On the use of Rotary Gas/gas Heat Exchangers as a Novel Integration Option for Heat and Water Management in Exhaust Gas Recycling Gas Turbine Plants.

Abstract

This work is a first-of-a-kind feasibility study investigating technology options with gas/gas rotary heat exchangers for the water management in the integration of Natural Gas Combined Cycle (NGCC) plants with post-combustion carbon capture, with and without exhaust gas recirculation (EGR). A range of configurations are examined for wet and dry cooling of the flue gas entering a postcombustion capture (PCC) absorption system, and regenerative heating of the CO2-depleted flue gas prior to the power plant stack. First, this work examines the addition of a gas/gas rotary heat exchanger to transfer heat from the exhaust gas entering the absorber into the CO2-depleted gas stream leaving the absorber. It then investigates the performance of a configuration with an additional air/gas rotary heater to further reduce exhaust flue gas temperature and water consumption, and, eventually, a more compact arrangement which combined the two heaters into a single gas/gas/air heater with a trisector configuration. A thermal performance analysis was conducted for each of the previous configurations, in order to evaluate the dimensions and the operational parameters of the heaters. By replacing the direct contact cooler traditionally used in PCC technology by a dry-cooling system, a significant reduction in the overall process water usage and cooling water consumption associated to the capture plant can be achieved. The second part of this work examines the use of a similar system for NGCC plant with EGR. This strategy increases CO2 concentration in gas turbine exhaust gases and reduce O2 induced solvent degradation. In addition to the heat and water balance around the absorber column of the PCC process, an important aspect of EGR is that recirculated gas stream temperature should be as low as possible so that the gas turbine performance is not compromised. The performance of the rotary heat exchanger configurations is analysed at different recirculation ratios.