Group Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Title: 5.3.3 - Effect of moisture content on conveying characteristic of pulverized coal for pressurized entrained flow gasification
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Permanent Link: http://ufdc.ufl.edu/UF00102023/00127
 Material Information
Title: 5.3.3 - Effect of moisture content on conveying characteristic of pulverized coal for pressurized entrained flow gasification Industrial Applications
Series Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Physical Description: Conference Papers
Creator: Liang, C.
Zhao, C.
Chen, X.
Xu, P.
Xu, C.
Publisher: International Conference on Multiphase Flow (ICMF)
Publication Date: June 4, 2010
 Subjects
Subject: pneumatic conveying
high pressure
moisture content
mass flow rate
pressure drop
 Notes
Abstract: During the pneumatic conveying, pulverized coal with different moisture content may develop substantial difference in flow characteristic, whose cause is not fully understood. This study focused on the influence of moisture content on conveying characteristic in an experimental test facility with the conveying pressure up to 4MPa. Results indicate that mass flow rates of bituminous coal ( 0.4%<M<6% ) and lignite with larger particle size ( 0.8%<M<9% ) increase at first and then decrease but mass flow rate of lignite with smaller particle size (3.2 %<M<9%) decreases with the increase in moisture content. Conveying optimal moisture content and extreme moisture content are revealed for different coal category. Conveying phase diagram and pressure drops through different test sections of pulverized coal are obtained and analyzed under high pressure. Bend equivalent length coefficient rises with increase in moisture content and is independent of conveying velocity and solid-gas ratio in dense-phase pneumatic conveying at high pressure.
General Note: The International Conference on Multiphase Flow (ICMF) first was held in Tsukuba, Japan in 1991 and the second ICMF took place in Kyoto, Japan in 1995. During this conference, it was decided to establish an International Governing Board which oversees the major aspects of the conference and makes decisions about future conference locations. Due to the great importance of the field, it was furthermore decided to hold the conference every three years successively in Asia including Australia, Europe including Africa, Russia and the Near East and America. Hence, ICMF 1998 was held in Lyon, France, ICMF 2001 in New Orleans, USA, ICMF 2004 in Yokohama, Japan, and ICMF 2007 in Leipzig, Germany. ICMF-2010 is devoted to all aspects of Multiphase Flow. Researchers from all over the world gathered in order to introduce their recent advances in the field and thereby promote the exchange of new ideas, results and techniques. The conference is a key event in Multiphase Flow and supports the advancement of science in this very important field. The major research topics relevant for the conference are as follows: Bio-Fluid Dynamics; Boiling; Bubbly Flows; Cavitation; Colloidal and Suspension Dynamics; Collision, Agglomeration and Breakup; Computational Techniques for Multiphase Flows; Droplet Flows; Environmental and Geophysical Flows; Experimental Methods for Multiphase Flows; Fluidized and Circulating Fluidized Beds; Fluid Structure Interactions; Granular Media; Industrial Applications; Instabilities; Interfacial Flows; Micro and Nano-Scale Multiphase Flows; Microgravity in Two-Phase Flow; Multiphase Flows with Heat and Mass Transfer; Non-Newtonian Multiphase Flows; Particle-Laden Flows; Particle, Bubble and Drop Dynamics; Reactive Multiphase Flows
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Volume ID: VID00127
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7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


Effect of Moisture Content on Conveying Characteristic of Pulverized Coal for
Pressurized Entrained Flow Gasification


Cai Liang, Changsui Zhao, Xiaoping Chen, Pan Xu and Chuanlong Xu


Southeast University, Nanjing, School of Energy and Environment
Si Pai Lou 2#, Nanjing, 210096, Jiangsu Province, China
Liangc@seu.edu.cn



Keyword: Pneumatic conveying; High pressure; Moisture content; Mass flow rate; Pressure drop





Abstract


During the pneumatic conveying, pulverized coal with different moisture content may develop substantial difference in flow
characteristic, whose cause is not fully understood. This study focused on the influence of moisture content on conveying
characteristic in an experimental test facility with the conveying pressure up to 4MPa. Results indicate that mass flow rates of
bituminous coal ( 0.4% mass flow rate of lignite with smaller particle size (3.2 % optimal moisture content and extreme moisture content are revealed for different coal category. Conveying phase diagram and
pressure drops through different test sections of pulverized coal are obtained and analyzed under high pressure. Bend
equivalent length coefficient rises with increase in moisture content and is independent of conveying velocity and solid-gas
ratio in dense-phase pneumatic conveying at high pressure.


