A rapid dehydration process for shield slurry

Abstract

The present invention discloses a shield mud, wherein a high molecular weight polymer and bentonite are added to the mud to achieve a funnel viscosity of 25 to 45 seconds and a filtration loss of less than 20 mL. The present invention also discloses a rapid dehydration system for the shield mud, comprising a waste mud mixing drum with a stirring mechanism, a polarized glass cover disposed outside the waste mud mixing drum, and a plate-and-frame filter press. Ultraviolet lamps are provided on the inner sidewall and bottom plate of the polarized glass cover, and light emitted by the ultraviolet lamps illuminates the waste mud mixing drum. The waste mud mixing drum includes a feed inlet and a discharge inlet, the feed inlet of the waste mud mixing drum being connected to a waste mud pool via a feed delivery pipe; the discharge inlet of the waste mud mixing drum being connected to the plate-and-frame filter press via a discharge delivery pipe.

Description

Technical Field

[0001] The invention relates to shield slurry and also to a rapid dehydration system for the shield slurry. Background Art

[0002] In recent years, slurry shield construction technology, with its advantages of low surface footprint and minimal ground disturbance, has been widely used in various projects such as subways and highways. This process generates a huge amount of waste mud. Slurry shields use pressurized mud to support the excavation face, continuously forming a mud film to maintain its stability. This waste mud inevitably contains some admixtures (the additives added when the mud film forms). This results in a complex composition of the waste mud, which has a significant negative impact on its dewatering rate.

[0003] At present, bentonite and CMC are often added to form a good mud film during the construction of slurry shield. That is, during the mud use stage, the mud film formed by adding bentonite and CMC can better maintain the stability of the slurry shield excavation face. However, in the subsequent dehydration process, the residual bentonite and CMC will form a mud film again under the action of the plate and frame filter press to hinder dehydration. Therefore, it is necessary to add various flocculants such as polyacrylamide to make the soil particles in the mud form large flocs, promote mud-water separation, and thus increase the dehydration speed.

[0004] In response to the problem of rapid dehydration and reduction of shield mud, there are currently a large number of studies on the addition of flocculants to accelerate dehydration. For example, the invention patent with application number 202110903283.0 discloses a new dehydration system. By adding PAM (polyacrylamide) liquid to the mud for mixed reaction and then centrifugal dehydration, the dehydration efficiency of the mud is guaranteed to a certain extent. For example, the invention patent with application number 201910003232.5 discloses a combined process of "rolling dehydration + hot gas vortex dehydration". During the hot gas vortex dehydration process, manganese carbonate and sodium peroxide are added to accelerate particle sedimentation, thereby achieving the purpose of efficient dehydration. However, the above processes all require continuous addition of agents during the dehydration process. Although there is a certain improvement effect on increasing the dehydration speed, a large amount of flocculants need to be added to completely dehydrate the huge amount of waste mud, which will greatly increase the cost of mud treatment. In summary, the existing technology is based on the large amount of waste mud that has been generated and promotes mud-water separation by adding various agents such as PAM (polyacrylamide), PAC (polyaluminum chloride), manganese carbonate and sodium peroxide to achieve the purpose of rapid dehydration, but such methods will greatly increase the cost of mud treatment. Summary of the Invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a shield mud, which can not only meet the construction requirements of the excavation face of slurry shield construction, but also can achieve rapid dehydration and weight reduction without adding any chemicals; another purpose of the present invention is to provide a rapid dehydration system for the above-mentioned shield mud, which cooperates with the components of the shield mud to achieve rapid dehydration and weight reduction of the shield mud without adding any chemicals.

[0006] Technical solution: The shield tunneling mud of the present invention is prepared by adding high molecular weight polymer and bentonite to the mud so that the mud meets the funnel viscosity value of 25 to 45s and the filtration loss of <20mL.

[0007] Wherein, the high molecular polymer is chitosan or modified starch.

[0008] The mass concentration of the prepared chitosan aqueous solution is 4%, the amount of chitosan added to the mud is 8% of the mud mass; and the amount of bentonite added is 3% of the mud mass.

[0009] The modified starch is prepared by etherifying starch with a quaternary ammonium salt. The modified starch aqueous solution is prepared at a concentration of 4% by mass. The amount of modified starch added to the mud is 20% by mass of the mud; the amount of bentonite added is 3% by mass of the mud. The modified starch of the present invention is prepared using the method reported in the following literature: Research Progress on Application of Green Starch Flocculants [J]. Sichuan Environment, 2010, 29(02): 104-108.

