Hydrothermal carbonization treatment process for high-solid-content sludge

Abstract

The invention relates to the technical field of sludge treatment and disposal, and discloses a high-solid-content sludge hydrothermal carbonization treatment process which comprises the following steps: (1) mixing sludge of which the water content is less than or equal to 75% with a catalyst in a mixing and preheating tank, and then preheating; (2) conveying the preheated sludge to a reaction kettle for hydrothermal carbonization reaction to obtain sludge biochar slurry; (3) conveying the sludge biochar slurry to a flash tank for flash evaporation, and returning flash evaporation steam and 10-50% of the flash-evaporated sludge biochar slurry to the mixing preheating tank; and (4) conveying the residual 50-90% of the flashed sludge biochar slurry to a cooling tank for cooling, and carrying out solid-liquid separation. According to the hydrothermal carbonization treatment process for the high-solid-content sludge, the treatment energy consumption can be effectively reduced, and the treatment efficiency can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of sludge treatment and disposal, and in particular to a hydrothermal carbonization treatment process for high-solid sludge. Background Art

[0002] Hydrothermal carbonization (HTC) technology is a technology that uses hydrothermal media to carbonize biomass raw materials under high temperature and high pressure conditions. Compared with conventional biomass pyrolysis technology, water does not undergo phase change during biomass hydrothermal carbonization, and the energy consumption is low. Organic matter with any water content can be used as raw materials, and there is no emission during the reaction process. It is a cutting-edge technology in the field of biomass treatment. This technology is carried out in a water-containing environment and does not require the material to be dried, so it is particularly suitable for water-rich biological organic waste and sludge.

[0003] The sludge hydrothermal carbonization process is to modify the sludge in a closed environment, release free water, and achieve sludge stabilization, harmlessness and reduction. The whole process does not have the latent heat of water vaporization, so the energy consumption is significantly reduced compared to traditional thermal drying and the treatment efficiency is high. However, the sludge hydrothermal carbonization technology is subject to the requirements of pump transportation, and the sludge needs to have a certain fluidity, so the water content of the sludge to be treated is limited to 75-90%, which is more difficult to treat for high-solid sludge and has high energy consumption.

[0004] Therefore, how to provide a hydrothermal carbonization treatment process for high-solid sludge with low energy consumption and high treatment efficiency is an urgent problem to be solved by technical personnel in this field. Summary of the invention

[0005] In view of this, the present invention provides a high-solid sludge hydrothermal carbonization treatment process to solve the problem that the existing high-solid sludge treatment is difficult and has high energy consumption.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] In one aspect, the present invention provides a hydrothermal carbonization process for high-solid sludge, comprising the following steps:

[0008] (1) Mixing sludge with a moisture content of ≤75% and a catalyst in a mixing preheating tank and preheating the mixture;

[0009] (2) transporting the preheated sludge to a reactor for hydrothermal carbonization reaction to obtain sludge biochar slurry;

[0010] (3) conveying the sludge biochar slurry to a flash tank for flash evaporation, and returning the flash steam and 10-50% of the flashed sludge biochar slurry to the mixing preheating tank;

[0011] (4) The remaining 50-90% of the sludge biochar slurry after flash evaporation is transported to a cooling tank for cooling and solid-liquid separation.

[0012] Preferably, the sludge has a moisture content of 60-75% and an organic matter content of 30-80%.

[0013] Preferably, the catalyst is an organic acid and / or an inorganic acid, and the mass of the catalyst is 1-5% of the mass of the sludge.

[0014] Preferably, the catalyst is at least one of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, oxalic acid, citric acid, tartaric acid, and lactic acid.

[0015] Preferably, the preheating temperature is 80-100°C.

[0016] Preferably, the reaction temperature of the hydrothermal carbonization reaction is 160-220° C., the reaction time is 2-6 h, and the reaction pressure is 1-4 MPa.

[0017] Preferably, the flash steam temperature in the flash tank is 100-150° C. and the pressure is 0.1-0.2 MPa.

