Process for the recovery of heat energy from biomass carbonization tail gas for limestone calcination

Abstract

This invention belongs to the field of limestone calcination technology, specifically relating to a process for recovering heat energy from biomass carbonization tail gas for limestone calcination. The process includes: pre-treating biomass raw materials and forming them into briquettes, then feeding them into a carbonization furnace for carbonization to produce carbonized products and tail gas; extracting the high-temperature carbonization tail gas and transporting it through insulated and heated pipelines, maintaining the pipe wall temperature above 500℃ to prevent tar condensation; after high-temperature stabilization and dust removal at ≥500℃, the tail gas is sent to a pre-combustion zone to mix with combustion air for complete combustion; the resulting high-temperature flue gas enters the lime kiln calcination zone to calcine the limestone, and auxiliary fuel is dynamically supplemented according to the kiln temperature and tail gas calorific value to maintain thermal stability; finally, the tail gas is discharged after dust removal, and the lime product is collected. This invention effectively solves the problem of tail gas tar clogging the pipeline, achieves efficient recovery of heat energy from carbonization tail gas, significantly reduces traditional fuel consumption, and achieves the goal of synergistic environmental protection and energy conservation.

Description

Technical Field

[0001] This invention belongs to the field of limestone calcination technology, specifically relating to a process for recovering heat energy from biomass carbonization tail gas for limestone calcination. Background Technology

[0002] Biomass carbonization is a crucial step in the production of charcoal, machine-made charcoal, bamboo charcoal, and carbonized products from agricultural and forestry waste. When biomass raw materials are heated and decomposed in a carbonization furnace, in addition to producing solid carbonized products, a certain amount of carbonization tail gas is also generated. This tail gas typically contains carbon monoxide, hydrogen, methane, light hydrocarbons, tar vapors, volatile components of wood vinegar, and particulate matter, possessing a certain degree of combustibility and thermal energy utilization value. However, in existing charcoal or machine-made charcoal production processes, carbonization tail gas is often treated through direct venting, simple flare incineration, or inadequate treatment. On the one hand, the combustible components in the tail gas are not effectively recovered, and a large amount of thermal energy is lost with the flue gas emission or simple combustion, resulting in low energy utilization. On the other hand, simple incineration processes usually lack stable air distribution, temperature control, and supporting dust removal and purification facilities, easily leading to the emission of particulate matter, black smoke, sulfur dioxide, nitrogen oxides, and odorous gases. This increases environmental governance pressure and is detrimental to the continuous and clean production of carbonization.

[0003] Calcination of limestone is the main process for producing quicklime. Limestone's main component is calcium carbonate, which decomposes into calcium oxide and carbon dioxide under normal pressure and high temperature. In industrial production, limestone calcination typically requires maintaining high calcination temperatures, resulting in significant energy consumption. Traditional lime production relies heavily on fuels such as coal, pulverized coal, coke, or coal gas for heating, with a few production lines using natural gas. While coal-fired calcination is relatively inexpensive, it produces pollutants such as smoke, sulfur oxides, and nitrogen oxides, and also suffers from high fuel consumption, limited thermal efficiency, and high environmental remediation costs. Cleaner fuels like natural gas produce less pollution upon combustion, but their higher cost makes them unsuitable for widespread adoption in some small- to medium-sized lime production areas. Therefore, utilizing combustible byproducts from surrounding industrial or agricultural production processes to replace some traditional fuels has become an important direction for reducing energy consumption in lime calcination and improving resource utilization.

[0004] Introducing biomass carbonization tail gas into the limestone calcination process can theoretically convert combustible tail gas, which would otherwise be vented or simply incinerated, into a heat source for the lime kiln, achieving synergistic utilization between carbonization production and lime calcination. However, directly using carbonization tail gas for limestone calcination still presents several engineering challenges. First, carbonization tail gas contains tar, wood vinegar, and heavy volatile organic compounds, which can easily condense, adhere, and gradually cause blockages in pipelines if the transport temperature is lowered. Second, carbonization tail gas may contain corrosive components such as sulfur and chlorine, and ordinary pipelines are prone to corrosion failure in high-temperature, corrosive flue gas environments. Third, the flow rate and calorific value of carbonization tail gas flue with changes in the carbonization stage; if directly fed into the lime kiln material layer for combustion, it may lead to unstable flame temperature, incomplete local combustion, and even affect the color and activity of the lime product. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a process for recovering heat energy from biomass carbonization tail gas for limestone calcination. This aims to solve the problems of direct venting, simple incineration, or inefficient treatment of combustible tail gas generated during the production of charcoal, machine-made charcoal, or other biomass carbonization processes, resulting in wasted tail gas heat energy, emissions of smoke and dust pollutants, and low energy utilization.

[0006] The technical objective of this invention is achieved through the following technical solution: A process for recovering heat energy from biomass carbonization tail gas for limestone calcination includes the following steps: S1: The biomass raw material is crushed, sieved and dried to obtain biomass pellet raw material suitable for briquetting or carbonization; S2: The biomass pellet raw material obtained in step S1 is fed into a briquetting equipment for pressing and molding to obtain biomass briquette material. S3: The biomass briquette material obtained in step S2 is fed into a carbonization furnace for carbonization treatment to obtain carbonized products and carbonization tail gas. S4: The carbonization tail gas generated in step S3 is drawn out from the tail gas outlet of the carbonization furnace at high temperature and sent into the high temperature conveying pipeline through the induced draft device. S5: The high-temperature conveying pipeline adopts a short-distance arrangement and is equipped with an insulation layer and a temperature control heat tracing layer on the outside of the pipeline to keep the carbonization tail gas at a high temperature during the conveying process. The inner wall temperature of the high-temperature conveying pipeline is kept above 500℃ to reduce the condensation and adhesion of tar, wood vinegar and heavy volatile substances in the carbonization tail gas inside the pipeline. S6: The carbonization tail gas conveyed in step S5 is sent to the high temperature stabilizing buffer section and / or high temperature pretreatment section, and under the condition of maintaining the tail gas temperature not lower than 500℃, the carbonization tail gas is subjected to pressure stabilization, flow equalization and high temperature settling dust removal or cyclone dust removal treatment to reduce the impact of dust, carbon black and solid particles entrained in the carbonization tail gas on the subsequent limestone calcination process. S7: The carbonized tail gas processed in step S6 is introduced into the inlet of the lime kiln or into the pre-combustion zone set in the lower part of the lime kiln chamber, or into the independent combustion zone, and combustion air is supplied to the pre-combustion zone or the independent combustion zone to mix and burn the carbonized tail gas with the combustion air; the carbonized tail gas is fully burned in the pre-combustion zone or the independent combustion zone first, so that the combustible components in the carbonized tail gas are burned off before entering the limestone calcination zone, forming high-temperature combustion flue gas; S8: Limestone is added to the lime kiln and calcined under the action of the high-temperature flue gas generated in step S7, causing the limestone to decompose into calcium oxide and carbon dioxide; the heating ratio of the carbonization tail gas is determined according to the lower heating value of the carbonization tail gas, the carbonization tail gas flow rate, the biomass feed rate, the limestone addition rate, and the temperature of the lime kiln calcination zone; when the calorific value, flow rate, or combustion temperature of the carbonization tail gas is insufficient to maintain the temperature of the lime kiln calcination zone, auxiliary fuel is added to the pre-combustion zone, independent combustion zone, or lime kiln combustion zone to keep the temperature of the lime kiln calcination zone within the range required for limestone decomposition. S9: The flue gas after the carbonization tail gas combustion is treated by dust removal before being discharged to obtain tail gas that meets the emission requirements; the calcined lime products are cooled, screened and packaged before being put into storage; during the high-temperature transportation, pre-combustion and limestone calcination of carbonization tail gas, the temperature of the high-temperature transportation pipeline, the pre-combustion zone, the lime kiln inlet and the lime kiln calcination zone is monitored, and the induced draft volume, the carbonization tail gas introduction volume, the combustion air supply volume, the temperature control and heating status and the auxiliary fuel supply volume are adjusted according to the temperature changes.

