Gas separation: processes – Selective diffusion of gases – Selective diffusion of gases through substantially solid...
Reexamination Certificate
2001-10-19
2003-07-01
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Selective diffusion of gases
Selective diffusion of gases through substantially solid...
C095S096000, C095S136000, C096S004000, C096S108000, C096S134000, C096S142000
Reexamination Certificate
active
06585801
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the method of operating a gas engine accommodating to sour gas, in which maintenance free, continuous operation of the gas engine for driving a compressor to pressure feed the gas in a gas field scattered in vast wasteland is made possible by the use of sweet gas decreased of hydrogen sulfide to such extent as causing no damage to the gas engine.
More specifically, the invention relates to the method of operating a gas engine accommodating to sour gas, in which sweet gas is created by separating hydrogen sulfide from a part of the compressed sour gas after removal of water and oil from the sour gas produced in a gas field to be pressure fed to a natural gas treating plant, the sweet gas is supplied to the gas engine to drive the compressor for compressing the sour gas, enabling maintenance free, continuous operation under the severe weather condition in a district where utilities such as electricity and water supply are not available and people seldom approach in winter season, and enabling atmospheric pollution preventing treatment by returning the separated hydrogen sulfide into the sour gas without releasing it to the atmosphere.
2. Description of the Related Art
In natural gas markets in the USA, Canada, and so forth, the natural gas is pressure fed by compressors driven by gas engines. Sweet gas not containing hydrogen sulfide has been used as fuel for gas engines in order to evade damage to the gas engines.
However, in recent years, sweet gas not containing hydrogen sulfide tends to be depleted, and the use of sour gas containing hydrogen sulfide is becoming unavoidable.
In the raw natural gas obtained in a gas field is contained frequently hydrogen sulfide and its concentration is often different according to the district where the gas field exist. This hydrogen sulfide generates corrosive substance when reacted with the water in the gas and induces corrosion in the gas engine to cause failure.
Under the situation where sweet gas not containing hydrogen sulfide is being depleted, the use of sour gas containing hydrogen sulfide is becoming unavoidable, and appearance of a gas engine which can accommodate to sour gas is strongly demanded.
On the other hand, when the sour gas is combusted as fuel, combustion gas containing a large amount of sulfur is exhausted from the gas engine, inducing environmental destruction due to atmospheric pollution. Now the situation is that the provision of an expensive exhaust gas treatment apparatus is inevitable for preventing air pollution even in the district where emission regulations are not enforced on the supposition that there also will be enforced regulations in near future.
Therefore, if it is possible to reduce sour gas to sweet gas containing less hydrogen sulfide on the fuel supply side to the gas engines, that makes possible the continued usage of conventional gas engine accommodating to sweet gas, and as the fuel is removed of said sulfur, SO
2
buildup after combustion is eliminated, which contributes to the suppression of environmental destruction.
As a means for excluding hydrogen sulfide from sour gas is used an adsorption type, membrane separator type, or combination of both type, and a variety of means are proposed and applied for patent.
Many of the adsorption type are disposable, and in the case of reusable type by reactivation, a heat source or gas for reactivation is needed, which requires time and cost.
On the other hand, a membrane separator type has an advantage in that it enables maintenance free, continuous operation for a prolonged time period when service condition is properly determined.
Inventions concerning the apparatus for making sweet gas utilizing membrane separator are disclosed in U.S. Pat. No. 4,370,150, and U.S. Pat. No. 6,053,965.
The usage of membrane separator type is thought to be most suitable in point of view of that sour gas field is located at a inconvenient place that does not allow permanent residence of people as mentioned above(without any sources of supplying cooling water and electricity, and a place where people can seldom approach during the winter season).
However, in the case of the membrane separator, there is a problem that the separating function can work with high efficiency for high pressure gas, but can not accommodate to low pressure gas at engine start.
Namely, when the membrane type separator is used, as high pressure gas can not be obtained for a while after starting, sweet gas removed of hydrogen sulfide can not be used during that time.
The invention described in the former patent office journal is shown in FIG.
2
. As seen in the drawing, sour gas
78
is compressed by a compressor
80
driven by a gas engine
81
to high pressure sour gas
83
a
to be pressure fed to an external plant. A part of the high pressure gas
83
a
, which is shown as
83
b
in
FIG. 2
is branched off to be introduced to membrane separator
82
, sweet gas
82
a
obtained therein is supplied to the gas engine
81
which drives the compressor
80
. The hydrogen sulfide gas
82
b
permeated through the membrane in the membrane separator
82
is returned to the suction part of the compressor
80
to be merged with the sour gas
78
.
The invention described in the latter patent office journal is shown in FIG.
3
. As seen in the drawing, sour gas
85
is compressed by a compressor
90
driven by a gas engine
91
to high pressure sour gas
86
to be pressure fed to an external plant. A part of the high pressure gas
86
is branched off, cooled in a heat exchanger
94
to be reduced to high pressure, low temperature gas, and introduced to a phase separator
95
where hydrocarbons
95
a
to be merged with the high pressure sour gas
86
are separated. Sweet gas
92
a
obtained by passing through the membrane unit
92
is reduced to low pressure low temperature sweet gas by the medium of an expansion valve
93
, the sweet gas
94
a
is heated in the heat exchanger
94
and supplied to the gas engine to drive the compressor
90
. The hydrogen sulfide
92
b
permeated through the membrane in the separator unit
92
is returned to the suction part of the compressor
90
to be merged with the sour gas
85
.
These two inventions for obtaining sweet gas for operating the gas engine to drive the compressor aim maintenance free, unattended operation for a prolonged period of time, and the features are as follows according to the disclosures.
1. Membrane Material
a) U.S. Pat. No. 4,370,150:
dimethyl silicone membrane, silicone polycarbonate membrane, polysulfone membrane with polyalkylsiloxane.
b) U.S. Pat. No. 6,053,965:
silicone rubber, polyamide-polyether block copolymer.
2. Temperature Adjustment of the Gas to be Treated
a) U.S. Pat. No. 4,370,150: not described.
c) U.S. Pat. No. 6,053,965:
cooled by the adiabatic expansion of treated gas.
3. Operating Method of the Gas Engine at Starting
a) U.S. Pat. No. 4,370,150: not described.
b) U.S. Pat. No. 6,053,965: not described.
In these inventions for obtaining sweet gas for operating the gas engine to drive the compressor by the use of membrane separator, temperature control which is most necessary in the separation by a membrane is not described, and the problem that sweet gas can not be obtained when the compressor output pressure is low for a while after starting is not considered.
Sour gas is frequently a gas saturated with water. The water and hydrogen sulfide in sour gas and the water contained in the air for the combustion in the gas engine cause not only deposit buildup and corrosion resulting in short life of the gas engine but also make the continuous operation impossible.
In the case of systems operated on gas fields in remote districts scattered in vast wasteland where utilities such as electricity and water supply is not always available as mentioned above, sufficient technical considerations should be given for each constituent apparatus to accommodate to the severe continuous operation under severe weather condition.
SUMMARY OF THE INVENTION
The present inv
Hattori Toshiro
Shinoda Yujiro
Yamada Kazue
Crowell & Moring LLP
Mayekawa Mfg. Co., Ltd.
Spitzer Robert H.
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