[0010] Among them, the above-mentioned rapid dehydration system of shield mud includes a waste mud mixing drum with a stirring mechanism, a polarized glass cover arranged outside the waste mud mixing drum, and a plate and frame filter press; ultraviolet lamps are provided on the inner side wall and the bottom plate of the polarized glass cover, and the light emitted by the ultraviolet lamp is irradiated on the waste mud mixing drum; the waste mud mixing drum includes a feed port and a discharge port, and the feed port of the waste mud mixing drum is connected to the waste mud pool through a feed conveying pipe; the discharge port of the waste mud mixing drum is connected to the plate and frame filter press through a discharge conveying pipe.

[0011] Among them, the polarized glass cover is made of polarized glass, so that the ultraviolet rays entering the polarized glass cover are continuously refracted in a limited space, and combined with the stirring action of the stirring mechanism in the waste mud mixing drum, the waste mud is fully irradiated with ultraviolet rays, that is, every part of the waste mud can be fully irradiated, thereby realizing the rapid conversion of high-water-content difficult-to-dewater slurry into low-water-content easy-to-dewater slurry, which is also conducive to subsequent rapid dehydration.

[0012] The waste mud mixing drum is made of ultraviolet-transparent quartz glass, allowing sunlight and ultraviolet radiation from the UV lamp to directly act on the waste mud. The transparent mixing drum can directly utilize the ultraviolet radiation in sunlight to degrade the waste mud when the sunlight is bright, saving costs.

[0013] Among them, the discharge port of the waste mud mixing drum is set at the bottom of the drum, and a solenoid valve is provided at the discharge port to facilitate controlling the stirring time of the mud in the mixing drum.

[0014] It also includes a mud pressure pump and a flow meter installed on the feed conveying pipeline and the discharge conveying pipeline. The flow meter located on the feed conveying pipeline is used to monitor the flow rate of the mud conveyed into the abandoned mud mixing drum; the flow meter located on the discharge conveying pipeline is used to monitor the flow rate of the mud after degradation.

[0015] This also includes a mud preparation pool. The mud prepared in the mud preparation pool is transported to the shield machine excavation face for shield tunneling construction. The waste mud generated during the construction process is transported to the waste mud pool, and the waste mud that cannot be recycled is sent into the waste mud mixing drum through the feed conveying pipeline.

[0016] The mud prepared in the mud preparation pool is transported to the shield machine excavation face for shield tunneling construction. The waste mud generated during the construction process is transported to the waste mud pool. The waste mud that cannot be recycled is transported through the feed pipeline at a rate of 500m 3 / h flow rate into the waste mud mixing drum for ultraviolet radiation degradation, with an irradiation intensity of 30.7mW / cm 2 , after 30 minutes, the viscosity and filtration loss of the mud in the waste mud mixing drum were sampled and tested. At this time, the viscosity of the mud was 5-8s, and the filtration loss was 45-48 mL (the present invention can achieve basically complete degradation of the high molecular polymer in the mud within 30 minutes at this speed and irradiation intensity). The mud pressure pump on the feed conveying pipeline and the stirring mechanism in the waste mud mixing drum were turned off, the supernatant in the mixing drum was extracted, and then the discharge port was opened and transported to the plate and frame filter press for dehydration through the discharge conveying pipeline.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) By formulating shield mud with specific components, the present invention can not only make the mud meet the construction requirements of the slurry shield, but also can quickly dehydrate it without adding any chemicals in the subsequent treatment of waste mud, thereby achieving rapid reduction of waste mud. (2) The dehydration system of the present invention cooperates with the components of the shield mud to quickly convert high-water-content difficult-to-dehydrate slurry into low-water-content easy-to-dehydrate slurry, and the dehydration process does not require the addition of flocculants and other chemicals. The system can be used continuously for a long time, and the water filtered out of the system process can be directly discharged without causing pollution to the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the system of the dehydration system of the present invention. DETAILED DESCRIPTION

[0019] like Figure 1 As shown, the rapid dehydration system of shield mud of the present invention includes a waste mud mixing drum 5 with a stirring mechanism, a polarized glass cover 6 covered on the outside of the waste mud mixing drum 5, and a plate and frame filter press 9; ultraviolet lamps 7 are provided on the inner side wall and the bottom plate of the polarized glass cover 6, and the light emitted by the ultraviolet lamps 7 is irradiated on the waste mud mixing drum 5; the waste mud mixing drum 5 includes a feed port and a discharge port, and the feed port of the waste mud mixing drum 5 is connected to the waste mud pool through a feed conveying pipe 4; the discharge port of the waste mud mixing drum 5 is connected to the plate and frame filter press 9 through a discharge conveying pipe 8.