[0007] Preferably, in step S1, the biomass raw material is one or more of sawdust, bamboo shavings, straw, fruit shells, and agricultural and forestry waste; the particle size of the crushed biomass raw material is controlled to be 3-10 mm after sieving; the drying temperature is 80-120℃, so that the moisture content of the dried biomass pellet raw material is controlled to be 8-18 wt%.

[0008] Preferably, in step S2, the briquetting method is mechanical extrusion, spiral extrusion or molding, the briquetting temperature is 120-220℃, and the pressing pressure is 10-30MPa; the diameter of the resulting biomass briquetting rod is 20-80mm and the length is 50-300mm.

[0009] Preferably, in step S3, the carbonization temperature is 450–600°C, the heating rate is 2–10°C / min, and the holding time is 2–8h; the carbonization furnace is arranged below or below the lime kiln combustion zone, so that the carbonization exhaust gas can be transported to the subsequent combustion and utilization stage via a shorter path.

[0010] Preferably, in step S4, the carbonization tail gas is directly extracted at high temperature without condensation and cooling treatment; the temperature of the carbonization tail gas at the tail gas outlet of the carbonization furnace or after heat preservation and supplementation in the outlet section is 500-700℃; when the outlet temperature of the carbonization tail gas is lower than 500℃, the outlet section is insulated and supplemented with heating when necessary to ensure that the temperature of the tail gas entering the high-temperature conveying pipeline is not lower than 500℃; the induced draft device is used to stably draw in the carbonization tail gas, so that the high-temperature conveying pipeline is kept under a slight negative pressure, the slight negative pressure being -100 to -300 Pa.

[0011] Preferably, in step S5, the length of the high-temperature conveying pipeline from the tail gas outlet of the carbonization furnace to the high-temperature pressure stabilizing buffer section, the pre-combustion zone, or the independent combustion zone is 2 to 8 m; the high-temperature conveying pipeline is covered with high-temperature resistant insulation material with an insulation layer thickness of 80 to 150 mm; the temperature control and heat tracing layer is connected to a temperature detection device to compensate for heating the pipeline through temperature control, so that the inner wall temperature of the high-temperature conveying pipeline is maintained at 550 to 650°C.

[0012] Preferably, in step S5, the high-temperature conveying pipeline is a high-temperature and corrosion-resistant pipeline, or a conveying pipeline formed by combining a high-temperature resistant metal outer pipe with a refractory material lining, a ceramic lining, or a corrosion-resistant lining, in order to adapt to the high-temperature conveying of carbonization tail gas and the corrosive environment.

[0013] Preferably, in step S6, the high-temperature pressure stabilizing buffer section and / or high-temperature pretreatment section is located between the high-temperature conveying pipeline and the pre-combustion zone or independent combustion zone; the inner wall temperature of the high-temperature pressure stabilizing buffer section and / or high-temperature pretreatment section is maintained above 500°C, preferably between 550°C and 650°C, to prevent tar, wood vinegar and heavy volatile substances in the carbonization tail gas from condensing in this section.

[0014] Preferably, in step S7, the combustion air is supplied through a primary air inlet and a secondary air inlet; the air volume ratio of the primary air to the secondary air is 40:60 to 60:40; the excess air coefficient of the combustion air is 1.10 to 1.50; the combustion air is preheated to 100 to 400°C by the waste heat of the lime kiln or the waste heat of the flue gas before being supplied, so as to improve the combustion temperature of the carbonization tail gas and the thermal energy utilization efficiency.

[0015] Preferably, in step S7, the combustion temperature of the pre-combustion zone or independent combustion zone is controlled at 900-1300℃, and the residence time of the carbonization tail gas in the pre-combustion zone or independent combustion zone is 0.5-3s, so that the carbon monoxide, hydrogen, methane, light hydrocarbons and tar vapor combustible components in the carbonization tail gas are burned as much as possible before entering the limestone calcination zone, and then enter the lime kiln calcination zone in the form of high-temperature flue gas.

[0016] Preferably, in step S8, the limestone particle size is 30-80mm; the temperature of the lime kiln calcination zone is controlled at 900-1100℃, and the calcination time is 2-8h; under the lime kiln structure, the effective heat utilization coefficient of the carbonization tail gas is 0.60-0.75; the heat generated by the combustion of the carbonization tail gas is used as part or all of the heat source for limestone calcination. When the lower heating value and flow rate of the carbonization tail gas meet the heat matching requirements with the amount of limestone added, the carbonization tail gas is used as the entire heat source for limestone calcination; when the lower heating value or flow rate of the carbonization tail gas is insufficient to maintain the temperature of the calcination zone, the carbonization tail gas is used as part of the heat source, and auxiliary fuel is added for stable temperature calcination.

[0017] Preferably, in step S8, the auxiliary fuel is one or more combustible gases such as coal gas and natural gas, or one or more solid fuels such as pulverized coal and biomass pellet fuel.

[0018] Preferably, in step S9, the flue gas after combustion is first treated by settling dust removal, cyclone dust removal, or high-temperature resistant filtration to remove particulate matter from the high-temperature flue gas; when a bag filter is used, the flue gas after combustion is first cooled down to the allowable operating temperature range of the bag filter material, and condensation of the flue gas in the dust collector is prevented before it enters the bag filter for further processing.

[0019] Preferably, in step S9, when the inner wall temperature of the high-temperature conveying pipeline is below 520°C, the compensation heating of the temperature-controlled heat tracing layer is activated or enhanced; when the inner wall temperature of the high-temperature conveying pipeline is below 500°C, the amount of carbonization tail gas conveyed is reduced, or the carbonization tail gas is switched to the bypass combustion path; when the temperature of the lime kiln calcination zone is below the lower limit of the preset calcination temperature range, the amount of combustion air supplied is increased, the amount of carbonization tail gas introduced is increased, or auxiliary fuel is added, so that the temperature of the lime kiln calcination zone is restored to the preset calcination temperature range.

