CO2-Argon-Steam Oxy-Fuel Production for (CARSOXY) Gas Turbines

Abstract

Due to growing concerns about carbon emissions, Carbon Capture and Storage (CCS) techniques have become an interesting alternative to overcome this problem. CO2-Argon-Steam-Oxy (CARSOXY)-fuel gas turbines are an innovative example that integrates CCS with gas turbine powergen improvement. Replacing air-fuel combustion by CARSOXY combustion has been theoretically proven to increase gas turbine efficiency. Therefore, this paper provides a novel approach to continuously supply a gas turbine with a CARSOXY blend within required molar fractions. The approach involves H2 and N2 production, therefore having the potential of also producing ammonia. Thus, the concept allows CARSOXY cycles to be used to support production of ammonia whilst increasing power efficiency. An ASPEN PLUS model has been developed to demonstrate the approach. The model involves the integrations of an air separation unit (ASU), a steam methane reformer (SMR), water gas shift (WGS) reactors, pressure swing adsorption (PSA) units and heat exchanged gas turbines (HXGT) with a CCS unit. Sensitivity analyses were conducted on the ASU-SMR-WGS-PSA-CCS-HXGT model. The results provide a baseline to calibrate the model in order to produce the required CARSOXY molar fraction. A MATLAB code has also been developed to study CO2 compression effects on the CARSOXY gas turbine compressor. Thus, this paper provides a detailed flowsheet of the WGS-PSA-CCS-HXGT model. The paper provides the conditions in which the sensitivity analyses have been conducted to determine the best operable regime for CARSOXY production with other high valuable gases (i.e., hydrogen). Under these specifications, the sensitivity analyses on the (SMR) sub-model spots the H2O mass flow rates, which provides the maximum hydrogen level, the threshold which produces significant CO2 levels. Moreover, splitting the main CH4 supply to sub-supply a SMR reactor and a furnace reactor correlates to best practices for CARSOXY. The sensitivity analysis has also been performed on the (ASU) sub-model to characterise its response with respect to the variation of air flow rate, distillation/boiling rates, product/feed stage locations and the number of stages of the distillation columns. The sensitivity analyses have featured the response of the ASU-SMR-WGS-PSA-CCS-HXGT model. In return, the model has been qualified to be calibrated to produce CARSOXY within two operability modes, with hydrogen and nitrogen or with ammonia as by-products.

Techno-economics of CO2-Argon-Steam Oxy-Fuel (CARSOXY) Gas Turbines

“…The CARSOXY cycle in Figure 1 has been modeled using the ASPEN PLUS software as a follow up of previous work [4]. It is based on the Peng-Robinson equation of state.…”

“…The molar fraction of each product stream is specified in Table 1. A series of steam methane reforming, water gas shifting and hydrogen purification processes have been calibrated to produce CH4, H2O and CO2 to match the required CARSOXY molar fractions rather than converting the entire amount of CH4 to H2 (the conventional approach) [4]. Steam methane reforming reactions (1 and 2) take place in the SMR unit.…”

“…CARSOXY gas turbines enable the use of both concepts, i.e. it captures CO2 and uses it as an alternative working fluid (CO2-Ar-H2O) in oxyfuel combustion to increase cycle efficiency ( by additional 13.93%) [4]. Moreover, it has theoretically zero-NOx emissions since air is not involved in the combustion process.…”

Planar Laser-Induced Fluorescence and Chemiluminescence Analyses of CO2-Argon-Steam Oxyfuel (CARSOXY) Combustion

“…Injecting the working fluid with inert gases with high heat capacities, such as argon, can increase power outputs, making up for the CCS efficiency losses. Moreover, humidification can also be employed to raise even further power outputs [12][13][14].…”

“…In addition, heat exchangers are excellent methods of heat recovery [13]. These methods have a higher potential to increase the cycle efficiency when a CARSOXY mixture is used as the working fluid [13,14]. If a suitable cycle configuration is used under specific operation conditions, high thermo-economic benefits can be reached.…”