Two-stage continuous sludge thermal hydrolysis full-chain resource utilization process

Abstract

The invention belongs to the technical field of sludge resource utilization, and particularly relates to a two-stage continuous sludge pyrohydrolysis full-chain resource utilization process, which comprises the following steps: directly mixing and contacting a carbon-rich material with sludge and steam, and carrying out two-time pyrohydrolysis flash wall breaking, the sludge thermal hydrolysis effect can be improved, the dehydration performance of hydrolysate can be enhanced, the hydrolysis time can be shortened, steam consumption can be reduced, the water content of a sludge cake after the hydrolysate is subjected to hydraulic filtration can be reduced to below 50%, the COD (Chemical Oxygen Demand) content of press filtrate can reach above 30000 mg / L, and the hydrolysis time can be shortened to 80 minutes; compared with alkaline pyrohydrolysis by adding lime, the calorific value of a mud cake obtained after hydrolysis liquid is pressed and filtered can be increased, and pipeline corrosion is relieved; the two times of flash evaporation can effectively break the wall of sludge cells, reduce the material temperature, recover heat and reduce energy consumption; the derived fuel preparation and low-temperature drying device can be used for preparing the hydrolyzed dry residues into sludge derived fuel, the calorific value reaches 2200 kcal / kg, and fuel utilization is realized; the denitrification device can reduce the ammonia nitrogen content of the filtrate, so that the carbon nitrogen ratio of the filtrate is increased, a rich and cheap carbon source is provided for a sewage plant, and the resource utilization of the filtrate is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of sludge resource utilization, and particularly relates to a two-stage continuous sludge hydrothermal hydrolysis full-chain resource utilization process. Background Art

[0002] Most sewage treatment plants adopt the activated sludge process, generating a large amount of surplus sludge. The huge sludge output has seriously increased the operating cost of sewage treatment plants. Sludge is a complex organic mixture containing a large amount of macromolecular proteins, carbohydrates, and lipids, and contains more microorganisms and pathogens. If the sludge is not harmlessly treated, it will pose a great threat to the environment. Therefore, realizing sludge reduction, resource utilization, and harmlessness is of great significance to the economic and social development.

[0003] The hydrothermal hydrolysis technology is an efficient hydrothermal treatment method. By means of high temperature and high pressure, it destroys the sludge cell wall and extracellular polymer, promotes the disintegration of the colloid structure and the release of intracellular organic matter, and at the same time promotes the hydrolysis of macromolecular organic matter into small molecule substances, which is beneficial to improving sludge dewatering and realizing sludge resource utilization. The efficiency of simple sludge hydrothermal hydrolysis is relatively low, so currently, alkali hydrothermal hydrolysis is mainly used, and the batch tank indirect heating process is mostly adopted; resulting in problems such as slow sludge heating, insufficient hydrothermal hydrolysis, difficult dehydration of hydrolysis liquid, serious pipeline corrosion, and the inability to directly utilize the filter press mud cake, which hinders the popularization and application of the hydrothermal hydrolysis technology. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a two-stage continuous sludge hydrothermal hydrolysis full-chain resource utilization process, which can solve the problems of long time consumption, incomplete reaction, difficult dehydration of hydrolysis liquid, inability to directly utilize the filter press mud cake, and pipeline corrosion in traditional batch sludge alkali hydrothermal hydrolysis.

[0005] Its technical solution is as follows: A two-stage continuous sludge hydrothermal hydrolysis full-chain resource utilization process, characterized in that it includes the following steps: Step (1): Mix sludge, carbon-rich waste, dosing water, and saturated steam evenly in the first steam-sludge mixing device to form high-temperature slurry; Step (2): Transport the prepared high-temperature slurry to the first hydrolysis and heat preservation unit for the first hydrolysis to obtain the primary sludge hydrolysis liquid; Step (3): Output the obtained sludge hydrolysis liquid to the first flash evaporation device to break the sludge cell wall, and at the same time recover the flash evaporation steam to the steam-sludge mixing device; Step (4): Re-heat the flash-evaporated primary hydrolysis liquid and saturated steam through the second steam-sludge mixing device, and then perform secondary heat preservation hydrolysis in the second hydrolysis and heat preservation unit; Step (5): Output the hydrolyzate after secondary hydrolysis to a secondary flash evaporation device to break the sludge cells again, while recovering the flash steam and reducing the temperature of the sludge hydrolyzate. Step (6): Output the hydrolyzate after secondary flash evaporation to a solid-liquid separation device to collect the filtrate and dry residue. Step (7): Feed the collected filtrate and alkaline agent into the denitrification system to adjust the pH and then conduct denitrification. The pressure filtrate after denitrification can be used as a carbon source and fed into the sewage treatment plant at fixed points and times; the separated dry residue is transported to the derived fuel preparation system to co-produce biomass fuel with carbon-rich waste, and then forms sludge-derived fuel rods through a low-temperature drying system.

