JP2015001347A - Vertical grinding classifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To implement transition between both modes without deteriorating combustion quality of fuel and without hindering mill operation, in the transition between the modes of a coal exclusive grinding mode and a biomass exclusive grinding mode.SOLUTION: A vertical grinding classifier 24 includes a feeder 41 for supplying fuel, a grinder comprising a rotating table and a grinding element, and a rotary classifier for classifying ground products. There are provided differential pressure measurement means for measuring a pressure difference ΔP measured at least at a downstream side Ps1 of a throat of a rotating table outer circumference side where the airflow flows and at an entrance side Ps2 of the rotary classifier, fuel feed rate measurement means of a feeder 41, and rotary classifier control means 46. Calculation means 42 controls the increase and decrease of the rotation 45 of the rotary classifier through the rotary classifier control means so that the measured differential pressure ΔP becomes the proper differential pressure, on the basis of the differential pressure ΔP being the difference in pressure between parts measured by the differential pressure measurement means and a proper differential pressure calculated on the basis of a fuel feed rate by the fuel feed rate measurement means.

Description

  The present invention relates to a boiler device that uses coal and biomass as fuel and co-fires them, and more particularly to a vertical pulverization and classification device for a boiler device.

  As shown in FIG. 8, the conventional technology of a boiler apparatus that uses coal and biomass for co-combustion conveys the biomass stored in the biomass silo 21 to a coal-carrying conveyor 22 and uses the bunker 23 for biomass. It is pulverized by a mill 24 and burned by a steam generator 26 through a biomass burner 25. Further, the recirculated gas is extracted from the wake of the electrostatic precipitator 29 installed in the wake of the air preheater 28, and then mixed with the air preheated by the air preheater 28 through the primary ventilator 33. There has been proposed a boiler apparatus that controls the oxygen concentration and the temperature (see, for example, Patent Document 1). FIG. 8 is a diagram showing a system configuration of a boiler apparatus that commonly uses coal and biomass for co-firing.

  As disclosed in the above-mentioned Patent Document 1, the boiler device for co-firing coal and biomass has a common route from the coal-carrying conveyor 22 to the burner 25 with the coal boiler device, and is different from the coal boiler device. These are the internal structure of the mill 24 and the structure of the burner 25.

  The mill 24 and the burner 25 take into consideration that the boiler load is maintained as much as possible even at the time of equipment failure or replacement of a worn part. Specifically, in order to enable switching to a coal mill and a coal burner at the time of the event, it has been modified to a biomass dedicated mill and a biomass dedicated burner. Therefore, work such as disassembly of the boiler device is prevented from occurring at the time of switching. As described above, the biomass mill 24 is obtained by remodeling the coal mill for biomass, and the burner has enhanced ignition so that coarse-grained biomass can be stably burned.

  Moreover, in the prior art as shown in the above-mentioned Patent Document 1, in consideration of the fact that biomass is more likely to deposit in the mill than the coal, and that dust explosion is likely to occur, the oxygen concentration inside the system configuration that handles biomass The safety level is kept below the lower explosion limit for preventing dust explosions and at least below the dust explosion risk of coal.

JP 2010-242999 A

  In the boiler apparatus using the biomass-coal common mill, the common burner, and the common exhaust gas recirculation system related to the prior art as shown in the above-mentioned Patent Document 1, there are a biomass exclusive-crushing / combustion mode and a coal-crushing / combustion mode. To do. And, when switching to each mode, the mill, burner, and exhaust gas recirculation system need not be modified.

  However, when mode switching is performed, it is not easy to automate the mode switching because the operating conditions of the mill (which is composed of a mill roll / mill table and a rotary classifier, also referred to as a pulverizer) are significantly different. It was. Specifically, the operating conditions in each mode are known, but switching between coal and biomass fuel is not possible instantaneously. Since the ratio is unknown, the operating conditions cannot be determined. This is because the bunker 23 is also shared because of the importance of cost reduction, so there are two types of fuel (coal and biomass) temporarily inside the bunker 23 at the time of fuel switching. This is because if segregated, it will not be stably supplied to the mill.

  In a boiler device that shares and co-fires coal and biomass as fuel, being able to share does not just mean supplying biomass or coal to the same mill and burner, but for each fuel of coal and biomass, It is required to automatically switch as necessary in consideration of various conditions of grindability, combustibility, and handling properties. The prior art as shown in the above-mentioned Patent Document 1 does not give a detailed description of the control in consideration of the above-mentioned various conditions accompanying the switching of fuel.

