Combustors reliability

Already prior to being supplied to Vbuamo, the special combustors and burners were tested in a rig in England utilising synthetic gas. Combustion has always been reliable in the turbine whether operating on gas fuel or liquid. The relatively low heating value of the gas (about 1/10 of natural gas) proved to be of no problem to the gas turbine and a stable flame has always been established even when the beating value has been lower than normal. 

The data determined directly by Knudsen cell measurements, plus a strong correlation between the bond strengths of metal hydroxide bonds and metal halide (in particular, chloride and fluoride bonds) in the gaseous metal hydroxides and halides were developed and allow us to more reliably estimate the enthalpy of formation of many hydroxide and oxyhydroxide metal compounds whose values of thermochemical heat and formation were previously unknown. These thermochemical properties were then used to estimate volatility of various supporting oxide substrates and catal)dically-active solids that were relevant for the fabrication of catalytic combustors. 

In addition to APCD, metal emissions from waste combustors can be minimized by 1) limiting the metal content of the waste feed via source control 2) designing and operating the combustion process to minimize metal vaporization and 3) designing and operating the primary combustion chamber to minimize fly-ash carryover. From a practical standpoint, the second method is likely to be the most difficult to implement because the objective of the incineration process is to burn all the combustible waste completely and avoid PIC formation, both of which require the use of high temperatures. Therefore, the most-reliable methods of limiting metal emissions are source control and efficient use of APCD. 

NO c emissions can also be reduced by using a dilute fuel/air mixture in so-called lean premixed combustion. Air and fuel are premixed at a low fuel air ratio before entering the combustor, resulting in a lower flame temperature and hence lower NOj emissions. Lean premix combustors (sometimes called dry low NO c combustors) based on this concept have generally achieved NO c levels of 25 ppm in commercial operation. To achieve lower NO levels, however, this technology must overcome some significant hurdles. As the fuel air mixture is increasingly diluted, the flame temperature approaches the flammability limit and the flame becomes unstable. The flame instability produces noise and vibration that can reduce the combustor life, increase maintenance costs and adversely impact the operational reliability of the turbine [3]. 

Thermal treatment appears to be the most readily available remedial action technology for dioxin. However, no data are available to confirm the maintainability, reliability and cost-effectiveness of transportable commercial systems. Through a competitive process, the USAF selected ENSCO Corporation for a full-scale field test of their rotary-kiln combustor. The test will be conducted at the NCBC, Mississippi and will involve treatment of approximately 9000 cubic yards of contaminated soil. An intense analytical program and engineering failure mode analysis will support the project. Testing is planned for November 1986 - March 1987. 

Two combustors have been prepared, one for predominantly high-pressure operation and the other for low-pressure work, especially ignition and fuel placement studies. The first set of experiments, both at elevated and normal pressure, uses a small (approximately 0.5 mm in diameter) electrically heated igniter located in the porous medium. The propulsion application puts a premium on reliable, simple ignition systems. 

The generation of strong Mach stem reflections downstream of the diffraction plane of an initiator combustor is a reliable reinitiation mechanism for the transmission of a detonation wave into a larger combustor. The reliable generation... 

These results indicated relatively low stresses at steady state and higher stresses after combustor shut down. Thus, the reliability analysis concentrated on Iho tensile stress state at 30 seconds after shut down. 

Fuel delivery Accurate and predictable delivery of fuel quantity is essential for achieving high overall system efficiency while maintaining an adequate safety margin to prevent an excessive combustor temperature. Also, the SOFC is operated at very specific levels of FU dictated by both stack reliability and efficiency requirements. Hence it is very important to have fast, accurate, and precise control of fuel flow to match the power demanded of the SOFC system. A fuel metering valve is commonly used for the system and selected based on the required fuel flows and other characteristics. Many system designs also employ a blower for anode gas recycle (AGR). 

By better monitoring this spread, we can warn against burner issues (i.e., plugged fuel nozzles), faulty combustors or bad thermocouples within an appropriate period of time. This will reduce the likelihood of deterioration of the combustion system. Figure 8 shows a typical output of the rule for a typical gas turbine, where the exhaust temperatures are plotted on-line. To achieve a reliable rule output, many checks must be performed to prevent false alarms and report a real spread event. Examples of these checks include thermocouple cross-checks to identify faulty sensors and adjacency checks to confirm a real spread, where adjacent thermocouples are compared to the one showing the minimum reading. 

The SURE model can also easily explain (24) the observed dependency of the oxygen concentration in the combustor outlet as a function of the excess air ratio X (Fig. 11) and the generally observed decrease of the desulfurization efficiency during substoichiometric (staged) combustion (Fig. 12). Quantitative validation of these last phenomena is, however, hampered by the lack of reliable data... 

The particularity of mechanical issues in SOFC is their intricate link with the physico-chemical and electrochemical properties of the materials. Indeed, unlike for TBC or ceramic combustors, the main requirement for the ceramic materials is not their temperature and mechanical resistance, but electrochemical properties. Therefore, to go further towards reliable lifetime predictions, hence effective mitigation of mechanical failure, the multiphysics nature of the problem must be fully acknowledged and not restricted to thermal, or isothermal stress. Dedicated experiments combined to REV simulations can provide insights into the complex faUiure... 

---