[0018] Preferably, the temperature of the sludge biochar slurry after flash evaporation is 90-110°C.

[0019] Preferably, the cooling temperature is 30-60°C.

[0020] The present invention provides a method for hydrothermal carbonization treatment of high-solid sludge. Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention divides the sludge biochar slurry after flash evaporation into two parts, one part of which is returned to the mixing preheating tank to be mixed with high-solid sludge to improve the fluidity of the sludge, and the remaining part enters the cooling tank for cooling and then solid-liquid separation, which can effectively reduce processing energy consumption and improve processing efficiency.

[0022] In addition, the present invention returns the steam in the flash tank to the mixing preheating tank, and uses the recovered steam to directly heat the sludge, which can achieve both pressure relief and temperature reduction, improve the waste heat recovery efficiency, and further reduce processing energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0024] Figure 1 It is a schematic diagram of a high-solid sludge hydrothermal carbonization treatment device according to an embodiment of the present invention.

[0025] In the figure:

[0026] 1- sludge silo, 2- mixing preheating tank, 3- reactor, 4- flash tank, 5- cooling tank, 6- screw conveyor, 7- screw pump, 8- steam pipe. DETAILED DESCRIPTION

[0027] The present invention will be described below by specific examples, and it will be appreciated by those skilled in the art that the following specific examples are only for illustrative purposes, and do not limit the scope of the present invention in any way. In addition, in the following examples, unless otherwise specified, the reagents and equipment used are all commercially available. If in the following examples, specific treatment conditions and treatment methods are not clearly described, then conditions and methods known in the art can be used to process.

[0028] In one aspect of the present invention, the present invention provides a hydrothermal carbonization process for high-solid sludge, comprising the following steps:

[0029] Step S100: Mix the sludge with a moisture content of ≤75% and the catalyst in the mixing preheating tank 2 and then preheat them.

[0030] In this step, the sludge entering the mixing preheating tank 2 can be sludge at room temperature, preferably 0-30°C, the water content of the sludge is preferably 60-75%, and the organic matter content is 30-80%. Among them, the higher the water content of the sludge, the higher the energy consumption of the system and the lower the processing capacity. If the water content is lower than 60%, the sludge has poor fluidity, the pipeline cannot be transported, and the sludge cannot be processed; in addition, if the organic matter content in the sludge is lower than 30%, the hydrothermal carbonization effect is poor and cannot meet the processing requirements.

[0031] Optionally, the catalyst is an organic acid and / or an inorganic acid, preferably, the catalyst is at least one of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, oxalic acid, citric acid, tartaric acid, and lactic acid. The mass of the catalyst is 1-5% of the mass of the sludge, for example, it can be 1%, 2%, 3%, 4%, 5%, etc. Among them, the use of the catalyst can reduce the reaction temperature, shorten the reaction time, and accelerate the hydrothermal carbonization reaction process, thereby reducing the energy consumption of the system; if the amount of the catalyst is less than 1%, the catalytic effect is not obvious, and the amount of the catalyst is greater than 5%, the catalytic performance is not significantly improved, and the biochar is strongly acidic, which is not conducive to terminal resource utilization.

[0032] Optionally, the preheating temperature in the preheating tank is 80-100°C, for example, 80°C, 90°C, 100°C, etc. The preheating temperature is an important parameter for the waste heat recovery efficiency of the system. The higher the preheating temperature, the higher the waste heat recovery efficiency, the lower the system energy consumption, and the lower the processing cost.

[0033] Step S200: The preheated sludge is transported to the reactor 3 for hydrothermal carbonization reaction to obtain sludge biochar slurry.

[0034] In this step, the reaction temperature of the hydrothermal carbonization reaction is 160-220°C, for example, 160°C, 200°C, 220°C, etc., the reaction time is 2-6h, for example, 2h, 4h, 6h, etc., and the reaction pressure is 1-4MPa, for example, 1MPa, 2MPa, 3MPa, 4MPa, etc. Among them, if the reaction temperature is lower than 160°C, the hydrothermal carbonization reaction rate is low, the reaction time is long, and the processing efficiency is low. If the reaction temperature is higher than 220°C, the hydrothermal carbonization reaction is not significantly improved, and the system energy consumption is high and the processing cost is high.

