Test results of a catalytically assisted combustor for a gas turbine

A catalytically assisted ceramic combustor for a gas turbine was designed and tested to achieve low NO_x emissions. This combustor is composed of a burner and a ceramic liner. The burner consists of an annular preburner, six catalytic combustor segments and six premixing nozzles, which are arranged in parallel and alternately. In this combustor system, catalytic combustion temperature is controlled under 1000 °C, premixed gas is injected from the premixing nozzles to the catalytic combustion gas and lean premixed combustion over 1300 °C is carried out in the ceramic liner. This system was designed to avoid catalyst deactivation at high temperature and thermal shock fracture of the ceramic honeycomb monolith of the catalyst. A 1 MW class combustor was tested using LNG fuel. Firstly, NO_x emissions from the preburner were investigated under various pressure conditions. Secondly, two sets of honeycomb cell density catalysts and one set of thermally pretreated catalysts ware applied to the combustor, and combustion tests were carried out under various pressure conditions. As a result, it was found that the main source of NO_x was the preburner, and total NO_x emissions from the combustor were approximately 4 ppm (at 16% O₂) at an adiabatic combustion temperature of 1350 °C and combustor inlet pressure of 1.33 MPa.     

Development of a catalytically assisted combustor for a gas turbine

A catalytically assisted low NO_x combustor has been developed which has the advantage of catalyst durability. This combustor is composed of a burner section and a premixed combustion section behind the burner section. The burner system consists of six catalytic combustor segments and six premixing nozzles, which are arranged alternately and in parallel. Fuel flow rate for the catalysts and the premixing nozzles are controlled independently. The catalytic combustion temperature is maintained under 1000°C, additional premixed gas is injected from the premixing nozzles into the catalytic combustion gas, and lean premixed combustion at 1300°C is carried out in the premixed combustion section. This system was designed to avoid catalytic deactivation at high temperature and thermal or mechanical shock fracture of the honeycomb monolith. In order to maintain the catalyst temperature under 1000°C, the combustion characteristics of catalysts at high pressure were investigated using a bench scale reactor and an improved catalyst was selected for the combustor test. A combustor for a 20 MW class multi-can type gas turbine was designed and tested under high pressure conditions using LNG fuel. Measurements of NO_x, CO and unburned hydrocarbon were made and other measurements were made to evaluate combustor performance under various combustion temperatures and pressures. As a result of the tests, it was proved that NO_x emission was lower than 10 ppm converted at 16% O₂, combustion efficiency was almost 100% at 1300°C of combustor outlet temperature and 13.5 ata of combustor inlet pressure.     

Development of a low NOx catalytic combustor for a gas turbine

Catalytic combustion is an advanced combustion technology and is effective as a NO_x control for a 1300°C class gas turbine for power generation, but the catalyst reliability at high temperatures is still insufficient. To overcome this difficulty, catalytic combustors combined with premixed combustion were designed. In this concept, it is possible to obtain combustion gas at a temperature of 1300°C while keeping the catalyst bed temperature below 1000°C. Catalyst segments are arranged alternately with premixing nozzles for the mixing of catalytic combustion gas and fresh premixture. An air bypass valve was fitted to this combustor for extending the range of stable combustion. As a result of the atmospheric combustion tests, NO_x emission was lower than 5 ppm, combustion efficiency was almost 100%, and high combustion efficiency was obtained in the range of 900–1300°C of the combustor exit gas temperature. A full-pressure combustion test is planned to prove the combustor performance.     

Development of a catalytic combustor for a heavy-duty utility gas turbine

Catalytic combustion is an attractive technology for gas turbine applications where ultra-low emission levels are required. Recent tests of a catalytic reactor in a full scale combustor have demonstrated emissions of 3.3 ppm NO_x, 2.0 ppm CO, and 0.0 ppm UHC. The catalyst system is designed to only convert about half of the natural gas fuel within the catalyst itself, thus limiting the catalyst temperature to a level that is viable for long-term use. The remainder of the combustion occurs downstream from the catalyst to generate the required inlet temperature to the turbine.

Catalyst development is typically done using subscale prototypes in a reactor system designed to simulate the conditions of the full scale application. The validity of such an approach is best determined experimentally by comparing catalyst performance at the two size scales under equivalent reaction conditions. Such a comparison has recently been achieved for catalysts differing in volume by two orders of magnitude. The performance of the full scale catalyst was similar to that of the subscale unit in both emission levels and internal temperatures. This comparison lends credibility to the use of subscale reactors in developing catalytic combustors for gas turbines.     

