Chemical‐looping combustion (CLC) is a promising and efficient method for power generation with in situ CO2capture. In this work, we focus on high‐pressure fixed‐bed CLC reactors integrated with combined cycle (CC) power plants. Specifically, the dynamic nature of fixed‐bed chemical‐looping reactors and the many kinetically controlled reactions necessitate the use of dynamic modeling to evaluate power plant performance, efficiency, stability, and feasibility under transient operation. We present a dynamic model for an integrated CLC–CC power plant and transient analyses of the integrated plant performance. A network of dynamically operated fixed‐bed reactors fed with natural gas comprises the CLC plant component. A dynamic model is developed and tuned to match the performance of a commercial combined cycle power plant. The transient variations of the integrated plant in terms of power, temperature, and pressure profiles are presented. The simulation results show that despite the inherent batch‐type operation of the CLC reactor, the operation of the combined cycle is relatively unaffected, and there are small oscillations of approximately 2 % around the desired steady‐state conditions.
Process intensification options are explored for near‐carbon‐neutral, natural‐gas‐fueled combined cycle (CC) power plants, wherein the conventional combustor is replaced by a series of chemical‐looping combustion (CLC) reactors. Dynamic modeling and optimization are deployed to design CLC‐CC power plants with optimal configuration and performance. The overall plant efficiency is improved by optimizing the CLC reactor design and operation, and modifying the CC plant configuration and design. The optimal CLC‐CC power plant has a time‐averaged efficiency of 52.52% and CO2capture efficiency of 96%. The main factor that limits CLC‐CC power plant efficiency is the reactor temperature, which is constrained by the oxygen carrier material. CLC exhaust gas temperature during heat removal and gas compressor to gas turbine pressure ratio are the most important operating variables and if properly tuned, CLC‐CC power plants can reach high thermodynamic efficiencies. © 2018 American Institute of Chemical Engineers
- PAR ID:
- 10461240
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- AIChE Journal
- Volume:
- 65
- Issue:
- 7
- ISSN:
- 0001-1541
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Abstract -
In 2021, the White House proposed a 50-52% reduction in greenhouse gas emissions by the year 2030; therefore, there is significant interest in energy sources and processes that reduce carbon dioxide emissions. This paper presents a sensitivity analysis of a nuclear microreactor-powered design for concurrent hydrogen (H2) and ammonia (NH3) production, with a focus on wastewater treatment plant applications. Wastewater with organic materials (e.g., municipal wastewater, swine lagoon waste, and food waste) are the analyzed feedstocks. The system integrates the anaerobic digestion of wastewater sludge with a Brayton cycle-based power generation unit heated by the microreactor. Using empirical data and an analytical model, the paper investigates the system's response to variations in key operational parameters. The sensitivity analysis explores the influence of parameters such as the chemical oxygen demand of the feedstock, compressor isentropic efficiency, and reactor temperature and pressure on H2 and NH3 production rates, Brayton cycle efficiency, and carbon dioxide emissions. Highlights from this analysis show a nonlinear dependence for Brayton efficiency on reactor temperature, the proportionality of ammonia and hydrogen production on chemical oxygen demand values, the major impact of compressor isentropic efficiency, and the minimal response from changing the pressure of steam methane reforming. These results signify opportunities to improve the system and ultimately lead to lowered greenhouse gas emissions.more » « less
-
Abstract Reconstructing the chemical and structural characteristics of the plant cell wall represents a promising solution to overcoming lignocellulosic biomass recalcitrance to biochemical deconstruction. This study aims to leverage hydroxyproline (Hyp)‐
O ‐glycosylation, a process unique to plant cell wall glycoproteins, as an innovative technology for de novo design and engineering in planta of Hyp‐O ‐glycosylated biopolymers (HypGP) that facilitate plant cell wall reconstruction. HypGP consisting of 18 tandem repeats of “Ser–Hyp–Hyp–Hyp–Hyp” motif or (SP4)18was designed and engineered into tobacco plants as a fusion peptide with either a reporter protein enhanced green fluorescence protein or the catalytic domain of a thermophilic E1 endoglucanase (E1cd) fromAcidothermus cellulolyticus . The engineered (SP4)18module was extensively Hyp‐O ‐glycosylated with arabino‐oligosaccharides, which facilitated the deposition of the fused protein/enzyme in the cell wall matrix and improved the accumulation of the protein/enzyme in planta by 1.5–11‐fold. The enzyme activity of the recombinant E1cd was not affected by the fused (SP4)18module, showing an optimal temperature of 80°C and optimal pH between 5 and 8. The plant biomass engineered with the (SP4)18‐tagged protein/enzyme increased the biomass saccharification efficiency by up to 3.5‐fold without having adverse impact on the plant growth. -
Abstract Low temperature plasmas (LTP) are a unique class of open‐driven systems in which chemical reactions are unpredictable using established concepts. The terminal state of chemical reactions in LTP, termed the
superlocal equilibrium state, is hypothesized to be defined by a proposed set of state variables. Using a LTP reactor wherein the state variables have been measured, it is shown that CO2spontaneously splits and the effluent speciation is independent of the influent speciation if the state variables are held constant and the residence time is long. CO2conversion at long residence times, which is expected to be nominally zero from equilibrium thermodynamics, can be as high as 70% in the LTP. The employed low pressure plasma reactor (P = 10 mbar) had a similar volume, productivity, and energy efficiency compared to an atmospheric pressure dielectric barrier discharge reactor, thanks to reaction rates that were three orders of magnitude faster. -
Abstract Chemical Looping Combustion (CLC) is a technology that efficiently combines power generation and CO 2 capture. In CLC, the fuel is oxidized by a metal oxide called an oxygen carrier (OC). CLC uses two reactors: a fuel reactor and an air reactor. The fuel reactor oxidizes the fuel and reduces the OC. The air reactor oxidizes the OC using air and then the OC is cycled back to the fuel reactor. It is typical for both the fuel and the air reactors to be fluidized beds (FBs). In this research, an Aspen Plus model was developed to simulate a CLC system. Aspen Plus has recently included a built-in FB unit operation module. To our knowledge, no literature has been reported using this FB module for simulating fluidized bed combustion or gasification. This FB unit process was investigated in Aspen Plus and a kinetic based model was used and compared the simulation results to experimental data and the commonly used Gibbs equilibrium model. The FB unit and the kinetic model well fit the experimental data for syngas and methane combustion within 2% of the molar composition of syngas combustion and within 4% for the methane combustion. An advantage of this model over other kinetic models in literature is that the core shrinking model kinetic rate equations have been converted into a power law form. This allows Aspen Plus to use a calculator instead of an external Fortran compiler. This greatly simplifies the modeling process. The reaction rate equations are given for all reactions. A sensitivity analysis of the reaction kinetics was conducted. All data, code, and simulation files are given.more » « less