US20120122042A1

US20120122042A1 - Method and assembly for improving the dynamic behavior of a coal-fired power plant

Info

Publication number: US20120122042A1
Application number: US13/262,391
Authority: US
Inventors: Hellmuth Brueggemann; Olivier DRENIK; Michael Heim; Haider Mirza
Original assignee: Individual
Current assignee: GE Vernova GmbH
Priority date: 2009-04-03
Filing date: 2010-03-19
Publication date: 2012-05-17
Also published as: DE102009016191A1; DE102009016191B4; CN102388267A; EP2414731A1; EP2414731B1; CN102388267B; WO2010115396A1; HUE029851T2; PL2414731T3; ES2597961T3; HRP20161325T1

Abstract

The invention relates to a method for improving the dynamic behavior of a coal-fired power plant for primary and/or secondary requirements of the power grid operator with respect to the current output into the grid, wherein the power plant has a nominal output (RC) and is operated by way of firing, wherein upon an increase in the primary and/or secondary requirements of the power grid operator with respect to the current output into the grid the coal dust volume that is supplied is raised with respect to the present actual output, and wherein upon a decrease in the primary and/or secondary requirements of the power grid operator with respect to the current output into the grid the coal dust volume that is supplied is lowered with respect to the present actual output and is stored, and to an assembly for carrying out the method.

Description

Method and assembly for improving the dynamic behavior of a coal-fired power plant for primary and/or secondary requirements of the power grid operator with respect to the current output into the grid.
The invention relates to a method and assembly for improving the dynamic behavior of a coal-fired power plant for primary and/or secondary requirements of the power grid operator with respect to current output into the grid.
Keeping the alternating voltage frequency in power grids constant constitutes an important objective. Deviations from the predetermined frequency can result in the failure of consumers connected to the grid and consequential damages resulting from such failure.
Deviations from the predetermined grid frequency value mainly occur when the power requirement on the power plants connected to the power grid suddenly changes because for instance a power plant is disconnected from the grid because of an accident or a large consumer is connected to the grid or because the grid configuration or grid distribution changes. In order to keep the grid frequency constant at the predetermined value or within a certain tolerance range it has to be ensured, within the scope of the so-called primary control or primary control output, that the generated power and the grid load remain balanced and as much electric power is always generated as is consumed by the grid load when operating with a predetermined grid frequency. In doing so, the primary control is additionally supported by the secondary control or secondary control output, which following the balancing of a sudden change of the consumed or the generated power through the primary control offsets quasi-stationary deviations both of the frequency as well as of the transfer power.
In order to be able to counteract deviations from the predetermined grid frequency value in the shortest time, some national grid operators stipulate in their standards conditions or targets under which this has to be accomplished. Thus, the British Grid Operator National Grid Electricity Transmission plc for example through its document “The Grid Code”, Issue 3, prescribes that in the event of a frequency deviation a power plant linked to the power grid, for example at an operating mode of 65% of its nominal output the power plant output within the scope of the primary control or the primary requirements is increased by 10% of its nominal output, within 10 seconds, thus counteracting the frequency deviation. This, in terms of time, very rapid and with respect to the power output very large change makes major demands on the power plant, particularly on a coal-fired power plant.
As a rule, large coal-fired power plants are designed with coal dust furnaces, with which the coal ground in the coal grinding plant can be directly fed to the firing box of the power plant via coal dust lines (so-called “direct” coal dust furnaces). The condition of the fuel is one of the main factors for good combustion, a sound efficiency, low emissions and little that is uncombusted in the ash in order to be able to utilize this by-product. For coal conditioning, the coal grinding plant or coal mill has to be in a stationary heat and mass flow equilibrium, which results in load changes on the coal dust furnace and thus on the power plant itself being able to be carried out only slowly and thus a delay time occurring when load changes are carried out or are required.
The delay time of the coal mill with changing fuel quantity or charge is a substantial part of the overall plant delay time. The delay time of the coal mill can be long depending on the raw coal conditioning process (dependent on fineness, moisture, hardness of the raw coal and the mill loading) and therefore has a detrimental effect on the delay time of the overall plant.
The object of the invention now is to create a method for improving the dynamic behavior of a coal-fired power plant for primary and/or secondary requirements of the power grid operator with respect to the current output into the grid, with which the delay time of the coal dust furnace of the power plant is reduced so that the power plant meets the targets or conditions of respective national operators of power grids. It is, moreover, an object of the invention to create an assembly for improving the dynamic behavior of a coal-fired power plant for primary and/or secondary requirements of the power grid operator with respect to the current output into the grid.
The object mentioned above is solved through the totality of the features of Patent Claim 1 with respect to the method and through the totality of the features of Patent Claim 9 with respect to the assembly.
Advantageous configurations of the invention can be taken from the subclaims.
Through the solution according to the invention a method and an assembly for improving the dynamic behavior of a coal-fired power plant for primary and/or secondary requirements of the power grid operator with respect to the current output into the grid is created, which has or have the following advantages:

- Creation of the possibility for power plant operators to obtain the required permits for building and operating power plants in agreement with the prescribed national grid frequency requirements.
- Through the sale of primary control reserve, the power plant operator is enabled to operate the plant more economically or achieve higher profits.
- The manufacturer or supplier of such power plants is enabled to offer or sell these power plants on world-wide markets, e.g. UK, Ireland, France, China, India, Singapore etc.

An advantageous embodiment of the invention provides that the silo having a storage volume V_Spin normal operation of the indirect firing system is filled, in terms of volume, approximately half with coal dust for storage and use upon increase of the primary and/or secondary requirements of the power grid operator with respect to the current output into the grid and the remaining storage volume is used for receiving and storing the excess-produced coal dust upon reduction of the primary and/or secondary requirements of the power grid operator with respect to the current output into the grid.
In an advantageous configuration of the invention, the increase or reduction of the indirectly fed-in coal dust quantity is effected through a controlled increase or reduction of the throughput rate of the apportioning organs. Thus, the needs or the dynamic behavior of the coal-fired power plant can be accurately taken into account.
An advantageous configuration provides increasing or reducing the volumetric flow of the conveying gas blower in a controlled manner upon an increase or a reduction of the indirectly fed-in coal dust quantity. Thus, the smooth input of the coal dust in the firing box is maintained.
It is advantageous that the increase or the reduction of the throughput rate of the apportioning organs and/or the increase or the reduction of the volumetric flow of the conveying gas blower is brought about by the block output control of the coal-fired power plant influenced by the requirements of the power grid. Through this measure it is ensured that in the event of a frequency change or a requirement in the power grid an influencing signal of the grid control is directly sent to the block output control of the coal-fired power plant and its furnace and a countermeasure without loss of time is thus initiated in order to optimize the dynamic behavior of the power plant.
In an advantageous embodiment of the invention, the primary requirement or the primary control is triggered through a remote-controlled signal. In a further advantageous embodiment of the invention the secondary requirement or the secondary control is likewise triggered through a remote-controlled signal.
The secondary requirement or the secondary control can be additionally triggered through written or oral instruction to the operating personnel of the power plant.

In the following, exemplary embodiments of the invention are explained in more detail by means of the drawings and the description.

FIG. 1 shows an extract from the British Electricity Grid Regulations (Grid Code (UK)), wherein the extract shows the minimum requirement profile of the frequency dependency for a 0.5 Hz frequency change from the target frequency (minimum frequency response requirement profile for a 0.5 Hz frequency change from target frequency),

FIG. 2 shows an extract from the British Power Grid Regulations (Grid Code (UK)), wherein the extract shows the interpretation of the primary and secondary control or primary and secondary requirement (interpretation of primary and secondary response values),

FIG. 3 shows, represented schematically, an assembly for improving the dynamic behavior of a coal-fired power plant for primary and/or secondary requirements of the power grid operator for the current output into the grid, wherein the coal grinding plant including coal dust lines of the furnace of the power plant are shown,

FIG. 4 shows, represented schematically, the relation of an output increase as a function of time and of the firing method.

