US3477650A - Apparatus to provide inert atmosphere in material reducing mills - Google Patents

Description

Nov. 11, 1969 R M, wl s 3,477,650

APPARATUS TO PROVIDE INERT ATMOSPHERE IN MATERIAL REDUCING MILLS Filed Nov. 28, 196'? 5 Sheets-Sheet 1 Nov. 11. 1969 R. M. WILLIAMS 3,477,650

APPARATUS To PROVIDE INLET ATMOSPHERE IN MATERTAIJ Nov. 11. 1969 R. M. W1LLIAMS ,477,

APPARATUS TO PROVIDE INILLRT ATMOSPHERE IN MATERIAL REDUCING MILLS Filed Nov. 28, 1967 5 Sheats-$heet FIG. 3.

United States Patent 3,477,650 APPARATUS TO PROVIDE INERT ATMOSPHERE IN MATERIAL REDUCING MILLS Robert M. Williams, Ladue, Mo., assignor to Williams Patent Crusher & Pulverizer Co., Inc., St. Louis, Mo., a corporation of Missouri Filed Nov. 28, 1967, Ser. No. 686,074 Int. Cl. B02c 21/00, 23/00; F26b 21/12 U.S. Cl. 241-47 Claims ABSTRACT OF THE DISCLOSURE Material reducing mill, crusher or grinder apparatus having means connected therewith to maintain the atmosphere within the apparatus at an oxygen level that will inhibit explosion and ambient pollution.

This invention relates to apparatus that will provide an inert atmosphere within the apparatus associated with and comprising a reducing mill, crusher or grinder.

The operation of most reducing apparatus for relatively dusty material is accompanied by the danger of explosion if a spark occurs when the oxygen and dust in the air reaches the proper concentration. Such a spark can be generated between the hammers of the reducing apparatus and any metallic object which may reach the hammers. To overcome this danger water spray is sometimes introduced into the reducing apparatus thereby minimizing the explosion possibility. The use of water spray, however, has a detrimental effect in that it makes separation of the dirt fiom the useful product most difiicult. It also creates a secondary problem in the dust collection means usually employed as the dust is reduced to a wet, sticky residue which interferes with the operation of the apparatus.

Most reducing apparatus are required to have dust collection means to meet air pollution control. Apparatus for reducing materials usually have an air intake disposed between the reducing mill and a cyclone separator, and in some systems there is a secondary collector connected between the cyclone separator and the atmosphere. The air velocity in the conduit system normally is of the order of 5000 to 6000 feet per minute which is sufficient to move large quantities of dust and dirt. When such quantities of dust and dirt contain water there is a significant plugging tendency in both the cyclone and secondary collectors. Even though the dust and dirt may be Wet an occasional hot piece of metal can be picked up in the air movement and conveyed into the collectors where a fire could start causing damage and shut-down of the apparatus.

Most apparatus of the character under consideration are now equipped with what is known as a Fenwal Explosion Protection System that consists of a series of bottles that contain fire or explosion suppression liquids under pressure. A pressure detection system is connected to the bottles to release the contents when pressure exceeds 3 to 5 pounds in the reducing mill. This safety system is expensive to install and maintain.

It is, therefore, an important object of this invention to overcome the above problems and to do away with the necessity of using such an expensive protection system.

It is also an important object of this invention to provide an inert atmosphere in reducing mill apparatus so as to prevent the possibilities of dust explosion and fire.

Another object of this invention is to create a nonexplosion and fire creating atmosphere within material reducing apparatus so that the material being processed Patented Nov. 11, 1969 can be worked in a relatively dry state which facilitates separation and classification operations.

Other objects of the invention will be set forth in more detail in the following description of certain preferred embodiments which have been disclosed in the accompanying drawings, wherein:

FIG. 1 is a schematic elevational view of apparatus for providing an inert atmosphere in connection with a hammer mill for reducing large metallic materials such as automobile bodies and the like;

FIG. 2 is a fragmentary elevational view showing a modification that may be applied to the apparatus of FIG. 1; and

FIG. 3 is a further schematic elevational view of apparatus for carrying out this invention in a pulverizer or roller mill.

