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Separation of carbon dioxide from offshore gas turbine exhaust
Pergamon
Energy Convers. Mgmt Vol. 36, No. 6-9, pp. 393-396, 1995 Copyright 0 1995 Elsevier Science Ltd 0196-8904(95)00028-3 Printed in Great Britain. All rights reserved 0196-8904/95 $9.50 + 0.00
SEPARATION OF CARBON DIOXIDE FROM OFFSHORE GAS TURBINE EXHAUST
OLAV FALK-PEDERSEN, YNGVIL BJERVE, GEIR GLITTUM AND SVEIN R0NNING Kvaemer Engineering a.s. Environmental Sandetjord, Norway Abstract - The introduction of a CO,-tax in 1991, on offshore combustion of natural gas has lead to an increased interest in both energy conservation and the possibility of separating COz from gas turbine exhaust. In this paper a possible process will be presented. The result of the assessment is that an amine absorption process using MEA and a gas absorption membrane, in combination with a combined cycle power generation unit with 40% recycling of the exhaust gas and a CO, compression unit, is best suited for CO2 removal among the options studied. 1. INTRODUCTION In 1989 the Norwegian Government initiated the objective that the total CO* emission in Norway will be stabilised at the 1989 level in the year 2000. This led to the introduction of the CO,-tax in 1991. The total CO&ax paid by the Norwegian oil companies is assumed to be MNOK 2600 (US$355 million) in 1994. This motivated the Norwegian oil companies to study new methods and technologies for reduction of the total CO, emissions. In 1992, Kvaemer Engineering a.s. Environmental initiated a joint effort program for CO, separation between major North Sea operators and the Norwegian authorities. This study is at present in phase three and will be fmalised in December 1994. This paper will present the development activities in the study and the preliminary results. The most crucial constraint when developing possible solutions for a CO2 removal process for offshore installations is that occupying volume and weight are expensive. The project started with a feasibility study where different possible solutions for removal of CO2 were evaluated. The basis for the study has been an LM2500 PE gas turbine. The conclusions were that an amine absorption process using MEA (monoethanolamine) in combination with 40% recycling of the exhaust was the best process, see figure 1.
Fig. 1. Overview of the selected process
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FALK-PEDERSEN et al.: CO2 FROM GAS TURBINE EXHAUST
2. THE CO, REMOVAL PROCESS A method for removing CO, from exhaust gas based on amine absorption (MEA) patented as the Fluor Daniel ECONAMINE FG process has been recommended for this project, Sander and Mariz [ 11. The ECONAMINE FG process with conventional components was used in the cost, size and weight study in phase one of the project. The weight and size turned out to be far too high and the internal rate of return was negative. The main target for phase two of the study was to optimise the process with respect to size, weight and cost. The development work focused on optimization of the following topics: the power generation process, the absorption unit, the desorption unit and the layout. 2.1. Power Generation Concepts The main condition that the power generation unit must fulfil, is to make the net power output from an LM 2500 simple cycle gas turbine (approximately 21 MW) available regardless of the power and heat requirements of the CO, removal process. This introduced the necessity of a waste heat recovery unit (WHRU). A study of the possibility of decreasing this large weight of a traditional WHRU (approx. 120 tonnes) was therefore initiated. The result of the study is a boiler which is approximately 40 tonnes lighter than a conventional WHRU unit. Another assessment was to find the power generation concept that would give the highest internal rate of return for the total process (inclusive the amine process). The following power generation processes were investigated: Combined Cycle with Spiking of 0, Conventional Steam Cycle, Steam Injected Gas Turbine (STIG) with Recycling of Exhaust, Gas Engines and Combined Cycle with 40% Recycling of Exhaust. Combined cycle with 40% recycling of exhaust is the best power generation system of the options studied in conjunction with removal of CO, on offshore installations. Both General Electric (Spector [2]) and Rolls Royce (Reynolds [3]) have in general agreed that the recycle ratio (40%) will not significantly influence gas turbine performance, though detailed testing is necessary to verify this. Detailed results and information from this part of the study can be found in the paper “Assessment of Power Generation Concepts on Oil Platforms in Conjunction with CO, Removal” , Bjerve et al.[4]. lofthe 2 2.