Introduction
Pneumatic conveying is usually classified into two
categories: dilute-phase and dense-phase. In dilute phase
conveying, the particles are usually transported in the form
of a suspension with the solids concentrations typically
below 10%. On the other hand, the dense-phase transport is
usually understood as conveying of particles, along a pipe,
which is filled with particles at one or more cross-sections
(Molerus, 1996). Dense-phase pneumatic conveying of
pulverized coal under high pressure is one of the key
technologies for pressurized entrained flow gasification.
Because of low velocity and high solid concentration in
transportation, the gas-solid two-phase flow becomes very
unsteady and complicated. Experimental and theoretical
study to understand the flow characteristic of conveying
upon powder is needed so that the processing parameters
and pneumatic conveying systems can be optimized to
avoid problems at the large scale. There is a great interest to
study flow characteristic of dense-phase under high


pressure. Hyder (2000) carried out an investigation using
five kinds of plastic materials at low pressure. It is apparent
that pressure drop increases with increasing particle size;
the degree of increase tends to be larger towards the smaller
particle sizes, diminishing as size increases and also
diminishing with increasing transport velocities. Vasquez
(2008) used the high-speed video camera and pressure
transmitters to study the dynamic behavior of the particles
and its influence on pressure drop during conveying. The
conveying trials were carried out in a 0.052 m I.D.
aluminum pipe conveying system approximately 35 m long.
For bituminous and hard polyethylene pellets, video
analysis reveals that the bituminous polyethylene particles
bounce more intensely during conveying than the hard
polyethylene particles. The bituminous pellets show very
random and intense bouncing with strong rotation, which
affects the rebound considerably. Pahk (2008) applied two
different types of plastic pellets to the determination and
development of distinguishing flow characteristics in










dilute-phase pneumatic conveying. The results show that
the total pressure drop for polyolefin is higher than that for
polystyrene. Pressure drop due to particle impact and
friction for polyolefin is much higher than that for
polystyrene. The solid-friction factor decreases when the
solid-loading ratio is increased for both materials, but the
friction factor for polyolefin decreases more with the
solid-loading ratio than the polystyrene. Li & Tomita (2000
& 2002) measured particle velocity and concentration in
horizontal and vertical dilute swirling flow pneumatic
conveying at low pressure. It is found that the particle
concentration profiles in the swirling flow pneumatic
conveying exhibits symmetric distributions with respect to
the pipe axis and the higher particle concentration appears
near the wall in the acceleration region. In developed region,
the particle concentration profiles of the swirling flow
pneumatic conveying shows anti-symmetric distributions
and the higher particle concentration appears at the bottom
of pipe. Laouar (1998) studied pressure drop characteristic
at a very low velocity and a general pressure drop law was
obtained which proves to be independent of both flow
regimes and pipe diameter. As related topics, there are
velocity measurements using electrostatic charge (Xu, et al
2008) and numerical simulations of particles behavior (Lain
& Sommerfeld 2008), attrition of granules (Konami, et al
2002; Rajniak, et al 2008) and pressure drop (Tan, et al
2008). While many of those researchers mainly worked in
the low pressure and dilute-phase pneumatic conveying.
The high pressure to transport these materials can be
substantially different. The particle behavior of dense-phase
pneumatic conveying under high pressure is highly affected
by moisture content, whose cause is not fully understood.
Moisture content in powder is an important parameter to
affect powder flow characteristic in pneumatic conveying. It
has strong effect on friction property, flowability,
dispersibility and briquettability of powder. As moisture
content in pulverized coal is higher, free water among
pulverized coal particles mainly exists as felted water,
sphenoid water and rising capillary water. Moisture content
and corresponding liquid induced adhesive forces strongly
affect flowability of powders during their storage and
conveying process. All of those factors lead to change in
flowability and stability of pulverized coals in pneumatic
conveying. However, references and experiences in this
field are very few. Complete understanding about the
influence of moisture content on conveying characteristic


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010
has yet to be established. The objective of this paper is to
investigate the effects of coal moisture content on
conveying characteristic under high pressure. The intention
is to provide better understanding of effects of moisture
content, flow regime and coal categories on conveying
characteristic.

