Drum-type petroleum coke drying equipment
Technical Field
The utility model discloses a technical field who relates to petroleum coke is dried and is used equipment especially relates to a drum-type petroleum coke drying equipment.
Background
Petroleum coke is black solid coke which is formed by cracking and coking vacuum residue of crude oil at 500-550 ℃ through a delayed coking device, and is a byproduct in the production of light oil products. The volatile content of the petroleum coke is about 10-18%, and the low-level heating value is more than 8000 kcal/kg. Therefore, the petroleum coke as a solid fuel has higher application value in the production practice of inorganic nonmetallic material products such as glass, cement, refractory materials and the like.
Generally, petroleum coke after delayed coking needs to be cooled by water spray, and the cooling process directly causes the moisture content of the petroleum coke to be as high as 8-12%. The conventional drying equipment can only reduce the moisture in the petroleum coke to about 3 percent, and the high moisture in the petroleum coke is not beneficial to the grinding of the petroleum coke powder-making process and the pneumatic transmission of the petroleum coke powder in a fuel pipeline. Particularly, in winter in the north, the petroleum coke powder with the moisture content of more than 1% is easy to block a pneumatic conveying pipeline, so that the continuous combustion of the petroleum coke powder is influenced, the temperature in a heating furnace and a heating kiln is reduced, and the situations of furnace shutdown, kiln shutdown and the like can be caused seriously, therefore, a dryer is required to be adopted for drying the petroleum coke.
In the production practice of petroleum coke powder making, all dryers adopt open chute sliding type feeding, and because the air in the cylinder body is discharged to the waste gas outlet, a large amount of fine particle powder can be taken away by the air flow, thus the load of a dust collector is increased; part of fine particle powder falls to the bottom of the feeding end socket, the leaked material discharge amount is about 200kg/h, the daily accumulation amount is 3-5 tons, manual cleaning is needed once every 2 hours, the labor intensity of workers is increased, and the environment is seriously polluted. In addition, the existing dryer has the problems of low heat transfer speed, low drying efficiency, poor drying effect and the like due to the structural design.
SUMMERY OF THE UTILITY MODEL
In view of this, the utility model provides a drum-type petroleum coke drying equipment to at least, there are drying efficiency low, the stoving effect is poor and particle powder leaks easily to solve current petroleum coke drying equipment, causes environmental pollution scheduling problem.
The utility model provides two kinds of drum-type petroleum coke drying equipment, a drying equipment includes: the device comprises a base 1, a drying material cylinder 2, a sealing feeding device 3, a transmission device 4 and two riding wheel supporting devices 5;
the drying material cylinder 2 is located above the base 1, the drying material cylinder 2 includes: the device comprises a horizontal rotary cylinder 21, a feeding end socket 22, a discharging end socket 23 and a plurality of groups of lifting blades 24;
the horizontal rotary cylinder 21 is obliquely arranged relative to the base 1 and is provided with a feeding end and a discharging end, the height of the feeding end is higher than that of the discharging end, and two wheel belts 211 are movably sleeved outside the horizontal rotary cylinder 21 at intervals along the axial direction;
the feeding end enclosure 22 is provided with a discharge hole, a feed hole and a first air outlet 221, and the discharge hole of the feeding end enclosure 22 is in sealed rotary connection with the feed end of the horizontal rotary cylinder 21;
the discharge end socket 23 is provided with a feed inlet, a discharge outlet and a first air inlet 231, and the feed inlet of the discharge end socket 23 is in sealed rotary connection with the discharge end of the horizontal rotary cylinder 21;
a plurality of groups of the material raising plates 24 are respectively installed on the inner wall of the horizontal rotary cylinder 21 at intervals along the axial direction of the horizontal rotary cylinder 21;
each set of the material raising plates 24 is composed of a plurality of material raising plate units 241, the plurality of material raising plate units 241 are respectively arranged in parallel along the circumferential direction of the horizontal rotary cylinder 21 at intervals, and the material raising plate units 241 in two adjacent sets of the material raising plates 24 are arranged in a staggered manner;
the sealing and feeding device 3 comprises: a material buffer bin 31 and a screw feeder 32;
a discharge hole of the material buffer bin 31 is connected with a feed hole of the screw feeder 32;
the discharge hole of the screw feeder 32 is hermetically connected with the feed hole of the feed seal head 22;
the transmission device 4 is fixedly arranged on the base 1 and is in driving connection with the drying material cylinder 2, and the horizontal rotary cylinder 21 in the drying material cylinder 2 can rotate relative to the axis of the horizontal rotary cylinder under the driving of the transmission device 4;
the two supporting device 5 are located between the base 1 and the drying material cylinder 2, the positions of the two supporting device 5 are respectively corresponding to the positions of the two belt pulleys 211 on the horizontal rotary cylinder 21, and each supporting device 5 is connected with the corresponding belt pulley 211 in a supporting mode.