[0035] Step S300: conveying the sludge biochar slurry to the flash tank 4 for flash evaporation, and returning the flash steam and 10-50% of the flashed sludge biochar slurry to the mixing preheating tank 2.

[0036] In this step, the flash steam temperature in the flash tank 4 is 100-150°C, for example, 100°C, 120°C, 150°C, etc., and the pressure is 0.1-0.2MPa, for example, 0.1MPa, 0.15MPa, 0.2MPa, etc. If the flash temperature is higher than 150°C, the amount of steam generated is small and the waste heat recovery efficiency is low. If the flash temperature is lower than 100°C, it is impossible to generate steam with sufficient pressure to heat the sludge.

[0037] Optionally, the temperature of the sludge biochar slurry after flash evaporation is 90-110°C, for example, 90°C, 100°C, 110°C, etc.

[0038] The present invention adopts a method of recovering the waste heat of steam of materials after hydrothermal carbonization, and uses steam to directly heat the original sludge, which can not only relieve the pressure of the flash tank 4 but also reduce the temperature, thereby improving the waste heat recovery rate.

[0039] Step S400: The remaining 50-90% of the sludge biochar slurry after flash evaporation is transported to the cooling tank 5 for cooling and solid-liquid separation.

[0040] In this step, the cooling temperature is 30-60°C, for example, 30°C, 40°C, 50°C, 60°C, etc.; the solid-liquid separation method can be mechanical dehydration, and the moisture content of the carbon cake after solid-liquid separation is 20-40%.

[0041] The present invention adopts the method of returning a part of the sludge biochar slurry after flash evaporation to the mixing preheating tank 2 to mix with the high-solid content sludge to improve the fluidity of the sludge, and the remaining part enters the cooling tank 5 for cooling and solid-liquid separation to achieve hydrothermal carbonization treatment of the high-solid content sludge. Considering that if the sludge carbon slurry returned to the preheating tank is less than 10%, the sludge fluidity will be poor and cannot meet the pipeline transportation requirements, and if it is higher than 50%, the system processing capacity is low and the energy consumption is high, therefore 10%-50% of the sludge carbon slurry is returned to the preheating tank, and the corresponding 50-90% of the sludge carbon slurry enters the cooling tank.

[0042] The hydrothermal carbonization treatment process of high-solid sludge of the present invention is described below through specific examples.

[0043] The treatment objects involved in the following embodiments and comparative examples are all dewatered sludge of excess sludge from a sewage treatment plant in Chuzhou, with a water content of 65% and an organic matter content of 40%.

[0044] If there is no special description in the following treatment process, the sludge treatment capacity of the high-solid sludge hydrothermal carbonization treatment device used is 1200L / d, and the structure of the treatment device is as follows:

[0045] The high-solid sludge hydrothermal carbonization treatment device comprises a sludge silo 1, a mixing preheating tank 2, a reactor 3, a flash tank 4 and a cooling tank 5 which are connected in sequence. The sludge silo 1 is connected to the mixing preheating tank 2 through a screw conveyor 6, a screw pump 7 and a control valve are provided between the mixing preheating tank 2 and the reactor 3, a control valve is provided between the reactor 3 and the flash tank 4, the steam outlet at the top of the flash tank 4 is connected to the mixing preheating tank 2 through a steam pipe 8, and a control valve and a steam flow meter are provided between the flash tank 4 and the mixing preheating tank 2, the discharge port at the bottom of the flash tank 4 is respectively connected to the cooling tank 5 and the mixing preheating tank 2, and a control valve and a liquid flow meter are respectively installed between the discharge port of the flash tank 4 and the cooling tank 5 and the mixing preheating tank 2.