[0006] It is further characterized in that in step (1), the dosage of carbon-rich waste is 25% - 35% of the dry basis of the sludge, and the water content of the high-temperature slurry is controlled at 83% - 86% and the temperature is controlled at 80°C - 100°C by adjusting the water distribution amount and steam usage amount; the carbon-rich waste is wood chip powder with a particle size of 300 - 400 µm. Further, in step (2), control the slurry flow rate in the first hydrolysis heat preservation unit and adjust the primary hot hydrolysis time of the sludge to 30 minutes. Further, in step (4), adjust the steam usage amount in the second steam-sludge mixing device to heat the primary hydrolyzate to 140°C - 160°C, and control the residence time of the material in the second hydrolysis heat preservation unit at 30 - 60 min by adjusting the material flow rate.

[0007] Further, in step (6), the secondary hydrolyzate is first temporarily stored and cooled in a cooling tank, and then solid-liquid separation is achieved through a plate and frame filter press device.

[0008] Further, in step (7), in the denitrification system, first adjust the pH to 9 - 10 by adding an alkaline agent, and use the stripping method for denitrification. The alkaline agent can be calcium oxide or sodium hydroxide, and the pH of the filtrate after denitrification is reduced to between 7 and 8.

[0009] Further, in step (7), the dry residue separated by solid-liquid separation is first crushed in the derived fuel preparation system, then mixed and extruded with wood chips to form fuel rods, and biomass-derived fuel is formed using low-temperature drying technology. The drying temperature is 80 - 100°C, the water content of the dry residue is reduced to less than 30%, the mass ratio of wood chips to the dry basis of the dry residue is 0.1 - 0.2, and the calorific value of the sludge-derived fuel is controlled at 2000 - 2500 kcal / kg. Further, in steps (1) and (4), the saturated steam is purchased from a nearby thermal power plant or obtained using a steam boiler, the temperature is 180°C - 200°C, and the steam-sludge mixing device is a spiral cone steam-sludge mixing device. Further, the outer surfaces of the hydrolysis heat preservation unit, flash evaporation device, and low-temperature drying device are all made of heat preservation materials.

[0010] After adopting the present invention, through the direct mixing and contact of carbon-rich materials, sludge and steam, and two-stage hydrothermal hydrolysis and flash evaporation for cell wall breaking, the hydrothermal hydrolysis effect of sludge can be improved, the dewatering performance of the hydrolysate can be enhanced, the hydrolysis time can be shortened, the steam consumption can be reduced, the water content of the filter cake after pressure filtration of the hydrolysate can be reduced to below 50%, the COD content of the filtrate after pressure filtration can reach above 30000 mg / L, and the hydrolysis time can be shortened to 80 minutes; compared with alkaline hydrothermal hydrolysis with the addition of lime, it can also increase the calorific value of the filter cake after pressure filtration of the hydrolysate and alleviate pipeline corrosion; the two-stage flash evaporation can effectively break the cell wall of sludge, while reducing the material temperature, recovering heat and reducing energy consumption; the preparation device for derived fuel and the low-temperature drying device can make the hydrothermal dry residue into sludge-derived fuel with a calorific value of 2200 kcal / kg, realizing fuel utilization; the denitrification device can reduce the ammonia nitrogen content of the filtrate, thereby increasing the carbon-nitrogen ratio of the filtrate, providing a rich and cheap carbon source for the sewage treatment plant and realizing the resource utilization of the filtrate; almost no additional waste is generated in the whole process. Description of the Drawings

[0011] Figure 1 It is a schematic diagram of the overall structure of a two-stage continuous sludge hydrothermal hydrolysis full-chain resource utilization process provided by the present invention; Figure 2 It is a schematic diagram of the structure of the hydrolysis and heat preservation device in a two-stage continuous sludge hydrothermal hydrolysis full-chain resource utilization process provided by the present invention; Figure 3 It is the COD and ammonia nitrogen contents of the filtrate after pressure filtration produced under 6 working conditions by using the process of the present invention (the reaction temperature is the secondary hydrolysis reaction temperature, and the reaction time is the secondary hydrolysis heat preservation time); Figure 4 It is the water content of the filter cake formed by the hydrolysate produced under 6 working conditions by using the process of the present invention under a medium-pressure filter plate frame (pressing pressure 1.2 Mpa, time 1 h).