In an electrical energy supply system (power grid) the generated power has to be constantly in equilibrium with the consumer power. Changes to the consumer load or power plant fault impair this equilibrium and cause frequency deviations in the grid, to which the machines involved in the primary control or the primary requirement, react. Because of its control behavior, the primary control or the equivalent primary requirement guarantees the restoration of the equilibrium between generated and consumed power within a few seconds, while the frequency is held within the permissible limit values. In the power grid, there are quasi-stationary deviations (with respect to the target values) both of the frequency Δ f as well as the transfer power Δ Pi between the individual control zones following the balancing of a sudden change of the consumed or generated power through the primary control or the primary requirement. In this connection, the secondary control or secondary requirement becomes functional whose objective it is to return the frequency to its target value and the transfer outputs to the agreed values and thus to have the entire activated primary control output again available as reserve.
FIG. 1 shows the interpretation of the primary and secondary control or primary and secondary control output or primary and secondary requirement (interpretation of primary and secondary response values) of the British Power Grid Regulations (Grid Code UK) that has to occur upon a frequency deviation (frequency change) of −0.5 Hz from the target frequency of the power grid. The diagram of FIG. 1 shows that a power plant connected to the power grid according to the primary control P has to react within a time span T_Spof 10 seconds with a plant response and thus increase the power plant output. The amount of the output increase within this time span T_Spis dependent on the load range with which the power plant happens to be operated at the time of the drop in frequency. The British Power Grid Regulations determine for example with a fixed required minimum load (minimum generation) of 65% of the nominal output (RC) (registered capacity) of the power plant that with this part load the power plant output has to be increased within the 10 seconds by 10% (percentage A_p) of the nominal output or capacity RC of the power plant (see FIG. 2). According to FIG. 2 (the abscissa shows the load range (in percent of the RC) of the power plant, the ordinate shows the primary or secondary control ranges (in percent of the RC)) the increase by 10% of the rated capacity RC of the power plant has to be guaranteed between the part load range of 65 to 80% of the nominal power plant output RC. Between the part load range of 80 to 100% of the nominal power plant output RC the power increase decreases linearly from 10% to 0.
In the event of the frequency being exceeded or a reduction of the primary and/or secondary requirements of the power grid operator with respect to the current output into the grid it is provided according to FIG. 2 to lower the power plant output in the part load range between 95% and 70% of the rated power of the power plant by 10% of the rated power RC of the power plant within the 10 seconds. Between the part load ranges of 70% to 65% of the nominal power plant output RC the output reduction decreases linearly from 10% to approximately 6.5 and between 100% and the part load range of 95%, the power reduction increases linearly from approximately 5% to 10%. FIG. 2 additionally shows the minimum load (minimum generation MG) of the power plant required by the British Power Grid, which is at 65% of the nominal power plant output.
FIG. 3 exemplarily shows how these requirements raised by the British Power Grid Regulations can be satisfied. To this end, the furnace 1 of the power plant according to the invention which is not shown is exemplarily designed with four coal grinding plants 2.1, 2.2, 2.3, 2.4, all of which directly fire the firing box of the power plant which is not shown (direct firing system), wherein at least one of the coal grinding plants 2.1, 2.2, 2.3, 2.4 is designed in such a manner that it can be used to fire the firing box indirectly (indirect firing system) instead of directly, i.e. that at least one of the coal grinding plants 2.1, 2.2, 2.3, 2.4 in addition to the direct firing system is additionally designed with an indirect firing system.
