Fundamental Study on Hydrogen Low-NOx Combustion Using Exhaust Gas Self-Recirculation

Hydrogen is expected to be a next-generation energy source that does not emit carbon dioxide, but when used as a fuel, the issue is the increase in the amount of NOx that is caused by the increase in flame temperature. In this study, we experimentally investigated NOx emissions rate when hydrogen was burned in a hydrocarbon gas burner, which is used in a wide temperature range. As a result of the experiments, the amount of NOx when burning hydrogen in a nozzle mixed burner was twice as high as when burning city gas. However, by increasing the flow velocity of the combustion air, the amount of NOx could be reduced. In addition, by reducing the number of combustion air nozzles rather than decreasing the diameter of the air nozzles, a larger recirculation flow could be formed into the furnace, and the amount of NOx could be reduced by up to 51%. Furthermore, the amount of exhaust gas recirculation was estimated from the reduction rate of NOx, and the validity was confirmed by the relationship between adiabatic flame temperature and NOx calculated from the equilibrium calculation by chemical kinetics simulator software.

Fundamental Study on Ammonia Low-NOx Combustion Using Two-Stage Combustion by Parallel Air Jets

Ammonia, which has advantages over hydrogen in terms of storage and transportation, is increasingly expected to become a carbon-free fuel. However, the reduction of fuel NOx emitted from ammonia combustion is an unavoidable challenge. There is the report that two-stage combustion with parallel independent jets could achieve Low-NOx combustion under ammonia/methane co-firing conditions. In order to further improve NOx reduction, we experimentally evaluated the effects of secondary air nozzle parameters, such as nozzle diameter and nozzle locations, on combustion characteristics in two-stage combustion of ammonia/natural gas co-firing using parallel independent jets. As a result of the experiments under various secondary air nozzle conditions, it was found that under the conditions where NOx was significantly reduced, the peak temperature in the furnace was observed at 300–500 mm in the axial direction from the burner, and then the temperature decreased toward the downstream of the furnace. We assumed that this temperature distribution reflected the mixing conditions of the fuel and secondary air and estimated the combustion conditions in the furnace. It was confirmed that the two-stage combustion was effective in reducing NOx by forming a fuel rich region near the downstream of the burner, and the lean combustion of the unburned portion of the first stage combustion with secondary air. We confirmed that the low NOx effects could be achieved by two-stage combustion using independent jets from the same wall under appropriate combustion and air nozzle conditions.

Overall Cooling Effectiveness of Effusion Cooled Can Combustor Liner under Reacting and Non-Reacting Conditions

Emphasis on lean premixed combustion in modern low NOX combustion chambers limits the air available for cooling the combustion liner. Hence the development of optimized liner cooling designs is imperative for effective usage of available coolant. An effective way to cool a gas turbine combustor liner is through effusion cooling. Effusion cooling (also known as full-coverage film cooling) involves uniformly spaced holes distributed throughout the liner's curved surface area. This paper presents findings from an experimental study on the characterization of the overall cooling effectiveness of an effusion-cooled liner wall, which was representative of a can combustor under heated flow (non-reacting) and lean-combustion (reacting) conditions. The model can-combustor was equipped with an industrial swirler, which subjected the liner walls to engine representative flow and combustion conditions. In this study, two different effusion cooling liners with an inline and staggered arrangement of effusion holes have been studied. These configurations were tested for five different blowing ratios ranging from 0.7 to 4.0 under both reacting and non-reacting conditions. Infrared Thermography (IRT) was used to measure the liner outer surface temperature, and detailed overall effectiveness values were determined under steady-state conditions. From this study, it is clear that the coolant-flame interaction for the reacting experiments significantly impacted the liner cooling effectiveness and led to different overall cooling effectiveness distribution on the liner as compared to the non-reacting experiments.

Cost-benefit evaluation of different low NOx combustors of natural gas boilers in Beijing

This study focuses on establishing a cost-benefit evaluation model of low NOx combustion technology and the environmental benefits and economic benefits evaluation of technology operation were carried out as well. Results showed that: (1) The operation cost per unit calorific supply of the low NOx combustor with larger capacity (14 MW) boilers was 1.5-2.1 yuan/GJ, which was 22.3% to 26.2% as much as that of boilers with smaller capacity (0.7 MW). Compared with scattered boilers with smaller capacity, it is more economical to use boilers with larger capacity for centralized heating. (2) The lower the NOx emission concentration was, the greater the NOx emission reduction was. Furthermore, the lower the NOx emission benefits of low NOx combustor per unit calorific supply was, the greater the economic benefit of NOx reduction per unit calorific supply was. Based on the environmental and economic benefits analysis, the lean premixed combustor is recommended for natural gas boilers with capacity of 7 MW and below, and flue gas recirculation combustor (FGR-30) could be selected for natural gas boilers with capacity above 7 MW to achieve the NOx retrofits requirements of 30 mg/m3 or 80 mg/m3.

Overall Cooling Effectiveness of Effusion Cooled Can Combustor Liner Under Reacting and Non-Reacting Conditions

Emphasis on lean premixed combustion in modern low NOx combustion chambers limits the availability of air for cooling the combustion liner. Hence the development of optimized liner cooling designs is imperative for effective usage of available coolant. Effusion cooling (also known as full-coverage film cooling) is a common method to cool the combustor liner, which involves uniformly spaced holes distributed throughout the liner curved surface area. This paper presents findings from an experimental study on the characterization of overall cooling effectiveness of an effusion-cooled liner wall, which was representative of a can combustor under heated flow (non-reacting) and lean-combustion (reacting) conditions. The model can-combustor was equipped with an industrial swirler, which subjected the liner walls to engine representative flow and combustion conditions. Inline and staggered arrangement of effusion holes have been studied. These configurations were tested for five different blowing ratios ranging from 0.7 to 4, under both reacting and non-reacting conditions. The experiments were carried out at a constant Reynolds number (based on combustor diameter) of 12,500. Infrared Thermography (IRT) was used to measure the liner outer surface temperature and detailed overall effectiveness values were determined under steady-state conditions. Under non-reacting conditions, the staggered configuration was found to be 9–25% more effective compared to inline configuration. Under reacting conditions, the staggered configuration was be 4–8% more effective compared to inline configuration. It is clear that the coolant-flame interaction for the reacting cases had a significant impact on the liner cooling effectiveness as compared to the non-reacting cases and results in less variation between inline and staggered configurations.

High Temperature Corrosion Behaviors of 20G Steel, Hastelloy C22 Alloy and C22 Laser Coating under Reducing Atmosphere with H2S

High-temperature corrosion behaviors of 20G steel, Hastelloy C22 alloy and C22 laser coating was evaluated by corrosion mass gain measurements at 450 °C. The corrosive atmosphere is 0.2 vol% H2S–0.1 vol% O2–N2, which simulated the severe high-temperature corrosion environment occurred under low-NOx combustion in pulverized-coal furnaces. Experimental results showed that the corrosion resistance of the C22 laser coating and the C22 alloy was obviously better than 20G steel. Furthermore, it should be noted that the C22 laser coating fabricated in this study displayed a higher corrosion resistance than the commercial C22 alloy although they had the same chemical composition. The severe pitting corrosion was observed in 20G steel with the corrosion products consisting of FeS2, Fe2O3 and Fe3O4. The C22 alloy and C22 laser coating exhibited the uniform corrosion and their main corrosion products were NiS2, CrS and a small amount of chromium and manganese oxides.