Three different types of absorption units were evaluated; absorption columns, rotating contact devices and gas absorption membranes. Absorption columns have been used for many years and the design procedures are well known. However, compared with new absorber equipments (rotating unit and gas absorption membranes) the size, weight and cost are too high.
The centrifugal force produced by rotating a packing bed, acts as an artificially high “g” force. The resulting high shear forces produce a very thin liquid film, rapidly renewed surface, and substantial turbulence so that efficient mass transfer takes place. The very large volume flow of exhaust gas entering the absorber will demand a very high packing or several units in parallel (the capacity is related to height or axial length). Compared with a gas absorption membrane unit, the size, weight and cost of the rotating contacting device are excessive.
FALK-PEDERSEN et al.: CO2 FROM GAS TURBINE EXHAUST
395
Gas Absorotion Membranes In our search for possible absorption systems we found an interesting study made for LEA by TN0 in The Netherlands, Feron [5]. The study showed that the potential of gas absorption membranes for CO, removal from exhaust gas was of interest. Separation is caused by the presence of an absorption liquid on one side of the membrane which selectively removes certain components from the gas stream on the other side of the membrane. The use of a gas absorption membrane has several advantages over conventional contacting equipment (e.g. packed columns). First of all, the gas absorption membrane will be compact and the weight will be reduced (approx. l/4 of a conventional absorber column). Absorber processes based on membranes have been tested in laboratory scale as well as pilot plant scale (SO, removal) and are on the verge of commercial introduction. However, the technology is not established for CO, removal, so the gas absorption membranes has to be tested further (see 3.2). 2.3. Ontimisation of the Desorntion Unit Working with the absorber revealed that the rotating contacting unit (see 2.2) was of interest due to the relatively low gas/steam flow rate in the stripper. Contact was made with Glitsch who own the commercial rights to Higee, a rotating contact unit. 2.4. Ontimisation of the Layout Because space is very expensive offshore, the layout study has been a very important part of the project. Detailed 3D-drawings are made of the process components using Kvaemer’s 20 years’ experience in design of offshore platforms and processes. Figure 4 shows the CO, removal process on an offshore platform. The conclusion in phase two of the project was that the CO, removal process seems to have au interesting internal rate of return if the new type of equipment could be made to work. This conclusion lead to the start of phase three, which will be fmalised December 3 1, 1994.
Fig. 2. Plant Layout
3. TESTS Since the absorber and the stripper are the two components in the process which have the best potential for reduction in size, weight and cost, a test program was started for the two components.
