CLIAMS:We claim,
1. A process for conversion of heavy oil into lighter fractions, the process comprising;
heating a reaction mixture, wherein the reaction mixture comprises the heavy oil, catalyst, water and hydrogen donor solvent, thereby obtaining resultant effluent;
cooling and condensing the resultant effluent;
separating the cooled and condensed effluent into liquid and gaseous products; and
separating the liquid products into desired fractions.
2. The process according to claim 1, further comprising, preheating the heavy oil.
3. The process according to claim 1, further comprising, preheating the reaction mixture.
4. The process according to one of claim 2 and 3, wherein the preheating temperature is chosen between 80 oC and 200 oC.
5. The process according to claim 1, wherein the water is added in the form of steam.
6. The process according to claim 1, wherein the step of heating the reaction mixture comprises:
heating the reaction mixture in a first reactor to a temperature chosen between 350 oC and 475 oC; and
heating the reaction mixture obtained from the first reactor, in a second reactor, to a temperature chosen between 350 oC and 500 oC.
7. The process according to claim 6, further comprising:
providing the reaction mixture with a liquid residence time chosen between 15 minutes and 60 minutes in the first reactor; and
providing the reaction mixture with a liquid residence time chosen between 5 minutes and 30 minutes in the second reactor.
8. The process according to claim 6, further comprising, maintaining pressure chosen between 4 kg/cm2and 40 kg/cm2 in the first reactor and the second reactor.
9. The process according to claim 1, wherein the heavy oil is one of, Visbroken Fuel Oil, Clarified Oil, and Mix of Vacuum Tower Bottom and Clarified Oil with clarified oil content higher than 50 wt%.
10. The process according to claim 1, wherein the catalyst is a Fe based catalyst.
11. The process according to claim 1, wherein the catalyst is acidified ferrous sulfate.
12. The process according to claim 1, wherein the amount of the catalyst in the reaction mixture is chosen between 0.1 to 5wt% of heavy oil.
13. The process according to claim 1, wherein the amount of the hydrogen donor solvent in the reaction mixture is chosen between 0.1 to 10 wt% of heavy oil.
14. The process according to claim 1, wherein the volume of water in the reaction mixture is less than 30% weight of heavy oil.
15. The process according to claim 1, wherein the hydrogen donor solvent is one of tetralin and toluene.
16. A system for conversion of heavy oil into lighter fractions, the system comprising;
a first reactor, wherein the first reactor is configured to heat a reaction mixture, wherein the reaction mixture comprises the heavy oil, catalyst, water and hydrogen donor solvent;
a second reactor, wherein the second reactor is configured to heat the reaction mixture obtained from the first reactor, thereby obtaining resultant effluent;
a cooler configured to cool and condense the resultant effluent; and
a separator configured to separate the cooled and condensed effluent into liquid and gaseous products.
17. The system according to claim 16, further comprising a pre-heater configured to heat the heavy oil to a temperature chosen between 80 oC and 200 oC.
18. The system according to claim 16, further comprising a steam generator configured to add the water in the form of steam.
19. The system according to claim 16, wherein,
the first reactor is configured to heat the reaction mixture to a temperature chosen between 350 oC and 475 oC; and
the second reactor is configured to heat the reaction mixture to a temperature chosen between 350 oC and 500 oC.
20. The system according to claim 16, wherein,
the first reactor is configured to provide the reaction mixture with a liquid residence time chosen between 15 minutes and 60 minutes; and
the second reactor is configured to provide the reaction mixture with a liquid residence time chosen between 5 minutes and 30 minutes.
21. The system according to claim 16, wherein the first reactor and the second reactor are configured to maintain pressure chosen between 4 kg/cm2and 40 kg/cm2.
22. The system according to claim 16, wherein the heavy oil is one of, Visbroken Fuel Oil, Clarified Oil, and Mix of Vacuum Tower Bottom and Clarified Oil with clarified oil content higher than 50 wt%.