Development of a hybrid catalytic combustor for a 1300°C class gas turbine

The hybrid catalytic combustor concept proposed by the authors has an advantage concerned with catalyst durability, because the catalyst is maintained below 1000°C even for application to 1300°C class gas turbines. A full-scale hybrid catalytic combustor has been designed for a 200 MW (1300°C) class gas turbine. The catalyst bed was 450 mm in diameter and consisted of a Pd/ alumina washcoat on a cordierite monolith. In experiments, the combustor has demonstrated the capability of meeting the NO_x emission level of SCR (selected catalytic reduction) during atmospheric pressure testing. To predict the catalyst performance at an elevated pressure, the characteristics of the catalyst were studied using a small scale reactor test, and a material property test using a DTA/TGA-Q.MASS system. The catalyst showed a higher activity in the oxidized state (PdO) than in the metallic state (Pd). This activity difference was governed by the equilibrium of the oxygen release from PdO in bulk. It was considered that oxidation rate of the metallic Pd in bulk was not so high and this caused self-oscillation for the Pd catalyst around the temperature of the oxygen release equilibrium. Even below the temperature of the oxygen release equilibrium, both surface and bulk (lattice) oxygen of the PdO was consumed by the methane oxidation reaction, and resulted in a lack of surface oxygen on the catalyst. This caused a reversible decrease in the catalyst activity during combustion testing, and indicated that the oxygen dissociation step was a rate limiting step in the catalytic combustion.     

Advanced technology catalytic combustor for high temperature ground power gas turbine applications

We report results from a lean burn ultra-low emission catalytic combustor. In a sub-scale rig, atmospheric testing with methane demonstrated NO_x<3, CO<5, and UHC<1 ppm, with stable combustion at inlet temperatures of 400–500°C (750–1020°F) and combustor discharge temperatures of 1150–1540°C (2100–2800°F). Catalyst temperatures were held well below metal substrate material limits, while combustor discharge temperatures of up to 1540°C (2800°F) were achieved.     

Application of catalytic combustion to a 1.5 MW industrial gas turbine

A catalytic combustor is described for a 1.5 MW gas turbine engine. The catalyst temperature is limited and the high combustor outlet temperatures required by the turbine are generated downstream of the catalyst. The combustor design places a low NO_x preburner upstream of the catalyst and uses this preburner to achieve optimum catalyst operation by providing the desired catalyst inlet temperature. The combustor system employs the catalyst during engine acceleration and loading. The catalyst design has been tested on a sub-scale rig under full pressure and flow conditions simulating turbine operation over the entire operating range including acceleration and loading. The design should achieve emissions at full load operation of <3 ppm NO_x and <10 ppm CO and UHC. Low emissions operation is expected over the 75–100% load range. In addition, long-term sub-scale rig test results are reported at simulated full load operating conditions including cyclic operation and full load trips.     

Numerical simulation of the two-dimensional flow in high pressure catalytic combustor for gas turbine

The objective of this paper is modeling the mechanism of high pressure and high temperature catalytic oxidation of natural gas, or methane. The model is two-dimensional steady-state, and includes axial and radial convection and diffusion of mass, momentum and energy, as well as homogeneous (gas phase) and heterogeneous (gas surface) single step irreversible chemical reactions within a catalyst channel. Experimental investigations were also made of natural gas, or methane combustion in the presence of Mn-substituted hexaaluminate catalysts. Axial profiles of catalyst wall temperature, and gas temperature and gas composition for a range of gas turbine combustor operating conditions have been obtained for comparison with and development of a computer model of catalytic combustion. Numerical calculation results for atmospheric pressure agree well with experimental data. The calculations have been extended for high pressure (10 atm) operating conditions of gas turbine.     

Achieving ultra low emissions in a commercial 1.4 MW gas turbine utilizing catalytic combustion

The drive to achieve low emissions from gas turbines has been an ongoing challenge for over 30 years with the reduction of NO_x levels representing the most difficult issue. Catalytic combustion represents the technological approach that can achieve the lowest level of NO_x, in the range of 3 ppm and lower depending on the combustion system design. The program to develop a catalytic combustion technology that can achieve ultra low levels of NO_x, CO and unburned hydrocarbons (UHCs), applicable to a wide range of gas turbine systems and with long term durability is described. The technological approach is to combust only a portion of the fuel within the catalyst with the remaining fuel combusted downstream of the catalyst allowing the catalyst to operate at a low temperature and thus obtaining good long term catalyst durability. This catalytic combustion approach is then applied to a 1.4 MW gas turbine to demonstrate feasibility and to obtain real field experience and to identify issues and areas needing further work. The success of this demonstration lead to a commercial combustor design. This combustor and the final commercial package is described and the performance specifications discussed.     

