A small-scale sludge pyrolysis gasification power generation method and system with net energy output

Abstract

The present application relates to a kind of small-scale sludge pyrolysis gasification power generation method of net energy output, comprising the following steps: S1, the remaining sludge after sludge dewatering workshop treatment is treated with conditioning and high pressure low heat / no heat mechanical drying, and the sludge with water content of 40%±5% is obtained;S2, the sludge is treated with segmented heat drying, and the water content is reduced to below 20%;S3, the sludge is treated with high-temperature pyrolysis gasification, and the pyrolysis temperature is 900±50 DEG C;S4, the pyrolysis gas is stored after purification, heat exchange treatment and rapid cooling;The heat energy of heat exchange is used for heat drying treatment;S5, the pyrolysis gas is used for power generation, and the heat energy of the generator tail gas after heat exchange treatment is used for heat drying treatment.The corresponding sludge pyrolysis gasification power generation system is also provided.The method system is more suitable for small-scale sludge treatment system, can realize net energy output, save electricity and sludge disposal fee, reduce carbon emission, and the product also meets pollution control standard.

Description

Technical Field

[0001] The present invention belongs to the field of sludge treatment and relates to a miniaturized sludge pyrolysis and gasification power generation method and system with net energy output. Background Art

[0002] Sludge, a sediment produced during sewage treatment with organic matter as its primary component, is characterized by fine particles and a low specific gravity. While it contains pollutants such as bacteria and heavy metals, its high organic content also makes it a significant resource. Currently, municipal sewage sludge is mostly treated by dewatering and then landfilling, or drying and then landfilling, without undergoing rigorous harmless treatment and without achieving high sludge recovery rates.

[0003] Sludge is a biomass resource that can be used for energy. Due to its high water content, direct incineration is generally not an option for sludge energy utilization. Currently, there are two mainstream technical approaches: anaerobic fermentation and pyrolysis and gasification. Anaerobic fermentation involves digesting sludge in an anaerobic environment to produce biogas. It offers significant sludge reduction, strong sustainability, and good biogas economics. However, due to the large footprint of biogas production equipment, the difficulty of handling liquid and residue biogas, the need for heating to maintain biogas production in low-temperature environments, and low energy conversion rates, it is not suitable for general sewage treatment plants. Pyrolysis and gasification, on the other hand, offer advantages such as short processing time, high energy conversion rates, a small footprint for treatment facilities, and a high degree of harmless treatment. It is a promising development direction for sludge-to-power technology, suitable for the construction of new "energy-self-sufficient" sewage treatment plants and the technical renovation of existing sewage treatment plants as "green parks." The amount of sludge (80% moisture content) generated by a typical sewage treatment plant is 1‰ of the total wastewater treatment volume, so sludge production generally does not exceed 50 tons. For on-site treatment of sewage plant sludge, small-scale (<50 tons / day) sludge power generation technology is urgently needed. However, due to the high initial moisture content of the sludge, the energy consumption during the thermal dehydration and drying process is very high, which often becomes a major bottleneck in the energy utilization of thermal treatment technology. The treatment cost is a constraint for many manufacturers who want to invest in large-scale thermal treatment.

[0004] Many environmental protection companies are pinning their hopes on pyrolysis and gasification, hoping to generate usable energy and transform sludge into a resource. However, because fuel or combustion aids are often added in practice, and significant energy recovery losses occur, the energy utilization rate of sludge needs to be improved, and existing technologies are not yet sufficient to utilize sludge as a net energy output source (electricity). In summary, there is currently a lack of a sludge power generation method that can achieve net energy output—that is, output energy during the sludge treatment process that exceeds the energy consumed in treatment and resource utilization—and does not add other energy sources. Summary of the Invention

[0005] The purpose of the present invention is to provide a miniaturized sludge pyrolysis and gasification power generation method and system with net energy output, which realizes the net energy (electricity) output of the whole process of sludge pyrolysis and gasification power generation. By utilizing the sludge energy, it feeds back the energy consumption during the operation of the entire sewage treatment plant, thereby helping to build an "energy-self-sufficient" sewage treatment plant.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a miniaturized sludge pyrolysis and gasification power generation method with net energy output, comprising the following steps:

[0008] S1, the residual sludge after the sludge dewatering workshop is conditioned and subjected to high-pressure low-heat / no-heat mechanical drying treatment to obtain sludge with a moisture content of 40% ± 5%;

[0009] S2, performing a staged thermal drying treatment on the sludge obtained in step S1 to further reduce the moisture content to 20% or less (e.g., 18%, 15%, etc.);

[0010] S3, subjecting the sludge obtained in step S2 to high-temperature pyrolysis and gasification treatment, with the pyrolysis temperature set at 900±50°C (e.g., 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C, etc.);

[0011] S4, the pyrolysis gas obtained in step S3 is purified and rapidly cooled by heat exchange and then stored; the heat energy in the pyrolysis gas is used for the thermal drying process in step S2;

[0012] S5, the pyrolysis gas obtained in step S4 is used to generate electricity through a gas internal combustion generator; the generator exhaust is subjected to heat exchange treatment and the heat energy is used for the thermal drying treatment in step S2.

