TWI805426B - Boron resource recovery system for waste liquid - Google Patents

Abstract

A boron resource recovery system for waste liquid is provided. It includes: a wastewater storage tank, a pH value adjustment tank, a solid-liquid separator, a first ion exchanger, an evaporation concentrator, a centrifugal dehydrator, a condenser and a second ion exchanger. In the present invention, the solid-liquid separator and the first ion exchanger are used to take out a large amount of miscellaneous ions that affect the crystallization of boron ions, and then the centrifugal dehydrator is used to recover useful sodium borate. During the process, all boron is recovered from the water containing boron ions is recovered to ensure that the discharged wastewater meets the requirements of environmental protection regulations. During the process, there is no need to use boron remover.

Description

Waste liquid boron resource recovery system

The invention relates to a resource recovery system, in particular to a waste liquid boron resource recovery system applied to boron-containing waste liquid.

Flue Gas Desulfurization (FGD) is a technology that removes sulfur oxides from flue gas emitted by petrochemical combustion power facilities, such as power generating units or incinerators. Taking coal-fired power plants as an example, the waste water produced by flue gas desulfurization contains a variety of pollutants, one of which is boron (Boron) and its compounds. Boron and trace heavy metals are suitable for removal by chemical treatment in order to meet the national discharge water standards. The so-called chemical treatment method usually refers to the use of boron removal agent, but the solid matter in the wastewater added with boron removal agent becomes waste and cannot be reused.

In addition to chemical treatment methods, commonly used boron removal methods include ion exchange, adsorption, reverse osmosis, extraction, etc., but each method has its limitations. Most importantly, the by-products produced by existing boron removal facilities are almost impossible to recycle and reuse, which also causes a burden on the environment. On the other hand, boron and its compounds are also commonly used resources in industry, and it would be a waste to let them be disposed of in the environment.

Therefore, in order to effectively extract boron from the waste liquid, the waste liquid boron resource recovery system of the present invention is proposed.

This paragraph extracts and compiles certain features of the present invention. Other features will be disclosed in subsequent paragraphs. It is intended to cover various modifications and similar arrangements within the spirit and scope of the appended claims.

The invention discloses one method, which includes: a waste water storage tank for storing boron-containing waste water; a pH adjustment tank connected with the waste water storage tank, and adding an alkaline regulator after introducing the boron-containing waste water to make the boron-containing waste water The pH value of the boron wastewater is adjusted to 10-12 to become an alkaline boron-containing wastewater; a solid-liquid separator communicates with the pH value adjustment tank, introduces and squeezes the alkaline boron-containing wastewater at high pressure to form a separation boron-containing ion water and solid waste; a first ion exchanger communicated with the solid-liquid separator, introducing the boron-containing ion water, exchanging part of the alkaline earth metal cations and acid radical anions in the boron-containing ion water to form a Soft boron-containing ionized water; an evaporation concentrator connected with the first ion exchanger to evaporate part of the water in the soft boron-containing ionized water at an average temperature lower than 80°C under negative pressure, leaving crystalline A boron-containing compound; and a centrifugal dehydrator, connected to the evaporation concentrator, introducing the boron-containing compound, taking out the moisture contained in the boron-containing compound by high-speed centrifugal rotation, leaving crystalline sodium borate.

According to the present invention, the first ion exchanger may further include: a pump for pumping the boron-containing ion water into the first ion exchanger; a plurality of cation exchange resin towers connected with the pump and connected in series Next, each cation exchange resin tower contains a cation exchange resin, and part of the alkaline earth metal cation exchange in the boron-containing ion water drawn in is taken out; and a plurality of anion exchange resin towers are connected with these cation exchange resin towers and connected in series Next, each anion exchange resin tower contains anion exchange resin, and the partial acid radical anion exchange in the boron-containing ion water after ion exchange by these cation exchange resin towers is taken out.

Preferably, the cation exchange resin is a weak acid cation exchange resin, and the anion exchange resin is a weak base anion exchange resin.