In order to solve the above problems, the present invention mainly adopts the following configuration.
Classifying a feeder for supplying fuel made of coal and biomass, a pulverizer for pulverizing the fuel by biting between a rotary table and a pulverizer, and a pulverized product conveyed by an air current blown from a throat on the outer peripheral side of the rotary table A vertical pulverizing and classifying device comprising: a rotary classifier having rotating fins; and a housing for accommodating the pulverizer and the rotary classifier,
The feeder is provided with fuel supply amount measuring means for measuring the fuel supply amount, and is provided with rotary classifier control means for controlling the rotation of the rotary classifier, and upstream of the throat through which the airflow flows in the housing. The pressure is measured at least at the downstream side of the throat and the inlet side of the rotary classifier among the downstream side of the throat, the inlet side of the rotary classifier, and the outlet side of the rotary classifier. Differential pressure measuring means for measuring a pressure difference between the parts, a differential pressure that is a pressure difference between the measured pressure parts measured by the differential pressure measuring means, and a fuel supply measured by the fuel supply amount measuring means Based on the appropriate differential pressure calculated based on the quantity, an operation for increasing / decreasing the rotation of the rotary classifier through the rotary classifier control means so that the measured differential pressure becomes the appropriate differential pressure A configuration in which a device is provided; That.

  Further, in the vertical crushing and classifying apparatus, the arithmetic unit calculates a predicted differential pressure value based on a fuel supply amount of the biomass when reaching the biomass combustion in the switching mode for switching from the coal combustion to the biomass combustion. Calculating a target control differential pressure in the switching mode from the calculated predicted differential pressure value, obtaining an appropriate differential pressure from the measured differential pressure at the fuel switching start time and the target control differential pressure, and during the switching mode The rotation of the rotary classifier is controlled to decrease so that the measured differential pressure becomes the appropriate differential pressure. Further, the calculation device calculates a predicted differential pressure value based on a fuel supply amount of coal when reaching the coal combustion in the switching mode for switching from the biomass combustion to the coal combustion, and calculates the predicted difference An appropriate differential pressure is obtained from the pressure value and the measured differential pressure at the fuel switching start time, and the rotation of the rotary classifier is increased and controlled so that the measured differential pressure becomes the appropriate differential pressure during the switching mode. The configuration.

  According to the present invention, at the time of transition between modes in the coal-crushing mode and the biomass-crushing mode, the measured mill differential pressure is controlled to be an appropriate differential pressure without remodeling of the mill or replacement of parts. It is possible to quickly shift between both modes without deteriorating fuel combustibility and without affecting the mill operation.

It is a figure which shows the system | strain structure of the boiler apparatus which has the vertical pulverization classification apparatus which concerns on embodiment of this invention. It is a figure which shows the structure of the mill of the vertical grinding | pulverization classification apparatus which concerns on this embodiment, and an internal pressure measurement position. It is a figure showing the time change of the state quantity in connection with operation | use of the vertical grinding | pulverization classification apparatus in the case of transfering from the coal monocrushing mode regarding this embodiment to the biomass monocrushing mode. It is a figure showing the time change of the state quantity in connection with operation | use of the vertical grinding | pulverization classification apparatus in the case of transfering from the biomass special crushing mode regarding this embodiment to coal special crushing mode. In the present embodiment, when switching from coal to biomass, a diagram showing a time change example of a state quantity related to operation of a vertical crushing and classifying apparatus when the classifier rotational speed is lowered at a constant rate without performing the mill differential pressure control. It is. In the present embodiment, when switching from biomass to coal, the classifier speed is controlled so that the mill differential pressure is constant, and after switching is completed, the classifier speed is reduced to the classifier speed at the time of coal-only firing. It is a figure showing the example of a time change of the state quantity in connection with type | mold grinding | pulverization classification apparatus operation. It is a figure which shows the control aspect of the mill differential pressure | voltage and classifier rotation speed at the time of fuel switching in this embodiment. It is a figure which shows the system | strain structure of the boiler apparatus which has a vertical grinding | pulverization classification apparatus regarding a prior art.

  A system configuration of a boiler apparatus having a vertical crushing and classifying apparatus according to an embodiment of the present invention will be described below with reference to the drawings. The system configuration of the boiler apparatus according to the present embodiment includes a mill (mill roller / mill table and rotary classifier) and a burner suitable for performing biomass co-firing in a coal fired boiler. That is, the system configuration of biomass co-firing in this embodiment is not different from the coal / biomass co-firing system used in the prior art. Although it is a dedicated mill and a biomass-burning burner, it is a system that enables automatic switching from biomass to coal and vice versa efficiently and without trouble without modification of the mill and burner.