Directly fired or a direct firing system means to say that the coal reduced in the coal grinding plant or coal mill 2.1, 2.2, 2.3, 2.4 is directly fed to the firing box by means of a carrier gas or support air via coal dust lines 3.1, 3.2, 3.3, 3.4 and fired therein. Here, according to FIG. 3, a burner level each can be serviced by each coal grinding plant 2.1, 2.2, 2.3, 2.4 and the coal dust lines 3.1, 3.2, 3.3, 3.4 originating from the respective coal grinding plants 2.1, 2.2, 2.3, 2.4 each service the burners which are not shown in the respective corners or side walls of the generally rectangular firing boxes of the coal-fired power plant.
Indirectly fired or an indirect firing system means to say that the coal reduced or ground in the coal grinding plant or coal mill 2.1, 2.2, 2.3, 2.4 is discharged via coal dust lines 3.1, 3.2, 3.3, 3.4 and initially conducted in the direction of the firing box, but then, via a coal dust switch 6 each arranged in the coal dust line 3.1, 3.2, 3.3, 3.4 and via storage lines 7.1, 7.2, 7.3, 7.4 is fed to a separator 4 common to all storage lines. In the separator 4, the coal dust is separated from the carrier gas or support air and via a connecting line 8 fed to a silo 5 and stored therein. Via feed lines 9.1, 9.2, 9.3, 9.4 and regulated apportioning organs 10 arranged in these feed lines the coal dust can be extracted from the silo 5 and via a charging device 15 each and a further coal dust switch 13 fed to the coal dust lines 3.1, 3.2, 3.3, 3.4 downstream of the first coal dust switches 6 in order to be conveyed into the firing box by these. For conveying the coal dust extracted from the silo 5 into the firing box the charging devices 15 arranged in the feed lines 9.1, 9.2, 9.3, 9.4 downstream of the apportioning organs 10 are supplied with a conveying gas, for example air, via a conveying gas line 11, which air is supplied by a conveying gas blower 12. The charging device 15 can for example be an injector, a feeder shoe, a dust pump or the like.
The carrier gas or support air separated in the separator 4 is discharged via a carrier gas discharge line 14 and fed into the atmosphere, while it is one more time cleaned before that in a dust separating system. Instead of into the atmosphere, the carrier gas can also be conducted into the firing box or the smoke gas drafts of the coal-fired power plant connected downstream of the firing box and freed of dust in the existing dust separating system (e.g. e-filter, hose filter of the like) of the power plant system.
Deviating from FIG. 3, each of the storage lines 7.1, 7.2, 7.3, 7.4 can each have its own separator 4 and its own silo 5 connected downstream, from which the respective feed lines 9.1, 9.2, 9.3, 9.4 then originate.
In normal operation of the power plant, the coal grinding plants 2.1, 2.2, 2.3 of the furnace 1 according to FIG. 3 work in such a manner that the coal dust ground therein is directly fed to the firing box for firing via the respective carbon dust lines 3.1, 3.2, 3.3, 3.4. In the case of the coal grinding plant 2.4, which exemplarily (instead of the grinding plant 2.4, it can also be any other grinding plant) is designed with an indirect firing system in addition to the direct firing system, the respective coal dust switches 6 and 13 arranged in the coal dust lines 3.1, 3.2, 3.3, 3.4 are each set in such a manner that the coal dust ground in the coal grinding plant 2.4 is not directly fed to the firing box, but to the firing box by way of the silo 5. To this end, the apportioning organs 10 arranged in the feed lines 9.1, 9.2, 9.3, 9.4 and charging devices 15 are in operation and conveying gas is provided to the charging devices 15 through the conveying gas line 11 and the conveying gas blower 12. In the charging devices 15, the conveying gas picks up the respective coal dust apportioned by the apportioning organs 10 and conveys it into the firing box. The operation of the grinding plant 2.4 is such that as a rule, at the start of the operation, the grinding output of the grinding plant 2.4 compared with the grinding output of the grinding plants 2.1, 2.2, 2.3 or compared with the current requirement of the grinding output of the grinding plant 2.4 or compared with the present actual output of the grinding plant 2.4 is increased in order to half fill the volume of the silo 5 having a storage volume V_Spwith the excess offer of ground fuel. Following completed filling of the silo 5 the grinding output of the grinding plant 2.4 is adapted to those of the grinding plant 2.1, 2.2, 2.3 or the current requirement of the grinding output of the grinding plant 2.4. With the exception of the filling operation of the silo 5, the discharge or conveying output of the apportioning organs 10 corresponds to the quantity-based grinding output of the grinding plant 2.4, i.e. after the filling operation, the quantity of coal dust as produced by the grinding plant 2.4 is discharged from the silo 5 and conveyed into the silo 5, while minute losses in the separator 4 are taken into account.
