US3833056A

US3833056A - High temperature cooling process and system

Info

Publication number: US3833056A
Application number: US00323996A
Authority: US
Inventors: Minn R Mc; M Jamison
Original assignee: Black Sivalls and Bryson Inc
Current assignee: Black Sivalls and Bryson Inc
Priority date: 1973-01-15
Filing date: 1973-01-15
Publication date: 1974-09-03
Anticipated expiration: 1991-09-03
Also published as: AT343707B; JPS5046505A; AU6443674A; CA999740A; FR2214091B1; IT1003368B; GB1453150A; FR2214091A1; IN140882B; ATA30474A; DE2401036A1; BE809619A

Abstract

A process and system for cooling a device subjected to high temperatures wherein a stream of coolant is flowed through the device. The resultant heated stream of coolant is passed in heat exchange relationship with a cooled stream of liquid heat transfer medium so that a quantity of heat is removed from the coolant substantially equal to the heat removed from the device. The stream of coolant is passed in heat exchange relationship with a heated stream of the liquid heat transfer medium so that the coolant is maintained at a desired temperature level and then the coolant is recirculated through the device.

Description

[451 Sept. 3, 1974 HIGH TEMPERATURE COOLING PROCESS AND SYSTEM [75] Inventors: Robert E. McMinn; Mickey B.

' Jamison, both of Oklahoma City,

Okla.

[73] Assignee: Black, Sivalls & Bryson, Inc.,

Oklahoma City, Okla.

22 Filed: Jan. 15, 1973 211 Appl. No.2 323,996

[52] US. Cl 165/107, 165/30, 239/132, 239/132.3, 266/34 L [51] Int. Cl. F28d 15/00 [58] Field of Search 165/107; 239/132, 132.1, 239/1323, 132.5; 266/34 L, 34 LM [56] References Cited UNITED STATES PATENTS 1,905,811 4/1933 Culver 165/107 2,832,733 4/1958 Szilard 176/52 3,008,271 11/1961 Cook 165/107 3,059,913 10/1962 Sands 165/107 3,537,515 11/1970 Byrd 165/107 H54 TEE SL/EGE MD STORAGE VESSEL FOREIGN PATENTS OR APPLICATIONS 187,553 12/1905 Germany 165/107 545,299 10/1922 France 165/107 962,498 7/1964 Great Britain 165/107 Primary ExamineF-Manu'el A. Antonakas Assistant Examiner-Daniel J. OConnor Attorney, Agent, or Firm-C. Clark Dougherty, Jr.

[5 7 ABSTRACT A process and system for cooling a device subjected to high temperatures wherein a stream of coolant is flowed through the device. The resultant heated stream of coolant is passed in heat exchange relationship with a cooled stream of liquid heat transfer medium so that a quantity of heat is removed from the coolant substantially equal to the heat removed from the device. The stream of coolant is passed in heat exchange relationship with a heated stream of the liquid heat transfer medium so that the coolant is maintained at a desired temperature level and then the coolant is recirculated through the device.

13 Claims, 1 Drawing Figure SURGE 4N0 EXPA/VS/OA/ VE55EL OXYGE'A/ LANCE PATENIEDISEP 31914 Saws Nubia \xuNOXXQ HIGH TEMPERATURE COOLING PROCESS AND SYSTEM BACKGROUND OF THE INVENTTON 1. Field of the Invention A The present invention relates to a process and system for cooling a device subjected to high temperatures, and more particularly, but not by way of limitation, to a process and system for cooling a device for introducing materials into the interior of a highly heated chamber.

2. Description of the Prior Art In many industrial processes, such as in the refining of metals, it is necessary to introduce materials into highly heated chambers by means of material introduction devices. For example, in the steel industry, introduction devices known as lances are commonly used for introducing oxygen or oxygen enriched air into molten metal so that impurities in the metal are removed. Commonly, the lance nozzle is positioned beneath the surface of the molten metal thereby subjecting the lance to extremely high temperatures, e.g., 2,000F to 3,000F. To withstand these temperatures such introduction devices must be continuously cooled. Heretofore, the cooling has been accomplished by circulating a cooling medium, generally at high pressures, through heat exchange passages disposed in the device. While these prior cooling systems have been used successfully, often they have not removed heat from the device being cooled at a uniform rate, causing premature failure of the device. Also, the use of a liquid cooling medium such as water to cool such devices at relatively high pressures is dangerous in that upon failure of the device, leakage of the liquid cooling medium into the high temperature zone can result in explosions, etc.

