Condensation-reboiling closed circulation method for tail gas generated by ultrafine grinding of superheated steam
Technical Field
The invention relates to the technical field of industrial waste gas treatment, waste heat recovery and low-level energy utilization, in particular to an energy-saving and emission-reducing method for closed cyclic utilization of chemical tail gas. .
Background
The superheated steam flow crushing is a processing technology of superfine powder materials. Compared with air, superheated steam as a crushing medium has high cleanliness and low viscosity, and can eliminate static electricity generated by particle friction in the crushing process so as to reduce the secondary cohesion phenomenon of particles, thereby becoming a preferred technology for processing high-end inorganic ultrafine powder products. One of the defects of the prior art is high energy consumption, because 1.2-2.5 MPa (absolute pressure, the same below) of superheated steam generated by a boiler at 280-420 ℃ is used as a crushing medium, the enthalpy of the superheated steam is converted into fluid kinetic energy through a supersonic nozzle, the proportion of the kinetic energy actually used in the crushing process is less than 25%, and more than 75% of the enthalpy of the superheated steam is remained in crushed tail gas at 95-125 kPa (absolute pressure, the same below) and 110-150 ℃. In the existing waste heat recovery technology, the tail gas is used for heating combustion-supporting air at 65-120 ℃ (Liushajun and the like, the application of airflow pulverization in titanium dioxide production, Guangzhou chemical industry, 2015, 43 (23): 215-216) or hot water at 65 ℃ (Chengsheng, titanium dioxide airflow pulverization production process optimization and energy-saving technology application, Shandong chemical industry, 2017, 46: 72-73), the grade of the recovered waste heat is too low, and the effect of reducing the primary energy consumption in the steam generation process is not great. The invention is a more effective waste heat utilization method, which maintains the enthalpy grade of the tail gas and replaces the primary energy consumed in the boiler steam generation process on the premise of ensuring the process condition of superheated steam supersonic speed grinding, thereby recycling the enthalpy of the tail gas accounting for 75 percent of the ratio and greatly reducing the energy consumption in the superheated steam supersonic speed grinding process.
According to the closed cycle method for condensing and reboiling the tail gas by ultrafine grinding of superheated steam, firstly, the tail gas is pressurized and condensed under the action of a water injection pump, and then the condensate is subjected to adiabatic reboiling under the pressure of 105-200 kPa, so that the tail gas is purified and regenerated into clean saturated steam. And then reduced to a superheated steam state required for the ultra-fine pulverization process by mechanical pressurization. By adopting the method, the purification and regeneration of the superheated steam flow ultrafine grinding tail gas are completed through pressurization condensation-adiabatic reboiling, and the cyclic utilization is realized, so that the steam generation energy consumption accounting for 75 percent of the traditional superheated steam flow ultrafine grinding method is saved, a steam boiler is replaced, and the method has the four benefits of remarkable energy conservation, emission reduction, consumption reduction and income increase.
Disclosure of Invention
The invention discloses a closed cycle method for condensing and reboiling tail gas generated by ultrafine grinding of superheated steam flow. The method is suitable for occasions where the superheated steam medium with the pressure of 1.2-2.5 MPa and the temperature of 280-420 ℃ is used for crushing water-insoluble particles to generate crushed tail gas with the pressure of 95-125 kPa and the temperature of 110-150 ℃. For example, in the process of crushing the superfine titanium dioxide by adopting a flat supersonic jet mill, superheated steam with the pressure of 1.8-2.0 MPa and the temperature of 280-320 ℃ is used as a crushing medium, and the main component of the generated tail gas is still the superheated steam, the pressure of which is 95-125 kPa, and the temperature of which is 110-140 ℃. The method for improving the tail gas waste heat recovery technology comprises the following steps: firstly, pressurizing and condensing the tail gas, and then, carrying out adiabatic reboiling on the condensate to generate clean saturated steam with the pressure of 105-200 kPa; and then the mixture is heated and pressurized by a steam pressurizing machine to form superheated steam which meets the requirements of supersonic airflow superfine grinding process and is 1.2-2.5 MPa and 280-420 ℃. The invention has the main idea that a pressurizing condensation-adiabatic reboiling tail gas purification and steam regeneration process and system are constructed according to the fluid statics, the gas-liquid two-phase fluid dynamics, the heat and mass transfer principle, the steam temperature-pressure-enthalpy correlation characteristic and the phase change law, the closed circulation of superheated steam supersonic speed crushing media is realized by utilizing mechanical pressurization, the primary energy consumption in the steam generation process is avoided, a boiler is not used, and economic and applicable low-carbon environmental protection technical progress is provided for superheated steam supersonic speed airflow crushing.
