Refrigeration – Processes – Circulating external gas
Reexamination Certificate
1999-10-29
2001-03-20
McDermott, Corrine (Department: 3744)
Refrigeration
Processes
Circulating external gas
C062S179000
Reexamination Certificate
active
06202424
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a system for treating and compressing contaminated gas (water saturated, heavy hydrocarbon natural gas with corrosive impurities etc.) which effectively compresses gas so as to process the contaminated gas into a less polluted, easier to handle and usable gas. Sources of contaminated gas are gas ejected from oilfields etc., off-gas, and vapor-recovery gas etc. discharged from heavy chemical industry facilities.
2. Description of the Related Art
Since natural gas produced along with crude oil from onshore and offshore oil production fields is typically a water saturated, heavy hydrocarbon gas contaminated with corrosive substances such as H
2
S (hydrogen sulfide), a system for performing a designated compression for such gas, in a stage prior to refinement or liquefaction, must change the contaminated gas into a more “user friendly” gas without being affected by the aforementioned water etc., so as to enable an effective compression.
However, historically, no where in the market place was there an offered system for compressing or liquefying gas which enabled effective, easy and low-cost compression and liquefaction, without any adverse effects to the system caused by contaminants, H
2
S, water and the like. For this reason, such contaminated natural gas was turned in the atmosphere at plant flare of a platform.
Obviously, since such burning and releasing impurity rich natural gas into the atmosphere are recognized as factors contributing to environmental pollution, and recently there has been a growing requirement to be able to easily compress or liquefy such natural gas, without suffering any adverse effects from the water and the like, and to make good use of the gas as an energy source, and resources.
For example, an invention disclosed in Japanese Patent Publication No. 5-59378 A is a technique of producing liquefied gas from unprocessed gas effusing from small offshore oil and gas production fields by separating the gas from liquid and solid materials, drying the gas, and cooling to liquefy the gas under pressure.
As for a liquid separating means, a drum liquid separator, as disclosed in published Japanese Unexamined Utility Model Application No. 63-20600, is well known to the public.
In published Japanese Examined Utility Model Application No. 2-45519, a volumetric oil injection type compressor, more specifically an oil injection type screw compressor used at Freon gas plants and COG (coke oven gas) refinement plants, is disclosed.
However, no technique has been disclosed where a compressing system effectively compresses contaminated gas with water, etc., (hereafter referred to as natural gas) such as natural gas, off-gas, and vapor-recovery gas without suffering from any adverse effects of toxic substances, including impurities, in the natural gas.
SUMMARY OF THE INVENTION
The present invention has been conceived to directly address the scenarios described above, and it is accordingly an object of the present invention to provide a compression system to effectively compress natural gas without suffering from any adverse effects caused by toxic substances, including impurities.
To achieve the object mentioned above, the present invention is a system for compressing contaminated gas (hereafter referred to as natural gas), which effectively compresses contaminated gas including water or natural gas contaminated with corrosive substances and saturated water, comprising
a path which heats a compressor, using a gas with a low dew-point temperature, such as water free gas or purified gas from outside the system, that is substantially free of water, or discharged gas after being compressed by the compressor;
a separator provided upstream of the suction section of the compressor, which separates water and the like from natural gas by cooling and condensation; and
a means for maintaining the temperature of gas discharged from the compressor above the dew-point temperature of the compressed gas, when compressing natural gas from which water etc. has been separated by the separator,
wherein a heating operation is performed using gas with a low dew-point temperature, such as discharged gas which has been compressed by the compressor, or water-free gas and purified gas, whereas contaminated gas contaminated with water, etc. is not sucked into the system while using said path during the heating operation.
The path which performs the heating operation may be a bypass pipe which is arranged to connect the system discharge line (including a non-return valve) to the inlet side of the compressor on the downstream side of the suction block valve, or the path may be a return pipe which returns gas from outside the system to the inlet side of the compressor.
In a concrete manner, an outlet of the bypass or return pipe is connected to a point located downstream of a shut-off valve, which introduces natural gas and the like to the compressor, and in this case, during the heating operation of the compressor, the shutoff valve is closed, so that only gas used for the heating operation is supplied.
Moreover, when providing gas for the heating operation through the heating path, a gradual rise in the compressor discharge pressure is enabled by controlling the suction pressure of the compressor by adjusting an opening of a valve on the heating operation path.
A temperature controller for the bypass gas is provided, when the path that performs a heating operation is the bypass line which recycles a portion of the compressed gas.
Furthermore, in a compression system using an oil injecting type compressor, a dew-point maintenance means is provided by controlling the temperature of discharged gas by temperature control of the injected oil. More specifically, the compressor is an oil injecting type compressor, and in a system for compressing gas equipped with an oil separator which separates oil from the oil-mixed compressed gas discharged from the compressor, a dew-point maintenance means is provided in an oil circulation path which connects an oil storage section in the separator and an oil injecting site in the compressor.
A temperature controller, such as a refrigerator which is capable of adjusting the temperature of the natural gas at the suction end of the compressor, is provided upstream of the separator.
According to the present invention, the operating life of the compressor may be extended, since a natural gas operation is performed after the operation of the compressor by gas with a low dew-point temperature, such as compressed gas discharged from the compressor, or inert gas like N
2
gas, water-free gas, and purified gas, which prevents interference with the operation of a compressor caused by water and other contaminants within the natural gas during heating operation.
Moreover, during the heating operation of the compressor, condensation of the discharged gas may be prevented by adjusting an opening of a valve on the bypass which opens and shuts the bypass pipe where the gas for heating operation flows, and controlling the suction pressure of the compressor, which enables a gradual rise in the pressure of the discharged gas, so that an excess rise of the dew-point temperature of the discharged gas is relieved.
Also, according to the present invention, by carrying under temperature control stored oil within the separator of a discharging side to the compressor via a circulation pipe, and by injecting temperature controlled oil into the compressing chamber, the temperature of the gas discharged from the compressor is maintained above the dew-point temperature, so as to prevent damage to the function and durability of the compressor caused by residual water, etc. in the natural gas.
Furthermore, lubrication of the compressor is well maintained by an oil purifying means provided on the circulation pipe, which enables cleaned oil to be supplied to the compressor at all times.
By means of the aforementioned controls, condensation and liquefaction of any of the contaminated gas compounds is avoided, and seizi
Hattori Toshiro
Kaneko Fumihiko
Evenson McKeown Edwards & Lenahan PLLC
Jiang Chen-Wen
Mayekawa Mfg. Co., Ltd.
McDermott Corrine
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