[0020] The beneficial effects of this invention are as follows: Compared with existing technologies, this invention extracts the carbonization tail gas generated during biomass carbonization at high temperatures and uses it as part or all of the heat source for the limestone calcination process, enabling the recovery and utilization of heat energy from combustible tail gas that would otherwise be directly vented or simply incinerated. This method reduces energy waste caused by the inefficient combustion or venting of combustible components in the carbonization tail gas, while also reducing dependence on traditional fuels such as coal and natural gas during limestone calcination, achieving synergistic utilization of biomass carbonization production and limestone calcination processes.

[0021] This invention employs a combination of high-temperature extraction, short-distance transportation, pipeline insulation, and a temperature-controlled heat tracing layer to maintain a high temperature of the carbonization tail gas during transportation. By maintaining the inner wall temperature of the high-temperature transportation pipeline above 500°C, preferably between 550 and 650°C, the condensation, adhesion, and accumulation of tar, wood vinegar, and heavy volatile substances within the pipeline can be reduced, thereby lowering the risk of pipeline blockage and improving the reliability of continuous transportation and stable utilization of the carbonization tail gas.

[0022] This invention incorporates a high-temperature pressure stabilization buffer and / or high-temperature pretreatment process before the carbonization tail gas enters the lime kiln calcination zone. It employs settling dust removal, cyclone dust removal, or high-temperature resistant filtration to remove dust, carbon black, and solid particles entrained in the tail gas. This treatment mitigates fluctuations in tail gas pressure and flow rate, reduces the adverse effects of particulate matter entering the lime kiln on limestone calcination and finished product quality, and avoids problems such as lime blackening, decreased activity, or uneven calcination that may occur if the carbonization tail gas directly enters the material layer.

[0023] This invention prioritizes the carbonization exhaust gas into the pre-combustion zone located at the inlet of the lime kiln or in the lower part of the kiln chamber, or into an independent combustion zone. There, it is thoroughly mixed and combusted with primary and secondary air, ensuring that combustible components such as carbon monoxide, hydrogen, methane, light hydrocarbons, and tar vapor are burned off as completely as possible before entering the calcination zone. The gas is then supplied to the lime kiln as high-temperature flue gas. This method improves combustion completeness and reduces direct contact between unburned tar and carbon black and limestone materials, thereby improving the color and calcination quality of the lime product.

[0024] This invention addresses the issues of fluctuating calorific value and flow rate of carbonization tail gas by implementing auxiliary fuel replenishment and temperature-linked control measures. When the carbonization tail gas is insufficient to maintain the temperature of the lime kiln calcination zone, coal gas, natural gas, pulverized coal, biomass pellet fuel, or other auxiliary fuels can be added. The induced draft volume, air distribution volume, temperature-controlled heating layer, and auxiliary fuel supply are adjusted according to the temperatures of the high-temperature conveying pipeline, pre-combustion zone, and calcination zone to stabilize the calcination zone temperature at 900–1100°C, reducing under-burning, over-burning, and temperature fluctuations within the kiln.

[0025] This invention also employs high-temperature and corrosion-resistant conveying pipes or composite-lined pipes, and discharges the flue gas after combustion after high-temperature dust removal, necessary cooling, and subsequent dust removal treatment. This improves the durability of the pipeline in high-temperature exhaust gas environments containing sulfur and chlorine, reduces fugitive emissions of smoke and dust, and mitigates the environmental pollution problems caused by direct venting of traditional carbonization exhaust gas or simple incineration. Overall, this invention combines heat recovery, anti-clogging conveying, stable calcination, product quality protection, and flue gas treatment, demonstrating significant energy-saving, environmental protection, and engineering application value. Attached Figure Description

[0026] Figure 1 A comparison chart of traditional fuel substitution rate and calcination zone temperature fluctuation for each group; Figure 2 A comparison chart of the quality of pipe attachments and lime activity for each group. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Unless otherwise specified, the raw materials involved in the present invention are purchased through conventional commercial channels. Experimental methods without specific conditions are conventional methods and conditions well known in the art, or according to the conditions recommended by the instrument manufacturer.

[0028] Unless otherwise specified, Nm 3 The dry standard volume is at 0℃ and 101.325kPa. The lower heating values ​​of carbonization tail gas and auxiliary fuel are calculated based on the lower heating values ​​under this condition. The lime kiln is a continuous vertical lime kiln, and the calcination time is the average residence time of limestone in the calcination zone.

[0029] Example 1: A process for recovering heat energy from biomass carbonization tail gas for limestone calcination, comprising the following steps: S1: Wood chips and bamboo chips are used as biomass raw materials, with a mass ratio of wood chips to bamboo chips of 7:3. They are crushed and sieved to control the particle size to 5 mm. Then, they are dried at 100℃ for 3 hours to achieve a moisture content of 12 wt% in the dried biomass pellet raw materials. S2: The biomass pellet raw material obtained in step S1 is fed into a screw extrusion briquetting equipment for molding. The briquetting temperature is 170℃ and the pressing pressure is 20MPa to obtain biomass briquetting rods with a diameter of 50mm and a length of 180mm. S3: The biomass briquette obtained in step S2 is fed into a carbonization furnace for carbonization. The biomass feed rate is 500 kg / h, the carbonization temperature is 520℃, the heating rate is 5℃ / min, and the holding time is 5h. Carbonized products and carbonization tail gas are obtained. The carbonization furnace is arranged below the kiln chamber of the lime kiln, and the carbonization tail gas is led out upward from the tail gas outlet of the carbonization furnace. S4: The carbonization tail gas generated in step S3 is extracted at high temperature without condensation or cooling. The temperature of the carbonization tail gas at the tail gas outlet of the carbonization furnace is 600℃, and the lower heating value is 5.2 MJ / Nm³. 3 The flow rate is 280 Nm 3 / h; The carbonization exhaust gas is sent into the high-temperature conveying pipeline through the induced draft device, so that the high-temperature conveying pipeline is kept under a slight negative pressure of -200Pa. S5: The inner diameter of the high-temperature conveying pipeline is 300mm, the pipeline length is 5m, and the flow velocity of the carbonization tail gas in the high-temperature conveying pipeline is controlled at 3.0~4.5m / s; the high-temperature conveying pipeline is covered with high-temperature resistant insulation material with a thickness of 120mm, and a temperature-controlled heat tracing layer is set to keep the inner wall temperature of the high-temperature conveying pipeline at 600℃. S6: The carbonized tail gas conveyed in step S5 is sent into a high-temperature pressure-stabilizing buffer section. The inner wall temperature of the high-temperature pressure-stabilizing buffer section is maintained at 600℃, and the effective volume is 0.60m³. 3 The carbonization tail gas is subjected to high-temperature settling dust removal and cyclone dust removal treatment after pressure stabilization and flow equalization. S7: The carbonization tail gas treated in step S6 is introduced into the pre-combustion zone at the inlet of the lime kiln, and combustion air is supplied through primary and secondary air inlets; the air volume ratio of primary air to secondary air is 50:50, the excess air coefficient of the combustion air is 1.30, and the combustion air is preheated to 250℃ by the waste heat of the flue gas before being supplied; the temperature of the pre-combustion zone is controlled at 1100℃, and the effective volume of the pre-combustion zone is 1.50m³. 3 The residence time of the carbonization tail gas in the pre-combustion zone is 1.5s, and the high-temperature flue gas after pre-combustion enters the lime kiln calcination zone. S8: Limestone with a particle size of 50mm is added to the lime kiln at a rate of 300kg / h. The temperature of the lime kiln calcination zone is controlled at 1000℃, and the calcination time is 5h. Based on the actual calcination heat consumption of limestone of 3.5MJ / kg, the heat required for limestone calcination in this embodiment is 1050MJ / h. The effective heat utilization coefficient of the carbonization tail gas is calculated to be 0.70, and the effective heat supply of the carbonization tail gas is 1019MJ / h. A lower heating value of 15MJ / Nm³ is used. 3 The coal gas is used as auxiliary fuel, with an effective heat utilization coefficient of 0.75, and the coal gas replenishment flow rate is 5 Nm³ during stable operation. 3 / h, the effective heat supply of gas is 56MJ / h, and the total effective heat supply is 1075MJ / h; During operation, when the temperature in the lime kiln calcination zone is below 900℃, increase the gas supply flow rate to 0–8 Nm³. 3 Adjust the flow rate within the specified range; when the calcination zone temperature rises above 950℃ and stabilizes for more than 10 minutes, gradually reduce the gas supply flow rate; when the calcination zone temperature stabilizes at 950~1050℃ and the carbonization tail gas heating meets the requirements, reduce the gas supply flow rate to 0~2Nm³. 3 / h or stop adding; S9: The flue gas after combustion is first treated by cyclone dust removal, then by high-temperature filtration, and then cooled by waste heat exchange. In this embodiment, the measured dew point of the flue gas after combustion is 150°C, and the inlet flue gas temperature of the bag filter is controlled at 180°C before entering the bag filter for treatment and then being discharged. The calcined lime product is cooled, screened, and packaged before being stored in the warehouse. During operation, when the inner wall temperature of the high-temperature conveying pipeline is lower than 520°C, the temperature control and heat tracing are enhanced. When the inner wall temperature of the high-temperature conveying pipeline is lower than 500°C, the carbonization tail gas conveying volume is reduced or switched to the bypass combustion path.