[0012] Figure 5 It is the calorific value of the sludge-derived fuel produced under 6 working conditions by using the process of the present invention. Detailed Embodiments

[0013] See Figure 1As shown in the figure, the system adopted by a two-stage continuous sludge hydrothermal hydrolysis full-chain resource utilization process includes a water tank, a carbon-rich waste storage tank, an alkaline reagent storage tank, a steam-sludge mixing device I, a hydrolysis and heat preservation unit I, a primary flash evaporation device, a steam-sludge mixing device II, a hydrolysis and heat preservation unit II, and a secondary flash evaporation device, which are connected in sequence through pipelines. The dry slag collected by the solid-liquid separation device is sent to the derived fuel preparation device for granulation, and then transported to the low-temperature drying system. The liquid flow pipeline port of the solid-liquid separation device is connected to the denitrification device through a pipeline, and then transported to the sewage treatment plant for use as a carbon source through a pipeline; the sludge-derived fuel particles produced by the low-temperature drying system are sent to the thermal power plant for incineration. The primary flash evaporation device and the saturated steam are connected to the steam-sludge mixing device I through a steam pipeline, and the secondary flash evaporation device and the saturated steam are connected to the backend low-temperature drying system through a steam pipeline, so as to recover the heat released by flash evaporation, and the generated steam condensate is stored back in the water tank for batching.

[0014] The process includes the following steps: Step (1): Mix the sludge, carbon-rich waste, batching water, and saturated steam evenly in the steam-sludge mixing device I to form high-temperature slurry; Step (2): Transport the prepared high-temperature slurry to the hydrolysis and heat preservation unit I for the first hydrolysis to obtain the primary sludge hydrolysis solution; Step (3): Output the obtained sludge hydrolysis solution to the primary flash evaporation device to break the sludge cells, and at the same time recover the flash steam to the steam-sludge mixing device; Step (4): Reheat the flash-evaporated primary hydrolysis solution and saturated steam through the steam-sludge mixing device II, and then perform secondary heat preservation hydrolysis in the hydrolysis and heat preservation unit II; Step (5): Output the hydrolyzed solution after the secondary hydrolysis to the secondary flash evaporation device to break the sludge cells again, and at the same time recover the flash steam to reduce the temperature of the sludge hydrolysis solution; Step (6): Output the hydrolyzed solution after the secondary flash evaporation to the solid-liquid separation device to collect the filtrate and dry slag; Step (7): Feed the collected filtrate and alkaline reagent into the denitrification system to adjust the pH and then denitrify. The pressure filtrate after denitrification can be used as a carbon source and fed into the sewage treatment plant at fixed points and times; the separated dry slag is transported to the derived fuel preparation system to co-produce biomass fuel with the carbon-rich waste, and then forms sludge-derived fuel rods through the low-temperature drying system.

[0015] The hydrolysis and heat preservation device I and the hydrolysis and heat preservation device II are horizontal tube bundle devices, as Figure 2 shown, composed of a shell and multiple internal serpentine pipes. The residence time of the material in the hydrolysis and heat preservation device I is controlled at 30 minutes by adjusting the flow rate of the sludge, and the residence time of the material in the hydrolysis and heat preservation device II is 30 minutes.

[0016] Part of the water used in the steam-sludge mixing device 1 is the steam condensate generated by the low-temperature drying device, and the insufficient part is supplemented with tap water.

[0017] Saturated steam can be obtained by purchasing from a nearby thermal power plant or using a steam boiler, with a temperature of 180°C - 200°C.

[0018] The flash steam generated by the primary flash evaporation device is introduced into the steam-sludge mixing device 1 to preheat the sludge, and the flash steam generated by the secondary flash evaporation device is introduced into the low-temperature drying device to dry the sludge-derived fuel rods.

[0019] The solid-liquid separation device includes a cooling tank and a plate-and-frame filter press device. Preferably, the feeding pressure of the plate-and-frame is controlled at 1 Mpa, the pressing pressure is 1.2 Mpa, and the pressing time is 1 h.

[0020] In the denitrification device, alkaline agents are first added to adjust the pH of the filtrate to 9 - 10, and the ammonia nitrogen content in the filtrate is reduced to less than 300 mg / L by the stripping method.

