US2894696A - Coal pulverizing apparatus - Google Patents

Description

July 14, 1959 E: c. MILLER 2,894,696 com. PULVERIZING APPARATUS Filed Aug. 23, 1957 ll //I 'l/l/ INVENTOR. [mus 6. MILLER United States Patent COAL PULVERIZKNG APPARATUS Earle C. Miller, Worcester, Mass, assignor to Riley Stoker Corporation, Worcester, Mass, a corporation of Massachusetts Application August 23, 1957, Serial No. 679,834

6 Claims. (Cl. 241-43) In the pulverizing of coal and other similar fuels for burning in furnaces and the like, it is common practice to pass the fuel along with a supply of so-called primary air into the pulverizer for comminution. The primary air supplied has been previously raised in temperature by passage through an air heater in heat transfer relationship to the discharge gases from the furnace. At certain times, however, a fuel is encountered which contains a great deal of water. The only way that this wet fuel can be properly pulverized is to have the water removed by evaporation into the primary air. For this purpose it is customary to raise the temperature of the primary gas even higher when wet fuel is encountered. Several ways are known by which this may be accomplished; one of these is the so-called furnace tap; by this process a supply of gas is withdrawn from the furnace and is introduced into the primary air duct adjacent the pulverizer. The difficulty experienced with the use of the furnace tap is that it requires a very favorable duct arrangement to prevent the accumulation of ash. It also requires a high suction within the duct in order to pull the gases out of the furnace. Another way of assuring an addition to the temperature of the primary air in the event of wet fuel is by the use of a secondary air heater; the secondary air heater has the disadvantage,

of course, that it involves an added piece of expensive equipment which in many installations cannot be justified because of the infrequent appearance of wet fuel. These and other difiiculties experienced in the past with prior art devices have been obviated by the present invention in a novel manner.

It is, therefore, an outstanding object of the invention to provide a pulverizer arrangement in which means is provided for adding to the temperature of the primary air in the event of wet fuel, which means is inexpensive to manufacture, requires little maintenance, and can be readily added to existing installations.

It is another object of this invention to provide a pulverizer apparatus which may be used satisfactorily with wet fuel even before the boiler has started up.

A still further object of the present invention is the provision of a pulverizer means which will not increase the forced draft or induced draft fan power and which will not influence the normal heat balance of the equipment.

Another object of this invention is the provision of a pulverizer apparatus in which means is provided for increasing the temperature of the primary air when wet fuel is encountered, which means does not create a hazard or nuisance by introducing ash into the duct system.

It is a still further object of the instant invention to provide means associated with a pulverizer for increasing the temperature of the primary air, which means constitutes a positive source of heat independent of burner operation and independent of furnace pass location; by use of this means, the extra heat is instantaneously available and is not dependent on boiler load, as is the case in a furnace tap .and in a secondary air heater arrangement.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered in the claims appended hereto.

The character of the invention, however, may be best understood by reference to one of its structural forms, as illustrated in the accompanying drawing in which:

The single figure is a longitudinal, vertical, sectional View of a pulverizer apparatus embodying the principles of the present invention.

Referring to the drawing, which shows the general features of the invention, the pulverizer arrangement, indicated generally by the reference numeral 10, is shown as consisting of a pulverizer 11, of the ball mill type, associated with a crusher-drier 12 of the type shown and described in US. Patent No. 2,647,695. The crusherdrier 12 is of the type through which fuel and air may be passed and in which revolving hammers crush the coal and mix it thoroughly with the air for flash-drying of the fuel. The pulverizer 11 is of the ball-tube type, consisting of a generally cylindrical housing 13 mounted on trunnions which are revolved by means 'of a motor 14. One end of the mill 11 is mounted in a bearing 15, and is provided with an axial inlet 16. The other end, through which the mill is driven, is provided with an outlet 17. A supply of balls 18 rests in the lower part of the mill and brings about the comminution of the fuel. A fuel-feeding device 19 overlies the crusher-drier and is connected by means of a conduit 21 to a primary air conduit 22, both of which terminate above the crusher-drier 12. A by-pass 23 extends around the crusher-drier and a pivoted vane 24 determines how .much air and fuel will by-pass the crusher-drier. The