The waste liquid boron resource recovery system may further include: a condenser, which communicates with the evaporative concentrator, introduces the evaporated water from the evaporative concentrator, and lowers the temperature of the evaporated water to room temperature in a water-cooled manner; and a first The second ion exchanger communicates with the condenser, introduces the condensed evaporated water, and exchanges part of the boron ions in the condensed evaporated water. If the boron ion content of the condensed evaporated water after passing through the second ion exchanger is lower than 0.1ppm, the condensed evaporated water is directly discharged; if the boron ion content of the condensed evaporated water passed through the second ion exchanger is higher than 0.1ppm, the condensed evaporated water is re-injected into the evaporative concentrator, mixed with the soft boron-containing ionized water and then evaporated again.

According to the present invention, the second ion exchanger may further include: a second pump for pumping condensed evaporated water into the second ion exchanger; and a plurality of boron ion exchange resin towers, connected with the second pump The pumps are connected and connected in series with each other, and each boron ion exchange resin tower contains boron ion exchange resin, and part of the boron ion exchange in the drawn-in condensed evaporated water is taken out.

Preferably, the alkalinity modifier is sodium hydroxide (NaOH).

Preferably, the alkaline earth metal cations comprise calcium ions (Ca ²⁺ ) and magnesium ions (Mg ²⁺ ).

Preferably, the acid anion is chloride ion (Cl ^- ), nitrate ion (NO ₃ ^- ) or sulfate ion (SO ₄ ^2- ).

Preferably, the solid-liquid separator is a centrifugal solid-liquid separator, a screen-type solid-liquid separator or a plate-and-frame filter press.

The invention uses the solid-liquid separator and the first ion exchanger to take out a large amount of hetero ions that affect the boron ion crystallization, and then recovers the useful sodium borate with the centrifugal dehydrator. During the process, all the water containing boron ions is recovered by boron ions to ensure that the discharged wastewater meets the requirements of environmental protection regulations. In the process, there is no need to use boron removal agent.

1: Waste liquid boron resource recovery system

10: Wastewater storage tank

20: pH adjustment tank

30: Solid-liquid separator

31: Main structure

32: filter plate

33: Oil pressure rod

34: High pressure liquid delivery pipe

35: Liquid collection tank

40: The first ion exchanger

41: The first water pump

42: Cation exchange resin tower

43: Anion exchange resin tower

50: evaporative concentrator

51: exhaust pipe

52: Conveyor mechanism

60: centrifugal dehydrator

61: opening

62: The first return pipe

70: condenser

71: water pipe

80: Second ion exchanger

81:Second water pump

82: Boron ion exchange resin tower

A: Alkaline regulator

BW: boron ionized water

P1: The first diversion pump

P2: The second diversion pump

S: source of generation

SW: solid waste

V1: first control valve

V2: Second control valve

Fig. 1 is a system schematic diagram of a waste liquid boron resource recovery system according to the present invention.

Figure 2 lists the changes of some ion concentrations after boron-containing wastewater is treated by some equipment in the waste liquid boron resource recovery system.

In order to make the description of the disclosed content more detailed and complete, the following provides illustrative descriptions for the implementation aspects and specific embodiments of the present invention.

Please refer to FIG. 1 , which is a schematic diagram of a waste liquid boron resource recovery system 1 according to the present invention. Waste liquid boron resource recovery system 1 includes a waste water storage tank 10, a pH value adjustment tank 20, a solid-liquid separator 30, a first ion exchanger 40, an evaporative concentrator 50, a centrifugal dehydrator 60, a The condenser 70 and a second ion exchanger 80 . The types and functions of these technical components and the overall operation of the waste liquid boron resource recovery system 1 will be described in detail below.

The function of the waste water storage tank 10 is to store a boron-containing waste water. The boron-containing wastewater can be collected from various sources S, such as power plants, chemical factories, incinerators, etc., and after passing through the waste liquid boron resource recovery system 1, the boron content and other harmful chemical components can be reduced, which meets the requirements of environmental protection regulations And discharged directly into the drainage pipeline or natural river.

The pH value adjustment tank 20 communicates with the waste water storage tank 10 (through the water pipeline), introduces the boron-containing waste water in the waste water storage tank 10 with a first diversion pump P1, and then adds an alkaline regulator A to make the boron-containing waste water The pH value is adjusted to between 10-12 to become an alkaline boron-containing wastewater. According to the present invention, the alkalinity modifier A may be, but not limited to, sodium hydroxide (NaOH). Since the amount and composition of the alkaline regulator A and the boron-containing wastewater can determine the pH value of the adjusted boron-containing wastewater, the pH value of the boron-containing wastewater in the pH value adjustment tank 20 can be measured to determine whether to stop the alkaline adjustment Addition of agent A. Preferably, the pH value of the adjusted boron-containing wastewater can be set around 11.