[0030] Example 2: A process for recovering heat energy from biomass carbonization tail gas for limestone calcination, comprising the following steps: S1: Take straw and fruit shells as biomass raw materials, with a straw to fruit shell mass ratio of 6:4. Crush and sieve them to control the particle size to 10mm; then dry them at 80℃ for 6 hours to achieve a moisture content of 18wt% for the dried biomass pellet raw materials. S2: The biomass pellet raw material obtained in step S1 is fed into a mechanical extrusion briquetting equipment for molding. The briquetting temperature is 120℃ and the pressing pressure is 30MPa to obtain biomass briquetting rods with a diameter of 80mm and a length of 300mm. S3: The biomass briquette obtained in step S2 is fed into a carbonization furnace for carbonization. The biomass feed rate is 350 kg / h, the carbonization temperature is 450℃, the heating rate is 2℃ / min, and the holding time is 8h. Carbonized products and carbonization tail gas are obtained. The carbonization furnace is arranged close to the lime kiln, and the carbonization tail gas is led out upward from the carbonization furnace tail gas outlet. S4: The carbonization tail gas generated in step S3 is extracted without condensation and cooling; an insulation layer and an electric heating jacket are installed outside the tail gas outlet section of the carbonization furnace. The electric heating jacket is connected to the temperature sensor of the outlet section to maintain the temperature of the carbonization tail gas at 500℃ before it enters the high-temperature conveying pipeline; the lower heating value of the carbonization tail gas is 4.2 MJ / Nm³. 3 The flow rate is 220 Nm 3 / h; The high-temperature conveying pipeline is kept under a slight negative pressure of -300Pa by the exhaust fan; S5: The inner diameter of the high-temperature conveying pipeline is 250mm, the pipeline length is 2m, and the flow velocity of the carbonization tail gas in the high-temperature conveying pipeline is controlled at 3.0~4.5m / s; the high-temperature conveying pipeline is covered with high-temperature resistant insulation material with a thickness of 150mm, and a temperature-controlled heat tracing layer is set to keep the inner wall temperature of the high-temperature conveying pipeline at 550℃. S6: The carbonized tail gas conveyed in step S5 is sent to the high-temperature stabilizing buffer section and the high-temperature pretreatment section, where the inner wall temperature is maintained at 550℃ and the effective volume is 0.80m³. 3 After being stabilized and evenly distributed, the carbonization tail gas is then subjected to high-temperature settling dust removal and cyclone dust removal treatment in sequence. S7: The carbonization tail gas processed in step S6 is introduced into the independent combustion zone, and combustion air is supplied through primary and secondary air inlets; the air volume ratio of primary air to secondary air is 40:60, the excess air coefficient of the combustion air is 1.50, and the combustion air is preheated to 400℃ by the waste heat of the lime kiln before being supplied; the temperature of the independent combustion zone is controlled at 900℃, and the effective volume of the independent combustion zone is 2.40m³. 3 The residence time of the carbonization tail gas in the independent combustion zone is 3 seconds, and the high-temperature flue gas after combustion enters the lime kiln calcination zone. S8: Limestone with a particle size of 80mm is added to the lime kiln at a rate of 180kg / h. The temperature of the lime kiln calcination zone is controlled at 900℃, and the calcination time is 8h. Based on the actual calcination heat consumption of limestone of 3.5MJ / kg, the heat required for limestone calcination in this embodiment is 630MJ / h. The effective heat utilization coefficient of the carbonization tail gas is calculated to be 0.60, and the effective heat supply of the carbonization tail gas is 554MJ / h. A lower heating value of 34MJ / Nm³ is used. 3 Natural gas is used as auxiliary fuel. Assuming an effective thermal efficiency coefficient of 0.75, the natural gas replenishment flow rate during stable operation is 3 Nm³. 3 / h, the effective heat supply of natural gas is 77MJ / h, and the total effective heat supply is 631MJ / h; During operation, when the temperature in the lime kiln calcination zone is below 900℃, increase the natural gas replenishment flow rate, which should be between 0 and 5 Nm³. 3 Adjust within the range of / h; when the temperature of the calcination zone recovers to 900-950℃ and remains stable for more than 10 minutes, gradually reduce or stop the natural gas supply; S9: The flue gas after combustion is first treated by settling dust removal and cyclone dust removal, and then cooled by waste heat exchange; in this embodiment, the measured dew point of the flue gas after combustion is 145℃, and the inlet flue gas temperature of the bag filter is controlled at 170℃ before entering the bag filter for treatment and then being discharged; the calcined lime product is cooled, screened and packaged before being stored in the warehouse; during operation, when the inner wall temperature of the high-temperature conveying pipeline is lower than 520℃, the temperature control and heat tracing are enhanced; when the inner wall temperature of the high-temperature conveying pipeline is lower than 500℃, the carbonization tail gas conveying volume is reduced or switched to the bypass combustion path.

