發(fā)布時間：2017-12-26 23:19

  本文關(guān)鍵詞：灰分沉積特性的理論和實驗研究　出處：《中國科學(xué)技術(shù)大學(xué)》2017年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 沉積 洗選廢棄物 機(jī)理 燒結(jié) 合成煤灰 硅鋁比 酸堿比 模型

【摘要】：在大型循環(huán)流化床中摻燒煤泥、煤矸石等煤洗選加工廢棄物不但能提高能源的綜合利用效率,而且還能阻止其對大氣、水質(zhì)、土壤污染,具有顯著的經(jīng)濟(jì)效益和環(huán)保效益。然而,已投產(chǎn)的鍋爐運行實踐表明,在爐膛內(nèi)部、換熱器表面或旋風(fēng)分離器內(nèi)表面、落料腿等部位發(fā)生的粘附、燒結(jié)、板結(jié)等灰分沉積現(xiàn)象,會腐蝕設(shè)備裝置,顯著降低鍋爐效率,影響鍋爐的穩(wěn)定運行,嚴(yán)重時,會造成停爐停產(chǎn),甚至帶來安全隱患。探究灰分沉積的機(jī)理及其影響因素,從而提供減輕灰分沉積傾向的可行方案,對鍋爐的穩(wěn)定運行及新鍋爐的設(shè)計都大有裨益,進(jìn)而對洗選廢棄物的處理、潔凈煤燃燒技術(shù)提供支撐�；曳殖练e本質(zhì)上是一個復(fù)雜的含化學(xué)反應(yīng)的高溫氣固兩相流邊界層問題�；曳殖练e包括灰分的粘附、發(fā)展、燒結(jié)和熔融等過程。本文圍繞灰分沉積過程的描述,沉積過程的實驗?zāi)M,運行參數(shù)、結(jié)構(gòu)參數(shù)、物性參數(shù)和成分參數(shù)對灰分沉積特性的影響規(guī)律等,開展了相關(guān)的研究工作。本文第一章介紹了灰分沉積特性研究的應(yīng)用背景和意義、灰分沉積的危害以及關(guān)于灰分沉積國內(nèi)外研究的現(xiàn)狀。本文第二章概述了研究灰分沉積特性的實驗方法和實驗平臺。分別對灰熔點測定方法、微觀樣貌測定方法、灰分成分測量方法及自創(chuàng)的體積形變實驗進(jìn)行了詳細(xì)的概述和總結(jié)。結(jié)合循環(huán)流化床鍋爐灰分沉積的特點,搭建了灰分沉積實驗平臺。分別對灰分沉積實驗平臺的設(shè)計目標(biāo)、主要部件構(gòu)成、工作模式及適用范圍作了詳細(xì)闡述。極限工況實驗表明,實驗平臺不能模擬出灰分沉積、熔融軟化的現(xiàn)象,實驗平臺有致命的設(shè)計缺陷。其主要原因是加熱元件的不能滿足實驗需求,灰分顆粒未能被加熱到熔融或半熔融狀態(tài)。最后,對試驗爐平臺加熱系統(tǒng)改進(jìn)、供料系統(tǒng)的可控性及沉積探針測量拆卸式探頭的溫度精度的提高等提出了改善性建議。本文第三章首先梳理了前人對沉積機(jī)理的探索,指出完備的沉積機(jī)理應(yīng)該包含顆粒尺度模型、顆粒物性模型、顆粒碰撞模型、顆粒受力模型、顆粒輸運過程以及顆粒沉積判據(jù)。隨后,分別對沉積輸運模型、顆粒受力模型、及沉積判據(jù)等做出了概述性總結(jié)。特別地,在對顆粒沉積判據(jù)的總結(jié)中,得出沉積評價指標(biāo)是基于結(jié)果導(dǎo)向的,每種指標(biāo)只適用于特定的范圍,需探索過程引導(dǎo)的微觀顆粒的沉積判據(jù)。在氣固兩相流的受力分析及各種力的尺度等級分析基礎(chǔ)上,結(jié)合沉積過程的具體現(xiàn)象,得出了不同粒徑顆粒在沉積過程中的受力情況。最后,梳理了煙氣飛灰顆粒從初始層的形成,到逐漸發(fā)展生長,沉積物形成過后內(nèi)部形態(tài)的變化,及最終形成板結(jié)的沉積塊的完備的沉積描述。本文第四章探究了硅鋁比對灰分燒結(jié)特性的影響規(guī)律。以Si02-Al203-MgO-Fe203-Ca0為原料,制備了五種不同硅鋁比的合成灰分樣品。在馬沸爐中對不同硅鋁比的灰分樣品進(jìn)行處理,讓樣品在馬沸爐中存留12小時,以制成燒結(jié)樣品。綜合運用VSR、DIL、SEM、XPS及XRD的實驗結(jié)果描述了燒結(jié)樣品的形貌特征及化學(xué)成分特征。實驗結(jié)果表明,燒結(jié)過程主要發(fā)生在溫度超過1000℃的第三階段,伴隨著VSR曲線顯著降低。過量的SiO2(S/A=0.45)會導(dǎo)致多孔結(jié)構(gòu)而過量的Al2O3(S/A=0.5)會產(chǎn)生大顆粒團(tuán)聚物并阻礙共晶體的生成和發(fā)展。其他三組樣品(S/A=1.5,2.5,3.5),燒結(jié)后具有致密的非晶體結(jié)構(gòu),主要由低熔融溫度的共晶體組成(例如輝石、瓦茲利石)。隨著硅鋁比的增加,燒結(jié)溫度首先急劇下降到較低水平,然后逐漸上升到一個相對較高的水平。實驗結(jié)果表明,在灰分中添加富含A1203的添加劑比添加富含Si02成分的添加劑對于減輕灰分的沉積現(xiàn)象更為有效。本文第五章探究了煤灰成分與軟化溫度之間的關(guān)系。在本章中,實驗所用的灰分為合成煤灰。選取48種不同成分的煤灰軟化溫度,運用二元回歸分析方法,建立軟化溫度與酸堿比和硅鋁比之間的經(jīng)驗?zāi)Ｐ�。熱變形分析方法所測得的軟化溫度以及X射線衍射所測量的晶體成分,用于驗證模型的有效性。實驗結(jié)果表明,合成煤灰軟化溫度與晶體成分的實驗結(jié)果與經(jīng)驗?zāi)Ｐ臀呛?由此可認(rèn)為,經(jīng)驗?zāi)Ｐ褪呛侠淼�。本文第六章對本論文工作進(jìn)行了總結(jié),提出了關(guān)于灰分沉積特性研究有待進(jìn)一步探究的課題。
[Abstract]:In large circulating fluidized bed, coal washing and processing waste such as coal and coal gangue can not only improve the comprehensive utilization efficiency of energy, but also prevent it from polluting the atmosphere, water and soil, which has significant economic and environmental benefits. However, the practice shows that the boiler operation has been put into operation, and in the internal surface of the heat exchanger or cyclone inner surface, blanking leg occurred adhesion, sintering, compaction and other ash deposition, corrosion equipment, significantly reduce the efficiency of the boiler, affect the boiler stable operation, serious, will