燃烧流体力学讲义 (5).ppt

Chapter 5 Fluidization
§1. Introduction
1. History
, Fritz Winkle observed the phenomena of fluidization and developed the gasifigator.
1939. Warren Lewis and Edwin Gillil and discovered the technique of catalytic cracking with fast fluidization.
1960’s Douglass Elliott began to use fluidized bed to produce steam.
1982 pany set up first CFB 84MW
2. Comparison of Different Kinds of Boilers
特性炉排燃烧鼓泡床循环床煤粉炉
床高或燃料
燃烧区高度(m) 1 - 2 15 - 40 27 - 45
截面风速(m/s) - 4-8 4 - 6
过量空气(%) 20-30 20-25 10-20 15-30
截面热负荷
(MW/m2) - - 3-5 4-6
特性炉排燃烧鼓泡床循环床煤粉炉
煤的粒度(mm) 6-32 6以下 6以下
负荷调节比例 4:1 3:1 3-4:1
燃烧效率(%) 85-90 90-96 95-99 99
Nox排放(ppm) 400-600 300-400 50-200 400-600
炉内脱硫效率
(%) 80-90 80-90 低
3. Characteristics of bustion
1) Wide fuel application;
2) High efficiency of desulphuration;
3) Low NOx emission;
4) Large charge regulation range
§2. Hydrodynamics
1. Fluidization Region
1) Packed bed (fixed bed)
no relative move between particles
(5-1)
Where f - spherisity of particles
= surface of sphere with same volume as particle/real surface
2) Bubbling bed
(5-2)
From (5-1), (5-2)
(5-3)
For small particles, umb > umf
(5-4)
Where F is mass factor of particles with dp < 45mm
3) Spouted bed
condition: Dbmax >
minimum spout velocity Usl = Umf + (gD) (5-5)
4) Turbulent bed
Initial velocity of transition
Terminal velocity of transition
Note: In the above mentioned states, the particles move within certain height above distributor.
5) Fast Fluidization (Circulating Fluidization)
uf - up > ut
Properties:
axis: S distribution
radii: core -annular flow
local: cluster
6) Fluidization Figure