[0046] The mixing preheating tank 2 has a volume of 500L and is provided with a double-helix agitator inside, wherein the agitator shaft and the spiral blades are both hollow structures, and steam outlet holes are provided on the surfaces of the agitator shaft and the spiral blades; the reactor 3 has a volume of 500L and is provided with a heat transfer oil heating jacket on the outside and is provided with a double-helix agitator inside, wherein the agitator shaft and the spiral blades are both hollow structures, and heated heat transfer oil is introduced into the jacket, and is equipped with a thermometer, a pH meter, a viscometer and a pressure gauge; the flash tank 4 has a volume of 500L and is provided with a stirring device inside, and is equipped with a thermometer and a pressure gauge; a steam pipe 8 is installed at the steam outlet of the flash tank 4, and is equipped with a thermometer and a pressure gauge.

[0047] Example 1

[0048] This embodiment provides a high-solid sludge hydrothermal carbonization treatment process, comprising the following steps:

[0049] (1) The sludge is transported to the mixing preheating tank at a sludge feeding rate of 50 L / h. The sludge is stirred and mixed with sulfuric acid catalyst in the mixing preheating tank. The amount of sulfuric acid catalyst used is 2% of the sludge weight. Steam is transported from the flash tank to the mixing preheating tank. At the same time, the carbon slurry in the flash tank returns to the mixing preheating tank at a rate of 5.2 L / h. It is stirred and mixed with the sludge. The sludge temperature is raised to 95°C.

[0050] (2) The preheated sludge is transported to the reactor by a screw pump with a sludge feed rate of 60 L / h. The reaction is carried out for 3 h at a temperature of 180 °C and a pressure of 2 MPa. The sludge is converted into sludge biochar slurry with a discharge flow rate of 50 L / h.

[0051] (3) Flash discharge: adjust the control valve between the reactor and the flash tank to maintain the sludge discharge rate at 60 L / h. In the flash tank, adjust the control valve between the flash tank and the mixing preheating tank to achieve a flash steam temperature of 110 °C, a pressure of 0.14 MPa, and a steam flow rate of 4.8 kg / h (steam production per ton of sludge is 80 kg / t). The steam is transported to the mixing preheating tank to directly heat the sludge. The sludge biochar slurry treatment flow rate in the flash tank is 60 L / h, of which 5.2 L / h returns to the mixing preheating tank to be stirred and mixed with the feed sludge to improve the fluidity of the material, and the remaining 50 L / h of the sludge enters the cooling tank for solid-liquid separation after cooling. The sludge biochar slurry in the flash tank is cooled to 100 °C, and the cooled sludge biochar slurry continues to be cooled.

[0052] Statistics show that the energy consumption of the sludge hydrothermal carbonization continuous treatment system is 0.4MJ / kg.

[0053] Example 2

[0054] This embodiment provides a high-solid sludge hydrothermal carbonization treatment process, comprising the following steps:

[0055] (1) The sludge is transported to the mixing preheating tank at a sludge feeding rate of 50 L / h. The sludge is stirred and mixed with oxalic acid catalyst in the mixing preheating tank. The amount of sulfuric acid catalyst is 1% of the sludge weight. Steam is transported from the flash tank to the mixing preheating tank. At the same time, the carbon slurry in the flash tank returns to the mixing preheating tank at a rate of 4.6 L / h. It is stirred and mixed with the sludge. The sludge temperature is raised to 98°C.

[0056] (2) The preheated sludge is transported to the reactor by a screw pump with a sludge feed rate of 60 L / h. The reaction is carried out for 6 h at a temperature of 160 °C and a pressure of 1 MPa. The sludge is converted into sludge biochar slurry with a discharge flow rate of 50 L / h.