  First, biomass co-firing in a coal fired boiler related to the prior art will be described with reference to FIG. FIG. 8 shows a biomass co-firing system in a coal-fired boiler using a conventional biomass / coal mill and burner. Note that the number of mills 24 and the number of burners 25 shown in FIG. 8 do not match the number when the actual machine is applied, and are illustrated as conceptual functions.

  As described in the background section above, the biomass mill 24 is a modified coal mill for biomass, and the biomass burner 25 enhances ignition so that coarse-grained biomass can be stably combusted. It is a thing. Furthermore, considering the attributes of biomass and coal, etc., the system configuration that handles biomass keeps the safety by keeping the oxygen concentration inside it below the lower explosion limit that prevents dust explosion.

  When the mill and burner in the prior art described in the background art column are applied to a boiler device, the heating value of biomass is lower than that of coal, and it is difficult to pulverize biomass compared to coal. Since the heat input is insufficient, there is a possibility that the boiler 100% load cannot be maintained. In order to solve this problem, it is required to add a separately installed biomass pulverization combustion system. On the other hand, the reason for constructing a mixed combustion system using both biomass and coal was based on the premise of space saving and low cost, so that this premise was satisfied and further improvement of the mixed combustion rate was required.

  Next, with reference to FIGS. 1 to 4, changes in the mill state quantity at the time of automatic fuel / coal switching of biomass / coal using the system configuration of the boiler apparatus having the vertical crushing and classifying apparatus according to the embodiment of the present invention. This will be described in detail below.

  FIG. 1 is a diagram showing a system configuration of a boiler apparatus having a vertical pulverizing and classifying apparatus according to an embodiment of the present invention, and FIG. 2 is a diagram showing a configuration of a mill and an internal pressure measurement of the vertical pulverizing and classifying apparatus according to the present embodiment. It is a figure which shows a position. Moreover, FIG. 3 is a figure showing the time change of the state quantity in connection with operation | movement of the vertical grinding | pulverization classification apparatus in the case of transfering from the coal monocrushing mode regarding this embodiment to the biomass monocrushing mode, and FIG. 4 is related with this embodiment. It is a figure showing the time change of the state quantity in connection with operation | use of the vertical crushing classification apparatus in the case of transfering from biomass exclusive crushing mode to coal crushing mode. Here, the above-mentioned state quantities (see “items” shown in FIG. 7) refer to fuel, mass flow rate, primary air quantity, mill differential pressure, and classifier rotation speed, as will be described in detail later.

  In the drawing, 21 is a biomass silo, 22 is a coal conveyor, 23 is a bunker, 24 is a biomass mill, 25 is a biomass burner, 26 is a steam generator, 27 is a denitration device, 28 is an air preheater, 29 is Electric dust collector, 30 is an induction fan, 31 is a desulfurizer, 32 is a chimney, 33 is a primary fan, 34 is a damper, 35 is a gas recirculator, 40 is a load cell, 41 is a feeder, 42 is an arithmetic unit, 45 Represents a rotary classifier motor, 46 represents an automatic boiler control device, and 47 represents an automatic plant control device.

  In FIG. 1, the fuel path from the biomass silo 21, the coal carrier 22 and the bunker 23 to the biomass burner 25 through the biomass / coal common mill 24, the primary ventilator 33, the air preheater 28, and The basic structure for forming the air passage for fuel conveyance of the gas recirculation ventilator 38 is the same as that of the prior art shown in FIG.

  In the vertical crushing and classifying apparatus according to the present embodiment, in addition to the mill, as will be described in detail later, fuel supply amount measuring means for measuring the amount of fuel supplied in the feeder 41, and fuel conveying air (primary air or airflow) Differential pressure measuring means for measuring pressures at a plurality of points in the mill 24 through which the pressure passes and obtaining the differential pressure, and based on the obtained differential pressure, the motor 45 of the rotary classifier The automatic boiler control device 46, which is a control means for controlling the number of revolutions, the differential pressure in the mill housing from the differential pressure measuring means, the fuel supply amount from the fuel supply amount measuring means in the feeder 41, and the like as inputs. And an arithmetic unit 42 that calculates and controls an appropriate differential pressure on the basis of the rotational classifier through the automatic boiler control means 46 so that the measured differential pressure becomes an appropriate differential pressure.