Another drying apparatus includes: the device comprises a base 1, a drying material cylinder 2, a sealing feeding device 3, a transmission device 4 and two riding wheel supporting devices 5;
the drying material cylinder 2 is located above the base 1, the drying material cylinder 2 includes: the device comprises a horizontal rotary cylinder 21, a feeding end socket 22, a discharging end socket 23 and a plurality of groups of lifting blades 24;
the horizontal rotary cylinder 21 is obliquely arranged relative to the base 1 and is provided with a feeding end and a discharging end, the height of the feeding end is higher than that of the discharging end, and two wheel belts 211 are movably sleeved outside the horizontal rotary cylinder 21 at intervals along the axial direction;
the feeding end enclosure 22 is provided with a discharge hole, a feed hole and a second air inlet 222, and the discharge hole of the feeding end enclosure 22 is in sealed rotary connection with the feed end of the horizontal rotary cylinder 21;
the discharge end socket 23 is provided with a feed inlet, a discharge outlet and a second air outlet 232, and the feed inlet of the discharge end socket 23 is in sealed rotary connection with the discharge end of the horizontal rotary cylinder 21;
a plurality of groups of the material raising plates 24 are respectively installed on the inner wall of the horizontal rotary cylinder 21 at intervals along the axial direction of the horizontal rotary cylinder 21;
each set of the material raising plates 24 is composed of a plurality of material raising plate units 241, the plurality of material raising plate units 241 are respectively arranged in parallel along the circumferential direction of the horizontal rotary cylinder 21 at intervals, and the material raising plate units 241 in two adjacent sets of the material raising plates 24 are arranged in a staggered manner;
the sealing and feeding device 3 comprises: a material buffer bin 31 and a screw feeder 32;
a discharge hole of the material buffer bin 31 is connected with a feed hole of the screw feeder 32;
the discharge hole of the screw feeder 32 is hermetically connected with the feed hole of the feed seal head 22;
the transmission device 4 is fixedly arranged on the base 1 and is in driving connection with the drying material cylinder 2, and the horizontal rotary cylinder 21 in the drying material cylinder 2 can rotate relative to the axis of the horizontal rotary cylinder under the driving of the transmission device 4;
the two supporting device 5 are located between the base 1 and the drying material cylinder 2, the positions of the two supporting device 5 are respectively corresponding to the positions of the two belt pulleys 211 on the horizontal rotary cylinder 21, and each supporting device 5 is connected with the corresponding belt pulley 211 in a supporting mode.
Preferably, said transmission means 4 comprise: a large ring gear 41, a drive motor 42, a speed reducer 43, and a pinion gear 44;
the large gear ring 41 is fixedly sleeved outside the horizontal rotary cylinder 21 and is positioned between the two belt pulleys 211;
the driving motor 42 is mounted on the base 1;
the power input end of the speed reducer 43 is in driving connection with the power output end of the driving motor 42;
the pinion 44 is fixedly sleeved at the power output end of the driving motor 42, and the pinion 44 is in driving engagement with the large gear ring 41.
Further preferably, the large gear ring 41 is fixedly sleeved outside the horizontal rotary cylinder 21 through a tangent spring plate.
