Evaluation of the Tube to Tubesheet Joining Process in an AL6XN® Feedwater Heater

Type 304 austenitic stainless steel is the most common tube material utilized for nuclear feedwater heaters, however, some utilities have experienced problems with Stress Corrosion Cracking (SCC), especially when they utilize brackish cooling water and have experienced condenser tube leaks. This has forced some utilities to explore other options when it comes to high pressure feedwater heaters (HP FWH) tubing materials. AL6XN® is considered a “super” stainless steel that is resistant to (SCC), however, it is not immune (AL6XN is a trademark of ATI Technologies). Based on the relative inexperience and unknowns related to the use of AL6XN tubing in high pressure, nuclear feedwater heater applications, a detailed mock-up procedure was outlined as part of the replacement heater specification which would allow the evaluation of the tube to tubesheet joining processes. Since AL6XN can still be affected by SCC; steps were taken in order to minimize the imposed stress levels and any potential for the inadvertent inclusion of contaminants during the fabrication steps at the tube mill and at the feedwater heater Manufacturer’s shop. The desire to minimize stresses also applies at the tube to tubesheet joint, therefore, it was desired not to stress the tube more than absolutely necessary in achieving a reliable, leak tight joint. The mock-up details and procedures were therefore generated with these objectives in mind, so as to give consideration for the ability to check different configurations in order to determine the most efficient tube to tubesheet joining process. Several tubes in the mock-up were subjected to a pull out test in order to quantify the joint strength in the different configurations. The mockup was then sectioned and inspected under a digital microscope to verify intimate contact between the tube and the tubesheet. Once the optimal procedure was identified, four identical HP FWHs were constructed utilizing AL6XN tubing. During heater production, over 30,000 tube ends were expanded, however, two tubes were identified to have failures as part of the tube expansion process. This paper shall describe the procedures utilized in developing and analyzing the tubesheet mock-up as well the actions taken to identify the root causes of the tube failures.

PED Certified Recuperator for Micro Gas Turbines

The design and certification of a high performance recuperator for micro gas turbines is presented. The component has been developed and built for a 100kWel micro gas turbine. The recuperator heated up compressed air at 3.5 bar with exhaust gas near atmospheric pressure and recuperates 300 kWth at an effectiveness of 90%. This concept can readily be adapted for other micro gas turbines due to its modular design. The certification has been realized under Pressure Equipment Directive 97/23/EC, equivalent to ASME Boiler and Pressure Vessel Code, covering closed pressurized devices. However, minor leakage in the recuperator is allowed, thus requiring an inventive design and validation approach for meeting the certification requirements. This leak is caused by weld porosity: the heat exchanging core plates are laser welded, having over 1200 meters of sealing weld length in a single recuperator. The maximum allowable leak amounts to 3 10−6 mm2 per meter weld length. The maximum leak was 0.2% of the massflow on the pressurized side at the nominal operating point, and therefore did not adversely affect the effectiveness of the recuperator. The finite element calculations and the resulting design loops on components and weld connections are presented. Validation of the entire component is done under the Experimental Design Method. A hydrostatic pressure test at 8.4 bar and ambient temperature is executed in the presence of a certified notified body to demonstrate that the welds are sufficiently robust. This pressure is higher than the operating pressure to simulate the effect of temperature on the steel properties. A laser scanner is used to map the deformation of the unit under pressure and subsequently referenced to its original state. The maximum deviation measured is equal to 0.26 mm for the pressurized part, which is acceptable considering the size of the unit is 1000mm × 600mm × 1000mm. The strain levels went back to the values before putting the unit under pressure, indicating there are no residual deformations. The test is further accompanied with leakage rate measurements before and after the hydrostatic pressure test. If the difference between these leakages rates is within limits, the recuperator will pass the test. The measured total leakage area is 0.4 mm2, well below the maximum allowable value, and equivalent to 0.01% of the massflow at the nominal operating point. This means the recuperator passed the test successfully. Furthermore, a burst test was executed to determine the safety factor and to identify the weakest element of the design. The burst pressure is observed at 18.3 bar, resulting in a safety margin of 218% and 523% in reference to the PED and operational design pressures, respectively. The component responsible for failure has been further optimized for the next generation of recuperators. Field data confirm that the lifetime of the high performance recuperator meets the requirements of 40.000 h operating time. Additionally, the traceability of the serial produced components is handled by the audited quality management system. It covers the used materials, including lot traceability, the measured process characteristics and welder certifications. The approach can also be used for ASME certification.

