U.S. patent application number 13/414108 was filed with the patent office on 2012-07-05 for method of processing gas associated with oil.
Invention is credited to Franz POCKSTALLER, Guenther Wall.
Application Number | 20120167621 13/414108 |
Document ID | / |
Family ID | 43446560 |
Filed Date | 2012-07-05 |
United States Patent
Application |
20120167621 |
Kind Code |
A1 |
POCKSTALLER; Franz ; et
al. |
July 5, 2012 |
METHOD OF PROCESSING GAS ASSOCIATED WITH OIL
Abstract
The invention relates to a method for producing combustible gas
for gas engines from associated gas obtained during oil production,
the associated gas containing methane, ethane, propane,
hydrocarbons having more than three carbon atoms, and optionally
propene, wherein a gaseous fraction and a liquid fraction are
obtained by partially condensing the associated gas, wherein the
condensation process is performed under such pressure and
temperature conditions that the liquid phase is substantially free
from methane, ethane, propane, and optionally propene, and that
substantially the entire methane, ethane, propane, and optionally
propene are contained in the gaseous phase.
Inventors: |
POCKSTALLER; Franz;
(Jenbach, AT) ; Wall; Guenther; (Bad Haering,
AT) |
Family ID: |
43446560 |
Appl. No.: |
13/414108 |
Filed: |
March 7, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/AT2010/000362 |
Oct 1, 2010 |
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13414108 |
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Current U.S.
Class: |
62/618 |
Current CPC
Class: |
F25J 2260/60 20130101;
C10L 3/12 20130101; F25J 3/0635 20130101; F25J 2290/12 20130101;
F25J 3/061 20130101; F25J 3/065 20130101; C10L 3/10 20130101 |
Class at
Publication: |
62/618 |
International
Class: |
F25J 3/08 20060101
F25J003/08 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 2, 2009 |
AT |
A 1557/2009 |
Claims
1. A method of producing combustible gas for gas engines from
associated gas which is produced in crude oil production and which
contains methane, ethane, propane, hydrocarbons having more than
three carbon atoms and optionally propene, wherein a gaseous
fraction and a liquid fraction are obtained by partially condensing
the associated gas, characterized in that the condensation process
is performed under such pressure and temperature conditions that
the liquid phase is substantially free from methane, ethane,
propane and optionally propene, and substantially the entire
methane, ethane, propane and optionally propene is contained in the
gaseous phase.
2. A method as set forth in claim 1 characterized in that the
condensation process is performed at a temperature of between -5
degrees Celsius and -14 degrees Celsius.
3. A method as set forth in claim 2 characterized in that the
condensation process is performed at a temperature of between -7
degrees Celsius and -12 degrees Celsius.
4. A method as set forth in claim 1 characterized in that the
condensation process is effected in a plurality of stages, wherein
cooling is effected to a temperature of between -5 and -8 degrees
Celsius in one stage and to a temperature of between -8 and -12
degrees Celsius in a further stage.
5. A method as set forth in claim 1 characterized in that the
pressure in the condensation process is between 1 bar and 16 bars,
preferably between 10 bars and 16 bars, particularly preferably
between 14 bars and 16 bars.
6. A method as set forth in claim 1 characterized in that the
gaseous fraction has a methane number of at least 40, preferably at
least 45.
7. A method as set forth in claim 1 characterized in that the
gaseous phase is substantially free from n-butane and
isobutane.
8. A method as set forth in claim 1 characterized in that water
vapor which is possibly present in the associated gas is
removed.
9. A method as set forth in claim 8 characterized in that the water
vapor is removed by condensation, absorption or combinations
thereof.
Description
[0001] The invention concerns a method of producing combustible gas
for gas engines from associated gas which is produced in crude oil
production and which contains methane, ethane, propane,
hydrocarbons having more than three carbon atoms and optionally
propene, wherein a gaseous fraction and a liquid fraction are
obtained by partially condensing the associated gas.
[0002] In crude oil production from crude oil deposits by means of
crude oil production stations an associated gas is produced, which
almost exclusively consists of hydrocarbons. This involves a
mixture of different gaseous hydrocarbons, primarily alkanes and
alkenes. That associated gas is frequently referred to as
"associated petroleum gas" or APG, and earlier also as "flare
gas".
