Abstrict A method of controlling a bowl-mill crusher that has cylinders
that remain in one position and roll over a rotating bowl with a
predetermined force. Raw coal and primary air are supplied to the
crusher and the crushed coal is removed from the crusher along with
the primary air through a separator and supplied to burners through
a pulverized-coal line. The pressure of the primary air where it
enters the bowl-mill crusher is controlled in accordance with load
and in a manner so that the pressure of the crushing cylinders against
the bowl is decreased in a predetermined manner when the desired
load-dependent level is not attained and is increased when the level
is exceeded.
Claims I claim:
1. A method of controlling a bowl mill crusher having cylinders
remaining in one position and rolling over a rotating bowl with
a predetermined force, comprising the steps of supplying raw coal
and primary air to the crusher; removing crushed coal from the crusher
along with the primary air through a separator; supplying thereafter
the crushed coal and primary air to burners through a pulverized-coal
line; controlling the pressure of the primary air at entry of the
bowl mill crusher according to a first function of load so that
pressure of the crushing cylinders against the bowl is decreased
according to a second function when a desired load dependent level
is not attained. said pressure being increased when said level is
exceeded said pressure being dependent on the amount of coal introduced
into the mill said pressure being additionally corrected indirectly
with respect to the supply of raw coal.
2. A method as defined in claim 1 wherein the volume of primary
air is increased also a the load increases.
3. A method as defined in claim 1 and including the step of increasing
the temperature at the exit from said separator as the load increases.
4. A method as defined in claim 1 including the step of providing
a silo with a mass of coal filling said silo at predetermined levels,
the level of coal in said silo being held constant when said pressure
is varied indirectly with respect to the supply of raw coal.
5. A method as defined in claim 1 wherein said primary air has
a desired pressure value in front of the mill, said desired pressure
value of said primary air being transmitted dependent on the amount
of coal introduced into the mill, in said desired pressure value
of said primary air producing variation in said force.
6. A method as defined in claim 1 wherein the pressure of said
primary air in front of said mill and within said mill is positive
over the entire load range.
7. A method of controlling a bowl mill crusher having cylinders
remaining in one position and rolling over a rotating bowl with
a predetermined force, comprising the steps of: supplying raw coal
and primary air to the crusher; removing crushed coal from the crusher
along with the primary air through a separator; supplying thereafter
the crushed coal and primary air to burners through a pulverized
coal line; controlling the pressure of the primary air at entry
of the bowl-mill crusher according to a first function of load so
that pressure of the crushing cylinders against the bowl is decreased
according to a second function when a desired load dependent level
is not attained, said pressure being increased when said level is
exceeded, said pressure being dependent on the amount of coal introduced
into the mill, said pressure being additionally corrected indirectly
with respect to the supply of raw coal; raw coal being supplied
to said crusher from a hopper through a distributor; injecting heated
primary air for coal drying and conveying through an air line; removing
crushed and dried coal through said separator and conveying to burners
of a furnace through a pulverized coal line; establishing coal output
in relation to load by level setting controls operating in conjunction
With a coal flow regulator: said coal regulator actuating a variable
drive on said distributor with speed monitored by a speed sensor;
said ingection of primary air in accordance with load being established
by saidglevel setting controls and being carried out by a primary
air flow regulator operating a primary-air control valve; monitoring
the volume of primary air by a volumeter; establishing the temperature
at said separator and monitoring said temperature for maintaining
said temperature at a predetermined level by mixing cold air into
said heated primary air; supplying said cold air from a cold air
line entering said crusher; providing a pressure gauge where said
cold air line enters said crusher. pressure indicated by said pressure
gauge being equal to the pressure of said primary air upstream of
where said primary air enters said crusher, said pressure gauge
communicating with pressure-to load controls and a comparison joint
communicating with said cylinders to generate pressure thereof;
said pressure to load controls establishing a desired primary-air
pressure as a function of load so that said pressure follows a predetermined
linear function curve supplied to said comparison point and compared
constantly with the actual pressure level measured by said gauge;
supplying a pulse to said cylinders when the actual pressure level
deviates from the desired load dependent level for varying said
force, said pressure being decreased when the desired load dependent
primary-air pressure is not attained and increased when it is exceeded:
said crusher being loadable to a desired extent independent of an
existing load condition that said crusher is being operated in,
so that a sufficient crushing pad is produced in said bowl to prevent
said cylinders from rolling directly over the bowl for producing
quiet operation of said crusher.
8. A method of controlling a bowl mill crusher having cylinders
remaining in on position and rolling over a rotating bowl with a
predetermined force, comprising the steps of: supplying raw coal
and primary air to the crusher; removing crushed coal from the crusher
along with the primary air through a separator; supplying thereafter
the crushed coal and primary air to burners through a pulverized
coal line; controlling the pressure of the primary air at entry
of the bowl mill crusher according to a first function of load so
that pressure of the crushing cylinders against the bowl is decreased
according to a second function when a desired load dependent level
is not attained, said pressure being increased when said level is
exceeded, said pressure being dependent on the amount of coal introduced
into the mill, said pressure being additionally corrected indirectly
with respect to the supply of raw coal; said crusher being loadable
to a desired extent independent of an existing load condition that
said crusher is being operated in to obtain sufficient crushing
pad in said bowl for preventing said cylinders from rolling directly
over the bowl to operate said crusher substantially quietly.
Description BACKGROUND OF THE INVENTION
The cylinders of bowl-mill crushers are oriented in relation to
the bowl in such a way as to ensure that their total force will
act on the material being crushed no matter how deep it is piled
in the bowl. To establish the particular force that is to be exerted
on the material in order to crush it, the cylinders are forced against
the bowl at a particular pressure, the extent of which depends on
how difficult the material is to crush. The pressure is maintained
constant during the operation. When crushing difficult-to-crush
coal with a low Hardgrove number and with a high percentage of fines
in the rough-coal composition, the crusher may begin running erratically
at certain stages and develop a considerable amount of vibration
accompanied by noise. This erratic operation cannot be corrected
satisfactorily by redesigning the crusher.