Acoustic Noise Reduction Under Distributed Combustion

Colorless Distributed Combustion (CDC) has been shown to provide unique benefits on ultra-low pollutants emission, enhanced combustion stability, and thermal field uniformity. To achieve CDC conditions, fuel-air mixture must be properly prepared and mixed with hot reactive gases from within the combustor prior to the mixture ignition. The hot reactive gases reduce the oxygen concentration in the mixture while increasing its temperature, resulting in a reaction zone that is distributed across the reactor volume, with lower reaction rate to result in the same fuel consumption. The conditions to achieve distributed combustion were previously studied using methane and other fuels with focus on pollutants emission and thermal field uniformity. In this paper, the impact of distributed combustion on noise reduction and increased stability is investigated. Such reduced noise is critical in mitigating the coupling between flame and heat release perturbations and acoustic signal to enhance the overall flame stability and reduce the propensity of flame instabilities which can cause equipment failure. Nitrogen-carbon dioxide mixture is used to simulate the reactive entrained gases from with the combustor. Increasing the amounts of nitrogen and carbon dioxide reduced the oxygen concentration within the oxidizing mixture, fostering distributed combustion. Upon achieving distributed combustion, the overall flame noise signature decreased from 80 dB to only 63 dB, as the flame transitioned from traditional swirl flame to distributed combustion. The flow noise under these conditions was 54 dB, indicating that distributed combustion has only 9 dB increase over isothermal case as compared to 26 dB for standard swirl flame. In addition, the dominant flame frequency around 490Hz disappeared under distributed combustion. For the traditional swirl flame, both the acoustic signal and heat release fluctuations (detected through CH∗ chemiluminescence) had a peak around 150Hz, indicating coupling between the heat release fluctuations and pressure variation. However, upon transitioning to distributed combustion, this common peak disappeared, outlining the enhanced stability of distributed combustion as there is no feedback between the heat release fluctuations and the recorded acoustic signal.

Upgradation of Low Grade Coal to High Quality Coal by Chemical Beneficiation Technique

Low rank or grade coals (LGC) are widely distributed over the world. Coal plays a vital role in the global energy demand especially through power generation and it mitigates the energy poverty. The major challenges by the utility of coal as regarding to energy security, a risk of climate change, and increasing of the energy demands are the main portfolio to develop the advanced technology for coal beneficiation. The gradual depletion of high quality coal and cost effective which become a significant issue for power generation while the low grade coals were served as low cost fuel and as an alternative energy security issue. In current research the low grade coal (>35% ash) has been upgraded to higher grade (<10%) by chemical cleaning method. The low grade coal was selected from Mahanadi Coalfields Limited, Odisha, India. Each test was conducted of 50 g coal (250 μm particle size) with 40% NaOH at 100 °C for 3 h and followed with 20% of H2O2, H2SO4, HCl, and HF acids at similar conditions. The research study revealed that ash content (mineral matter) of coal is reduced to >70% by NaOH followed HF treatment as compared to other solvents. The greater liberation of mineral results increases the ash reduction from low grade coal because mineral associated in the coal matrix may formed elution by the leaching effect. The greater extent of demineralization was caused due to the high affinity of OH− and F− with minerals in the coal matrix. The characterization of pre and post treatment coal and coal ash was investigated by the FESEM, XRF and XRD analysis. Overall the current research study challenges the chemical cleaning of low grade coal has been efficient techniques for reducing the minerals to a certain limit.