23. The system according to claim 16, wherein the catalyst is a Fe based catalyst.
24. The system according to claim 16, wherein the catalyst is acidified ferrous sulfate.
25. The system according to claim 16, wherein the amount of the catalyst in the reaction mixture is chosen between 0.1 to 5 wt% of heavy oil.
26. The system according to claim 16, wherein the amount of the hydrogen donor solvent in the reaction mixture is chosen between 0.1 to 10 wt% of heavy oil.
27. The system according to claim 16, wherein the volume of water in the reaction mixture is less than 30% weight of heavy oil.
28. The system according to claim 16, wherein the hydrogen donor solvent is one of tetralin and toluene. ,TagSPECI:BACKGROUND
Field
[0001] In general, subject matter relates to the field of conversion of heavy oil. More particularly, but not exclusively, the subject matter relates to conversion of heavy oil using visbreaking process to produce higher amount of lighter fraction (350-material) and stable heavier fraction (350+material).
Discussion of related field
[0002] Visbreaking process is a thermal cracking process, which is used in petroleum industry, to breakdown the heavy oil into products having reduced pour point and viscosity. In this process, free radicals are formed, which are highly unstable. It shall be noted that, the presence of these free radicals results in product instability at higher temperature. Further, it is always desirable to increase the conversion in visbreaking process, so that lesser amount of costly cutter stock is required. However, it is not possible, as beyond a certain cracking temperature, the heavier fraction (350+ material) becomes unstable.
[0003] Conventional visbreaking processes have been disclosed in US patents 6540904, 4615791, 4814065 and 5057204.
[0004] US Patent No.6540904 discloses a process for upgradation of only vacuum tower bottom, which is a heavy oil. In this process, Fe based catalyst and water are used. It shall be noted that, the instant reference discloses feed to water ratio of 2:1. It has been observed that, in a commercial visbreaking process, addition of water in accordance with the instant ratio is not feasible. Further, it shall be noted that, if water were to be added in accordance with the instant ratio, then residence time of the reactants will be reduced substantially, and such reduced residence time may not be sufficient for completion of the desired cracking process. Further, the instant reference does not seem to address the issue with respect to stability of 350+ fraction.
[0005] US Patent No.4615791 discloses a process for carrying out visbreaking operation at higher severity using hydrogen donor solvent. The instant reference attempts to reduce coke formation and produce a product of reduced viscosity, pour point and sedimentation characteristics. However, the instant reference does not suggest the use of any catalyst. Further, the instant reference, as was the case with the previous reference, does not seem to address the issue with respect to stability of 350+ fraction.
[0006] US Patent No. 4814065 discloses a method for accelerating the exchange of hydrogen between a hydrogen donor and a petroleum residue. The method includes incorporating an aqueous solution of ammonium sulfide into a mixture of hydrogen donor and petroleum residue. Thereafter, the mixture is subjected to a period of heat soaking at an elevated temperature. It shall be noted that, even this reference does not seem to address the issue with respect to stability of 350+ fraction.
[0007] US Patent No. 5057204 discloses a process for increasing severity in visbreaking process using SeO2 catalyst. This catalyst enhances the transfer of hydrogen from residue feed to the portion of the feed having reactive radicals formed during the reaction. It shall be noted that, hydrogen donor solvent has not been used in the aforementioned process. Hence, there are chances that some of the free radicals formed during the cracking process may not get saturated and may be mixed with the product, thereby resulting in product instability.
[0008] In light of the foregoing discussion, there is a need for a technique to convert heavy oil using visbreaking process to produce higher amount of lighter fraction (350-material) and stable heavier fraction (350+material).

