Sludge drying method and sludge concentration tank for coal natural gas project

Abstract

The invention relates to a sludge drying method for a coal natural gas project and a sludge thickening tank. S01, the collected wet sludge is subjected to concentration and dehydration treatment, and a mud cake with the water content lower than 80% is obtained; s02, conveying the sludge cake into a sludge drying machine in a sludge dewatering room through a shaftless screw conveyor and an inclined shaftless screw conveyor for drying; s03, drying the wet sludge by a sludge drying machine to obtain sludge particles with the water content of less than 35% and tail gas; s041, the sludge particles are conveyed into a dry sludge storage bin through a spiral conveyor and a bucket elevator to be stored, and then the sludge particles are conveyed out through a sludge vehicle. The method has the beneficial effects that through the steps, on the basis that the service life of equipment is prolonged, sludge can be effectively dried, and tail gas generated during drying can be effectively treated.

Description

Technical Field

[0001] The present invention relates to the technical field of sludge drying, and specifically to a method for drying sludge in a coal-to-natural gas project and a sludge thickening tank. Background Art

[0002] In the coal gasification stage of a coal-to-natural gas project, a large amount of sewage is easily generated due to tap water washing water, steam, etc. This sewage, together with a small amount of domestic sewage, plant floor flushing water, and initial rainwater in the plant area, which are sewage containing organic pollutants, enters the sewage treatment device.

[0003] In the sewage treatment stage, a large amount of coal chemical sludge is easily generated in equipment such as sedimentation tanks (biochemical sludge), flotation tanks (wastewater scum and sediment sludge), and secondary sedimentation tanks (chemical sludge) in the sewage treatment device; these coal chemical sludges have good plasticity, so they have a high water content, making the sludge itself viscous and easy to adhere to the inner wall of the dryer during the drying process, increasing the difficulty of drying, not only affecting the drying efficiency but also easily damaging the drying equipment; at the same time, because part of the sewage comes from the coal-to-natural gas production process, it is easy to contain volatile organic compounds, and during the drying process, a large amount of toxic gases are easily generated, which is equivalent to the tail gas (water vapor and escaping dust) generated during ordinary sludge drying, and is more harmful to the environment and human health. Therefore, when treating the sludge produced from coal chemical wastewater, more strict and effective measures need to be taken to prevent the emission and diffusion of harmful gases. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for drying sludge in a coal-to-natural gas project and a sludge thickening tank to solve the above problems existing in the prior art.

[0005] The technical solution for the present invention to solve the above technical problems is as follows: A method for drying sludge in a coal-to-natural gas project includes the following steps;

[0006] Step S01: Concentrate and dehydrate the collected wet sludge to obtain a mud cake with a water content of less than 80%;

[0007] Step S02: Send the mud cake into a sludge dryer in the sludge dehydration room through a shaftless screw conveyor and an inclined shaftless screw conveyor for drying;

[0008] Step S03: After the wet sludge is dried by the sludge dryer, obtain sludge particles with a water content of less than 35% and tail gas;

[0009] Step S041: Transport the sludge particles to a dry sludge storage bin through a screw conveyor and a bucket elevator for storage, and then transport them out by a sludge truck;

[0010] Step S042: The tail gas is transported through a pipeline into the dust collector for dust removal to obtain gas with a lower powder content. The gas is sent to the scrubber for subsequent treatment. Meanwhile, the dust collected by the dust collector is transported into the dry sludge storage bin through a screw conveyor;

[0011] Step S0421: The gas is introduced into the scrubber to directly contact with process water for cooling, washing, and dust removal. The washing water is discharged into the nearby sewage well. After the purified tail gas is demisted, it is pressurized by a draft fan and discharged into the deodorization system.

[0012] The beneficial effects of the present invention are as follows: Before the sludge is sent to the sludge dryer for drying, the wet sludge is concentrated and dehydrated to reduce the water content of the wet sludge to less than 80%, so that the water to be removed during the drying process of the sludge dryer is reduced, and the processing efficiency of the dryer is improved. At the same time, due to the reduction of the sludge water content, a large amount of free water and interstitial water in the sludge are removed, and the interaction force between sludge particles is weakened, thereby reducing the viscosity of the sludge, reducing the contact area and adhesion force between the sludge and the inner wall of the equipment, thus reducing the occurrence of adhesion phenomena, further reducing the friction with the equipment, extending the service life of the equipment, and reducing the maintenance cost; When the drying is completed, the tail gas is sequentially dusted and washed, which can greatly remove harmful components such as particulate matter, acidic gases (such as SO2, HCl, etc.), heavy metal compounds, and volatile organic compounds in the tail gas, reducing the pollution to the atmosphere. At the same time, after the tail gas is purified, the gas is demisted and then pressurized by a draft fan and discharged into the deodorization system, which can further reduce the pollution to the atmosphere; Through the above steps, on the basis of extending the service life of the equipment, the sludge can be effectively dried, and the tail gas generated during drying can be effectively treated.