Further preferably, each of the supporting devices 5 includes two supporting units, and each of the supporting units includes: a base 51, four bearings and two riding wheels 52;
the base 51 is fixed on the base 1, two sides of the base 51 are respectively provided with a support plate extending vertically upwards, and the upper part of each support plate is provided with two mounting holes along the width direction;
the four bearings are respectively arranged in the mounting holes of the two support plates in the base 51;
the two supporting wheels 52 are arranged between the supporting plates at two sides of the base 51 in parallel, one end of each supporting wheel 52 is fixedly nested in the bearing of the mounting hole at one side, and the other end of each supporting wheel 52 is fixedly nested in the bearing of the corresponding mounting hole at the other side.
Further preferably, the inclination of the horizontal rotary cylinder 21 with respect to the base 1 is 1% to 6%.
Further preferably, a heat insulating layer is provided outside the horizontal rotary cylinder 21.
Further preferably, each of the material raising plate units 241 is L-shaped.
Further preferably, the height of each material raising plate unit 241 is 1/8-1/12 of the diameter of the horizontal rotary cylinder 21, and the length of each material raising plate unit 241 is 500mm-550 mm.
Further preferably, the drum-type petroleum coke drying equipment further comprises: and the two catch wheel devices 6 are respectively positioned at two sides of the wheel belt 211 close to one end of the discharging seal head 23, and the axis of each catch wheel in each catch wheel device 6 is perpendicular to the horizontal rotary cylinder 21.
The utility model provides a drum-type petroleum coke drying equipment mainly comprises base, stoving feed cylinder, sealed feed arrangement, transmission and two riding wheel strutting arrangement, and wherein, the base supports as drying equipment's whole, and the stoving feed cylinder is drying equipment's main part, and this stoving feed cylinder can rotate under transmission's drive, and then makes its inside petroleum coke remove the in-process and dry to improve its stoving effect. In addition, adopt closed feed mode among this drying equipment, constitute by material buffering storehouse and screw feeder, treat that the stoving material is at first in the buffering of material buffering storehouse pile up in order to get rid of cold air, then carry the stoving feed cylinder by screw feeder in, not only can reduce the calorific loss of stoving feed cylinder, compare current uncovered formula feed mode moreover, still can effectively solve the petroleum coke granule and leak, the environmental pollution problem that causes. The two riding wheel supporting devices are arranged to realize the inclined supporting of the drying material cylinder.
The utility model provides a drum-type petroleum coke drying equipment not only has advantages such as simple structure, reasonable in design, still has following advantage:
1) the utility model provides a drum-type drying equipment carries out drying process to the petroleum coke material in rolling to the petroleum coke material can advance at the stoving cylinder inner loop and remove, lets the material carry out the heat exchange with the hot gas flow more fully, when making the moisture content in the petroleum coke fall to below 1%, can realize the serialization production of petroleum coke powder process technology.
2) The utility model provides a drum-type drying equipment, through sealed feed arrangement of sealed, the setting of the outside thermal-insulated heat preservation of horizontal gyration drum of cooperation simultaneously makes the heat dissipation loss of stoving feed cylinder reduce, and the inner wall temperature risees, and the steam cooling slows down, enlarges with the difference in temperature of material to accelerate heat transfer rate, improved heat transfer efficiency.
3) In the production practice, sealed feed arrangement compares with traditional uncovered chute landing formula feed, through adjusting screw feeder's in the sealed feed arrangement feed speed, avoids appearing a large amount of materials in feeding head department and piles up the condition, effectively solves the material problem of revealing in feeding head department, and this sealed feed arrangement's design not only alleviates equipment load, reaches energy-conserving effect, extension equipment life, and workman intensity of labour reduces by a wide margin moreover, obtains effectively improving the influence of all ring edge borders.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description, serve to explain the principles of the invention.
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic structural view of a drum-type petroleum coke drying device provided by the embodiment of the present disclosure;
fig. 2 is a top view of a drum-type petroleum coke drying apparatus provided by an embodiment of the present disclosure;
FIG. 3 is a cross-sectional view along AA of FIG. 2;
fig. 4 is a schematic structural view of another drum-type petroleum coke drying equipment provided by the embodiment of the present disclosure.