Nomenclature


G Mass flow rate of pulverized coal (kgh')


M External moisture content of coal (%)


P1 Pressure in the feeding hopper (Mpa)


P2 Pressure in the receiving hopper (Mpa)


AP Pressure drop through test sections (kpa)


APh Pressure drop through horizontal pipe section (kpa)


APhb Pressure drop through horizontal bend (kpa)


APv Pressure drop through vertical pipe section (kpa)


APvb Pressure drop through vertical bend (kpa)


U Superficial velocity (ms-')





Greek letters





t Solid loading ratio (kgm')





Subsripts


BEC Bend equivalent length coefficient


Experimental and materials
(1) Pneumatic conveying system
The pressurized experimental facility is shown










schematically in Fig.l. High pressure N2 from the buffer
tank was divided into pressurizing gas, fluidizing gas and
supplementary gas. The feeding hopper adopted the
bottom-fluidization and top-discharge arrangement.
Pulverized coal in the feeding hopper was fluidized by
fluidizing gas and entered the conveying pipeline through
the accelerating segment. Supplementary gas was imported
to enhance the conveying ability of gas at the outlet of the
feeding hopper. In order to adjust pulverized coal moisture
content, water through measuring pump was injected into
the pulverized coal in the conveying pipeline. The pressure
in the receiving hopper was controlled by the motor-driven
control valve. Each of the feeding hopper and receiving
hopper had a capacity of 0.648m3. The conveying pipeline
was made of a smooth stainless steel tube with an inside
diameter of 10mm and a length of about 45m. The length of
horizontal pipe and vertical pipe which were used to
measure the pressure drop was 100cm. The 900 mild bends
with the radii of 20cm were about 63cm in length. The gas
volume rates were measured by the metal tube variable-area
flow meter, and the fluctuation of solid mass flow rate was
gained by the weigh cells. Pressure and pressure drop were
measured by the semiconductor pressure transducers with
precision of 0.0577%. The particle electrostatic charge was
obtained in conveying process using electrostatic sensor
(Xu, et al 2008). Signals of pressure drops, pressure and so
on were obtained by a multi-channel sampling system and
then were sent to a computer through an A/D converter.
Conveying gas was N2 with the maximum pressure of up to
4.0MPa.


6

12
2

3
1


i'


7


Fig. Schematic diagram of pneumatic conveying system of
pulverized coal at high pressure
1-Buffer tank, 2-Supplimentary gas, 3-Pressuring gas,
4-Fluidizing gas, 5-Hopper, 6-Weight cell, 7-Date
acquisition system, 8-Observation window, 9-Electrostatic
charge cell, 10-Control valve, 11-Water, 12- Pump


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

(2) Material properties of pulverized coal
Bituminous coal and two kinds of lignite samples were used
to investigate influence of moisture content on conveying
characteristic in this paper. Two lignite samples used for
comparative test were from the same parent coal. The major
difference between two lignite samples was particle size
distribution as shown in Table 1 and Fig.2. Lignite with
smaller size and bituminous coal had similar mean particle
size and density. The initial moisture contents in coals were
different because of coal categories and handling processes.
The external moisture content and the total moisture content
of pulverized coals were measured using procedures set out
in Chinese national measuring standards of coal in Table 1.
Table 1 Material property of pulverized coal samples

Bituminou
Lignite Lignite
s coal

External moisture
3.2 0.8 0.4
content (%)

Total moisture
13 12.5 1.8
content (%)

Mean particle size
56 300 56
(pun)

Apparent Density
(kg1490 1470 1500
(kgm-3)


10 100 1000
Particle size/tim
Fig.2 Particle size distribution of pulverized coal

Results and analysis

(1) Effect of moisture content on the mass flow rate
Moisture content is an important parameter for flowability
of powder material. Surface tension of water causes traction
between two particles and so-called liquid bridge is formed.