[0013] On the basis of the above technical solutions, the present invention can also be improved as follows.

[0014] Further, the concentration and dehydration treatment in step S01 specifically includes the following steps:

[0015] Step S011: The wet sludge is transported to the sludge thickening tank for sedimentation separation and concentration of mud and water, so that the water content of the wet sludge is reduced from 99.7% to 98.0%, and the solid content is increased from 0.3% to 2.0%;

[0016] Step S012: The preliminarily dehydrated wet sludge is sent to a horizontal spiral centrifuge for secondary dehydration to obtain a mud cake with a water content lower than 80% and a chemical agent consumption reduced by more than 20%; the solid content is increased from 2.0% to more than 20%.

[0017] The beneficial effects of adopting the above further solution are as follows: The water content of the sludge after secondary dehydration can be reduced to less than 80%, or even lower, reaching the ideal state before drying; The sludge with a low water content is easier to remove the remaining water during the drying process, improving the drying efficiency.

[0018] Further, a circulation pipeline is provided on the scrubbing tower in step S0421, and two circulation pumps are arranged in parallel on the circulation pipeline; meanwhile, a water replenishment, spraying, and filter media filtration system is arranged inside the scrubbing tower.

[0019] The beneficial effects of adopting the above further solution are as follows: The circulation pipeline enables the washing liquid to be recycled inside the scrubbing tower. By continuously contacting the tail gas and absorbing the pollutants therein, the washing efficiency is improved; while the water replenishment system is used to replenish fresh washing liquid into the scrubbing tower to maintain the normal liquid level and concentration of the washing liquid. Description of the Drawings

[0020] Figure 1 It is a flow chart of a sludge drying method for a coal-to-natural gas project of the present invention;

[0021] Figure 2 It is a system diagram of a sludge drying method for a coal-to-natural gas project of the present invention;

[0022] Figure 3 It is a schematic structural diagram of a sludge thickening tank of the present invention. Specific Embodiments

[0023] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0024] Embodiment 1

[0025] As Figure 1 shown, a sludge drying method for a coal-to-natural gas project includes the following steps;

[0026] Step S01: Concentrate and dehydrate the collected wet sludge to obtain a mud cake with a water content of less than 80%;

[0027] Step S02: Send the mud cake to a sludge dryer in the sludge dewatering room through a shaftless screw conveyor and an inclined shaftless screw conveyor for drying;

[0028] Step S03: After the wet sludge is dried by the sludge dryer, sludge particles with a water content of less than 35% and tail gas are obtained;

[0029] Step S041: Convey the sludge particles to a dry sludge storage bin through a screw conveyor and a bucket elevator for storage, and then transport them out by a sludge truck;

[0030] Step S042: Convey the tail gas to the inside of a dust collector through a pipeline for dust removal to obtain a gas with a low powder content, send the gas to a scrubbing tower for subsequent treatment, and at the same time, convey the dust collected by the dust collector to the dry sludge storage bin through a screw conveyor;

[0031] Step S0421: Pass the gas into the scrubbing tower to directly contact with process water for cooling, washing, and dust removal. The washing water is discharged into the nearby sewage well or collection pond, and the purified tail gas is de-misted and then pressurized by an induced draft fan and discharged into the deodorization system.

