investigation on the effect of moisture content on conveying ......liang cai et al. investigation of...
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9th International Freiberg Conference on IGCC & XtL Technology, 3-8 June 2018, Berlin Page 1
Investigation on the effect of moisture
content on conveying and resistance
characteristics of dense-phase pneumatic
conveying Zhen Liu
Department of Energy and Power Engineering
Tsinghua University
Beijing, China
9th International Freiberg Conference on IGCC & XtL Technology, 3-8 June 2018, Berlin
Outline
Page 2
Background
Experimental system
Results and discussion
Conclusion
9th International Freiberg Conference on IGCC & XtL Technology, 3-8 June 2018, Berlin
Pulverized coal
Gas
Gas
Carrier gas
Oxygen
Stock bin
Lock hopper
Feeding hopper
Gasifier
Background
Page 3
– Dense-phase pneumatic conveying is key technology to dry-fed entrained flow coal gasifier
Pneumatic
conveying
• Dense phase
• High pressure The original start-up curve of a dry-fed gasifier. Pulverized coal flow fluctuations often produce the so-called "positive feedback" effect, which can in consequence lead to unstable operation for the gasifier, and finally triggered the shutdown interlock in just 30 min.
9th International Freiberg Conference on IGCC & XtL Technology, 3-8 June 2018, Berlin
Background
Page 4
Influencing factors
Structure
• Top/down/side
discharge
• Pipeline
diameter
• Pipeline layout
and distance
Carrier
gas
• N2/CO2
Material
• Coal rank
• Particle size
• Moisture
content
Operating
parameter
•Pressure
•Total differential
pressure
•Gas velocity
• Solid/gas mass flow rate
• Solid concentration / Solid
loading ratio
• Particle velocity
• Pressure drop
Moisture and energy consumption
• Current dry-fed gasification process
requires the moisture content of
pulverized coal shall be lower than 2%;
• The milling & drying unit cost about 480
MJ to dry 1 ton coal from a moisture
content of 16% to 2%;
• If higher moisture content coal powders
could be transport, it would be a great
energy-saving for the dry-fed gasifiers
and improve the plant economics.
9th International Freiberg Conference on IGCC & XtL Technology, 3-8 June 2018, Berlin
Background
Effect of moisture content
• Small amount: lubrication, friction force between particles decreases (Xie et al, 2007); enhances
electrical conductivity of particles and attenuates the effects of static electricity (Liang et al, 2012)
• Large amount: forming liquid bridge, agglomerability and cohesiveness of particles increases,
flowability decreases (Wang et al, 2008)
• Unstable conveying and blockage when moisture content exceeds 6% for bituminous coal and 9%
for lignite coal (Liang et al, 2013)
Page 5
Xie Xiaoxu et al. Effect of moisture content on the flow characteristics of pulverized coal (in Chinese). Energy Research & Utilization. 2007, (02): 21~23
Liang Cai et al. Investigation of influence of coal properties on dense-phase pneumatic conveying at high pressure. Particuology, 2012,10(3):310-316.
Wang Chuanghong et al. Effects of particle size and moisture content of Shenfu soft coal powder on its fluidity parameters. Journal of East China University of Science and Technology
(Natural Science Edition) (in Chinese). 2008, 34(03): 377~382
Liang Cai et al. Flow characteristics and stability of dense-phase pneumatic conveying of pulverized coal under high pressure. Experimental Thermal and Fluid Science, 2012,41(10):149-
157.
