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Recovery boiler fireside deposu thermal shock resistance and thermal conductivity

Başlık çevirisi mevcut değil.

  1. Tez No: 403270
  2. Yazar: SELÇUK ÖZCAN
  3. Danışmanlar: Belirtilmemiş.
  4. Tez Türü: Yüksek Lisans
  5. Konular: Kimya Mühendisliği, Makine Mühendisliği, Chemical Engineering, Mechanical Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1991
  8. Dil: İngilizce
  9. Üniversite: University of Toronto
  10. Enstitü: Yurtdışı Enstitü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 141

Özet

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Özet (Çeviri)

Removal of fireside deposits from the heat transfer tubes in kraft recovery boiiers is carried out by sootblovving, and occasionally“chill-and-blow”practice. During chili-and-blovv, black liquor flow is reduced to rapidly cool the deposit. Thermal stresses generated in the deposit as a resuit of thermal shock can effectively vveaken the deposit, facilitating its cleaning. This work consists of two parts. The first part invoives the investigation of the mechanical vveakening effect of thermal stresses generated by the transient temperature gradient, and by the difference in thermal expansion of the deposit and the tube. The second part invoives the measurement of the thermal conductivity of the deposit both in-situ and in the laboratory. The mechanical vveakening of the deposit as a consequence of transient temperature gradients generated during thermal shock was determined using polycrystalline sodium chloride as raw material. The thermal shock procedure consisted of quenching of a preheated sodium chloride disk with an air jet. The mechanical vveakening vvas quantified by measuring the decrease in biaxial flexure strength, at various quenching times and surface heat transfer coefficients. İt could occur via transient thermal stresses and crack propagation. Approximately 35% loss in biaxial flexure strength could be achieved at heat transfer coefficients above roughly 4.9x103 W/m2K, and at quenching durations above roughly 40 seconds. The effectiveness of the stresses generated in the deposit-steel interface was investigated by measuring the shear stress required to break the bond betvveen a stainless steel plate, and a synthetic deposit disk that rested on it. This composite structure was heated up to a temperature vvhich was above the first melting point of the disk, and then cooled to a final temperature at vvhich the measurement was taken. İt vvas found that the shear stress required to break the bond, was zero at temperatures belovv 460 K, above vvhich it increased, and vvent through a maximum at about 620 K. Above 620 K, it gradually decreased, and became zero at 1070 K. The results of the thermal conductivity study shovved that: i) the thermal conductivity of lovver superheater deposit vvas 1.8 ± 0.9 W/m K almost unchanged in a temperature range from 860 K to 1040 K, ii) thermal conductivity of precipitator dust pellets of various densities vvas approximately 1.1 W/m K, after they had been sintered, and iii) the thermal conductivity of the precipitator dust vvas strongly related to % density increase.

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