| A large amount of piled fly ash has caused serious waste of resources,land occupation and environmental pollution.Its large-scale utilization is the dual demand of sustainable resources and environmental protection.At present,the utilization of fly ash presents key industry pain points such as low efficiency,low value,and high energy consumption.It is difficult to achieve large-scale ultrafine grinding with traditional pulverization technology,which limits the large-scale utilization of fly ash.To this end,this paper proposes to use industrial waste heat to prepare superheated steam as a pulverizing medium for large-scale,low-cost ultrafine grinding of fly ash.In this paper,through theoretical analysis and FLUENT fluid simulation,the energy conversion law of industrial waste heat to crushing kinetic energy is studied,and the relationship between key control conditions such as equipment structure size,steam parameters and crushing classification flow field is analyzed,and the dynamics of steam crushing is revealed.Mechanism,established a key technology control system for steam pulverization.Based on the above research,a steam jet mill industrial production line with a single steam capacity of 10 t/h was designed and built.The key control technology system of steam pulverization was verified and optimized through industrial experiments,and the economic and environmental benefits were analyzed.The main research work and achievements are as follows:(1)Based on the first law of thermodynamics,from the perspective of matching the energy conversion process and the kinetic energy utilization rate of the crushing medium,the energy conversion process and conversion rate of the industrial waste heat to the crushing medium,the characteristics of the steam crushing classification flow field,and the steam energy-crushing power are studied.The transformation relationship reveals the key parameters and transformation mechanism of steam energy conversion into effective pulverization kinetic energy,and establishes the kinetic mechanism of steam pulverization.Steam pulverization using industrial waste heat as energy supply has the characteristics of few energy conversion links,high conversion rate of effective pulverization kinetic energy,and large pulverizing kinetic energy.The kinetic energy conversion rate of air pulverization decreases with the increase of the pulverizing pressure.The average kinetic energy utilization rate in the conventional air pulverization pressure range of 0.5-1.3 MPa is 8.58%,while the average kinetic energy of steam pulverization in the conventional pressure range of 0.5-4.0MPa is 8.58%.The utilization rate is 17%,and the minimum utilization rate is 10%;the speed of steam pressure 4.0 MPa can reach 1200 m/s,which is twice that of conventional air pulverization.(2)The characteristics of the steam phase transition,pulverizing flow field,particle acceleration,and classification flow field of the nozzle were studied under different key control conditions such as steam parameters,nozzle size and number,blade angle,feed particle size,and cylinder angle.According to the changing law of steam pulverization,the key control technology system of steam pulverization is established.The results show that when the steam pressure at the inlet of the nozzle is 0.5 MPa and the temperature is higher than the saturation of 120 ℃,the steam at the outlet of the nozzle will not undergo phase change;the higher the Mach number,the better the particle acceleration performance.The maximum velocity is 320m/s higher;the larger the particle,the worse the acceleration.At 1.48 Ma,the position where the 20μm particle obtains the maximum velocity and the maximum velocity is 550 m/s and11.7 times,while that of the 1000μm particle is 147 m/s and 19.1 times.The research on the flow field characteristics of steam staging shows that the optimal key control conditions for steam staging under this condition are the flow rate of 1.4 kg/s,the blade angle of 25°,and the cylinder angle of 9°.(3)The research results of the coupled flow field characteristics of crushing and grading show that the coupled flow field formed by the 3 nozzles is more uniform than that of the 6nozzles,and the streamlines in the grading wheel area have no eddy currents,and the swirl streamlines are better than those of the 6 nozzles;The maximum velocity difference obtained by particles under the same particle size is 50 m/s,and the particle acceleration characteristics of 3 nozzles are better than that of 6 nozzles.Overall,the design of large steam jet mills can choose 3 nozzles design.(4)The steam jet mill pulverizing fly ash industrial production line with a single machine steam consumption of 10 t/h was designed and built.It has been running stably for 3 years.The steam parameters,nozzle size and number,blade angle and the impact of key control conditions such as feed particle size on output,finished product particle size and energy consumption,verified and optimized the key control technology system established in chapters three and four.The industrial experiment results show that the optimal control conditions for producing d90 < 10 μm with raw ash are: the number of nozzles is 3,the steam inlet pressure is 1.0 MPa,and the blade angle is 0.At this time,the output is 2.56 t/h,and the energy consumption is 3.34 t steam/h.t output;the optimal control conditions for producing d90 < 10μm with primary ash are: when the number of nozzles is 3,the steam pressure is 0.95 MPa and the blade angle is 25°,the output is 3.06 t/h,and the energy consumption is 3.01 t steam/t output.(5)The economic benefit analysis of 10 t/h steam mill shows that the output of primary ash is 216,000 tons/year,the total investment is 12.7 million yuan(excluding land costs),and the investment recovery period is 9 months(excluding factory construction),40% energy saving than the traditional mill,with better economic benefits.This paper provides a new way for the efficient utilization of industrial waste heat,provides new methods,new processes and new equipment for the crushing of fly ash with high yield and low energy consumption,and establishes a new mechanism for energy conservation and emission reduction of fly ash by industrial waste heat large-scale ultrafine grinding,which lays a foundation for promoting the application of large solid waste resources in the chemical industry. |
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