Detailed Description
Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatus consistent with certain aspects of the invention, as detailed in the appended claims.
In order to solve the problem that the existing petroleum coke drying equipment has low drying efficiency, poor drying effect and easy leakage of particle powder, and causes environmental pollution, the embodiment provides two types of drum-type petroleum coke drying equipment respectively, and the drum-type petroleum coke drying equipment is as follows:
one, drum-type petroleum coke drying equipment against current
Referring to fig. 1 and 2, the device mainly comprises a base 1, a drying material cylinder 2, a sealing feeding device 3, a transmission device 4 and two riding wheel supporting devices 5.
Wherein, base 1 mainly comprises concrete foundation and pre-buried iron, and mainly used supports and the use of fixed stoving feed cylinder.
The drying material cylinder 2 is positioned above the base 1, the drying material cylinder 2 mainly comprises a horizontal rotary cylinder 21, a feeding end enclosure 22, a discharging end enclosure 23 and a plurality of groups of material lifting plates 24, the horizontal rotary cylinder 21 is supported by steel plates with certain thickness in a roll welding mode, the horizontal rotary cylinder 21 is obliquely arranged relative to the base 1 and is provided with a feeding end and a discharging end, the height of the feeding end is higher than that of the discharging end, and two wheel belts 211 are movably sleeved outside the horizontal rotary cylinder 21 along the axial direction at intervals. In order to realize smooth feeding of the horizontal rotary cylinder 21, as an improvement of the technical scheme, a material stop ring and a material stop plate can be arranged at the feeding end of the horizontal rotary cylinder 21, and an internal heat mouth guard plate is arranged at the feeding end of the horizontal rotary cylinder 21 in order to improve the durability of the horizontal rotary cylinder 21. Preferably, the inclination of the horizontal rotary cylinder 21 is 1% -6% relative to the base 1, and in order to reduce the heat dissipation rate of the cylinder wall of the horizontal rotary cylinder, a heat insulation layer may be provided outside the horizontal rotary cylinder 21.
The feeding end socket 22 is provided with a discharge hole, a feed hole and a first air outlet 221, wherein the first air outlet 221 vertically extends upwards, the discharge hole of the feeding end socket 22 is connected with the feed end of the horizontal rotary cylinder 21 in a sealing and rotating manner, the discharging end socket 23 is provided with a feed hole, a discharge hole and a first air inlet 231, the first air inlet 231 is arranged in parallel relative to the axial direction of the horizontal rotary cylinder 21, the feed hole of the discharging end socket 23 is connected with the discharge end of the horizontal rotary cylinder 21 in a sealing and rotating manner, the feeding end socket 22 and the discharging end socket 23 are both fixed on the ground by steel supports and do not rotate along with the horizontal rotary cylinder 21, and sealing rings can be arranged between the feeding end socket 22 and the horizontal rotary cylinder 21 and between the discharging end socket 23 and the horizontal rotary cylinder.
Referring to fig. 3, a plurality of sets of material raising plates 24 are respectively installed on the inner wall of the horizontal rotary cylinder 21 at intervals along the axial direction of the horizontal rotary cylinder 21, and the interval distance is not too small, otherwise, large materials are easily clamped, each set of material raising plates 24 is composed of a plurality of material raising plate units 241, the plurality of material raising plate units 241 are respectively arranged in parallel along the circumferential direction of the horizontal rotary cylinder 21 at intervals, and the material raising plate units 241 in two adjacent sets of material raising plates 24 are arranged in a staggered manner, so that the chance of meeting materials and hot air is increased, the contact area of the materials and the air flow is increased, the heat exchange capacity in the horizontal rotary cylinder is increased, and the drying speed of the.