[0031] Example 3: A process for recovering heat energy from biomass carbonization tail gas for limestone calcination, comprising the following steps: S1: Wood chips and agricultural and forestry waste are used as biomass raw materials, with a mass ratio of wood chips to agricultural and forestry waste of 8:2. The raw materials are crushed and sieved to control the particle size to 3 mm. Then, they are dried at 120℃ for 1 hour to achieve a moisture content of 8 wt% for the dried biomass pellets. S2: The biomass pellet raw material obtained in step S1 is fed into a screw extrusion briquetting equipment for molding. The briquetting temperature is 220℃ and the pressing pressure is 10MPa to obtain biomass briquetting rods with a diameter of 20mm and a length of 50mm. S3: The biomass briquette obtained in step S2 is fed into a carbonization furnace for carbonization. The biomass feed rate is 700 kg / h, the carbonization temperature is 600℃, the heating rate is 10℃ / min, and the holding time is 2h. Carbonized products and carbonization tail gas are obtained. The carbonization furnace is arranged below the kiln chamber of the lime kiln, and the carbonization tail gas is led out upward from the tail gas outlet of the carbonization furnace. S4: The carbonization tail gas generated in step S3 is extracted at high temperature without condensation or cooling. The temperature of the carbonization tail gas at the tail gas outlet of the carbonization furnace is 700℃, and the lower heating value is 6.0 MJ / Nm³. 3 The flow rate is 400 Nm 3 / h; The carbonization exhaust gas is sent into the high-temperature conveying pipeline through the induced draft device, so that the high-temperature conveying pipeline is kept under a slight negative pressure of -100Pa. S5: The inner diameter of the high-temperature conveying pipeline is 350mm, the pipeline length is 8m, and the flow velocity of the carbonization tail gas in the high-temperature conveying pipeline is controlled at 3.5~5.0m / s; the high-temperature conveying pipeline is covered with high-temperature resistant insulation material with a thickness of 80mm, and a temperature-controlled heat tracing layer is set to keep the inner wall temperature of the high-temperature conveying pipeline at 650℃. S6: The carbonized tail gas conveyed in step S5 is sent into a high-temperature pressure-stabilizing buffer section, wherein the inner wall temperature of the high-temperature pressure-stabilizing buffer section is maintained at 650℃, and the effective volume is 0.35m³. 3 The carbonization exhaust gas is subjected to high-temperature cyclone dust removal treatment after pressure stabilization and flow equalization. S7: The carbonization tail gas treated in step S6 is introduced into the pre-combustion zone located at the bottom of the lime kiln, and combustion air is supplied through primary and secondary air inlets; the air volume ratio of primary air to secondary air is 60:40, the excess air coefficient of the combustion air is 1.10, and the combustion air is preheated to 100℃ by the waste heat of the flue gas before being supplied; the temperature of the pre-combustion zone is controlled at 1300℃, and the effective volume of the pre-combustion zone is 0.80m³. 3 The residence time of the carbonization tail gas in the pre-combustion zone is 0.5s, and the high-temperature flue gas after combustion enters the lime kiln calcination zone. S8: Limestone with a particle size of 30mm is added to the lime kiln at a rate of 480kg / h. The temperature of the lime kiln calcination zone is controlled at 1100℃, and the calcination time is 2h. Based on the actual calcination heat consumption of limestone of 3.6MJ / kg, the heat required for limestone calcination in this embodiment is 1728MJ / h. The effective heat utilization coefficient of carbonization tail gas is calculated to be 0.72, and the effective heat supply of carbonization tail gas is 1728MJ / h. No auxiliary fuel is added during stable operation. When the carbonization tail gas flow rate decreases or the temperature of the calcination zone is lower than 900℃, coal powder with a low heating value of 24MJ / kg is added to the pre-combustion zone. The amount of coal powder added is adjusted within the range of 0-5kg / h. During operation, when the temperature in the calcination zone recovers to 1080-1120℃ and remains stable for more than 10 minutes, the coal powder replenishment should be gradually reduced or stopped. S9: The flue gas after combustion is first treated by cyclone dust removal and high-temperature resistant filtration, and then cooled by waste heat exchange. In this embodiment, the measured dew point of the flue gas after combustion is 160℃, and the inlet flue gas temperature of the bag filter is controlled at 200℃ before entering the bag filter for further treatment and then being discharged. The calcined lime product is cooled, screened, packaged, and then stored. During operation, when the inner wall temperature of the high-temperature conveying pipeline is lower than 520℃, the temperature control heating is activated. When abnormal induced draft, abnormal combustion, pipeline overheating, or abnormal temperature in the calcination zone occurs, the carbonization tail gas conveying volume is reduced or the bypass combustion path is switched.

[0032] Comparative Example 1: Unlike Example 1, this comparative example follows the procedures in S1-S3 of Example 1 for pretreatment of biomass raw materials, briquetting, and carbonization to obtain carbonized products and carbonization tail gas. Instead of introducing the carbonization tail gas into the lime kiln for heat recovery, the tail gas is switched to a bypass combustion path for simple combustion treatment. The lime kiln independently uses coal gas as the calcination heat source, with a stable coal gas supply flow rate of 94.0 Nm³. 3 / h.

[0033] Comparative Example 2: Unlike Example 1, in S5, the temperature control and heat tracing layer outside the high-temperature conveying pipeline was removed, and the thickness of the insulation layer was adjusted from 120mm to 20mm; the length of the high-temperature conveying pipeline was still 5m, and the inner diameter of the pipeline was still 300mm; during continuous operation, the inner wall temperature of the high-temperature conveying pipeline was 450℃.

[0034] Comparative Example 3: Unlike Example 1, this comparative example omits the high-temperature pressure stabilization buffer section and the high-temperature pretreatment section in S6. The carbonization tail gas does not undergo pressure stabilization, flow equalization, high-temperature settling dust removal and cyclone dust removal after passing through the high-temperature conveying pipeline, but directly enters the pre-combustion zone at the lime kiln inlet.

[0035] Comparative Example 4: Unlike Example 1, this comparative example omits the pre-combustion zone in S7. After high-temperature stabilization and pretreatment, the carbonization tail gas is not fully combusted in the pre-combustion zone, but is directly introduced into the lime kiln combustion zone from the lower part of the lime kiln chamber, where it mixes and combusts with the combustion air inside the kiln.

[0036] Comparative Example 5: Unlike Example 1, in S8 and S9 of this comparative example, the auxiliary fuel replenishment amount is not determined based on the lower heating value of the carbonization tail gas, the carbonization tail gas flow rate, the limestone addition amount, and the temperature of the lime kiln calcination zone, nor is auxiliary fuel linkage combustion performed; the coal gas replenishment flow rate is fixed at 0 Nm³. 3 / h, the pre-combustion and calcination process is maintained only by adjusting the amount of carbonization exhaust gas introduced and the amount of combustion air supplied.