Development of a Durable Vapor Phase Deposited Superhydrophobic Coating for Steam Cycle Power Generation Condenser Tubes

The condenser performance benefits afforded by dropwise condensation have long been unattainable in steam cycle power plant condensers due to the unavailability of durable and long lasting wetting inhibiting surface treatments. However, recent work in superhydrophobic coating technology shows promise that durable coatings appropriate for use on condenser tubes in steam cycle power generation systems may soon become a reality. This work presents a nano-scale, vapor phase deposited superhydrophobic coating with improved durability comprised of several layers of rough alumina nano-particles and catalyzed silica with a finishing layer of perfluorinated silane. This coating was applied to solid, hemi-cylindrical test surfaces fabricated from several common condenser tube materials used in power generation system condensers: Titanium, Admiralty brass, Cupronickel, and Sea Cure stainless steel condenser tube materials as well as 304 stainless steel stock. The development evolution of the coating and its effect on condensation behavior on the above materials are presented. Results show that the performance enhancement, measured in rate of heat transfer spikes corresponding to condensate roll-off events, was best for the titanium surface which produced 64% more events than the next most active material when coated using the most durable surface treatment tested in this work.

Experimental Study of Spray Flame Characteristics in Hot-Diluted Oxidant Through Advanced Image Processing Technique

This paper presents a study of ethanol jet spray flame characteristics in a hot-diluted oxidant with different co-flow oxygen concentrations and fuel/air mass flow rate ratios (MF/MA ratios) through advance image processing technique. An air-blast atomizer was located in a McKenna burner which was utilized to provide stable combustion surroundings and variable combustion atmosphere for ethanol jet spray. The co-flow oxygen concentrations were set to 5%, 10%, 15% and 21% (by volume) by adjusting the mass flow rates of CH4, O2 and N2. The MF/MA ratios were set to 0.245, 0.490, 0.735, and 0.980 by adjusting the fuel mass flow rate and the carrier air mass flow rate. A high-speed RGB CCD camera was employed to capture spray flame images continuously. Spray flame edge is detected using an auto-adaptive edge-detection algorithm which could detect the spray flame edge continuously and clearly. A flame zone is defined as the region surrounded by the detected flame edge to obtain flame parameters. Spray flame characteristics are described using the measured flame parameters, involving flame area, length, brightness, nonuniformity and temperature which are derived from the spray flame images. Spray flame area, length, brightness and nonuniformity are extracted through image processing technique directly. Moreover, two-dimensional (2D) temperature profiling of spray flame is obtained by coupling image processing technique with two-color pyrometry based on Planck’s radiation law. The effects of co-flow oxygen concentration and MF/MA ratio on spray flame characteristics are investigated in this work. The spray flame parameters are observed to be sensitive to both co-flow oxygen concentration and MF/MA ratio. The results show that the fuel mass flow rate (MF) has opposite effects on spray flame characteristics compared with the carrier air mass flow rate (MA) in hot-diluted oxidant. Spray flame area and length are shown to decrease for higher co-flow oxygen concentrations, while spray flame brightness, uniformity and temperature are observed to increase for higher co-flow oxygen concentrations, owing to the enhancement of the combustion rate. A higher MF/MA ratio leads to higher spray flame area, length, brightness, uniformity and temperature, due to the increase of the droplet residence time or droplet concentration in hot-diluted oxidant. In the same MF/MA ratio, spray flame area and length are found to be smaller at a higher fuel flow rate (or carrier air flow rate). However, spray flame brightness, uniformity and temperature are demonstrated to be enhanced at a higher fuel flow rate (or carrier air flow rate). (CSPE)

Effects of Cooling System Operations on Withdrawal for Thermoelectric Power

A new dataset released by the Energy Information Administration (EIA) — which combines water withdrawal, electricity generation, and plant configuration data into a single database — enables detailed examination of cooling system operation at thermoelectric plants at multiple scales, most importantly at the unit level. This dataset was used to explore operations across the population of U.S. thermoelectric plants, leading to the conclusion that roughly 32% of all thermoelectric water withdrawal occurs while power plants are not generating electricity. Based on interviews with industry representatives, a unit’s location on the dispatch curve will largely dictate how the cooling system is operated. Peaking plants and intermediate plants might keep their cooling system running to maintain dispatchability. Other considerations include minimizing wear and tear on the pumps and controlling water chemistry. This observation has implications for understanding water use at thermoelectric plants, policy analysis, and modeling. Previous studies have estimated water use as a function of cooling technology, fuel type, prime mover, pollution controls, and ambient climate (1) or by calculating the amount of water that is thermodynamically necessary for cooling (2). This, however, does not capture all the water a plant is withdrawing simply to maintain dispatchability. This paper uses the new data set from EIA and interviews with plant operators to illuminate the role cooling systems operations play in determining the amount of water a plant withdraws.