  Here, the differential pressure measuring means measures the pressure at a plurality of points and calculates the differential pressure. However, means for performing the pressure measurement and the differential pressure calculation separately may be provided. In FIG. 1, the differential pressure is illustrated to be calculated by the calculation device 42, but the differential pressure measuring means performs pressure measurement at each part of the mill and differential pressure calculation by this pressure measurement. The result may be sent to the computing device 42.

  Next, regarding the structure of a mill (mainly composed of a mill roll / mill table and a rotary classifier, also referred to as a pulverizer) and a pressure measurement site inside the mill in the vertical pulverization / classification apparatus according to the present embodiment This will be described with reference to FIG. FIG. 2 is a diagram showing the configuration of the mill and the internal pressure measurement position in the vertical crushing and classifying apparatus according to this embodiment, and describes the simplified structure of the mill, the static pressure measurement points, and the differential pressure. Here, FIG. 2 does not accurately reflect the actual structure of the vertical mill, but emphasizes the components and functions of the mill.

  In FIG. 2, coal or biomass fuel is quantitatively supplied from a feeder 41 at the top of the mill, pulverized by a mill roller on the upper surface of a rotary table (mill table), and then conveyed to the outside in the radial direction by the rotation of the table. Passed by the flow of the primary air supplied from the ventilator 33 and the gas recirculation ventilator 38, it passes through the primary classification section. Since the primary classification is gravity classification, the coarse particles are not accompanied by the flow and are pulverized again on the table surface.

  The fine powder pulverized to a predetermined particle size is conveyed to the secondary classification unit, and only finer particles pass through the rotary classifier and are conveyed to the burner 25 by airflow. The rotating classifier is an air classifier, and the classification point of particles is determined by the balance between the drag force caused by the airflow and the centrifugal force generated by the rotation speed of the rotating classifier. Naturally, if the rotational speed is high, centrifugal force> drag, and only fine particles pass through the rotary classifier, so the particle size of the fuel becomes fine.

  In FIG. 2, Ps is the static pressure at each location as shown in FIG. 2, and ΔP is the differential pressure. ΔP1 is a differential pressure before and after the table, and is proportional to the square of the primary air amount. ΔP2 is due to the layer height of the particles that circulate inside the mill, and increases as the amount of particles circulating increases. ΔP3 is a differential pressure in the rotary classifier, and has a positive correlation with the rotational speed of the rotary classifier, but is a lower value than ΔP1 and ΔP2.

  The mill differential pressure referred to in the embodiment of the present invention represents ΔP2 or (ΔP1 + ΔP2) or (ΔP1 + ΔP2 + ΔP3). Although ΔP2 is more consistent with the physical phenomenon, it is more sensitive to fluctuations in the flow inside the mill, and is sensitive and large. Therefore, as a means of information processing, in addition to ΔP2, (ΔP1 + ΔP2) and / or (ΔP1 + ΔP2 + ΔP3) May be selected.

  Thus, since the mill differential pressure during coal and biomass pulverization is a function of the raw material type (fuel type), the supply amount, the particle size, and the primary air amount, the mill differential pressure is a function F (raw material type, supply amount, It is possible to predict by particle size, primary air amount, etc. There is a mil differential pressure for each raw material (fuel), but since the mixing ratio is not known when the fuel is switched, an allowable mil differential pressure is assumed, and a limited differential pressure for safety is given to this value. A feedback control in which the rotational speed of the rotary classifier is changed using the limited differential pressure as a control target can be considered.

  Next, the operation at the time of automatic fuel switching of biomass / coal in the present embodiment will be described as follows. This embodiment is composed of a conventional biomass-only mill and a dedicated combustion burner, and a boiler exhaust gas recirculation system for safely operating these, and the oxygen concentration of the system from the mill to the burner is below the lower explosion limit oxygen concentration of biomass, or coal The system adopts the operating oxygen concentration of biomass equivalent to the state quantity at the time of exclusive firing. Here, safety is maintained by reducing the oxygen concentration in the system between the mill and the burner, but on the other hand, since stable ignition with the burner becomes difficult, the oxygen concentration in the vicinity of the burner flame holder is reduced. The conventional well-known technique which can be improved and stable ignition is adopted.