cause the stop furnace production, and even bring security risks. To explore the mechanism and influencing factors of ash deposition, so as to provide a feasible plan to reduce the tendency of ash deposition, which is beneficial to the stable operation of boiler and the design of new boiler, and to provide support for the treatment of cleaning waste and the technology of clean coal combustion. The ash deposition is essentially a complex boundary layer of high temperature gas-solid two-phase flow with chemical reactions. Ash deposition includes the process of adhesion, development, sintering and melting of ash. This paper focuses on the description of ash deposition process, experimental simulation of deposition process, operation parameters, structural parameters, physical parameters and composition parameters on the influence of ash deposition characteristics. In the first chapter, the application background and significance of the study on ash deposition characteristics, the harm of ash deposition and the status of the research on ash deposition at home and abroad are introduced. The second chapter of this paper gives an overview of the experimental and experimental platform for the study of ash deposition characteristics. The ash melting point determination method, microscopic appearance measurement method, ash composition measurement method and self created volume deformation test were summarized and summarized. In combination with the characteristics of ash deposition in a circulating fluidized bed boiler, an experimental platform for ash deposition is set up. The design objectives, main components, working mode and scope of application of the ash deposition experimental platform are described in detail. The experiment shows that the experimental platform can not simulate the phenomenon of ash deposition and melt softening, and the experimental platform has fatal design defects. The main reason is that the heating element can not meet the needs of the experiment, and the ash particles can not be heated to the melting or semi melting state. Finally, suggestions for improvement of the heating system of the test platform, the controllability of the feeding system, and the improvement of the temperature accuracy of the probe with the probe of the dismantling probe are put forward. In the third chapter, we first summarize the previous exploration of sedimentary mechanism, and point out that the complete sedimentary mechanism should include particle size model, particle physical model, particle collision model, particle force model, particle transport process and particle deposition criterion. Then, the sedimentary transport model, the particle loading model and the sedimentary criterion are summarized. Especially, in the summary of the criterion of particle deposition, it is concluded that the evaluation index of sedimentation is based on result oriented, and each index is applicable to a specific range, and we need to explore the sedimentary criterion of microscopic particles guided by the process. Based on the force analysis of the gas-solid two-phase