OBJECTIVES OF THE INVENTION

[0009] A first objective is to increase the conversion of heavy oil in visbreaking process by using catalyst in combination with water and hydrogen donor solvent.
[0010] Another objective is to increase the conversion in visbreaking process while improving the stability of 350+ fraction.
[0011] Yet another objective is to provide a system for achieving increased conversion of heavy oil and at the same time producing a stable 350+ fraction.
[0012] A further objective is to increase the conversion of heavy oil with improved quality of 350+ fraction, viz lower sulfur content, higher stability as compared to the conventional visbreaking process.

SUMMARY
[0013] In one aspect, a process for conversion of heavy oil into lighter fractions is provided. The method includes, heating a reaction mixture, wherein the reaction mixture comprises the heavy oil, catalyst, water and hydrogen donor solvent, thereby obtaining resultant effluent; cooling and condensing the resultant effluent; separating the cooled and condensed effluent into liquid and gaseous products; and separating the liquid products into desired fractions.
[0014] In another aspect, a system for conversion of heavy oil into lighter fractions is provided. The system includes a first reactor, a second reactor, a cooler and a separator. The first reactor is configured to heat a reaction mixture, wherein the reaction mixture comprises the heavy oil, catalyst, water and hydrogen donor solvent. The second reactor is configured to heat the reaction mixture obtained from the first reactor, thereby obtaining resultant effluent. The cooler is configured to cool and condense the resultant effluent, and the separator is configured to separate the cooled and condensed effluent into liquid and gaseous products.

BRIEF DESCRIPTION OF DRAWINGS
[0015] Embodiments are illustrated by way of example and not limitation in the Figures of the accompanying drawings, in which like references indicate similar elements and in which:
[0016] FIG. 1 is a schematic illustration of a system 100 for improving the conversion of heavy oil, in accordance with an embodiment; and
[0017] FIG. 2 is a flow chart 200 of an exemplary method for improving the conversion of heavy oil, in accordance with an embodiment.