[0032] Before the sludge is sent to the sludge dryer for drying, the wet sludge is concentrated and dehydrated to reduce the water content of the wet sludge to less than 80%, so that the amount of water to be removed during the drying process of the sludge dryer is reduced, and the processing efficiency of the dryer is improved. At the same time, due to the reduction of the sludge water content, a large amount of free water and interstitial water in the sludge are removed, the interaction force between sludge particles is weakened, thereby reducing the viscosity of the sludge, reducing the contact area and adhesion force between the sludge and the inner wall of the equipment, thus reducing the occurrence of adhesion phenomena, further reducing the friction with the equipment, prolonging the service life of the equipment, and reducing the maintenance cost; when the drying is completed, the tail gas is sequentially dusted and washed, which can greatly remove harmful components such as particulate matter, acidic gases, heavy metal compounds, and volatile organic compounds in the tail gas, reducing the pollution to the atmosphere. At the same time, after purifying the tail gas, the gas is de-misted and then pressurized by an induced draft fan and discharged into the deodorization system, which can further reduce the pollution to the atmosphere; through the above steps, on the basis of prolonging the service life of the equipment, the sludge can be effectively dried, and the tail gas generated during drying can be effectively treated.

[0033] Among them, the components in the sludge dryer and the screw conveyor that come into contact with the sludge are all made of 304 stainless steel. 304 stainless steel has excellent corrosion resistance and can resist the erosion of most chemical media, including acids, alkalis, and salts. During the sludge treatment process, the coal chemical wet sludge contains various chemical substances, and the corrosion resistance of 304 stainless steel can ensure the long-term stable operation of the components.

[0034] In specific implementation, the dust collector uses a rotary valve for air locking, which can achieve automatic ash discharge without manual operation by staff, realizing automation.

[0035] Example 2

[0036] As Figure 2 shown, this embodiment is a further improvement on the basis of Embodiment 1, specifically as follows:

[0037] Step S011: Transport the wet sludge to the sludge thickening tank for sedimentation separation and concentration of mud and water, so that the water content of the wet sludge is reduced from 99.7% to 98.0%, and the solid content is increased from 0.3% to 2.0%;

[0038] Step S012: The wet sludge after primary dewatering is sent to a horizontal screw centrifuge for secondary dewatering, obtaining a sludge cake with a water content lower than 80% and a chemical consumption reduction of more than 20%; the solid content increases from 2.0% to more than 20%.

[0039] The horizontal screw centrifuge uses centrifugal force for solid-liquid separation, which can quickly remove most of the free water and interstitial water in the sludge, achieving primary dewatering. After primary dewatering, the water content of the sludge decreases, laying a foundation for subsequent secondary dewatering and improving the overall dewatering efficiency. Using the horizontal screw centrifuge for secondary dewatering can further remove the water in the sludge, especially the bound water and capillary water that are difficult to remove. The water content of the sludge after secondary dewatering can be reduced to less than 80%, or even lower, reaching an ideal state before drying. The sludge with a low water content is easier to remove the remaining water during the drying process, improving the drying efficiency.

[0040] Example 3

[0041] As Figure 3 shown, a sludge thickening tank is used for thickening the sludge in step S011. The sludge thickening tank includes a sludge thickening tank body in the shape of a conical hopper, a baffle inside the body, and a sludge scraper installed at the top of the sludge thickening tank body. The sludge thickening tank is connected to the wet sludge inlet through a sludge feeding pump; a weir is settled at the mouth of the sludge thickening tank body. The supernatant outside the weir goes to the plant production sewage pipe or the collection tank for use in centrifuge flushing, realizing the recycling of water; the bottom of the sludge thickening tank body is connected to the horizontal screw centrifuge through a sludge discharge pipe; a sludge discharge pump is arranged on the sludge discharge pipe. The sludge enters the inlet pipe of the sludge scraper through the sludge feeding pump. The sludge settles to the bottom of the tank by gravity and is discharged from the sludge discharge pipe. The sewage surges upward to the outside of the weir and flows into the plant production sewage pipe. Under the continuous sludge scraping of the sludge scraper and the overflow effect of the weir, the water content of the sludge can be decreased and the solid content can be increased. The flushing circulation pipeline forms an oblique jet flow towards the bottom of the tank body, which can solve the problem of sludge deposition and blockage at the bottom of the cone; the sludge concentration after increasing the sludge solid content rate is relatively stable, the sludge treatment capacity is greatly increased, and the chemical consumption is reduced; at the same time, the system sludge discharge is no longer restricted by the insufficient sludge treatment capacity. Specific Example 1

[0043] (1) In terms of direct economy:

[0044] Through the comparison of operation data, the chemical consumption is reduced by at least more than 20%, and the annual chemical cost savings are more than 500,000 yuan.