[0020] Polarized glass cover 6 is installed around the waste mud mixing drum 5, covering the waste mud mixing drum 5 and refracting ultraviolet rays. Polarized glass cover 6 is made of polarized glass, so that the ultraviolet light within polarized glass cover 6 is continuously refracted within the limited space. Combined with the stirring action of the stirring mechanism within the waste mud mixing drum 5, the waste mud is fully irradiated with ultraviolet rays. Ultraviolet lamp 7 is installed on the inner wall of polarized glass cover 6, providing an ultraviolet light source to irradiate the waste mud. The waste mud mixing drum 5 is made of ultraviolet-transmissive quartz glass, allowing sunlight and ultraviolet rays radiated by the ultraviolet lamp to directly act on the waste mud. A plate and frame filter press 9 is installed at the end of the discharge conveying pipe 8 to filter and dehydrate the degraded waste mud to form a mud cake.

[0021] The discharge port of the waste mud mixing drum 5 is set at the bottom of the drum, and a solenoid valve is provided at the discharge port to facilitate the control of the stirring time of the mud in the mixing drum. The dehydration system of the present invention also includes a mud pressure pump 2 and a flow meter 3 arranged on the feed conveying pipe 4 and the discharge conveying pipe 8. The flow meter located on the feed conveying pipe 4 is used to monitor the flow rate of the mud conveyed into the waste mud mixing drum 5; the flow meter located on the discharge conveying pipe 8 is used to monitor the flow rate of the mud after degradation. By comparing the flow rate changes before and after the degradation of the mud, the change in the viscosity of the waste mud can be known, which facilitates the adjustment of the pressure of the mud pressure pump 2 on the feed conveying pipe 4, thereby controlling the feed speed of the waste mud mixing drum 5 and achieving more efficient degradation.

[0022] The dehydration system of the present invention also includes a mud preparation pool 1. The mud preparation pool 1 cannot be exposed to sunlight for a long time and needs to be covered with shading materials to prevent the prepared shield mud from changing its properties under the irradiation of sunlight. The mud prepared in the mud preparation pool 1 is transported to the excavation face of the shield machine for shield tunneling construction. The waste mud generated during the construction process is transported to the waste mud pool. The waste mud that cannot be recycled is sent to the waste mud mixing drum 5 through the feed conveying pipe 4. The mud preparation pool 1 is used to prepare shield mud that meets the construction requirements of the slurry shield. It is connected to the shield machine through a mud transport pipeline. The mud pool needs to be covered with shading materials to prevent the high molecular polymers in the mud from being degraded under sunlight for a long time, which affects the film-forming effect of the mud during the slurry shield construction process. The waste mud pool is used to store waste mud generated during the operation of the shield machine. Some of the waste mud with better properties can be reused in the preparation of shield mud through the transportation pipeline, and some mud with poorer properties (non-recyclable) is transported to the waste mud mixing drum 5 for degradation through the feed delivery pipeline 4. The mud pressure pump 2 on the feed delivery pipeline 4 is used to adjust the mud delivery pressure so that the mud transportation speed in the system can be adjusted. The waste mud mixing drum 5 contains two components: one is the mud stirring component and the other is the photodegradation irradiation component. The mud stirring component continuously stirs the waste mud in the mixing drum, and with the continuous irradiation of the photodegradation irradiation component, the mud is degraded in a relatively fast time. The basis for the completion of degradation is that the mud viscosity value drops to 5-8s and the filtration loss reaches 45-48mL.

[0023] Example 1

[0024] Through experiments, it was found that when the chitosan aqueous solution concentration was 4%, the addition amount was 8% of the mud mass, and the bentonite addition amount was 3% of the mud mass, the requirements for the mud funnel viscosity value and filtration loss were met. At this time, the mud funnel viscosity value was 38s and the filtration loss was <20mL.