DETAILED DESCRIPTION
I. OVERVIEW
II. FIRST EXEMPLARY SYSTEM
III. EXEMPLARY METHOD
IV. EXAMPLES
V. CONCLUSION
I. OVERVIEW
[0018] Embodiments relate to the field of visbreaking. More particularly, but not exclusively, the embodiments relate to a process and system for visbreaking, to convert heavy oil in the presence of a catalyst, water and hydrogen donor solvent, to obtain higher amount of lighter fraction (350-material) and stable heavier fraction (350+material).
[0019] In an embodiment, heavy oil, which is the feedstock, is heated and fed to a feed tank. In the feed tank, water, Fe based catalyst and hydrogen donor solvent are added, to form a reaction mixture. The reaction mixture is thereafter introduced into a pre-heater. In the pre-heater, the reaction mixture is heated to a temperature chosen between 80 oC and 200 oC. The heated reaction mixture is thereafter introduced into a first reactor. In the first reactor, the reaction mixture is heated to a temperature chosen between 350 oC and 475 oC. Thereafter, the reaction mixture is introduced into a second reactor. In the second reactor, the reaction mixture is heated to a temperature chosen between 350 oC and 500 oC. The resultant products are passed through a cooler, and thereafter separated into gaseous and liquid products in a separator. The liquid product is then separated into water and hydrocarbons. The hydrocarbon is further separated into different product fractions like 150-, 150-350 and 350+ materials. It has been observed that, the instant process results in relatively stable heavier fraction (350+material).
[0020] The following detailed description includes references to the accompanying drawings, which form part of the detailed description. The drawings show illustrations in accordance with example embodiments. These example embodiments are described in enough detail to enable those skilled in the art to practice the present subject matter. However, it will be apparent to one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to unnecessarily obscure aspects of the embodiments. The embodiments can be combined, other embodiments can be utilized or structural and logical changes can be made without departing from the scope of the invention. The following detailed description is, therefore, not to be taken as a limiting sense.
[0021] In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one. In this document, the term “or” is used to refer to a nonexclusive “or,” such that “A or B” includes “A but not B,” “B but not A,” and “A and B,” unless otherwise indicated.
II. FIRST EXEMPLARY SYSTEM
[0022] Embodiments disclose technique for improving conversion of heavy oil into lighter products, wherein FIG. 1 is a schematic illustration of a system 100 for improving the conversion of heavy oil, in accordance with an embodiment. The system 100 comprises a feed tank 102, a feed pump 104, a pre-heater 106, a first reactor 108, a second reactor 110, a back pressure valve 112, a cooler 114, a separator 116, a water tank118, a water pump 120 and a steam generator122.
[0023] In an embodiment, the feed tank 102 comprises of a stirrer that is configured to stir the contents received by the feed tank 102. The stirrer may be configured to rotate at a speed chosen between 200 and 500 rpm.
[0024] The feed tank 102 is at least configured to receive the feedstock, which is a heavy oil.
[0025] In an embodiment, the feedstock, can be, for example, Clarified Oil (CLO), Visbroken Fuel Oil (VBFO), mix of Vacuum Tower Bottom (VTB) and Clarified Oil Tar, among others.
[0026] In an embodiment, the feed tank 102 is further configured to receive one or more of, a catalyst, water and a hydrogen donor solvent, along with the feedstock.
[0027] In an embodiment, the catalyst used is Fe based catalyst. The Fe based catalyst can be ferrous sulphate.
[0028] In an embodiment, the catalyst is dissolved in water and acidified using sulfuric acid so as to maintain its pH between 4 and 5.
[0029] In an embodiment, the amount of catalyst added is 0.1 to 5 wt% of the feedstock (heavy oil).
[0030] In an embodiment, the hydrogen donor solvent is tetralin. It shall be noted that. other suitable hydrogen donor solvents can also be used.
[0031] In an embodiment, the amount of hydrogen donor solvent added is 0.1 to 10 wt% of the feedstock (heavy oil).
[0032] In an embodiment, the volume of water added is not more than 30% of the volume of feedstock (heavy oil).
[0033] The feed pump 104 is configured to pump the contents of the feed tank 102 into the pre-heater 106.
[0034] In an embodiment, the feed pump 104 is configured to pump the contents of the feed tank 102 into the pre-heater 106 at a rate of 2kg/hr to 6 kg/hr.
[0035] The pre-heater 106 is configured to heat the content received from the feed tank 102.
[0036] In an embodiment, pre-heater 106 is configured to heat the content to temperature chosen between 80 oC and 200 oC.
[0037] The preheated content is fed to the first reactor 108. It shall be noted that, means, such as, pump, may be used to feed the content from the pre-heater 106 into the first reactor 108.
[0038] In an embodiment, the first reactor 108 is configured to heat the content received by it to temperature ranging between 350 oC and 475 oC.
[0039] In an embodiment, the first reactor 108 is maintained at a pressure chosen between 4 kg/cm2and 40 kg/cm2.
[0040] In an embodiment, the catalyst, water and hydrogen donor solvent is added to the first reactor 108, rather than adding them to the feed tank 102.
[0041] In an embodiment, the first reactor 108 is a vertical continuous stirred tank reactor having stirring facility with speed up to 300 rpm.
[0042] In an embodiment, the first reactor 108 is configured to provide a liquid residence time chosen between 15 minutes to 60 minutes.
[0043] In an embodiment, wherein the water is added to the first reactor 108, the water is converted into steam using the steam generator 122, which receives water from the water tank 118, via the water pump 120.
[0044] The content of the first reactor 108 is passed on to the second reactor 110. In an embodiment, the second reactor 110 is a vertical tubular reactor.
[0045] In an embodiment, the second reactor 110 is configured to heat the content received by it to temperature ranging between 350 oC and 500 oC.
[0046] In an embodiment, the second reactor 110 is maintained at a pressure chosen between 4 kg/cm2and 40 kg/cm2. The pressure in the second reactor 110 is controlled by the back pressure control valve 112.
[0047] In an embodiment, the second reactor 110 is configured to provide a liquid residence time chosen between 5 minutes to 30 minutes.
[0048] In an embodiment, the reactor effluent obtained from the second reactor 110 is cooled by passing it through the cooler 114. The effluent after being cooled is passed through the separator 116 and separated into gaseous products and liquid products. The liquid product is then separated into water and hydrocarbons. The hydrocarbon is further separated into different product fractions like 150-, 150-350 and 350+ materials. It has been observed that, the instant process results in relatively stable heavier fraction (350+material).