[0003] It will be noted however that this associated gas is
unsuitable for feeding into a gas pipeline as, in comparison with
natural gas which contains methane as its main component, it has a
complex mixture of different hydrocarbons. Consumers which are
optimized for given gas compositions and gas qualities cannot be
optimally operated with such mixtures. Therefore that associated
gas has long been of low significance for energy utilization. For
many years it was burnt without being put to use, and the earlier
term of "flare gas" is also derived from that consideration. That
method is not only environmentally harmful but it also represents a
waste of valuable resources.
[0004] A possible way of using the associated gas involves
combustion in boilers operated with gas burners. It will be noted
however that the thermal energy requirement at the oil production
stations which are situated in the most exposed locations is
generally not as great as there is associated gas. Direct
utilization of the gas, by it being burnt in gas engines operated
on the basis of the Otto cycle in order to produce power by means
of a generator as a further consequence falls foul of the
excessively low methane number of the associated gas. The methane
number is a measurement in respect of anti-knock quality and an
excessively low methane number means that the anti-knock quality of
the associated gas is excessively low to convert it into power and
heat with co-generating heat and power installations.
[0005] To make the associated gas useable for combustion in a gas
engine using the Otto cycle a gas processing installation generally
has to be disposed upstream of the gas engine. Different
technologies are known for that purpose, inter alia the membrane
technology or cooling the gas to extremely low temperatures. In
that respect it is usual to produce almost natural gas quality,
that is to say to increase it to a methane content of over 85%.
Deposited higher-grade hydrocarbons can further be used as a
valuable substance by cracking or by direct thermal
utilization.
[0006] The membrane technology for processing associated gases
represents a relatively high technical and financial involvement.
The alternative, cooling the gas with the aim of providing that the
higher-grade hydrocarbons condense out, is also very complicated
and expensive, nonetheless requiring very low temperatures of the
order of magnitude. Thus for example propane (C.sub.3H.sub.8)
becomes liquid at -42 degrees Celsius, and ethane (C.sub.2H.sub.6)
even becomes liquid only at -89 degrees Celsius. Such temperatures
can be produced for example with turbo-expanders. That also
requires a very high level of technical and financial
implementation.
[0007] WO 2007/070198 A2 presents a method of processing associated
gas in crude oil production. That method primarily involves
producing a methane-rich gaseous phase and a liquid phase with a
low methane content. In that respect different pressure and
temperature conditions are referred to, wherein attention is
primarily directed to very low temperatures and very high pressures
so that this affords a gaseous phase containing almost exclusively
methane and small traces of ethane. It will be noted however that
the liquid phase produced in that case still has a high methane and
ethane content, which can be deduced from the described method
conditions and examples. That however is also understandable as the
production of a liquid phase with a high useful energy value is in
the forefront in WO 2007/070198 A2.
[0008] The methods applied hitherto, in which the associated gas
was cooled to such low temperatures and pressures that almost pure
gaseous methane and a condensate with the other hydrocarbons is
produced, is extremely complicated and expensive in energy terms as
cooling to the boiling point of ethane or ethene is required to
achieve enrichment of methane in the gaseous phase. WO 2007/070198
A2 allows certain residues of hydrocarbon compounds with two carbon
atoms in the gas. It will be noted however that the choice of the
method conditions provides that the liquid phase has a very high
methane content which is naturally at the expense of the quality of
the gaseous phase obtained. The gaseous phase obtained is therefore
suitable for implementation in a gas engine in view of the methane
number but the complicated and expensive method conditions make
operation of the gas engine uneconomical. The high-grade liquid
phase obtained however still has to be transported away.
[0009] The object of the present invention is to improve the method
of the kind set forth in the opening part of this specification
such that the products obtained can be better employed in further
utilization. In particular the invention seeks to provide that the
gaseous fraction obtained can be burnt in a gas engine operated on
the basis of the Otto cycle in order to produce power and heat by
way of a co-generating heat and power installation. In that respect
production of the gaseous fraction is to be as inexpensive as
possible from the economic point of view by making use of the
prevailing temperature and pressure conditions of the associated
gas obtained in oil production.
[0010] In a method of the general kind set forth in the opening
part of this specification that object is attained in that the
condensation process is performed under such pressure and
temperature conditions that the liquid phase is substantially free
from methane, ethane, propane and optionally propene, and
substantially the entire methane, ethane, propane and optionally
propene is contained in the gaseous phase.