As shown in the attached figure, a vibration metering screw conveyor 1 adds the particle raw materials to be crushed into a superheated steam flow crusher 2, the superheated steam with the pressure of 1.2-2.5 MPa and the temperature of 280-420 ℃ sent by a steam compressor 3 carries out ultrafine crushing under the supersonic speed condition, the steam flow is cooled, decelerated and kept in an overheated state to carry ultrafine powder products into a bag filter 4 for separation, the ultrafine powder products are collected from a lower outlet, and crushing tail gas is output from an upper outlet of the bag filter 4, kept in the overheated state, kept at the pressure of 95-125 kPa and the temperature of 110-150 ℃. The tail gas is sucked into a water jet condenser 5, is wrapped by 100-120 ℃ circulating liquid jet flow conveyed by a reboiling liquid circulating pump 6, flows down along a vertical downcomer 10 and directly reaches 1m below the liquid level of the lower section of a heat insulation reboiler 7, is subjected to rotational flow when the temperature is raised to 110-125 ℃ to be boiled and vaporized, and generates heat insulation reboiling saturated steam of 120-200 kPa, and is sucked into a front steam inlet of a steam pressurizer 3; circulating liquid cooled to 2-5 ℃ due to vaporization passes through a liquid lifting pipe embedded below the liquid level, rises through a partition plate, enters an upper space of a heat insulation reboiler 7, is continuously boiled and vaporized, is further cooled to 2-5 ℃, 70% of generated 105-175 kPa heat insulation reboiled saturated steam is sucked into a middle steam inlet of a steam compressor 3, the rest 30% of generated 105-175 kPa heat insulation reboiled saturated steam continuously rises and flows into a pipe of a pipe shell type falling film degasser 8 directly communicated with a top cover of the heat insulation reboiler 7, is condensed and conveyed to a post-process, the condensed heat in the pipe is transferred to the outside of the pipe, and the saturated steam generated by the falling film evaporation outside the pipe is sucked into a rear steam inlet of the steam compressor 3 and has a temperature of 80. According to the mass and heat balance rule of the adiabatic reboiling process, the amount of the water vapor sucked by the water injection condenser 5 is equal to the total amount of the vapor generated by the adiabatic reboiler 7, and the ratio of the vapor generation amount of the lower section to the vapor generation amount of the upper section is equal to the ratio of the temperature reduction amplitude of the circulating liquid passing through the lower section to the upper section; saturated steam entering the steam pressurizer 3 from the front-mounted steam inlet, the middle-mounted steam inlet and the rear-mounted steam inlet is mixed, pressurized and heated to 1.2-2.5 MPa, the temperature of the saturated steam is 280-420 ℃, the saturated steam is conveyed to the superheated steam flow pulverizer 2 to complete a pulverizing task, tail gas is sucked into the water jet condenser 5, circulating liquid is subjected to adiabatic reboiling on the lower section and the upper section, the temperature of the circulating liquid is recovered to 100-120 ℃, the circulating liquid is conveyed to the water jet condenser 5 by the circulating pump 6 to suck and pulverize the tail gas, and the steps are repeated in this way and circulated in a closed manner, so that the continuous and stable superheated steam supersonic flow superfine pulverization is realized, and only mechanical energy required by superfine.
The reboiled circulating liquid at 100-120 ℃ is heated by the crushed tail gas at 110-150 ℃ through the water injection condenser 5 to increase the temperature by deltatMass flow rate delivered by the steam press 3m(kg/h) and the mass flow of the reboiler circulation pump 6W(kg/h) varies by a factor oft>(mr)/(WC) The relational expression (c) wherein physical property datar(kJ/kg) is the latent heat of condensation of water vapor,C(kJ/kg. ℃ C.) is the specific heat capacity of water.
Synchronously with the steps, the tail gas dedusting and purifying are completed, so that the dust at the outlet of the bag filter 4 is not more than 30mg/m3) The tail gas is condensed and absorbed by reboiling circulating liquid through a water injection condenser 5 and is conveyed to a heat insulation reboiler 7, the powder particles are enriched due to vaporization of water, the mass percentage concentration of the powder particles is not more than 0.05 percent, the displacement liquid discharge amount at the bottom of the heat insulation reboiler 7 is determined according to the index, the discharged liquid is subjected to solid-liquid separation, the recovered clean clear liquid is supplemented with pure water to be not less than the displacement liquid discharge amount, and the clean clear liquid is added with pure waterThe temperature is adjusted to 80-95 ℃, and the liquid is added into an outer tube falling film space of the falling film degasser 8 from the upper part to be vaporized as a replenishing liquid and returns to the tail gas for closed circulation.
The vertical downcomer 10 extends from the water injection condenser 5 to the lower section below the liquid level through the top cover and the middle partition plate of the heat insulation reboiler 7, and the total height is 15-16 m; the liquid level position of the lower section is 1.5-2.0 m lower than that of the middle partition plate; the lower pipe mouth of the vertical riser pipe 9 penetrating through the middle partition plate and embedded below the liquid level of the lower section is 2.5-3.0 m lower than the partition plate, and the upper pipe mouth is 0.2-0.5 m higher than the partition plate; the adiabatic reboiling circulating liquid rises from the lower section of the adiabatic reboiler 7 to the upper section through the liquid lifting pipe 9, the formed liquid level is 0.3-0.6 m higher than that of the partition plate, the circulating liquid enters an inlet of the reboiling liquid circulating pump 6 from the lower part of the partition plate through a connecting pipeline, and the inlet is 11-12 m lower than the partition plate.