III. EXEMPLARY METHOD

[0049] FIG. 2 is a flow chart of an exemplary method for improving the conversion of heavy oil, in accordance with an embodiment. At step 202, the feedstock, which is heavy oil, is heated, thereby facilitating transferring and handling of the feedstock. In an embodiment, the feedstock is heated up to 120 oC. The heated feedstock is introduced into the feed tank 102.
[0050] Further, in addition to the heated feedstock, water, catalyst, and hydrogen donor solvent are fed to the feed tank 102. If the water, catalyst, and hydrogen donor solvent are not fed to the feed tank 102, then the same are introduced, at step 208, after pre-heating the feedstock.
[0051] If one or more of, water, catalyst, and hydrogen donor solvent are fed to the feed tank 102, then the contents of the feed tank 102 are stirred at a speed chosen between 200 and 500 rpm to obtain a mixture. The mixture so obtained, is pre-heated to temperature chosen between 80 oC and 200 oC, at step 206.
[0052] In an embodiment, the pre-heating is carried out in the pre-heater 106. The preheated feedstock along with the water, catalyst and hydrogen donor solvent forms a reaction mixture.
[0053] It shall be noted that, water, in the form of steam, as may be desired, is added to form the reaction mixture.
[0054] The reaction mixture, at step 210, is heated to temperature chosen between 350 oC and 475 oC. This heating can be carried out in the first reactor 108.
[0055] In an embodiment, the reaction mixture is heated at a pressure chosen between 4 kg/cm2and 40 kg/cm2.
[0056] In an embodiment, the reaction mixture, while being heated, is provided with a liquid residence time chosen between 15 minutes to 60 minutes.
[0057] The cracking process initially starts during this phase of heating, for example, in the first reactor 108. It shall be noted that, the hydrogen donor solvent is used to saturate the free radicals formed during the cracking process. Further, to accelerate the transfer of hydrogen to the feedstock, the catalyst is used.
[0058] The heated reaction mixture, at step 212, is further subjected to heating to temperature chosen between 350 oC and 500 oC. This heating can be carried out in the second reactor 110.
[0059] In an embodiment, the reaction mixture is heated at a pressure chosen between 4 kg/cm2and 40 kg/cm2.
[0060] In an embodiment, the reaction mixture, while being heated, is provided with a liquid residence time chosen between 5 minutes to 30 minutes.
[0061] The cracking process also continues during this phase of heating, and undergoes completion, for example, in the second reactor 110.
[0062] The reactor effluent obtained at the end of the cracking process is further subjected to quenching, at step 214. In this step, the reactor effluent is passed through the cooler 114, to terminate the cracking process and reduces coke formation.
[0063] At step 216, the quenched mixture is passed through the separator 116. In this step, the quenched mixture is separated into gaseous and liquid products. The liquid products may be further separated into water and hydrocarbons. The hydrocarbons are further separated into lighter fraction (350- material) and heavier fraction (350+ fraction).
[0064] It has been observed that embodiments result in conversion of heavy oil to higher amount of lighter fraction (350-material) and stable heavier fraction (350+ material). Some examples are provided in the next section.
IV. EXAMPLES
[0065] In the following examples, it has been observed that, the resultant products have improved stability of heavier fraction (350+), reduced sulfur content and improved conversion into lighter fraction.
[0066] It shall be noted that 350+ fraction is then tested for stability using ASTM method D-7060 i.e. P-Value test. For stability of 350+ fraction, values higher than 1.05 are considered as stable product.
[0067] The following examples are given for illustration purpose only and should not be construed as the limiting the scope of the present invention.
[0068] Typical properties of the feed components used during the experiments are as follows:
Unit VTB CLO VBFO
Density Kg/m3 1.062 1.01 0.9739
Viscosity@ 1000C cSt 1000 5 80
CCR Wt% 25 10 12
Simulated Distillation
IBP °C 350 280 218
10% °C 420 386 322
30% °C 470 411 461
50% °C 490 427 538
70% °C 520 449 -
90% °C 570 - -
EP °C - -

EXAMPLE 1: Cracking of CLO
[0069] This example illustrates the effect of catalyst on the conversion of CLO. These experiments were conducted in a continuous pilot plant with feed rate of 4 kg/hr and having residence time of 30 minutes in first reactor 108 and 10 minutes in second reactor 110. The product yield and quality are shown below:

Parameters Unit CLO Run#1 Run#2
Catalyst % 0 1.0
Water rate % 25 25
Pre-heat Temperature °C 250 250
First Reactor Temperature °C 405 407
Second Reactor Temperature °C 415 418
Pressure Kg/cm2 20 20
Product Yield, wt%
150- 0.0 1.8 4.0
150-350 12.0 11.9 12.2
350+ 88.0 86.3 83.8
Sulfur content of 350+ fraction Wt% 2.78 2.53 2.40
Stability of 350+ fraction >3.00 1.20 1.20

[0070] The above example shows the crackability of CLO is poor as it is quite refractory in nature. By heating CLO in the presence of water, reduction in 350+ fraction is 1.7 wt% as indicated by experiment Run#1. However, adding catalyst along with water, improves the conversion and 350+ fraction is reduced by 4.2 wt% as indicated in experiment Run#2, which shows the effectiveness of the catalyst in improving conversion of CLO. It is also seen that the sulfur content in 350+ fraction is also reduced by addition of catalyst and water together. Further, the P-value of 350+ fraction is not decreased even if the temperature is increased in Run#2 as compared to Run#1.