  The outline of the vertical crushing and classifying apparatus according to the present embodiment is based on the conventional basic components shown in FIG. 8, and the static pressures P0 and P1 before and after the table inside the mill and the static pressure before and after the rotary classifier. The pressures P2 and P3 are monitored, and the coal bed differential pressure (ΔP2 shown in FIG. 2) or (throat differential pressure (ΔP1 shown in FIG. 2)) + coal bed differential pressure (see FIG. (ΔP2 shown in FIG. 2) (ΔP1 + ΔP2 + ΔP3 shown in FIG. 2 is also possible), and the rotational speed of the rotary classifier is automatically controlled during fuel switching so that these become estimated values after the fuel switching ends. Control system. Or, based on the fuel switching start time and the differential pressure at that time, and the estimated differential pressure value at the switching end estimated time and the differential pressure at that time, the rotation classifier is set to an appropriate differential pressure corresponding to the time during switching. It is a control system characterized by automatically controlling the rotation speed. Then, a fuel switching end signal (used as a control signal required in various operation control required for combustion with the fuel at the time when the fuel switching is completed) from the stable state of the rotational speed of the rotary classifier Is a control system characterized in that

Next, an event that occurs at the time of fuel switching in the present embodiment and a change in state quantity when the control system for automatic fuel switching of biomass and coal is applied will be described with reference to FIG. FIG. 7 is a diagram showing a control mode of the mill differential pressure and the classifier rotation speed at the time of fuel switching in the present embodiment.
FIG. 7 (1) shows the state quantities when switching from coal pulverization to biomass pulverization, and corresponds to the various events shown in FIG. In FIG. 7 (1), regarding the mill input condition, when the coal supply amount at the time of coal pulverization is set to 100, it becomes 70 at the time of biomass pulverization. The reason for this was considered based on the fact that 50% of coal in terms of calorie was pulverized and burned.

  When biomass is considered to be wood pellets, the amount of heat of the fuel is approximately 70% of that of coal, so the supply amount of biomass is 50 / 0.7 = 70%. Therefore, the feeder can also be shared. When switching from coal to biomass, the fuel supply mass flow rate will fall from 100% to 70% (considering feeder sharing, the biomass supply mass flow rate must be 70%). As a mill input condition, the flow rate of the primary air that is the fuel carrier gas also decreases in accordance with the decrease in the fuel flow rate.

  In the prior art, immediately after obtaining a fuel switching signal at the start (for example, a signal for supplying biomass to the coal conveyor 22), the situation in which the fuel switching has not actually started continues, on the other hand, to the mill Since the coal supply amount of the coal has started to decrease, the coal bed level at the top of the table has decreased, the mill differential pressure (ΔP2) has decreased, and the classifier rotation speed remains unchanged (the classifier in the prior art). Because the number of revolutions is not controlled). That is, when there is no mill differential pressure control performed in this embodiment during fuel switching, the rotational speed of the rotary classifier during coal pulverization is maintained. At the time of fuel switching, it is estimated that coal and biomass are mixed and supplied to the mill, so the biomass does not pass through the rotating classifier, so it stays in the mill and the mill differential pressure gradually increases. . And when it changes to biomass completely, if a mill differential pressure exceeds a limit value (for example, value which becomes a mill trip), it will become a mill trip.

  On the other hand, in the present embodiment, the mill differential pressure is stabilized by monitoring the mill differential pressure, controlling the rotational speed of the classifier based on this, and incorporating appropriate control of the mill differential pressure. In the case of biomass pulverization, the rotary classifier is almost stopped.

  In other words, if the classifier speed is set to 0 at the time of fuel switching, coarse coal particles will be supplied to the burner at the time of fuel switching, resulting in unstable ignition and increased unburned fuel. In the embodiment, the classifier rotational speed is not automatically set to 0 during fuel switching, but the classifier rotational speed is automatically controlled with a value equal to or lower than the limit value of the mill differential pressure as a differential pressure target value.

  When the fuel is completely switched from coal to biomass, the classifier rotational speed becomes constant. Therefore, the differential pressure control is terminated with that point as the true fuel switching point. If the rotation classifier rotation speed is> 0 at that time, the rotation classifier rotation speed is switched to 0 to automatically monitor the stabilization of the mill differential pressure, and the fuel is completely switched at that time. Evaluate and output a switching signal. Here, the switching signal is used as a control signal for carrying out various operation modes required for biomass combustion with complete fuel switching.