[0013] The ash obtained in step S3 of this method and the pyrolysis gas after purification and rapid cooling treatment in step S4 meet the emission requirements of relevant national pollution control standards: "Pollution Control Standard for Incineration of Municipal Waste" (GB18485-2014), "Technical Standard for Pyrolysis and Gasification of Sludge in Municipal Wastewater Treatment Plants" (T / CAMIE 10-2022) and "Technical Specification for Pyrolysis and Gasification Treatment Equipment of Organic Solid Waste" (T / CAMIE 15-2020).

[0014] In step S1, a conditioning agent is first added, followed by a high-pressure, low-heat, or heatless mechanical drying process. Step S1 is preferably completed using a high-pressure, low-heat, or heatless sludge drying system, yielding sludge with a moisture content of approximately 40%. Due to the high-pressure, heatless nature of this equipment, the dehydration and drying process is purely mechanical, requiring no additional heat source and saving energy compared to thermal drying. Preferably, the heat energy released by the cooling of the mechanical equipment's motor in step S1 can be used for thermal drying in step S2, such as preheating the initial thermal drying stage in step S2. The pressure of the high-pressure, low-heat, or heatless mechanical drying process is preferably above 25 MPa.

[0015] In step S2, the thermal drying treatment adopts a segmented thermal drying treatment, that is, the drying treatment is carried out in segments, and the heat source energy formed in steps S1, S4 and / or S5 is used. The so-called segmented thermal drying treatment is to let it air dry for an appropriate period of time after a period of heating and drying treatment, relying on its own residual heat and the lower vapor pressure of the surrounding environment to emit water vapor, and through capillary action to transport the moisture inside the sludge to the sludge surface, and then carry out the next stage of heating and drying treatment until the required drying target is achieved. Experiments have proved that this method can save energy and improve processing efficiency; it is more preferred to adopt a two-stage or three-stage drying process, which can reduce the energy consumption of sludge drying by about 20% and save 20% of drying time compared with one-time thermal drying. This technological innovation improves the efficiency of equipment operation, saves energy, and brings practical and reliable benefits to the project.

[0016] In step S3, the pyrolysis temperature of the high-temperature pyrolysis and gasification treatment is set at 900±50°C, which can meet the furnace temperature requirements in the "Standard for Pollution Control of Municipal Waste Incineration" (GB18485-2014), "Technical Standard for Pyrolysis and Gasification of Sludge in Urban Wastewater Treatment Plants" (T / CAMIE10-2022) and "Technical Specification for Pyrolysis and Gasification Treatment Equipment of Organic Solid Waste" (T / CAMIE 15-2020). The pyrolysis temperature is preferably set at 900°C, and the calorific value of the pyrolysis gas generated at this temperature can reach 2200kcal / Nm 3 It can maximize the sludge gasification energy conversion rate.

[0017] In step S4, the pyrolysis gas obtained in step S3 is stored after being cooled by purification treatment and heat exchange treatment; the heat energy recovered by heat exchange treatment is used for the heat drying treatment in step S2. The purification treatment refers to purifying the pyrolysis gas to remove particulate matter, nitrogen oxides, sulfur dioxide and the like to meet environmental protection requirements, and remove gas components that do not generate heat, such as most CO2, to increase the calorific value of the combustible gas per unit volume. The purpose of the heat exchange treatment is to recover the heat energy in the pyrolysis gas and use it for the heat drying treatment in the method to make the best use of energy and serve the construction of an "energy self-sufficient" sewage plant. When the pyrolysis gas is cooled by heat exchange treatment, the pyrolysis gas is preferably cooled to below 200 DEG C to facilitate subsequent storage in a gas storage tank, and cooling from above 850 DEG C to below 200 DEG C can ensure that dioxins are not generated. Further preferably, the pyrolysis gas is cooled to room temperature after heat exchange to further increase the calorific value of the pyrolysis gas; the cooled pyrolysis gas is stored in a gas storage tank for subsequent power generation; and the heat energy (heat exchange gas) in the pyrolysis gas is preferably used for the first-stage heat drying treatment in step S2.

[0018] In step S5, on the one hand, the pyrolysis gas obtained in step S4 is used to generate electricity, such as by an internal combustion generator, and the generated electric energy can be used by the sewage plant or sold to obtain economic benefits; on the other hand, the exhaust gas from the generator is used for heat exchange, and the recovered heat energy is used for the heat drying treatment in step S2, preferably, the recovered heat energy is used for the heat drying treatment in the subsequent stage in step S2. The generator is provided with a flue gas recycling system to recover the heat energy in the flue gas, further saving energy and serving the construction of an "energy self-sufficient" sewage plant.

[0019] The remaining heat energy in steps S1, S4 and S5 is used in step S2 to form a segmented heat drying mode, which improves the heat drying efficiency, saves energy, and ensures the normal operation of the sewage sludge pyrolysis gasification into the furnace and the entire "net energy output" sewage sludge power generation process.

