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.
Highlights
Generating power with high efficiency has become a necessity rather than an option
The developed approach of producing the required CARSOXY molar fraction involves the integrations of an air separation unit (ASU), a steam methane reformer (SMR), water gas shift (WGS)
The sensitivity analysis provided to adjust the ASU-SMR-WGS-pressure swing adsorption (PSA)-heat exchanged gas turbines (HXGT) cycle in order to fulfill the requirements of any desiredActual performance
Summary
Generating power with high efficiency has become a necessity rather than an option. Conventional power generation methods that employ fossil fuel-fired plants have unquestionably increased carbon dioxide emissions and tightened up tolerance margins across the world [1]. The use of alternative working fluids in gas turbines promises both to increase cycle efficiency and limit carbon emissions [2]. Energies 2019, 12, 3580 working fluids, and CO2 -Ar-H2 O The latter is used for a novel concept called CARSOXY gas turbines [2,3]. The developed approach of producing the required CARSOXY molar fraction involves the integrations of an air separation unit (ASU), a steam methane reformer (SMR), water gas shift (WGS). SMR is one of the fully developed technologies used to produce hydrogen [11] Light hydrocarbon fuels such as methane (CH4 ) react with steam to be converted into hydrogen as the main product, carbon monoxide, and carbon dioxide as by-products. Equation (1) requires 206 kJ to react one mole of methane with one mole of steam
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