By the present invention an improved process and system for cooling a device subjected to high temperatures is provided which includes circulating a coolant through the device at low pressures.

SUMMARY OF THE INVENTION The present invention relates to a process for cooling a device subjected to high temperatures which comprises the steps of flowing a stream of coolant through the device so that heat is transferred into the stream of coolant and the device is cooled, passing the resultant heated stream of coolant in heat exchange relationship with a cooled stream of a liquid heat transfer medium so that a quantity of heat is removed from the stream of coolant substantially equal to the heat removed from the device. passing the stream of coolant in heat ex change relationship with a heated stream of the liquid heat transfer medium so that the stream of coolant is maintained at a desired temperature level and recirculating the stream of coolant through the device. Systems for carrying out the process of the invention are also provided.

It is, therefore, a general object of the present invention to provide an improved process and system for cooling a device subjected to high temperatures.

A further object of the present invention is the provision of a process for cooling a device subjected to high temperatures wherein a stream of coolant is circulated through the device at low pressures so that heat is removed from the device at a uniform rate and the possibility of explosion is minimized.

Yet a further object of the present invention is the provision of a process for cooling a device subjected to high temperatures with a stream of coolant wherein a single liquid heat transfer medium'is utilized to achieve both heating and cooling of the stream of coolant.

Still another object of the present invention is the provision of a system for cooling a device subjected to high temperatures which is relatively simple and inexpensive to install and operate. I

Other and further objects and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments of the invention taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING In the DRAWING, a system of the present invention is illustrated in diagrammatic form.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the'drawing, a system of the present invention is illustrated diagrammatically, generallydesignated by the numeral 10. The system 10 is shown connected to a device 12 which may be any of a variety of devices which are subjected to high temperatures and which include heat exchange passages disposed therein for circulating a cooling medium therethrough. In the drawing, the device 12 is illustrated in the form of an oxygen lance, and includes an inner tubular member 16 having a pair of cylindrical

outer enclosure members

18 and 20 concentrically attached thereto. The tubular member 16 includes a nozzle at its lower end 17 for emitting oxygen into a highly heated chamher. The

enclosure members

18 and 20 form'annular passages for the flow of a stream of coolant which removes heat from the lance components and prevents the lance from becoming overheated.

The stream of coolant enters the lance 12 by way of a connection 22 disposed in the enclosure member 20 and flows through the annular space formed between the walls of the

enclosure members

18 and 20 to the other end 17 of the lance 12. The stream of coolant then enters the annular space formed between the walls of the enclosure member 18 and the tubular member 11 and flows to the other end of the lance 12 from where it exits by way of a connection 24 attached to the enclosure member 18.

The system 10 for circulating the stream of coolant through the device 12 so that the device 12 is continuously cooled includes a vessel 26 for charging the system 10 with coolant. The charge vessel 26 may take a variety of forms, but preferably includes an insulated outer enclosure 28 having inlet and

outlet connections

30 and 32 therein, and an inner shell 34 disposed within the outer enclosure 28. The inner shell 34 is positioned within the enclosure 28 in .a manner such that a passageway 35 is formed between the outer enclosure 28 and the inner shell 34 which is communicated with the inlet and

outlet connections

30 and 32. As will be described further hereinbelow, a heated liquid heat transfer medium is circulated through the passageway 35 of the vessel 26 and the inner shell 34 thereof forms a container for receiving a charge of coolant and maintaining it in the molten state. The charge vessel 26 further includes a coolant inlet connection 36 and a coolant outlet connection 38 which are attached to the inner shell 34 in a manner such that a stream of coolant can be flowed by way of the connections 36 and 38 to and from the inner shell 34 without communicating with the liquid heat transfer medium flow passage 35. The coolant outlet connection 38 is connected to a conduit 40 which is in turn connected to the inlet of a conventional pump 42 which has the capability of pumping the stream of coolant utilized. The conduit 40 includes an outer cylindrical shell 44 concentrically attached thereto in a manner such that an annular flow passage is formed between the conduit 40 and the shell 44. The discharge connection of the pump 42 is connected to a conduit 46 having a cylindrical shell 48 concentrically attached thereto so that an annular flow passage is formed between the conduit 46 and shell 48.; The conduit 46 is connected to the inlet connection 22 of the lance 12. The coolant outlet connection 24 of the lance 12 is connected to a conduit 50 which includes a cylindrical shell 52 concentrically attached thereto. The conduit 50 is connected to a conventional heat exchanger 54. Preferably, the heat exchanger 54 is of the shell and tube type with the conduit 50 connected to the tube side inlet connection thereof. The tube side outlet connection of the exchanger 54 is connected to a conduit 56 which is in turn connected to the coolant inlet connection 36 of the charge vessel 26 previously described. The conduit 56 includes an outer cylindrical shell 58 concentrically attached thereto forming a flow passage between the conduit 56 and the outer shell 58.

