EP2025408B1 - Method and assembly for regulating the grind drying procedure of a coal dust ventilator mill - Google Patents

Description

The invention relates to a method and an arrangement for controlling the grinding drying process of a pulverized coal fan mill.

Coal dust fan mills or impact mills are used in power plants where fossil, solid fuel, especially lignite coal is dried and ground to pulverize coal and the pulverized coal is then fed by means of pulverized coal pipes burners and burned in the combustion chamber or furnace of a steam generator. For drying and conveying the material to be ground hot combustion exhaust gas is used, which is taken from the upper region of the combustion chamber and sucked through a flue gas Rücksaugeschacht of the fan mill. The raw fuel or raw lignite coal to be ground and dried is generally provided in coal bunkers and fed to the flue-gas recirculation shaft by means of bunker removal devices and / or coal feeders and via this to the pulverized coal fan mill. In order to be able to change or regulate the coal throughput through the mill or mills, the rotational speed or conveying speed of the bunker removal devices or coal feeder can be adjusted or regulated.

The mill control in power plants or the regulation of the grinding drying process in the power plant coal mills is generally dependent primarily on the power specification of the block or the power plant control system. The specifications of the block control system increase or reduce the total fuel mass flow to the mills until the required block performance is achieved. The total fuel mass flow is divided among the operating mills. The amount of fuel throughput of the individual mills is dependent on their Mahltrocknungs- or ventilation performance. The regulation of the mills is based on the coal throughput. Depending on the coal throughput (eg represented in the form of allocator speed, Bunkeraustragsgröße or amount or the like) are further relevant mill parameters, such as the mill speed controlled by pilot cams. In order to achieve a certain flexibility in the grinding drying process, the various pilot curves of the mill parameters to be controlled are designed with max and min values or max and min curves.

The previous mill regulations have been developed from the point of view of mill drying or ventilation, ie the mill speed and the temperature monitoring according to mill (the temperature at the coal dust outlet of the mill). With increasing service life of the mills it comes as a result of wear of the mill grinding tools, as there are, inter alia, heads, impact plates and corner armor, and especially for mills with feeders and without classifier to a significant coarsening of the fuel or coal dust produced in the mill. The publication DE 10100331 A1 describes an apparatus and a method for producing carbon dusts in grinding drying plants. Flue gas temperature measuring devices detect a temperature distribution, which allows immediate conclusions about the imbalance or centering of the fireball in the furnace. An imbalance can arise, among other things, that the mills are worn differently. The capacity of the mills decreases with increasing wear. By means of the detection of the flue gas temperatures at the tapping points, the mill device according to the invention permits the detection of the imbalance of the fireball and thus a countermeasure by a corresponding increase in the mill revolutions of the mills conveying too low or a better adaptation of the ratio of the coal throughput to the mill speed and the state of wear. For firing, a coarsening of the fuel dust means that more coarse particles with a higher water content are fed to the burners. The ignition conditions as well as the combustion conditions of the introduced coarsened pulverized coal are thereby deteriorated. Furthermore, the Brennstaubvergröberung leads to a deterioration of the transport conditions within the mill spiral and in the downstream pulverized coal pipes. In addition, in classifier mills, ie in fan mills with classifier arranged on the pulverized coal outlet, there is an increase in the internal circulation of solids, since a larger proportion of coarser material is returned to the mill. Worn corner armor increases both in mills and mills with classifier the gas / solid circulation in the spiral and lead to a deterioration of the mill and firing conditions.

By publication DE 198 53 925 C2 a method for controlling the grinding drying process of a pulverized coal fan mill and an apparatus for carrying out the method has become known, in which or the Mill drying process of the mill is controlled in all operating cases even at lower Temperierungsgasmengen such that no inadmissible excess temperatures in the mill and at its periphery, ie occur in the mill intake and mill outlet channel or mill classifier.

• Brennstaubfeinheit und -feuchte über längeren Zeitraum gleich,
• Förderstabilität innerhalb der Kohlenstaubleitungen bei feinem Brennstaub höher,
• Feststoffrezirkulation bei Sichtermühlen ist geringer,
• Gas-/Feststoffumlauf in Mühlenspirale ist niedriger,
• Zündbedingungen am Brenner längere Zeit gleich.

