WO2005068920A1

WO2005068920A1 - System and method for cryogenic cooling using liquefied natural gas

Info

Publication number: WO2005068920A1
Application number: PCT/US2003/041738
Authority: WO
Inventors: Robert A. Shatten; John Carrier; Johnny Dean Jackson
Original assignee: Supercool Llc
Priority date: 2003-12-29
Filing date: 2003-12-29
Publication date: 2005-07-28
Also published as: AU2003300152A1

Abstract

A system and method for cooling a material with liquefied fuel gas where liquefied gas and the material to be cryogenically cooled are brought into direct or indirect contact and cooled material and a combination of liquefied gas and vaporized gas are removed. Cooling may also employ an intermediate cooling medium such as a refrigerant or nitrogen. In the case of converting rubber in tires (131) to rubber crumb (145), cooling of the products of a hammer mill (135) and a fine grind mill (142) by nitrogen subsequent to the cooling of nitrogen by a refrigerant and the refrigerant by liquefied gas converts shredded tires (131) into recyclable rubber crumb (148). Liquefied gas may also be used to cool electrical conductors. The vaporized gas, in either application, is then distributed to customers.

Description

Attorney Docket: 2598/101WO System and Method, for Cryogenic Cooling Using Liquefied Natural Gas Field of the Invention The invention relates generally to the generation of cryogenic cooling of materials by regassification of liquefied fuels or other gases, and, more particularly, to the application of cryogenic cooling to the cryogenic grinding of materials in production or recycling, such as elastomers, for example, and, more particularly, scrap tires.

Background of the Invention Most of the 270 million scrap tires produced in the U.S. are disposed of in landfills, converted to fuel, or recycled by shredding. Of these methods, cryogenic grinding and ambient wet attrition provide the highest resale value for the tire components and are the environmentally superior solutions by allowing for the creation of new products from these materials. These methods currently are used on less than 1 % of the scrapped tires. The traditional method of using liquid nitrogen to cool tires to below -200 °F adds approximately $0.40 - 0.6O in processing costs per tire. The use of air cooled to -202 °F by means of an on-site cryogenic air cooler has been claimed to have reduced refrigeration costs to $0.2O to $0.60 per tire. The wet attrition grinding method avoids the processing costs associated with the consumption of liquid nitrogen or refrigerated air, but is energy intensive and requires much specialized equipment that is expensive to buy and to maintain.

Summary of the Invention In accordance with, preferred embodiments of the invention, a method is provided for a converting a material into crumb and for vaporizing a liquefied fuel gas. The method has steps of shredding the material, transferring heat from the shredded material to the liquefied gas so as to cool the shredded material and to vaporize the gas, crashing the cooled, shredded material, separating the crushed, shredded material into components including crumb, and collecting the vaporized gas for distribution to customers. In accordance with, other embodiments of the invention, the method may also have a step of transferring heat from the crumb to the liquefied gas so as to cool the crumb, grinding the cooled crumb into ground product, and sorting the ground product into constituents, the constituents including fiber, steel, rubber crumb, and oversized rubber crumb. The final three steps may be repeated. Additional steps may include a. transferring heat from a first refrigerant to the liquefied gas; b. transferring heat from a second refrigerant to the first refrigerant; and transferring heat from the shredded tires to the second refrigerant, where the second refrigerant may be nitrogen, for example. Refrigeration of the crumb may also occur through an intermediary heat-transfer process that may include a plurality of gases. In accordance with further embodiments of the invention, crashing the cooled, shredded material may include crushing with a hammer mill, and grinding the cooled crumb may include grinding with a grinding mill. A system may be provided, in accordance with yet further embodiments of the invention, for grinding a material with liquefied gas. The system has a heat exchanger for transferring heat from the material to the liquefied gas for creating cryogenically glassified material, a mill for grinding the cryogenically glassified material into ground material, a transporter for removing ground material, and a distribution network for providing vaporized gas to customers. In accordance with yet another embodiment of the invention, a method is provided for cooling an electrical conductor to a superconducting transition temperature. The method has steps of: a. providing liquefied fuel gas; b. transferring heat from the electrical conductor to the liquefied natural gas, thereby vaporizing at least a portion of the liquefied natural gas to produce natural gas; and c. collecting the vaporized gas for distribution to customers. Brief Description of the Drawings The foregoing features of the invention will be more readily understood by reference to the following detailed description taken with the accompanying drawings: FIG. 1 is a process overview for using L G to provide cooling for materials, in accordance with preferred embodiments of the invention; Fig. 2a is a schematic depiction of direct cooling of recyclable material by LNG and Fig. 2b is a schematic depiction of indirect cooling of recyclable material flowing within a pipe by LNG flowing within a jacket surrounding the pipe, both in accordance with embodiments of the invention. FIG. 3 is a process flow sheet for the recycling, in accordance with embodiments of the current invention, of tire feedstock into rubber crumb where the tire feedstock is cooled by gaseous nitrogen which had been previously cooled by a refrigerant which had been first cooled by LNG.