Experimental Investigation on the Influence of Air Velocity on the Particle Dispersion Behavior of Rice Husk in a Fuel-Rich/Lean Burner

Recently the firing of biomass at existing power plant has drawn much attention because biomass fuels result in less pollutant emission. It is desirable to investigate the flow characteristics of biomass particles in existing combustors in order to determine whether the coal burners also have good adaptability for biomass fuel. The particle dispersion in the burner has a close relationship with pollutant emissions. In this paper, a monitoring system based on a charge-coupled device (abbreviated as CCD) camera was employed to measure the particle distribution of rice husk in a fuel-rich/lean burner. The influence of air velocity was taken into consideration. The particle-rich/lean ratio is 19.49, 16.23, 14.86, and 12.94 (corresponding to the air velocity of 9.5, 11, 12.5, and 14 m/s, respectively) at the exit of the burner model. The results indicates that the air velocity has a negative effect on the separation performance. In order to verify the particle distributions obtained by the digital imaging technique, specially designed filter bags were used to collect rice husk from both the fuel-rich side and fuel-lean side. Then mass and size distributions of the collected particles were analyzed. The results agrees with the trend above and indicates that the block-type concentrator has greater impacts on large particles. More large particles were collected from the fuel-rich side. The dispersion mechanism of rice husk particles revealed in this paper can propose solutions to the actual operation of plants that combust/co-combust the rice husk. (CSPE)

Performance of a Supercharged Engine Fueled With a CTL Binary Mixture at Different Injection Pressures

Performance of an experimental diesel engine was investigated when fueled with CTL20 (80% ULSD#2 (ultra-low sulfur diesel) blended with 20% Fischer-Tropsch coal-to-liquid (CTL) fuel. CTL fuel was selected given its potential as an alternative fuel that can supplement the ULSD supply. Combustion and emissions were studied in a common rail, supercharged, single cylinder DI engine with 15% exhaust gas recirculation operated at 1500 RPM and 4.5 bar IMEP in reference to a diesel baseline. The injection pressure was varied from 800–1200 bar while injection timing was tested from 15° to 22° CAD BTDC to optimize combustion. Similar in-cylinder pressures and temperatures were observed for both fuels at the same injection pressure and timing; the maximum heat release and in cylinder pressure and temperatures increased with higher rail pressure. CTL20 had a retarded premixed burn peak by 5 to 8 J/CAD compared to diesel at the same injection pressure and timing. This can be related to a delayed ignition of CTL20 which allowed for higher peak premixed combustion. In-cylinder convection and radiation heat fluxes were stable across injection pressures for both fuels around 1.7 MW/m2 and 0.4 MW/m2, respectively. NOx decreased with CTL20 at higher injection pressure while soot was relatively increased at lower injection pressure. CTL20 decreased BSFC by 3–5% compared to ULSD#2 at 800–1200 bar injection. The mechanical efficiency was maintained around 65% for ULSD#2 as well as for CTL20 during operation at all injection pressures. The study suggests that CTL fuel can be used at 20% as a binary mixture in ULSD#2 while sustaining performance in the experimental engine.

The Enlightenment of Updated Development of the USC Coal Fired Units

An comparison of technical specification and updated operation results between two USC coal fired boilers namely RDK-8, Germany and WGQ-3, China has been considered under the global scenario related to the variation of industrial production structure, power demand cut down, more stringent carbon dioxide depression and larger quantity of renewable units engaged into the grid, in this respect a discussion and analysis have been carried out subjected to low grade heat recovering and harmful emission prevention from boiler flue gas and introduction carbon harmful emission prevention from boiler flue gas and their multiple benefits on energy saving and environmental protection, moreover the experience and gains in the field of flue gas heat recovering and mitigating pollution, including the proprietary technique (WGGH) by SPERI are briefly stated, thereby a conclusion of enlightenment for further development of these units is mentioned.