Magnus Genrup

A Novel Approach of Retrofitting a Combined Cycle With Post Combustion CO2 Capture

Most state-of-the-art natural gas-fired combined cycle (NGCC) plants are triple-pressure reheat cycles with efficiencies close to 60%. However, with carbon capture and storage, the efficiency will be penalized by almost 10% units. To limit the energy consumption for a carbon capture NGCC plant, exhaust gas recirculation (EGR) is necessary. Utilizing EGR increases the CO2 content in the gas turbine exhaust while it reduces the flue gas flow to be treated in the capture plant. Nevertheless, due to EGR, the gas turbine will experience a different media with different properties compared with the design case. This study looks into how the turbomachinery reacts to EGR. The work also discusses the potential of further improvements by utilizing pressurized water rather than extraction steam as the heat source for the CO2 stripper. The results show that the required low-pressure level should be elevated to a point close to the intermediate-pressure to achieve optimum efficiency, hence, one pressure level can be omitted. The main tool used for this study is an in-house off-design model based on fully dimensionless groups programmed in the commercially available heat and mass balance program IPSEPRO. The model is based on a GE 109FB machine with a triple-pressure reheat steam cycle. [DOI: 10.1115/1.4001988] (Less)

Detection and interactive isolation of faults in steam turbines to support maintenance decisions

Abstract The maintenance of steam turbines is expensive, particularly if dismantling is required. A concept for the provision of support for the maintenance engineer in determining steam turbine status in relation to the recommended maintenance interval is presented here. The concept embodies an artificial neural network which is conditioned to recognise patterns known to be related to faults. The faults simulated are not known to be recognized on-line and the concept is in an early stage of development. An example of a Bayesian network structure containing expert knowledge is proposed to be used, in a dialogue with the operator, to isolate the root causes of a number of fault types. The aim is to be well informed about the statue of the turbine in order to take earlier and better informed maintenance actions. The detection procedure has been validated in a simulation environment.

Novel High-Performing Single-Pressure Combined Cycle With CO2 Capture

The European electric power industry has undergone considerable changes over the past two decades as a result of more stringent laws concerning environmental protection along with the deregulation and liberalization of the electric power market. However, the pressure to deliver solutions in regard to the issue of climate change has increased dramatically in the last few years and has given rise to the possibility that future natural gas-fired combined cycle (NGCC) plants will also be subject to CO2 capture requirements. At the same time, the interest in combined cycles with their high efficiency, low capital costs, and complexity has grown as a consequence of addressing new challenges posed by the need to operate according to market demand in order to be economically viable. Considering that these challenges will also be imposed on new natural gas-fired power plants in the foreseeable future, this study presents a new process concept for natural gas combined cycle power plants with CO2 capture. The simulation tool IPSEpro is used to model a 400 MW single-pressure NGCC with post-combustion CO2 capture using an amine-based absorption process with monoethanolamine. To improve the costs of capture, the gas turbine GE 109FB is utilizing exhaust gas recirculation, thereby, increasing the CO2 content in the gas turbine working fluid to almost double that of conventional operating gas turbines. In addition, the concept advantageously uses approximately 20% less steam for solvent regeneration by utilizing preheated water extracted from heat recovery steam generator. The further recovery of heat from exhaust gases for water preheating by use of an increased economizer flow results in an outlet stack temperature comparable to those achieved in combined cycle plants with multiple-pressure levels. As a result, overall power plant efficiency as high as that achieved for a triple-pressure reheated NGCC with corresponding CO2 removal facility is attained. The concept, thus, provides a more cost-efficient option to triple-pressure combined cycles since the number of heat exchangers, boilers, etc., is reduced considerably. (Less)

Operational Improvements for Startup Time Reduction in Solar Steam Turbines

Solar steam turbines are subject to high thermal stresses as a result of temperature gradients during transient operation, which occurs more frequently due to the variability of the solar resource. In order to increase the flexibility of the turbines while preserving lifing requirements, several operational modifications for maintaining turbine temperatures during offline periods are proposed and investigated. The modifications were implemented in a dynamic thermal turbine model and the potential improvements were quantified. The modifications studied included: increasing the gland steam pressure injected to the end-seals, increasing the back pressure and increasing the barring speed. These last two take advantage of the ventilation and friction work. The effects of the modifications were studied both individually as well as in different combinations. The temperatures obtained when applying the combined modifications were compared to regular turbine cool-down temperatures and showed significant improvements on the start-up times of the turbine.