FALK-PEDERSEN
396 I
et al.: CO2 FROM GAS TURBINE EXHAUST
3.1. &inner Testing The following three options are under evaluation: use of a rotating stripper unit (Higee), use of membranes (same principle as in the absorber) and the use of glass tibre (GRP) in the stripper tower shell. The Higee unit was tested in cooperation between Glitsch (the owner of the unit), SRP (the University of Texas, Austin) and Kvmmer. This is the first time the Higee unit has been tested as a stripper for this type of process. The lack of experience and theory lead to problems during testing. However, the preliminary conclusion is that Higee, used as a stripper in the CO, removal process, is not as efficient as expected with respect to size and cost. The test of a membrane stripper and GRP materials will be started in mid October 1994. 3.2. Testing of Gas Absorption Membranes The first task was a verification of the principle. The scope of work was to verify the two most critical parameters: the wettability of the membranes (the membranes must not be wetted) and the total mass transfer coefficient to be used in the scale up calculations. The result of the study is that PTFE membranes are the only membranes that can be used. The PTFE membrane tested was not wetted and the mass transfer coefficient was very close to the the value calculated in our in-house simulation program. The positive result from the testing initiated a cooperation between W.L. Gore & Associates, Inc. (the PTFE membrane tested was delivered by Gore) and Kvaemer. A new feasibility study has been initiated. The preliminary conclusion of the study (the study will be fmalised in December 1994) is that conventional membrane modules cannot be used due to poor mechanical stability, low active membrane surface and high production cost. A new type of membrane module has been developed. This module fulfils the requirements with respect to pressure drop, mechanical stability and production cost. However, since this is a prototype development, the potential for the gas absorption membrane has to be contirmed by testing of the new type of module. It is important that the tests confirm the high mass transfer coefficient measured in earlier tests and that problems with leakages do not arise. 4. CONCLUSIONS The object of the project is to investigate which CO, removal process would be optimal for offshore use.The preliminary conclusions from the study are: (1) an amine absorption process using MEA is the best process, (2) 40% of the exhaust gas should be recycled to the gas turbine inlet, to reduce the exhaust gas flow and to increase the CO, concentration entering the absorber, (3) it is indicated that gas absorber membranes are the best alternative to conventional absorption columns, (4) the potential for the gas absorption membrane has to be confirmed by the testing, (5) the proposed CO, removal process seems to have an interesting internal rate of return if the suggested technology could be made to work. REFERENCES 1. 2. 3. 4. 5.
M. T. Sander and C. L. Mariz, Energy Convers. Mgmt., Vol 33, No.58, pp 341-348 (1992) R. 3. Spector, Personal communication with Richard B. Spector, GE Marine & Industrial Engines, Cincinnati, USA (1993) G. Reynolds, Personal communication with Greham Reynolds, Rolls Royse Industrial & Marine Gas Turbines Ltd., Coventry, England (1993) Y. Bjerve and 0. Bolland, Presented at the International Gas Turbine and Aeroengine Congress and Exposition, The Hague, Netherlands (1994) P. H. M. Feron, IEA/92/OE%, TN0 (1992)
Energy Convers. Mgmt Vol. 36, No. 6-9, pp. 393-396, 1995 Copyright 0 1995 Elsevier Science Ltd 0196-8904(95)00028-3 Printed in Great Britain. All rights reserved 0196-8904/95 $9.50 + 0.00
SEPARATION OF CARBON DIOXIDE FROM OFFSHORE GAS TURBINE EXHAUST
OLAV FALK-PEDERSEN, YNGVIL BJERVE, GEIR GLITTUM AND SVEIN R0NNING Kvaemer Engineering a.s. Environmental Sandetjord, Norway Abstract - The introduction of a CO,-tax in 1991, on offshore combustion of natural gas has lead to an increased interest in both energy conservation and the possibility of separating COz from gas turbine exhaust. In this paper a possible process will be presented. The result of the assessment is that an amine absorption process using MEA and a gas absorption membrane, in combination with a combined cycle power generation unit with 40% recycling of the exhaust gas and a CO, compression unit, is best suited for CO2 removal among the options studied. 1. INTRODUCTION In 1989 the Norwegian Government initiated the objective that the total CO* emission in Norway will be stabilised at the 1989 level in the year 2000. This led to the introduction of the CO,-tax in 1991. The total CO&ax paid by the Norwegian oil companies is assumed to be MNOK 2600 (US$355 million) in 1994. This motivated the Norwegian oil companies to study new methods and technologies for reduction of the total CO, emissions. In 1992, Kvaemer Engineering a.s. Environmental initiated a joint effort program for CO, separation between major North Sea operators and the Norwegian authorities. This study is at present in phase three and will be fmalised in December 1994. This paper will present the development activities in the study and the preliminary results. The most crucial constraint when developing possible solutions for a CO2 removal process for offshore installations is that occupying volume and weight are expensive. The project started with a feasibility study where different possible solutions for removal of CO2 were evaluated. The basis for the study has been an LM2500 PE gas turbine. The conclusions were that an amine absorption process using MEA (monoethanolamine) in combination with 40% recycling of the exhaust was the best process, see figure 1.