[0021] The derived fuel preparation device can be a screw extrusion molding machine, a drum-type mixing granulator, a twin-screw extrusion granulator, etc., which granulates after mixing dry slag and carbon-rich waste powder.

[0022] The low-temperature drying system is a belt dryer, a thin-layer dryer, a hot plate dryer, etc., which indirectly heats the sludge-derived fuel through saturated steam and the recovered flash steam, controls the drying temperature at 80°C, reduces the moisture content to 15%, and the generated steam condensate is introduced into the water tank.

[0023] The outer surfaces of the hydrolysis insulation device, the flash evaporation device, and the low-temperature drying device are all made of heat-insulating materials to maintain the working temperature and reduce heat loss.

[0024] A variable-frequency stirring device is arranged in the denitrification device, the stirring speed is set at 70 rpm, and the generated ammonia gas is uniformly sent to the deodorization system.

[0025] Example 1 A two-stage continuous sludge hot hydrolysis full-chain resource utilization method includes the following steps: (1) Sludge blending and temperature rising: In the steam-sludge mixing device 1, the sludge with a moisture content of 83% is mixed evenly with carbon-rich waste and water in proportion, the dosage of carbon-rich waste is controlled at 25% of the dry basis of the sludge, and the moisture content of the materials in the batching tank is controlled at 85% and the temperature is 90°C by adjusting the water consumption and steam. (2) Primary hydrolysis and flash evaporation of sludge: The high-temperature sludge is introduced into the hydrolysis insulation unit 1 for hydrolysis reaction, the sludge hot hydrolysis time is adjusted to 30 minutes by controlling the material flow rate, and after the primary hydrolysis is completed, it enters the primary flash evaporation device. The pressure in the primary flash evaporation system is set at 0.05 Mpa, and the flash steam is introduced into the steam-sludge mixing device 1 to preheat the sludge; (3) Secondary hydrolysis and flash evaporation of sludge: The primary hydrolysis liquid after the first flash evaporation is fed into the second steam-sludge mixing device. Adjust the steam usage to raise the sludge temperature to 150 °C again, and then transport it to the second hydrolysis insulation unit to stay for 40 minutes for hydrolysis reaction. After that, it is sent to the secondary flash evaporation system. Set the pressure in the secondary flash evaporation system to 0.06 Mpa, and the generated flash steam is fed into the low-temperature drying device.

[0026] (4) The hydrolysis liquid after the secondary flash evaporation is first transported to the cooling tank for cooling and temporary storage, and then pumped into the plate and frame filter press for solid-liquid separation. Set the feeding pressure to 0.9 Mpa, the feeding time to 90 minutes, the pressing pressure to 1.1 Mpa, and the pressing time to 60 minutes. After the filtrate passes through the filtering device, water-insoluble substances are removed.

[0027] (5) First, add alkaline agents to the collected filtrate to adjust the pH of the filtrate to 9, and then transport it to the denitrification device. Use the stripping method to reduce the ammonia nitrogen content of the filtrate and increase the carbon-nitrogen ratio of the filtrate. The filtrate after denitrification is fed into the domestic sewage treatment plant for use as a carbon source. (6) The dry residue separated by solid-liquid separation is transported to the derived fuel preparation device. After being crushed, it is mixed with wood chips and extruded to form fuel rods, and then passes through the low-temperature drying device to form derived fuel. The drying temperature is 80 °C, the moisture content of the dry residue is reduced to 25%, the mass ratio of dry basis of wood chips to dry residue is 0.15, and the derived fuel is sent to the power plant for incineration.

[0028] Example 2 A two-stage continuous sludge hydrothermal hydrolysis full-chain resource utilization method includes the following steps: (1) Sludge blending and temperature raising: In the first steam-sludge mixing device, mix the sludge with 80% moisture content, carbon-rich waste, and water in proportion evenly. Control the dosage of carbon-rich waste to be 30% of the dry basis of the sludge. Adjust the water usage and steam to control the moisture content of the materials in the batching tank to be 86% and the temperature to be 100 °C. (2) Primary hydrolysis and flash evaporation of sludge: Feed the high-temperature sludge into the first hydrolysis insulation unit for hydrolysis reaction. Adjust the sludge hydrothermal hydrolysis time to 30 minutes by controlling the material flow rate. After the primary hydrolysis is completed, it enters the first flash evaporation device. Set the pressure in the first flash evaporation system to 0.06 Mpa, and the flash steam is fed into the first steam-sludge mixing device to preheat the sludge. (3) Secondary hydrolysis and flash evaporation of sludge: Feed the primary hydrolysis liquid after the first flash evaporation into the second steam-sludge mixing device. Adjust the steam usage to raise the sludge temperature to 160 °C again, and then transport it to the second hydrolysis insulation unit to stay for 50 minutes for hydrolysis reaction. After that, it is sent to the secondary flash evaporation system. Set the pressure in the secondary flash evaporation system to 0.07 Mpa, and the generated flash steam is fed into the low-temperature drying device.