The object of the invention is to provide a method of controlling
a bowl-mill crusher that will allow it to run quitely in all operating
situations.
How smoothly a bowl-mill crusher runs depends on, among other factors,
how full it is, a situation that is expressed in a loss of primary-air
pressure between the intake into the crusher and the outlet from
the burner or in other words in a particular primary-air pressure
upstream of the crusher. It has been demonstrated that the air turbulence
increases in spurts once the primary-air pressure exceeds a particular
level. With this discovery as a point of departure accordingly,
a method of controlling a crusher is proposed wherein the pressure
of the cylinders is varied when the load-dependent primary-air pressure
deviates from a prescribed level. This method can be exploited to
drive a bowl-mill crusher quietly.
One embodiment of the invention will now be described with reference
to the drawing, wherein
FIG. 1 is a partly sectional schematic view of a bowl-mill crusher,
FIG. 2 is a flow chart illustrating the control method in accordance
with the invention,
FIG. 3 is a graph illustrating how the primary-air/pressure varies
with load, and
FIG. 4 is a graph illustrating how the cylinder pressure is to
be varied in accordance with the primary air-pressure deviation.
The illustrated bowl-mill crusher 1 consists of a rotating bowl
2 and of cylinders 3 that remain in one position and roll over the
bowl. The shafts of cylinders 3 are mounted on cylinder bearings
in a frame 4. Three tie rods 5 only one of which is illustrated,
engage frame 4 at three points.
Tie rods 5 are secured to the base by a system of hydraulic cylinders
6. The pressure of cylinders 3 against bowl 2 can be varied through
tie rods 5 and frame 4 by supplying a pressure medium to hydraulic
cylinders 6. A buffer 7 ensures that crushing cylinders 3 will yield
resiliently.
Rough coal is supplied to bowl-mill crusher 1 from a hopper 8 through
a distributor 9. Coal-drying and conveying gas in the form of heated
primary air is injected through an air line 10. The crushed and
dried coal is removed through a separator 11 and conveyed to the
bureers of a furnace 13 through a pulverized-coal line 12. The output
of coal in relation to load, the furnace-end consumption in other
words, is established by level-setting controls 29 and carried out
by coal-flow regulator 14. Coal regulator 14 acts on the variable
drive mechanism 15 of distributor 9. The speed is monitored by an
rpm sensor 28. The injection of primary air in accordance with load
is established by level-setting controls 25 and carried out by a
primary-air flow regulator 16 that acts on a primary-air control
valve 17. The volume of primary air is monitored by a primary-air
volumeter 26.
The temperature at separator 11 is established by level-setting
controls 30 and monitored by a temperature sensor 27. To maintain
the temperature at a prescribed level, cold air is mixed into the
heated primary air from a cold-air line 18. The temperature of the
separator is controlled by separator-temperature controls 19 that
act on a cold-air control valve 20. There is a pressure gauge 21
in air line 10 between where cold-air line 18 enters and crusher
1. The pressure determined by gauge 21 equals the pressure of the
primary air upstream upstream of where it enters bowl-mill crusher
1. Pressure gauge 21 communicates with pressure-to-load ratio-setting
controls 23 and a comparison point 24. Comparison point 24 communicates
with hydraulic cylinders 6 through pressure controls 22 to generate
the pressure of the crushing cylinders.
Pressure-to-load ratio-setting controls 23 establish the desired
primary-air pressure as a function of load in such a way that the
pressure will follow the linear-function curve illustrated in FIG.
3. This curve is supplied to comparison point 24 and constantly
compared with the actual level measured by pressure gauge 21. If
the actual level deviates from the desired load-dependent level,
the pump in the system of hydraulic cylinders 6 receives a pulse
from pressure controls 22 and varies the pressure of crushing cylinders
3. As will be evident from FIG. 4 the pressure is decreased when
the desired load-dependent primary-air pressure is not attained
and increased when it is exceeded. The numerical quantities in FIG.
4 are intended to represent only the tendency to vary.
The control method described herein makes it possible to load the
crusher to the extent desired, independent of the particular load
situation that the crusher is being operated in, and to accordingly
obtain enough of a crushing pad in bowl 2 to prevent the crushing
cylinders from rolling directly over the bowl. This ensures that
the bowl-mill crusher will operate quietly. The volume of primary
air will also increase in the same direction as the load increases.
Level-setting controls 25 that communicate with primary-air volumeter
26 will accordingly establish the desired volume of primary air,
which increases with load. Separator-temperature controls 19 and
cold-air control valve 20 will also increase the temperature (separator
temperature) of the primary air at the exit from separator 11 as
the load increases. The increase can range for example from 75.degree.
C. at a load of 40% to 85.degree. C. at a load of 100%.
An increase in the load will be signaled to coal-level setting
controls 29 and forwarded to primary-air level-setting controls
in accordance with a constant function. The speed of distributor
9 increases and primary-air control valve 17 opens. The extent of
variation is monitored by rpm sensor 28 and primary-air volumeter
26. Separator-temperature level-setting controls 30 simultaneously
establish in accordance with a constant function a higher separator
temperature, which is increased by closing cold-air control valve
20 and monitored by temperature sensor 27. A higher desired primary
air-pressure level is likewise signaled to pressure-to-load ratio-setting
controls 23 in accordance with a constant function.
If the detected primary-air pressure deviates from the desired
level, pressure controls 22 supply a pulse to hydraulic cylinders
6 until the actual level equals the desired level. |