Power plants – Combustion products used as motive fluid – Process
Reexamination Certificate
2001-11-20
2003-12-02
Casaregola, Louis J. (Department: 3746)
Power plants
Combustion products used as motive fluid
Process
Reexamination Certificate
active
06655150
ABSTRACT:
This application is a 371 application of PCT/N00/00018 filed Jan. 26, 2000.
The present invention relates to a method for removing and recovering CO
2
from exhaust gas from a power and/or heat generating plant by chemical absorption and desorption for deposition as convenient at the location.
Due to the environmental aspects of CO
2
as a gas with greenhouse effect, and taxes on the emission of CO
2
by some national governments, the possibility of reducing the emissions of CO
2
to the atmosphere from a power and/or heat generating processes, in particular from exhaust gas from gas turbines offshore, in a way that implies reduced energy consumption and investment costs, has been widely discussed.
Conventional power and/or heat generating processes, using carbon containing fuels and where the oxygen source is air, have carbon dioxide concentrations of 3-15% in the combustion products, hereinafter called exhaust gas, dependent on the fuel and the combustion and heat recovery process applied. E.g. in natural gas fired gas turbines the concentration of CO
2
in the exhaust gas is only 3-4%. Thus, a reduction in the emission of carbon dioxide to the atmosphere makes it necessary to separate the carbon dioxide from the exhaust gas because it will be too expensive to compress and deposit the whole exhaust gas. The compression of the recovered CO
2
for deposition in e.g. a geological formation is an implied part of any recovery method.
The concentration of carbon dioxide in the exhaust gas may be raised to higher levels by recirculating exhaust gas suggested by e.g. Chiesa et al. (paper presented at the International Gas Turbine & Aeroengine Congress & Exhibition Stockholm, Sweeden-Jun. 2-5, 1998) in a coal based Integrated Gasification and Combined Cycle (IGCC) plant or described by Ronning et al. in Norwegian patent 180520.
CO
2
can be removed from exhaust gas by means of several separation processes, e.g. chemically active absorption processes, physical absorption processes, adsorption by molecular sieves, membrane separation, and cryogenic techniques. Chemical absorp-tion by means of alkanolamines is presently considered the most practical and economical method to separate CO
2
from exhaust gas at near atmospheric pressure. In fact MEA (monoethanolamine) is the absorption medium that dominates due to its high affinity for CO
2
even at low partial pressure of CO
2
.
The application of MEA for absorbing CO
2
from exhaust gas has been described in the literature by Pauley et al. (Proceedings of the Gas Conditioning Conference, Norman, Ok, Mar. 5-7, 1984, paper H; an abbreviated version in Oil & Gas J., May 14, 1984, p 87-92). They describe a CO
2
removal system based on MEA with additives. There are, however, descriptions of corrosion problems. MEA degradation, and high chemicals consumption. In the described method the exhaust gas pressure was essentially atmospheric with typically 8.5% CO
2
in the feedstream to the absorber. This represents a higher CO
2
partial pressure than will be experienced in gas turbine exhaust gas.
It is further known (see e.g. Fang-Yuan Jou et al., Can.J.Chem.Eng., 1993, vol 71, April, 264-268) that use of other amines than MEA, particularly tertiary amines like MDEA (methyidiethanolamine) is less prone to degradation, and its vapor pressure is lower than MEA's leading to lower losses of amine vapor with the gas streams leaving. The corrosion problems are also lower than if MEA is used. The use of tertiary amines, however, for treating gas turbine exhaust gas is to day uneconomical due to these amines' lower affinity for CO
2
compared to MEA. Hence CO
2
removal from exhaust gas is done by absorption in a more reactive amine like MEA. The application of MDEA requires that exhaust gas is compressed to an elevated pressure to increase the partial pressure of CO
2
since this increases the possible loading (mol CO
2
/mol amine) of CO
2
in the MDEA solution.
These low pressure MEA-based CO
2
absorption processes require heavy and voluminous equipment. Furthermore, corrosion in the process equipment, degradation of the amine due to the temperature levels normally used, and generally high consumption of chemicals (e.g. amine) are major problems in these processes.
Furthermore, these processes will consume a substantial amount of heat and/or power. The application of the Selexol process, commercialised by Union Carbide, is suggested by Chiesa et al. (paper presented at the International Gas Turbine & Aeroengine Congress & Exhibition Stockholm, Sweden-Jun. 2-5, 1998) to recover CO
2
from a coal based Integrated Gasification and Combined Cycle (IGCC) plant. This process, however, needs a very high feed gas pressure. Chiesa et al estimated that an operating pressure of minimum 41 bar is needed to recover 90% CO
2
from exhaust gas when CO
2
in the exhaust gas was about 20%. They considered that at least 50 bar was required to obtain a reasonable driving force for mass transfer. To achieve this pressure, a partly inter cooled compressor is used. The pressurised exhaust gas is cooled to near ambient temperature by a recuperative heat exchanger, and ducted to the absorption column where CO
2
is captured by Selexol. The nitrogen-rich CO
2
depleted exhaust gas, exiting the Selexol process, is heated to about 600° C. in the gasification down stream process and is further expanded with reheating between stages. The drawback of the process scheme suggested by Chiesa et al., is the required absorption pressure of 50 bar which reduces the efficiency of the process and prevent efficient use of available process heat.
Australian patent AU 9,728,540-A relates to a process for treating a high-pressure raw gas selected from high-pressure natural gas and various synthesis gases with a carbon dioxide absorbing fluid, whereby highly concentrated carbon dioxide is almost fully removed from the raw gas to obtain a refined gas having a carbon dioxide concentration of 10 to 10000 ppm, and moreover for recovering carbon dioxide partially at high-pressure from the absorbing fluid as well as a system therefore.
The Australian patent teaches partial desorption of CO
2
at elevated pressure which is defined in that patent as at least 2 kp/cm 2 abs (approximately 2 bar). The referred patent further limits the desorption pressure in its first separator to the pressure of the absorber which in most cases makes it impossible to condense recovered CO
2
by cooling water which is an advantage if CO
2
shall be compressed to the required pressure for deposition in a geological formation. Typically this would require 50 bar or above. The Australian patent defines any pressure above 2 bar as high pressure. Carryover of the active part (typically an alkanolamine) of the aqueous solution may take place from the first gas-liquid separator in the described process, and this may also be a problem in conventional absorption/desorption systems. The Australian patent specifies 90° C. to 150° C. as the temperature level at which CO
2
is partially desorbed at elevated pressure in their first desorption stage. Energy to preheat the absorbent must be available at a few degrees higher, typically 10 degrees or more. The temperature level needed in their reboiler (12) in their
FIG. 1
is dictated by the boiling point of the CO
2
-free absorbent plus an increase to provide driving force.
The main object of the present invention was to arrive at an improved method for removing and recovering CO
2
from exhaust gas from a power and/or heat generating process by chemical absorption and desorption in a way that implies reduced weight and volume of the equipment used in the absorption and desorption process.
Another object of the present invention was to arrive at an improved method for removing and recovering CO
2
from exhaust gas from a power and/or heat generating process by chemical absorption and desorption in a way that implies more efficient use of other amines than MEA compared to previously known CO
2
absorption and desorption methods.
A further object of the invention was to arriv
Åsen Knut Ingvar
Eimer Dag Arne
Casaregola Louis J.
Norsk Hydro Asa
Wenderoth , Lind & Ponack, L.L.P.
LandOfFree
Method for removing and recovering CO2 from exhaust gas does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for removing and recovering CO2 from exhaust gas, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for removing and recovering CO2 from exhaust gas will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3180639