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Use of alternate refrigerants in optimized cascade process

a cascade process and refrigerant technology, applied in the direction of lighting and heating apparatus, chemistry apparatus and processes, solidification, etc., can solve the problems of flammable materials, vapor cloud explosion, and certain inherent safety risks of hydrocarbon processing techniques

Inactive Publication Date: 2014-06-05
CONOCOPHILLIPS CO
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The present invention relates to methods for liquidizing natural gas using nonflammable refrigerants. The methods involve cooling the natural gas stream through indirect heat exchange with at least one nonflammable refrigerant during multiple refrigeration cycles. The use of nonflammable refrigerants helps to improve the safety and efficiency of the liquefaction process.

Problems solved by technology

While LNG and LNG facilities are generally considered safe there are certain inherent safety risks associated with hydrocarbon processing techniques.
One potential catastrophic outcome arising from an accidental release of flammable materials is a vapor cloud explosion.
As processing plants become more congested and confined, risk of explosion can increase.
Even short-duration deflagrations can result in significant damage to buildings, equipments, and people.
Potential damage is primarily a function of total amount of fuel burned, the maximum flame velocity that is achieved, and the manner in which the expansion of the combustion gases is contained.

Method used

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  • Use of alternate refrigerants in optimized cascade process
  • Use of alternate refrigerants in optimized cascade process
  • Use of alternate refrigerants in optimized cascade process

Examples

Experimental program
Comparison scheme
Effect test

example 1

[0052]In this Example, laminar burning velocities for various compounds were measured. The tests were performed using a constant-volume vessel in which gases were introduced using a partial pressure method, allowed to mix, and ignited. The resulting dynamic pressure trace was analyzed in order to calculate the LBV.

[0053]The measured LBV values are summarized in Table 1 below. The reactivity of a compound increases as LBV increases. This reactivity is typically a function of the strength of hydrogen bonding in the compound and not the heat of combustion or the thermal unit (e.g., BTU) value.

TABLE 1CompoundLBV (m / s)Methane~0.40Propane~0.46Ethylene~0.75Acetylene~1.55Hydrogen~3.25

[0054]FIG. 1 illustrates the results of an experiment in which various nonflammable refrigerants and compounds such as hydrofluoro-olefin (HFO1234yf), R-410A, and CO2 were added to propane. As the nonflammable refrigerant fraction increases, the laminar burning velocity decreases.

[0055]FIG. 2 illustrates the re...

example 2

[0056]Certain characteristics of an optimized cascade process improved when R-410A was used as a nonflammable refrigerant in place of propane. These characteristics were simulated using REFPROP (version 8) in the Aspen Physical Property System and verified against National Institute of Standards and Technology (NIST) tables. For example, the actual air compressor capacity (ACFM) decreased by 10-30% which allows for a smaller compressor bundle. R-410A also provides a greater vapor density (69.4 kg / m3) as compared to propane (25.6 kg / m3) which permits higher system mass flow and reduces pressure drop losses, allowing smaller diameter piping and smaller equipment to obtain the same refrigerant duty achieved by propane. Table 2 below summarizes simulated properties of R410A using Aspen HYSYS®, a modeling software available through Aspentech Technology, Inc. (Burlington, Mass.). These results suggest that R410A may be stable and behaves predictably throughout the given temperature range....

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PUM

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Abstract

Methods and systems for liquefying natural gas using nonflammable refrigerants are provided. Methods of liquefaction include cooling a natural gas stream via indirect heat exchange with a first nonflammable refrigerant selected from the group consisting of: difluoromethane, pentafluoromethane, trifluoromethane, hexafluoroethane, tetrafluoroethane, pentafluorethane, trifluoroethane, pentafluoroethane, any derivative thereof, and any combination thereof during a first refrigeration cycle; and cooling the natural gas stream via indirect heat exchange with a second refrigerant during a second refrigeration cycle.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a non-provisional application which claims benefit under 35 USC §119(e) to U.S. Provisional Application Ser. No. 61 / 733,304 filed Dec. 4, 2012, entitled “USE OF ALTERNATE REFRIGERANTS IN OPTIMIZED CASCADE PROCESS,” which is incorporated herein in its entirety.FIELD OF THE INVENTION[0002]The present invention relates generally to methods for liquefying natural gas. More particularly, but not by way of limitation, embodiments of the present invention include methods and systems for liquefying natural gas using nonflammable refrigerants.BACKGROUND OF THE INVENTION[0003]Natural gas is an important resource widely used as energy source or as industrial feedstock used in, for example, manufacture of plastics. Comprising primarily of methane, natural gas is a mixture of naturally occurring hydrocarbon gases and is typically found in deep underground natural rock formations or other hydrocarbon reservoirs. Other components of ...

Claims

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Application Information

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IPC IPC(8): F25J1/02F25J1/00
CPCF25J1/0022F25J1/0211C09K5/042C09K5/045F25J1/0097F25J1/0256F25J1/0278C09K2205/12C09K2205/22
Inventor DAVIES, PAULHARRIS, JR., JAMES LEETHOMAS, EMERY JAYSAPP, GREGG
Owner CONOCOPHILLIPS CO
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