The object of the invention is therefore to provide a method for controlling the grinding drying process of a pulverized coal fan mill, in particular the grinding drying process of raw lignite in a pulverized coal fan mill, which avoids the aforementioned disadvantages. In particular, it is an object of the invention to provide a method for controlling the grinding drying process of a pulverized coal fan mill, in which the fineness of the produced pulverized coal or coal is maintained over a longer period substantially at the same fineness level. It is a further object of the invention to propose an arrangement for controlling the grinding drying process of a pulverized coal fan mill.
The above object is achieved in terms of the method by the features of claim 1 and in terms of the arrangement by the features of claim 6.
Advantageous embodiments of the invention can be found in the dependent claims.
The solution according to the invention provides a method and an arrangement for controlling the grinding drying process of a pulverized coal fan mill which has the following advantages:

• Fuel dust fineness and moisture equal over a longer period,
• Delivery stability within the pulverized coal pipes higher with fine fuel dust,
• Solids circulation in classifier mills is lower,
• Gas / solids circulation in mill spiral is lower,
• Ignition conditions at the burner for a long time equal.

The invention provides that the state of wear V _{IST is} determined by measurement on at least one of the grinding tools of suggestive heads, impact plates and corner armor, and the measured value is included as a correction variable in the control of the mill speed control _cam VSK _{mill speed} . The measurement is carried out by at least one sensor. Due to the direct measurement of the wear state V _IST on the grinding tool by means of a sensor, the change in Real milling tool incorporated into the regulation of the grinding drying process. The measurement can be done with commercially available devices, for example by optical or other measuring devices or sensors.

In an advantageous embodiment, which is not covered by the invention, the wear state V _{IST is determined} on at least one of the grinding tools proposal heads, impact plates and corner armor by empirical determination over the life of the grinding tool and a derived correction quantity goes into the control of the mill speed pilot cam VSK _{Mill speed} . On the one hand, it is possible to spare one or more sensors and, on the other hand, to make use of the many years of experience of wear conditions on the grinding tools over the life of a fan mill.
In an advantageous embodiment of the invention, the parameter temperature before coal is controlled by means of a determined in dependence on the coal flow rate pilot valve VSK _{Temp before coal} , wherein the pilot curve VSK _{Temp before coal has} a minimum and maximum curve. This measure ensures that material and process temperature limits can be maintained in the mill.
An advantageous embodiment of the invention provides that when exceeding or falling below the associated maximum or minimum curve of one of the controlled parameters, at least one other of the controlled parameters at constant coal throughput within its max and min curves is changed until the exceeding parameter within its assigned max and min curves. This ensures that the grinding drying process of a pulverized coal fan mill can be operated completely automatically within the limits or curves of certain pilot cams.
A further advantageous embodiment of the invention provides that in the case in which, due to the change of at least one of the other controlled parameters, the exceeding parameter does not lie within its associated max and min curves, the coal throughput is changed until the exceeding one Parameter within its assigned max and min curves. This ensures that the Mahldrocknungsprozess a pulverized coal fan mill can be operated completely automatically within the limits or curves of certain pilot cams, although a correction of the coal throughput must be made by lowering or raising.

Embodiments of the invention with reference to the drawings and the description are explained in more detail.

Fig. 1

schematisch dargestellt eine Kohlenstaub-Ventilatormühle mit Sichter im Querschnitt,

Fig. 2

wie Figur 1, jedoch im Längsschnitt,

Fig. 3

schematisch dargestellt eine Kohlenstaub-Ventilatormühle mit Vorschläger und ohne Sichter im Querschnitt,

Fig. 4

wie Figur 3, jedoch im Längsschnitt,

Fig. 5

Vorsteuerkurven der geregelten Mühlen-Parameter,

Fig. 6

schematisch dargestellt den Verschleißzustand V_IST an den Mahlwerkzeugen Vorschlägerkopf bzw. Schlagplatte bzw. Eckpanzer.

It shows:

Fig. 1

schematically shown a pulverized coal fan mill with classifier in cross section,

Fig. 2

as FIG. 1 but in longitudinal section,

Fig. 3

schematically shown a pulverized coal fan mill with proposal and without classifier in cross section,

Fig. 4

as FIG. 3 but in longitudinal section,

Fig. 5

Pilot curves of the controlled mill parameters,

Fig. 6

schematically shows the state of wear V _IST on the grinding tools proposal head or impact plate or corner armor.

