121.4 / Clarifier 9 19.7 9.7 <![CDATA[12m 3 / h]]> Sludge thickening tank 6 21.3 10.2 249t / h catch basin 0.8 20.6 12.3 / Example 2 A method for treating silicon-containing wastewater in molecular sieve preparation comprises the following steps: (1) Silicon-containing wastewater is generated during the preparation of catalytic cracking catalyst molecular sieves. The silicon content in the silicon-containing wastewater is 628 mg / L. The silicon-containing wastewater is introduced into the first reaction tank at the top of the tank. Agent A is added to the first reaction tank and stirred. Agent A includes Al2O3 and Na2O. The Al2O3 content in Agent A is 35.1 g / L, the Na2O content is 130.6 g / L, and the density of Agent A is 1.2~1.4 g / cm 3 , every 1m 3 The volume dosage of Agent A corresponding to the silicon-containing wastewater is 10L, the flow rate of Agent A is 82L / h, and the pH value of the mixed wastewater is controlled to be 11.0 after static sedimentation.

[0022] (2) The supernatant in the first reaction tank overflows into the second reaction tank, and Agent B and Agent C are added into the second reaction tank, stirred and mixed, and allowed to settle. Agent B is sulfuric acid with a concentration of 70%, and Agent C is polyferric sulfate. Based on the maximum volume of mixed wastewater that can be stored in the second reaction tank, the amount of polyferric sulfate is 20 mg / L, and the pH value of the mixed wastewater is controlled to be 7.0.

[0023] (3) The supernatant in the second reaction tank overflows into the third reaction tank, into which agent D is added for stirring and mixing. Agent D is polyacrylamide (PAM). Based on the maximum volume of mixed wastewater that can be stored in the third reaction tank, the amount of polyacrylamide is 2 mg / L, and the flow rate of PAM addition is 82 g / h. The mixture is allowed to settle and the supernatant overflows into the clarification tank.

[0024] (4) When the third reaction tank is full, the overflow flows into the clarification tank. At the same time, the scraper and the sludge pump are turned on. The scraper scrapes the sludge at the bottom of the clarification tank to the inverted cone bottom of the clarification tank. The settled sludge slurry is discharged to the sludge thickening tank through the sludge pump. After settling, it is pumped to the plate and frame filter press. The filter sludge is collected and transported out. The clean water after the filter press flows into the collection tank by gravity. When the clarification tank is full, the overflow flows into the feed tank of the deammonification nitrogen removal device. At the same time, the supernatant of the sludge thickening tank flows into the collection tank by gravity through the valves of the overflow port with different liquid level heights. The clean water in the collection tank is automatically controlled by the liquid level and the pump linkage, and the sewage in the collection tank is sent to the third reaction tank for reuse.

[0025] The silicon content, turbidity and sludge discharge of the supernatant in each treatment step of Example 2 were tested, and the obtained data are shown in Table 2.

[0026] Table 2 Sewage treatment effect data of each treatment process Processing facilities Settling time, h Silicon content in supernatant, mg / L Supernatant turbidity, NTU Mud discharge The first reaction tank 0.35 628 163.3 / The second reaction tank 0.33 221 272.3 / The third reaction tank 4 58 102.1 / Clarifier 6 20.1 10.1 <![CDATA[11m 3 / h]]> Sludge thickening tank 6 21.3 10.3 235t / h catch basin 0.8 21.0 11.9 / Example 3 A method for treating silicon-containing wastewater in molecular sieve preparation comprises the following steps: (1) Silicon-containing wastewater is generated during the preparation of catalytic cracking catalyst molecular sieves. The silicon content in the silicon-containing wastewater is 523 mg / L. The silicon-containing wastewater is introduced into the first reaction tank at the top of the tank. Agent A is added to the first reaction tank and stirred. Agent A includes Al2O3 and Na2O. The Al2O3 content in Agent A is 110.0 g / L, the Na2O content is 289.8 g / L, and the density of Agent A is 1.2~1.4 g / cm 3 , every 1m 3 The volume dosage of Agent A corresponding to the silicon-containing wastewater is 2L, the flow rate of Agent A is 89L / h, and the pH value of the mixed wastewater is controlled to be 12.1 after static sedimentation.

[0027] (2) The supernatant in the first reaction tank overflows into the second reaction tank, and Agent B and Agent C are added into the second reaction tank, stirred and mixed, and allowed to settle. Agent B is sulfuric acid with a concentration of 30%, and Agent C is polyferric sulfate. Based on the maximum volume of mixed wastewater that can be stored in the second reaction tank, the amount of polyferric sulfate is 80 mg / L, and the pH value of the mixed wastewater is controlled to be 9.5.