[0025] First, cover the mud preparation pool with a light shield, then prepare the shield mud according to the above ratio, test its funnel viscosity and filtration loss, and use it for slurry shield construction after it meets the construction requirements. After screening the waste mud generated during the construction process, send the waste mud that cannot be recycled to the waste mud mixing drum through the feed conveying pipeline, turn on the mud pressure pump, flow meter, and stirring mechanism and ultraviolet lamp of the waste mud mixing drum on the feed conveying pipeline, and adjust the mud pressure pump on the feed conveying pipeline to make the mud flow rate at 500m 3 / h, when the mud in the mixing drum reaches about 90% of the drum volume, the mud pressure pump is turned off, the delivery of waste mud is stopped, and ultraviolet degradation of the waste mud in the mixing drum is started. The mixing speed of the mixing drum is 500r / min, and the irradiation intensity is 30.7mW / cm 2After 30 minutes of degradation, the viscosity and filtration loss of the mud funnel were tested. At this time, the mud viscosity value dropped to 5s and the filtration loss reached 48mL, indicating that the degradation was completed. At this time, the supernatant with mud and water separation was extracted from the top, and the discharge port at the bottom of the mixing drum and the mud pressure pump on the discharge conveying pipeline were opened. The mud was transported to the plate and frame filter press through the discharge conveying pipeline for filtration and dehydration. The dehydration rate could reach about 70% in 1 hour.

[0026] The cost of manufacturing the mud admixture in Example 1 is 53.49 yuan / ton. Since no admixture is added during dehydration, the dehydration cost is 0, and the total cost is 53.49 yuan / ton.

[0027] Example 2

[0028] The treatment method of Example 2 is essentially the same as that of Example 1, with the only difference being that modified starch is used as the slurry additive in Example 2. The modified starch aqueous solution has a mass concentration of 4% and is added in an amount of 20% by mass of the slurry, and the bentonite content is 3% by mass of the slurry. At this point, the slurry funnel viscosity is 36s and the fluid loss is less than 20mL. The remaining steps of Example 2 are consistent with those of Example 1, and approximately 68% of the water removal rate can be achieved in 1 hour.

[0029] After the on-site sampling test of Example 2, the shield mud prepared with modified starch can form a good mud film at the bottom after vacuum filtration (high density, which can effectively prevent water seepage), indicating that it has good film-forming stability and also achieves good results in the subsequent photodegradation process.

[0030] The cost of manufacturing the mud admixture in Example 2 is 56.42 yuan / ton. Since no admixture is added during dehydration, the dehydration cost is 0, and the total cost is 56.42 yuan / ton.

[0031] Comparative Example 1

[0032] Comparative Example 1 uses the shield mud preparation method of bentonite + CMC in the existing technology, the bentonite blending amount is 6% of the mud mass, the mass concentration of CMC in the CMC aqueous solution is 2%, and the blending amount is 2% of the mud mass. At this time, the mud funnel viscosity value is 36s and the filtration loss is <20mL.

[0033] The waste mud is subsequently dehydrated by adding a flocculant, and the flocculant is PAC (polyaluminium chloride) with a blending amount of 5%. Comparative Example 1: Shield mud prepared based on bentonite + CMC is dehydrated by adding PAC (polyaluminium chloride) for flocculation.

[0034] During the implementation process, it was found that if PAC was not added, the dehydration rate was very slow, with only about 7% of the dehydration achieved in 1 hour. By adding PAC (polyaluminium chloride) to treat the waste mud, a better mud-water separation effect was achieved, which significantly improved the subsequent dehydration rate, with about 70% of the dehydration achieved in 1 hour. However, due to the large amount of waste mud generated during shield construction, if flocculants were used for treatment, a large amount of agents would need to be added, which would greatly increase the cost of dehydrating the waste mud in the project. In Comparative Example 1, the cost of the slurry admixture was 45.46 yuan / ton, and due to the addition of PAC as a dehydration aid, the dehydration cost was 22.6 yuan / ton, with a total cost of 68.06 yuan / ton.

[0035] Comparative Example 2

[0036] Comparative Example 2 uses the shield mud preparation method of bentonite + CMC in the prior art, the bentonite blending amount is 6% of the mud mass, the mass concentration of CMC in the CMC aqueous solution is 2%, and the blending amount is 2% of the mud mass. The subsequent waste mud is dehydrated using the dehydration system of the present invention (the various process parameters in the dehydration process are consistent with those in Example 1).

[0037] During implementation, it was found that the shield mud prepared with bentonite + CMC was still poorly dehydrated by the filter press after being degraded for 6 hours by the photodegradation device in the dehydration system, with only about 18% of the water removed in 6 hours. This is because ultraviolet rays cannot destroy the mud film formed by the residual bentonite + CMC in the mud under the filter press. Therefore, not all shield muds can be quickly dehydrated using the system of the present invention.

[0038] Comparative Example 3

[0039] The shield mud preparation process of Comparative Example 3 is consistent with that of Example 1, except that the photodegradation process of the waste mud is not completed in the dehydration system of Example 1, but is naturally photodegraded in an open-air mud pool.