Numerical Investigation of the Effect of Different Back Sweep Angle and Exducer Width on the Impeller Outlet Flow Pattern of a Centrifugal Compressor With Vaneless Diffuser

This paper presents a numerical investigation of the effect of different back sweep angles and exducer widths on the steady-state impeller outlet flow pattern of a centrifugal compressor with a vaneless diffuser. The investigations have been performed with commercial computational fluid dynamics (CFD) and in-house programmed one-dimensional (ID) codes. CFD calculations aim to investigate how flow pattern from the impeller is quantitatively influenced by compressor geometry parameters; thereby, the location of wake and its magnitude (flow angle and relative velocity magnitude) are analyzed. Results show that the increased back sweep impeller provides a more uniform flow pattern in terms of velocity and flow deviation angle distribution, and offers better potential for the diffusion process inside a vaneless (or vaned) diffuser Secondary flux fraction and flow deviation angle from CFD simulation are implemented into the ID two-zone program to improve ID prediction results. (Less)

Steady-State and Transient Compressor Surge Behavior Within a SOFC-GT-Hybrid System

Future pressurized Solid Oxide Fuel Cell- (SOFC) Gas Turbine Hybrid Systems (HS) promise high efficiency at both full-and part-load on account of the upper and lower SOFC temperature limit and the compressor surge line [1]. The compressor surge constraint is also evident in transient HS operation, caused by the slow transients of SOFC temperature imposed by large SOFC plenum, and fast turbo-machinery transients. This paper presents steady-state and unsteady-state HS modeling and calculation results with regard to surge. The transient compressor and SOFC models have been validated against literature. Calculation results of the coupled SOFC-GT-HS reveal a small operational window in case of unmatched turbine and the critical transient characteristics for HS shut-down. (Less)

Optimization of an Oxyfuel Combined Cycle Regarding Performance and Complexity Level

The aim of this paper is to establish and motivate the design parameters of a 125 MW Oxyfuel Combined Cycle (OCC) also referred to as the Semi-Closed Oxyfuel-Combusted Combined Cycle (SCOC-CC). This paper proposes a compatible OCC that does not include any unconventional features, beyond what is state-of-the-art in gas turbine technology today. Such features could challenge the feasibility to bring the concept to the market in a reasonable time.The OCC requires a higher pressure ratio compared to a conventional combined cycle in order to achieve exhaust conditions that fit the design of the bottoming cycle. However, a high gas turbine pressure ratio increases the complexity of the machine and must be weighted against the gain in efficiency. The OCC gas turbine is modeled using a cooling model which keeps the metal temperature of all cooled turbine stages constant while seeking the optimum pressure ratio.As the cycle is semi-closed the compressor inlet temperature is a design parameter: it is shown that there is an efficiency optimum clearly in the range of what is normally achievable. As the gas properties of the OCC flue gas differ from the conventional plant, the effects of this on the HRSG design are explored.© 2013 ASME

Post-Combustion CO2 Capture for Combined Cycles Utilizing Hot-Water Absorbent Regeneration