In the embodiments shown in FIGS. 1 and 3, an air removal system is preferably connected to the reducing mill, either at the mill housing or at a suitable point of the product removal conveyor. The air directing conduit leads to a cyclone type separator, and the outlet from the cyclone separator leads the now somewhat cleaned air to a primary air moving fan which delivers the air through a return conduit connected into the reducing mill depending on the character of material being reduced. In some apparatus the return conduit is connected to the input side of the mill and in other apparatus it is connected into the mill reducing chamber. At a suitable point in the return conduit on the discharge side of the primary air moving fan a portion of the air volume is exhausted to a secondary separator where additional dirt is extracted prior to air movement toward an exhaust fan on the outlet side of the secondary separator. The exhaust fan removes air from the aforementioned system, and thereby develops a negative pressure condition throughout the entire system. A part of the exhaust air is conducted to a furnace where it is mixed with fresh air and heated and then conducted back to the air in the return conduit from the primary fan.

The heated air from the furnace will have a large percentage of its oxygen consumed in the furnace which results in reducing the air in the system to an inert or low oxygen condition so much so that the atmosphere is rendered incapable of supporting an explosion or fire. The air from the exhaust fan which is supplied to the furnace is mixed with fresh air so that there is suflicient total air to control the temperature of the furnace output air to a desired level. The volume of fresh air is modulated to a point where the furnace operation is just sutficient to avoid inefficiency, or at the point where the furnace operates at or near ratio burning to consume all or nearly all of the oxygen in the fresh air. Ordinarily the furnace outlet temperature when consuming all of the fresh air oxygen would be close to 2000 F., but due to the recycling of part of the discharge from the exhaust fan the furnace output temperature is lowered to about 900 F.

In the preferred apparatus as above described, the control over the amount of fresh air entering the furnace renders the atmosphere in the entire system inert. In the system of FIG. 1, the atmosphere returned to the input side of the mill is cooled by a water spray which is modulated to a point where the cooling effect on the atmosphere reduces the temperature to about 200 F. and in the cooling function the spray is converted into steam which further reduces the oxygen content of the gas. As a result, the oxygen content is held to approximately 11 to 12 percent. The conversion of the spray to steam avoids directly watering the incoming material and the residual heat evaporates the water sufficiently to yield a substantially dry product delivery from the mill.

The foregoing operation of the preferred system will move suflicient gases through the exhaust fan to prevent the atmosphere in the system from reaching the dew point. The result reached by the improved system is that the mill can deliver a substantially dry product which is ready for separation operation, and the system is easily rendered inert to the occurrence of dust explosions and fire. It is also evident that such an improved system operates under a negative pressure so that any leaks will be inward to avoid air pollution problems. Since the operation is carried on in a substantially dry state, there will be avoided any tendency to plug the separators. This latter good effect is especially important where local codes do not permit the use of a second or secondary cyclone separator, in which cases a bag collector can readily be used as the secondary separator without encountering plugging problems.

With the foregoing principles of operation in mind, attention will now be directed to the apparatus of FIG. 1. In this View the reducing mill is of a character described and claimed in my Patent No. 3,283,698, granted Nov. 8, 1966. The mill 10 is seen to have a hopper 11 into which material is fed from a suitable conveyor 12, the material passing through a flexible curtain 13 to prevent excessive air entering at this point. The material is reduced in a hammer mill operating in a suitable casing 14. The casing 14 has an outlet 15 where the reduced product is delivered onto a suitable conveyor 16 operating in a housing 17. Flexible curtains 18 and 19 at the ends of the conveyor housing 17 prevent excess air entry.

The air moving system for the mill 10 includes a hood 20 connected to the conveyor housing 17 adjacent the curtain 19, and a conduit 21 leads from the hood 20 to the inlet adapter 22 of a cyclone separator 23. The cyclone 23 is provided with an outlet 24 to which an outlet conduit 25 is connected. The latter conduit leads to the inlet of the primary fan 26, while the primary fan outlet is connected to a discharge conduit 27. The conduit 27 directs the flow to a riser conduit 28 adjacent the mill and hopper. The riser conduit 28 has its main outlet 29 open to the Zone of hopper 11, and its secondary outlet 30 is connected into the conveyor housing 17. A weighted damped 31 is operably mounted adjacent outlet 30 to keep this end of the riser conduit 28 closed, except when the weight of any solids collected therein over-balances the damper weight 32. Thus, solids that escape out of the hopper 11 will be dumped upon the conveyor 16.

P16. 1 also shows an alternate conduit 21a in broken line view which may be employed in place of the connection of conduit 21 to hood 20. When employing the alternate conduit 21a it is preferred to connect it to the mill casing portion 14a which is open to the space on the output side of the usual grate bars (not shown).

