Timothy Griffin

High-pressure experiments and modeling of methane/air catalytic combustion for power-generation applications

The catalytic combustion of methane/air mixtures is investigated experimentally and numerically at gas turbine relevant conditions (inlet temperatures up to 873 K, pressures up to 15 bar and spatial velocities up to 3 × 10 6 h −1 ). Experiments are performed in a sub-scale test rig, consisting of a metallic honeycomb structure with alternately coated (Pd-based catalyst) channels. Simulations are carried out with a two-dimensional elliptic fluid mechanical code that incorporates detailed transport and heat loss mechanisms, and realistic heterogeneous and homogeneous chemistry description. The methodology for extracting heterogeneous kinetic data from the experiments is presented, and the effects of catalytic activity and channel geometry (length and hydraulic diameter) on reactor performance are elucidated. A global catalytic kinetic step provides excellent agreement (at temperatures below 950 K) between the measured and predicted fuel conversion, over a wide range of parameter variation (channel hydraulic diameter and length, pressure, and inlet temperature). It is shown that, under a certain combination of catalytic activity and channel length, the absolute temperature rise across the catalyst becomes essentially independent of pressure, a feature highly desirable for many practical systems. Even though the computed catalyst surface temperatures remain well below the decomposition temperature of PdO, a significant section of the catalyst—amounting up to 30% of the total reactor length—contributes minimally to the total fuel conversion, suggesting catalytic activity design improvements in the reactor entry.

Advanced zero emissions gas turbine power plant

The AZEP advanced zero emissions power plant project addresses the development of a novel zero emissions, gas turbine-based, power generation process to reduce local and global CO 2 emissions in the most cost-effective way. Process calculations indicate that the AZEP concept will result only in a loss of about 4% points in efficiency including the pressurization of CO 2 to 100 bar, as compared to approximately 10% loss using conventional tail-end CO 2 capture methods. Additionally, the concept allows the use of air-based gas turbine equipment and, thus, eliminates the need for expensive development of new turbomachinery. The key to achieving these targets is the development of an integrated MCM-reactor in which (a) O 2 is separated from air by use of a mixed-conductive membrane (MCM), (b) combustion of natural gas occurs in an N 2 -free environment, and (c) the heat of combustion is transferred to the oxygen-depleted air by a high temperature heat exchanger. This MCM-reactor replaces the combustion chamber in a standard gas turbine power plant. The cost of removing CO 2 from the combustion exhaust gas is significantly reduced, since this contains only CO 2 and water vapor The initial project phase is focused on the research and development of the major components of the MCM-reactor (air separation membrane, combustor, and high temperature heat exchanger), the combination of these components into an integrated reactor, and subsequent scale-up for future integration in a gas turbine. Within the AZEP process combustion is carried out in a nearly stoichiometric natural gas/O 2 mixture heavily diluted in CO 2 and water vapor The influence of this high exhaust gas dilution on the stability of natural gas combustion has been investigated, using lean-premix combustion technologies. Experiments have been performed both at atmospheric and high pressures (up to 15 bar), simulating the conditions found in the AZEP process. Preliminary tests have been performed on MCM modules under simulated gas turbine conditions. Additionally, preliminary reactor designs, incorporating MCM, heat exchanger, and combustor, have been made, based on the results of initial component testing. Techno-economic process calculations have been performed indicating the advantages of the AZEP process as compared to other proposed CO 2 -free gas turbine processes.

Catalytic combustion of methane over bimetallic catalysts a comparison between a novel annular reactor and a high-pressure reactor

Abstract The effects of adding a co-metal, Pt or Rh, to Pd/γ-Al2O3 catalysts were studied with respect to the catalytic activity for methane combustion and compared to a Pd/γ-Al2O3 catalyst, using both a pressurized pilot-scale and a lab-scale annular reactor. Temperature programmed oxidation (TPO) experiments were also carried out to investigate the oxygen release/uptake of the catalyst materials. Palladium showed an unstable behavior both in the pilot and lab-scale experiments at temperatures well below the PdO to Pd transformation. An addition of Pt to Pd stabilized, and in some cases increased, the catalytic activity for methane combustion. The TPO experiments showed that the oxygen release peak was shifted to lower temperatures even for low additions of Pt, i.e. Pd:Pt=2:1. For additions of rhodium only small beneficial effects were seen. The steady-state behavior of the lab-scale annular reactor correspond well to the pressurized pilot-scale tests.

