Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Reexamination Certificate
1999-04-05
2001-03-20
Doerrler, William (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
C062S646000, C060S039120
Reexamination Certificate
active
06202442
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an integrated apparatus for generating power and/or oxygen-enriched fluid and a process for the operation thereof.
BACKGROUND OF THE INVENTION
All present oxygen production facilities extract oxygen from air. Air has the advantage of being free and available everywhere. One of the drawbacks is that because air is at atmospheric pressure, it contains a lot of water and CO2 at low partial pressure. And pressure drops in process cycles are energy expensive close to atmospheric pressure. It is the reason why most oil, chemical or petrochemical processes operate in the range of 10-40 bar. The pressure drops are less costly, heat exchange is easier, and the size of plants is reduced, drastically decreasing overall cost.
In the case of oxygen production, as air contains 80% nitrogen, a low pressure waste gas containing the nitrogen is normally produced. In case of cryogenic distillation, the cold heat contained in the waste nitrogen has to be recuperated through heat exchangers which are costly both in investment and related energy needs.
Some oxygen plants operate at higher than normal pressure with some means and additional investment to recover the energy lost in the waste nitrogen.
FIG. 1
shows a basic power gas turbine arrangement in which an air compressor
1
sends air
3
at between 8 and 35 bar to a combustor
5
fed by fuel
6
. The combustion gas
7
mixed with dilution air
4
forms mixture stream
8
which is expanded in gas turbine
9
having an inlet temperature between 900 and 1400° C. and generates power. To achieve good combustion in the bumer, a close to stoichiometric mixing is necessary to use fuel efficiently and produce minimum pollution. But in this case, combustion produces a hot gas at temperatures higher than 2000° C., well above what any kind of hot turbine can accept. For this reason, quench type cooling takes place by mixing this very hot flue gas
7
with compressed dilution air
4
from the compressor at the same pressure as stream
3
but much lower temperature. The dilution air flow
4
is of the same order of magnitude as the combustion air flow
3
.
Because this dilution air
4
does not participate in the combustion, oxygen is not necessary. So it is possible to extract the oxygen contained in the dilution air
4
as shown in FIG.
2
. The air
4
is cooled, purified and distilled in separation unit
12
producing oxygen
10
and nitrogen
11
. The nitrogen
11
is mixed with combustion gas
7
.
Generally the separation unit used is a double column comprising a thermally linked high pressure column and low pressure column. However it is known to use a single column with a top condenser and a bottom reboiler for this purpose.
If the amount of nitrogen
11
is limited, it may alternatively be mixed with air stream
3
and sent to combustor
5
as described in U.S. Pat. No. 4,224,045. Another option is to send the nitrogen to be mixed with the fuel stream
6
.
SUMMARY OF THE INVENTION
According to the present invention, there is provided an integrated apparatus for generating power and/or oxygen enriched fluid comprising a first air separation unit, a gas turbine comprising a combustor and an expander, a first compressor, means for sending air from the first compressor to the combustor and to the air separation unit, means for sending combustion gases from the combustor to the expander, means for sending nitrogen from the air separation unit to a point upstream of the expander and means for either compressing the nitrogen sent to a point upstream of expander, further compressing the air sent to the first air separation unit from the first compressor or expanding the air sent to the combustor from the first compressor
characterized in that the first air separation unit comprises at least a single column fed by air and the apparatus comprises means for sending liquid nitrogen from an external source to the top of the single column, said external source not being a condenser fed by gaseous nitrogen from the top of the single column, and means for removing gaseous nitrogen from the top of the single column and for removing an oxygen-enriched fluid from the bottom of the column.
According to further optional aspects of the invention:
the single column has no bottom reboiler and no top condenser;
the apparatus comprises a second compressor and means for sending air from the further compressor to the single column;
the external source of liquid nitrogen is a second air separation unit comprising at least one distillation column;
the second air separation unit comprises a high pressure column and a low pressure column which are thermally linked;
there are means for withdrawing the liquid nitrogen from the high pressure column or the low pressure column, where necessary pressurizing it and sending it to the top of the single column in liquid form and/or means for sending the oxygen-enriched liquid from the bottom of the single column to the high pressure column and/or the low pressure column;
there are means for sending air to the double column from one of the first, second or a third compressor;
Alternatively there may be means for sending gaseous nitrogen from the single column to the double column and/or means for sending nitrogen from the double column to a point upstream of the expander.
The apparatus may additionally include a gasifier, means for sending oxygen from the air separation unit and a carbon containing substance to the gasifier and means for sending fuel from the gasifier to the combustor.
According to a still further aspect of the invention, there is provided a process for generating power and/or oxygen enriched fluid using an integrated power generation system comprising compressing air in a first compressor, sending air from the first compressor to a combustor and to a first air separation unit, sending nitrogen from the air separation unit to a point upstream of an expander, sending fuel to the combustor, sending combustion gas from the combustor to the expander and either compressing the nitrogen sent to a point upstream of expander, further compressing the air sent to the first air separation unit from the first compressor or expanding the air sent to the combustor from the first compressor
characterized in that the first air separation unit comprises at least one column and the process comprises feeding a column of the first air separation unit column with air, sending liquid nitrogen from an external source to the top of the single column, the external source not being a condenser fed by gaseous nitrogen from the top of the s column and removing gaseous nitrogen from the top of the single column and an oxygen enriched fluid from the bottom of the column.
Further features of the process may include:
said column having no bottom reboiler and no top condenser;
sending air from a second compressor to the single column;
the external source being a second air separation unit comprising at least one column
the external source comprises a high pressure column and a low pressure column which are thermally linked;
withdrawing the liquid nitrogen from the high pressure column, pressurizing and sending it to the top of the column of the first air separation unit;
sending the liquid from the bottom of the single column to the second air separation unit, optionally to the high pressure column or low pressure column of the second air separation unit;
sending air to the second air separation unit from one of the first, second or a third compressor;
sending gaseous nitrogen from the column of the first air separation unit to the second air separation unit;
means for sending nitrogen from the second air separation unit to a point upstream of the expander;
wherein the column of the first air separation unit operates at between 8 and 35 bar;
the highest pressure of the second air separation unit is between 5 and 25 bar;
the amount of air sent from the first compressor to the first air separation unit and the amount of nitrogen sent upstream of the expander differ by no more than 10%, pre
Doerrler William
L'Air Liquide, Societe Anonyme pour l'Etude et l'
Young & Thompson
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