Olav Bolland

A novel methodology for comparing CO2 capture options for natural gas-fired combined cycle plants

Abstract Three concepts for capturing CO 2 from natural gas-fired combined gas/steam turbine power plants are evaluated and compared in this paper: (A) separation of CO 2 from exhaust gas coming from a standard gas turbine power plant, using chemical absorption by amine solutions. (B) Gas turbine combined cycle (CC) using a semi-closed gas turbine with near to stoichiometric combustion using oxygen from an air separation unit as an oxidizing agent. This produces CO 2 and water vapour as the combustion products. The gas turbine working fluid is mainly CO 2

Comparison of two CO2 removal options in combined cycle power plants

In this paper, two concepts of CO2 removal in CC are compared from the performance point of view. The first concept has been proposed in the framework of the European Joule II pro- gramme and is based on a semi-closed gas turbine cycle using CO2 as the working fluid and a combus- tion with pure oxygen generated in an air separation unit. This is a zero emission system as the excess CO2 produced in the combustion process is totally captured without the need of costly and energy con- suming devices. The second concept calls for a partial recirculation of the flue gas at the exit of the heat recovery boiler of a CC. The remaining flow is sent to a CO2 scrubber. Ninety percent of the CO2 is removed in an absorber/stripper device. The two systems are compared to a state-of-the-art CC when the most advanced technology is used, namely a 9FA type gas turbine and a three pressure level and heat recovery boiler. Our results show also that the CO2 semi-closed CC cycle performances are not very dependent on the configuration of the heat recovery boiler and that the recirculated gas CC per- formances are only slightly sensitive to the recirculation ratio. A high value of this latter mainly gives a significant reduction of the size and hence of the cost of the CO2 scrubber. From the performance point of view, the results show that the system eAciency with partial recirculation and a CO2 scrubber is always higher by 2-3% points than the CO2-based CC eAciency in comparable conditions. # 1998 Published by Elsevier Science Ltd. All rights reserved CO2 removal CO2/O2 combustion CO2 semi-closed cycle Flue gas recirculation The objective of this study is to assess the impact of CO2 removal and transportation on de- sign and performance of a natural gas-fired gas turbine plant. Two diAerent concepts were ana- lysed; one including downstream removal of CO2 from combined cycle power plant flue gas and one with air separation prior to a CO2-based power cycle with near stoichiometric oxygen com- bustion. These alternatives are compared to a standard natural gas fired combined cycle where no measures are taken in order to reduce the CO2 emissions. The two mentioned options are considered here for a comparison because the Norwegian and Belgian research teams under the leaderships of O. Bollard and Ph. Mathieu, developed respect- ively a modelling of the CC with flue gas partial recirculation and of the semi-closed CO2-based power cycle. In the semi-closed cycle option, the big advantage is the 100% extraction of the excess CO2 produced in the combustion process from the CO2 working fluid with a simple valve, hence without an energy consuming and costly device like the MEA scrubber but on the other hand it requires an ASU. This is a zero CO2 emission concept.

Comparative Evaluation of Combined Cycles and Gas Turbine Systems With Water Injection, Steam Injection, and Recuperation

Combined cycles have gained widespread acceptance as the most efficient utilization of the gas turbine for power generation, particularly for large plants. A variety of alternatives to the combined cycle that recover exhaust gas heat for re-use within the gas turbine engine have been proposed and some have been commercially successful in small to medium plants. Post notable have been the steam-injected, high-pressure aeroderivatives in sizes up to about 50 MW. Many permutations and combinations of water injection, steam injection, and recuperation, with or without intercooling, have been shown to offer the potential for efficient improvements in certain ranges of gas turbine cycle design parameters. A detailed, general model that represents the gas turbine with turbine cooling has been developed. The model is intended for use in cycle analysis applications. Suitable choice of a few technology description parameters enables the model to represent accurately the performance of actual gas turbine engines of different technology classes. The model is applied to compute the performance of combined cycles as well as that of three alternatives. These include the simple cycle, the steam-injected cycle, and the dual-recuperated intercooled aftercooled steam-injected cycle (DRIASI cycle). The comparisons are based on state-of-the-art gas turbine technology and cycle parameters in four classes: large industrial (123-158 MW), medium industrial (38-60 MW), aeroderivatives (21-41 MW), and small industrial (4-6 MW). The combined cycles main design parameters for each size range are in the present work selected for computational purposes to conform with practical constraints. For the small posterns, the proposed development of the gas turbine cycle, the DRIASI cycle, are found to provide efficiencies comparable or superior to combined cycles, and superior to steam-injected cycles. For the medium posterns, combined cycles provide the highest efficiencies but can be challenged by the DRIASI cycle. For the largest posterns, the combined cycle was found to be superior to all of the alternative gas turbine based cycles considered in this study