[0020] More preferably, according to the energy requirements of each stage in the segmented heat drying treatment, the heat energy exchanged by the high-temperature pyrolysis gas and the hot gas generated by the motor cooling in the high-pressure low-heat / heatless mechanical drying treatment are recovered as the heat source for the first-stage heat drying treatment, and the heat energy in the flue gas from the generator is recovered as the heat source for the subsequent-stage heat drying treatment. Because the pyrolysis gas has a high temperature, a large amount of energy can be exchanged, which is used as the heat source for the first-stage drying, and the heat energy recovered from the generator exhaust gas is used as the heat source for the subsequent-stage drying, which can make the best use of energy.

[0021] The method provided by the present application not only treats sewage sludge, a pollutant, and has the advantages of heat treatment technology, but also uses it as a biomass energy source, which has great potential to help achieve the construction of an energy self-sufficient sewage plant. The energy balance calculation of the reaction process is as follows:

[0022] (1) The heat required for sludge drying is calculated as follows:

[0023]

[0024] in:

[0025] Q1——Total heat absorbed by sludge drying, MJ / kg;

[0026] m driss ——Total mass of sludge dry matter;

[0027] m H2Oss - the mass of water in the sludge before drying;

[0028] ΔT - the temperature difference between the beginning and end of the drying process (usually from 25°C to 100°C);

[0029] Cp ss ——Specific heat capacity of sludge dry matter is 1.15×10 -3 MJ / kg·K;

[0030] Cp H2O(l) ——Specific heat capacity of liquid water, 4.18×10 -3 MJ / kg·K calculation;

[0031] m H2O,evap ——The mass of water evaporated during the sludge drying process;

[0032] ΔH vap,H2O ——The enthalpy of vaporization of water at its boiling point is 2.26 MJ / kg at 100°C.

[0033] It can be calculated from the above formula that during the thermal drying process, the moisture content of the sludge drops from 40% to 20%, and the energy required to be absorbed is about 177kcal / kg.

[0034]

[0035] in:

[0036] Q2 - total heat absorbed by the gas during sludge drying, MJ;

[0037] V air，25 ——The volume of gas introduced during sludge drying is 10m3 at 25℃. 3 / kg water calculation;

[0038] m H2O,evap ——The mass of water evaporated during the sludge drying process;

[0039] ρ air ——The density of air at 25℃ is 1.2kg / m3 calculate;

[0040] ΔT – the temperature difference between the beginning and end of the drying process (usually from 25°C to 100°C);

[0041] C air ——The specific heat capacity of air is 1.013×10 at 25℃ -3 MJ / kg·K.

[0042] According to the above formula, during the thermal drying process, the moisture content of the sludge decreases from 40% to 20%, and the energy required to be absorbed by the incoming air is about 908×10 3 kcal.

[0043] The total energy required to dry 16.65t of sludge (water content reduced from 40% to 20%) is 3860×10 3 kcal(Q1+Q2).

[0044] (2) For the energy balance in the pyrolysis reaction, if the pyrolysis gasifier is regarded as an adiabatic furnace (i.e., the heat loss of the furnace body can be ignored), the pyrolysis reaction heat of the sludge can be calculated from the enthalpy of the air flow in and out of the pyrolysis furnace:

[0045] Right now:

[0046] Q3=△H 出 -ΔH 进

[0047] Where Q3 is the reaction heat of pyrolysis, ΔH 进 and ΔH 出 They represent the enthalpy of the airflow entering and leaving the furnace respectively.

[0048] The enthalpy of the airflow before and after the reaction, i.e., in and out of the furnace, can be expressed as follows based on the reaction kinetics:

[0049]

[0050] in:

[0051] m i ——Mass flow rate of each compound

[0052] T ref， T——reference temperature (298K) and actual pyrolysis temperature

[0053] Cp i ——is the specific heat capacity of each compound

[0054] —The standard enthalpy of each substance at the reference temperature

[0055]

[0056] ——The standard enthalpy of the substances produced after combustion (CO2, H2O, etc.).

[0057] According to the above calculation procedure, the heat of the pyrolysis reaction (including the cooling and condensation of the steam) is approximately Q3 = -0.70MJ / kg. This data shows that if the energy of the pyrolysis gas during cooling and condensation is effectively utilized, the pyrolysis of sludge can be an autothermal process.

[0058] In a second aspect, the present invention further provides a miniaturized sludge pyrolysis and gasification power generation system with net energy output, comprising:

[0059] The sludge drying treatment unit is configured to condition and perform high-pressure, low-heat / no-heat mechanical drying on the residual sludge after treatment in the sludge dewatering workshop to obtain sludge with a moisture content of 40% ± 5%;

[0060] The thermal drying unit is configured to further perform a staged thermal drying treatment on the sludge to reduce the moisture content to below 20%;

[0061] The high-temperature pyrolysis and gasification treatment unit is configured to further perform high-temperature pyrolysis and gasification treatment on the sludge to obtain pyrolysis gas, with the pyrolysis temperature set at 900±50°C;

[0062] A gas purification unit is configured to spray, absorb, adsorb, filter and purify the pyrolysis gas;

[0063] a first heat exchange unit configured to cool the pyrolysis gas and recover heat;

[0064] a power generation unit configured to use the cooled pyrolysis gas for power generation;

[0065] a second heat exchange unit configured to recover waste heat from the generator exhaust;

[0066] The first heat exchange unit and the second heat exchange unit are configured to respectively transfer the recovered heat to the thermal drying unit.