FIGS. 1 and 2 schematically shows a pulverized coal fan mill 1 with classifier 3, in which the inventive method is used. In such a fan mill 1 is raw fuel, in particular raw lignite coal from a coal bunker not shown by an allocating device 16, for example a Kohlezuteiler, a bunker extraction device or another Zuteilorgan, and introduced through a coal inlet 8 in the flue gas Rücksaugeschacht 7, from which the raw fuel passes through the mill inlet 9 in the mill 1. The raw fuel is dried in the fan mill or impact wheel mill 1 and comminuted or ground by means of the grinding tools 13, 14. For drying, combustion exhaust gas or flue gas is sucked in by the fan mill 1 from the upper region of the combustion chamber, not shown, of a power plant steam generator fueled by the mill 1, wherein the combustion exhaust gas is fed to a respective mill 1 through a respective flue gas suck-back shaft 7. The combustion exhaust gas is further added primary air, which together form the drying and conveying gas 17 for the raw fuel to be dried and ground or after the mill drying for the ground pulverized coal. The pulverized coal pulverized coal leaving the mill 1 at the outlet 10 and passes through the separator 3, in which coarser grain separated and can be fed back to the mill 1, to the pulverized coal pipe 11, through which the coal dust to the not shown burners is guided on the combustion chamber. The mill housing 4 of the mill 1 has a mill spiral 5, within which the responsible for the comminution of coal and formed with impact plates 13 beater 6 is arranged. The metering device 16 is adjustable in terms of flow rate, so that the coal throughput is set in accordance with the specification of the block or power plant output. Since a coal-fired block or fired power plant has a plurality of mills 1, the coal throughput to be enforced in accordance with the given block power is divided among the mills 1 and their allocating means 16 in operation.

In contrast to the Figures 1 and 2 have the FIGS. 3 and 4 a fan mill 1 without classifier 3, but with upstream proposers 2 on. Here, therefore, eliminates the sighting of the ground material, but this is pre-shredded before the actual grinding within the mill spiral 5 by proposer 2. For this purpose, the suggestors 2 are formed with Vorschlägerköpfen 12, which serve as grinding tools.

In the inventive method for controlling the grinding drying process of a pulverized coal fan mill 1, in particular the grinding drying process of raw lignite, at least the parameters "mill speed", "temperature mill" and "primary air quantity" are regulated, the mill speed denotes the rotational speed of the mill impact wheel 6, the temperature according to mill the temperature of the mixture Mahlgut- / conveying gas flow 18 at its outlet 10 from the mill 1 and designated the amount of primary air, the amount of air, the sucked back from the fan mill 1 from the combustion chamber, not shown, flue gas inlet 9 into the mill 1 is added. The control of these parameters is carried out in each case by a pilot control _curve VSK _{mill speed} , VSK _{Temp to mill} , VSK _{primary air quantity} , wherein the pilot _curves VSK _{mill speed} , VSK _{Temp to mill} , VSK _{primary air} quantity depending on the coal flow rate determined or fixed, see FIG. 5 , The respective pilot control _curves VSK _{mill speed} , VSK _{Temp to Mill} , VSK _{primary air quantity} have min and max values or min and max curves, which allow a certain flexibility of the respective parameter within the minimum and maximum values or min. And max Allow max curves. Furthermore, according to the invention, the mill speed pre- _cam VSK _{mill speed is corrected} as a function of the state of wear V _{IST of} the grinding _tool or of the grinding tools 12, 13, 14 of the fan mill 1.

The wear state V _{IST of} the grinding tool or of the grinding tools 12, 13, 14 can be determined by one or more measuring instrument (s), for example a measuring sensor 15, locally on the grinding tool 12, 13, 14 according to FIG FIG. 6 be measured and determined and fed as a measured value of the wear state-actual value of the control. However, it can also be determined by empirical determination of the operating time of the grinding tool 12, 13, 14 and a dependent characteristic or correction variable can be supplied as a measure of the control, so to speak. If only one or possibly two sensors 15 are used to determine the wear state V _{IST of} the grinding tool or of the grinding tools 12, 13, 14, then it is obvious that one or the two sensors 15 on the critical grinding tools 12, 13, 14 to set. Empirical experiences make it possible to determine the wear state V _{IST of} the grinding tool or of the grinding tools 12, 13, 14 of the grinding tools not monitored by means of the measuring sensor 15. In that case, that the state of wear V _{IST is determined} by means of measuring sensor 15 on all the grinding tools, ie on the coiler heads 12, on the striking plates 13 and on the corner armor 14, attention is paid to the most critical grinding tool 12, 13 with regard to the grinding drying process control and the mill maintenance , 14 and its wear state V _{IST is} set. This is to say that the grinding tool 12, 13, 14 with the most severe or advanced state of wear V _{IST is used} for the grinding-drying process control and the mill maintenance. When measuring the state of wear V _IST by the one or more sensors 15, the wear of the grinding tools 12, 13, 14 can be measured or determined either in mm or in wear proportions (percentage) of the respective grinding tool 12, 13, 14. For example, 10 mm of wear or 20% wear of the grinding tool 12, 13, 14 are determined. In the example mentioned, this would mean that a total of 50 mm of wearing material would be available before the worn ones had to be replaced by new grinding tools 12, 13, 14.