As will be understood, the various flow passages formed by the

cylindrical shells

44, 48, 52 and 58 and

conduits

40, 46, 50 and 56 respectively are connected together in series so that a stream of heated liquid heat transfer medium can be flowed through the flow passages and the various conduits are heated. That is, one end of the cylindrical shell 44 is connected to a conduit 60 which conducts the stream of heated liquid heat transfer medium thereto. The other end of the shell 44 is connected to the shell 48 by a conduit 62. The shell 48 is connected to the shell 52 by a conduit 64 and the shell 52 is connected to the shell 58 by a conduit 66. A conduit 68 is connected to the shell 58 for withdrawing the stream of heated liquid heat transfer medium as will be described further hereinbelow.

The system 10 includes a liquid heat transfer medium heating circuit comprised of a conventional heater 70 having a heating coil 72 disposed therein. The outlet connection 73 of the heating coil 72 is connected by a conduit 74 to the liquid heat transfer medium inlet connection 30 of the charge vessel 26. The liquid heat transfer medium outlet connection 32 of the charge vessel 26 is connected by a conduit 76 to a surge and expansion tank 77. The conduit 68 previously described connected to the cylindrical shell 58 is connected to the conduit 76, and a conduit 78 is also connected to the conduit 76. The other end of the conduit 78 is connected to the inlet of a conventional pump 80. The discharge of the pump 80 is connected to a conduit 82 which is in turn connected to the inlet connection 84 of the heating coil 72.

A liquid heat transfer medium cooling circuit is provided in the system 10 which includes a surge tank 86 having inlet and

outlet connections

88 and 90 disposed therein. The outlet connection 90 of the surge tank 86 is connected by a conduit 92 to the inlet connection of a conventional pump 94. The discharge connection of the pump 94 is connected by a conduit 96 to the shell side inlet connection of the heat exchanger 54. The shell side outlet connection of the exchanger 54 is connected by a conduit 98 to a conventional cooler 100. The cooler 100 may take any of a variety of forms, but is preferably a conventional forced atmospheric air heat exchanger. A conduit 102 connects the outlet connection of the cooler 100 to the inlet connection 88 of the surge tank 86.

A conduit 104 is connected between the conduit 96 and the conduit 82, and a shutoff valve 106 is disposed in the conduit 104. As will be understood by those skilled in the art, the system 10 includes conventional valves, instruments and controls (not shown) for controlling the flow rates, temperatures, and other conditions of the streams of coolant and liquid heat transfer medium flowing therethrough.

OPERATION OF THE SYSTEM 10 In operation of the system 10, a charge of the coolant material utilized to cool the device 12 is introduced into the charge vessel 26, i.e., into the inner shell 34 of the charge vessel 26. The coolant used can be any of a variety of metals, mixtures of metals or other materials having a melting point below about 600F. Preferably, the coolant is a metal or a mixture of metals which will not cause an explosion or other hazardous condition if it leaks into a highly heated chamber upon failure of the device 12. The most preferred coolant for use in accordance with the present invention is a eutectic mixture of lead and bizmuth having a melting point of about 270F.

A stream of heated liquid heat transfer medium is continuously circulated through the passage 35 of charge vessel 26 and through the heating circuit of the system 10. While a variety of liquid heat transfer materials may be used, a commercial high temperature heat transfer oil having a flash point above about 600F is preferred.

The liquid heat transfer medium is pumped by the pump 80 through the conduit 82 and through the heating coil 72 of the heater 70. While passing through the heating coil 72, the stream of liquid heat transfer medium is heated to a temperature of approximately 600F. The thus heated liquid heat transfer medium exits the flow coil 72 of the heater 70 and passes I through the conduit 74. A major portion of the stream of heated liquid heat transfer medium flows through the passageway 35 of the charge vessel 26 thereby heating the charge vessel 26 and the charge of coolant material contained therein. A minor portion of the heated liquid heat transfer medium flows from the conduit 74 into the conduit 60 and through the flow passages formed by the

shells

44, 48, 52 and 58 attached to the

conduits

40, 46, 50 and 56, and through the

conduits

62, 64 and 66 connecting the shells together in series. As will be understood, the

conduits

40, 46, 50 and 56 are heated by the flow of heated liquid heat transfer medium through the passages formed by the

cylindrical shells

44, 46, 52 and 58.