9th International Freiberg Conference on IGCC & XtL Technology, 3-8 June 2018, Berlin Page 6
Background
Experimental system
Results and discussion
Conclusion
9th International Freiberg Conference on IGCC & XtL Technology, 3-8 June 2018, Berlin
Experimental facility
Page 7
Vessel volume,V 5 m3
Max. operating
pressure, P 6 MPa(G)
Operating
temperature, T Room temperature
Carrier gas Nitrogen
• nitrogen supply
• screw feeder
• coal delivery
• conveying and measurement
• coal receiving
• data acquisition and control
Storage
tank
Nitrogen tank
P
P
P
P dP
Pressure reducing valves
Pressurizing gas
Fluidizing gas
Supplementary gas
Conveying pipeline
Relieving gas
Pressure transducer
Differential pressure
transducer
Solid mass flowmeter
Gas flowmeterRegulating
valve
Load cell
Gas
Gas and particles
Delivery
tank
Receiving
tank
Dust
collector
9th International Freiberg Conference on IGCC & XtL Technology, 3-8 June 2018, Berlin
Layout of conveying pipeline
Page 8
Main parameters of measuring instruments
Instrument Measurement range Accuracy
Gas vortex flowmeter 0~20m3/h ±1%
Gas mass flowmeter 0~100Nm3/h ±0.5%
Pressure transducer 0~10MPa ±0.05%
Differential pressure
transducer 0~30kPa, 0~60kPa ±0.05%
Load cell 0~4t ±0.03%
Solid mass flowmeter Velocity: 0~15m/s,
concentration: 0~700kg/m3 ±2%
• Inner diameter of pipeline: 25mm, 15mm, 10mm
• Conveying distance: 197m, 108m
• Straight pipe: horizontal, vertical upward/downward
• Bends: various orientations
dPP
dP
P
dP
dP
P
dP P
dP P
dP
P dP
P
14m (H)
8m (H
)
10.3m
(VU)
2.3m (H
)
1.5m (H
)
2.3m (H
)
10m
(VU)
10m
(VD)
5m
(VD)
Inlet
Outlet
Solid mass
flowmeter
Coal distributor
8m (H
)
Differential
pressure
transducer
Pressure
transducer
Valves for changing
conveying distance
H: horizontal
VU: vertical upward
VD: vertical downward
9th International Freiberg Conference on IGCC & XtL Technology, 3-8 June 2018, Berlin
Material
• Chinese high-volatile bituminous coal
• HMC: coal with high moisture content
• LMC: coal with low moisture content
• Geldart A type particles, Pan PC1 type
particles, suitable for pneumatic
conveying
Page 9
Coal property
Parameter HMC LMC Parameter HMC LMC
Mar/% 6.44 3.02 Cdaf/% 82.46 84.22
Vdaf/% 39.48 36.90 Hdaf/% 4.78 5.24
FCd/% 55.66 55.14 Odaf/% 11.49 9.00
Ad/% 8.03 12.62 Ndaf/% 0.96 1.10
Qnet, ar/(MJ·kg-1) 25.96 26.95 Sdaf/% 0.30 0.44
Property and flowability of pulverized coal
Parameter HMC LMC Parameter HMC LMC
External moisture content/% 4.84 1.63 Median particle diameter/μm 35.3 30.6
Internal moisture content/% 1.60 1.39 Compressibility/% 39.2 39.8
Particle density/(kg·m-3) 1449 1427 Angle of repose/° 48 41
Tap density/(kg·m-3) 852 758 Angle of wall friction/° 27 26
Loosely packed density/(kg·m-3) 518 456 Flow function 3.1 3.1
9th International Freiberg Conference on IGCC & XtL Technology, 3-8 June 2018, Berlin
Data processing and experimental range
– The slopes of weight loss curves and
weight gain curves of the vessels were
calculated as average solid flow rate, and
were used to calibrate the instantaneous
mass flow rate Ms and concentration C
which were measured by the solid mass
flowmeter.