[0057] (3) Flash discharge, adjust the control valve between the reactor and the flash tank to keep the sludge discharge at 60L / h. In the flash tank, the flash steam temperature is 100℃, the pressure is 0.10MPa, and the steam flow rate is 5.4kg / h (steam production per ton of sludge is 90kg / t) by adjusting the control valve between the flash tank and the mixing preheating tank. The steam is transported to the mixing preheating tank to directly heat the sludge; the sludge biochar slurry treatment flow in the flash tank is 60L / h, of which 4.6L / h returns to the mixing preheating tank to mix with the feed sludge to improve the fluidity of the material, and the remaining 50L / h of the slurry enters the cooling tank for solid-liquid separation after cooling. The sludge biochar slurry in the flash tank is cooled to 90℃, and the sludge biochar slurry after cooling continues to be cooled.

[0058] Statistics show that the energy consumption of the sludge hydrothermal carbonization continuous treatment system is 0.43 MJ / kg. Compared with Example 1, the hydrothermal carbonization reaction temperature of this embodiment is low, the reaction time is prolonged, and the system operation energy consumption is high.

[0059] Example 3

[0060] This embodiment provides a high-solid sludge hydrothermal carbonization treatment process, comprising the following steps:

[0061] (1) The sludge is transported to the mixing preheating tank at a sludge feeding rate of 50 L / h. The sludge is stirred and mixed with sulfuric acid catalyst in the mixing preheating tank. The amount of oxalic acid catalyst used is 2% of the sludge weight. Steam is transported from the flash tank to the mixing preheating tank. At the same time, the carbon slurry in the flash tank returns to the mixing preheating tank at a rate of 5.0 L / h. It is stirred and mixed with the sludge. The sludge temperature is raised to 97°C.

[0062] (2) The preheated sludge is transported to the reactor by a screw pump with a sludge feed rate of 60 L / h. The reaction is carried out for 4 h at a temperature of 190 °C and a pressure of 2 MPa. The sludge is converted into sludge biochar slurry with a discharge flow rate of 50 L / h.

[0063] (3) Flash discharge: adjust the control valve between the reactor and the flash tank to maintain the sludge discharge rate at 60 L / h. In the flash tank, adjust the control valve between the flash tank and the mixing preheating tank to achieve a flash steam temperature of 105 °C, a pressure of 0.12 MPa, and a steam flow rate of 5 kg / h (steam production per ton of sludge is 80 kg / t). The steam is transported to the mixing preheating tank to directly heat the sludge. The sludge biochar slurry treatment flow rate in the flash tank is 60 L / h, of which 5 L / h returns to the mixing preheating tank to be stirred and mixed with the feed sludge to improve the fluidity of the material, and the remaining 50 L / h of the sludge enters the cooling tank for solid-liquid separation after cooling. The sludge biochar slurry in the flash tank is cooled to 100 °C, and the cooled sludge biochar slurry continues to be cooled.

[0064] Statistics show that the energy consumption of the sludge hydrothermal carbonization continuous treatment system is 0.45MJ / kg.

[0065] Compared with Example 1, the hydrothermal carbonization reaction temperature of the oxalic acid catalyst in this embodiment is higher than that of the sulfuric acid catalyst, the reaction time is longer, and the system energy consumption is higher.

[0066] Comparative Example 1

[0067] In the treatment device used in comparative example 1, the discharge port at the bottom of the flash tank is only connected to the cooling tank, but not to the mixing preheating tank. The treatment process of hydrothermal carbonization of high-solid sludge using this treatment device is as follows:

[0068] (1) The sludge is transported to the mixing preheating tank with a sludge feeding rate of 50 L / h. The sludge is stirred and mixed with sulfuric acid catalyst in the mixing preheating tank. The catalyst dosage is 2% of the sludge weight. Steam is transported from the flash tank to the mixing preheating tank, and is contacted and mixed with the sludge while stirring. The sludge temperature rises to 60°C. The steam utilization efficiency is low, and material transportation is difficult.

[0069] (2) The preheated sludge is transported to the reactor by a screw pump (screw pump transportation is difficult and has high energy consumption), with a sludge feed rate of 54.4 L / h. The sludge is reacted for 3 hours at a temperature of 180 °C and a pressure of 2 MPa. The sludge is converted into sludge biochar slurry, and the discharge flow rate is 50 L / h.