[0037] Performance Testing: To verify the heat recovery effect, continuous operation stability, lime product quality, and flue gas treatment effect of the process of this invention, performance tests were conducted using the processes obtained in Examples 1-3 and Comparative Examples 1-5. Except for the differences in the processes of each group, all tests were conducted using a continuous vertical lime kiln. Temperature sensors, pressure sensors, flow meters, and flue gas analyzers were calibrated before testing. During the test, the state of the carbonization tail gas after entering the high-temperature conveying pipeline was taken as the starting point for tail gas utilization, and the stable operation starting point was taken as the temperature of the lime kiln calcination zone stabilizing within the set range (Comparative Example 1 does not involve the carbonization tail gas entering the high-temperature conveying pipeline; its test starting point was when the lime kiln gas heating system was running stably; the flue gas emission data of Comparative Example 1 were statistically analyzed based on the combined emission results of the carbonization tail gas bypass combustion outlet and the lime kiln outlet).

[0038] Each process group first underwent a pre-run of no less than 2 hours to allow the carbonization furnace, tail gas conveying pipeline, pre-combustion zone, and lime kiln calcination zone to reach a stable state; then, continuous testing was conducted for 8 hours. During the test, the inner wall temperature of the high-temperature conveying pipeline, the pressure difference across the pipeline, the temperature of the pre-combustion zone, and the temperature of the lime kiln calcination zone were recorded every 1 minute; the carbonization tail gas flow rate, combustion air flow rate, auxiliary fuel supply, and CO concentration in the flue gas were recorded every 10 minutes; and the biomass feed rate, limestone addition, and ash output were recorded every hour. Each test group was repeated 3 times, and the average value of the results was taken.

[0039] The carbonization tail gas heating, auxiliary fuel consumption, and lime kiln temperature stability were tested in Examples 1-3 and Comparative Examples 1-5 under continuous operation. The lower heating value of the carbonization tail gas was determined using a gas calorific value analyzer, and the flow rate of the carbonization tail gas was measured using a high-temperature resistant gas flow meter. The auxiliary fuel consumption was recorded by the corresponding gas flow meter or solid fuel metering device. The temperature of the lime kiln calcination zone was measured by thermocouples installed at three locations: the upper, middle, and lower parts of the calcination zone, and the average value of the three measuring points was taken as the calcination zone temperature.

[0040] The heat input of carbonization tail gas is calculated using the following formula: Heat input of carbonization tail gas / (MJ / h) = Lower heating value of carbonization tail gas / (MJ / Nm³) 3 )×Carbonization exhaust gas flow rate / (Nm 3 / h).

[0041] The auxiliary fuel heat input is calculated using the following formula: Auxiliary fuel heat input / (MJ / h) = Lower heating value of auxiliary fuel × Auxiliary fuel supply.

[0042] The heat required for limestone calcination is calculated based on the actual heat consumption of limestone calcination, which is taken as 3.5 MJ / kg; when using high-temperature short-time operating conditions, the actual heat consumption of limestone calcination is taken as 3.6 MJ / kg. The traditional fuel substitution rate is calculated using the following formula: Traditional fuel substitution rate / % = Effective heat supply of carbonization tail gas / Heat required for limestone calcination × 100%.

[0043] Wherein, the effective heat supply of carbonization tail gas = heat input of carbonization tail gas × effective heat utilization coefficient of carbonization tail gas. The effective heat utilization coefficients of carbonization tail gas in Examples 1, 2, and 3 are 0.70, 0.60, and 0.72, respectively; the heat utilization coefficients of the corresponding examples are used under the same operating conditions in the comparative examples. The average temperature of the calcination zone, the temperature fluctuation range, the cumulative time below 900℃, and the auxiliary fuel consumption are recorded.

[0044] The anti-condensation and anti-clogging effects of Examples 1-3 and Comparative Example 2 during the carbonization tail gas transportation process were tested. Before the test, the initial pressure difference at the inlet and outlet of the high-temperature transportation pipeline was recorded. After 8 hours of continuous operation, the change in pressure difference before and after the pipeline was recorded. If the pipeline pressure difference continued to rise and exceeded twice the initial pressure difference during operation, or if there was poor tail gas transportation or abnormal induced draft, the maximum continuous stable operating time of this group was recorded (the maximum continuous stable operating time refers to the continuous operating time when the pipeline pressure difference, tail gas transportation, pre-combustion zone or combustion zone temperature fluctuation, CO concentration, and lime kiln calcination zone temperature are all within the set control range; when there is abnormal pipeline pressure difference, poor tail gas transportation, significant combustion fluctuation, abnormal increase in CO concentration, or continuous deviation of calcination zone temperature from the set range, the maximum continuous stable operating time of this group is recorded).

[0045] After the test was completed and the temperature was cooled to a safe level, an inspection section of the same length in the middle of the high-temperature conveying pipeline was opened. A representative pipe section with a length of 1m was taken, and the deposits on the inner wall of the pipe were collected and weighed. The results are expressed in g / m. For Comparative Example 2, since the high-temperature insulation and conveying above 500℃ was cancelled, the focus was on recording the pipe inner wall temperature, pressure difference rise, deposit mass, and continuous running time to evaluate the condensation and adhesion of tar, wood vinegar, and heavy volatile substances.

[0046] The pretreatment and pre-combustion effects of exhaust gas in Examples 1-3, Comparative Examples 3 and 4 were tested. During the tests, the temperature fluctuation range in the pre-combustion zone or the lime kiln combustion zone was recorded, the CO concentration in the flue gas was recorded, and the flame stability was observed. The CO concentration was measured at the outlet of the pre-combustion zone or at the flue gas passage before entering the lime kiln calcination zone. Measurements were taken every 10 minutes, and the average value was taken after 8 hours of continuous measurement. The temperature fluctuation range in the pre-combustion zone was calculated as the difference between the highest and lowest temperatures during the test. For Comparative Example 4, if the carbonized exhaust gas directly entered the lime kiln combustion zone, the CO concentration was measured at the outlet of the lime kiln combustion zone, and whether obvious black deposits appeared on the surface of the limestone material layer was recorded.

[0047] The quality of the lime products obtained in Examples 1-3 and Comparative Examples 1-5 was tested. After stable operation, lime samples were collected from the discharge end of the lime kiln every 1 hour for each group, with 1 kg of sample taken each time. After 5 consecutive samplings, the samples were mixed evenly and the test samples were obtained by quartering.

[0048] The testing items included calcium oxide content, loss on ignition, activity, and appearance color. Calcium oxide content was determined using acid-base titration; loss on ignition was calculated using the mass difference before and after high-temperature ignition; activity was determined using hydrochloric acid titration, expressed as the volume of hydrochloric acid consumed per unit mass of lime within a specified time; appearance color was determined using a whiteness meter. Before testing, the lime sample was crushed and sieved to the same particle size range. Each indicator was tested in triplicate, and the average value was taken.

[0049] The emissions of flue gas after combustion were tested in Examples 1-3 and Comparative Examples 1-5. Flue gas sampling points were set at the outlet of the final dust removal device. After stable operation, flue gas samples were collected every 1 hour for 5 consecutive times to determine particulate matter concentration, CO concentration, and flue gas opacity. Particulate matter concentration was determined using the isokinetic sampling and weighing method, CO concentration was determined using a flue gas analyzer, and flue gas opacity was determined using the Ringelmann opacity method or the equivalent opacity test method.