[0067] Preferably, the sludge drying treatment unit is configured to transfer heat generated by cooling the motor to the thermal drying unit.

[0068] Preferably, in the sludge drying treatment unit, a high-pressure low-heat / heatless sludge drying system is used to complete the conditioning and drying treatment; the high pressure is above 25 MPa.

[0069] Preferably, the thermal drying unit is configured to implement a two-stage or three-stage drying process. For example, the thermal drying unit includes at least one drying device, and can be configured as two or three drying devices, each performing a first-stage drying process and a subsequent-stage drying process. Furthermore, the first heat exchange unit is configured to transfer recovered heat to the first-stage drying process, the second heat exchange unit is configured to transfer recovered heat to the subsequent-stage drying process, and the sludge drying unit is configured to transfer heat generated by motor cooling to the first-stage drying process, generally for preheating.

[0070] Preferably, the pyrolysis temperature in the high-temperature pyrolysis and gasification treatment unit is set at 900° C. The high-temperature pyrolysis and gasification treatment unit is a pyrolysis and gasification furnace.

[0071] Preferably, the first heat exchange unit is configured to rapidly cool the pyrolysis gas to below 200° C., and further rapidly cool it to room temperature.

[0072] Preferably, it further comprises a gas storage unit configured to store the cooled pyrolysis gas outputted by the first heat exchange unit; the gas storage unit may be a gas storage cabinet or other equipment.

[0073] In this application, "miniaturization" means that the daily processing capacity of the sludge treatment system is less than 50 tons, generally referring to the scenario where the sludge treatment of the sewage treatment plant adopts on-site treatment.

[0074] Compared with the prior art, the solution of the present invention has the following beneficial effects:

[0075] (1) The present invention utilizes municipal sewage sludge through segmented drying, high-temperature pyrolysis and gasification, and reuses multiple different heat sources, thereby utilizing the sludge as a resource and energy in a net energy output manner, generating electricity for grid connection or self-use. Economically, the present invention can save on sludge disposal costs while generating revenue by supplying electricity for self-use or connecting to the grid. Since the treatment process is a net energy output, it can reduce the operating electricity costs of the sewage treatment plant, generating considerable economic benefits.

[0076] (2) The technical concept of the present invention is to improve the energy conversion efficiency by using high-temperature pyrolysis (900±50℃), and at the same time, to use high-temperature pyrolysis gas rapid cooling and heat exchange, which not only recovers most of the heat but also removes dioxins. Furthermore, the pyrolysis gas is purified to remove most of the CO2 to increase the calorific value of the pyrolysis gas. While producing significant technical effects, it fully complies with existing relevant environmental protection standards and meets very high environmental protection requirements. For example, the gas emissions contain no dioxins and other organic pollutants, and no biochar (or very little) is produced, with a ignition loss rate of <5%. Only a small amount of ash is produced, and almost no wood vinegar and tar are produced. If a small amount of tar is produced, it can be returned to the furnace for treatment, that is, it can be put into the furnace together with the sludge and then pyrolyzed at high temperature. Therefore, the entire process does not discharge wood vinegar and tar to the outside.

[0077] (3) The method and system provided by the present invention are more suitable for "miniaturized" sludge treatment systems, such as the scenario where the sludge treatment of sewage treatment plants adopts on-site treatment (the designed daily sludge production (water content 80%) is calculated as 50 tons), which can achieve net energy output. The relevant project can save 4.5835 million yuan in electricity costs (calculated at 0.8 yuan / kWh) (taking into account the power generation and the power consumption of the old water plant before the transformation), and save 5.9787 million yuan in sludge disposal fees (calculated at 360 yuan / ton of sludge). After deducting the project operating cost of 7.4402 million yuan, the annual net income is 2.8226 million yuan. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 A flow chart of a miniaturized sludge pyrolysis and gasification power generation method with net energy output provided by a preferred embodiment of the present invention is shown.

[0079] Figure 2 The direct drying characteristic curve obtained in the staged sludge drying experiment is shown.

[0080] Figure 3 The quality change curves of direct drying, two-stage drying and three-stage drying obtained in the staged sludge drying experiment are shown.

[0081] Figure 4 The moisture content change curves of direct drying, two-stage drying and three-stage drying obtained in the staged sludge drying experiment are shown.

[0082] Figure 5 The figure shows how the total calorific value of the gas produced by pyrolysis of unit mass of sludge changes with the pyrolysis temperature in the sludge high-temperature pyrolysis and gasification experiment.