The solid-liquid separator 30 communicates with the pH value adjustment tank 20 (through the water pipeline), introduces the alkaline boron-containing wastewater with a second water diversion pump P2 and squeezes the alkaline boron-containing wastewater with high pressure to form separated boron-containing wastewater. Boron ion water BW and solid waste SW (marked with a slash bottom in FIG. 2 ). In practice, the solid-liquid separator 30 can be a centrifugal solid-liquid separator, a screen-type solid-liquid separator or a plate-and-frame filter press. In terms of operability, the plate and frame filter press is better, and the plate and frame filter press is also shown in Figure 1 as an example. The plate and frame filter press includes a main structure 31 , several filter plates 32 that can be arranged in parallel, an oil pressure rod 33 , a high-pressure liquid delivery pipe 34 and a liquid collection tank 35 . The filter plates 32 are arranged horizontally and parallel to each other on the main structure 31 , and are pushed to one side by the hydraulic rod 33 . The high-pressure liquid delivery pipe 34 injects the alkaline boron-containing wastewater from the second water diversion pump P2 into a through hole (not shown) in the middle of each filter plate 32 at high pressure, and then fills the concave space between the filter plates 32 (solid waste the space where the SW is located). Therefore, the second diversion pump P2 is a high pressure pump. Under the effect of high pressure, the boron-containing ion water BW flows downward from the gap in the middle of the filter plate 32 and collects in the liquid collection tank 35 . The solid waste SW stays in the respective concave spaces. When the amount of solid waste SW is saturated, the oil pressure rod 33 returns to its original position, and the filter plate 32 can be taken out to shake off the solid waste SW. The filter plate 32 from which the solid waste SW has been removed can be reused. Under the aforementioned operations, the solid waste SW contains most of the alkaline earth metal hydroxides in the original boron-containing wastewater, such as magnesium hydroxide (Mg(OH) ₂ ) and calcium hydroxide (Ca(OH) ₂ ). Therefore, part of the magnesium ions and calcium ions are removed from the boron-containing wastewater, and the boron-containing water BW is softened. There is no large amount of harmful boron in the solid waste SW, so it can be disposed of directly.

Next, the content of alkaline earth metal cations and acid radical anions should be further reduced from the boron ion-containing water BW. The first ion exchanger 40 is the means used to perform this work. The first ion exchanger 40 communicates with the solid-liquid separator 30 (through the water pipeline), and can introduce boron-containing ion water BW, and exchange part of the alkaline earth metal cations and acid radical anions in the boron-containing ion water BW to form a soft Contains boron ionized water. In order to achieve the aforementioned purpose, the first ion exchanger 40 includes a first water pump 41 , a plurality of cation exchange resin towers 42 and a plurality of anion exchange resin towers 43 . The first water pump 41 can pump the boron-containing ion water BW into the first ion exchanger 40 . In the present embodiment, two cation exchange resin columns 42 are used as an example to describe. In practice, the number of cation exchange resin columns 42 can be more. These cation exchange resin towers 42 communicate with the first water pump 41 and are connected in series with each other. Each cation exchange resin tower 42 contains a cation exchange resin, which can exchange part of the alkaline earth metal cations in the boron-containing ion water BW drawn in. take out. Mainly, the cation exchange resin tower 42 is to exchange calcium ions (Ca ²⁺ ) with magnesium ions (Mg ²⁺ ) and take them out to soften the boron ion-containing water BW. Preferably, the cation exchange resin is a weakly acidic cation exchange resin, and the weakly acidic cation exchange resin is a resin containing weakly acidic functional groups, such as carboxyl-COOH, as an exchange group. In the following examples, a weakly acidic cation exchange resin produced by Mitsubishi Chemical Co., Ltd. with a brand name of DIAION WK60L was used. The cation exchange resin towers 42 are connected in series, so when the exchange force of one of them decreases, it can be removed from the first ion exchanger 40 for reagent backwashing. After the exchange force is improved, it can be put back into the first ion exchanger 40 to continue to operate.