^^ ^ 10










Granulation appears among the coal particles and small
particles are easily aggregated into larger particles. Effect of
internal moisture content on flow characteristic in the
pneumatic conveying under high pressure is few (Hemery,
et al 2009, Emery, et al 2009). Moisture content of
pulverized coal in this paper is the external moisture
content.
All of the operating parameters were same except moisture
content of pulverized coal. Effect of moisture content on
mass flow rates of lignite and bituminous coal is presented
in Fig.3. With the increase in moisture content, mass flow
rates of bituminous coal and lignite with mean particle size
of 300tm increase at first and then decrease but lignite with
mean particle size of 56tm decreases. Different sizes and
shapes of particles are commonly considered in these
granular systems due to repeated mechanical attrition
caused by interactions between granular materials with
system parts. During the particle conveying processes, solid
particles have a natural tendency to acquire electrostatic
charges due to collisions with surfaces of different material
types. Some of coal particles might have sharper covers
and rough surfaces. Such structures have higher charging
capacity in subsequent particle-particle and particle-pipe
collisions thus giving rise to particle charge enhancement.
As external moisture content of pulverized coal is below
1%, coal particle with lower external moisture acts like
insulators, by being able to store more charges. Therefore,
coal particles get more charged and lost their surface
potential more slowly. Particle charges result in the fine
particles agglomerating to form coarser particles and
cohesive arching. Flowability and stability of the pulverized
coal become worse. Many fine particles adhered to the
silica tube of observation window and pressure drop
appeared greater fluctuation as shown in Fig.4 (a). With the
increase in moisture content, flowabilities of bituminous
coal and lignite with larger particle size become better and
particle charges in conveying process diminish as shown in
Fig.5. Pressure drop appears stable (Fig.4 (b)) and fine
particles adhered to the silica tube disappear. There has a
strong increase in the conductivity of materials when
increasing their water content, and suggests that the water
molecules adsorbed at the surface of the materials create a
phase in which the charge carrying molecules (like ions)
can move, creating electrical conduction across the powder
surface. This decrease in resistivity (and thus the increase of
powder's conductivity) with increasing moisture content


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010
has also been observed by Hemery, et al (2009), Engers, et
al (2007) and Grosvenor, et al (1996). As continuing to
increase external moisture content, electrostatic forces
decrease with increasing moisture content because of the
conductive properties of water. Thus mass flow rates of
bituminous coal and lignite with larger particle size rise
with the increase in moisture content. As moisture content
continuous to increase, electrostatic charge of coal particle
disappears and cohesive force rises. This is believed to be
due to the fine particles in the micron size range
agglomerating to form coarser particles by absorbing
external moisture. Flowability of pulverized coal becomes
worse and pulverized coal is more difficult to flow in the
feeding hopper and conveying pipe. So mass flow rate
decreases with the increase in moisture content. Because
initial moisture content of lignite with smaller particle size
is more than 3%, weak electrostatic charge doesn't affect
the flowability of pulverized coal. Consequently mass flow
rate of lignite with smaller particle size decreases with the
increase in moisture content. As external moisture contents
of lignite and bituminous coal is above 9% and 6%
respectively, the flow becomes very difficult. Blockage and
arching often happen in conveying process. Experimental
results indicate that optimal conveying moisture contents of
bituminous coal and lignite is about 1-2% and 3-4%
respectively. Extreme moisture contents of lignite and
bituminous coal is 9% and 6% separately. In addition, Fig.3
shows that mass flow rate of lignite is greater than that of
bituminous coal in the similar operating parameters, particle
size and external moisture content. Coal has the rich pore
structure which is related to coal rank. Lignite with lower
coal rank is loose and has much excellent pore which offers
the condition for water storage. When external moisture
content increases, a part of external moisture enters into
pore and is difficult to be removed by drainage, screening
or centrifuging or by normal evaporation room temperature.
This part of moisture content can't increase thickness of the
surface moisture layer and adhesive force, which is less
influence on the material flowability in pneumatic
conveying under high pressure. Surface moisture is the
extraneous water held as films on the surface of the coal
and its content can vary in a coal over time. Therefore
lignite has better flowability than bituminous coal at similar
operating parameters and external moisture content.










A r4r~r%


900-


S800-


700-


600-]
0 2 4 6 8 10
M/%
Fig.3 Effect of moisture content on mass flow rate
(P2=2.8MPa, Q-r0.4m3/h; Qs=0.6m3/h)


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010
0r\


OL

24

18

12


0 100 200 300 40U
t/S

(c) Pressure drops at M=8.18%
Fig.4 Influence of moisture content on pressure drop