[0083] Figure 6 The figure shows how the calorific value of unit volume of pyrolysis gas changes with the pyrolysis temperature in the sludge high-temperature pyrolysis gasification experiment. DETAILED DESCRIPTION

[0084] Municipal sewage sludge is a major waste product generated by sewage treatment plants. Sludge reduction, harmless treatment, and resource utilization are key issues within the industry. As a pollutant, sludge requires safe and appropriate treatment and disposal methods; at the same time, as a biomass energy source, its resource utilization is also attracting significant attention. High moisture content is a key characteristic of sewage sludge. Primary sludge can have a moisture content exceeding 99%, giving it a surface appearance close to mud. After a series of sedimentation, conditioning, and dewatering processes, the resulting tertiary sludge has a moisture content of around 70%. Faced with such a high moisture content, existing technologies often use mechanical dehydration combined with thermal drying to reduce the sludge moisture content to 20%-15% before thermal treatment, a process that consumes significant energy. Existing technologies often focus solely on the high production capacity of sludge pyrolysis and gasification, overlooking the energy consumption of the front-end and processing stages. This results in insufficient production capacity to justify the energy consumption of the entire treatment process.

[0085] The method provided by the present invention realizes the net energy generation in the whole process of sludge pyrolysis and gasification power generation, which is a step towards "energy self-sufficient" sewage treatment plants. By fully utilizing the sludge energy, it feeds back the energy consumption during the operation of the entire sewage treatment plant.

[0086] In the field of sludge thermal treatment and sludge power generation, there are the following problems from the perspective of existing engineering projects:

[0087] (1) High water content leads to high energy consumption in sludge thermal treatment: Due to the high water content of sludge, the energy consumption in the treatment (dehydration and drying) process is high, resulting in the current technology facing the problem that the sludge production capacity cannot balance its treatment energy consumption, making it impossible to achieve positive energy output when it is used as an energy material.

[0088] (2) The pyrolysis process is inefficient: The pyrolysis and gasification process of sludge is very complicated. The relevant reaction properties and conditions compiled by the inventors of this application are shown in Table 1 below. Studies have shown that when sludge is continuously heated from room temperature, gas can be produced at 400°C, but Boudouard reaction, water-gas reaction and steam reforming reaction all require high temperatures of more than 700°C to occur. At the same time, low-temperature pyrolysis has a high tar yield and a low gas yield, while high-temperature pyrolysis has a high gas yield but very little tar yield. This shows that if you want the sludge to convert more energy into the pyrolysis gas products, a high-temperature reaction environment is required. However, it is still unknown to what extent the high-temperature environment can fully convert the energy in the sludge into the pyrolysis gas products. Most of the sludge pyrolysis devices currently on the market remain at the low-temperature pyrolysis stage.

[0089] Table 1 Relevant reactions during pyrolysis and gasification of sludge

[0090]

[0091]

[0092] (3) Low utilization of pyrolysis gas

[0093] Currently, the utilization of pyrolysis gas is limited to its use as a fuel. If the heat energy generated is not utilized on-site, it will quickly dissipate and cannot be properly stored or transferred for use. However, if pyrolysis gas is used to generate electricity through a generator, the generated electricity becomes a high-quality energy source that is easy to store and has a certain degree of universal application.

[0094] Based on this, the present invention proposes a solution based on staged sludge drying, high-temperature pyrolysis and gasification, and energy recovery and utilization to promote the construction of an energy-self-sufficient sewage treatment plant.

[0095] The present invention will be further described in detail below through examples. The protection scope of the present invention includes but is not limited to the following examples.

[0096] If specific experimental steps or conditions are not specified in the examples, the experiments can be carried out according to the conventional steps or conditions described in the literature in the art.

[0097] Unless otherwise specified, all reagents and raw materials used in the examples are commercially available products.

[0098] Example 1 Segmented sludge drying experiment

[0099] The sludge material used in this embodiment is the residual sludge produced by the dehydration workshop of a domestic sewage treatment plant in Yangjiang City, Guangdong Province. The sludge is a mud cake and irregular granular dark brown solid with a moisture content of 69.5%, a dry basis ash content of 69.90%, and a dry basis calorific value of 11.45 MJ / kg.

[0100] Direct drying, two-stage drying and three-stage drying experiments were carried out on the above-mentioned residual sludge.

[0101] The experiment used an electric-heated, constant-temperature drying oven to conduct a comparative experiment on sludge drying in separate stages. For each sludge sample, larger particles were selected, their particle size measured with a vernier caliper, and their mass measured and recorded using an analytical balance. This ensured uniformity in particle size and mass within each group, minimizing any potential errors. The resulting average particle size was 14.6 mm. The samples were then placed on trays and placed in the drying oven, where the drying temperature was set to 105°C and the oven fan was turned on. During the drying process, the sludge was removed at regular intervals and its mass recorded.

[0102] The experiment first quantified the direct drying characteristics of sludge. The sludge particles were placed in a petri dish and placed in an oven. The petri dish was taken out and measured every 20 minutes. After the measurement, the petri dish was quickly returned to the oven. The above operation was repeated until the difference between the two consecutive measured masses did not exceed 0.02g, indicating that the sludge was completely dried. Based on the results, the direct drying characteristic curve of sludge was drawn. Figure 2 It can be seen that the sludge drying process can be divided into three parts: acceleration stage, constant speed stage and deceleration stage. The acceleration stage is from 0 to 30 minutes. During this stage, the moisture content of the sludge is maintained above 50%, and the rate of moisture reduction continues to increase; the constant speed stage is from 30 to 90 minutes. During this stage, the moisture content drops from 50% to 30%, and the rate of moisture reduction is basically constant; after 90 minutes, it is the deceleration stage. During this stage, the moisture content of the sludge is lower than 30%, and most of the free water and surface adsorbed water have been removed. The remaining bound water is inside the sludge and is not easy to remove, so the rate of moisture reduction continues to decrease.