Catalytic combustion technology to achieve ultra low NOx, emissions: Catalyst design and performance characteristics

A catalytic combustion system has been developed which feeds full fuel and air to the catalyst but avoids exposure of the catalyst to the high temperatures responsible for deactivation and thermal shock fracture of the supporting substrate. The combustion process is initiated by the catalyst and is completed by homogeneous combustion in the post catalyst region where the highest temperatures are obtained. Catalysts have been demonstrated that operate at inlet temperatures as low as 320°C at 11 atm total pressure and conditions typical of high performance industrial gas turbines. The ignition temperature is shown to correlate with the specific catalytic activity of the washcoat layer over a rather broad range of activities. A reaction model has been developed that can predict ignition behavior from the measured catalytic activity.     

Catalytic combustion for power generation

Catalytically stabilised combustion (CST) has the potential to become the best available low NO_x combustion technology with demonstrated NO_x emissions less than 3 ppm. Gas turbines incorporating CST may therefore eventually enjoy a significant market share; as such, the leading gas turbine manufacturers are actively working in this field. However, the demands made upon catalysts are challenging indeed. The present paper discusses practical issues concerning the application of catalytically stabilised combustion to gas turbines. It additionally reports on the ongoing investigation of methane/air CST (using palladium catalysts) at conditions relevant to gas turbines (inlet temperatures up to 500 °C, pressures up to 30 bar and spatial velocities up to 10⁶ h⁻¹).     

Emissions and wall temperatures for lean prevaporized premixed gas turbine combustor

Experimental studies are carried out for investigating emission and wall temperature for traditional gas turbine combustor converted to lean premixed prevaporized (LPP) combustor. Vortex chamber, air preheating system, flat flame burner and inlet temperature control system are designed. Vortex chamber was maintained at the main air inlet port for controlling secondary air flow rate and wall temperature. Kerosene/air mixture temperature at exit from burner and entering combustion chamber was kept constant at 650 K for all runs. Special considerations were given for measuring NO_X, UHC, CO, local A/F ratio, flame temperature, exhaust gases temperature and wall temperature. For swirl and non swirl cases, secondary air ratio and primary zone air/fuel ratio were varied. The different operating parameters affecting flame temperature through it is affecting on local A/F ratio which is the main parameter for controlling flame temperature, emissions and walls temperatures. Flat flame burner and vortex chamber are useful tools for reducing emission and controlling walls temperatures. The inner liner wall temperatures are more affected by primary zone equivalence ratio while the outer liner wall temperatures are more affected by secondary air flow rate. Semi empirical correlations for NO_X, UHC and CO concentrations, exhaust gases temperature and maximum inner liner wall temperature are carried out. Good agreement between the measured and the calculated results are obtained. The present results are useful for further development of the traditional gas turbine combustor converted to LPP combustor.     

Development of a high-temperature combustion catalyst system and prototype catalytic combustor turbine test results

A new combustion catalyst system for gas turbines composed of high-temperature durable ceramic catalysts made of fine manganese-substituted hexaaluminate particles and noble metal-carrying cordierite honeycomb catalysts has been developed. A 160 kW prototype catalytic combustor turbine rigged with a 220 mm in diameter catalyst system was constructed and tested including a continuous 215-hour operation and repeated sudden stops. The results showed practical combustion performance with ultra-low NO_x emissions less than 40 ppm (converted to 0% oxygen) and the feasibility of long term catalyst durability.     

Cyclone gasifier and cyclone combustor for the use of biomass derived gas in the operation of a small gas turbine in cogeneration plants

An inverted cyclone gasifier and secondary cyclone combustor have been developed for use in a biomass fired small-scale cogeneration plant. The gasifier was designed with a vortex collector pocket (VCP) and a central collector pocket (CCP) to maximise particle and ash separation from the flow, and remove alkali and other heavy metal traces that agglomerate with the ash particles. The gasifier design was robust and suitable for firing with varying input conditions. The gasifier exhaust gas is suitable for directly firing into the secondary cyclone combustor without any complex hot gas clean up systems. The cyclone combustor produces a strong swirling flow with good mixing and burnout patterns, creating stable combustion conditions. The use of an additional VCP situated before the combustor exit removes the need for additional cyclone separators. An exhaust mounted tangential off-take on the combustor reduces pressure drop across the system and gives near uniform exhaust velocity profiles. The gasifier achieved 98–99% burnout with good separation/retention rates and 50% alkali, Na and K removal. A good quality low calorific value (LCV) gas was produced that could be effectively utilised in the cyclone combustor. The cyclone combustor produces a stable flow, with good mixing and burnout rates, and uniform exit conditions and could be operated in a lean mode to minimize NO_x. The additional use of a VCP removed particles above 5 μm, as specified by turbine inlet conditions. The gas was suitable for directly firing into the gas turbine. Low pressure drop was found across the system.     