  Next, the switching from biomass monolithic to coal monopoly in this embodiment will be described with reference to FIG. Various aspects shown in FIG. 7B correspond to the contents shown in FIG. The fuel flow rate and primary air amount during switching are the reverse of switching from coal to biomass.

  In the initial state, the rotary classifier is stopped or finely moved and has no classification function. During switching, coal and primary air are increased towards the target coal conditions. The mill differential pressure decreases because the residence of the pulverized biomass particles inside the mill decreases. However, it is not necessary to make the pressure below the mill differential pressure during coal pulverization, and it is necessary to switch the fuel while ensuring the particle size necessary for combustion.

  Therefore, the mill differential pressure does not need to be lower than that at the time of coal pulverization, so control is performed to maintain the pressure differential at the time of coal pulverization.

  Next, the time series change of the state quantity related to the operation of the vertical crushing and classifying apparatus at the time of fuel switching will be described with reference to FIG. 3 and FIG. FIG. 3 shows the process of switching from coal to biomass, and FIG. 4 shows the process of switching from biomass to coal.

  First, the switching state from the biomass monocrushing to the coal monocrushing in FIG. 4 will be described. Since the amount of fuel supplied during biomass pulverization is 70% of that at coal, the amount of fuel supplied gradually increases to 100 when switching. However, since the mill differential pressure (ΔP2) is very high under the biomass digestion conditions (refer to FIG. 3 that the differential pressure ΔP2 for biomass digestion is high), the fuel is actually the biomass immediately after the start of switching. Since it has not switched to coal, the fuel flow rate cannot be increased. Therefore, the point at which the mill differential pressure begins to decrease is regarded as the true fuel switching time, and the coal fuel supply amount is increased from this point to the estimated fuel switching end time.

  If the mill differential pressure seems to increase, hold the coal fuel supply, and when the mill differential pressure coincides with that during coal pulverization, the rotational speed of the rotary classifier will maintain that differential pressure. Increase. Then, when the rotational speed of the rotary classifier is stabilized, it is determined that the fuel switching is completed, and a fuel switching completion signal is output.

  Here, the specific configuration of the vertical crushing and classifying apparatus according to the present embodiment will be described below with reference to FIG. The differential pressure between the biomass firing and the coal firing can be predicted as a function of each fuel supply amount measured by the fuel supply measuring means provided in the feeder 41, and can be calculated as a differential pressure prediction value. . At the time of switching of each fuel having the calculated differential pressure prediction value, it is difficult to calculate the differential pressure prediction value of the mixed fuel because the fuel is mixed. Mode) is calculated based on the predictable differential pressure at the time of coal burning at the expected end time of switching to coal and the measured differential pressure at the start time of fuel switching from biomass to coal. .

  In the example of FIG. 4, an appropriate differential pressure having a curve in which the differential pressure gradually decreases in the switching mode is calculated, and the measured differential pressure is compared with the measured differential pressure measured in the switching mode. The rotation of the rotary classifier is controlled so that the pressure difference becomes an appropriate differential pressure. In the example of FIG. 4, the rotational speed of the rotary classifier is controlled to be a gradually increasing curve (the actual rotational speed is as indicated by a dotted line). In other words, as shown in FIG. 4, during the fuel switching, the measured differential pressure ΔP2 and the appropriate differential pressure calculated based on the fuel supply amount are obtained, and the differential pressure ΔP2 becomes the appropriate differential pressure. In this way, the classifier is controlled to increase gradually.

  Next, a control process relating to fuel switching from coal to biomass will be described with reference to FIG. Regarding the supply of biomass fuel, the estimated fuel switching end time is calculated and estimated from the fuel switching start signal, the fuel bunker level, and the fuel supply signal. Then, the fuel supply amount is reduced toward the time. The fuel transfer air also decreases corresponding to the fuel flow rate. The rotation speed of the rotary classifier is maintained immediately after switching.

  Then, the time when the mill differential pressure starts to increase is set as the true fuel switching start time, and from this time, the differential pressure appropriate control is started with the allowable differential pressure of the mill as the target differential pressure. The rotation speed of the rotary classifier is changed so that the differential pressure is controlled appropriately. The point at which the classifier speed decreases and stabilizes is the true fuel switching end point. At this time, the mill differential pressure is higher than the differential pressure level at the time of biomass exclusive crushing, so the classifier rotation speed is set to 0 after the mill differential pressure control is finished. Corresponding to this operation, the mill differential pressure converges to a steady differential pressure during biomass crushing. Then, a signal is outputted as the fuel switching end time at the point where the mil differential pressure is stabilized.