It can be seen in FIG. 1 that a portion of the discharge from the primary fan 26 will be diverted into conduit 33 by the diverter valve 33a, such diverted flow being conducted to the inlet of a secondary separator 34. The secondary separator 34 in this view is a bag type collector of known character, but a cyclone separator such as is seen at 23 may be employed without altering the system operation. The secondary separator 34 has its outlet connected to a discharge conduit 35 which leads to the inlet of an exhaust fan 36. The fan 36 draws a negative pressure in the system and discharges to atmosphere through conduit 37. A portion of the discharge in conduit 37 is directed by a conduit 38 to a mixing chamber 39 where it is combined with fresh air from the inlet 40. A suitable control damper 41 in the inlet regulates the proportions of fresh air and recycled gas under the control of a temperature sensor 42 mounted in the discharge conduit 43 leading from the furnace 44 as stated, the sensor 42 is set to maintain a furnace discharge temperature of approximately 900 F. The furnace discharge conduit 43 is connected to the primary fan discharge conduit 27 at a point beyond the flow diversion conduit 33 so that the heated gas will be delivered to the outlet 29 of the riser conduit for flow into the hopper 11.

The hopper 11 is provided with a water supply header pipe 45 which feeds a plurality of spray nozzles 46 located in the upper zone of the hopper. The pipe 45 is provided with a controllable valve 47 which is modulated by a temperature sensor 48 located in the conduit 21 which responds to the temperature level there in order that the hopper temperature may be maintained at approximately 200 F. The temperature sensors 42 and 48, together with motor means for responding to control the damper 41 and valve 47, are of known character and need not be set forth in detail. It will be sufficient to understand that the sensor 42 will be set to indicate furnace combustion efficiency of the order to obtain a fully inert gas discharge in conduit 43. Thereby, the system will after a short period from start-up reach the desired low oxygen content to render the atmosphere in the system inert to explosions and fire. It is also contemplated that sensor 42 could be an oxygen analyzer and this unit would be used to open and close damper 41 to maintain a constant oxygen content in outlet pipe 43.

FIG. 2 illustrates in fragmentary manner an alternate system to that described for FIG. 1, and wherever possible, like parts will be designated by like reference numerals. In FIG. 2, it is seen that the secondary separator 34 is now moved to a position where its inlet is connected to the exhaust discharge conduit 37, and its outlet conduit 35 opens to the atmosphere. In order to install the separator 34 in this alternate position, the diverter conduit 33 must be connected to the conduit 35. As a result of this alteration, any fine particles moving with the gas flow from the primary fan 26 will go through the exhaust fan 36 and a portion of this fine material will be recycled into the furnace at conduit 38 and consumed. Also, a certain amount of vaporous contaminents will be recycled with the gas to the furnace 44 and be consumed which is an advantage as it reduces the chance of pollutant vapors escaping from the system.

The system and apparatus shown in FIG. 3 embodies the principles of the invention in connection with a material pulverizer mill 50. The mill 50 has a casing 50a for the reducing mechanism which is operated by motor means 51 through the usual separator casing 53 to a conduit 54 which connects to the inlet adapter 55 of a primary cyclone separator 56. The product is delivered from the cyclone valved discharge 57 into a conduit 58 where it is collected by suitable means (not shown). The gas flow from the cyclone separator 56 is delivered by the cyclone outlet 59 to a conduit 60 which connects with the inlet of a primary fan 61. The primary fan 61 has its outlet or discharge connected by conduit 62 to a flow receiver casing 63 mounted on the mill housing 50a where the flow is into the mill.

A portion of the output from the fan 61 is diverted by conduit 64 and conducted to the inlet side of the secondary separator 65. The flow from the secondary separator or bag collector is conducted by conduit 66 to the exhaust fan 67 and to a discharge conduit 68. A portion of the flow in the discharge conduit 68 is conducted by conduit 69 into a mixing chamber 70 where it is mixed with fresh air admitted through inlet conduit 71 under the control of a suitable valve 72. The mixed flow of fresh air and recycled air enters the furnace 75. The admission of fresh air is controlled by the valve 72 and this valve is modulated by a temperature sensor 73 mounted in the furnace discharge conduit 74. The reason for modulating the valve 72 by the sensor 73 is to obtain a reliable and close control over the temperature of the flow in the conduit 74 so that it does not exceed about 900 F. It is also contemplated that sensor 73 could be an oxygen analyzer and the unit would be used to open and close damper 72 to maintain a constant oxygen content in outlet pipe 74. Conduit 74 is connected. into the mill casing 50a at 76.