[0070] (3) Flash discharging, adjust the control valve between the reactor and the flash tank to maintain the sludge discharge at 54.4L / h. In the flash tank, by adjusting the control valve between the flash tank and the mixing preheating tank, the flash steam temperature is 110℃, the pressure is 0.14MPa, and the steam flow rate is 4.4kg / h (steam production per ton of sludge is 80kg / t). The steam is transported to the mixing preheating tank to directly heat the sludge; the sludge biochar slurry treatment flow in the flash tank is 54.4L / h, of which all the charcoal slurry enters the cooling tank for solid-liquid separation after cooling, and the sludge biochar slurry in the flash tank is cooled to 100℃. After cooling, the sludge biochar slurry continues to be cooled.

[0071] Statistics show that the energy consumption of the sludge hydrothermal carbonization continuous treatment system is 0.92MJ / kg.

[0072] Compared with Example 1, the feed sludge of Comparative Example 1 has a low moisture content, no biochar slurry reflux, poor sludge fluidity, difficult transportation, low heat transfer efficiency, and high energy consumption.

[0073] Comparative Example 2

[0074] This comparative example provides a hydrothermal carbonization treatment process for high-solid sludge, comprising the following steps:

[0075] (1) The sludge is transported to the mixing preheating tank at a sludge feeding rate of 50 L / h. The sludge is stirred and mixed with sulfuric acid catalyst in the mixing preheating tank. The amount of sulfuric acid catalyst used is 0.5% of the sludge weight. Steam is transported from the flash tank to the mixing preheating tank. At the same time, the carbon slurry in the flash tank returns to the mixing preheating tank at a rate of 5.2 L / h. It is stirred and mixed with the sludge. The sludge temperature is raised to 95°C.

[0076] (2) The preheated sludge is transported to the reactor by a screw pump with a sludge feed rate of 60 L / h. The reaction is carried out for 7 h at a temperature of 180 °C and a pressure of 2 MPa. The sludge is converted into sludge biochar slurry with a discharge flow rate of 50 L / h.

[0077] (3) Flash discharge: adjust the control valve between the reactor and the flash tank to maintain the sludge discharge rate at 60 L / h. In the flash tank, adjust the control valve between the flash tank and the mixing preheating tank to achieve a flash steam temperature of 110 °C, a pressure of 0.14 MPa, and a steam flow rate of 4.8 kg / h (steam production per ton of sludge is 80 kg / t). The steam is transported to the mixing preheating tank to directly heat the sludge. The sludge biochar slurry treatment flow rate in the flash tank is 60 L / h, of which 5.2 L / h returns to the mixing preheating tank to be stirred and mixed with the feed sludge to improve the fluidity of the material, and the remaining 50 L / h of the sludge enters the cooling tank for solid-liquid separation after cooling. The sludge biochar slurry in the flash tank is cooled to 100 °C, and the cooled sludge biochar slurry continues to be cooled.

[0078] Statistics show that the energy consumption of the sludge hydrothermal carbonization continuous treatment system is 1.35MJ / kg.

[0079] Compared with Example 1, the amount of sulfuric acid catalyst used in Comparative Example 2 is small, the reaction time is long, and the energy consumption is high.

[0080] Comparative Example 3

[0081] This comparative example provides a hydrothermal carbonization treatment process for high-solid sludge, comprising the following steps:

[0082] (1) The sludge is transported to the mixing preheating tank at a sludge feeding rate of 50 L / h. The sludge is stirred and mixed with sulfuric acid catalyst in the mixing preheating tank. The amount of sulfuric acid catalyst used is 6% of the sludge weight. Steam is transported from the flash tank to the mixing preheating tank. At the same time, the carbon slurry in the flash tank returns to the mixing preheating tank at a rate of 5.2 L / h. It is stirred and mixed with the sludge. The sludge temperature is raised to 95°C.

[0083] (2) The preheated sludge is transported to the reactor by a screw pump with a sludge feed rate of 60 L / h. The reaction is carried out for 3 h at a temperature of 180 °C and a pressure of 2 MPa. The sludge is converted into sludge biochar slurry with a discharge flow rate of 50 L / h.