[0045] (2) In terms of indirect economy:

[0046] Two horizontal scroll centrifuges are shut down, and only one is used: 2*(55 + 15) Kw = 140 Kw / h; The annual electricity cost savings is 140 Kw / h * 24 h * 365 days * 0.5 yuan / Kw = 610,000 yuan; At the same time, the consumption of spare parts and the frequency of maintenance and defect elimination are reduced.

[0047] Reduce the flushing water volume: During the operation of the horizontal scroll centrifuge, production water needs to be used for flushing every shift to prevent sludge blockage; Flushing water volume: 5 m 3 / day * 30 days * 12 months = 1800 m 3 ; The annual water cost savings is 1800 m 3 * 0.5 yuan = 900 yuan.

[0048] There is no increase in moving equipment in this project, no chemical agent consumption and other energy consumption. Only by using the cylindrical body and the bottom cone (cone angle is 105°) structure of the sludge thickening tank can the best sludge-water separation effect and the ability of gravity sludge discharge be achieved.

[0049] After the project is put into operation, the sludge treatment capacity is increased from an average of 35 m 3 / h to 55 m 3 / h, and the flexibility of the system for sludge disposal is increased; The benefits generated after this transformation are put into operation have reached the expected goal, and the material costs are saved.

[0050] Example 4

[0051] As Figure 3 shown, this example is a further improvement on the basis of Example 3, specifically as follows:

[0052] The inner wall of the sludge thickening tank body is inclined upward with a mud baffle; A distribution cone is provided outside the nozzle of the vertical inlet pipe of the sludge scraper; There are multiple sludge discharge holes at the lower part of the sludge thickening tank body, which are correspondingly connected to multiple sludge discharge pipes, and each sludge discharge pipe is connected to the main sludge discharge pipe; The outlet end of the main sludge discharge pipe is connected to the horizontal scroll centrifuge; A flushing pipe and a drain pipe are connected in parallel to the main sludge discharge pipe. The distribution cone can increase the sludge scraping area of the sludge scraper; The sludge discharge of multiple sludge discharge pipes can improve the sludge discharge speed, and at the same time, it can also avoid the system failure that the sludge cannot be discharged in time due to the blockage of a single sludge discharge pipe; After the sludge thickening tank body is emptied through the drain pipe, it is flushed through the flushing pipe, and the flushing circulating pipeline forms an oblique jet flow at the bottom of the tank body, which can solve the problem of sludge deposition and blockage at the bottom of the cone. During specific implementation, the included angle between the mud baffle and the inlet pipe of the sludge scraper is 60°.

[0053] Example 5

[0054] As Figure 2 shown, this example is a further improvement on the basis of Examples 1 to 2, specifically as follows:

[0055] The sludge dryer in step S03 is a paddle dryer, which is an indirect drying type. Indirect drying is achieved through the indirect contact between the heat source and the sludge, and the heat transfer is used to evaporate the moisture in the sludge. This method avoids the direct mixing contact between the heat source and the sludge, reducing the increase in viscosity and caking phenomenon directly caused by high temperature in the sludge. In specific implementation, to prevent material accumulation inside the sludge dryer and sludge sticking to the wall, a scraping plate can be set at the end of the blade. The gap between the scraping plate and the inner wall of the shell needs to be controlled between 15 and 25 mm, which can effectively prevent the sludge from sticking to the inner wall of the shell. At the same time, the drying heat source of the sludge dryer in step S03 uses 0.5 MPa saturated low-pressure steam. After the low-pressure steam is used up, it is transported through a pipeline to the condensate recovery system for recycling. Since a coal chemical company is prone to generating a large amount of steam during the production process, this steam can be directly used as the heat source of the sludge dryer. Since the steam itself is a by-product generated during the production process, using this steam as the heat source can significantly reduce the enterprise's energy cost. Compared with using other external heat sources such as electricity or natural gas, using its own steam resources can save a large amount of energy costs.

[0056] Example 6

[0057] As Figure 2 shown, this embodiment is a further improvement based on Embodiments 1 to 2, specifically as follows:

[0058] A circulation pipeline is provided on the scrubbing tower in step S0421, and two circulation pumps are connected in parallel on the circulation pipeline; at the same time, a water replenishment, spraying, and filter media filtration system is provided inside the scrubbing tower. The circulation pipeline enables the washing liquid to be recycled inside the scrubbing tower. By continuously contacting the tail gas and absorbing the pollutants therein, the washing efficiency is improved. The two circulation pumps connected in parallel ensure the stable flow rate and pressure of the washing liquid during the circulation process, further improving the washing effect; while the water replenishment system is used to supplement fresh washing liquid into the scrubbing tower to maintain the normal liquid level and concentration of the washing liquid. As the washing process progresses, the pollutant concentration in the washing liquid will gradually increase. By supplementing fresh washing liquid, the pollutant concentration can be reduced and the washing effect can be maintained.