Palladium-catalyzed combustion of methane: simulated gas turbine combustion at atmospheric pressure

Abstract Atmospheric pressure tests were performed in which a palladium catalyst ignites and stabilizes the homogeneous combustion of methane. Palladium exhibited a reversible deactivation at temperatures above 750°C, which acted to “self-regulate” its operating temperature. A properly treated palladium catalyst could be employed to preheat a methane/air mixture to temperatures required for ignition of gaseous combustion (ca. 800°C) without itself being exposed to the mixture adiabatic flame temperature. The operating temperature of the palladium was found to be relatively insensitive to the methane fuel concentration or catalyst inlet temperature over a wide range of conditions. Thus, palladium is well suited for application in the ignition and stabilization of methane combustion.

Micro-engineered catalyst systems: ABB's advancement in structured catalytic packings

Abstract ABB has advanced catalysis with micro-engineered catalyst (MEC) systems by providing a uniquely small particle size on a formable catalyst support through the integration of catalysis and reaction engineering. A mechanically strong catalytic web of micro-fibers has been engineered and shaped utilizing both computational fluid dynamics (CFD) and cold flow experiments to optimize flow characteristics. This article discusses techniques used for the development of novel catalytic structured packings for catalytic distillation applications. CFD models (verified through experiments performed on small-sized structures) were shown to be of great utility in screening new structure ideas. Results will illustrate achievement of both high gas–liquid contacting and bulk mixing at low pressure drop with the potential to provide enhanced catalyst utilization by taking advantage of the intrinsic MEC properties, particularly its high porosity and exposed geometric fiber and catalyst surface area. This was shown by the successful testing of one of these catalyzed structures in the selective hydrogenation of C4 acetylenes.

Staged Catalytic Combustion Method for the Advanced Zero Emissions Gas Turbine Power Plant

The AZEP (Advanced Zero Emissions Power Plant) project addresses the development of a novel “zero emissions,” gas turbine-based, power generation process to reduce CO2 emissions. Preliminary calculations indicate the attractiveness of this concept in comparison to conventional tail-end CO2 capture. Key to achieving the AZEP project targets is the development of a combustion system to burn natural gas with nearly stoichiometric amounts of oxygen and high levels of exhaust gas dilution. Within the first part of this study the fundamental combustion properties of AZEP gas mixtures are quantitatively determined. Significant inhibition results from the high level of exhaust gas dilution. In the second part a staged, rich–lean combustion concept, proposed to improve combustion stability, is investigated. It was shown that significant levels of hydrogen could be produced by a first stage, partial catalytic oxidation (PCO) of methane. Furthermore, it is shown that the addition of this produced hydrogen improves the stability of the downstream, second stage burnout zone. It was demonstrated that the produced syngas could act to reduce the blowout limit by ca. 100 K as compared to homogeneous gas phase combustion.Copyright

Technology Options for Gas Turbine Power Generation With Reduced CO2 Emission

ALSTOM Power R&D laboratories run various programs aimed at finding options that reduce or avoid CO 2 emissions through the following: (a) high efficiency power generation equipment to utilize fossil fuels with the lowest possible emissions, and (b) technologies to remove and sequester CO 2 created in power plants in an environmentally and economically favorable manner. In this paper, an overview of ongoing CO 2 mitigation activities for gas turbine power generation is addressed. Energy efficiency improvements for both new and existing fossil fuel power plants are briefly reviewed. Customer requirements for future power plants with reduced CO 2 emissions are discussed. Novel power generation cycles with exhaust gas recirculation for enhanced CO 2 removal are introduced and evaluated. Conclusions are drawn regarding their efficiency, energy consumption, and technical feasibility.

Chapter 31 – Techno-Economic Evaluation of an Oxyfuel Power Plant Using Mixed Conducting Membranes

Publisher Summary This chapter evaluates the techno-economic performance of gas turbine power plants with zero or low CO2 emission. The plant concepts make use of “Mixed Conducting Membranes” (MCMs) to extract oxygen from the inlet air and thus enable combustion of gaseous hydrocarbon fuels in a nitrogen-free environment. Three different base configurations are identified, each run in two different modes with and without supplementary firing. These six cases are compared to a conventional non-capture, gas turbine plant. The thermodynamic process simulations showed penalties in terms of the net electrical efficiency between 2.4 and 6.8%-points for the different configurations. These penalties include the capture, purification, and compression of the carbon dioxide. The economic evaluation revealed very promising figures, estimating costs of CO2 avoided from 17.3 US

Heat transfer characterization of support structures for catalytic combustion

/ton to as low as 7.3 US

CO2 control technologies: Alstom power approach

/ton, if a value of 20 US