EXAMPLE 2: Cracking of VBFO

[0071] This example illustrates the cracking study of VBFO carried out in accordance with one or more embodiments. The experiments were done at feed rate of 4kg/hr with residence time of 30 minutes in first reactor 108 and 10 minutes in second reactor 110. The results as shown below:

Parameters Unit VBFO Run#1 Run#2
Catalyst % 0 1.0
Water rate % 10 10
Pre-heat Temperature °C 250 250
First Reactor Temperature °C 405 405
Second Reactor Temperature °C 418 418
Pressure Kg/cm2 20 20
Product Yield, wt%
150- 0.0 4.2 5.0
150-350 10.0 16.4 16.5
350+ 90.0 79.5 78.5
Sulfur content of 350+ fraction Wt% 2.58 2.36 2.32
Stability of 350+ fraction 1.60 1.00 1.00

[0072] The above example shows that the crackability of VBFO is good, as the 350- fraction improves by 10.5 wt% by adding water as indicated in Run#1. By addition of the catalyst, the conversion improvement is more as compared to without using catalyst at the same second reactor 110 temperature. The sulfur content in 350+ fraction is reduced by addition of the catalyst and water.

EXAMPLE 3: Cracking of Mix of VTB and CLO

[0073] This example illustrates the cracking study of mix of VTB and CLO, wherein the % of CLO content is 70%. The experiments were carried out in pilot plant at feed rate of 4 kg/hr with residence time of 30 minutes in the first reactor 108 and 10 minutes in the second reactor 110. The results as shown below:
Unit Feed Run#1 Run#2 Run#3 Run#4
Catalyst % 0 1.0 1.0 1.0
Hydrogen donor solvent % 0 0 5.0 5.0
Water rate % 3 3 3 3
Pre-heat Temperature °C 250 250 250 250
First reactor Temperature °C 401 407 407 407
Second Reactor Temp °C 446 453 453 470
Pressure Kg/cm2 20 20 20 20
Product Yield, wt%
150- 0.0 7.6 9.0 8.8 10.5
150-350 20.0 19.7 22.0 21.8 23.5
350+ 80.0 72.6 69.0 69.4 66.0
Stability of 350+ fraction 1.90 1.25 1.25 1.45 1.25

[0074] As seen in example-1, the crackability of CLO is poor. However, when VTB is added, the crackability of mix of VTB and CLO is improved. The above table shows that, by adding catalyst along with water, the conversion is higher as compared to conversion without using catalyst, while maintaining the same stability of 350+ fractions.
[0075] The above example shows that by adding hydrogen donor solvent along with catalyst and water, the conversion decreases marginally. However, the stability improves. For getting the same stability of 1.25, by using combination of catalyst and hydrogen donor solvent of the present invention, it is possible to increase the second reactor 110 temperature up to 470 °C from 453 °C while resulting in improvement in conversion by 3.4%.

V. CONCLUSION
[0076] Use of water and hydrogen donor solvents in the process results in saturation of the free radicals obtained during the cracking process. In this process, it is seen that, in addition to the hydrogen donor solvents, water also donates hydrogen to the reaction process to stabilise the free radicals formed. Therefore, the heavier fractions obtained at the end of the reaction process are stable.
[0077] The processes described above is described as sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, or some steps may be performed simultaneously.
[0078] Although embodiments have been described with reference to specific example embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the system and method described herein. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.
[0079] Many alterations and modifications of the present invention will no doubt become apparent to a person of ordinary skill in the art after having read the foregoing description. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. It is to be understood that the description above contains many specifications; these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the personally preferred embodiments of this invention. Thus the scope of the invention should be determined by the appended claims and their legal equivalents rather than by the examples given.