[0029] (4) The hydrolyzate completed by secondary flash evaporation is first transported to a cooling tank for temperature reduction and temporary storage, and then pumped into a plate and frame filter press for solid-liquid separation. The feeding pressure is set at 1.0 Mpa, the feeding time is 90 minutes, the pressing pressure is 1.2 Mpa, and the pressing time is 80 minutes. After the pressed filtrate passes through the filtering device, water-insoluble substances are removed.

[0030] (5) First, alkaline agents are added to the collected filtrate to adjust the pH of the filtrate to 10, and then it is transported to a denitrification device. The stripping method is used to reduce the ammonia nitrogen content of the filtrate and increase the carbon-nitrogen ratio of the filtrate. The denitrified filtrate is introduced into a domestic sewage treatment plant for use as a carbon source. (6) The dry residue separated by solid-liquid separation is first crushed, and then extruded with wood chips to form fuel rods, which are then formed into biomass-derived fuels using low-temperature drying technology. The drying temperature is 90 °C, the moisture content of the dry residue is reduced to 20%, the mass ratio of wood chips to the dry basis of the dry residue is 0.2, and the derived fuel is sent to the power plant for incineration.

[0031] Example 3 A two-stage continuous sludge hydrothermal hydrolysis full-chain resource utilization method includes the following steps: (1) Sludge blending and temperature rising: In steam-sludge mixing device 1, sludge with a moisture content of 82% is mixed evenly with carbon-rich waste and water in proportion. The dosage of carbon-rich waste is controlled at 35% of the dry basis of the sludge. By adjusting the water consumption and steam, the moisture content of the materials in the batching tank is controlled at 84% and the temperature is 100 °C. (2) Primary sludge hydrolysis and flash evaporation: The high-temperature sludge is introduced into hydrolysis insulation unit 1 for hydrolysis reaction. The hydrothermal hydrolysis time of the sludge is adjusted to 30 minutes by controlling the material flow rate. After the primary hydrolysis is completed, it enters the primary flash evaporation device. The pressure in the primary flash evaporation system is set at 0.07 Mpa, and the flash steam is introduced into steam-sludge mixing device 1 to preheat the sludge. (3) Secondary sludge hydrolysis and flash evaporation: The primary hydrolyzate after primary flash evaporation is introduced into steam-sludge mixing device 2. The steam usage is adjusted to raise the sludge temperature to 140 °C again, and then it is transported to hydrolysis insulation unit 2 and stays for 50 minutes for hydrolysis reaction. After completion, it is sent to the secondary flash evaporation system. The pressure in the secondary flash evaporation system is set at 0.08 Mpa, and the generated flash steam is introduced into the low-temperature drying device.

[0032] (4) The hydrolyzate completed by secondary flash evaporation is first transported to a cooling tank for temperature reduction and temporary storage, and then pumped into a plate and frame filter press for solid-liquid separation. The feeding pressure is set at 0.8 Mpa, the feeding time is 90 minutes, the pressing pressure is 1.0 Mpa, and the pressing time is 90 minutes. After the pressed filtrate passes through the filtering device, water-insoluble substances are removed.

[0033] (5) First, add alkaline agents to the collected filtrate to adjust the pH of the filtrate to 9, and then transport it to the denitrification device. Use the stripping method to reduce the ammonia nitrogen content in the filtrate, increase the carbon-nitrogen ratio of the filtrate, and the denitrified filtrate is sent to the domestic sewage treatment plant for use as a carbon source; (6) The dry residue separated by solid-liquid separation is first crushed, and then extruded with wood chips to form fuel rods, and then biomass-derived fuel is formed by using low-temperature drying technology. The drying temperature is 100 °C, the moisture content of the dry residue is reduced to 30%, the mass ratio of wood chips to the dry basis of the dry residue is 0.1, and the derived fuel is sent to the power plant for incineration.