As a wear-prone grinding tools are essentially to be considered heads 12 on the or the proposal (s) 2, impact plates 13 on the beater 6 and corner armor 14 on the mill housing 4 and at the narrowest point of the mill spiral 5 of the fan mill 1. If after a certain period of operation of the fan mill 1, for example 1000 hours, wear has occurred on at least one of the grinding tools 12, 13, 14, the pilot control _curve VSK _{mill speed of} the mill rotational speed is corrected by the measured value supplied to the controller _{according to} the invention. The correction takes place to such an extent that, depending on the wear state V _IST, the mill speed is increased, so that despite the wear on the grinding tools 12, 13, 14, the fineness of the ground pulverized coal remains substantially constant and no coarsening of the ground material occurs. The size of the gradual and quantitative increase or increase in the mill speed as a function of the wear on the grinding tools 12, 13, 14 to achieve a substantially constant fineness of the ground material during the operating phase with increasing wear on the Grinding tools 12, 13, 14 can be determined by tests or determined by empirical values.

In addition to the parameters mentioned above, the parameter "temperature before coal" can also be used to control the grinding drying process. This parameter is the temperature of the combustion or flue gas before the coal inlet 8, ie the flue gas side upstream of the coal inlet 8, in the flue gas Rücksaugeschacht 7 and to the regulation of this temperature. As already stated above, the mill 1 supplied flue gas is withdrawn from the upper part of the combustion chamber, not shown, and sucked by the flue gas Rücksaugeschacht 7 of the mill 1. For the regulation of the temperature of the flue gas before the _carbon inlet 8, a pilot control curve VSK _Temp is also set _{before coal} with minimum and maximum curves or minimum and maximum values, whereby the pilot curve VSK _{Temp before coal} again depends on the coal throughput , please refer FIG. 5 ,

The from the FIG. 5 VSK _{mill speed} , VSK _{temp to mill} , VSK _{primary air quantity} , VSK _{temp before coal} and their minimum and maximum curves depending on the coal throughput are based on procedural and control technical calculations and operating experience. The pilot _curves VSK _{mill speed} , VSK _{Temp to Mill} , VSK _{primary air quantity} , VSK _{Temp before coal} and their minimum and maximum curves are necessarily fuel or coal dependent, ie depending on, among other things, their water and ash content. The minimum and maximum curves of the respective pilot cams can vary depending on the type and mode of action of the system components and fuel-dependent. For example, the min and max curves may be parallel to the pilot curve to determine a minimum and a maximum curve. See for example the minimum and _maximum curve of the pilot valve VSK _{temperature to mill} over the coal throughput range 0 to 100%. However, the minimum and maximum curves can also determine, for example over a part or over the whole of the coal throughput range 0 to 100%, a constant value. See for example the min. And max. Curve of the pilot valve VSK _{primary air} quantity over the coal throughput range 0 to 100%. Furthermore, the pilot cam can a range Defined by a minimum and a maximum curve, as exemplified in the pilot curve VSK _{Temp before coal} to see.

By the minimum and maximum values or minimum and maximum curves of the pilot cams according to the FIG. 5 a sliding operation of the mill 1 or the Mahltrocknungsprozesses is made possible within the parameter limits given by these values. If one of the controlled variables or one of the controlled parameters leaves the defined range for the current coal throughput, for example coal throughput for 80% steam generator or power plant output, then one or more of the other controlled parameters is changed until the deviating or exceeding controlled variable is again defined Range, ie within the min. Or max. Curve. If this is unsuccessful, the coal throughput of mill 1 is changed, ie increased or reduced, until all controlled variables or regulated parameters again lie within a defined control range, ie within the minimum or maximum curves. In this case, according to the change in coal flow rate, the steam generator or power plant capacity is correspondingly increased or reduced.

