Activated carbon–carbon dioxide based two stage adsorption compression Brayton cycle power generation

Abstract

Enhancement of energy delivery of a carbon dioxide (CO2) Brayton cycle without compression work liability is achievable using low grade heat for thermal compression. The limitation of the expansion ratios of a single stage adsorption thermal compression is obviated by opting for pressure build up in two stages. Despite the use of a large number of adsorbers, it is shown that, specific work output can be augmented substantially with no undue penalty on the overall cycle efficiency albeit with a marginal shortfall in work output per unit mass of adsorbent. These features are elucidated through an activated carbon based thermal compression of CO2 yet limiting high side pressures to 80 bar and the principal heat source at a temperature equal to or less than 300 °C in tandem with another low grade source at 100 °C for thermal compression. The net outcome is a substantial reduction in the size of the power block and heat exchangers resulting from enhancement of the expansion ratio and reduction in the mass flow rate in the circuit.