outlet of the crusher-drier and the by-pass conduit 23 are joined and connected by a conduit 25 to the inlet 15 of the mill 11. The outlet 17 of the mill is connected by a conduit 26 to an existing fan 27, whose outlet is con nected through a valve 28 and through a conduit 29, to the furnace burners, not shown. A centrifugal separator 31 is located in the conduit 26 between the mill and the fan 27. A mill level control 34 is associated with the feeder 19 and with the mill 11, and consists of a pick-up 35 which extends into the mill and has a dependent portion which resides near the level of material in the mill. This pick-up is surrounded by a housing 36 which is open to the mill space well above the level of material. A source of air under pressure is connected through a valve 37 and an air flow measuring device 38 to a line 39 which is connected to the pick-up 35. The line 39 is also connected to a mill-level control 41, while a similar line 42 connects the housing 36 to the control. A hydraulic linear actuator 43 is mechanically connected to the control handle 44 of the feeder 19. Hydraulic lines 45 and 46 are connected to opposite ends of the cylinder 43 and, at their outer ends, to the mill-level control 41.

The duct 22 extends horizontally away from the connection to the crusher-drier 12 and then vertically for connection to the air heater of a steam generating unit. In the vertical portion is located a vacuum damper 47 which is actuated by a crank arm 48 connected to the piston rod 49 of a hydraulic linear actuator 51. The actuator 51 is connected by hydraulic lines 52 and 53 to vacuum control 54 which receives its signal through a line 55 which is connected to a temperature measuring device 56 located in the horizontal portion of the duct 22, just ahead of the crusher-drier.

An oil burner 57 of the short-flame type is mounted in the wall of the duct 22 in such a position as to fire along the horizontal portion thereof. An oil control valve 58 is located at the outer end of the burner and is actuated through a linkage 59. The linkage is connected to the piston rod 61 by a hydraulic linear actuator 62. The linear actuator is connected by hydraulic lines 63 and 64; to a temperature control 65 which receives a signal from a line 66, which signal originates in a temperature measuring device 67 located in the duct 26 between the mill and the classifier 31.

A tempering inlet box 68 is located on the vertical portion of the duct 22 and is normally covered by a damper 69. The damper is pivoted on the upper part to the box and is actuated by a crank arm 71, Whose other end is connected to a piston rod 61 of the linear actuator 62.

A small blower 72 is connected to the classifier 31 for the operation thereof and a conduit 73 connects the discard portion of the classifier back to the conduit 25 just below the crusher-drier 12, for returning coarse material from the classifier to the mill.

it is preferable that the burner 57 be of the thermal high-velocity type which incorporates a means of vaporizing the oil Within the burner prior to the combustion process; hence, there are no liquid droplets of oil to be caught and the products of combustion leave the burner as a non-luminous stream of gases with visible length of flame less than at maximum output. Although the refractory walls of the burner will not exceed 2500 F. in temperature, it is recommended that a heat-resistant steel duct lining be used in the vicinity of the burner front.

The burner 57 is provided with a blower 74, mounted thereover and connected through a control damper 75 to the burner. The linkage 59 is connected to the damper '75 for the actuation thereof by means of an arm 76.