- AP
_- ap

- I tht
APvb



)- ------- ^---


, U ,U UU 4


40-


30-


20-
<
10-


0-




1Q


cZ
P214-

" 12-

10-

8-

6-


200
t/s
(a) M=0.4%


0 100


200
t/s
(b) M=1.45%


0 400 800 1200 1600 2000
t/(s/200)
Fig.5 Effect of moisture content on particle charge in
pneumatic conveying under high pressure
( 2 ) Phase diagram and flow regime
The conveying phase diagram of dense-phase pulverized
coal under high pressure is shown in Fig.6. All of
conveying tests had the similar mass flow rate and pressure
in receiving hopper. It indicates that the pressure drops
through different test sections decrease at first and then
increase with the increase in superficial velocity. The flow
is quite dilute and pulverized coal is conveyed
homogeneously when the superficial velocity is very high
as shown in Fig.7(b). The pressure drop is attributed mainly
by gas movement. Here particles are carried in the gas
while bouncing frequently against the pipe wall. As the
superficial velocity decreases, the particle concentration
increases. Pressure drop of gas phase decreases and
pressure drop of solid phase rises. When increment of the
pressure drop caused by the solid phase equals to decrement
in pressure drop caused by the gas phase, the pressure drop
appears to be the minimum. This conveying velocity is
called the economical velocity. Near the economical
velocity, two phases, a suspended phase and a settled layer


* soft coal, 56aim
* lignite, 56aim
lignite, 3001tm


_-APh
hv

APv
~c~ nPh
"si


0


I


V







7th International Conference on Multiphase Flow
ICMF 2010. Tamoa. FL USA. Mav 30-June 4. 2010


of pulverized coal are frequently observed. As conveying
velocity is greater than economical velocity, a flow regime
typically describes as a dilute flow. When conveying
velocity is lower than economical velocity, dunes or
clusters can be seen riding on a settled layer of pulverized
coal as shown in Fig. 7(c). A further reduction in the gas
velocity will lead to a region typically characterized by
unstable flow. At even lower gas velocities the material
may flow as plugs in Fig. 7(d). From the Fig.6, it also can
be seen that pressure drop through vertical bend is larger
than pressure drop through vertical pipe. The conveying
mixtures must be change the direction when it flows from
bend, the particle inertia and gravity will cause a separation
of the mixture, whereby rather dense ropes of solids may be
formed in the vertical bend. The increasing local solids
concentration supports the occurrence of inter-particle and
wall collisions. This results in a dispersion of the particles
out of a dense rope due to the transfer of momentum from
the main stream direction to the transverse component.
Hence, collisions between particles may cause a destruction
of dense ropes and therefore also will have a drastic effect
on the particle transport and the wall collision frequency in
such two-phase systems. Although length the ratio of bend
to straight pipe is 0.63, pressure drop through vertical bend
pipe is much higher than that through vertical pipe in the
experiment. The conveying gas must be getting over the
mixture gravity besides the energy loss of friction and
collision in vertical pipe. Therefore, pressure drop through
vertical pipe is larger than that through horizontal pipe. For
the bend with the same length and radius, pressure drop
through horizontal bend is less than that through vertical
bend in the conveying process.
28
P,=2.8MPa h
24 G=820~860kg/h *
Z VAP
hb
S20- AP
yv *
16- -

12-
.

2 4 6 /(s8 10 12
U/(m/s)
Fig.6 Phase diagram of bituminous coal


(a) Pure gas


(b) Suspended flow


(c) Dune flow


(d) Plug flow
Fig.7 Flow regime of different conveying velocity
(3) Effect of moisture content on pressure drop through
bend
As the mixture of gas and pulverized coal make a turn
within a bend, pulverized coal particles form a rope-like
structure because of inertial effects. A particle rope, which
carries most of the conveyed material in a small portion of
the pipe cross-section, acts as a third phase in the pneumatic
conveying line, with lower particle velocities and relatively
high particle concentration. As moisture content of
pulverized coal increases, the flowablity and adhesiveness
of two-phase flows will be changed. The operating
parameters in the experiment were similar and pressure in
the receiving hopper was 2.8MPa. Influence of moisture
content on pressure drop through horizontal bend is plotted
in Fig.8. Pressure drop through horizontal bend of lignite
decreases while pressure drop through horizontal bend of
bituminous coal increases at first and then decreases with
increase in moisture content. For pulverized coal with
different moisture content, the solid loading ratio is a main
parameter of affecting pressure drop. When moisture
content of conveying pulverized coals increases, the lignite










with higher initial external and internal moisture content
(Table 1) has good electrical conductivity and the
electrostatic charge of coal particle wouldn't conduct to
affect the flowablity in pneumatic conveying. Hence, the
increasing moisture content leads to decrease of lignite solid
loading ratio and pressure drop through horizontal bend
decreases with the increase in moisture content. But for
bituminous coal, the initial moisture content is very lower
as shown in Table 1. Particle charge would result in
decrease in flowability when the bituminous coal has lower
moisture content. Mass flow rate increases at first and then
decreases with increase in moisture content (Fig.3).
Therefore, the results show that pressure drop through
horizontal bend keeps the similar trend with mass flow rate
of bituminous coal as moisture content rose in Fig.9 (b).