  In the example shown in FIG. 4, an appropriate differential pressure is calculated based on the differential pressure of fuel at the true fuel switching start time and the target allowable differential pressure at the time of exclusive combustion of biomass at the expected end time of fuel switching. The rotation of the rotary classifier is controlled so that the measured differential pressure becomes an appropriate differential pressure by comparing the pressure and the measured differential pressure during switching.

  Next, the time series change of the state quantity related to the operation of the vertical crushing and classifying apparatus by adopting another configuration example of the control system at the time of fuel switching will be described below with reference to FIGS. 5 and 6. FIG. 5 shows a time change example of state quantities related to the operation of the vertical pulverization classifier when the classifier rotation speed is lowered at a constant rate without controlling the mill differential pressure when switching from coal to biomass in the present embodiment. FIG. 6 is a diagram showing the classification, and when switching from biomass to coal in this embodiment, the classifier rotation speed is controlled so that the mill differential pressure becomes constant, and after the switching is completed, the classifier rotation speed is classified at the time of coal combustion. It is a figure showing the example of a time change of the state quantity in connection with a vertical crushing and classifying apparatus operation when making it reduce to machine rotation speed.

  FIG. 5 shows the state quantities at the time of fuel switching from coal to biomass as in FIG. The difference from Fig. 3 is not to properly control the mill differential pressure at the time of fuel switching, but to reduce the classifier speed at a constant rate and further lower the classifier speed if the target differential pressure is exceeded. do. Although this control method is more stable and controllable than the proper control method for mill differential pressure, it is inferior to the proper control method for mill differential pressure shown in FIG. In FIG. 5, the dotted curve indicated by the differential pressure ΔP2 represents the characteristics that are actually expected (the characteristics of the differential pressure that are actually expected when the classifier rotational speed is controlled to decrease at a constant rate). Represents).

  FIG. 6 shows a case where the mill differential pressure is controlled to be constant until the end of switching when switching from bio to coal. This control method is superior in coal fuel particle size compared to the control method of FIG.

  As described above, the outline of the vertical crushing and classifying apparatus according to the present embodiment is basically determined by predicting the mill differential pressure from the supply amount and the particle size of the fuel (coal or biomass) after the switching, and the switching is completed. Thereafter, control is performed so that the classifier speed corresponds to the predetermined differential pressure.

  Explaining the general events that occur at the time of fuel switching, when switching from a biomass-pulverized state to coal-only coal, when coal is input without changing the mill conditions while maintaining the mill conditions at the time of biomass-only grinding, At the time of biomass pulverization, the function of the rotary classifier is eliminated so that biomass fine powder is quickly discharged from the inside of the mill to the burner (the rotation speed of the classifier is 0), so in coal, coarse particles flow to the burner. Combustibility deteriorates.

  On the other hand, when shifting from the coal pulverization condition to the biomass pulverization condition, the biomass is pulverized while leaving the classification function by the rotary classifier. (Because the classifier is rotating, the lightweight biomass does not pass through the classifier), the mill differential pressure and the mill power increase, causing a mill trip.

  Therefore, it is important to control the mill operation so that there is no hindrance (mill trip) at the time of switching, and when biomass and coal are mixed, it is important to accurately predict the state of fuel discharge from the bunker. Because it is difficult, the operation state quantity of the mill is monitored, and as the control to make the mill differential pressure appropriate among the operation state quantity, the rotation speed of the rotary classifier that is most effective is changed, and the inside of the carrier gas inside the mill It is a feature of this embodiment that the differential pressure at is appropriate. Specifically, among the mil differential pressure, a mil differential pressure obtained by adding a throat differential pressure ΔP1 when carrier gas is jetted and supplied to the inside of the mill and a differential pressure (ΔP2) related to the flow of fuel particles inside the mill, Or, it is intended to make this differential pressure appropriate by paying attention to the differential pressure related to the flow of fuel particles inside the mill.

  Any of the control methods described above is common in terms of mill differential pressure control, but since it is long and short, it is assumed that the control method can be selected after confirming operability. Or you may make it select a control system, after grasping | ascertaining the characteristic according to biomass previously by simulation or a large sized test facility.

  Furthermore, since some biomass species have significantly different crushing characteristics, it is possible to cope with a method of switching fuel by dividing the fuel supply amount into two stages. That is, although it differs depending on the calorific value, the biomass has a mass flow ratio of 70 with respect to the coal 100 and the input heat amount becomes 1/2 that of coal. This is a limitation due to the performance of the mill and may change in the future.