flow and the scale analysis of all kinds of forces, combined with the specific phenomena of the deposition process, the forces acting on different particle sizes during the deposition process are obtained. Finally, the formation of flue gas ash particles from the initial layer to the gradual growth and development, the change of the internal morphology after the formation of the sediments, and the complete deposition description of the final forming of the deposition blocks are combed. In the fourth chapter, the influence of silicon and aluminum ratio on ash sintering characteristics is investigated. Five kinds of synthetic ash samples with different Si / Al ratios were prepared with Si02-Al203-MgO-Fe203-Ca0 as raw material. To deal with the different silicon aluminum ash samples than in muffle furnace, let the sample remain 12 hours in boiling, to produce sintered samples. The experimental results of VSR, DIL, SEM, XPS and XRD were used to describe the characteristics of the morphology and chemical composition of the sintered samples. The experimental results show that the sintering process mainly occurs in the third stage of the temperature over 1000 degrees C, with the VSR curve decreasing significantly. Excessive SiO2 (S/A=0.45) can lead to porous structure and excessive Al2O3 (S/A=0.5) produces large particle agglomeration and hinders the formation and development of eutectic. The other three groups of samples (S/A=1.5,2.5,3.5), sintered with dense amorphous structure, mainly consist of eutectic with low melting temperature (such as pyroxene and Waziri S). With the increase of the ratio of silicon and aluminum, the sintering temperature drops sharply to a lower level, and then gradually rises to a relatively high level. The experimental results show that adding A1203 rich additives in ash is more effective than adding additives rich in Si02 components to reduce the deposition of ash. The fifth chapter of this paper explores the relationship between the composition of the coal ash and the softening temperature. In this chapter, the ash used in the experiment is synthetic coal ash. The softening temperature of 48 different components is selected and the empirical model between the softening temperature, the ratio of acid to base and the ratio of silicon and aluminum to the ratio of softening and alkali to the ratio of silicon and aluminum is established by the two element regression analysis. The softening temperature measured by the thermal deformation analysis method and the crystal composition measured by X ray diffraction are used to verify the validity of the model. The experimental results show that the experimental results of the fly ash softening temperature and crystal composition are in agreement with the empirical model, thus the empirical model is reasonable. The sixth chapter of this paper is a summary of the work of this paper, and the subject of further research on the research of ash deposition characteristics is put forward.
【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：TQ530

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