Development of a catalytic combustor with heat exchanger

Catalytic combustion is thought to be a considerable improvement on the traditional one under specific conditions. Due to its special features, catalytic combustion has two strong points compared to flame: no NO_x emission and high reaction efficiency. However, the preheating process of catalytic combustion is an obstacle that deteriorates profitability in operation. So the HTHE (High Temperature Heat Exchanger) is adapted to the system to reinforce the preheating process, and we show that the catalytic combustion is maintained steadily without exceptional heat injection. As a result, the stability on the catalytic surface is the most important operational factor. To achieve it, both mixture gas property and temperature distribution should be controlled.     

Catalytic combustion system for a 10 MW class power generation gas turbine

In early 2000, GE Energy launched a program to develop a catalytic combustion system for one of its small power generation gas turbines, the GE10-1 engine. The target was to release to the market a new combustor able to guarantee NO_x emissions lower than 2.5 ppmvd (referred to 15 vol.% O₂). Today, a full-scale engine test campaign has been completed, during which measured NO_x emissions were as low as 1 ppmvd in the 90–100% load range.

The article is aimed to illustrate the developed technology and the results obtained. The combustion system's configuration is briefly described, focusing on the XONON^® catalyst module installed. Reported data show combustion system's performances, mainly in terms of pollutant emissions and operability. Perspectives for future development of such combustion system are outlined.     

Identification of a smart bond coating for gas turbine engine applications

A smart bond coating was successfully identified for thermal barrier coatings (TBCs) that promotes appropriate protective scales preferentially during service depending on the environmental conditions. It enhances the life of super alloy components life significantly, which is essential for increasing the efficiency of advanced gas turbine engines. It is expected to be a potential bond coating for advanced gas turbine engine blades of different types, i.e., aero, industrial, and marine for their protection against high temperature oxidation, type I, and type II hot corrosion.     

Automatic heat-shrink sleeve applicator using the low-temperature catalytic combustor

Catalytic combustion for applying heat shrink sleeves (HSS) to a pipeline in KOGAS was investigated. We used a low temperature catalytic combustor in order to place HSS in the conduit. The surface temperature of the catalytic combustor maintained the conditions at which HSS can become well-adhesive at the conduit. Therefore, the automatic HSS construction provided the chance to establish gas pipeline safety by an automatic catalytic combustor device.     

Catalytic combustion concept for gas turbines

Catalytic combustion for gas turbines was investigated, based on a partial catalytic combustion section followed by a homogeneous combustion zone. A pressurized test rig (<25 bar) was built to test the influence of various parameters on this concept using Pd and Pt catalysts.

The pressure influence on the apparent catalytic reaction rate was of the order 0.4, assuming that the reaction kinetics could be described by a power rate function which was of first order with respect to methane. Pd catalysts showed a pressure-dependent temperature for the transition of the active PdO to the much less active Pd. Combining Pd and Pt within one catalyst resulted in a considerably lower transition temperature.

Homogeneous combustion reactions set on from 650°C, depending on the methane concentration, pressure and flow. With inlet temperatures above 800°C the homogeneous combustion always started. At outlet temperatures below 1050°C high CO concentrations could be measured. At higher temperatures the CO, CH₄ and NO_x concentrations were lower than 5 ppm. During several experiments total conversion of CH₄ and CO was observed.     

Recent developments on catalytic membrane for gas cleaning

Catalytic membrane, a novel membrane separation technology that combines catalysis and separation, exhibits significant potential in gas purification such as formaldehyde, toluene and nitrogen oxides(NO_x). The catalytic membrane can remove solid particles through membrane separation and degrade gaseous pollutants to clean gas via a catalytic reaction to achieve green emissions. In this review, we discussed the recent developments of catalytic membranes from two aspects: preparation of catalytic membrane and its application in gas cleaning.Catalytic membranes are divided into organic catalytic membranes and inorganic catalytic membranes depending on the substrate materials. The organic catalytic membranes which are used for low temperature operation(less than 300 °C) are prepared by modifying the polymers or doping catalytic components into the polymers through coating, grafting, or in situ growth of catalysts on polymeric membrane. Inorganic catalytic membranes are used at higher temperature(higher than 500 °C). The catalyst and inorganic membrane can be integrated through conventional deposition methods, such as chemical(physical) vapor deposition and wet chemical deposition. The application progress of catalytic membrane is focused on purifying indoor air and industrial exhaust to remove formaldehyde, toluene, NO_x and PM2.5, which are also summarized. Perspectives on the future developments of the catalytic membranes are provided in terms of material manufacturing and process optimization.