The portion of the liquid heat transfer medium flowing through the passageway 35 of charge vessel 26 exits the vessel 26 by way of the connection 32 and the conduit 76 and flows into the conduit 78. The portion of the liquid heat transfer medium flowing through the

cylindrical shells

44, 48, 52 and 58 passes by way of the conduit 68 into the conduit 76 where it combines with the portion from the vessel 26. The vessel 77 is connected to the conduit 76 and functions as a surge and thermal expansion chamber. The combined stream of liquid heat transfer medium passes from the conduit 76 through the conduit 78 into the suction of the pump 80. Thus, as will be understood, a stream of liquid heat transfer medium is continuously circulated through the heating circuit of the system 10, i.e., through the heater 70, the charge vessel 26, and the flow passages formed by the

shells

44, 48, 52 and 58 so that the coolant charged to the charge vessel 26 is melted and maintained at a desired temperature level, e.g., in the molten state, as it is circulated through the device 12.

A stream of coolant is pumped by the pump 42 to the device 12 by way of the conduit 46. The stream of coolant flows through the device 12 so that heat is removed therefrom and the resultant heated stream of coolant exits the device 12 by way of the conduit 50. From the conduit 50 the stream of coolant passes through the tube side of the heat exchanger 54 wherein a quantity of heat substantially equal to the heat removed from the device 12 is removed from the stream of coolant. From the heat exchanger 54 the stream of coolant passes by way of the conduit 56 through the inlet connection 36 of the charge vessel 26 and into the inner shell 34 thereof. From the charge vessel 26 the stream of coolant passes by way of the conduit 44 to the suction connection of the pump 42. The stream of coolant is continuously circulated through the device 12 and the system so that the device 12 is continuously cooled.

The stream of heated liquid heat transfer medium passing through the charge vessel 26 and the flow passages formed between the

shells

44, 48, 52 and 58 functions to maintain the stream of coolant at a desired minimum temperature as it is circulated. For example. when the coolant used is a metal or mixture of metals, the temperature thereof is maintained at a level so that the coolantremains in the molten state. Further. in the event the system 10 is shut down and the coolant allowed to solidify within the system 10, the solidified coolant can be quickly remelted by circulating the heated liquid heat transfer medium through the system 10 prior to starting circulation of the stream of coolant through the device 12.

A stream of the liquid heat exchange medium is continuously circulated through the shell side of the heat exchanger 54 and through the cooling circuit of the system 10 to continuously remove a quantity of heat from the stream of coolant substantially equal to the heat removed from the device 12. That is. a stream of liquid heat transfer medium is pumped by the pump 94 through the conduit 96 and into the shell side of the heat exchanger 54. As the stream of liquid heat transfer medium flows through the heat exchanger 54 it passes in heat exchange relationship with the stream of coolant so that heat is transferred from the coolant to the heat transfer medium. The thus heated liquid heat transfer medium flows from the heat exchanger 54 by way of the conduit 98 to the cooler 100. As will be anderstood. the quantity of heat removed from the stream of liquid heat transfer medium by the coolor 100 is controlled at a level equal to the quantity of heat added to the stream of liquid heat transfer medium as it passes through the heat exchanger 54. From the cooler 100 the stream of liquid heat transfer medium flows by way of the conduit 102 into the surge vessel 86. From the surge vessel 86, the stream of liquid heat transfer medium flows by way of the conduit 92 to the suction of the pump 94.

As the system 10 is operated to continuously cool the device 12 additional coolant required is added to the system 10 by way of the charge vessel 26. Prior to starting up the system 10 a quantity of liquid heat transfer medium is added to the surge vessel 86 through a fillv connection thereof (not shown). The pump 94 is then started so that a stream of the heat transfer medium is caused to flow through the cooling circuit of the system 10. The valve 106 disposed in the conduit 104 is next opened so that a quantity of the liquid heat transfer medium is caused to flow into the heating circuit of the system 10 and into the surge and expansion vessel 77 thereof. Once the system 10 is charged with liquid heat transfer medium in this manner, the pump is started to cause a stream of the liquid heat transfer medium to circulate through the heating circuit of the system 10. As the system 10 is operated additional liquid heat transfer medium required is added to the surge vessel 86.

