Power plants – Combustion products used as motive fluid
Reexamination Certificate
1999-06-15
2001-04-03
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
C060S039010, C060S039120, C060S039465
Reexamination Certificate
active
06209308
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for co-generation of electrical energy and steam, by means of a gas turbine and a boiler for recovering heat from the exhaust gas of this gas turbine, at an industrial site of which a unit supplies a gaseous sub-product containing methane and hydrogen.
The invention is particularly applicable to the co-generation carried out at petrochemical sites, particularly at petroleum refineries.
DESCRIPTION OF THE RELATED ART
At present, co-generation units are frequently installed at petrochemical sites, because of their high energy output. These units comprise a gas turbine whose combustion chamber is supplied with natural gas and which is followed by a boiler for recovering the heat of the exhaust gases of the turbine, this boiler producing steam under pressure.
To permit complying with more and more restrictive regulations concerning NO
x
emissions from such units, gas turbine manufacturers provide versions operating with combustion in a dry chamber and with a low NO
x
emission. These gas turbines are generally known as “Dry Low NO
x
,” turbines, or DLN or as “Dry Low Emission” or DLE and can be of the so-called “Heavy Duty” type or of the so-called “Aeroderivative” type. An example of these machines is the gas turbine GEF6FA DLN, of 70 MW, of the General Electric company.
As is well known, the DLN or DLE gas turbines derive their properties from a particular burner technology, generally with staged combustion, and with high output regulation means.
The se DLN or DLE gas turbines however impose constraints on the composition of the combustible gas which resupplies them. In particular, this gas must generally not comprise more than 5% hydrogen (by volume), and sometimes even less, and must have a relatively stable composition.
It has also been proposed, to reduce NO
x
emissions, to inject water or steam into the combustion chamber of a gas turbine of conventional design, which is to say is not of the DLN or DLE type. However, there has not generally been achieved in this manner very low NO
x
contents (25 ppm) required by current regulations. Moreover, this technique consumes large quantities of demineralized water, which can amount to several tens of tons per hour, which is then lost to the atmosphere.
Refineries and other major petrochemical units produce moreover gaseous sub-products containing a variable proportion of hydrogen (20 to 95%). According to the requirements of downstream user units, a portion of the hydrogen can be recovered commercially from sub-products containing the most hydrogen (generally≧50%). The balance of the gaseous sub-products, which, in most cases, cannot be sold, must most often be burned as an unavoidable product in boilers for stream production.
For a given steam requirement, this unavoidable production of vapor correspondingly reduces the size of the co-generation unit which it is possible to install on the site, thereby rendering this unit less profitable, reducing the increase of overall energy output of the complex and preventing further decreasing the overall level of CO
2
emitted by the production line of steam and electricity.
SUMMARY OF THE INVENTION
The invention has for its object to make commercially attractive in a more efficacious manner the gaseous sub-products by improving both the environmental protection and the overall energy output of the complex, and by reducing water consumption.
To this end, the invention has for its object a process of the above type, characterized in that:
if necessary, said sub-product is compressed;
this sub-product is reduced in hydrogen to a hydrogen level at most equal to 5% and preferably at most equal to 2%, to form a combustible gas principally constituted by methane; and
there is used this combustible gas to supply the combustion chamber of the gas turbine.
The process according to the invention can comprise one or several of the following characteristics, taken alone or in all possible technical combinations:
there is used at least one fraction of the residual gas of the operation of reducing hydrogen, enriched in hydrogen, as a combustible in a post-combustion operation at the inlet of the recovery boiler;
there is used a fraction of the residual gas from the operation of reducing hydrogen content, enriched in hydrogen, as a combustible in an auxiliary boiler for the production of steam;
there is added to said combustible a supplemental amount of an auxiliary combustible, particularly natural gas;
at least a fraction of the residual gas from the hydrogen reduction operation, enriched in hydrogen, is purified to produce a substantially pure hydrogen flow;
there is added to said combustible gas an extra amount of an auxiliary combustible, particularly natural gas;
there is carried out a pre-treatment for the elimination of impurities and/or of dirt from said sub-product before the operation of reducing hydrogen content;
said reduction of hydrogen content is a treatment of said sub-product by selective permeation;
the gas turbine is of the type with a dry combustion chamber and low emission of NO
x
;
the gas turbine operates with water injection or steam injection into its combustion chamber;
said gaseous sub-product contains 20 to 60% methane, 10 to 65% hydrogen and other constituents;
said unit is a petrochemical installation, particularly a petroleum refinery, and the gaseous sub-product has the following composition:
CH
4
=30 to 70%
H
2
=10 to 40%
&Sgr;C
2
=0 to 40%
miscellany=0 to 20%;
said combustible gas has for its composition:
CH
4
=40 to 90%, particularly 50 to 90%
H
2
=0 to 5%
&Sgr;C
2
=0 to 45%
miscellany=0 to 25%;
said unit is a ferrous metallurgical unit and the gaseous sub-product is a coke oven gas whose composition is as follows:
CH
4
=20 to 30%
H
2
=55 to 65%
&Sgr;C
2
=2 to 8%
N
2
=1 to 6%
CO=2 to 10%
miscellany=0 to 10%;
said combustible gas has for its composition:
CH
4
=60 to 70%
H
2
=0 to 5%
&Sgr;C
2
=5 to 20%
N
2
=5 to 15%
CO=5 to 15%
miscellany=0 to 10%.
The invention also has for its object an installation for co-generation adapted to practice such a process.
This installation, of the type comprising a gas turbine and a boiler for recovery of the heat of the exhaust gases of this gas turbine, is characterized in that it comprises: if necessary, compression means for said sub-product; means for reducing in hydrogen the compressed sub-product to form a combustible gas; and means for supplying the combustion chamber of the gas turbine with said combustible gas.
The invention also has for its object an industrial complex comprising an industrial unit which supplies a gaseous sub-product containing methane and hydrogen, and an installation for co-generation as described above.
The expression “containing methane and hydrogen” as here used must of course be considered to include the possibility of the presence of other constituents.
REFERENCES:
patent: 3930367 (1976-01-01), Gasparoli
patent: 4942734 (1990-07-01), Markbreiter et al.
patent: 5899175 (1999-05-01), Manikowski et al.
patent: 5980609 (1999-11-01), Baker et al.
patent: 2 261 225 (1993-05-01), None
patent: WO 96/14495 (1996-05-01), None
Freay Charles G.
L'Air Liquide, Societe Anonyme pour l'Etude et l'
Young & Thompson
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