[0040] During the implementation process, it was found that a large amount of mud accumulated in the mud pool. For the mud that had already settled in the lower part, the ultraviolet rays in natural light could not penetrate the upper mud to effectively degrade it. After 24 hours of degradation under natural light conditions, the dehydration effect was still relatively poor, and only about 35% of the water could be dehydrated in 24 hours, which failed to achieve the purpose of rapid dehydration and reduction.

Claims

1. A rapid dehydration process for shield slurry, characterized by: The shield tunneling mud is prepared by adding a high molecular weight polymer and bentonite to the mud so that the mud meets the funnel viscosity value of 25-45s and the filtration loss of less than 20mL; wherein the high molecular weight polymer is chitosan or modified starch. When the high molecular weight polymer is chitosan, the mass concentration of the prepared chitosan aqueous solution is 4%, and the amount of chitosan added to the mud is 8% of the mud mass; the amount of bentonite added is 3% of the mud mass; when the high molecular weight polymer is modified starch, the mass concentration of the prepared modified starch aqueous solution is 4%, and the amount of modified starch added to the mud is 20% of the mud mass; the amount of bentonite added is 3% of the mud mass; the modified starch is prepared by an etherification reaction between starch and a quaternary ammonium salt; The dehydration process adopts the following dehydration system for dehydration, the dehydration system includes a waste mud mixing drum (5) with a stirring mechanism, a polarized glass cover (6) arranged outside the waste mud mixing drum (5), and a plate and frame filter press (9); an ultraviolet lamp (7) is provided on the inner wall and the bottom plate of the polarized glass cover (6), and the light emitted by the ultraviolet lamp (7) is irradiated on the waste mud mixing drum (5); the waste mud mixing drum (5) includes a feed port and a discharge port, the feed port of the waste mud mixing drum (5) is connected to the waste mud pool through a feed conveying pipe (4); the discharge ... The material port is connected to the plate and frame filter press (9) through the discharge conveying pipe (8); and the device also includes a mud preparation pool (1); the mud preparation pool (1) is covered with a light shield, and the mud prepared in the mud preparation pool (1) is transported to the shield machine excavation face for shield tunneling construction. The waste mud generated during the construction process is transported to the waste mud pool, and the waste mud that cannot be recycled is sent to the waste mud mixing drum (5) through the feed conveying pipe (4) at a flow rate of 500m³ / h for ultraviolet irradiation degradation. The stirring speed of the waste mud mixing drum (5) is 500r / min, and the irradiation intensity is 30.7mW / cm 2 , after 30 minutes, the viscosity and filtration loss of the mud in the waste mud mixing drum (5) were sampled and tested. At this time, the viscosity of the mud was 5~8s, and the filtration loss was 45~48mL. The mud pressure pump (2) on the feed conveying pipe (4) and the stirring mechanism in the waste mud mixing drum (5) were closed, and the supernatant in the waste mud mixing drum (5) was extracted. Then, the discharge port was opened and the supernatant was transported to the plate and frame filter press (9) for dehydration through the discharge conveying pipe (8).

2. The rapid dehydration process for shield slurry according to claim 1, characterized in that: The polarized glass cover (6) is made of polarized glass, so that the ultraviolet light in the polarized glass cover (6) is continuously refracted in a limited space, and cooperates with the stirring action of the stirring mechanism in the waste mud stirring drum (5) to ensure that the waste mud is fully irradiated with ultraviolet light.

3. The rapid dehydration process for shield slurry according to claim 1, characterized in that: The waste mud mixing drum (5) is made of ultraviolet-transmissive quartz glass, so that sunlight and ultraviolet rays radiated by the ultraviolet lamp can directly act on the waste mud.

4. The rapid dehydration process for shield slurry according to claim 1, characterized in that: The waste mud mixing drum (5) has a discharge port arranged at the bottom of the drum, and a solenoid valve is provided at the discharge port to facilitate control of the stirring time of the mud in the mixing drum.

5. The rapid dehydration process for shield slurry according to claim 1, characterized in that: It also includes a mud pressure pump (2) and a flow meter (3) arranged on a feed delivery pipeline (4) and a discharge delivery pipeline (8). The flow meter located on the feed delivery pipeline (4) is used to monitor the flow rate of the mud delivered to the waste mud mixing drum (5); and the flow meter located on the discharge delivery pipeline (8) is used to monitor the flow rate of the mud after degradation.

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