In the case of a frequency change or a frequency drop or a frequency undershot by for example 0.5 Hz of the power grid the block output control of the coal-fired power plant is influenced via the grid control of the power grid or its primary and/or secondary requirements of the power grid operator with respect to the current output into the grid, which substantially increases the quantity of the coal dust discharged by the apportioning organs 10 from the silo 5 and indirectly fed to the firing box relative to the present actual output or relative to the coal dust quantities in each case supplied by the coal grinding plants 2.1, 2.2, 2.3. During this, the coal dust stored and stocked in the silo 5 for these purposes can be introduced into the firing box for firing in a very short time and thereby, on the part of the furnace, a substantial contribution can be made for improving the dynamic behavior of the coal-fired power plant. The present actual output designates the output or the part load with which the coal-fired power plant is currently operated and on which the fuel quantity fed in to the firing box and thus also the respective throughput rate of the individual coal grinding plants 2.1, 2.2, 2.3, 2.4 is dependent.
In the event of a frequency being exceeded for example by 0.5 Hz of the power grid the block output control of the coal-fired power plant is influenced via the grid control of the power grid or its primary and/or secondary requirements of the power grid operator with respect to the current output into the grid, which substantially reduces the quantity of the coal dust discharged by the apportioning organs 10 from the silo 5 and indirectly fed to the combustion chamber compared with the present actual output or compared with the coal dust quantities supplied in each case by the coal grinding plants 2.1, 2.2, 2.3 and thus, as with the increase of the coal dust quantity, a substantial contribution is made by the furnace to the improvement of the dynamic behavior of the coal-fired power plant. Here, coal dust provided by the grinding plant 2.4 during this process and which is not necessary, i.e. excess, is buffer-stored in the silo 5.
For realizing the improvement of the dynamic behavior of a coal-fired power plant the silo 5 connected downstream of the coal grinding plant 2.4 is dimensioned and designed with a receiving capacity or a storage volume V_Spfor the coal dust to be stored. However, additional coal grinding plants of the exemplary four coal grinding plants 2.1, 2.2, 2.3, 2.4 in FIG. 3 can each be designed with an indirect firing system and thus with a silo 5 for the storage of coal dust. If for example two, three or all four coal grinding plants 2.1, 2.2, 2.3, 2.4 are additionally designed with an indirect furnace or an indirect firing system the entire storage volume or the receiving capacity V_Spof coal dust can be divided over the existing number of silos 5 or the storage volume V_Spincreased through the increased number of silos 5. Through the additional design of a plurality of grinding plants with indirect firing system and thus increased coal dust storage capacity in the silos 5 the dynamics of the fuel apportioning of the coal-fired power plant can be further improved if required. Through this improvement of the dynamics of the fuel the primary and secondary reserve of the coal-fired power plant can also be improved or increased.