[0028] (3) The supernatant in the second reaction tank overflows into the third reaction tank, into which agent D is added for stirring and mixing. Agent D is polyacrylamide (PAM). Based on the maximum volume of mixed wastewater that can be stored in the third reaction tank, the amount of polyacrylamide is 7 mg / L, and the flow rate of PAM addition is 83 g / h. The mixture is allowed to settle and the supernatant overflows into the clarification tank.

[0029] (4) When the third reaction tank is full, the overflow flows into the clarification tank. At the same time, the scraper and the sludge pump are turned on. The scraper scrapes the sludge at the bottom of the clarification tank to the inverted cone bottom of the clarification tank. The settled sludge slurry is discharged to the sludge thickening tank through the sludge pump. After settling, it is pumped to the plate and frame filter press. The filter sludge is collected and transported out. The clean water after the filter press flows into the collection tank by gravity. When the clarification tank is full, the overflow flows into the feed tank of the deammonification nitrogen removal device. At the same time, the supernatant of the sludge thickening tank flows into the collection tank by gravity through the valves of the overflow port with different liquid level heights. The clean water in the collection tank is automatically controlled by the liquid level and the pump linkage, and the sewage in the collection tank is sent to the third reaction tank for reuse.

[0030] The silicon content, turbidity and sludge discharge of the supernatant in each treatment step of Example 3 were tested, and the obtained data are shown in Table 3.

[0031] Table 3 Sewage treatment effect data of each treatment process Processing facilities Settling time, h Silicon content in supernatant, mg / L Supernatant turbidity, NTU Mud discharge The first reaction tank 0.33 523 159.8 / The second reaction tank 0.33 153 264.6 / The third reaction tank 10 59 127.3 / Clarifier 12 21.3 10.1 <![CDATA[13.1m 3 / h]]> Sludge thickening tank 6 20.9 10.3 234t / h catch basin 0.8 20.3 12.2 / Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and such modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily conceive of changes or substitutions within the technical scope disclosed by the present invention, and such changes or substitutions shall be within the scope of protection of the present invention.

Claims

1. A method for treating silicon-containing wastewater in the preparation of molecular sieves, characterized in that: The steps include: (1) Silicon-containing wastewater is passed into the first reaction tank, and agent A is added into the first reaction tank for stirring and mixing, and the mixture is allowed to settle, and the pH value of the mixed wastewater is controlled to be 11.0-13.

0. Agent A includes Al2O3 and Na2O; (2) The supernatant in the first reaction tank overflows to the second reaction tank, and Agent B and Agent C are added to the second reaction tank, stirred and mixed, and allowed to settle. The pH value of the mixed wastewater is controlled to be 7.0-9.

5. Agent B is sulfuric acid, and Agent C is polyferric sulfate; (3) The supernatant in the second reaction tank overflows into the third reaction tank, and agent D is added into the third reaction tank, stirred and mixed, and allowed to settle. After the third reaction tank is full, it overflows into the clarification tank. Agent D is polyacrylamide.

2. The method for treating silicon-containing wastewater in the preparation of molecular sieves according to claim 1, characterized in that: In step (1), the mass ratio of Al2O3 to Na2O is 3.5~11:13~29.

3. The method for treating silicon-containing wastewater in the preparation of molecular sieves according to claim 2, characterized in that: In step (1), every 1m 3 The volume dosage of Agent A corresponding to silicon-containing wastewater is 2~29L.

4. The method for treating silicon-containing wastewater in the preparation of molecular sieves according to claim 1, characterized in that: In step (2), the concentration of sulfuric acid is 30% to 98%.

5. The method for treating silicon-containing wastewater in the preparation of molecular sieves according to claim 1, characterized in that: In step (2), based on the maximum volume of the mixed wastewater that can be stored in the second reaction tank, the amount of polyferric sulfate used is 20-80 mg / L.

6. The method for treating silicon-containing wastewater in the preparation of molecular sieves according to claim 1, characterized in that: In step (2), based on the maximum volume of the mixed wastewater that can be stored in the third reaction tank, the amount of polyacrylamide used is 2-7 mg / L.

7. The method for treating silicon-containing wastewater in the preparation of molecular sieves according to claim 1, characterized in that: In step (3), the sludge settled at the bottom of the clarifier is discharged to the sludge thickening tank through a sludge pump. After further clarification, the supernatant overflows into the collection tank, and the water in the collection tank is returned to the third reaction tank for reuse.

8. The method for treating silicon-containing wastewater in the preparation of molecular sieves according to claim 7, characterized in that: The concentrated sludge in the sludge thickening tank is sent to the plate and frame filter press for filtration, and the clear liquid after filtration is sent to the collection tank.