Super-critical Carbon Dioxide Brayton Power Cycles
Electric power generation is a crucial factor necessary to expedite India's economic growth and foster overall human development. Over the years, there has been significant increase in the country's electricity demand and is expected to surge further in the future.
The need of the hour today is to cater to the enormous power demand while keeping in mind the challenge of economical and environment-friendly power generation. While the share of renewables in power generation has considerably increased over the last few years, thermal-based power production (coal, gas or diesel) continues to be the major shareholder in the Indian context to this date.
Conventional thermal power plants fired by coal/gas operate on a Rankine cycle with steam as working fluid. A supercritical carbon dioxide(s-CO2) Brayton cycle works on similar principles, except that the working fluid (Carbon dioxide) remains in the gaseous/supercritical state throughout the cycle. S-CO2 cycles are seen as potential replacements to steam Rankine cycles due to the following advantages:
1. Smaller turbomachinery sizes - This facilitates easy installation and reduced initial costs thus becoming a viable option for distributed power generation with cycle efficiencies comparable to steam Rankine cycles.
2. Quick start-stop time scales that facilitate easy integration into a number of applications - gas turbine bottoming applications, waste heat recovery, captive power generation, coal/gas/diesel fired generation, concentrated solar power.
3. Single phase operation throughout the cycle prevents turbomachinery blade erosion due to two phase flow. Also, since the operating pressures everywhere in the cycle are much above the atmospheric pressure, there are no problems of ambient air ingestion into the cycle.
In its simplest form, a s-CO2 Brayton consists of a turbine, external heater, compressor, gas cooler and an internal heat exchanger (recuperator). This configuration is called the simple recuperated configuration and is most suitable for Concentrated Solar Power (CSP) / nuclear energy. The heat input occurs in the external heater while the turbine produces electrical power which is partly consumed by the compressor. A fraction of the heat input is rejected at temperatures close to ambient by the gas cooler as a thermodynamic requirement for a closed cycle heat engine.
Another potential avenue for sCO2 cycles lies in Waste Heat Recovery (WHR). Potential industries that use WHR for power generation include cement, fertilizer, process, paper & pulp, and metal (Steel, Aluminum, etc.). WHR is also relevant in Gas Turbine bottoming applications. Conventional layouts such as the simple recuperated / recompression layout cannot be used for WHR. In this regard, we have come up with novel sCO2 cycle layouts for WHR (applied for patent). Details can be shared upon request.