Detailed Description of Specific Embodiments The present invention may further advantageously reduce refrigeration costs by exploiting the cryogenic refrigeration capacity of liquefied fuel gas, typically liquefied natural gas (LNG), stored at LNG receiving/distribution terminals. In the present description, the fuel gas will be referred to as LNG, without limiting the scope of the present invention and of any appended claims. By permitting exploitation of the lower temperatures associated with LNG, as opposed to liquefied air, for example, preferred embodiments of the present invention may, for example, permit reduction of the particle size of rubber crumb, the preferred powder end product of tire recychng. While detailed description is directed toward the embodiment of the invention for tire recychng, it is to be understood that other applications of cooling by means of regassifying fuels are within the scope of the present invention. These may include, without limitation, production operations, preparation of materials, or recycling of materials, including thermoplastics, theimosets, foodstuffs, chemicals, and agricultural products. Cryogenic grinding may be applied to thermoplastic particles, for example, for use as a substrate for antiviral or antimicrobial agents. Ultra- high molecular weight polymers may be cryogenically ground as drag reducing agents for flowing hydrocarbons, as taught, for example, in US Patent no. 6,399,676, to Labude, et al. In addition to application to the recychng of elastomers, as discussed below, cryogenic techniques are known to be applicable to the recychng of electronic components. Cryogenic tire recychng may advantageously complement the distribution of LNG in the following sense. LNG is delivered to the LNG terminal at -258 °F, but must be vaporized and heated to ambient temperature prior to distribution. A typical LNG terminal uses natural gas as a fuel to vaporize the LNG and both loses the benefit of the refrigeration capacity in the LNG and on average consumes approximately 2% of the total received liquefied natural gas in order to vaporize it. In accordance with certain embodiments of the invention, a slipstream or portion of liquefied natural gas from an LNG f acility vaporizes in the process of cryogenically coohng scrap tires. The vaporized natural gas remains in the facility's existing natural gas distribution infrastructure. This method is analogous to traditional cogeneration utilized at electric power stations where a portion of the steam energy remaining after expansion is used for heating instead of being wasted during condensation. In this case, the coohng capability of the LNG is harnessed instead of being wasted wheri the LNG is vaporized prior to distribution to customers. The coohng capability may be used for the coohng of electrical conductors to superconducting temperatures, and for recychng applications, as now discussed. Because LNG permits the inexpensive coohng of tires relative to current cryogenic techniques, embodiments of the invention produce a product more efficiently and cost effectively. In addition, the more refrigeration capacity utilized by the method, the more efficient both the LNG f acility and the cryogenic grinding facihty may become. This can enable finer grinding of materials significantly more cost effectively since finer grinding requires the most refrigeration. Conventional grinding takes place by cutting, attrition, impact actions upon the material, or by a combination of one or more of these techniques. Elastic materials can usually be most efficiently ground by cutting and attrition. Brittle materials can usually be most efficiently ground by impact because the feed material shatters into many smooth faceted pieces along crystal boundaries and microfissures. Many materials such as tire rabber are elastic at ambient temperatures but become brittle when cooled below their glass transition temperature. For rubber, cutting and attrition size reduction at ambient temperature requires several times the energy as does grinding embrittled rabber by impact. This grinding energy generates heat in the rubber crumb and can limit the capacity of the equipment. If the rubber is cooled below the glass transition temperature, impact grinding can be advantageously utilized to create crumb. Cooling the rubber to lower temperatures provides more capacity for grinding work to be performed on it without raising it above the glass transition temperature. This results in finer product. Fine mesh crumb rabber finds application beyond filling of asphalt. Uses include bound rubber products, new tire manufacturing, turf applications, athletic and recreational flooring applications, molded/extruded products, automotive parts, construction products, animal bedding, and modifiers to plastics. An embodiment of the invention where liquefied fuel gas, typically liquid natural gas (LNG) provides cryogenic coohng capacity for cryogenic scrap tire recychng is now described with reference to Fig. 1. LNG 101 at -258 °F is pumped by pump 102 at the LNG f acihty into heat exchanger 103, sized to meet the coohng requirements of a cryogenic tire recycling facility 100. Natural gas and residual hquefied natural gas 104 leave the heat exchanger and return to the hquefied natural gas f acility via return 105. The LNG flow rate is controlled via pressure P₂ of the natural gas and residual hquefied natural gas leaving the heat exchanger. Materials 106 such as scrap tires enter the heat exchanger and leave as cryogenic materials 107. Several heat exchanger types and arrangements may be used, including, but not limited to: direct contact, indirect coohng through the use of an intermediate coohng medium, such as air, nitrogen, heat transfer fluid, or other refrigerant, and indirect coohng in a jacketed pipe, where the recyclable material is pumped through a central pipe while LNG is pumped into a coohng jacket, preferably in a counter-current fashion. In the heat exchanger, the LNG is partially-to-fully vaporized and is subsequently returned to the LNG facihty. During vaporization, heat extracted from the recyclable material (either directly, indirectly, or via an intermediate coohng medium, such as air) cools the recyclable material to a temperature below its glass point (i.e. < -58 °F for styrene butadiene rabber (SBR) and -95 °F for natural rubber). SBR and natural rubber are the major components in tires although up to 6 or more rabber compounds are typically used in tires. At this temperature, the recyclable material can be ground into fine particles, greatly reducing grinding energy costs, as well as capital and maintenance costs. A complete discussion of cryogenic grinding of rubber may be found in Kohler, et al., "Enhancements in Cryogenic Fine Grinding", Rubber & Plastics News, June 1, 1998, pages 12-13. Examples of specific heat exchanger arrangements are shown in Figure 2. Figure 2a shows direct cooling of recyclable material 106 by liquefied natural gas (LNG) 101 in direct contact heat exchanger 108. The hquefied natural gas is converted into natural gas vapor 104. Recyclable material 106 enters the heat exchanger and leaves as cooled material 107. Figure 2b shows indirect cooling of recyclable material 106 to cryogenic materials 107 during passage through central pipe 109 surrounded by jacket 110. Liquefied natural gas 101 enters the jacket and a combination of natural gas and residual hquefied natural gas 104 leaves. Figure 3 shows coohng following two intermediate cooling stages. In a process of recychng tires now described with reference to Fig. 3, incoming tire feedstock 131, in accordance with embodiments of the invention, is continuously fed into a primary shredder 132 where it is reduced to a nominal 1" to 2" size. The size is controlled by a screen 133 in the discharge of the shredder that separates the oversized pieces 143 and returns them to the shredder. The tire pieces (not shown) are fed to cryogenic heat exchanger 113 where they are cooled with nitrogen gas 120 blown through the cryogenic heat exchanger by nitrogen blower 116 to below the glass transition temperature of rabber. Frozen, embrittled rubber 134 is then fed to primary hammer mill 135 where it is ground by impact of the hammers. The high intensity energy used for the grinding step causes rabber to be hberated from the steel and fiber components of the tire. The ground product 150 first passes through dryer 136 before entering separator classifier 137 where, through processes known in the art that may utilize magnets, screens, and aspiration, rabber is isolated. Drying is accomphshed by atmospheric air 151 heated in heater 141, cleaned by bag house 152, and drawn through the dryers 136 and 143 by blower 140. Most of the steel 138 is separated and collected in a condition suitable for recychng. The fiber 139, with some residual steel and rabber, is disposed of as a waste material. The energy expended in the grinding step normally raises the temperature of the rabber back to ambient temperature or higher. Because moisture causes fiber to foul the screen openings in the classifier separator, it is important to remove any residual moisture introduced with the feed material as well as any moisture that may have condensed on cold material that was exposed to moist air. After the drying step, the classifier removes fiber and steel and separates rabber crumb meeting desired product specifications 149 from rubber that is oversized 140. The oversized rubber crumb 140 from the separator classifier is again cooled below its glass transition temperature by cold nitrogen gas 120 in cryogenic heat exchanger 114. The embrittled rubber 141, along with cold nitrogen gas for supplemental refrigeration 120, is fed to a secondary fine grind mill 142 that is operated at higher energy intensity and lower temperature than the primary hammer mill. Following passage through dryer 143, another separator classifier 144 removes more the trace steel 146 and fiber 145 contaminants from the rabber and size classifies the rubber by screens into rubber crumb product 148 and oversize rubber crumb 147. The oversize crumb is returned to the cryogemc heat exchanger 114 preceding the fine grind mill 142 for further coohng and processing. The final product consists of pieces of metal wires, fiber, and finely ground rabber crumb. Product quality depends upon properties of the recycled material sucb. as particle size and contaminants such as metal, fiber, dirt, and stone dust. These properties, in turn, depend upon the degree of cooling achieved. By coohng rubber to a temperature well below its glass transition temperature, the process may advantageously produce rubber crumb with the cleanliness and particle size distribution commanding a market price premium. To reduce risk of fire, in accordance with a preferred embodiment of the invention, LNG 101 is isolated by using a suitable heat transfer fluid to transport refrigeration through a closed loop system into the plant. At the cryogenic tire facihty 100, refrigerant 118 is used to cool gaseous nitrogen 120 in cryogenic heat exchanger 112. Through this process, the refrigerant is warmed and is then pumped back to the LNG cryogenic heat exchanger 111 by refrigerant pump 115. A portion of the LNG stream is vaporized through the process of transferring the heat from the refrigerant 118 to the LNG. Auxihary vaporizer 117 completes the vaporization of the combined natural gas and hquefied natural stream 119 leaving the cryogenic heat exchanger. The resulting natural gas 153 is introduced into the natural gas system of the LNG facility. Nitrogen is one preferred heat transfer intermediary to be in direct contact with the rubber and to purge the mills. High transit temperatures and sparks created by the steel in the mills during grinding and conveying can ignite the fiber and fine rubber crumb. Maintaining an atmosphere in the equipment that does not have enoixgh oxygen to support combustion mitigates this risk. To reduce nitrogen costs, the nitrogen is recirculated following cleaning. There is makeup only for the nitrogen necessary to maintain the required low oxygen atmosphere. Having thus described various illustrative embodiments of the present invention, some of its advantages and optional features, it will be apparent that such embodiments are presented by way of example only and are not by way of limitation. Those skilled in the art could readily devise alternations and improvements on these embodiments, as well as additional embodiments, without departing from the spirit and scope of the invention. All such modifications are within the scope of the invention as claimed.