By taking into account the wear conditions V _IST of coiler heads 12 and / or impact plates 13 and / or corner armor 14 in the mill control, the fineness of the generated dust can be kept at a substantially constant level over a relatively long period of time. The delivery conditions within the mill 1 and within the leading to the coal dust burners not shown downstream pulverized coal pipes 11 remain unchanged as well as the conditions for the combustion of coal dust within the combustion chamber for a long time unchanged. The change cycles for the wear parts 12, 13, 14 can be optimized targeted shredding technical view.

LIST OF REFERENCE NUMBERS

1

fan mill

2

Vorschläger

3

sifter

4

mill housing

5

mill spiral

6

beater

7

Flue gas back eye shaft

8th

Coal entry into the return shaft

9

mill entry

10

Coal dust outlet

11

Pulverized coal conduit

12

Vorschlägerkopf

13

impact plate

14

Eckpanzer

15

probe

16

batching means

17

Drying and conveying gas

18

Mixture of coal dust / conveying gas

Claims (7)

1. Method for controlling the grinding and drying process of a coal dust fan mill, in particular the grinding and drying process of raw brown coal, wherein at least the parameters of mill speed, temperature after the mill and primary air quantity are controlled, comprising
   a pre-control curve (VSK_{mill speed}) for controlling the mill speed,
   a pre-control curve (VSK_{temp after mill}) for controlling the temperature after the mill,
   a pre-control curve (VSK_{primary air quantity}) for controlling the primary air quantity, wherein the pre-control curves (VSK_{mill speed}, VSK_{temp after mill}, VSK_{primary air} quantity) are each determined as a function of the coal throughput and have minimum and maximum curves, characterised in that
   the wear state (V_IST) is determined at least on one of the grinding tools by measurement and the measured value is incorporated as a correction variable into the control of the mill speed pre-control curve (VSK_{mill speed})
   and the mill speed pre-control curve (VSK_{mill speed}) is corrected as a function of the wear state (V_IST).
2. Method according to claim 1, characterised in that the grinding tools are pre-beater heads, beater plates and corner armour.
3. Method according to claim 1, characterised in that the parameter of temperature before coal is controlled by means of a pre-control curve (VSK_{temp before coal}) determined as a function of the coal throughput and the pre-control curve (VSK_{temp before coal}) has a minimum and maximum curve.
4. Method according to claim 1, characterised in that when the assigned maximum or minimum curve of one of the controlled parameters is exceeded or fallen below, with constant coal throughput at least one other of the controlled parameters is changed within its maximum and minimum curves until the exceeded parameter comes to lie within its assigned maximum and minimum curves.
5. Method according to claim 4, characterised in that in the case in which, due to the changing of at least one of the other controlled parameters, the exceeded parameter does not come to lie within its assigned maximum and minimum curves, the coal throughput is changed until the exceeded parameter comes to lie within its assigned maximum and minimum curves.
6. Arrangement for controlling the grinding and drying process of a coal dust fan mill (1) operated with solid fossil fuels, wherein the coal dust fan mill (1) is configured with grinding tools (12, 13, 14) which wear when considered over the operating time of the fan mill (1) and at least the parameters of mill speed, temperature after mill and primary air quantity can be controlled,
   with a device (VSK_{mill speed}) for controlling the mill speed,
   with a device (VSK_{temp after mill}) for controlling the temperature after the mill,
   with a device (VSK_{primary air quantity}) for controlling the primary air quantity,
   wherein the pre-control curves (VSK_{mill speed}, VSK_{temp after mill}, VSK_{primary air quantity}) of the devices in each case can be determined as a function of the coal throughput and have minimum and maximum curves, characterised in that the wear state (V_IST) on at least one of the grinding tools can be determined by means of at least one measuring sensor (15), and the determined value can be supplied as control variable to the mill speed device (VSK_{mill speed}), and the mill speed pre-control curve (VSK_{mill speed}) of the mill speed device can be corrected as a function of the wear state (V_IST) of at least one grinding tool (12, 13, 14) of the fan mill (1).
7. Arrangement according to claim 6, characterised in that the grinding tools are pre-beater heads (12), beater plates (13) and corner armour (14).

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