本文選題：多組分顆粒　切入點：循環(huán)流化床　出處：《哈爾濱工業(yè)大學(xué)》2016年碩士論文

【摘要】：循環(huán)流化床鍋爐(CFB)技術(shù)是一項近20年來才發(fā)展起來的燃煤技術(shù),因其燃燒效率高、污染物排放低和燃料適應(yīng)性強等契合能源發(fā)展趨勢的特色優(yōu)勢,受到廣泛的關(guān)注和研究。然而在其內(nèi)部稠密氣固兩相流動過程中,高隨機性、多種作用耦合和固相屬性不均等復(fù)雜因素給數(shù)值研究帶來了很大的困難。目前的數(shù)值研究中,由于模擬條件的限制和實際物性的復(fù)雜,對于寬篩分的煤炭顆粒進(jìn)行理想化處理已經(jīng)成為共識。大多數(shù)的循環(huán)流化床內(nèi)的流動、燃燒傳熱反應(yīng)模擬主要基于平均顆粒屬性(包括粒徑和密度)的假設(shè),極大減少了計算量和對數(shù)學(xué)模型的要求。然而實際床料顆粒的粒徑和密度等屬性存在明顯差異,單組分顆粒的模擬過度簡化,將對模擬結(jié)果產(chǎn)生很大的影響。在多組分顆粒流化模擬方面,盡管有雙組分顆粒模擬的先例,然而模型依舊很不完善,忽略了顆粒間碰撞的動量交換,且兩種顆粒的假設(shè)并不夠典型。因此有必要建立一套基于多組分顆粒假設(shè)的模擬模型,并對循環(huán)流化床內(nèi)的流動和燃燒進(jìn)行數(shù)值模擬研究,進(jìn)行氣固兩相流向?qū)嶋H寬篩分顆粒體系發(fā)展的探索,為循環(huán)流化床甚至內(nèi)部存在氣固流動的化工設(shè)備的發(fā)展提供數(shù)值借鑒。根據(jù)煤炭顆粒粒徑符合Rosin-Rammler分布的特點,將顆粒粒徑細(xì)化為典型的細(xì)、中、粗三組分顆粒群進(jìn)行研究,以顆粒動力學(xué)理論為出發(fā)點,考慮多組分顆粒間的各種相互作用,運用雙流體模型,建立基于氣體-多組分顆粒的數(shù)值模擬模型。模擬采用多相流程序軟件,由于其開源特性,更便于根據(jù)需要搭配模型。文中詳細(xì)分析了固相應(yīng)力模型和關(guān)鍵的顆粒動力學(xué)相關(guān)理論,之后考慮多組分煤炭顆粒燃燒的主要反應(yīng),編寫并調(diào)試了完整的模擬程序。本文進(jìn)行了三維流化床提升管的模型驗證對比、二維冷態(tài)循環(huán)流化床流動模擬和熱態(tài)流化床燃燒模擬。提升管的模擬驗證了模型的可行性,對比了多組分顆粒假設(shè)相比于單組分顆粒的優(yōu)點,并對比了兩種主要固相應(yīng)力模型的區(qū)別。冷態(tài)循環(huán)流化床模擬得出關(guān)于多組分顆粒存在時濃度場、速度場、湍動度等流場特性,并分析顆粒密度、流化氣速對多組分顆粒群的流動影響。最后進(jìn)行了二維流化床熱態(tài)燃燒模擬,燃燒主要考慮了煤的熱解、煤焦燃燒、揮發(fā)分和CO燃燒以及CO2的還原反應(yīng),著重分析了組分場分布、各相顆粒相關(guān)的反應(yīng)速率和溫度場特性等參數(shù)。探討了一二次風(fēng)配比對燃燒的影響,對比了揮發(fā)分差異較大的煙煤和無煙煤的燃燒情況,分析各類顆粒的燃燒特點及其對整體燃燒的影響。
[Abstract]:Circulating Fluidized bed Boiler (CFB) is a coal-fired technology developed in recent 20 years. Because of its high combustion efficiency, low pollutant emission and strong fuel adaptability, it has attracted extensive attention and research.However, in the process of dense gas-solid two-phase flow, the complex factors of high randomness, interaction coupling and imparity of solid properties bring great difficulties to numerical research.In the present numerical research, due to the limitation of simulation conditions and the complexity of actual physical properties, it has become a consensus to idealize the treatment of coal particles with wide sieving.In most circulating fluidized beds, the simulation of combustion heat transfer reaction is based on the assumption of average particle size and density, which greatly reduces the computational complexity and the requirement of mathematical model.However, there are obvious differences in the particle size and density of the actual bed particles, and the simplification of the simulation of the single component particles will have a great impact on the simulation results.In the multi-component particle fluidization simulation, although there is a precedent of two-component particle simulation, the model is still imperfect, ignoring the momentum exchange between particles, and the assumption of the two particles is not typical enough.Therefore, it is necessary to establish a simulation model based on the assumption of multi-component particles, and to simulate the flow and combustion in a circulating fluidized bed, and to explore the development of gas-solid two-phase flow to the actual wide sieve particle system.It provides a numerical reference for the development of chemical equipment with gas-solid flow in circulating fluidized bed and even inside.According to the characteristics of coal particle size according to Rosin-Rammler distribution, the particle size is refined into typical fine, medium and coarse three component particle groups. Based on the theory of particle dynamics, various interactions between multicomponent particles are considered.A numerical simulation model based on gas-multi-component particles was established by using two-fluid model.The multiphase flow software is used in the simulation, because of its open source feature, it is more convenient to match the model according to the need.The solid stress model and the relevant theory of particle dynamics are analyzed in detail. After considering the main reaction of multi-component coal particle combustion, a complete simulation program is compiled and debugged.In this paper, the model verification and comparison of three-dimensional fluidized bed riser, two-dimensional cold circulating fluidized bed flow simulation and hot fluidized bed combustion simulation are carried out.The simulation of the riser validates the feasibility of the model, compares the advantages of the multicomponent particle hypothesis over that of the single component particle, and compares the differences between the two main solid stress models.The characteristics of concentration field, velocity field and turbulence degree in the presence of multi-component particles are obtained by cold circulating fluidized bed simulation, and the effects of particle density and fluidized gas velocity on the flow of multi-component particle groups are analyzed.Finally, the thermal combustion simulation of a two-dimensional fluidized bed is carried out. The combustion mainly considers the pyrolysis of coal, the combustion of coal char, the combustion of volatile matter and CO, and the reduction reaction of CO2. The distribution of compositional field is emphatically analyzed.The parameters of reaction rate and temperature field related to each phase particle.The influence of the ratio of primary and secondary air on combustion was discussed. The combustion conditions of bituminous coal and anthracite with big difference in volatile content were compared, and the combustion characteristics of various kinds of particles and their effects on the overall combustion were analyzed.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2016
【分類號】：TK229.66
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本文編號：1724142