Claims

WE CLAIM:

1. A method for converting a material into crumb and for vaporizing a hquefied fuel gas, the method comprising: a. shredding the material; b. transferring heat from the shredded material to the hquefied gas so as to cool the shredded material and to vaporize the gas; c. crushing the cooled, shredded material; d. separating the crashed, shredded material into components including crumb; and e. collecting the vaporized gas for distribution to customers.

2. A method according to claim 1 , further comprising: a. transferring heat from the crumb to the hquefied gas so as to cool the crumb; b. grinding the cooled crumb into ground product; and c. sorting the ground product into constituents, the constituents including fiber, steel, rabber crumb, and oversized rubber crumb.

3. A method according to claim 2, further comprising repeating steps a through c.

4. A method according to claim 1, further comprising: c. transferring heat from a first refrigerant to the hquefied gas; d. transferring heat from a second refrigerant to the first refrigerant; and e. transferring heat from the shredded tires to the second refrigerant.

5. A method according to claim 4, wherein the second refrigerant is nitrogen.

6. A method according to claim 1 , further comprising: a. transferring heat from a first refrigerant to the hquefied gas ; b. transferring heat from a second refrigerant to the first refrigerant; and c. transferring heat from the crumb to the second refrigerant.

7. A method according to claim 6, wherein the second refrigerant is nitrogen.

8. A method according to claim 1, wherein crushing the cooled, shredded material includes crashing with a hammer mill.

5 9. A method according to claim 8, wherein grinding the cooled crumb includes grinding with a grinding mill.

10. A system for grinding a material with hquefied gas, the system comprising: a. a heat exchanger for transferring heat from the material to the hquefied gas for o creating cryogenically glassified material; b. a mill for grinding the cryogenically glassified material into ground material; c. a transporter for removing ground material; and d. a distribution network for providing vaporized gas to customers. 5

11. A system according to claim 10 wherein the heat exchanger comprises a container to which liquefied gas is added and from which vaporized gas is removed and to which material is added and from which cooled material is removed.

12. A system according to claim 11 , wherein the heat exchanger comprises:0 a. a pipe into which the material enters at one end and from which cooled material leaves at the other end; and b. a j acket surrounding the pipe having an input into which hquefied gas enters and an output from which a combination of hquefied gas and vaporized gas is extracted.5

13. A method for cooling an electrical conductor to a superconducting transition temperature, comprising: a. providing hquefied fuel gas; d. transferring heat from the electrical conductor to the hquefied natural gas,0 thereby vaporizing at least a portion of the hquefied natural gas to produce natural gas; and e. collecting the vaporized gas for distribution to customers.

14. A method according to claim 13, further comprising: a. transferring heat from a first refrigerant to the hquefied natural gas; b. transferring heat from a second refrigerant to the first refrigerant; and c. transferring heat from the electrical conductor to the second refrigerant.

15. A method according to claim 14, wherein the second refrigerant is nitrogen.

16. A method according to claim 15, further comprising: a. transferring heat from a refrigerant to the hquefied fuel gas; and b. transferring heat from the electrical conductor to the refrigerant.

17. A method according to claim 16, wherein the refrigerant is nitrogen.