A Comparative Evaluation of Advanced Combined Cycle Alternatives

This paper presents a comparison of measures to improve the efficiency of combined gas and steam turbine cycles. A typical modern dual pressure combined cycle has been chosen as a reference. Several alternative arrangements to improve the efficiency are considered. These comprise the dual pressure reheat cycle, the triple pressure cycle, the triple pressure reheat cycle, the dual pressure supercritical reheat cycle, and the triple pressure supercritical reheat cycle. The effect of supplementary firing is also considered for some cases. The different alternatives are compared with respect to efficiency, required heat transfer area, and stack temperature. A full exergy analysis is given to explain the performance differences for the cycle alternatives. The exergy balance shows a detailed breakdown of all system losses for the HRSG, steam turbine, condenser, and piping.

Gas Turbine Combined Cycle With CO2-Capture Using Auto-Thermal Reforming of Natural Gas

A concept for capturing and sequestering CO 2 from a natural-gas fired combined-cycle power plant is presented. Previously, a number of methods for capturing CO 2 from power plants have been suggested, among other including chemical absorption of CO 2 from exhaust gas and stoichiometric combustion with pure oxygen. The present approach is to de-carbonise the fuel prior to combustion by reforming natural gas, producing a hydrogen-rich fuel. The reforming process consists of an air-blown pressurised auto-thermal reformer that produces a gas containing H 2 , CO and a small fraction of CH4 as the combustible components. The gas is then led through a water-shift reactor, where the equilibrium of CO and H 2 O is shifted towards CO 2 and H 2 . The CO 2 is then captured from the resulting gas by chemical absorption. The gas turbine of this system is then fed with a fuel gas containing approximately 50% H 2 . A very important aspect of this type of process is the integration between the combined cycle and the reforming process. The pressurised air for the reforming is taken from a gas turbine compressor bleed, and there is an exchange of MP- and HP-steam between the steam cycle and the reforming process. This integration is necessary in order to achieve acceptable level of fuel-to-electricity conversion efficiency.

Chemical Looping Combustion-Analysis of Natural Gas Fired Power Cycles With Inherent CO2 Capture

In this paper an alternative to so-called ‘oxy-fuel’ combustion has been evaluated. Chemical Looping Combustion (CLC) is an innovative concept of CO2 capture from combustion of fossil fuels in power plants. CLC is closely related to oxy-fuel combustion as the chemically bound oxygen reacts in a stoichiometric ratio with the fuel. In CLC, the overall combustion takes place in two steps. In a reduction reactor fuel is oxidised by the oxygen carrier i.e. the metal oxide MeO which is reduced to metal oxide with a lower oxidation number, Me. Me flows to an oxidation reactor where it is oxidised by oxygen in the air. In this way pure oxygen is supplied to fuel without using an energy intensive traditional air separation unit. This paper presents thermodynamic cycle analysis of a CLC-power plant. A steady-state model has been developed for the solid-gas reactions occurring in the reactor system. The model is applied to analyse the system under two configurations; a combined cycle and a conventional steam cycle. A turbine-cooling model has also been implemented to evaluate the turbine cooling penalty in the combined cycle configuration. Effects of exhaust recirculation for coking prevention and incomplete fuel conversion have also been investigated. Performance of the oxygen carrier has been idealised except for the degrees of reduction and oxidation. Energy needs for CO2 capture have properly been taken into account. The results show that an optimum efficiency of 49.7% can be achieved under given conditions with a CLC-combined cycle at zero emissions level. With turbine cooling, efficiency falls by 1.2% points under the same conditions. The CLC-steam cycle is capable of achieving 40.1% efficiency with zero emissions. The results show that CLC has high potential for power generation with inherent CO2 capture. This work will be useful in designing CLC systems after the reactor system has been analysed experimentally for long-term operations.Copyright