The various streams of coolant and liquid heat transfer medium are circulated through the system 10 at low 7 pressure levels thereby allowing the use of low pressure equipment and obviating hazards associated with the operation of high pressure systems. Additionally, by the process and system of the present invention, a single liquid heat transfer medium is utilized for both cooling the stream of coolant used to cool the device 12 and maintaining the stream of coolant in the molten state.-

As mentioned above, the use of a stream of coolant such as a stream of molten metal is advantageous in that if the device 12 fails and the coolant enters a highly heated chamber into which the device 12 is inserted, the possibility of an explosion is minimized.

Thus, the present invention is well suited to carry out the objects and advantages mentioned as well those inherent therein. While presently preferred embodiments of the invention are given for the purpose of this disclosure, numerous changes in the details of the process and system and arrangement of steps and parts can be made which will readily suggest themselves to those skilled in the art andwhich are encompassed within the spirit of the invention and the scope of the appended claims.

What is claimed is:

i l. A process for cooling a-lance subjected to high temperatures which comprises the steps of:

a. flowing a stream of coolant having a melting point in the range of from about 270F to about 600F through said lance so that heat is transferred into the stream of coolant and the lance is cooled;

b. passing the resultant heated stream of coolant in heat exchange relationship with a cooled stream of a liquid heat transfer medium so that a quantity of 1 2. The process of claim 1 wherein the coolant is a eutectic mixture of lead and bizmuth.

3. The process of claim 2 wherein the liquid heat transfer medium is high temperature heat transfer oil having a flash point above about 600F.

4. A process for continuously cooling a lance for introducing materials into the interior of a highly heated chamber which comprises the steps of:

a. flowing a stream of molten metal through said device so that heat is transferred into the stream of molten metal and the device is cooled;

b. passing the resultant heated stream of molten metal in heat exchange relationship with a first stream of liquid heat transfer medium so that a quantity of heat is continuously removed from said stream of molten metal substantially equal to the quantity of heat transferred thereinto from said lance;

c. passing the stream of molten metal in heat transfer relationship with a second stream of liquid heat transfer medium so that the stream of molten metal is maintained in the molten state; and

d. continuously recirculating said stream of molten metal through said lance.

5. The process of claim 4 wherein the molten metal has a melting point below about 600F.

6. The process of claim 5 wherein the molten metal is a eutectic mixture of lead and bizmuth.

7. The process of claim 6 wherein the liquid heat transfer medium is high temperature heat transfer oil having a flash point above about 600F.

8. The process of claim 7 wherein the first stream of liquid heat transfer medium is continuously circulated in a cooling circuit wherein it is cooled to a temperature of about 1 l5F.

9. The process of claim 8 wherein the second stream of liquid heat transfer medium is continuously circulated in a heating circuit wherein it is heated to a temperature of about 600F.

10. A system for cooling a lance subjected to extra high temperatures, said system including a lance having heat exchange passages for circulating a stream of coolant therethrough to remove heat therefrom and which comprises:

a heated charge vessel for receiving and melting a charge of coolant, said charge vessel having coolant inlet and outlet connections disposed therein;

first conduit means connected between the heat exchange passages of said lance and the coolant inlet and outlet connections of said charge vessel;

first heat exchange means connected in said first conduit means for cooling the stream of coolant whereby a quantity of heat is removed therefrom substantially equal to the quantity of heat removed from said lance;

second heat exchange means connected to said charge vessel and to said first conduit means for heating said charge vessel and said first conduit means whereby the stream of coolant is maintained at a desired temperature level; and

pump means disposed in said first conduit means for circulating the stream of coolant through said conduit means, through the heat exchange passages of said lance, through the first and second heat exchange means and through the heated charge vessel.

11. The system of claim 10 wherein the first heat exchange means comprises:

a heat exchanger for passing the stream of coolant in heat exchange relationship with a cooled stream of liquid heat transfer medium;

means for cooling the stream of liquid heat transfer medium;

second conduit means connected between said heat exchanger and said means for cooling the stream of liquid heat transfer medium; and

pump means disposed in the second conduit means for continuously circulating the stream of liquid heat transfer medium through said second conduit means, said heat exchanger and said means for cooling the stream of liquid heat transfer medium.

12. The system of claim 11 wherein the means for cooling the stream of liquid heat transfer medium is an atmospheric air heat exchanger.