Fig. 1. Overview of the selected process
1 393
394
FALK-PEDERSEN et al.: CO2 FROM GAS TURBINE EXHAUST
2. THE CO, REMOVAL PROCESS A method for removing CO, from exhaust gas based on amine absorption (MEA) patented as the Fluor Daniel ECONAMINE FG process has been recommended for this project, Sander and Mariz [ 11. The ECONAMINE FG process with conventional components was used in the cost, size and weight study in phase one of the project. The weight and size turned out to be far too high and the internal rate of return was negative. The main target for phase two of the study was to optimise the process with respect to size, weight and cost. The development work focused on optimization of the following topics: the power generation process, the absorption unit, the desorption unit and the layout. 2.1. Power Generation Concepts The main condition that the power generation unit must fulfil, is to make the net power output from an LM 2500 simple cycle gas turbine (approximately 21 MW) available regardless of the power and heat requirements of the CO, removal process. This introduced the necessity of a waste heat recovery unit (WHRU). A study of the possibility of decreasing this large weight of a traditional WHRU (approx. 120 tonnes) was therefore initiated. The result of the study is a boiler which is approximately 40 tonnes lighter than a conventional WHRU unit. Another assessment was to find the power generation concept that would give the highest internal rate of return for the total process (inclusive the amine process). The following power generation processes were investigated: Combined Cycle with Spiking of 0, Conventional Steam Cycle, Steam Injected Gas Turbine (STIG) with Recycling of Exhaust, Gas Engines and Combined Cycle with 40% Recycling of Exhaust. Combined cycle with 40% recycling of exhaust is the best power generation system of the options studied in conjunction with removal of CO, on offshore installations. Both General Electric (Spector [2]) and Rolls Royce (Reynolds [3]) have in general agreed that the recycle ratio (40%) will not significantly influence gas turbine performance, though detailed testing is necessary to verify this. Detailed results and information from this part of the study can be found in the paper “Assessment of Power Generation Concepts on Oil Platforms in Conjunction with CO, Removal” , Bjerve et al.[4]. lofthe 2 2.
Three different types of absorption units were evaluated; absorption columns, rotating contact devices and gas absorption membranes. Absorption columns have been used for many years and the design procedures are well known. However, compared with new absorber equipments (rotating unit and gas absorption membranes) the size, weight and cost are too high.
The centrifugal force produced by rotating a packing bed, acts as an artificially high “g” force. The resulting high shear forces produce a very thin liquid film, rapidly renewed surface, and substantial turbulence so that efficient mass transfer takes place. The very large volume flow of exhaust gas entering the absorber will demand a very high packing or several units in parallel (the capacity is related to height or axial length). Compared with a gas absorption membrane unit, the size, weight and cost of the rotating contacting device are excessive.
FALK-PEDERSEN et al.: CO2 FROM GAS TURBINE EXHAUST
395
Gas Absorotion Membranes In our search for possible absorption systems we found an interesting study made for LEA by TN0 in The Netherlands, Feron [5]. The study showed that the potential of gas absorption membranes for CO, removal from exhaust gas was of interest. Separation is caused by the presence of an absorption liquid on one side of the membrane which selectively removes certain components from the gas stream on the other side of the membrane. The use of a gas absorption membrane has several advantages over conventional contacting equipment (e.g. packed columns). First of all, the gas absorption membrane will be compact and the weight will be reduced (approx. l/4 of a conventional absorber column). Absorber processes based on membranes have been tested in laboratory scale as well as pilot plant scale (SO, removal) and are on the verge of commercial introduction. However, the technology is not established for CO, removal, so the gas absorption membranes has to be tested further (see 3.2). 2.3. Ontimisation of the Desorntion Unit Working with the absorber revealed that the rotating contacting unit (see 2.2) was of interest due to the relatively low gas/steam flow rate in the stripper. Contact was made with Glitsch who own the commercial rights to Higee, a rotating contact unit. 2.4. Ontimisation of the Layout Because space is very expensive offshore, the layout study has been a very important part of the project. Detailed 3D-drawings are made of the process components using Kvaemer’s 20 years’ experience in design of offshore platforms and processes. Figure 4 shows the CO, removal process on an offshore platform. The conclusion in phase two of the project was that the CO, removal process seems to have au interesting internal rate of return if the new type of equipment could be made to work. This conclusion lead to the start of phase three, which will be fmalised December 3 1, 1994.