[0050] When using a baghouse dust collector, record the inlet flue gas temperature and simultaneously record the dew point temperature of the flue gas to ensure that the inlet flue gas temperature is higher than the dew point temperature and within the allowable operating temperature range of the filter media. If condensation, bag clogging, or abnormal increase in dust collector pressure difference occurs during the test, record the time of the abnormality and the pressure difference change.

[0051] Table 1 shows the energy utilization and temperature stability test results of the examples and comparative examples, recording the lower heating value of carbonization tail gas, carbonization tail gas flow rate, auxiliary fuel consumption, traditional fuel substitution rate, average temperature of the calcination zone, temperature fluctuation range, and cumulative time below 900°C.

[0052] Table 2 shows the high-temperature transport and pre-combustion stability test results of the examples and comparative examples. The inner wall temperature of the high-temperature transport pipeline, the increase in pipeline pressure difference, the mass of pipeline deposits, the temperature fluctuation of the pre-combustion zone, the CO concentration at the outlet of the pre-combustion zone, and the maximum continuous stable operation time are recorded.

[0053] Table 3 shows the test results of lime product quality and flue gas emissions for the examples and comparative examples, recording calcium oxide content, loss on ignition rate, activity, whiteness, particulate matter emission concentration, flue gas CO concentration, and flue gas opacity.

[0054] Figure 1 The graph shows the comparison of the traditional fuel substitution rate and the temperature fluctuation of the calcination zone for each group. The horizontal axis represents Examples 1-3 and Comparative Examples 1 and 5, the left vertical axis represents the traditional fuel substitution rate, and the right vertical axis represents the temperature fluctuation range of the calcination zone.

[0055] Figure 2 The graph shows a comparison of the quality of pipe attachments and lime activity for each group. The horizontal axis represents Examples 1-3, Comparative Examples 2, 3, and 4, the left vertical axis represents the quality of pipe attachments, and the right vertical axis represents the lime activity.

[0056] Table 1. Energy utilization and temperature stability test results of the examples and comparative examples (Note: In Comparative Example 1, the carbonization tail gas was not introduced into the lime kiln, therefore the lower heating value, flow rate, and conventional fuel substitution rate of the carbonization tail gas were not calculated. In Comparative Example 2, the inner wall temperature of the high-temperature conveying pipeline was fixed at 450°C, which is lower than the anti-condensation conveying temperature requirement of 500°C or higher of this invention. The carbonization tail gas still exhibited certain condensation adhesion and reduced effective flow rate during the conveying process. The lower heating value and flow rate of the carbonization tail gas in Comparative Example 2 are the average effective measured values ​​before entering the pre-combustion zone after low-temperature conveying).

[0057] Table 2. High-temperature transport and pre-combustion stability test results of the examples and comparative examples

[0058] Table 3. Test results of lime product quality and flue gas emissions in the examples and comparative examples.

[0059] From Table 1 and Figure 1 It can be seen that Examples 1-3 can all achieve stable calcination with low auxiliary fuel consumption. The lower heating value of the carbonization tail gas in Example 1 is 5.2 MJ / Nm³. 3 The flow rate is 280 Nm 3 / h, the traditional fuel substitution rate reaches 97.1%, requiring only 5.0 Nm³ of supplemental gas. 3With a flow rate of [amount] / h, the average temperature of the calcination zone can be stabilized at 1003℃, with a temperature fluctuation range of only 38℃. In Example 2, under low-temperature long-term operating conditions, the traditional fuel substitution rate still reached 88.0%, and the average temperature of the calcination zone was 906℃. In Example 3, the heating demand could be met by utilizing the high calorific value and large flow rate of carbonized tail gas, achieving a traditional fuel substitution rate of 100%. This demonstrates that after high-temperature transportation, pre-combustion, and heat matching, carbonized tail gas can effectively replace traditional fuels in limestone calcination.

[0060] Comparative Example 1, which did not recover carbonization tail gas, had an average calcination zone temperature of 1002℃ and a temperature fluctuation range of 42℃, but required the consumption of 94.0 Nm³ of coal gas. 3 / h, with a traditional fuel substitution rate of 0. Compared to Example 1, under essentially the same calcination temperature, the gas consumption decreased from 94.0 Nm³ / h. 3 / h decreased to 5.0 Nm 3 The / h indicates that the present invention can significantly reduce the amount of traditional fuel used. Although the proportion of carbonization tail gas used for heating in Comparative Example 5 is relatively high, after the auxiliary fuel linkage combustion is cancelled, the temperature fluctuation range in the calcination zone increases to 182℃, and the cumulative time below 900℃ reaches 76min / 8h. This indicates that the calorific value and flow rate of carbonization tail gas fluctuate, and it is difficult to achieve stable calcination in the long term by relying solely on air distribution and induced draft regulation. The linkage control of combustion is necessary to prevent underburning and temperature field fluctuations.

[0061] From Table 2 and Figure 2 It is evident that high-temperature transport significantly affects the anti-clogging effect. In Examples 1-3, the pipe inner wall temperatures were 600℃, 550℃, and 650℃, respectively, with pipe deposit mass values ​​of only 7.8 g / m, 12.5 g / m, and 5.2 g / m. The increase in pipe pressure difference did not exceed 1.0 kPa, and the continuous stable operating time was greater than 8 hours. In Comparative Example 2, the pipe inner wall temperature was fixed at 450℃, lower than the control requirement of 500℃ or higher in this invention. The pipe deposit mass increased to 94.8 g / m, the increase in pressure difference reached 6.3 kPa, and the continuous operating time was shortened to 5.8 hours. This indicates that tar, wood vinegar, and heavy volatiles are more easily condensed and adhered to the low-temperature pipe wall, leading to increased resistance and fluctuations in exhaust gas flow.

[0062] Comparative Example 3, after removing the high-temperature pressure stabilization buffer and pretreatment, showed a similar quality of pipe deposits to Example 1, but the temperature fluctuation in the pre-combustion zone increased to 118°C, and the CO concentration rose to 390 mg / m³. 3 This indicates that the main problem is not condensation blockage, but rather the failure to reduce exhaust gas pressure, flow rate, and particulate entrainment, leading to uneven combustion and reduced burnout. In Comparative Example 4, after the pre-combustion zone was removed, the CO concentration further increased to 620 mg / m³. 3The whiteness dropped to 65.6 and the activity dropped to 296mL, indicating that when the carbonization tail gas was directly burned in the kiln, the tar vapor, carbon black and unburned combustible components were more likely to come into contact with the limestone material, causing the product to turn black and its activity to decrease.

[0063] Table 3 shows that the lime products obtained in Examples 1-3 were of good quality, with a calcium oxide content of 90.8%-92.6%, an activity of 334-368 mL, a smoke opacity of 0.5, and a particulate matter emission concentration of 15.2-21.5 mg / Nm³. 3 In contrast, Comparative Examples 2, 3, 4, and 5, due to insufficient condensation during transport, inadequate pretreatment, insufficient pre-combustion, and lack of afterburning control, respectively exhibited problems such as decreased calcium oxide content, increased loss on ignition, reduced activity, or increased CO emissions. In summary, the effectiveness of this invention does not stem from a single exhaust gas introduction, but rather from the synergistic effect of processes including high-temperature anti-condensation transport, pressure-stabilized pretreatment, pre-combustion burnout, afterburning temperature stabilization, and dust removal emissions.

