Method of removing solid carbon dioxide

This application is a divisional of U.S. application Ser. No. 10/525,476 having a 35 U.S.C 371 date of Aug. 26, 2005 that was PCT filed Aug. 27, 2003 having PCT No. PCT/EP03/09575 claiming priority from Australian Patent Application No. 2002951005 filed Aug. 27, 2002, which are all incorporated herein by reference.

The present invention relates to a method of removing solid carbon dioxide (CO₂) from cryogenic equipment, in particular from cryogenic equipment used in gas conditioning or gas deep-extraction processes, and more particularly from cryogenic equipment used in the production of Liquefied Natural Gas (LNG).

Natural gas contains a wide range of species which are capable of forming solids during the cryogenic process of producing LNG known as liquefaction. One of the species that causes considerable problems to LNG producers is carbon dioxide. In a conventional LNG facility, pretreatment of the natural gas is conducted to decrease the carbon dioxide content to between 50 and 125 ppm prior to the natural gas entering the liquefaction process.

On average, carbon dioxide compositions in a natural gas feed stream can range between 0.5% and 30% mol and can be as high as 70% mol in commercially viable reservoirs like Natuna, Indonesia. Carbon dioxide is typically removed using chemical reactions such as reversible absorption processes with amine solvents. These are expensive and complex processes and commonly encounter operational problems such as foaming, corrosion, blocked filters and amine degradation. Losses of amine, water and hydrocarbons are commonly encountered. These processes also consume significant amounts of energy to regenerate and pump the solvent.

LNG refrigeration systems are expensive because so much refrigeration is needed to liquefy natural gas. A typical natural gas stream enters a LNG plant at pressures from about 40 bar to about 76 bar and temperatures from about 20° C. to about 40° C. Natural gas, which is predominantly methane, cannot be liquefied by simply increasing the pressure, as is the case with heavier hydrocarbons used for energy purposes. The critical temperature of methane is −82.5° C. This means that methane can only be liquefied below that temperature regardless of the pressure applied. Since natural gas is a mixture of gases, it liquefies over a range of temperatures. The critical temperature of natural gas is typically between about −85° C. and −62° C. Natural gas compositions at atmospheric pressure will typically liquefy in the temperature range between about −165° C. and −155° C. Since refrigeration equipment represents such a significant part of the LNG facility cost, cleaning of this equipment is important.

In conventional LNG plants, the natural gas is typically cooled in one or more heat exchangers. If insufficient carbon dioxide is removed prior to the natural gas entering the heat exchangers, carbon dioxide precipitates as a solid and accumulates on the cold surfaces of the heat exchangers and other plant equipment eventually rendering these items inoperable. When fouling has reached a critical level, the vessel must be taken off-line for the carbon dioxide solids to be removed. This can be achieved by warming-up the affected equipment. However, this causes considerable downtime and energy-loss for the plant. Alternatively, the solid carbon dioxide may be removed mechanically. In such a case of mechanical defouling of equipment, the vessel, baffles and/or pipework may be damaged, which only encourages further fouling in the next production cycle. Moreover, solids condensing on metal surfaces form an insulating film reducing the thermal efficiency of the heat exchanger.

There is a need for a simpler, more economical process for the removal of solid carbon dioxide that has fouled plant equipment under cryogenic conditions.

According to one aspect of the present invention, there is provided a method of removing solid carbon dioxide from cryogenic equipment, the method comprising the steps of:

(a) introducing a stream including ethane to said cryogenic equipment to convert solid carbon dioxide to liquid form whereby a mixture of liquid ethane and liquid carbon dioxide is formed; and
(b) removing the mixture of liquid ethane and carbon dioxide from the cryogenic equipment.

According to another aspect of the present invention, there is provided a method of removing carbon dioxide fouling of cryogenic equipment containing LNG, the method comprising the steps of:

(a′) removing the LNG from the said cryogenic equipment;
(a) introducing a stream including ethane to convert solid carbon dioxide to liquid form whereby a mixture of liquid ethane and liquid carbon dioxide is formed; and
(b) removing the mixture of liquid ethane and liquid carbon dioxide from the cryogenic equipment whereby the cryogenic equipment is defouled of solid carbon dioxide and available for the reintroduction of the LNG stream.

Continue reading about Method of removing solid carbon dioxide...
Full patent description for Method of removing solid carbon dioxide

Brief Patent Description - Full Patent Description - Patent Application Claims

Click on the above for other options relating to this Method of removing solid carbon dioxide patent application.

Patent Applications in related categories:

20090282864 - Iso-pressure open refrigeration ngl recovery - The present invention relates to an improved process for recovery of natural gas liquids from a natural gas feed stream. The process runs at a constant pressure with no intentional reduction in pressure. An open loop mixed refrigerant is used to provide process cooling and to provide a reflux stream ...

20090282865 - Liquefied natural gas and hydrocarbon gas processing - A process for the recovery of ethane, ethylene, propane, propylene, and heavier hydrocarbons from a liquefied natural gas (LNG) stream and a hydrocarbon gas stream is disclosed. The LNG feed stream is divided into two portions. The first portion is supplied to a fractionation column at a first upper mid-column ...


###


How KEYWORD MONITOR works... a FREE service from FreshPatents
1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored.
3. Each week you receive an email with patent applications related to your keywords.  
Start now! - Receive info on patent apps like Method of removing solid carbon dioxide or other areas of interest.
###


Previous Patent Application:
Multiple reflux stream hydrocarbon recovery process
Next Patent Application:
Multiple reflux stream hydrocarbon recovery process
Industry Class:


###