The operation of the apparatus will now be readily understood, in view of the above description. Fuel enters the system through the fuel feeder 19, the amount of coal being regulated by the setting of the actuating handle 34. The fuel passes down through conduit 21 which it meets the incoming air in the conduit 22. The air in the conduit 22 has passed through the air heater of the steam generating unit which the furnace serves. The fuel and air mix at the end of the conduit 22 and the mixture may either pass downwardly through the bypass conduit 23, or through the crusher-drier l2, depending on the setting of the damper 24. The fuel-air mixture which passes through the conduit 23 is not treated, but that which passes through the crusher-drier 12 is subjected to a violent agitation and partial comminution, combined with a drying effect. Surface water on the coal is evaporated into the air and then the mixture passes through the inlet 25 into the mill 1!. The mill is rotated slowly by means of the motor 14 and the balls 18 are rotated upwardly until they fall downwardly into the mass of material in the bottom of the mill. By this comminuting action the coal is crushed into a fine dust which in turn is picked up by the air which flows through the upper part of the chamber. This air-coal mixture leaves the mill through the outlet 17 and passes upwardly into the conduit 26. In the classifier 31 the coarser particles of fuel are separated out and returned through the conduit 23 to the entrance of the mill for re-treatment. The air and fine particles pass through the fan 27 upwardly through the valve 28 and the conduit 29 to the burners of the furnace. The amount of mixture of fuel and balls 18 in the bottom of the mill 11 is quite important, since too little of the mixture means that the capacity of the mill is not being used, and too much of the mixture clogs the mill and inhibits the production of the proper percentage of fine particles. The signal in the conduit 34 which is connected to the housing 36 represents an air suction pressure inside the mill housing 13, well above the level of the fuel and balls in the bottom of the mill. The pressure in the conduit 39 is at a high value when the mill level is high enough to shut off the mouth of the pick-up 35. On the other hand, When the level of material in the mill is well below the mouth of the pick-up 35, the pressure in the conduit 39 is quite loW. The differences between the air pressures in the conduits 34 and 39 make themselves felt in the control 41 which sends the proper signal through the hydraulic lines 45 and 46 to the hydraulic linear actuator 43, thus moving the actuating control handle 44 of the feeder 19 and regulating the amount of fuel which is fed into the mill. The air flow measuring device 38 permits the operator, by use of valve 37, to regulate the flow of air to an amount for which the control 41 has been calibrated.

it is desirable that the amount of negative pressure in the duct 22 be carefully regulated so that the amount of air being introduced and the temperature of the incoming air is at an optimum value. For this purpose, the control 5- 3- receives a temperature signal from the temperature measuring device 56 and transmits a signal through the hydraulic lines 52 and 53 to the linear actuator 51. This in turn acts through the piston rod 49 and the crank arm 48 to set the damper 47 at a desired value. It is desirable when the fuel is very wet, to supplement the heat avialable in the incoming primary air by means of burner 57. It is well known that warmer air is capable of absorbing more water than colder air; furthermore, a ball mill tends to clog considerably when there is too much surface moisture in the coal. Therefore, when the temperature measuring device 67 in the duct 28 which measures the temperature of the output air of the mill indicates that the temperature is low, it sends a signal to that effect through the line 66 to the control 65. It is a fact that the output air temperature will be lower when the water in the coal is higher because of the absorption of heat by the water in evaporating. A low temperature, therefore, in duct 26 indicates that the fuel entering the mill is wet and it would be desirable to use a higher temperature primary air in the duct 22. The signal to that effect is transmitted by the control 65 through the hydraulic lines 63 and 64 to the linear actuator 62. The hydraulic pressure is such that the piston rod 61 will be drawn downwardly. This acts through the linkage 59 to increase the amount of oil flowing through the valve 58 to the burner 57 and, at the same time, adjusts the damper 75 by means of the arm 76 so that a greater amount of air flows into the burner; the burner heat is thus increased. At the same time, the damper 69 is closed so that there will be very little tempering air entering the system. This brings about an increase in the temperature of the primary air passing into the mill. A rise in temperature of the proper amounts in the conduit 26 will make itself known to the temperature measuring device 67 and eventually will cause the piston rod 61 ot rise, shutting off air and oil passage to the burner S9 and cutting down its firing rate and, at the same time, opening the damper 69 to admit small amounts of tempering air into the duct.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new, and desired to secure by Letters Patent, is:

l. A coal pulverizing apparatus, comprising a comminuting mill, a coal feeder, an air duct, a crusher-drier, the feeder and the duct being connected to mix the air and coal, the crusher-drier connecting the feeder and duct to the mill for drying the coal, a by-pass conduit also joining the duct and feeder to the mill, means for causing the coal-air mixture to pass either through the crusherdrier or through the by-pass conduit, a burner mounted to fire directly into the duct, a tempering damper in the said duct, and means controlled by the temperature of the coalair mixture leaving the mill to regulate the rate of firing of the burner and the amount of tempering air admitted by the tempering damper.