[0103] according to Figure 2 The direct drying characteristic curve of the sludge shown in the figure sets the two-stage drying experiment as follows: the sludge is placed in the oven and dried for 90 minutes, then the petri dish is taken out and the mass is measured, the sludge is then placed outside the oven to dry for 90 minutes and the mass change is measured, and after the measurement is completed, the sludge is placed back in the oven and dried for 90 minutes before being taken out and the mass is measured.

[0104] The three-stage drying experiment involved placing the sludge in the oven and drying it for 60 minutes. The sludge was then removed from the dish and its mass was measured. The sludge was then allowed to air dry outside the oven for 45 minutes, and the mass change was measured. This process was repeated once. After the measurement, the sludge was returned to the oven and dried for another 60 minutes before being removed and its mass measured. The total drying and airing times for the three-stage drying experiment were the same as for the two-stage drying experiment.

[0105] Figure 3 The quality change curves of direct drying, two-stage drying and three-stage drying obtained in the staged sludge drying experiment are shown. Figure 4The following graph shows moisture content curves obtained from a staged sludge drying experiment using direct drying, two-stage drying, and three-stage drying. The graph clearly shows that the sludge loses mass while being air-dried after being removed from the drying oven. This is due to the evaporation of moisture caused by the residual heat of the sludge. Drying experiments show that drying sludge with an average particle size of 14.6 mm and a moisture content of 69.5% to a moisture content of 15% at 105°C takes 3 hours using direct drying, 2.5 hours using the two-stage drying method, and 2.16 hours using the three-stage drying method. This indicates that staged drying can save over 17% of drying time. In addition, it can be observed that the mass remaining after the water is completely evaporated by two-stage drying and three-stage drying is lower than that by direct drying. This is because the use of segmented drying can evaporate more water. This is because the capillary action of the sludge sample when it is left outside the oven converts a part of the intracellular water and bound water that cannot be removed by conventional dehydration into free water that is easier to remove. Therefore, through the segmented drying process, the water inside the sludge becomes easier to remove.

[0106] Example 2 Sludge high temperature pyrolysis gasification experiment

[0107] The sludge with an average particle size of 14.6 mm and a moisture content of 69.5% used in Example 1 was dried in three stages at 105° C. to a moisture content of about 15%, and then subjected to a high-temperature pyrolysis and gasification experiment of the sludge.

[0108] The experimental system was connected in the following order: A nitrogen cylinder was connected to the inlet of the tubular furnace to provide an inert environment for the experiment. To prevent the high-temperature gases from melting the pipes, a section of polytetrafluoroethylene tubing was connected to the outlet of the tubular furnace. This was followed by a condenser. The condenser consisted of three large beakers nested within impact-type absorption bottles. During the experiment, the beakers were filled with an ice-water mixture as the condensate. The condenser was then connected to a drying unit, consisting of two 300mL impact-type absorption bottles filled with silica gel desiccant. An air bag was then connected to the drying unit, which collected the gases generated by the sludge pyrolysis and then fed into the test chamber for sampling.

[0109] After connecting the above experimental device, start the tubular furnace heating program and introduce nitrogen at the same time. The nitrogen introduction rate is 2L / min for a total of 20 minutes. After the ventilation is completed, close the tubular furnace inlet. Before the pyrolysis experiment, the sludge sample is weighed and spread flat in a quartz boat. The quartz boat is a semi-cylindrical quartz container with a diameter of 8.5cm and a length of 15cm. About 30g of sludge sample is weighed in the experiment. When the tubular furnace is heated to the reaction temperature (high temperature section, specifically 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, and 950℃), open the tubular furnace feed port flange, push the quartz boat in, and immediately close the feed port flange after pushing the material. Wait for white smoke to come out of the gas collecting port and connect the air bag to collect the gas. After 30 minutes of constant temperature pyrolysis (calculated from the time the sludge enters the furnace body), the air bag is removed and stored, and then the gas sample composition is uniformly detected by gas chromatography (GC) as shown in Table 2 below, where C2+ is the sum of non-condensable gases with more than two carbon atoms, that is, the sum of C2H4, C2H6, C3H8, and C3H6.