– Solid mass flux 𝐺𝑠 =𝑀𝑠
𝐴=
𝑀𝑠
0.25𝜋𝐷2
– The volume flow rate of carrier gas
𝑄𝑔 = 𝑄𝑝 + 𝑄𝑓 + 𝑄𝑠 −𝑀𝑠 𝜌𝑠
– Superficial gas velocity 𝑈𝑔 =𝑄𝑔
𝐴=
𝑄𝑔
0.25𝜋𝐷2
– Solid loading ratio 𝜇 =𝑀𝑠
𝜌𝑔𝑄𝑔
Page 10
Experimental range
Pipe diameter (mm) 25 15 10
No. of experiments 226 183 63
Back pressure (MPag) 1~4 1~4 1~4
Solid mass flow rate(kg/h) 330~5327 171~2123 96~586
Solid mass flux (kg/(m2·s)) 187~3014 268~3337 338~2072
Solid concentration (kg/m3) 24~641 20~437 18~180
Solid loading ratio (kg/kg) 1~25 1~17 1~7
Superficial gas velocity (m/s) 1.5~14.4 4.3~20.5 8.8~22.6
9th International Freiberg Conference on IGCC & XtL Technology, 3-8 June 2018, Berlin Page 11
Background
Experimental system
Results and discussion
Conclusion
9th International Freiberg Conference on IGCC & XtL Technology, 3-8 June 2018, Berlin
The effect of moisture content on conveying characteristics
Page 12
D=25mm, L=197m
• In the region of high gas velocity (dilute phase), no effects of moisture, because particles are in
suspension state and particle-particle interactions are weak.
• In the region of low gas velocity (dense phase), solid mass flow rate and solid concentration is larger for
coal with lower moisture content, because resistance and cohesiveness increases with increasing
moisture content.
Ug vs C
D=25mm, L=197m
Ug vs Gs
9th International Freiberg Conference on IGCC & XtL Technology, 3-8 June 2018, Berlin
The effect of moisture content on conveying characteristics
Page 13
D=25mm, L=197m
Ug vs Ug –us, ∆P=0.25MPa
• At 1.0MPag, the slip velocity is larger for coal with low moisture content
• At 4.0MPa, the slip velocity is nearly the same for the two coals
D=25mm, L=197m
Ug vs Ug –us, ∆P=0.50MPa
9th International Freiberg Conference on IGCC & XtL Technology, 3-8 June 2018, Berlin
Pipeline resistance – Straight pipes (calculation of 𝜆𝑧)
Page 14
Solid loading ratio, μ
Density ratio, ρs/ρg
Reynolds number, Re
Froude number, Fr
Diameter ratio, dp/D
• Solid concentration
• Inelastic collision of
particle/particle and
particle/wall
• The conveying
ability of carrier
gas
• Re=ρgUgD/μg
• Ratio between inertia
force to viscous force
• Turbulent intensity
of gas phase
• Fr=Ug/(gD)0.5
• Ratio between
inertia force to
gravity
• The effect of
gravity on two-
phase flow
• Particle distribution
and wall effects
• Different friction
factor for different
pipe diameter
𝜆𝑧
𝜆𝑧 = 𝑥0𝜇𝑥1 (𝜌𝑠 𝜌𝑔 )𝑥2𝑅𝑒𝑥3𝐹𝑟𝑥4 (𝑑𝑝 𝐷 )𝑥5
𝜆𝑧 = 𝑥0𝐹𝑟𝑥4 (𝑑𝑝 𝐷 )𝑥5
Eliminate the dimensionless number
of small exponent
∆𝑃𝑇 ∆𝐿 = ∆𝑃𝑔 ∆𝐿 + ∆𝑃𝑠 ∆𝐿 = (𝜆𝑔+𝜇𝜆𝑧)𝜌𝑔𝑈𝑔
2
2𝐷
9th International Freiberg Conference on IGCC & XtL Technology, 3-8 June 2018, Berlin
Pipeline resistance – Straight pipes
Horizontal pipe:
HMC 𝜆𝑧 = 2.990 × 10−3𝐹𝑟−0.946 (𝑑𝑠 𝐷 )−0.637
LMC 𝜆𝑧 = 0.06594𝐹𝑟−0.832 (𝑑𝑠 𝐷 )−0.103
Vertical upward pipe:
HMC 𝜆𝑧 = 2.047 × 10−4𝐹𝑟−1.095 (𝑑𝑠 𝐷 )−1.233
LMC 𝜆𝑧 = 0.03642𝐹𝑟−0.430 (𝑑𝑠 𝐷 )−0.003