Similarly, in this embodiment, the two anion exchange resin columns 43 are used as an example and demonstrated. In practice, the number of anion exchange resin columns 43 can be more. The anion exchange resin towers 43 communicate with the aforementioned cation exchange resin towers 42 through water pipes, and the anion exchange resin towers 43 are connected in series. Each anion-exchange resin tower 43 contains anion-exchange resin, and part of the anion-exchange of acid radicals in the boron-containing ion water BW after the ion-exchange in these cation-exchange resin towers 42 is taken out. Mainly, the anion exchange resin column 43 is to exchange and remove contained chloride ions (Cl ⁻ ), nitrate ions (NO ₃ ⁻ ) or sulfate ions (SO ₄ ²⁻ ). Preferably, the anion exchange resin is a weak base type anion exchange resin. Weak base anion exchange resin is an anion exchange resin with primary, secondary and tertiary amino groups as active groups on the cross-linked polystyrene skeleton or polyacrylate skeleton. It cannot be exchanged with anionic neutral salts such as NaCl and Na ₂ SO4, but it can be ion-exchanged with inorganic acids such as HCl and H ₂ SO ₄ and weakly basic anionic salts such as NH ₄ Cl. In the following examples, a weakly basic anion exchange resin produced by Mitsubishi Chemical Co., Ltd. with a brand name of DIAION JA310 was used. The anion exchange resin towers 43 are connected in series, so when the exchange force of one of them decreases, it can be removed from the first ion exchanger 40 for reagent backwashing. After the exchange force is improved, it can be put back into the first ion exchanger 40 to continue to operate.

Next, to remove the boron ions in the soft boron ion-containing water as much as possible, the evaporation concentrator 50 needs to be used. The evaporative concentrator 50 is communicated with the first ion exchanger 40 (through the water pipeline), so as to Part of the moisture in the soft boron-containing ionized water is evaporated at an average temperature lower than 80° C. under negative pressure, leaving a crystalline boron-containing compound. In practice, the evaporative concentrator 50 can be a three-effect condensing evaporator. The three-effect concentrated evaporator is an evaporation operation process combined by three evaporators. When the three evaporators are evaporating, the operating pressure of the after-effect and the boiling point of the solution are lower than those of the previous effect, and the secondary steam of the previous effect is introduced as the after-effect. The heating medium of the after effect, that is, the heating chamber of the after effect becomes the condenser of the secondary steam of the front effect, and only the first effect needs to consume raw steam. According to the present invention, a negative pressure, such as 380mmHg, can be maintained in the third evaporator, while the temperature of the vapor generated by the second evaporator is about 70-80°C. In this way, because the pressure in the third evaporator is low, the temperature of water during evaporation will be lowered, reducing the energy consumption during operation. Part of the boron ions, about 10-50ppm, is included in the evaporated moisture, which is led to the condenser 70 by the exhaust pipe 51 . The crystallized boron-containing compound is transferred to the centrifugal dehydrator 60 by the conveying mechanism 52 (such as a conveyor belt).

The centrifugal dehydrator 60 communicates with the evaporative concentrator 50, introduces the boron-containing compound, removes the water contained in the boron-containing compound by high-speed centrifugal rotation, and leaves crystallized sodium borate (Na ₂ Ba ₄ O ₇ ). Sodium borate, namely borax, has a wide range of industrial applications and can be taken out from the opening 61 of the centrifugal dehydrator 60 (as shown by the white dot arrow on a black background). The water taken out passes through a first return pipe 62, and is reinjected into the first ion exchanger 40 through switching of the first control valve V1 for ion exchange again without being directly discharged into the environment.

The condenser 70 communicates with the exhaust pipe 51 of the evaporative concentrator 50, introduces the evaporated moisture of the evaporative concentrator 50, and lowers the temperature of the evaporated moisture to room temperature (such as about 25° C., depending on the space during operation) in a water-cooled manner. depends on the temperature). The condensed evaporated water flows to the second ion exchanger 80 along the water pipe 71 .

