Advanced Gas Turbine cycles for high efficiency and sustainable future conventional generation

燃气轮机(GT)将在补充可再生能源产生的间歇性电力方面发挥重要作用，而到2050年，各种燃料来源可能包括生物燃料(前者是甲烷、一氧化碳、二氧化碳和氮气的混合物--本质上是低热值燃料)，或许还有页岩气和氢气。在实现二氧化碳排放目标时，将优先考虑(I)具有最高燃料转换效率和(Ii)与碳捕获和封存相结合的设计。此类设计包括湿空气涡轮机(HAT)或广泛排气的方案，或使用富氧空气的烟道气体再循环方案。对这些设计进行了广泛的技术经济评估，没有首选的“赢家”，很可能每种设计都会得到广泛的应用。因此，需要设计燃烧低热值气体的燃烧室，“氧化剂”气流包括高达30%(w/w)的蒸汽、纯氧气或严重稀释二氧化碳的氧气。这些变化给火焰的稳定和灭火带来了巨大的困难。低NOx燃烧室的设计已经显示出计算流体力学(CFD)在开发商业上可行的设计方面的价值，这一趋势将得到加强。最后，合适的传感器在开发过程中的价值证明了它的价值。这项研究确定了现有物理理解、CFD和光学传感器方面的空白，需要通过“基础研究”来解决，这些空白需要填补，以便行业能够开发阶跃变化GT技术。这项建议将开发如下工具和理解：(I)在线、接近实时的光学传感器，以测量进入燃气轮机的燃料的‘沃贝’指数，因为快速了解高度可变的生物燃料的热值对于控制未来的燃气轮机非常重要。(Ii)火焰的稳定性和熄灭与存在临界的‘拉伸速率’和火焰可经历的最大层流火焰速度有关，这是由于燃烧室的空气动力学流场。使用CFD进行燃烧室流动预测的设计者需要知道燃料和氧化剂范围的这些临界值，这些临界值将使用到2050年。因此，这项建议将测量预混和非预混火焰中的这些值作为预热和压力的函数，并分析实验室和中试规模模型燃烧室中的火焰熄灭过程，其中包括使用平面激光诱导荧光检测CO和甲醛。(Iii)低NOx排放要求燃料充分预混，开发工程师可以获得一种仪器，该仪器可以在试验台上测量局部燃料/空气比。在之前成功开发了一种基于火焰自然化学发光发射的仪器的基础上，将对其校准作为压力和湿度的函数进行评估，后者在HAT燃气轮机设计的背景下进行评估。(Iv)热声不稳定性是一种破坏性的高强度‘极限环’，要么在操作上避免，要么通过反复尝试的方法大大改进设计。直到最近，向这个极限环的转变和极限环本身都是通过频率和相谱分析来表征的。我们最近的工作表明，非线性时间序列分析表明，向高振幅振荡的转变保持了混沌理论所确定的结构。我们将使用这种形式的分析来确定造成这种行为的流体机械结构，目的是设计方法，至少警告燃气轮机操作员即将到来的热声不稳定。(V)将使用逆流和模型燃烧室几何形状的测量来评估可用的最佳LES CFD方法。还将通过测量直接评估大涡模拟方法对计算的“次网格”贡献。

Gas Turbines (GTs) will figure prominently in complimenting the intermittent power generated by renewables, while varied fuel sources by 2050 are likely to include biofuels (the former a mixture of methane, carbon mono- and di-oxide and nitrogen - essentially low calorific value fuel) and perhaps shale gas and hydrogen. In meeting CO2 emissions targets, there will be a premium on designs that (i) have the highest fuel conversion efficiency and (ii) integrate with carbon capture and storage. Such designs include either humid air turbines (HAT) or schemes with extensive exhaust, or flue, gas recirculation together with the use of oxygen-enriched air. There is extensive techno-economic evaluation of these designs with no preferred 'winner' and it is likely that each will find extensive application. Thus, there will be a need to design combustion chambers to burn low calorific gases, with "oxidant" streams including up to 30% (w/w) of steam, pure oxygen or oxygen heavily diluted with Carbon dioxide. Such changes present formidable difficulties to flame stability and extinction. The design of low NOx combustion chambers has shown the value of computational fluid dynamics (CFD) in developing commercially viable designs and this trend will strengthen. Finally, the value of suitable sensors during development has proved its worth. This research identifies the gaps in existing physical understanding, CFD and optical sensors, to be addressed by "fundamental research", that need to be filled so that step change GT technologies can be developed by industry. This proposal will develop tools and understanding as follows:(i) On-line, near real time optical sensor to measure the 'Wobbe' index of fuel entering the gas turbine, since fast knowledge of the calorific value of highly variable bio- fuels is important for control of future GTs.(ii) Flame stability and extinction is associated with the existence of a critical 'rate of stretch' and the largest laminar flame speed that the flame can experience due to the aerodynamic flow field of the combustors. Designers, using CFD for flow prediction in combustion chambers, need to know these critical values for the range of fuels and oxidants, which will be in use up to 2050. Thus, this proposal will obtain measurements of these values in premixed and non-premixed flames as a function of preheat and pressure and analyse the process of flame extinction in laboratory and pilot scale model combustors using, amongst other instruments, detection of CO and formaldehyde by planar laser induced fluorescence.(iii) Low NOx emissions require the fuel to be well premixed and it is useful for development engineers to have access to an instrument, which can measure local fuel/air ratio on test stands. Building on previous successful development of an instrument based on natural chemiluminescent emissions from a flame, there will be an evaluation of its calibration as a function of pressure and humidity, the latter in the context of a HAT gas turbine design.(iv) Thermoacoustic instability is a destructive high intensity 'limit cycle', which is either avoided operationally or designs are improved largely by cut and try methods. Until recently, the transition to this limit cycle and the limit cycle itself were characterised by frequency and phase spectral analysis. Our recent work has shown that non-linear time series analysis reveals that transition to high amplitude oscillations retains a structure as determined by chaos theory. We will use this form of analysis to identify the fluid mechanical structures responsible for this behaviour, with the aim of devising methods to at least warn gas turbine operators of impending thermoacoustic instability.(v) The best available LES CFD methods will be evaluated using the measurements in the counterflow and model combustor geometries. There will also be direct assessment, through the measurements, of the 'sub-grid' contribution of LES methodology to calculations