Vertical downward pipe:
HMC 𝜆𝑧 = 1.018 × 10−13𝐹𝑟1.206 (𝑑𝑠 𝐷 )−3.519
LMC 𝜆𝑧 = 8.220 × 10−9𝐹𝑟0.129 (𝑑𝑠 𝐷 )−2.042
Page 15
∆𝑃𝑇 ∆𝐿 = ∆𝑃𝑔 ∆𝐿 + ∆𝑃𝑠 ∆𝐿 = (𝜆𝑔+𝜇𝜆𝑧)𝜌𝑔𝑈𝑔
2
2𝐷
• The absolute value of exponents of the Froude number is
smaller for LMC, showing smaller effect of gas velocity on
solid friction factor for coal with lower moisture content
Range: pipe diameter 10~25mm, particle diameter 35μm,
carrier gas is N2, back pressure is 1~4MPag
Measurement(kPa/m)
Ca
lcu
lation
(kP
a/m
)
Horizontal
Vertical upward
HMC
LMC
Measurement(kPa/m)
Ca
lcu
lation
(kP
a/m
)
Vertical downward
HMC
LMC
9th International Freiberg Conference on IGCC & XtL Technology, 3-8 June 2018, Berlin
Pressure drop due to gas phase:
∆𝑃𝑔 = 𝜉𝜌𝑔𝑈𝑔
2
2=𝜉
2∙𝜌𝑔𝑈𝑔𝐴
𝐴∙ 𝑈𝑔 =
𝜉
2∙ 𝐺𝑔𝑈𝑔 = ng ∙ 𝐺𝑔𝑈𝑔
Pressure drop due to the presence of solid particles:
∆𝑷𝒔 = 𝒏𝒔 ∙ 𝑮𝒔𝑼𝒈
Pipeline resistance – Bends
Page 16
∆𝑃𝑇 = ∆𝑃𝑔 + ∆𝑃𝑠
1m
1m
R
b
Rb/D=15.2 (D=25mm)
Rb/D=21.3 (D=15mm)
Rb/D=26.7 (D=10mm)
Pressure measuring point
Pressure measuring point
– Additional pressure drop model
Measurement(kPa/m)
Calc
ula
tion
(kP
a/m
)
HMC
LMC 𝒏𝒔
Pipe diameter 25mm 15mm
Coal HMC LMC HMC LMC
Horizontal to horizontal 1.03 0.95 0.79 0.72
Horizontal to vertical upward 1.69 1.40 1.32 1.09
Vertical upward to horizontal 1.26 0.69 0.85 0.78
Horizontal to vertical downward 0.94 0.92 0.77 0.80
• LMC coal has smaller ns, due to smaller cohesiveness and
resistance
9th International Freiberg Conference on IGCC & XtL Technology, 3-8 June 2018, Berlin Page 17
Background
Experimental system
Results and discussion
Conclusion
9th International Freiberg Conference on IGCC & XtL Technology, 3-8 June 2018, Berlin
Conclusion
– Pneumatic conveying of two kinds of high-volatile bituminous coal powder with different
moisture content was carried out on an experimental facility using 25mm, 15mm, and
10mm pipes , and at back pressures of 1.0~4.0MPag
– The characteristics of solid mass flow rate, solid concentration and particle velocity were
obtained. Resistance and cohesiveness increases with increasing moisture content, so
solid mass flow rate and solid concentration is larger for coal with low moisture content in
the dense-phase region. While in the dilute-phase region, moisture content has minor
effect on conveying characteristics.
– The pressure drop of the two-phase flow is modeled by additional pressure drop models
for straight pipes and bends. For coal with lower moisture content, the effect of gas velocity
on solid friction factor is smaller and ns is smaller, due to its smaller cohesiveness and
resistance
Page 18
9th International Freiberg Conference on IGCC & XtL Technology, 3-8 June 2018, Berlin
Thanks for your attention !
Zhen Liu
Department of Energy and Power Engineering
Tsinghua University
Beijing, China
(Tel.) +86-10-57339813
(Mob.) +86-13520030865
(E-mail) [email protected]