13. The system of claim 10 wherein the second heat exchange means comprises:

said charge vessel including heat exchange passages disposed therein for circulating heated liquid heat transfer medium therethrough whereby said charge vessel is heated;

said first conduit means including heat exchange passages for circulating heated liquid heat transfer medium therethrough whereby the conduit means are heated;

a liquid heat transfer medium heater;

third conduit means connected between the heat exchange passages of the charge vessel, the heat exchange passages of the first conduit means and the liquid heat transfer medium heater; and

pump means disposed in said third conduit means for circulating a stream of liquid heat transfer medium through the third conduit means, said heater and the heat exchange passages of the charge vessel and the first conduit means.

Claims

1. A process for cooling a lance subjected to high temperatures which comprises the steps of: a. flowing a stream of coolant having a melting point in the range of from about 270*F to about 600*F through said lance so that heat is transferred into the stream of coolant and the lance is cooled; b. passing the resultant heated stream of coolant in heat exchange relationship with a cooled stream of a liquid heat transfer medium so that a quantity of heat is removed from said stream of coolant substantially equal to the heat transferred thereinto from said lance; c. passing the stream of coolant in heat exchange relationship with a heated stream of the liquid heat transfer medium so that the stream of coolant is maintained at a desired temperature level; and d. recirculating the stream of coolant through said lance.

2. The process of claim 1 wherein the coolant is a eutectic mixture of lead and bizmuth.

3. The process of claim 2 wherein the liquid heat transfer medium is high temperature heat transfer oil having a flash point above about 600*F.

4. A process for continuously cooling a lance for introducing materials into the interior of a highly heated chamber which comprises the steps of: a. flowing a stream of molten metal through said device so that heat is transferred into the stream of molten metal and the device is cooled; b. passing the resultant heated stream of molten metal in heat exchange relationship with a first stream of liquid heat transfer medium so that a quantity of heat is continuously removed from said stream of molten metal substantially equal to the quantity of heat transferred thereinto from said lance; c. passing the stream of molten metal in heat transfer relationship with a second stream of liquid heat transfer medium so that the stream of molten metal is maintained in the molten state; and d. continuously recirculating said stream of molten metal through said lance.

5. The process of claim 4 wherein the molten metal has a melting point below about 600*F.

7. The process of claim 6 wherein the liquid heat transfer medium is high temperature heat transfer oil having a flash point above about 600*F.

8. The process of claim 7 wherein the first stream of liquid heat transfer medium is continuously circulated in a cooling circuit wherein it is cooled to a temperature of about 115*F.

9. The process of claim 8 wherein the second stream of liquid heat transfer medium is continuously circulated in a heating circuit wherein it is heated to a temperature of about 600*F.

10. A system for cooling a lance subjected to extra high temperatures, said system including a lance having heat exchange passages for circulating a stream of coolant therethrough to remove heat therefrom and which comprises: a heated charge vessel for receiving and melting a charge of coolant, said charge vessel having coolant inlet and outlet connections disposed therein; first conduit means connected between the heat exchange passages of said lance and the coolant inlet and outlet connections of said charge vessel; first heat exchange means connected in said first conduit means for cooling the stream of coolant whereby a quantity of heat is removed therefrom substantially equal to the quantity of heat removed from said lance; second heat exchange means connected to said charge vessel and to said first conduit means for heating said charge vessel and said first conduit means whereby the stream of coolant is maintained at a desired temperature level; and pump means disposed in said first conduit means for circulating the stream of coolant through said conduit means, through the heat exchange passages of said lance, through the first and second heat exchange means and through the heated charge vessel.

11. The system of claim 10 wherein the first heat exchange means comprises: a heat exchanger for passing the stream of coolant in heat exchange relationship with a cooled stream of liquid heat transfer medium; means for cooling the stream of liquid heat transfer medium; second conduit means connected between said heat exchanger and said means for cooling the stream of liquid heat transfer medium; and pump means disposed in the second conduit means for continuously circulating the stream of liquid heat transfer medium through said second conduit means, said heat exchanger and said means for cooling the stream of liquid heat transfer medium.

13. The system of claim 10 wherein the second heat exchange means comprises: said charge vessel including heat exchange passages disposed therein for circulating heated liquid heat transfer medium therethrough whereby said charge vessel is heated; said first conduit means including heat exchange passages for circulating heated liquid heat transfer medium therethrough whereby the conduit means are heated; a liquid heat transfer medium heater; third conduit means connected between the heat exchange passages of the charge vessel, the heat exchange passages of the first conduit means and the liquid heat transfer medium heater; and pump means disposed in said third conduit means for circulating a stream of liquid heat transfer medium through the third conduit means, said heater and the heat exchange passages of the charge vessel and the first conduit means.