[0110] Table 2 Test results of gas sample composition obtained from sludge high temperature pyrolysis gasification experiment

[0111]

[0112] The generated combustible gas output and calorific value are calculated and added together to obtain the total calorific value of the gas generated by pyrolysis and gasification of unit mass of sludge at different temperatures. Figure 5 As shown. Figure 5 It can be seen that under different pyrolysis temperature conditions from 650℃ to 950℃, the total calorific value of the generated gas first increases and then decreases, reaching a peak of 1720kacl / kg at a pyrolysis temperature of 900℃. The increase in the total calorific value of the generated gas from 650℃ to 900℃ is because during this stage, as the pyrolysis temperature increases, the output of H2, CO, and CH4 gases continues to increase, which brings about an increase in the total calorific value of the generated gas. When the temperature exceeds 900℃, although more H2 and CO are produced due to the decomposition of CH4, due to the large amount of energy consumed in the process of cracking CH4, the calorific value of the generated H2 and CO cannot make up for the calorific value loss caused by the reduction of CH4. Therefore, when the pyrolysis temperature is higher than 900℃, the decomposition of CH4 will lead to a decrease in the total calorific value of the pyrolysis gas.

[0113] and Figure 6 The results show that the lower heating value (LHV) of sludge pyrolysis gas (mixed gas) per unit volume changes with the pyrolysis temperature. The pyrolysis gas with the highest calorific value is 3972kcal / Nm at a pyrolysis temperature of 900℃. 3 , reaching 50% of ordinary household natural gas.

[0114] It can be seen from this that the gas produced by pyrolysis of unit mass of sludge at a pyrolysis temperature of 900℃ has the highest total calorific value, and the calorific value of the gas product produced by pyrolysis at this temperature is the highest.

[0115] Example 3

[0116] This embodiment provides a sludge pyrolysis and gasification power generation method with net energy output, which is used for sludge treatment in small and medium-sized sewage treatment plants (designed daily sludge production (water content 80%) is 50 tons), and includes the following steps:

[0117] S1. Sludge conditioning and drying. The residual sludge in the secondary sedimentation tank of the sewage treatment plant has a water content of basically 80% after being treated in the sludge dewatering workshop. The residual sludge is conditioned and mechanically dried using a high-pressure, low-heat / heatless sludge drying system (Beijing Houde Tiancheng Technology Co., Ltd., model 600T+100T). First, sludge conditioning agents are added through the dosing conditioning subsystem, and then the sludge is sent to the mechanical filter press system for further dehydration. The water is removed by converting electricity into pressure, and no external heat source is added during the process, which saves energy compared to hot drying. In this step, the water content of the sludge is reduced to about 40%, 2.5t of conditioning agents are added, and 35.5t of water is removed.

[0118] The mechanical filter press has a daily operating time of 16h / d, a specification of 19.3kW, an original sludge processing capacity of 50t / unit / d, a moisture removal capacity of 35t / unit / d, and a power consumption of 308.8kwh / d.

[0119] S2. Thermal drying of sludge. The sludge with a moisture content of 40% removed from the drying system is sent to a thermal dryer for thermal drying. The drying method adopts a two-stage drying method. The heat sources used by the two dryers are the heat exchange air after the pyrolysis gas is rapidly cooled and the heat exchange air of the generator exhaust gas. The drying temperature is set at approximately 160°C, the drying time is 60 minutes per stage, the airing time is 60 minutes, and the feed amount for each stage in the first stage is 700kg. The moisture content of the sludge after thermal drying is below 20%. According to the "Technical Standard for Pyrolysis and Gasification of Sludge in Municipal Wastewater Treatment Plants" (T / CAMIE 10-2022), the moisture content of the sludge after drying should be 10%-20%, thus meeting the standard requirements.

[0120] In this step, 4.15 tons of water are removed. The dryer power is 11 kW, the dryer water removal rate is 180 kg / h, and the power consumption is 264 kWh / d. The drying heat of the drying stage is calculated to be 153.67 kcal / kg. For 16.65 tons of sludge with a moisture content of 40%, the sum of the drying heat of the two stages of sludge thermal drying is 2558×10 3 kcal.

[0121] S3. Pyrolysis and gasification of sludge. The sludge after thermal drying is pushed into the pyrolysis and gasification furnace for pyrolysis and gasification treatment. The pyrolysis temperature is set to 900°C, which can meet the furnace temperature in the "Standard for Pollution Control of Municipal Waste Incineration" (GB18485-2014), "Technical Standard for Pyrolysis and Gasification of Sludge in Urban Sewage Treatment Plants" (T / CAMIE 10-2022) and "Technical Specification for Pyrolysis and Gasification Treatment Equipment of Organic Solid Waste" (T / CAMIE 15-2020). The pyrolysis gas is rapidly cooled to room temperature after heat exchange, and the calorific value of the pyrolysis gas after purification is 2200kcal / Nm 3 12.5t of sludge with a moisture content of 20% enters the pyrolysis gasification furnace, and about 35% of the sludge undergoes pyrolysis and gasification reaction, with a total gas production of approximately 3330m 3 The remaining 65% of the sludge undergoes oxidation reaction to maintain the furnace temperature. The pyrolysis gas is passed into the gas storage cabinet for storage after heat exchange. The obtained pyrolysis gas is used for the first stage of thermal drying treatment in step S2 after purification and heat exchange.

[0122] The calorific value of sludge is 11.5MJ / kg. 65% of the sludge is oxidized and releases heat, which can exchange 6750×10 3 kcal (heat utilization rate is 30% of calorific value).