The second ion exchanger 80 communicates with the condenser 70, introduces the condensed evaporated water, and exchanges part of the boron ions in the condensed evaporated water. The second ion exchanger 81 includes a second water pump 81 and a plurality of boron ion exchange resin towers 82 . The function of the second water pump 81 is to pump the condensed evaporated water into the second ion exchanger 80 . FIG. 1 shows two boron ion exchange resin towers 82 as an example for illustration, and the number is not limited to two in practice. These boron ion exchange resin towers 82 are communicated with the second water pump 81, each other This concatenation. Each boron ion exchange resin tower 82 contains a boron ion exchange resin, which can exchange part of the boron ion exchange in the drawn-in condensed evaporated water. Boron ion exchange resin is a kind of chelating resin with multi-point functional groups, which can interact with boron ions like pincers to adsorb boron ions. The boron chelating resin of Purolite company model S108 is used in the following examples. During saturated adsorption, the boron ion exchange resin tower 82 can be dismantled, and the boron ions adsorbed by the boron chelating resin are replaced with hydrochloric acid, and backwashed back to a workable (boron ion exchange) state with sodium hydroxide. According to the present invention, if the boron ion content of the condensed evaporated water after passing through the second ion exchanger 80 is lower than 0.1 ppm, the condensed evaporated water is directly discharged into the environment (as indicated by the hollow arrow in FIG. 1 ). If the boron ion content of the condensed evaporated water after passing through the second ion exchanger 80 is higher than 0.1 ppm, the condensed evaporated water is cut by the second control valve V2 and returned to the evaporative concentrator 50 through the second return pipe. , mix the soft boron ion-containing water and evaporate again to ensure that the boron ion content is lower than 0.1ppm.

Hereinafter, an example is used to illustrate the treatment result of boron-containing wastewater after passing through the waste liquid boron resource recovery system 1 .

Please refer to FIG. 2 , which shows the changes in the concentration of some ions after the boron-containing wastewater is treated by some equipment in the waste liquid boron resource recovery system 1 in this embodiment. The boron-containing wastewater is industrial wastewater after flue gas desulfurization in power plants, and the experimental volume is 5 tons. After the boron-containing wastewater enters the wastewater storage tank 10, the concentrations of B ³⁺ , Ca ²⁺ , Mg ²⁺ , Cl ^- , NO ₃ ^- and SO ₄ ^2- were measured to be 533.3ppm, 1563.4ppm, 1611.0ppm, 7736.1ppm, 765.9ppm and 4139.6ppm. After passing through the solid-liquid separator 30, the concentration of each ion in the boron-containing ion water has decreased, and the reason is that a part is included in the solid waste. The solid waste mainly adsorbed Ca ²⁺ and Mg ²⁺ in a large proportion, and the hardness of boron-containing water decreased obviously, but it was still quite "hard". Therefore, after passing through the first ion exchanger 40, the concentration of all listed ions except B3 ⁺ decreased. Ca ²⁺ and Mg ²⁺ are reduced to 0.5ppm, which makes the boron-containing ion water truly called soft boron-containing ion water. The content of Cl ^- is still significant, but it has not caused the restriction on environmental discharge.

Regarding B ³⁺ , its concentration in the evaporated water of the evaporative concentrator 50 has dropped to 47.6ppm, which is still below the discharge standard. Therefore, after being treated by the second ion exchanger 80, most of the B ³⁺ in the condensed evaporated water is exchanged and taken out, so that the B ³⁺ concentration of the treated condensed evaporated water is effectively reduced to less than 0.1ppm, which can direct discharge. At the same time, in the water obtained by centrifugal dehydrator 60 through high-speed centrifugation, the B ³⁺ concentration has been mixed with crystallized sodium borate water, so the B ³⁺ concentration does not drop but rises. However, the amount of recovered water here is very small, and ion exchange can be performed again to ensure that the excessively high concentration of B ³⁺ will not pollute the environment.

Although the present invention has been disclosed above in terms of implementation, it is not intended to limit the present invention. Anyone with ordinary knowledge in the technical field may make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, The scope of protection of the present invention should be defined by the scope of the appended patent application.