2. A coal pulverizing apparatus, comprising a comminuting mill, a coal feeder, an air duct, a crusher-drier, the feeder and the duct being connected to mix the air and coal, the crusher-drier connecting the feeder and duct to the mill for drying the coal, a by-pass conduit also joining the duct and feeder to the mill, means for causing the coal-air mixture to pass either through the crusher-drier or through the by-pass conduit, a burner mounted to fire directly into the duct, a tempering damper in the said duct, an indicating device located in the outlet of the mill for measuring the temperature of the coalair mixture leaving the mill, a controller to which the device is connected, an actuator connected to the controller and acting to regulate the rate of firing of the burner and the amount of tempering air admitted by the tempering damper.

3. A coal pulverizing apparatus, comprising a comminuting mill, a coal feeder, a level control including a measuring device located in the mill and connected to the feeder to maintain the feeding rate at such a value as to maintain the level of coal in the mill at a preselected Value, an air duct, a crusher-drier connecting the feeder and duct to the mill for drying the coal, a by-pass conduit also joining the duct and feeder to the mill, means for causing the coal-air mixture to pass either through the crusherdrier or through the by-pass conduit, a burner mounted to fire directly into the duct, a tempering damper in the said duct, and means controlled by the temperature of the coal-air mixture leaving the mill to regulate the rate of firing of the burner and the amount of tempering air admitted by the tempering damper.

4. A coal pulverizing apparatus, comprising a comminuting mill, a coal feeder, an air duct, :1 crusher-drier, the feeder and the duct being connected to mix the air and coal, the crusher-drier connecting the feeder and duct to the mill for drying the coal, a by-pass conduit also joining the duct and feeder to the mill, means for causing the coal-air mixture to pass either through the crusher-drier or through the by-pass conduit, a burner mounted to first directly into the duct, a tempering damper in the said duct, a vacuum damper in the air duct ahead of the burner, a temperature-measuring apparatus located in the duct at a position following the burner, a controller connected to the temperature-measuring apparatus and to the vacuum damper to regulate the temperature of the air, and means controlled by the temperature of the coal-air mixture leaving the mill to regulate the rate of firing of the burner and the amount of tempering air admitted by the tempering damper.

5. A coal pulverizing apparatus, comprising a comminuting mill, a coal feeder, a level control including a measuring device located in the mill and connected to the feeder to maintain the feeding rate at such a value as to maintain the level of coal in the mill at a preselected value, an air duct, a crusher-drier, the feeder and the duct being connected to mix the coal and air, the crusher-drier connecting the feeder and the duct to the mill for drying the coal, a by-pass conduit also joining the duct and feeder to the mill, means for causing the coal-air mixture to pass either through the crusher-drier or through the by-pass conduit, a burner mounted to fire directly into 'the duct, a tempering damper in the said duct, a vacuum damper in the air duct ahead of the burner, a temperature-measuring apparatus located in the duct at a position following the burner, a controller connected to the temperature-measuring apparatus and to the vacuum damper to regulate the temperature of the air, and indicating device located in the outlet of the mill for measuring the temperature of the coal-air mixture leaving the mill, a controller to which the device is connected, an actuator connected to the controller and acting to regulate the rate of firing of the burner and the amount of tempering air admitted by the tempering damper.

6. A coal pulverizing apparatus, comprising a comminuting mill, a coal feeder, an air duct, a crusher-drier, the feeder and the duct being connected to mix the air and coal, the crusher-drier connecting the feeder and duct to the mill for drying the coal, a by-pass conduit also joining the duct and feeder to the mill, means for causing the coalair mixture to pass either through the crusher-drier or through the by-pass conduit, a burner mounted to fire directly into the duct, a valve controlling the amount of fuel admitted to the burner, a tempering damper in the said duct, an indicating device located in the outlet of the mill for measuring the temperature of the coal-air mixture leaving the mill, a controller to which the device is connected, an actuator connected to the controller on the one hand and to the valve and the tempering damper on the other hand to regulate the rate of firing of the burner and the amount of tempering air admitted by the tempering damper.

References Cited in the file of this patent UNITED STATES PATENTS 2,716,002 Craig Aug. 23, 1955

Images