[0123] The total power of the pyrolysis gasification furnace is 15kw, and the operating power consumption is 360kwh / d.

[0124] S4. Pyrolysis gas power generation: Use a generator set with a rated power of 150 kW to pass the pyrolysis gas in the gas storage tank into the generator for combustion and power generation. The power generation efficiency is 33-35%, and the generated electricity is 3000 kWh.

[0125] S5, generator exhaust utilization. The waste heat of the generator exhaust is recovered and used for the second stage of heat drying in step S2. The energy available in the generator exhaust is about 30% of the total calorific value of the gas, that is, the energy available is about 2200×10 3 kcal.

[0126] In summary, the power generation of the generator can meet the power consumption of a series of processes such as sludge dehydration, drying, and pyrolysis, and generate a net energy output (electricity). The sum of the heat exchange of pyrolysis gas and the heat exchange of generator exhaust gas can meet the drying heat required for sludge thermal drying under the condition that the heat utilization rate reaches 30%-40%. 3 kcal(Q1+Q2), thermal drying process does not require the use of external heat source.

[0127] The project saves electricity fee of 4.5835 million yuan (calculated at 0.8 yuan / kwh) (including the power generation and the power consumption of the old water plant before the reconstruction), saves sludge disposal fee of 5.9787 million yuan (calculated at 360 yuan / ton of sludge), and has a net income of 2.8226 million yuan per year after deducting the project operation cost of 7.4402 million yuan.

[0128] It should be noted that in the present application, except as otherwise understood in connection with the full text, if there is a description of "A and / or B", it should be interpreted as any one of the following three parallel situations: A; B; A and B.

[0129] It should also be noted that in the present application, except as otherwise understood in connection with the full text, if there is a description of "A and / or B", it should be interpreted as any one of the following three parallel situations: A; B; A and B.

[0130] Although the present application has been disclosed by the description of the specific embodiments of the present application above, it should be understood that those skilled in the art can design various modifications, improvements or equivalents of the present application within the spirit and scope of the appended claims. These modifications, improvements or equivalents should also be considered to be included in the scope of the present application.

Claims

1. A miniaturized sludge pyrolysis and gasification power generation method with net energy output, characterized in that: Including steps: S1, the residual sludge after the sludge dewatering workshop is conditioned and subjected to high-pressure low-heat / no-heat mechanical drying treatment to obtain sludge with a moisture content of 40%±5%; S2, performing a staged thermal drying treatment on the sludge obtained in step S1 to reduce the moisture content to 20% or less; The segmented heat drying process adopts a three-stage drying process. The segmented heat drying process is to perform a heating and drying process, then leave the sludge in the air for a suitable period of time, and rely on its own residual heat and the lower surrounding vapor pressure to release water vapor, and transport the water inside the sludge to the sludge surface through capillary action, and then perform the next heating and drying process until the required drying target is achieved. S3, the sludge obtained in step S2 is subjected to high-temperature pyrolysis gasification treatment, and the pyrolysis temperature is set at 900°C; the pyrolysis gas with the highest calorific value at 900°C is 3972kcal / Nm 3 ; S4, the pyrolysis gas obtained in step S3 is purified and heat-exchanged, and then rapidly cooled to below 200°C and stored; the heat energy obtained from the heat exchange of the pyrolysis gas is used for the thermal drying process in step S2; S5, the pyrolysis gas obtained in step S4 is used to generate electricity through a gas internal combustion generator; the heat energy obtained by heat exchange treatment of the generator exhaust gas is used for the thermal drying treatment in step S2.

2. The miniaturized sludge pyrolysis and gasification power generation method with net energy output according to claim 1 is characterized in that: In step S1, a conditioning agent is first added, and then a high-pressure, low-heat / no-heat mechanical drying process is adopted.

3. The miniaturized sludge pyrolysis and gasification power generation method with net energy output according to claim 2 is characterized in that: In step S1, the pressure of the high-pressure low-heat / heatless mechanical drying treatment is above 25 MPa.

4. The miniaturized sludge pyrolysis and gasification power generation method with net energy output according to claim 3 is characterized in that: Step S1 is completed by a high-pressure low-heat / heatless sludge drying system.

5. The miniaturized sludge pyrolysis and gasification power generation method with net energy output according to claim 1 is characterized in that: The heat energy released by cooling the working motor of the mechanical equipment in step S1 is used for the thermal drying process in step S2.

6. The miniaturized sludge pyrolysis and gasification power generation method with net energy output according to any one of claims 1 to 5, characterized in that: In step S4, the pyrolysis gas is rapidly cooled to room temperature after heat exchange.

7. The miniaturized sludge pyrolysis and gasification power generation method with net energy output according to any one of claims 1 to 5, characterized in that: The heat energy obtained from the heat exchange treatment of the pyrolysis gas in step S4 is used for the first stage of thermal drying treatment in step S2.

8. The miniaturized sludge pyrolysis and gasification power generation method with net energy output according to claim 7, characterized in that: The heat energy obtained by heat exchange treatment of the generator exhaust in step S5 is used for the subsequent thermal drying treatment in step S2.

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