[0059] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for drying sludge in a coal-to-natural gas project, characterized in that: The method comprises the following steps: Step S01: Concentrating and dehydrating the collected wet sludge to obtain a sludge cake with a water content of less than 80%; Step S02: sending the mud cake to a sludge dryer in a sludge dewatering room through a shaftless screw conveyor and an inclined shaftless screw conveyor for drying; Step S03: The wet sludge is dried by the sludge dryer to obtain sludge particles and tail gas with a water content of less than 35%; Step S041: conveying the sludge particles to a dry sludge storage bin through a screw conveyor and a bucket elevator for storage, and then transporting them out through a sludge truck; Step S042: The tail gas is conveyed to the dust collector through a pipeline for dust removal to obtain gas with a low powder content, and the gas is conveyed to a washing tower for subsequent treatment. At the same time, the dust collected by the dust collector is conveyed to a dry sludge storage bin through a screw conveyor; Step S0421: The gas is passed into the washing tower to directly contact with process water for cooling, washing and dust removal. The washing water is discharged to the nearest sewage well. The tail gas is purified and demisted, and then pressurized by an induced draft fan and discharged into the deodorization system.

2. The sludge drying method for a coal-to-natural gas project according to claim 1, characterized in that: The concentration and dehydration process in step S01 specifically includes the following steps: Step S011: transporting the wet sludge to a sludge concentration tank for mud-water static sedimentation separation and concentration, so that the moisture content of the wet sludge is reduced from 99.7% to 98.0%, and the solid content is increased from 0.3% to 2.0%; Step S012: The wet sludge after the initial dehydration is sent to a horizontal screw centrifuge for secondary dehydration to obtain a mud cake with a water content of less than 80%, a reagent consumption reduced by more than 20% and a solid content increased from 2.0% to more than 20%.

3. A sludge thickening tank, characterized in that: Used for thickening the sludge in step S011, the sludge thickening tank comprises a conical sludge thickening tank body, a baffle plate inside the body and a scraper arranged on the top of the sludge thickening tank body, the sludge thickening tank is connected with the wet sludge inlet through a sludge feeding pump; an overflow weir is arranged at the pool mouth of the sludge thickening tank body, and the supernatant outside the overflow weir is discharged to the factory production sewage pipe or collection tank; the bottom of the sludge thickening tank body is connected with the horizontal screw centrifuge through a mud discharge pipe; and a mud discharge pump is arranged on the mud discharge pipe.

4. The sludge thickening tank according to claim 3, characterized in that: The inner wall of the sludge thickening tank body is inclined upwardly provided with a mud guard; the scraper is provided with a distribution cone outside the vertically arranged mud inlet pipe; the lower part of the sludge thickening tank body is provided with a plurality of mud discharge holes, correspondingly connected to a plurality of mud discharge pipes, each mud discharge pipe is connected to the mud discharge main pipe; the outlet end of the mud discharge main pipe is connected to the horizontal screw centrifuge; the mud discharge main pipe is connected with a flushing pipe and a drain pipe.

5. The sludge drying method for a coal-to-natural gas project according to claim 1, characterized in that: The sludge dryer in step S03 is a paddle dryer, which is an indirect drying type.

6. The sludge drying method for a coal-to-natural gas project according to claim 1, characterized in that: The drying heat source of the sludge dryer in step S03 is 0.5 MPa saturated low-pressure steam, and the low-pressure steam is transported to the condensate recovery system through a pipeline after use.

7. The sludge drying method for a coal-to-natural gas project according to claim 1, characterized in that: The washing tower in step S0421 is provided with a circulation pipeline, and two circulation pumps are arranged in parallel on the circulation pipeline; meanwhile, the washing tower is provided with a water replenishment, spraying, and filter material filtering system.

8. The method for drying sludge in a coal-to-natural gas project according to claim 1, characterized in that: The parts in contact with the sludge in the sludge dryer and the screw conveyor are all made of 304 type stainless steel.

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