Drawings
FIG. 1 is a schematic diagram of a closed cycle method of condensing and reboiling tail gas generated by ultrafine grinding of superheated steam, provided by the invention, wherein: 1-vibrating a metering screw conveyor; 2-a superheated steam flow pulverizer; 3-a steam press; 4-bag filter; 5-water injection condenser; 6-reboiling liquid circulating pump; 7-an adiabatic reboiler; 8-a falling film degasser; 9-a riser tube; 10-a downcomer.
The figures are further illustrated with reference to examples.
Detailed Description
The following examples are given to illustrate specific embodiments of the present invention.
Example (b): the superheated steam supersonic speed grinding closed cycle process of the annual production of 3 ten thousand tons of the superfine titanium dioxide. Superheated steam parameters: the mass flow is 2000kg/h, the temperature is 380 ℃, and the pressure is 1.5 MPa. Crushing tail gas parameters: volumetric flow 3300 Nm3At 140 ℃ under 120kPa, a dust content of 28 mg/Nm/h3. The local atmospheric pressure value is 98 kPa.
As shown in the figure, a vibration metering screw conveyor 1 is used for adding the particle raw materials to be crushed into a superheated steam flow crusher 2, after the supersonic speed super-fine crushing of the superheated steam at 380 ℃ at 1.5MPa and 2000kg/h sent by a steam pressurizer 3, the super-fine crushing enters a bag filter 4 for steam-powder separation and collection of products, and the pressure of the exhausted tail gas is120kPa, 140 ℃, the steam is sucked into a water jet condenser 5, and is wrapped by a circulating liquid jet flow at 101 ℃ conveyed by a reboiling liquid circulating pump 6 to directly reach a position 1m below the liquid level of the lower section of an adiabatic reboiler 7 along a vertical downcomer to form a rotational flow, the temperature reaches 113 ℃, and 1000 kg/h of adiabatic reboiling saturated steam which is generated by boiling vaporization and 140-150 kPa is sucked into a front steam inlet of a steam pressurizer 3; circulating liquid cooled to 5 ℃ due to vaporization passes through a partition plate through a liquid lifting pipe buried below the liquid level and rises to enter the upper section of a heat insulation reboiler 7 to be continuously boiled and vaporized for further cooling to 5-7 ℃ to generate heat insulation reboiled saturated steam of 107-115 kPa (kilopascal pressure) 1000-1200 kg/h, 700-840 kg/h of the heat insulation reboiled saturated steam is directly sucked into a middle steam inlet of a steam pressurizer 3, the rest of the heat insulation reboiled saturated steam is continuously ascended to flow into a shell-and-tube falling film degasser 8 which is directly communicated with a top cover of the heat insulation reboiler 7 to be condensed and non-condensable gas is discharged to a post-process, the condensed heat in the tube is transferred to the falling film evaporation outside the tube to generate saturated steam of 90 ℃ 160-300 kg/h, and the. The total amount of saturated steam entering the steam pressurizer 3 from the front-mounted steam inlet, the middle-mounted steam inlet and the rear-mounted steam inlet is 2000kg/h, and the saturated steam is mixed by the pressurizer, pressurized, heated to 1.5MPa and at 380 ℃ and is conveyed to the superheated steam flow pulverizer 2 as a pulverizing medium, so that the continuous stable closed-cycle superheated steam supersonic flow ultrafine grinding is realized in cycles. The power of the steam pressurizing machine of 2000kg/h in the embodiment is 380 kW; the power of the reboiling liquid circulating pump is 25kW, and the circulating flow is 110 m3H, the lift is 45 m; the reboiled circulating liquid at 101 ℃ is heated by the crushed tail gas at 140 ℃ and 120kPa through a water injection condenser to raise the temperature deltatEqual to 10-12 ℃.
The mass percentage concentration of the water-insoluble powder particles in the adiabatic reboiler 7 does not exceed 0.05%, and the displacement of the bottom discharge liquid of the adiabatic reboiler 7 is determined to be 0.3 m according to the index3H, 0.25 m of clean clear liquid obtained by solid-liquid separation and recovery3H, supplementing to 0.3 m with pure water3And/h, adding the mixture into the upper part of the falling film degasser 8 for returning and circulating.
The beneficial effects of the embodiment on the supersonic speed grinding process of the superfine titanium dioxide consuming 2000kg/h of superheated steam are as follows: 1) the waste heat of 140 ℃ crushed tail gas is recycled to generate reboiling steam, and the primary energy consumed by replacing 2000kg/h of boiler steam is about 200 kg/h of standard coal; 2) the production process of the superheated steam supersonic speed crushed superfine titanium dioxide powder is free from the dependence on a steam boiler, and the clean production technology is favorably implemented; 3) the power consumption of the embodiment is 405kW, and the energy cost is saved by more than 25% compared with the energy cost of using 2000kg/h boiler steam.
The invention is not limited to the above-described embodiments, the technical solutions of which have been described in the summary of the invention.