1: Waste liquid boron resource recovery system

10: Wastewater storage tank

20: pH adjustment tank

30: Solid-liquid separator

31: Main structure

32: filter plate

33: Oil pressure rod

34: High pressure liquid delivery pipe

35: Liquid collection tank

40: The first ion exchanger

41: The first water pump

42: Cation exchange resin tower

43: Anion exchange resin tower

50: evaporative concentrator

51: exhaust pipe

52: Conveyor mechanism

60: centrifugal dehydrator

61: opening

62: The first return pipe

70: condenser

71: water pipe

80: Second ion exchanger

81:Second water pump

82: Boron ion exchange resin tower

A: Alkaline regulator

BW: boron ionized water

P1: The first diversion pump

P2: The second diversion pump

S: source of generation

SW: solid waste

V1: first control valve

V2: Second control valve

Claims (10)

A waste liquid boron resource recovery system, comprising: a waste water storage tank for storing a boron-containing waste water produced during the process of removing sulfur oxides from flue gas emitted by petrochemical combustion power facilities; a pH value adjustment tank, and The wastewater storage tank is connected, and after introducing the boron-containing wastewater, an alkaline regulator is added to adjust the pH value of the boron-containing wastewater to between 10-12 to become an alkaline boron-containing wastewater; a solid-liquid separator, and The pH value adjustment tank is connected to introduce and squeeze the alkaline boron-containing waste water with high pressure to form separated boron-containing ion water and solid waste; a first ion exchanger is connected to the solid-liquid separator to introduce the boron-containing wastewater Ionized water, exchanging part of the alkaline earth metal cations and acid radical anions in the boron-containing ion water to form a soft boron-containing ion water; an evaporation concentrator, connected to the first ion exchanger, for Evaporating part of the moisture in the soft boron-containing ion water at a temperature lower than 80°C, leaving a crystallized boron-containing compound; and a centrifugal dehydrator, connected to the evaporation concentrator, introducing the boron-containing compound, and rotating at a high speed The method removes the moisture contained in the boron-containing compound, leaving crystalline sodium borate. The waste liquid boron resource recovery system as described in Claim 1, wherein the first ion exchanger further includes: a pump for pumping the boron-containing ion water into the first ion exchanger; a plurality of cation exchange resin towers , communicated with the water pump and connected in series with each other, each cation exchange resin tower contains a cation exchange resin to exchange part of the alkaline earth metal cations in the pumped water containing boron ions; and A plurality of anion exchange resin towers are communicated with these cation exchange resin towers and connected in series with each other, each anion exchange resin tower contains an anion exchange resin, and the boron-containing ion water after ion exchange through these cation exchange resin towers is The partial acid radical anion exchange is taken out. The waste liquid boron resource recovery system as described in Claim 2, wherein the cation exchange resin is a weak acid type cation exchange resin, and the anion exchange resin is a weak base type anion exchange resin. The waste liquid boron resource recovery system as described in Claim 1, further comprising: a condenser, communicated with the evaporative concentrator, introducing the evaporated water from the evaporative concentrator, and reducing the temperature of the evaporated water to room temperature; and a second ion exchanger, which communicates with the condenser, introduces the condensed evaporated water, and takes out part of the boron ion exchange in the condensed evaporated water. The waste liquid boron resource recovery system as described in claim 4, wherein if the boron ion content of the condensed evaporated water after passing through the second ion exchanger is lower than 0.1ppm, the condensed evaporated water is directly discharged; if the condensed evaporated water After the water passes through the second ion exchanger and the boron ion content is higher than 0.1 ppm, the condensed evaporated water is injected back into the evaporation concentrator, mixed with the soft boron ion-containing water and then evaporated again. The waste liquid boron resource recovery system as described in Claim 4, wherein the second ion exchanger further comprises: a second pump for pumping condensed evaporated water into the second ion exchanger; and a plurality of boron ions The exchange resin tower communicates with the second water pump and is connected in series with each other. Each boron ion exchange resin tower contains boron ion exchange resin, and part of the boron ion exchange in the drawn-in condensed evaporated water is taken out. The waste liquid boron resource recovery system as described in Claim 1, wherein the alkalinity regulator is sodium hydroxide (NaOH). The waste liquid boron resource recovery system according to claim 1, wherein the alkaline earth metal cations include calcium ions (Ca ²⁺ ) and magnesium ions (Mg ²⁺ ). The waste liquid boron resource recovery system according to Claim 1, wherein the acid anion is chloride ion (Cl ^- ), nitrate ion (NO ₃ ^- ) or sulfate ion (SO ₄ ^2- ). The waste liquid boron resource recovery system as described in Claim 1, wherein the solid-liquid separator is a centrifugal solid-liquid separator, a screen-type solid-liquid separator or a plate-and-frame filter press.

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