[0011] The basic idea of the invention, in the production of
associated gas, is to transfer hydrocarbons with a high methane
number into the gas phase and to condense out hydrocarbons with a
low methane number. That provides a gaseous mixture which contains
substantially all the methane, ethane, propane and possibly
propene. In that way the methane number in the gaseous phase and
thus also the anti-knock quality of the gas can be increased. The
particular realization is that hydrocarbons with more than three
carbon atoms enormously reduce the anti-knock quality while
hydrocarbons with up to three carbon atoms can be excellently well
used in a gas engine. In particular n-butane and isobutane are
responsible for the anti-knock rating being reduced while a gas
with the main constituents methane, ethane and propane (optionally
also propene) has a methane number which is excellently well suited
for implementation in gas engines, in particular also those with
upstream-connected compressor devices. The aim therefore is to
separate off n-butane and isobutane.
[0012] In contrast to the state of the art therefore a particularly
high-grade gaseous phase can be obtained in that way, with the
valuable constituents methane, ethane and propane, while the liquid
phase contains the higher-grade hydrocarbons, wherein that phase is
still excellently well suited for possible further utilization.
From that point of view the liquid phase with a high methane
content, as is obtained in accordance with WO 2007/070198 A2, is a
waste when considered in energy terms as gas engines are markedly
more sensitive than installations for combustion of the liquid
phase produced. The gas obtained in accordance with WO 2007/070198
A2 is also not optimum in terms of energy yield as a large part of
the methane is lost.
[0013] It is preferably provided in accordance with the invention
that the condensation process is performed at a temperature of
between -5 degrees Celsius and -14 degrees Celsius. Particularly
preferably the temperature range is between -7 degrees Celsius and
-14 degrees Celsius. As the boiling point of isobutane is -11.7
degrees Celsius, it is therefore desirable if the temperature is
below -11.7 degrees Celsius. In many geographical areas of use of
the method the prevailing ambient temperatures are in the region of
those values so that expensive cooling can thereby either be
entirely avoided or can be effected in correspondingly inexpensive
fashion, thereby permitting economically particularly advantageous
production of the gaseous fraction.
[0014] It is preferably provided that the condensation process is
effected in a plurality of stages, wherein cooling is effected to a
temperature of between -5 and -8 degrees Celsius in one stage and
to a temperature of between -8 and -14 or -12 degrees Celsius in a
further stage. In that way low-boiling hydrocarbons can be
collected in a first fraction and higher-boiling hydrocarbons can
be collected in a second liquid fraction. In that way however it is
also possible for any water contained in the associated gas to be
condensed in a first step.
[0015] It is advantageous under the above-selected temperature
conditions if at the same time certain pressure conditions are set
as temperature and pressure are responsible for the condensation
characteristics of gases. It is preferably provided in that respect
that the pressure in the condensation process is between 1 bar and
16 bars, preferably between 10 bars and 16 bars, particularly
preferably between 14 bars and 16 bars. In many cases the
associated gas produced in crude oil production issues at a
pressure in the region of those values so that the choice of that
range permits economically particularly advantageous production of
the gaseous fraction. In addition the costs of pressure equipment
for pressures to be generated of up to 16 bars are relatively low
in comparison with pressure equipment in a higher pressure
equipment category.
[0016] It is further preferably provided that the gaseous fraction
has a methane number of at least 40, preferably at least 45. The
methane number as a measurement of the anti-knock quality of the
engine is important for the further purpose of use. In the present
case the gaseous fraction obtained is in fact to be used in a gas
engine so that there should be a methane number of at least 40,
preferably at least 45.
[0017] In addition in a variant it can be provided that the gaseous
phase is substantially free from n-butane and isobutane.
[0018] In a further variant it can be provided that water vapor
which is possibly present in the associated gas is removed. In that
respect it is possible to use for example absorption agents and
molecular sieves like zeolites or known drying agents like
inorganic salts. A composition of a possible associated gas from an
oil production station will now be described by reference to an
example in following Table 1:
TABLE-US-00001 TABLE 1 Composition of an associated gas (Example):
Compound Mol. % CO.sub.2 0.05 N.sub.2 3.78 Methane CH.sub.4 36.67
Ethane 15.29 Propane 23.17 Isobutane 6.16 n-Butane 9.73 Isopentane
2.08 n-Pentane 1.88 Hexane 0.76 Cyclohexane 0.06 Heptanes 0.18
Octanes 0.14 Nonanes 0.04 Decanes and higher-grade 0.01
hydrocarbons Total 100
[0019] The mixture described in the Table has a methane number of
32.7 and is not suitable for combustion in an Otto-cycle gas
engine. After cooling to about -14 degrees Celsius there was a
gaseous mixture which almost exclusively consisted of methane,
ethane and propane and has a methane number of 45. In addition the
gas contains traces of carbon dioxide and nitrogen. The other
constituents are almost completely contained in the condensate.