The storage volume V_Spof the silo 5 is dimensioned in such a manner that upon normal operation, i.e. with stationary state, the storage volume V_Spof the silo 5 is filled to about half and thereby has stored sufficient coal dust in order to be able to introduce an increased coal dust quantity into the firing box in the event of a frequency drop or a primary and/or secondary requirement of the power grid operator with respect to the current output into the grid, i.e. of an instationary state, in order to improve the dynamic behavior of the power plant. On the other hand, the silo 5 still has to have sufficient storage capacity in order to be able to introduce a reduced coal dust quantity into the firing box in the event of a frequency being exceeded or a primary and/or secondary requirement of the power grid operator with respect to the current output into the grid, i.e. in turn of an instationary state, and thereby receive or store the excess coal dust quantity produced by the grinding plant 2.4 during the instationary state in the silo 5.
In addition to the silo or the silos 5 the apportioning organs 10, the charging devices 15 and the coal dust lines (feeding lines 9.1, 9.2, 9.3, 9.4 and coal dust lines 3.1, 3.2, 3.3, 3.4) can be suitably designed dimensionally downstream of the silo or of the silos 5 as far as to the firing box in order to be able to conduct and feed to the firing box the required fuel quantities in the short time required. The conveying gas or support air required for this purpose is supplied in a controlled manner through the conveying gas line 11 and by means of the conveying gas blower 12.
FIG. 4 schematically shows the dynamic behavior of a direct and an indirect furnace or of a direct as well as an indirect firing system of a coal-fired power plant. While the increase of the boiler output from L₀to L₁with the direct furnace starting out from t₀takes the time t₂, the increase of the same boiler output with the indirect furnace starting out from t₀only requires the time t₁and thus comes substantially closer to an ideal, rapid increase within a time t₀(step response). Through the method according to the invention or the assembly according to the invention of designing at least one of the coal grinding plants 2.1, 2.2, 2.3, 2.4 in addition to the direct furnace with an indirect furnace and operating said furnace as indirect furnace and upon a frequency change in the power grid or a primary and/or secondary requirement of the power grid operator with respect to the current output into the grid of increasing or reducing the quantity of the coal dust discharged from the silo 5 and indirectly fed to the firing box compared with the indirectly supplied coal dust quantity upon stable grid frequency, the dynamic behavior of the furnace according to FIG. 4 and thus also the plant response behavior, i.e. the dynamic behavior of the coal-fired power plant can be substantially improved. The increase of the boiler output from L₀to L₁constitutes a percentage A_pof the nominal power plant output RC, for example an increase by 10% of the nominal power plant output RC.
In the event of a maintenance or a failure of an apportioning organ 10 or of a charging device 15 of the indirect firing system on the coal grinding plant 2.4 the operation of the coal grinding plant 2.4 as direct firing system can be continued in that the coal dust switches 6 and 13 are reset and the coal dust through the coal dust lines 3.1, 3.2, 3.3, 3.4 is directly fed to the firing box and the silo 5 as well as the apportioning organs 10 and the charging device 15 are thus bypassed. If further coal grinding plants 2.1, 2.2, 2.3 are additionally designed with an indirect firing system, one or a plurality of coal grinding plants can be reset by means of resetting of the coal dust switches 6 and 13 to the operation as indirect firing system and thus temporarily replace the indirect firing system of the coal grinding plant 2.4 currently undergoing maintenance.
Obviously, with the method according to the invention or the assembly according to the invention regarding the primary and secondary control or the primary and secondary requirement and from this the plant response behavior or with respect to the improved dynamic behavior of a coal-fired power plant not only the exemplarily mentioned British Power Grid Regulations and their requirements can be maintained or satisfied, but also further national or international regulations requiring a rapid or improved dynamic behavior of the coal-fired power plant. To this end, if required, merely the storage volume V_Spof the silo or silos 5 and the throughput rates of the apportioning organs 10 and/or of the charging devices 15 and/or of the conveying gas blower 12 have to be adapted to the regulations.

