ON THE USE OF ROTARY HEAT EXCHANGERS AS A NOVEL INTEGRATION OPTION FOR HEAT AND WATER MANAGEMENT
IN EXHAUST GAS RECYCLING GAS TURBINE PLANTS Laura Herraiz a *,, Dougal Hogg b, Jim Cooper b, Jon Gibbins a, Mathieu Lucquiaud a a The University of Edinburgh, School of Engineering, The Kings Buildings, Edinburgh EH9 3JL, United Kingdom
b Howden Global, Old Govan, Renfrew, PA4 8XJ, United Kingdom * Corresponding autor: [email protected] +44 (0) 7587161599
• An hybrid cooling system reduces cooling water consumpPon by around 60% compared to a configuraFon with a single DCC.
• A dry cooling system using ambient air instead of water as the cooling fluid shows good performance.
• Stack temperature in excess of 70ºC and a temperature around 43ºC at the inlet of the absorber are reached in an air-‐fired CCGT.
• As the recirculaPon raPo increases, the CO2-‐depleted flow rate decrease, which results in a reducPon of the overall cooling capacity at constant heaPng surface area. The buoyancy of the flue gas entering the stack is higher.
• A dry cooling system using a single gas/gas/air heater resulted in a more compact design, with lower booster fan power consumpPon and smaller foot print.
ACKNOWLEDGEMENTS:
CONFIGURATIONS: 1. Wet cooling system: direct contact cooler The gas is brought into direct contact with process water in a counter current configuraFon in a packed bed. Cooling water in the heat exchanger is provided by the primary plant cooling system.
2. Hybrid cooling system: gas/gas heater and direct contact cooler A gas/gas heater transfers heat from the EFG leaving the HRSG into the CO2-‐depleted gas, exiFng the water wash secFon at the top of the absorber. Further cooling is, however, necessary for the untreated gas stream in a direct contact cooler.
3. Dry cooling system: gas/gas heater and air/gas heater The direct contact cooler is replaced by two consecuFve regeneraFve heaters in a dry cooling system. Ambient air is used as cooling fluid in the air/gas rotary heater.
4. Dry cooling system: gas/gas/air heater in a tri-‐sector configuraPon The two consecuFve rotary heat exchangers are replaced by a single heater with a tri-‐sector arrangement.
A similar thermal performance analysis is also conducted for a NGCC plant with EGR, at different recirculaFon raFos for the same design of rotary heaters as in the air-‐fired case.
• Technology opFons with gas/gas rotary heat exchangers are invesFgated for the water and heat management in the integraFon of Combined Cycle Gas Turbines (CCGT) plants with post-‐combusPon carbon capture (PCC), with and without exhaust gas recirculaFon (EGR).
• The aim is to replace the Direct Contact Cooler (DCC), typically used for amine-‐based scrubbing technology, with the consequent reducPon in the overall process water requirements and cooling water consumpPon.
• A range of configuraFons are examined for wet and dry cooling of the Exhaust Flue Gas (EFG) entering the absorber and reheat the CO2-‐depleted gas leaving the water wash secFon at the top of the absorber before being released into the atmosphere through the stack of the plant.
• With EGR, the fracPon of the flue gas re-‐diverted is cooled down before it is mixed with ambient air, as lower inlet temperature increase the gas turbine power output.
• Feasible heater configuraPon, dimensional and operaPonal parameters are selected to achieve a desired outlet temperature for the EFG and CO2-‐depleted gas streams at the cold and hot end respecFvely, with a minimum leakage level and pressure drop.
KEY REFERENCES: [1] InternaFonal Energy Agency of Greenhouse Gases, CO2 Capture at Gas Fired Power Plants, 2012/8, July 2012. [2] Huizeling, E. and Van der Weijde, G., ROAD CCS non-‐confidenFal FEED study report: special report for the Global Carbon Capture and Storage InsFtute, 2011. [3] Kigo, J.B and Stultz, S.C., Steam, its generaFon and use, EdiFon 41st.The Babcock and Wilcox Company, 1992, ISBN 0-‐9634570-‐1-‐2.
• In regeneraPve heat exchangers heat is indirectly transferred by convecFon as a heat storage medium is periodically exposed to hot and cold fluid streams, in a counter current arrangement [3].
• Larger specific surface area and smaller equivalent diameter , compared to recuperaFve heat exchangers.
Fig.2. Cooling water, process water and cooling air mass flow required for each configuraFon, within the boundary limits, in an air-‐fired GTCC plant and a GTCC plant with EGR (40% recirculaFon raFo), both with post-‐combusFon capture technology.
Fig.3. Booster fan, air fan, cooling and process water pumps power consumpFon, in an air-‐fired CCGT plant and a CCGT plant with EGR (40% recirculaFon raFo), both with post-‐combusFon capture technology.
The EFG leaves the HRSG and needs to be cooled down unFl it reaches the saturaFon temperature at the inlet of the absorber [1,2]. Why? A low temperature enhances the absorpFon process by increasing the solvent capacity and the driving force for mass transfer.
At the top of the absorber (water wash secFon), the CO2-‐depleted gas stream is reheated in a dry stack design [1]. Why? in order to increase buoyancy forces and avoid plume visibility and corrosion due to water condensaFon in the stack.
1. INTRODUCTION AND MOTIVATION
Fig.1 Example of a typical regeneraFve gas/gas rotary heater used in coal power plants [Courtesy of Howden].
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DCC DCC (EGR 40%)
GGH and DCC
GGH and DCC
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GGH and AGH
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GGAH GGAH (EGR 40%)
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s flo
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ate
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Cooling water mass flow Process water mass flow Cooling air mass flow
DCC : direct contact cooler GGH and DCC : gas/gas heaer and direct contact cooler GGH and AGH : gas/gas heater and air/gas heater GGAH : gas/gas/air tri-sector heater
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GGAH (EGR 40%)
Pow
er (M
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Water pumps power consumption Air fan power consumption Booster fan power consumption
4. ENGINEERING ASSESSMENT
A. Air -‐ fired CCGT plant with PCC
B. EGR -‐ CCGT with PCC
2. ROTARY HEAT EXCHANGER TECHNOLOGY
3. NOVEL INTEGRATION OPTIONS FOR HEAT AND WATER MANAGEMENT IN CCGT WITH PCC
Cooling and process water consumpPon Booster fan power consumpPon