DESCRIBING MASS TRANSFER IN CIRCULATING FLUIDIZED BEDS BY OZONE DECOMPOSITION

Abstract The objective of this work was lo improve understanding of the mass transfer between gas and solids in the riser section of a gas-solids circulating fluidized bed (CFB). In order to experimentally investigate gas-solids mass transfer in a CFB, a suitable low-temperature mass transfer process was applied: the decomposition of ozone (O3) using particles as catalyst. Particles used were angular cast steel with an average diameter (mass mean) of 134μm. The experiments were carried out in a semi-industrial sized CFB. Operating conditions were varied, with superficial gas velocity of up to 7.2 ms−1 at 60°C riser temperature, and riser net solids mass flux up to 53kgs−1m2. The overall solids concentration was around 2-2.5% and about 10% in the lower part of the riser. Ozone concentration profiles, axial pressure profiles, solids net mass flux as well as local particle velocities were measured. Gas velocity profiles were assumed in order to calculate the total transport of ozone at different heights in the riser. The importance of the lower part of the riser with respect to mass transfer is shown.

SOFC and gas turbine power systems—Evaluation of configurations for CO2 capture

Publisher Summary This chapter highlights that pressurized solid oxide fuel cells (SOFC) integrated in a gas turbine cycle is a promising power generation concept. The benefit of such combined systems is the potential for high electrical efficiency at small scale. By including an afterburner for the fuel cell, the remaining fuel in the anode exit gas is fully converted to water and CO2 while the anode and cathode streams from the fuel cell are kept separated. This enables the CO2 capture from an exhaust stream consisting of only CO2 and water. This chapter evaluates, three afterburner technologies based on different membrane conductors from the perspective of thermodynamic cycle analysis and materials technology. The total SOFC and gas turbine system with the different afterburners has been modeled in a general purpose flow sheet simulator, and mass and energy balances have been calculated. The electrical efficiency has been determined and compared for each of the three afterburners. The potential of the three technologies for future use as afterburners is evaluated.

BENCHMARKING OF GAS-TURBINE CYCLES WITH CO2 CAPTURE

Publisher Summary This chapter explores that cycle performance studies are carried out with different models and computational assumptions. Consequently, results from various sources are difficult to compare. The intention of is to make a comparison of various natural gas-fired power cycle concepts with CO2 capture. Nine different concepts for natural gas fired power plants with CO2 capture have been investigated, and a comparison is made based on cycle performance. These cycles constitute one post-combustion, six oxy-fuel and 2 pre-combustion concepts. A common basis for the comparison of all concepts is defined and employed in heat- and mass-balance simulations of the various concepts. As turbine cooling impacts the performance at high turbine inlet temperatures, a simplified model has been applied in the simulations. It is shown that the concepts, in which emerging technology is employed, exhibit the best performance with respect to efficiency.

Weight and power optimization of steam bottoming cycle for offshore oil and gas installations

Offshore oil and gas installations are mostly powered by simple cycle gas turbines. To increase the efficiency, a steam bottoming cycle could be added to the gas turbine. One of the keys to the implementation of combined cycles on offshore oil and gas installations is for the steam cycle to have a low weight-to-power ratio. In this work, a detailed combined cycle model and numerical optimization tools were used to develop designs with minimum weight-to-power ratio. Within the work, single-objective optimization was first used to determine the solution with minimum weight-to-power ratio, then multi-objective optimization was applied to identify the Pareto frontier of solutions with maximum power and minimum weight. The optimized solution had process variables leading to a lower weight of the heat recovery steam generator while allowing for a larger steam turbine and condenser to achieve a higher steam cycle power output than the reference cycle. For the multi-objective optimization, the designs on the Pareto front with a weight-to-power ratio lower than in the reference cycle showed a high heat recovery steam generator gas-side pressure drop and a low condenser pressure.