LIST OF REFERENCE NUMBERS

1 Furnace
2.1 Coal grinding plant
2.2 Coal grinding plant
2.3 Coal grinding plant
2.2 Coal grinding plant
3.1 Coal dust line
3.2 Coal dust line
3.3 Coal dust line
3.4 Coal dust line
4 Separator
5 Silo
6 Coal dust switch
7.1 Storage line
7.2 Storage line
7.3 Storage line
7.4 Storage line
8 Connecting line
9.1 Feed line
9.2 Feed line
9.3 Feed line
9.4 Feed line
10 Apportioning organ
11 Conveying gas line
12 Conveying gas blower
13 Coal dust switch
14 Carrier gas discharge line
15 Charging device

Claims

1. A method for improving the dynamic behavior of a coal-fired power plant for primary and/or secondary requirements of the power grid operator with respect to the current output into the grid, wherein the power plant has a nominal output (RC) and is operated with a furnace comprising at least one firing box for the firing of the fuel, at least two coal grinding plants for the grinding of the fuel having a direct fuel system, wherein at least one of these coal grinding plants comprises an additional indirect firing system and the coal dust is indirectly fed to the firing box via the indirect firing system having at least one silo and apportioning organs and the further coal grinding plant(s) directly feeds the coal dust to the firing box via the direct firing system, and wherein upon an increase of the primary and/or secondary requirements of the power grid operator with respect to the current output into the grid the coal dust quantity indirectly fed in via silo and apportioning organs compared with the present actual output or compared with the coal dust quantity fed in through each of the coal grinding plant(s) is increased and in the process coal dust stocked in the silo is withdrawn and introduced into the firing box, and wherein upon a reduction of the primary and/or secondary requirements of the power grid operator with respect to the current output into the grid the coal dust quantity indirectly fed in via silo and apportioning organs is reduced compared with the present actual output or compared with the coal dust quantity fed in through each of the coal grinding plant(s) is reduced and in the process coal dust excessively produced by the grinding plant stored in the silo.

2. The method as claimed in claim 1, characterized in that the silo has a storage volume (V_Sp) and in normal operation of the indirect firing system with regard to volume is filled to about half with coal dust for stocking and use upon an increase of the primary and/or secondary requirements of the power grid operator with respect to the power output into the grid and the remaining storage volume is used for receiving and storing the excess produced coal dust upon reduction of the primary and/or secondary requirements of the power grid operator with respect to the current output into the grid.

3. The method as claimed in claim 1, characterized in that the increase or reduction of the indirectly fed-in coal dust quantity is effected through controlled increase or reduction of the throughput rate of the apportioning organs.

4. The method as claimed in claim 1, characterized in that upon an increase or a reduction of the indirectly fed-in coal dust quantity the volumetric flow of the conveying gas blower is increased or reduced in a controlled manner.

5. The method as claimed in claim 3, characterized in that the increase or the reduction of the throughput rate of the apportioning organs and/or the increase or reduction of the volumetric flow of the conveying gas blower is brought about by the block output control of the coal-fired power plant influenced by the requirements of the power grid.

6. The method as claimed in claim 1, characterized in that the primary requirement is triggered through a remote-controlled signal.

7. The method as claimed in claim 1, characterized in that the secondary requirement is triggered through a remote-controlled signal.

8. The method as claimed in claim 1, characterized in that the secondary requirement is triggered through written or oral instruction to the operating personnel of the power plant.

9. An assembly for improving the dynamic behavior of a coal-fired power plant for primary and/or secondary requirements of the power grid operator with respect to the current output into the grid, wherein the power plant has a nominal output (RC) and is designed with a furnace (1) which substantially comprises at least one firing box for the firing of the fuel, at least two coal grinding plants (2.1, 2.2) for the grinding of the fuel comprising a direct firing system, wherein at least one of these coal grinding plants (2.1, 2.2) comprises an additional indirect firing system and the coal dust can be indirectly fed to the firing box via the indirect firing system having at least one silo (5) and apportioning organs (10) and with the further coal grinding plant(s) (2.1, 2.2) the firing box can be directly fed with coal dust via the direct firing system,

and wherein upon an increase of the primary and/or secondary requirements of the power grid operator with respect to the current output into the grid the coal dust quantity that can be indirectly fed in via silo (5) and apportioning organs (10) compared to the present actual output or compared to the coal dust quantity that can be fed in by the coal grinding plant(s) (2.1, 2.2) in each case can be increased and in the process coal dust stocked in the silo (5) can be withdrawn and introduced into the firing box

and wherein upon a reduction of the primary and/or secondary requirements of the power grid operator with respect to the current output into the grid the coal dust quantity that can be indirectly fed in via silo (5) and apportioning organs (10) compared with the present actual output or compared with the coal dust quantity that can be fed in through the coal grinding plant(s) (2.1, 2.2) in each case can be reduced and in the process excess coal dust produced by the grinding plant (2.1, 2.2) can be stored in the silo (5).