[0034] Example 4 A two-stage continuous sludge hydrothermal hydrolysis full-chain resource utilization method includes the following steps: (1) Sludge blending and temperature raising: In the first steam-sludge mixing device, mix the sludge with a moisture content of 81% with carbon-rich waste and water in proportion, control the dosage of carbon-rich waste to be 35% of the dry basis of the sludge, and adjust the moisture content of the materials in the batching tank to 86% and the temperature to 100 °C by adjusting the water consumption and steam; (2) Primary sludge hydrolysis and flash evaporation: Feed the high-temperature sludge into the first hydrolysis and heat preservation unit for hydrolysis reaction. Adjust the sludge hydrothermal hydrolysis time to 30 minutes by controlling the material flow rate. After the primary hydrolysis is completed, enter the first flash evaporation device. Set the pressure in the first flash evaporation system to 0.06 Mpa, and the flash steam is fed into the steam-sludge mixing device 1 to preheat the sludge; (3) Secondary sludge hydrolysis and flash evaporation: Feed the primary hydrolysis liquid after the first flash evaporation into the second steam-sludge mixing device, adjust the steam usage to raise the sludge temperature to 150 °C again, and then transport it to the second hydrolysis and heat preservation unit to stay for 50 minutes for hydrolysis reaction. After completion, send it to the second flash evaporation system. Set the pressure in the second flash evaporation system to 0.08 Mpa, and the generated flash steam is fed into the low-temperature drying device.

[0035] (4) The hydrolysis liquid after the second flash evaporation is first transported to the cooling tank for cooling and temporary storage, and then pumped into a plate and frame filter press for solid-liquid separation. Set the feeding pressure to 0.8 Mpa, the feeding time to 90 minutes, the pressing pressure to 1.0 Mpa, and the pressing time to 70 minutes. After the filtrate passes through the filtering device, water-insoluble substances are removed.

[0036] (5) First, add alkaline agents to the collected filtrate to adjust the pH of the filtrate to 10, and then transport it to the denitrification device. Use the stripping method to reduce the ammonia nitrogen content in the filtrate, increase the carbon-nitrogen ratio of the filtrate, and the denitrified filtrate is sent to the domestic sewage treatment plant for use as a carbon source; (6) The dry residue separated by solid-liquid separation is first crushed, and then extruded with wood chips to form fuel rods, and then biomass-derived fuel is formed by using low-temperature drying technology. The drying temperature is 90 °C, the moisture content of the dry residue is reduced to 20%, the mass ratio of wood chips to the dry basis of the dry residue is 0.2, and the derived fuel is sent to the power plant for incineration.

[0037] Example 5 A two-stage continuous sludge hydrothermal hydrolysis full-chain resource utilization method, comprising the following steps: (1) Sludge blending and temperature rising: In the first steam-sludge mixing device, sludge with a water content of 82% is evenly mixed with carbon-rich waste and water in proportion. The dosage of carbon-rich waste is controlled at 30% of the dry basis of the sludge. By adjusting the water consumption and steam, the water content of the materials in the batching tank is controlled at 85% and the temperature is 100 °C; (2) Primary sludge hydrolysis and flash evaporation: The high-temperature sludge is fed into the first hydrolysis insulation unit for hydrolysis reaction. The sludge hydrothermal hydrolysis time is adjusted to 30 minutes by controlling the material flow rate. After the primary hydrolysis is completed, it enters the primary flash evaporation device. The pressure in the primary flash evaporation system is set at 0.06 Mpa, and the flash steam is fed into the first steam-sludge mixing device to preheat the sludge; (3) Secondary sludge hydrolysis and flash evaporation: The primary hydrolysis liquid after the primary flash evaporation is fed into the second steam-sludge mixing device, and the steam usage is adjusted to raise the sludge temperature to 150 °C again. Then it is transported to the second hydrolysis insulation unit and stays for 30 minutes for hydrolysis reaction. After completion, it is sent to the secondary flash evaporation system. The pressure in the secondary flash evaporation system is set at 0.07 Mpa, and the generated flash steam is fed into the low-temperature drying device.

[0038] (4) The hydrolysis liquid after the secondary flash evaporation is first transported to the cooling tank for temperature reduction and temporary storage, and then pumped into a plate and frame filter press for solid-liquid separation. The feeding pressure is set at 0.8 Mpa, the feeding time is 90 minutes, the pressing pressure is 1.0 Mpa, and the pressing time is 60 minutes. After the filtrate passes through the filtering device, water-insoluble substances are removed.