Referring to fig. 1 and 2, the sealed feeding device 3 mainly comprises a material buffer bin 31 and a screw feeder 32, wherein a discharge port of the material buffer bin 31 is connected with a feed port of the screw feeder 32, a discharge port of the screw feeder 32 is connected with a feed port of the feeding end enclosure 22 in a sealing manner, and by adopting the sealed feeding device 3, before the material is conveyed into the drying material cylinder by the screw feeder to be dried, the discharged cold air is naturally accumulated in the material buffer bin, so that the heat loss degree caused by the material entering the drying material cylinder is reduced. In addition, sealed feed arrangement in this scheme compares current chute landing formula feed, not only can alleviate the dust collector load, reaches energy-conserving effect, extension equipment life, the row's of the feeding head department that can significantly reduce moreover volume of discharging, only has a small amount of dust to need the clearance, and workman intensity of labour reduces by a wide margin, and the influence to all ring edge borders is effectively improved, and its leading reason lies in: in the prior chute sliding type feeding mode, the falling speed of the material is not controllable, the material is accumulated in a large amount at the feeding end socket, the leaked material is about 200kg/h, the daily accumulation amount is 3-5 tons, and the material is manually cleaned once every 2 hours, the feeding is carried out by adopting the screw feeder in the scheme, the adaptive rotating speed of the variable frequency motor in the screw feeder can be adjusted according to the material condition at the feeding end socket, the accumulation condition of a large amount of material at the feeding end socket is avoided, and the problem existing in the existing chute sliding type feeding mode is effectively solved.
The transmission device 4 is fixedly arranged on the base 1 and is in driving connection with the drying material cylinder 2, and the horizontal rotary cylinder 21 in the drying material cylinder 2 can rotate relative to the axis of the horizontal rotary cylinder under the driving of the transmission device 4.
The two supporting devices 5 are located between the base 1 and the drying material cylinder 2, the positions of the two supporting devices 5 correspond to the positions of the two belt pulleys 211 on the horizontal rotary cylinder 21 one by one, each supporting device 5 is connected with the corresponding belt pulley 211 in a supporting mode, and the supporting devices 5 close to the discharging end enclosure 23 are omitted in the process of drawing display clarity in fig. 1.
The specific working process of the countercurrent drum-type petroleum coke drying equipment in the embodiment is as follows: taking the diameter of the horizontal rotary cylinder as 2200mm and the length as 14000mm as an example, the inlet temperature of hot air is generally controlled at 450-500 ℃, and the outlet temperature is preferably controlled at 60-100 ℃. When the drying equipment is used for drying petroleum coke, an air outlet in a feeding end enclosure is required to be communicated with an induced draft fan, before drying, the induced draft fan is started to exhaust gas in a horizontal rotary cylinder, hot air is input from an air inlet of a discharging end enclosure, the hot air moves from a hot end to a cold end and is finally discharged from an air outlet of the feeding end enclosure, the petroleum coke to be dried is conveyed to a material cache bin for caching, then the petroleum coke is conveyed into the drying material cylinder by a screw feeder, the horizontal rotary cylinder is driven to rotate by a transmission device, in the rotating process of the horizontal rotary cylinder, the hot air can slide from the feeding end to the discharging end and meet with the hot air for heat exchange, under the action of the material raising plate unit, the contact area between the material and the airflow can be increased, the drying speed of the material is accelerated, and further ensure that the moisture content of the material can be reduced to below 1 percent in the process of entering the material from the feed inlet of the feed seal head and discharging the material from the discharge outlet of the discharge seal head.
Two, downstream drum-type petroleum coke drying equipment
Referring to fig. 4, the overall structure of the concurrent flow drum type petroleum coke drying equipment is basically the same as that of the above-mentioned countercurrent flow drum type petroleum coke drying equipment, and the only difference is that: the air inlet position and the air outlet position in the equipment are adjusted, specifically, a second air inlet 222 is arranged on the feeding end enclosure 22, the second air inlet 222 is arranged in parallel relative to the axial direction of the horizontal rotary cylinder 21, a second air outlet 232 is arranged on the discharging end enclosure 23, the second air outlet 232 extends vertically upwards, and other parts which are not described in detail can refer to countercurrent drum-type petroleum coke drying equipment, and are not described in detail herein.