Following Tables 2 and 3 also show once again the difference
between the subject-matter of the invention and the state of the
art.
TABLE-US-00002 TABLE 2 Gas processing by cooling to -12 degrees
Celsius Compound Boiling point (.degree. Celsius) H.sub.2 Hydrogen
-253 N.sub.2 Nitrogen -196 CO Carbon monoxide -192 O.sub.2 Oxygen
-183 CH.sub.4 Methane -162 C.sub.2H.sub.4 Ethene -104
C.sub.2H.sub.6 Ethane -89 CO.sub.2 Carbon dioxide -79
C.sub.3H.sub.6 Propene -48 C.sub.3H.sub.8 Propane -42
C.sub.4H.sub.10 Isobutane -12 C.sub.4H.sub.10 n-Butane -1
C.sub.5H.sub.12 Isopentane 28 C.sub.5H.sub.12 Pentane 36
C.sub.5H.sub.12 n-Pentane 36 C.sub.6H.sub.14 Hexane 69
C.sub.6H.sub.6 Benzene 80 C.sub.7H.sub.16 Heptane 98
TABLE-US-00003 TABLE 3 Gas processing by cooling to -48 degrees
Celsius Compound Boiling point (.degree. Celsius) H.sub.2 Hydrogen
-253 N.sub.2 Nitrogen -196 CO Carbon monoxide -192 O.sub.2 Oxygen
-183 CH.sub.4 Methane -162 C.sub.2H.sub.4 Ethene -104
C.sub.2H.sub.6 Ethane -89 CO.sub.2 Carbon dioxide -79
C.sub.3H.sub.6 Propene -48 C.sub.3H.sub.8 Propane -42
C.sub.4H.sub.10 Isobutane -12 C.sub.4H.sub.10 n-Butane -1
C.sub.5H.sub.12 Isopentane 28 C.sub.5H.sub.12 Pentane 36
C.sub.5H.sub.12 n-Pentane 36 C.sub.6H.sub.14 Hexane 69
C.sub.6H.sub.6 Benzene 80 C.sub.7H.sub.16 Heptane 98
[0020] As can be seen from Tables 2 and 3 the subject-matter of the
invention (Table 2) provides that all gaseous constituents with
boiling points below isobutane are collected in the gaseous phase
and those with a boiling point thereabove are collected in the
condensate. In the state of the art (Table 3) which involves
cooling to -48 degrees Celsius enrichment in the gaseous phase is
effected exclusively in respect of those compounds which have a
boiling point of CO.sub.2 and below, concentration of the other
constituents occurs in the condensate. In accordance with WO
2007/070198 A2 only enrichment in respect of CH.sub.4 in the
gaseous phase would be observed at all, clean separation is not
effected.
[0021] The applicant's calculations showed that, with typical
associated gas which occurs in oil production stations, only few
higher-grade hydrocarbons have to be separated off to be able to
operate modern internal combustion engines which are designed or
adapted specifically for gases with a low resistance to knocking.
These include heptane (C.sub.7H.sub.16), benzene (C.sub.6H.sub.6),
n-pentane and isopentane (C.sub.5H.sub.12) as well as n-butane and
isobutane (C.sub.4H.sub.10). All those components already condense
at -12 degrees Celsius so that it is sufficient for the gas to be
cooled down to that temperature. That can be implemented
inexpensively and with a low level of complication with commercial
refrigerating machines such as for example water chillers and with
commercially available heat exchangers and condensate locks.
[0022] The advantage of the method is that the gas does not have to
be cooled down to very low temperatures as was otherwise usual but
only to between about -5 and -14 degrees Celsius, preferably -12
degrees Celsius, to make the gas suitable specifically for internal
combustion engines in regard to anti-knock rating. That achieves a
marked reduction in costs.
* * * * *