[0039] (5) The collected filtrate is first added with an alkaline agent to adjust the pH of the filtrate to 9, and then transported to the denitrification device. The stripping method is used to reduce the ammonia nitrogen content of the filtrate and increase the carbon-nitrogen ratio of the filtrate. The denitrified filtrate is fed into the domestic sewage treatment plant as a carbon source; (6) The dry residue separated by solid-liquid separation is first crushed, and then extruded with wood chips to form fuel rods, and then the biomass-derived fuel is formed by using low-temperature drying technology. The drying temperature is 80 °C, the water content of the dry residue is reduced to 20%, the mass ratio of wood chips to the dry basis of the dry residue is 0.2, and the derived fuel is sent to the power plant for incineration.

[0040] Example 6 A two-stage continuous sludge hydrothermal hydrolysis full-chain resource utilization method, comprising the following steps: (1) Sludge blending and temperature rising: In the first steam-sludge mixing device, sludge with a water content of 83% is evenly mixed with carbon-rich waste and water in proportion. The dosage of carbon-rich waste is controlled at 30% of the dry basis of the sludge. By adjusting the water consumption and steam, the water content of the materials in the batching tank is controlled at 86% and the temperature is 100 °C; (2) Primary hydrolysis and flash evaporation of sludge: The high-temperature sludge is fed into Hydrolysis Insulation Unit 1 for hydrolysis reaction. The hydrolysis time of the sludge is adjusted to 30 minutes by controlling the material flow rate. After the primary hydrolysis is completed, it enters the primary flash evaporation device. The pressure in the primary flash evaporation system is set to 0.06 Mpa, and the flash steam is fed into the steam-sludge mixing device 1 to preheat the sludge. (3) Secondary hydrolysis and flash evaporation of sludge: The primary hydrolyzate after the primary flash evaporation is fed into the steam-sludge mixing device 2. The steam usage is adjusted to raise the sludge temperature to 150 °C again, and then it is transported to Hydrolysis Insulation Unit 2 and stays for 60 minutes for hydrolysis reaction. After completion, it is sent to the secondary flash evaporation system. The pressure in the secondary flash evaporation system is set to 0.08 Mpa, and the generated flash steam is fed into the low-temperature drying device.

[0041] (4) The hydrolyzate after the secondary flash evaporation is first transported to the cooling tank for cooling and temporary storage, and then pumped into the plate and frame filter press for solid-liquid separation. The feeding pressure is set to 0.9 Mpa, the feeding time is 90 minutes, the pressing pressure is 1.2 Mpa, and the pressing time is 70 minutes. After the filtrate passes through the filtering device, water-insoluble substances are removed.

[0042] (5) The collected filtrate is first added with alkaline agents to adjust the pH of the filtrate to 9, and then transported to the denitrification device. The stripping method is used to reduce the ammonia nitrogen content of the filtrate and increase the carbon-nitrogen ratio of the filtrate. The denitrified filtrate is fed into the domestic sewage treatment plant as a carbon source. (6) The dry residue separated by solid-liquid separation is first crushed, and then extruded with wood chips to form fuel rods, and then the biomass-derived fuel is formed by using low-temperature drying technology. The drying temperature is 100 °C, and the moisture content of the dry residue is reduced to 25%. The mass ratio of wood chips to the dry basis of the dry residue is 0.2. The derived fuel is sent to the power plant for incineration.

[0043] The experimental data are as follows: Under different working conditions, the properties of the filtrate after sludge hydrolysis, the moisture content of the dry residue, and the calorific value of the sludge-derived fuel are shown in the appendix Figures 3 - 5 as follows. When the dosage of the carbon-rich waste powder is 30% of the dry basis of the sludge, the secondary hot hydrolysis temperature is 150 °C, and the holding time is 50 minutes, the COD content of the filtrate generated by the solid-liquid separation system reaches 34,900 mg / L. The carbon-nitrogen ratio of the filtrate after denitrification is as high as over 80, and the moisture content of the filter cake after hydrolysis filtration is 48.5%. When preparing the derived fuel, when the dosage of the carbon-rich waste is 15% of the dry basis of the dry residue and the moisture content is 25%, the calorific value of the sludge-derived fuel is 2,285 kcal / kg, which is about 45.7% of the calorific value of lignite. Therefore, the present invention solves the technical problems of incomplete hydrolysis of municipal sludge, poor solid-liquid separation effect, and difficult outlet of dry residue filtrate, and realizes the full-chain energy and resource utilization of sludge.