c 18

16


(a) Pressure drop through horizontal bend for lignite with
smaller particle size

26

24

22
$--j
20

18
6


2

(b) Pressure horizontal bend for bituminous coal

Fig.8 Effect of moisture content on pressure drop through
horizontal bend
In order to assess the two-phase pressure drop in bend the
easiest and most obvious approach is to apply the bend
equivalent length coefficient (BEC). Pressure drops through


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010
horizontal pipe and horizontal bend were investigated to
obtain the influence of moisture content on BEC for
different pulverized coals. Comparison of pressure drop
through horizontal pipe and horizontal bend with different
moisture content in same length is plotted in Fig.9 and
Fig. 10. From the Fig.9, It indicates that the BEC is constant
with increase in superficial velocity for the same moisture
content. Therefore BEC is independent of conveying
velocity and solid loading ratio in dense-phase pneumatic
conveying at high pressure. BEC for different moisture
content are plotted in Fig.10. Results show that the BEC
rises with increase in moisture content and BEC with larger
particle size is greater than that with smaller particle size.
Increasing moisture content in fine coal particles results in
granulation phenomena. These growing coal particles,
which are trapped permanently in the corer, affected the
particle-particle collisions and rebound of the solids
moving through the bend. In the solids clusters formed in a
bend, such particle-particle and particle-wall collisions are
frequently encountered and they are believed to the inelastic
collision. Momentum transfers between particles and wall
lead to the oscillation of conveying pipe. Some cluster like
pattern appears constantly in the region above the bend,
where the mass of solids starts to form groups with higher
concentration. These higher concentration groups separate
into distinct clusters at a further distance from the bend,
producing a pulsing effect. Hence BEC increases with
increase in moisture content. In Fig. 10, it can be seen that
7.


4 6 8 10 12
U(m/s)
Fig.9 Influence of moisture content on bend equivalent
length coefficient
BEC of bituminous coal is greater than that of lignite at the
same moisture content and particle size. As moisture
content of pulverized coals increases, the surfaces of
bituminous coal particles form the liquid layer but external
moisture content of lignite is absorbed by the developed


bituminous coal
M=0.4%
M=3.34%
M=5.57%

.-6*- *










pore structure. Therefore, increasing moisture content for
bituminous coal has the more influence on BEC.
10
1 bituminous cola, 56im
lignite, 56lm
8g lignite, 300min


6-


4



0 2 4 6 8 10
M/%
Fig. 10 Bend equivalent length coefficient of different coal
with increase in moisture content
Conclusions
Effect of moisture content on conveying characteristic of
lignite and bituminous coal was investigated. Mass flow
rates of bituminous coal (0.4% larger particle size (0.8% decrease but mass flow rate of lignite with smaller particle
size (3.2 % content. As external moisture content of lignite is above 9%
and external moisture content of bituminous coal is above
6%, the flow became very difficult. Blockage and arching
often happened. Experimental results indicate that optimal
conveying moisture content of bituminous coal and lignite
is 1-2% and 3-4% respectively. Under similar operating
parameters and material properties, flowability of lignite is
better than that of bituminous coal.
With the increase in conveying velocity, pressure drops
through different test sections increase first and then
decrease in phase diagram. Three types of regimes are
identified: suspension flow, slug flow and plug flow.
Pressure drop through bend is mainly affect by the
solid-gas ratio and therefore appears the different trend with
increase in moisture content for different coals. BEC
increases with increase in moisture content and is
independent of conveying velocity and solid loading ratio in
dense-phase pneumatic conveying at high pressure. BEC of
bituminous coal is greater than that of lignite at the same
moisture content and particle size. BEC of large particle
size is greater than that of small particle size.



Acknowledgements


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010
Supported by the Special Funds of National Key Basic
Research and Development Program of China
(2010C B22"'i i2) and National Natural Science Foundation
of China (50906011)


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