Milling plant and method for milling raw materials

Details Milling plant and method for milling raw materials Milling plant and method for milling raw materials

1999-08-04

2001-08-21

Ostrager, Allen (Department: 3725)

Solid material comminution or disintegration

Apparatus

Including means applying fluid to material

C241S057000, C241S119000

Reexamination Certificate

active

06276620

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a milling plant having a roller grinding mill, a classifier and an exhaust gas fan, which follows a filter, particularly a plant for the production of cement, and to a method for cement production in a compound system.
BACKGROUND OF THE INVENTION
In the production of cement raw material mill drying plants are operated in combination with a clinker burning process, in order to supply the exhaust gases formed in a cement rotary kiln, following heat exchangers, to a further heat utilization.
A known milling system can be gathered from a circuit diagram according to FIG.
3
. Exhaust gases
3
from a calcining process are supplied by a kiln fan
5
into an exhaust gas pipe
6
, via a shutoff device
6
a
to a roller grinding mill
2
. The term kiln fan
5
is used here to define the fan feeding a gas flow to a mill. In combined circuits of cement rotary kilns and heat exchangers with an air-swept roller grinding mill, the kiln or kiln/heat exchanger-fan supplies the kiln gas flow and heat flow to a roller grinding mill, e.g. an air swept roller grinding mill. The term mill fan is used to define the fan, which delivers the gas flow necessary for the mill and which as fan
7
is positioned in the flow direction below the filter
8
functioning as a dust separator. Said fan
7
supplies the exhaust gas
3
with fines or meal
34
produced in the roller grinding mill
2
, by means of a dust-exhaust gas pipe
9
, which contains a shutoff device
9
a
, to the filter
8
. The fines
34
separated in the filter
8
are delivered by means of not shown conveying systems into silos. The dust-freed exhaust gas
3
is supplied with the aid of the fan
7
following the filter
8
to a not shown chimney flue and ejected.
In a compound operation, in which the milling plant is operated on line with a not shown cement rotary kiln, a shutoff device
15
a
in a bypass line
15
remains closed. Unusable thermal energy is dissipated in a cooling tower
22
, which generally follows the kiln fan
5
, or in the roller grinding mill
2
, e.g. by water injection.
Individual components of a raw material mixture
33
are supplied from bunkers
31
by means of weighting belts
30
to a feed belt
32
and fed to the roller grinding mill
2
. The feed device can be constituted by a flap lock
25
, which acts as an air excluder. Coarse material
26
separated in the roller grinding mill
2
is at least partly admixed with the raw material mixture
33
by means of a conveying machinery
24
and is supplied again to the roller grinding mill
2
.
In combined operation the milling plant according to
FIG. 3
is operated in such a way that the pressure-zero point, i.e. the point of atmospheric pressure, is located shortly upstream of the entry of the exhaust gases into the roller grinding mill
2
, so that said grinding roller mill
2
, an integrated classifier
13
and the filter
8
operate under a relatively high sub-atmospheric pressure and corresponding sealing mechanisms and stable structures are required, which will be discussed hereinafter.
In direct operation the milling plant according to
FIG. 3
is out of action and only the not shown cement rotary kiln is operated. In combined operation the dust produced by the mill
2
and the residual dust from the heat exchanger are separated in the filter
8
, so that the term “filter plant” is used. However, in direct operation only the residual dust from the exhaust gas
3
from the not shown heat exchanger is separated. The shutoff device
6
a
in the exhaust gas pipe
6
and the shutoff device
9
a
in the dust-exhaust gas pipe
9
are then closed and the exhaust gas flow
3
from the calcining process, following the cooling tower
22
, is passed directly via the bypass line
15
into the filter
8
, where it is dedusted and fed by means of the following fan
7
and a not shown chimney flue into the atmosphere. In direct operation the fan
7
serves as an exhaust gas fan for the heat exchanger.
For the production of cement raw material independently of the calcining process, e.g. when the cement rotary kiln is out of action or on recommissioning, as no exhaust gas is available, fresh air
4
is supplied by means of a control flap
4
a
and a hot gas generator
37
to the roller grinding mill
2
. The shutoff devices
6
a
and
15
a
in the exhaust gas pipe
6
and bypass line
15
are then closed, whereas the shutoff device
9
a
in the dust exhaust gas pipe
9
between roller grinding mill
2
and filter
8
is opened.
FIG. 4
shows a circuit diagram of a further raw material mill drying system, which is also known as the “three-blower version”. For identical features the same reference numerals as in
FIG. 3
are used. A first blower, which corresponds to the kiln fan
5
of
FIG. 3
, but which is not shown, is located in the flow direction upstream of a cooling tower
22
and feeds the exhaust gases
3
from the calcining process to a roller grinding mill
2
. A second blower
28
, which acts as a mill fan, is located downstream of a multiple-unit cyclone
29
and feeds a partial gas flow, via a return line
16
back into the roller grinding mill
2
. The remaining exhaust gas part from the multiple-unit cyclone
29
is supplied by means of a control and shutoff device
14
to a filter
8
. The filter
8
is followed by a third blower
38
as exhaust gas fan and which feeds the remaining exhaust gases
3
into a not shown chimney flue as filter exhaust gas. The fines
34
,
35
separated in the multiple-unit cylone
29
and in filter
8
are supplied by corresponding conveyer mechanisms
36
to a not shown silo. Reference is made to the remarks concerning
FIG. 3
in connection with the devices for the production and supply of a raw material mixture
33
to the roller grinding mill
2
.
The mill drying plant according to
FIG. 4
can operate independently of the gas and thermal balance of the compound system. By means of a bypass line
15
excess exhaust gas and heat flows from the kiln and calcining process can be bypassed the roller grinding mill
2
with classifier
13
and multiple-unit cyclone
29
and can be dedusted together with the exhaust gases from the roller grinding mill
2
in the following filter plant
8
.
FIG. 6
shows an exemplified pressure curve of the combined circuit variant of the plant of FIG.
4
. The essential devices with the corresponding association are shown above the pressure curve and given the reference numerals of FIG.
4
.
FIG. 6
shows that the filter
8
operates in a relatively low sub-atmospheric pressure range and therefore only has to be protected against air infiltrations by relatively limited expenditure. However, the roller grinding mill
2
, which is operated with a vacuum of about −50 to −80 mbar, must be virtually “hermetically” sealed to avoid air infiltrations.
Disadvantages also result from the multiple-unit cyclone
29
, which is associated with relatively high construction and space consumption costs and is subject to wear, so that there are also high maintenance costs.
A high degree of separation in the multiple-unit cyclone
29
also requires relatively high energy costs and a further disadvantage of the known plant is the splitting up of the end product into coarser fines
35
from the cyclones and finer fines
34
from the filter
8
(FIG.
4
).
The flexibility of the milling plant is limited, because the separation level of the multiple-unit cyclone
29
is coupled with the load state (=gas flow) of the mill. The cyclone separation level drops in the case of a partial load, so that there is a rise in the residual dust content in the line
39
following the multiple-unit cyclone
29
to the mill fan
28
, which leads to wear phenomena.
Although admittedly the mill drying plant according to
FIG. 3
has a simpler pipe layout, lower energy costs and relatively low capital costs due to a compact plant construction. As can be seen from the exemplified pressure curve of the compound circuit variant of the plant according to
FIG. 3
shown in

Affiliated with

Also associated with

Rating

Milling plant and method for milling raw materials does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Milling plant and method for milling raw materials, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Milling plant and method for milling raw materials will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2525082