[0064] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims.

Claims

1. A process for recovering heat energy from biomass carbonization tail gas for limestone calcination, characterized in that, Includes the following steps: S1: The biomass raw material is crushed, sieved and dried to obtain biomass pellet raw material; S2: The biomass pellet raw material obtained in step S1 is fed into a briquetting equipment for pressing and molding to obtain biomass briquette material. S3: The biomass briquette material obtained in step S2 is fed into a carbonization furnace for carbonization treatment to obtain carbonized products and carbonization tail gas. S4: The carbonization tail gas generated in step S3 is drawn out from the tail gas outlet of the carbonization furnace at high temperature and sent into the high temperature conveying pipeline through the induced draft device. S5: In step S4, an insulation layer and a temperature-controlled heat tracing layer are installed on the outside of the high-temperature conveying pipeline to keep the inner wall temperature of the high-temperature conveying pipeline above 500°C. S6: The carbonization tail gas conveyed in step S5 is sent to the high temperature stabilizing buffer section and / or high temperature pretreatment section to stabilize the pressure, equalize the flow and remove dust from the carbonization tail gas. S7: The carbonized tail gas after step S6 is introduced into the pre-combustion zone set up in conjunction with the lime kiln or into an independent combustion zone, and combustion air is supplied to mix and burn the carbonized tail gas with the combustion air. S8: Limestone is added to the lime kiln and calcined under the action of the high-temperature flame or high-temperature flue gas generated in step S7; the heating ratio of carbonization tail gas is determined according to the low heating value, flow rate and temperature of the lime kiln calcination zone of the carbonization tail gas; when the carbonization tail gas is insufficient for heating, auxiliary fuel is added to the pre-combustion zone, independent combustion zone or lime kiln combustion zone to maintain the temperature required for limestone calcination. S9: The flue gas after carbonization tail gas combustion is discharged after dust removal treatment, and the calcined lime product is collected; during the high-temperature transportation, pre-combustion and limestone calcination of carbonization tail gas, the temperature of the high-temperature transportation pipeline, the pre-combustion zone, the lime kiln inlet and the lime kiln calcination zone is monitored, and the induced draft volume, carbonization tail gas introduction volume, combustion air supply volume, temperature control and heat tracing status and auxiliary fuel supply volume are adjusted according to temperature changes.

2. The process for recovering heat energy from biomass carbonization tail gas for limestone calcination according to claim 1, characterized in that, In step S1, the particle size of the pulverized biomass raw material is controlled to be 3-10 mm after sieving; the drying temperature is 80-120℃, and the moisture content after drying is 8-18 wt%; in step S2, the briquetting temperature is 120-220℃, and the pressing pressure is 10-30 MPa; the diameter of the obtained biomass briquette is 20-80 mm, and the length is 50-300 mm; in step S3, the carbonization temperature is 450-600℃, the heating rate is 2-10℃ / min, and the holding time is 2-8 h.

3. The process for recovering heat energy from biomass carbonization tail gas for limestone calcination according to claim 1, characterized in that, In step S4, the carbonization tail gas is directly extracted at high temperature without condensation and cooling treatment; the temperature of the carbonization tail gas at the tail gas outlet of the carbonization furnace or after heat preservation and supplementation of the outlet section is 500-700℃; when the outlet temperature of the carbonization tail gas is lower than 500℃, the outlet section is insulated and supplemented with heating when necessary to ensure that the temperature of the tail gas entering the high-temperature conveying pipeline is not lower than 500℃; the induced draft device is used to stably draw in the carbonization tail gas and maintain a slight negative pressure state in the high-temperature conveying pipeline, the slight negative pressure being -100 to -300 Pa.

4. The process for recovering heat energy from biomass carbonization tail gas for limestone calcination according to claim 1, characterized in that, In step S5, the length of the high-temperature conveying pipeline from the tail gas outlet of the carbonization furnace to the high-temperature pressure stabilizing buffer section, pre-combustion zone, or independent combustion zone is 2-8m; the high-temperature conveying pipeline is a high-temperature resistant and corrosion-resistant pipeline, or a conveying pipeline formed by combining a high-temperature resistant metal outer pipe with a refractory material lining, a ceramic lining, or a corrosion-resistant lining; the high-temperature conveying pipeline is covered with a high-temperature resistant insulation material with an insulation layer thickness of 80-150mm; the temperature control and heat tracing layer is connected to a temperature detection device to compensate for heating the pipeline through temperature control, so that the inner wall temperature of the high-temperature conveying pipeline is maintained at 550-650℃.

5. The process for recovering heat energy from biomass carbonization tail gas for limestone calcination according to claim 1, characterized in that, In step S6, the high-temperature pressure stabilizing buffer section and / or high-temperature pretreatment section are located between the high-temperature conveying pipeline and the pre-combustion zone or independent combustion zone; the inner wall temperature of the high-temperature pressure stabilizing buffer section and / or high-temperature pretreatment section is maintained at 550-650℃.

6. The process for recovering heat energy from biomass carbonization tail gas for limestone calcination according to claim 1, characterized in that, In step S7, combustion air is supplied through primary air inlet and secondary air inlet; the air volume ratio of primary air to secondary air is 40:60 to 60:40; the excess air coefficient of combustion air is 1.10 to 1.50; the combustion air is supplied after being preheated to 100 to 400°C by waste heat from lime kiln or flue gas.

7. The process for recovering heat energy from biomass carbonization tail gas for limestone calcination according to claim 1, characterized in that, In step S7, the combustion temperature of the pre-combustion zone or independent combustion zone is controlled at 900-1300℃, and the residence time of the carbonized exhaust gas in the pre-combustion zone or independent combustion zone is 0.5-3s.

8. The process for recovering heat energy from biomass carbonization tail gas for limestone calcination according to claim 1, characterized in that, In step S8, the limestone has a particle size of 30-80 mm; the temperature of the lime kiln calcination zone is controlled at 900-1100℃, and the calcination time is 2-8 h; under the lime kiln structure, the effective heat utilization coefficient of the carbonization tail gas is 0.60-0.

75.

9. The process for recovering heat energy from biomass carbonization tail gas for limestone calcination according to claim 1, characterized in that, In step S8, the auxiliary fuel is one or more combustible gases, such as coal gas or natural gas, or one or more solid fuels, such as pulverized coal or biomass pellet fuel.

10. The process for recovering heat energy from biomass carbonization tail gas for limestone calcination according to claim 1, characterized in that, In step S9, when the inner wall temperature of the high-temperature conveying pipeline is below 520°C, the compensation heating of the temperature-controlled heat tracing layer is activated or enhanced; when the inner wall temperature of the high-temperature conveying pipeline is below 500°C, the amount of carbonization tail gas conveyed is reduced, or the carbonization tail gas is switched to the bypass combustion path; when the temperature of the lime kiln calcination zone is below the lower limit of the preset calcination temperature range, the amount of combustion air supplied is increased, the amount of carbonization tail gas introduced is increased, or auxiliary fuel is added.

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