[0084] (3) Flash discharge: adjust the control valve between the reactor and the flash tank to maintain the sludge discharge rate at 60 L / h. In the flash tank, adjust the control valve between the flash tank and the mixing preheating tank to achieve a flash steam temperature of 110 °C, a pressure of 0.14 MPa, and a steam flow rate of 4.8 kg / h (steam production per ton of sludge is 80 kg / t). The steam is transported to the mixing preheating tank to directly heat the sludge. The sludge biochar slurry treatment flow rate in the flash tank is 60 L / h, of which 5.2 L / h returns to the mixing preheating tank to be stirred and mixed with the feed sludge to improve the fluidity of the material, and the remaining 50 L / h of the sludge enters the cooling tank for solid-liquid separation after cooling. The sludge biochar slurry in the flash tank is cooled to 100 °C, and the cooled sludge biochar slurry continues to be cooled.

[0085] Statistics show that the energy consumption of the sludge hydrothermal carbonization continuous treatment system is 0.4MJ / kg.

[0086] Compared with Example 1, the amount of sulfuric acid catalyst used in Comparative Example 3 is large, resulting in strong acidity of biochar and high sulfur content, which is not conducive to resource utilization.

[0087] Comparative Example 4

[0088] This comparative example provides a hydrothermal carbonization treatment process for high-solid sludge, comprising the following steps:

[0089] (1) The sludge is transported to the mixing preheating tank at a sludge feeding rate of 50 L / h. The sludge is stirred and mixed with sulfuric acid catalyst in the mixing preheating tank. The amount of sulfuric acid catalyst used is 2% of the sludge weight. Steam is transported from the flash tank to the mixing preheating tank. At the same time, the carbon slurry in the flash tank returns to the mixing preheating tank at a rate of 7.8 L / h. It is stirred and mixed with the sludge. The sludge temperature is raised to 80°C.

[0090] (2) The preheated sludge is transported to the reactor by a screw pump with a sludge feed rate of 60 L / h. The reaction is carried out for 8 h at a temperature of 150 °C and a pressure of 1.4 MPa. The sludge is converted into sludge biochar slurry with a discharge flow rate of 50 L / h.

[0091] (3) Flash discharge: adjust the control valve between the reactor and the flash tank to maintain the sludge discharge rate at 60 L / h. In the flash tank, adjust the control valve between the flash tank and the mixing preheating tank to achieve a flash steam temperature of 110 °C, a pressure of 0.14 MPa, and a steam flow rate of 2.4 kg / h (steam production per ton of sludge 40 kg / t). The steam is transported to the mixing preheating tank to directly heat the sludge. The sludge biochar slurry treatment flow rate in the flash tank is 60 L / h, of which 7.8 L / h returns to the mixing preheating tank to be mixed with the feed sludge to improve the fluidity of the material, and the remaining 50 L / h of the sludge enters the cooling tank for solid-liquid separation after cooling. The sludge biochar slurry in the flash tank is cooled to 100 °C, and the cooled sludge biochar slurry continues to be cooled.

[0092] Statistics show that the energy consumption of the sludge hydrothermal carbonization continuous treatment system is 1.12MJ / kg.

[0093] Compared with Example 1, the reaction temperature of Comparative Example 4 is low, the hydrothermal carbonization effect is poor, and the energy consumption is high.

[0094] Comparative Example 5

[0095] This comparative example provides a hydrothermal carbonization treatment process for high-solid sludge, comprising the following steps:

[0096] (1) The sludge is transported to the mixing preheating tank at a sludge feeding rate of 50 L / h. The sludge is stirred and mixed with sulfuric acid catalyst in the mixing preheating tank. The amount of sulfuric acid catalyst used is 2% of the sludge weight. Steam is transported from the flash tank to the mixing preheating tank. At the same time, the carbon slurry in the flash tank returns to the mixing preheating tank at a rate of 7.2 L / h. The sludge is stirred and mixed with the sludge. The sludge temperature is raised to 100°C.

