Inverted Brayton Cycle With Exhaust Gas Recirculation—A Numerical Investigation
Inverted Brayton Cycle With Exhaust Gas Recirculation—A Numerical Investigation
复制标题
带废气再循环的倒布雷顿循环——数值研究
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
M. Aigner
中科院分区：
文献类型：
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作者：
M. Henke;T. Monz;M. Aigner
基于微燃气轮机（MGT）的热电联产（CHP）装置提供了一种高效、低污染的技术，可以从化石能源和可再生能源中提供热量和电力；然而，电功率范围从1到5千瓦的增压MGT系统使用非常小的涡轮增压器组件。这些组件遭受更高的损失，如密封和尖端泄漏，导致电气效率降低。基于逆布雷顿循环（IBC）的系统可以避免这个缺点。在IBC中，热气体在大气压力下在燃烧室中产生。随后，废气在涡轮中从大气压力水平膨胀到亚大气压力水平。为了提高电效率，涡轮废气中的热量被回收到燃烧空气中。回收后，气体被压缩到大气压力，从循环中排出。为了降低压缩机的功率需求，从而提高电气循环效率，在压缩前进一步从气体中提取余热功率至关重要。加热装置提供的冷却液流可以利用这种热量供应与排放的废气的热量相结合。IBC的低压水平导致了高容量的气体流量，从而可以使用大型、高效的涡轮增压器组件。由于这种效率效益和所述的冷却需求，微型热电联产应用为IBC的利用提供了一个理想的领域。为了进一步提高总效率，排出的废气可以部分再循环到循环的进气口。本文对一个具有废气再循环（EGR）的IBC进行了稳态分析，并与具有等效组分特性的传统布雷顿循环的性能进行了比较。使用EGR，可以发现电循环效率对冷却液温度的敏感性进一步提高。接下来的讨论主要集中在总效率和电气效率之间的权衡，这取决于冷却剂温度和EGR速率。结果表明，EGR可使总效率提高10% ~ 15%，而电气效率降低0.5% ~ 1%。当冷却剂温度低于35℃时，废气中的水蒸气会发生冷凝，进一步提高热回收效率。基于涡轮增压器图的内部验证仿真工具已被用于计算。
Microgas turbine (MGT) based combined heat and power (CHP) units provide a highly efficient, low-pollutant technology to supply heat and electrical power from fossil and renewable energy sources; however, pressurized MGT systems in an electrical power range from 1 to 5 kWel utilize very small turbocharger components. These components suffer from higher losses, like seal and tip leakages, resulting in a reduced electrical efficiency. This drawback is avoided by an inverted Brayton cycle (IBC) based system. In an IBC hot gas is produced in a combustion chamber at atmospheric pressure. Subsequently, the exhaust gas is expanded in a turbine from an atmospheric to a subatmospheric pressure level. In order to increase electrical efficiency, heat from the turbine exhaust gas is recuperated to the combustion air. After recuperation, the gas is compressed to atmospheric pressure and is discharged from the cycle. To decrease the power demand of the compressor, and thereby increasing the electrical cycle efficiency, it is crucial to further extract residual thermal power from the gas before compression. Coolant flows provided by heating applications can use this heat supply combined with heat from the discharged exhaust gas. The low pressure levels of the IBC result in high volumetric gas flows, enabling the use of large, highly efficient turbocharger components. Because of this efficiency benefit and the described cooling demand, micro-CHP applications provide an ideal field for utilization of the IBC. To further increase the total efficiency, discharged exhaust gas can be partially recirculated to the air inlet of the cycle. In the present paper a steady state analysis of an IBC with exhaust gas recirculation (EGR) is shown, and compared to the performance of a conventional Brayton cycle with equivalent component properties. Using EGR, it could be found that the sensitivity of the electrical cycle efficiency to the coolant temperature further increases. The sequent discussion focuses on the trade-off between total efficiency and electrical efficiency, depending on coolant temperature and EGR rate. The results show that EGR can increase the total efficiency by 10% to 15% points, while electrical efficiency decreases by 0.5% to 1% point. If the coolant temperature is below 35 °C, condensation of water vapor in the exhaust gas leads to a further increase of heat recovery efficiency. A validated in-house simulation tool based on turbocharger maps has been used for the calculations.