Fig. 2. Plant Layout
3. TESTS Since the absorber and the stripper are the two components in the process which have the best potential for reduction in size, weight and cost, a test program was started for the two components.
FALK-PEDERSEN
396 I
et al.: CO2 FROM GAS TURBINE EXHAUST
3.1. &inner Testing The following three options are under evaluation: use of a rotating stripper unit (Higee), use of membranes (same principle as in the absorber) and the use of glass tibre (GRP) in the stripper tower shell. The Higee unit was tested in cooperation between Glitsch (the owner of the unit), SRP (the University of Texas, Austin) and Kvmmer. This is the first time the Higee unit has been tested as a stripper for this type of process. The lack of experience and theory lead to problems during testing. However, the preliminary conclusion is that Higee, used as a stripper in the CO, removal process, is not as efficient as expected with respect to size and cost. The test of a membrane stripper and GRP materials will be started in mid October 1994. 3.2. Testing of Gas Absorption Membranes The first task was a verification of the principle. The scope of work was to verify the two most critical parameters: the wettability of the membranes (the membranes must not be wetted) and the total mass transfer coefficient to be used in the scale up calculations. The result of the study is that PTFE membranes are the only membranes that can be used. The PTFE membrane tested was not wetted and the mass transfer coefficient was very close to the the value calculated in our in-house simulation program. The positive result from the testing initiated a cooperation between W.L. Gore & Associates, Inc. (the PTFE membrane tested was delivered by Gore) and Kvaemer. A new feasibility study has been initiated. The preliminary conclusion of the study (the study will be fmalised in December 1994) is that conventional membrane modules cannot be used due to poor mechanical stability, low active membrane surface and high production cost. A new type of membrane module has been developed. This module fulfils the requirements with respect to pressure drop, mechanical stability and production cost. However, since this is a prototype development, the potential for the gas absorption membrane has to be contirmed by testing of the new type of module. It is important that the tests confirm the high mass transfer coefficient measured in earlier tests and that problems with leakages do not arise. 4. CONCLUSIONS The object of the project is to investigate which CO, removal process would be optimal for offshore use.The preliminary conclusions from the study are: (1) an amine absorption process using MEA is the best process, (2) 40% of the exhaust gas should be recycled to the gas turbine inlet, to reduce the exhaust gas flow and to increase the CO, concentration entering the absorber, (3) it is indicated that gas absorber membranes are the best alternative to conventional absorption columns, (4) the potential for the gas absorption membrane has to be confirmed by the testing, (5) the proposed CO, removal process seems to have an interesting internal rate of return if the suggested technology could be made to work. REFERENCES 1. 2. 3. 4. 5.
M. T. Sander and C. L. Mariz, Energy Convers. Mgmt., Vol 33, No.58, pp 341-348 (1992) R. 3. Spector, Personal communication with Richard B. Spector, GE Marine & Industrial Engines, Cincinnati, USA (1993) G. Reynolds, Personal communication with Greham Reynolds, Rolls Royse Industrial & Marine Gas Turbines Ltd., Coventry, England (1993) Y. Bjerve and 0. Bolland, Presented at the International Gas Turbine and Aeroengine Congress and Exposition, The Hague, Netherlands (1994) P. H. M. Feron, IEA/92/OE%, TN0 (1992)