The specific working process of the concurrent flow drum-type petroleum coke drying equipment in the embodiment is as follows: taking the diameter of the horizontal rotary cylinder as 2000mm and the length as 16000mm as an example, the inlet temperature of hot air is generally controlled at 450-500 ℃, and the outlet temperature is preferably controlled at 60-100 ℃. When the drying equipment is used for drying petroleum coke, an air outlet in a discharging end enclosure is required to be communicated with an induced draft fan, before drying, the induced draft fan is started to exhaust gas in a horizontal rotary cylinder, hot air is input from an air inlet of a feeding end enclosure, the hot air moves from a hot end to a cold end and is finally discharged from an air outlet of the discharging end enclosure, the petroleum coke to be dried is conveyed to a material cache bin for caching, then the petroleum coke is conveyed into the drying material cylinder by a screw feeder, the horizontal rotary cylinder is driven to rotate by a transmission device, during the rotation process of the horizontal rotary cylinder, the material can slide down from the feeding end to the discharging end, at the moment, the moving direction of the material is consistent with the moving direction of hot air flow, under the effect of the lifting blade unit, the material is taken to a high position to be continuously sprayed down, the material is subjected to heat exchange with high-temperature airflow, and the material is naturally discharged through a discharge hole of the discharge end socket after being fully dried.
Above-mentioned two kinds of drying equipment during operation are in the draught fan intercommunication at the air outlet, consequently under the effect of draught fan, this drying equipment's stoving feed cylinder is dried under negative pressure state, and then strengthens the leakproofness of the feed end of feeding head and horizontal gyration drum and the discharge end of ejection of compact head and horizontal gyration drum, prevents to take place the problem that the material was revealed.
The transmission device in the two drying devices can adopt various structures, and mainly can realize the rolling drive of the horizontal rotary cylinder. Referring to fig. 2, the transmission device 4 mainly includes a large gear ring 41, a driving motor 42, a speed reducer 43, and a pinion 44, wherein the large gear ring 41 is fixedly sleeved outside the horizontal rotary cylinder 21 and located between two pulleys 211, the driving motor 42 is installed on the base 1, a power input end of the speed reducer 43 is connected with a power output end of the driving motor 42 through a belt drive, the pinion 44 is fixedly sleeved on a power output end of the driving motor 42, and the pinion 44 is in driving engagement with the large gear ring 41, wherein the large gear ring 41 is fixedly sleeved outside the horizontal rotary cylinder 21 through a tangent spring plate, and the driving motor 42 can be a variable frequency motor to reduce energy consumption.
The specific working process of the transmission device is as follows: after the driving motor is started, the driving motor is output after speed change through the speed reducer, the pinion is driven to rotate, and then the bull gear meshed with the pinion is driven to rotate.
Referring to fig. 1, each of the above supporting roller supporting devices 5 is composed of two supporting roller supporting units arranged side by side to form two gears, each supporting roller supporting unit is composed of a base 51, four bearings and two supporting rollers 52, wherein the base 51 is fixed on the base 1, and two sides of the base 51 are respectively provided with a vertical supporting plate extending upwards, two mounting holes are respectively arranged on the upper portion of each supporting plate along the width direction of the supporting plate, the four bearings are respectively mounted in the mounting holes of the two supporting plates in the base 51, the two supporting rollers 52 are arranged between the supporting plates at two sides of the base 51 in parallel, the uniform end of each supporting roller 52 is fixedly nested in the bearing of the mounting hole at one side, and the other end of each supporting roller is fixedly nested in the bearing of the corresponding mounting hole.
In order to improve the action effect of the material raising plate units 241, each material raising plate unit 241 is L-shaped, the height of each material raising plate unit 241 is 1/8-1/12 of the diameter of the horizontal rotary cylinder 21, and the length of each material raising plate unit 241 is 500mm-550 mm.
In order to avoid axial movement of the horizontal rotary cylinder in the rotating process, two catch wheel devices 6 can be arranged in the drum-type petroleum coke drying equipment, the two catch wheel devices 6 are respectively positioned at two sides of a wheel belt 211 close to one end of a discharging end socket 23, and the axis of a catch wheel in each catch wheel device 6 is perpendicular to the horizontal rotary cylinder 21.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
It will be understood that the invention is not limited to the precise arrangements described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.