In the system shown in FIG. 3 the material to be reduced is received in the hopper 77 where it passes through a. suitable rotor controlled by drive 78 into the mill casing 50a. The material to be ground usually is of a type which has its own moisture and is therefore not particularly dusty at the time it reaches the hopper 77. In view of the condition ofthe incoming material, it is not necessary in this system to provide the spray means 45 and 46 which is shown with the layout of FIG. 1. Nevertheless, there must be control over the temperature and relative oxygen content of the flow in the casing 53, This control is obtained by mounting a temperature sensor 79 at a convenient point in the separator casing 53 and connecting the sensor by a suitable cable 80 to the burner unit 81 mounted on the furnace 75.,In this manner the operation of the furnace burner81 may be modulated so as to obtain the proper temperature condition in the separator casing 53. The system when operating as desired should have an oxygen content in the casing 53 of approximately 11 to 12 percent, whereas the oxygen content in the conduit 74 should be approxiately 15 percent at a temperature of approximately 900 F. After a short period of operation of the system shown in FIG. 3, wherein the initial air in the various conduits and operating apparatus will have been recycled it can be appreciated that the oxygen content will be reduced through the operation of the furnace 75 to render the same substantially inert to support explosion or fire. This is exceedingly important because the volume of flow created by the several fans in the system is sufficiently capable of moving metallic pieces into the dust and dirt collected in the primary separator 66 or the secondary separator 65 where fire might easily be started because the material being reduced or ground can be potentially explosive such as coal and any spark created by metalto-metal contact of the grinding parts could thereby create an explosion.

The system of FIG. 3 is also important as it provides means for simultaneously pulverizing or grinding material while drying the same. This is important where materials deposited in the hopper 77 carry considerable moisture.

The alternate system shown in FIG. 2 may apply without substantial change to the system shown in FIG. 3. That is to say, that the secondary separator 34 of FIG. 2 may be connected into the exhaust conduit 68 and the respective conduit 64 and 66 of FIG. 3 would then be altered sufficiently to provide continuous flow into the exhaust fan 67.

The principles of the present invention are set forth in the foregoing description when taken in connection with the accompanying drawings, and certain preferred arrangements of apparatus have been disclosed. However, changes and modifications may be made once the principles of the invention are Well understood, and it is the purpose to include all possible changes and modifications to the extent permitted by the prior art within the scope of the appended claims.

What is claimed is:

1. In apparatus for reducing materials having dirt and dust producing foreign matter mixed therewith, the improvement of means controlling the atmosphere within the material reducing apparatus to suppress dust explosion and fire tendencies, said improvement means ineluding: reducing apparatus; a first system for at least partially conditioning dust laden air from said reducing apparatus, said first system having a primary dust separator and air moving means connected in series relationship to said material reducing apparatus; and a second system for at least partially further conditioning dust laden air from said reducing apparatus, said second system having air moving means and a source of heat connected in series relationship to said first system, said second system reducing the pressure in said first system and said reducing apparatus to less than ambient atmospheric pressure and increasing the temperature of the atmosphere in said first system and said reducing apparatus to a level to assure dry conditions in said primary dust separator.

2. The improvement set forth in claim 1 wherein said source of heat has an ambient air supply converted into said second system ahead of said source of heat, valve means controlling said ambient air supply, and sensor means operably connected to said valve means and disposed in said second system in a location to selectively admit more or less ambient air in accordance with a predetermined temperature or oxygen content adjacent said heat source.

3. The improvement set forth in claim 1 wherein said reducing apparatus includes a material receiving hopper, said first system being connected to said hopper and the heated atmosphere in said second system being brought by said first system into said hopper.

4. The improvement set forth in claim 3 wherein moisture supply means is connected into said hopper, and control sensor means operably connected to said supply means is disposed in said hopper to limit the heat level in said hopper.

5. In apparatus of the character described, the coInbination of: material reducing mill means; a primary dust and dirt separator connected to said mill means; an air moving fan connected between said primary separator and said mill means to withdraw dust and dirt laden air from said primary separator and return relatively clean air; a diverter conduit having one end connected between said air moving fan and said mill means, means connecting the opposite end of said diverter conduit in air flow relation to an exhaust fan; a source of heat; conduit means connecting said exhaust fan to said source of heat and connecting said source of heat to said reducing mill means; and means to admit variable amounts of ambient air to said conduit means in advance of said source of heat to regulate the heat output by said source of heat, said exhaust fan maintaining a pressure in said combination less than ambient pressure, and said heat source consuming a substantial portion of the oxygen in the air moving to said reducing mill means.

References Cited UNITED STATES PATENTS 1,627,766 5/1927 Bergman 24l47 3,078,048 2/1963 Russell et a1 24l65 GERALD A. DOST, Primary Examiner US. Cl. X.R. 34--72; 241--

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