The partly hot-water driven CO2 capture plant offers a significant potential for improvement in performance when implemented in a combined-cycle power plant (CCPP). It is possible to achieve the same performance with a dual-pressure steam cycle as in a triple-pressure unit. Even a single-pressure plant can attain an efficiency competitive with that achievable with a triple-pressure plant without the hot-water reboiler. The underlying reasons are better heat utilization in the heat recovery unit and less steam extraction to the absorbent regenerating unit(s). In this paper, the design criteria for a combined cycle power plant utilizing hot-water absorbent regeneration will be examined and presented. The results show that the most suitable plant is one with two steam pressure levels. The low-pressure level should be much higher than in a conventional combined cycle in order to increase the amount of heat available in the economizer. The external heat required in the CO2 capture plant is partly supplied by the economizer, allowing temperature optimization in the unit. The maximum value of the low-pressure level is determined by the reboiler, as too great a temperature difference is unfavourable. This work evaluates the benefits of coupling the economizer and the reboiler in a specially designed CCPP. In the CO2 separation plant both monoethanolamine (MEA) and ammonia are evaluated as absorbents. Higher regeneration temperatures can be tolerated in ammonia-based plants than in MEA-based plants. When using a liquid heat carrier the reboiler temperature is not constant on the hot side, which results in greater temperature differences. The temperature difference can be greatly reduced by dividing the regeneration process into two units operating at different pressures. The possibility of extracting more energy from the economizer to replace part of the extracted steam increases the plant efficiency. The results show that very high efficiencies can be achieved without using multiple pressure-levels. (Less)

Conceptual Design of a Mid-Sized Semi-Closed Oxy-Fuel Combustion Combined Cycle

This paper presents the study of a mid-sized semi-closed oxy-fuel combustion combined cycle (SCOC-CC) with net power output around 108 MW. The paper describes not only the power balance and the performance of the SCOC-CC, but also the conceptual design of the SCOC turbine and compressor. A model has been built in the commercial heat and mass balance code IPSEpro to estimate the efficiency of semi-closed dual-pressure oxy-fuel combustion combined cycle using natural gas as a fuel. In order to obtain the real physical properties of the working fluids in IPSEpro, the code was linked to the NIST Reference Fluid Thermodynamic and Transport Properties Database (REFPROP). The oxy-fuel turbine was modeled with the in-house Lund University package LUAX-T. Important features such as stage loading, loss modeling, cooling and geometric features were included to generate more accurate results. The oxy-fuel compressor has been modeled using a Chalmers university in-house tool for conceptual design of axial compressors. The conceptual design of the SCOC-CC process has a net efficiency of 47 %. The air separation unit and CO2 compression reduce the cycle efficiency by 10 and 2 percentage points, respectively. A single-shaft configuration was selected for the gas turbine simplicity. The rotational speed chosen was 5200 rpm and the turbine was designed with four stages. All stage preliminary design parameters are within ranges of established industrial axial turbine design limits. The main issue is the turbine exit Mach number; the stage must be lightly loaded in terms of pressure ratio to maintain the exit Mach number below 0.6. The compressor is designed with 18 stages. The current value of the product of the annulus area and the blade rotational speed squared (AN2) was calculated and found to be 40*10^6.

Optimal Combined Cycle For Co2 Capture With EGR

Most state-of-the-art natural gas fired combined cycle (NGCC) plants are triple-pressure reheat cycles with efficiencies close to 60 percent. However, with carbon capture and storage, the efficiency will be penalized by almost 10 percent units. To limit the energy consumption for a carbon capture NGCC plant, exhaust gas recirculation (EGR) is necessary. Utilizing EGR increases the CO2 content in the gas turbine exhaust while it reduces the flue gas flow to be treated in the capture plant. Nevertheless, due to EGR, the gas turbine will experience a different: media with different properties compared to the design case. This study looks into how the turbo machinery reacts to EGR. The work also discusses the potential of further improvements by utilizing pressurized water rather than extraction steam as the heat source for the CO2 stripper. The results show that the required low-pressure level should be elevated to a point close to the intermediate-pressure to achieve optimum efficiency; hence one pressure level can be omitted. The main tool used for this study is an in-house off-design model based on fully dimensionless groups programmed in the commercially-available heat and mass balance program IPSEpro. The model is based on a GE 109FB machine with a triple-pressure reheat steam cycle. (Less)