Maximizing Energy Efficiency: The Power of Capstone's Recuperator Technology

July 24, 2023

Capstone's Recuperator Sets a New Standard

The annular recuperator integrated into every Capstone Microturbine plays a pivotal role in maximizing electrical efficiency and power output. A recuperator is a gas-gas heat exchanger, it enables the transfer of energy from hot turbine exhaust to the fresh air used for combustion. For comparison, the same turbine engine without a recuperator will produce electricity at about 50 percent of the efficiency of a recuperated design. The advanced design features and manufacturing expertise all contribute to the reliable and robust microturbine engines sold in every microturbine product.

Engineering Excellence in Recuperator Design

Figure 1 showcases the intricacies of a single cell in our Capstone annular recuperator, which boasts an exceptionally high surface area achieved through the folding of thin foil material. By stacking these cells, we form an annular (or donut) shaped device. This design facilitates a laminar and uniform flow of hot exhaust gas between the narrow foil cells, ensuring maximum efficiency by minimizing dead spots. Furthermore, the fluid to which heat is added flows up and through the inside of these cells.

In Figure 2 below, note the flow direction arrows, with the red arrows indicating the flow of hot exhaust gases, and the blue arrows indicating the flow of cool air from the compressor stage. The recuperator allows these two streams to exchange heat in a counter-flow direction, as opposed to the less effective cross-flow recuperator designs used by some turbine manufacturers.

The annular design allows for a very compact engine design. The engine “power head” assembly (including turbine, compressor, generator, and air bearing system) sits inside the annular recuperator, resulting in class-leading compact engines designs.

Due to starts and stops during normal operation, any gas turbine engine will experience thermal cycling as the system heats up and cools down. The unique annular and axisymmetric shape of the Capstone recuperator allows the heat exchanger cells and engine housing to expand together around the core engine, minimizing thermal stresses and fatigue damage over the life of the engine.

The recuperator is a passive device, requiring no active control or monitoring for the life of the product. Additionally, the device is one of the most expensive components in the system. This makes quality manufacturing of the recuperator perhaps the most critical aspect of Capstone microturbine production. High first-quality allows recuperators to perform well-beyond the 80,000-hour design life.

Excellence in Manufacturing

The base component of the Capstone recuperator is the “cell”. The modular cell design is easily produced in high volumes, allowing the production costs to be minimized. The cell consists of two stainless steel HR120 plates that have been fin-folded to maximize the heat transfer surface area. These two plates are then welded together to eliminate leak paths between the hot and cold sides. Each cell is precision fabricated and welded at our corporate headquarters in Van Nuys, CA. Capstone weld technicians produce one cell every 45 seconds. The cells are assembled in sectors, and then the sectors are assembled into a single core. In a C200 engine for example, there are 31 cells in a sector, and 10 sectors in a core, for a total of 310 cells in each recuperator. 

The quality of each cell is confirmed through flow tests and multiple visual and dimensional inspections by Capstone AWS-certified weld inspectors. Once assembled into a core, a final pressure decay test confirms the performance of the core is meeting specification. Finally, an engine case and diffuser cone is welded around the recuperator core by a Capstone partner and the remainder of the engine assembly process can continue.

Driving Positive Change 

We remain dedicated to pushing the boundaries of energy efficiency and sustainability, and our recuperator technology is a prime example of this commitment. By leveraging this innovative solution, Capstone Green Energy is driving positive change in the industry and empowering our customers to embrace greener and more efficient energy solutions.  

Stay tuned for more exciting updates and industry insights from Capstone Green Energy. Together, let's create a cleaner, more sustainable future.