[0097] (2) The preheated sludge is transported to the reactor by a screw pump with a sludge feed rate of 60 L / h. The reaction is carried out for 3 h at a temperature of 230 °C and a pressure of 3.0 MPa. The sludge is converted into sludge biochar slurry with a discharge flow rate of 50 L / h.

[0098] (3) Flash discharge: adjust the control valve between the reactor and the flash tank to maintain the sludge discharge rate at 60 L / h. In the flash tank, adjust the control valve between the flash tank and the mixing preheating tank to achieve a flash steam temperature of 110 °C, a pressure of 0.14 MPa, and a steam flow rate of 7.2 kg / h (steam production per ton of sludge is 120 kg / t). The steam is transported to the mixing preheating tank to directly heat the sludge. The sludge biochar slurry treatment flow rate in the flash tank is 60 L / h, of which 2.8 L / h returns to the mixing preheating tank to be mixed with the feed sludge to improve the fluidity of the material, and the remaining 50 L / h of the sludge enters the cooling tank for solid-liquid separation after cooling. The sludge biochar slurry in the flash tank is cooled to 100 °C, and the cooled sludge biochar slurry continues to be cooled.

[0099] Statistics show that the energy consumption of the sludge hydrothermal carbonization continuous treatment system is 0.78MJ / kg.

[0100] Compared with Example 1, the hydrothermal carbonization reaction temperature of Comparative Example 5 is high and the energy consumption is high.

[0101] In the description of this specification, the description with reference to the terms "one embodiment", "another embodiment", "yet another embodiment", "some embodiments", "some specific embodiments", "some other specific embodiments" and the like means that the specific features, structures, materials or characteristics described in conjunction with the embodiment are included in at least one embodiment of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples, unless they are contradictory. In addition, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated.

[0102] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A hydrothermal carbonization process for high-solid sludge. It is characterized in that The following steps are involved: (1) Mixing sludge with a moisture content of ≤75% and a catalyst in a mixing preheating tank and preheating the mixture; (2) transporting the preheated sludge to a reactor for hydrothermal carbonization reaction to obtain sludge biochar slurry; (3) conveying the sludge biochar slurry to a flash tank for flash evaporation, and returning the flash steam and 10-50% of the flashed sludge biochar slurry to the mixing preheating tank; (4) The remaining 50-90% of the sludge biochar slurry after flash evaporation is transported to a cooling tank for cooling and solid-liquid separation.

2. The high-solid sludge hydrothermal carbonization treatment process according to claim 1, It is characterized in that The sludge has a moisture content of 60-75% and an organic matter content of 30-80%.

3. The high-solid sludge hydrothermal carbonization treatment process according to claim 1, It is characterized in that The catalyst is an organic acid and / or an inorganic acid, and the mass of the catalyst is 1-5% of the mass of the sludge.

4. The high-solid sludge hydrothermal carbonization treatment process according to claim 1 or 3, It is characterized in that The catalyst is at least one of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, oxalic acid, citric acid, tartaric acid, and lactic acid.

5. The high-solid sludge hydrothermal carbonization treatment process according to claim 1, It is characterized in that The preheating temperature is 80-100°C.

6. The high-solid sludge hydrothermal carbonization treatment process according to claim 1, It is characterized in that The reaction temperature of the hydrothermal carbonization reaction is 160-220° C., the reaction time is 2-6 hours, and the reaction pressure is 1-4 MPa.

7. The high-solid sludge hydrothermal carbonization treatment process according to claim 1, It is characterized in that The flash steam temperature in the flash tank is 100-150° C. and the pressure is 0.1-0.2 MPa.

8. The high-solid sludge hydrothermal carbonization treatment process according to claim 1, It is characterized in that The temperature of the sludge biochar slurry after flash evaporation is 90-110°C.

9. The hydrothermal carbonization process for high-solid sludge according to claim 1, It is characterized in that The cooling temperature is 30-60°C.

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