  When switching from coal 100 to biomass 70, after the coal is reduced from 100 to 70, the fuel is switched while maintaining the same mass flow rate. The switching operation is in accordance with FIGS. Further, when switching from biomass 70 to coal 100, the mass flow rate is increased to coal 100 after switching with coal 70 once.

  Although such a two-stage switching is not shown in the figure, it is a natural idea that reducing the change factors leads to stabilization, and direct switching in one stage depending on the characteristics of the biomass species and coal. Both are possible in the application of the control system.

21 Biomass silo 22 Coal conveyor 23 Bunker 24 Biomass mill 25 Biomass burner 26 Steam generator 27 Denitration device 28 Air preheater 29 Electric dust collector 30 Induction ventilator 31 Desulfurization device 32 Chimney 33 Primary ventilator 34 Damper 35 Gas re- Circulating ventilator 40 Load cell 41 Feeder 42 Computing device 45 Rotary classifier motor 46 Automatic boiler controller 47 Automatic plant controller

Claims (6)

A feeder for supplying fuel comprising coal and biomass;
A pulverizer for pulverizing the fuel by biting a rotary table and a pulverizer;
A rotating classifier having rotating fins for classifying the pulverized material conveyed by the air flow spouted from the throat on the outer peripheral side of the rotating table;
A vertical pulverizing and classifying device comprising a housing for accommodating the pulverizer and the rotary classifier,
The feeder is provided with a fuel supply amount measuring means for measuring a fuel supply amount,
A rotation classifier control means for controlling the rotation of the rotation classifier is provided;
In the housing, at least the downstream side of the throat and the rotational classification of the upstream side of the throat through which the airflow flows, the downstream side of the throat, the inlet side of the rotary classifier, and the outlet side of the rotary classifier A differential pressure measuring means for measuring the pressure at the inlet side of the machine and measuring the pressure difference between the measured pressure parts is provided,
Based on a differential pressure that is a pressure difference between the measured pressure sites measured by the differential pressure measuring means and an appropriate differential pressure calculated based on the fuel supply amount measured by the fuel supply amount measuring means. And a vertical pulverizing and classifying device, characterized in that an arithmetic unit is provided for controlling the rotation of the rotary classifier through the rotary classifier control means so that the measured differential pressure becomes the appropriate differential pressure. In claim 1,
The calculation device calculates a predicted differential pressure value based on the amount of fuel supplied to the coal when reaching the coal burning, in the switching mode for switching from the biomass burning to the coal burning, and the calculated predicted pressure difference The appropriate differential pressure over the switching mode is obtained from the measured differential pressure at the fuel switching start time, and the rotation of the rotary classifier is increased so that the measured differential pressure becomes the appropriate differential pressure during the switching mode. A vertical crushing and classifying device characterized by being controlled. In claim 1,
The arithmetic unit calculates a predicted differential pressure value based on a fuel supply amount of biomass when reaching a biomass-only firing in a switching mode for switching from a coal-fired to a biomass-only firing, and the calculated predicted differential pressure value From the measured differential pressure at the fuel switching start time and the target control differential pressure to obtain an appropriate differential pressure over the switching mode, and the measured differential pressure during the switching mode. The vertical crushing and classifying apparatus is characterized in that the rotation of the rotary classifier is decreased and controlled so that the pressure becomes the appropriate differential pressure. In claim 2 or 3,
The vertical pulverizing and classifying device, wherein the arithmetic device outputs a fuel switching end signal when the measured differential pressure is stable and the rotational speed of the rotary classifier becomes a stable and constant value. In claim 2,
The arithmetic unit obtains a constant differential pressure value from the start time to the end time of the switching mode instead of increasing / decreasing the rotation of the rotary classifier so as to be the appropriate differential pressure, and during the switching mode The vertical crushing and classifying device characterized in that the rotation of the rotary classifier is increased and controlled so that the measured differential pressure becomes the differential pressure constant value. In claim 3,
Instead of increasing / decreasing the rotation of the rotary classifier so as to achieve the appropriate differential pressure, the arithmetic device reduces the rotational speed of the rotary classifier at a constant rate, and the measured differential pressure is used as the target control. When the pressure exceeds the differential pressure, the vertical pulverizing / classifying apparatus is further controlled to further reduce the rotational speed of the rotary classifier.