Claims

1. A two-stage continuous sludge thermal hydrolysis full-chain resource utilization process, characterized in that: It includes the following steps: Step (1): in a steam-sludge mixing device 1, the sludge is mixed evenly with carbon-rich waste, batching water and saturated steam in a certain proportion to form a high-temperature sludge; Step (2): transporting the prepared high-temperature sludge to the first hydrolysis and heat preservation unit for the first hydrolysis, thereby obtaining the primary hydrolyzate of sludge; Step (3): outputting the obtained sludge hydrolyzate to a primary flash evaporation device to break the sludge cell walls, and recovering the flash evaporation steam to a steam-sludge mixing device; Step (4): the flashed primary hydrolyzate and saturated steam are heated again by the steam-mud mixing device 2, and then a secondary heat preservation hydrolysis is performed in the hydrolysis heat preservation unit 2; Step (5): outputting the hydrolyzate after the secondary hydrolysis to a secondary flash evaporation device to break the sludge cell walls again, while recovering the flash steam to reduce the temperature of the sludge hydrolyzate; Step (6): outputting the hydrolyzate after the secondary flash evaporation to a solid-liquid separation device, and collecting the filtrate and dry residue; Step (7): The collected filtrate and alkaline agent are introduced into the denitrification system to adjust the pH and then denitrify. The denitrified filtrate can be introduced into the sewage treatment plant as a carbon source for fixed-point and regular delivery. The separated dry residue is transported to the derivative fuel preparation system to prepare biomass fuel in coordination with carbon-rich waste, and then passed through a low-temperature drying system to form sludge-derived fuel rods.

2. A two-stage continuous sludge thermal hydrolysis full-chain resource utilization process according to claim 1, characterized in that: In step (1), the amount of carbon-rich waste added is 25% to 35% of the dry basis of the sludge, and the water content of the high-temperature sludge is controlled at 83% to 86% and the temperature is controlled at 80°C to 100°C by adjusting the water distribution amount and the steam usage; the carbon-rich waste is sawdust powder with a particle size of 300 to 400µm.

3. A two-stage continuous sludge thermal hydrolysis full-chain resource utilization process according to claim 1, characterized in that: In step (2), the sludge flow rate in the hydrolysis and heat preservation unit 1 is controlled to adjust the first thermal hydrolysis time of the sludge to 30 minutes.

4. A two-stage continuous sludge thermal hydrolysis full-chain resource utilization process according to claim 1, characterized in that: In step (4), the steam usage in the steam-mud mixing device 2 is adjusted to raise the temperature of the primary hydrolyzate to 140°C-160°C, and the material flow rate is adjusted to control the material to stay in the hydrolysis and insulation unit 2 for 30-60 minutes.

5. A two-stage continuous sludge thermal hydrolysis full-chain resource utilization process according to claim 1, characterized in that: In step (6), the secondary hydrolyzate is first temporarily stored in a cooling tank for cooling, and then solid-liquid separation is achieved by a plate and frame filter press.

6. A two-stage continuous sludge thermal hydrolysis full-chain resource utilization process according to claim 1, characterized in that: In step (7), the pH of the denitrification system is first adjusted to 9-10 by adding an alkaline agent, and denitrification is carried out by air stripping. The alkaline agent can be calcium oxide or sodium hydroxide. After denitrification, the pH of the filtrate is reduced to between 7 and 8.

7. A two-stage continuous sludge thermal hydrolysis full-chain resource utilization process according to claim 1, characterized in that: The dry residue separated from the solid and liquid in step (7) is first crushed in the derivative fuel preparation system, and then mixed with sawdust and extruded to form a fuel rod, and low-temperature drying technology is used to form biomass derived fuel. The drying temperature is 80-100°C, and the moisture content of the dry residue is reduced to less than 30%. The dry basis mass ratio of sawdust to dry residue is 0.1-0.2, and the calorific value of the sludge derived fuel is controlled to be 2000-2500 kcal / kg.

8. A two-stage continuous sludge thermal hydrolysis full-chain resource utilization process according to claim 1, characterized in that: In steps (1) and (4), saturated steam is purchased from a nearby thermal power plant or obtained using a steam boiler, with a temperature of 180°C to 200°C, and the steam-sludge mixing device is a spiral cone steam-sludge mixing device.

9. A two-stage continuous sludge thermal hydrolysis full-chain resource utilization process according to claim 1, characterized in that: The outer surfaces of the hydrolysis insulation unit, flash evaporation device and low-temperature drying device are all made of insulation materials.

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