Chemical looping method for the combustion of heavy liquid hydrocarbon fractions (IFP Energies Nouvelles)

CATEGORY: CHEMICAL LOOPING
Chemical looping method for the combustion of heavy liquid hydrocarbon fractions (IFP Energies Nouvelles)

Type	Patent
Inventor	Ann Forret
Inventor	William Pelletant
URL	Free Full Text Source:  http://www.google.com/patents/US9297528
Assignee	IFP Energies Nouvelles,
Patent Number	US9297528 B2
Issue Date	Mar 29, 2016
Abstract	The invention relates to a method for upgrading heavy liquid fractions resulting from oil refining, by combustion in a fluidized-bed chemical looping process. The method according to the invention allows energy to be produced by oxidizing totally the heavy liquid feeds while allowing direct capture of the CO2 emitted in the combustion fumes. The method according to the invention also allows a synthesis gas to be produced.

Iron-containing mixed-oxide composites as oxygen carriers for Chemical Looping with Oxygen Uncoupling (CLOU)

CATEGORY: CHEMICAL LOOPING
Iron-containing mixed-oxide composites as oxygen carriers for Chemical Looping with Oxygen Uncoupling (CLOU)

Type	Journal Article
Author	Arya Shafiefarhood
Author	Amy Stewart
URL	http://www.sciencedirect.com/science/article/pii/S0016236114007832
Volume	139
Pages	1-10
Publication	Fuel
Date	January 1, 2015
Abstract	Chemical Looping with Oxygen Uncoupling (CLOU) is a promising technique for converting solid carbonaceous fuels with inherent carbon dioxide capture. It employs oxygen carriers that allow easy and reversible exchange of their lattice oxygen with external environment under varying oxygen partial pressures. The varying and often tunable thermodynamic properties of mixed oxides of first row transition metals make them viable for CLOU applications. Researchers synthesized and evaluated mixed iron–cobalt and iron–manganese oxides in terms of their ability to uncouple oxygen. The effects of adding a secondary perovskite phase on the uncoupling properties of these primary transition metal oxides were studied, as well. Results revealed that different cation compositions exhibit different oxygen uncoupling properties.

Rotating bed reactor for CLC: Bed characteristics dependencies on internal gas mixing

CATEGORY: CHEMICAL LOOPING 
Rotating bed reactor for CLC: Bed characteristics dependencies on internal gas mixing

Type	Journal Article
Author	Silje Fosse Håkonsen
Author	Carlos A. Grande
Author	Richard Blom
URL	http://www.sciencedirect.com/science/article/pii/S0306261913003395
Volume	113
Pages	1952-1957
Publication	Applied Energy
Date	January 2014
Abstract	Presents a novel continuous lab-scale rotating bed reactor for chemical looping combustion using CuO/Al2O3 oxygen carrier spheres and methane as fuel which provides approximately 90% CH4 conversion and >90% CO2 capture efficiency based on converted methane at 800 °C. However, a series of experiments using a  range of operating conditions potential yielded CO2 purities only in the range 20–65%. This was due to nitrogen slip from the air side of the reactor into the effluent CO2 stream. Researchers created a mathematical model to explore the air-mixing phenomena. The model reflects the gas slippage tendencies observed when varying the process conditions such as rotation frequency, gas flow and the flow if inert gas in the two sectors dividing the air and fuel side of the reactor. Results suggest that significant improvements can be made to reduce gas mixing in future modified and scaled-up reactor versions.

Modeling the Chemical Looping Reforming Process Operated in a Circulating Fluidized Bed Reactor Consisting of Two Bubbling Bed Units: Model Validation

CATEGORY: CHEMICAL LOOPING 
Modeling the Chemical Looping Reforming Process Operated in a Circulating Fluidized Bed Reactor Consisting of Two Bubbling Bed Units: Model Validation

Type	Journal Article
Author	Rafael A. Sánchez
Author	Hugo A. Jakobsen
URL	http://dx.doi.org/10.1021/ie5005064
Volume	53
Issue	23
Pages	9616-9630
Publication	Industrial & Engineering Chemistry Research
Date	June 11, 2014
Abstract	Describes a transient one-dimensional model for simulation of the chemical looping reforming process in a circulating fluidized bed (CFB). Authors present a CFB reactor model consisting of two connected bubbling bed units consisting of the fuel reactor (FR) and the air reactor (AR). Simulated results are validated by comparison with experimental data available in the literature. Researchers simulated three cases with varying oxygen-carrier-to-fuel ratios until the equilibrium concentrations are established in the solid phase. The hydrogen conversion and oxygen carrier conversion results from the simulations were compared with experimental data from the literature, showing that the numerical results are in fair agreement with the experimental results.

Influence of the Type of Oxygen Carriers on the Performance of a Hybrid Solar Chemical Looping Combustion System

CATEGORY: CHEMICAL LOOPING 
Influence of the Type of Oxygen Carriers on the Performance of a Hybrid Solar Chemical Looping Combustion System

Type	Journal Article
Author	Mehdi Jafarian
Author	Maziar Arjomandi
Author	Graham J. Nathan
URL	http://dx.doi.org/10.1021/ef402542b
Volume	28
Issue	5
Pages	2914-2924
Publication	Energy & Fuels
Date	May 15, 2014
Abstract	Offers a thermal analysis of a hybrid solar chemical looping combustion (Hy-Sol-CLC) system to identify the energetic performance of various combinations of fuel and oxygen carriers. Three fuels, namely, natural gas, carbon monoxide, and hydrogen, are assessed in combination with the oxides of five metals, namely, Co, Cu, Fe, Mn, and Ni as oxygen carrier. The heat of the fuel oxidation reaction is critical due to its relation to chemical solar thermal energy storage. Researchers also assessed their solar share, the fraction of stored energy relative to the total input energy from both the fuel and the concentrated solar energy, the fuel conversion efficiency, the system Carnot efficiency, the metal oxides energy density, and the volumetric heat capacity. The calculations show that, from the assessed pairs, only CoO/Co, NiO/Ni, and Fe2O3/Fe3O4 can be utilized in Hy-Sol-CLC systems working with natural gas.

Reactors Focused on Oxygen Carrier Utilization and Reactor Efficiency

CATEGORY: CHEMICAL LOOPING
Aerosol and Air Quality Research, 14: 559–571, 2014
Overview of Chemical-Looping Reduction in Fixed Bed and Fluidized Bed
Reactors Focused on Oxygen Carrier Utilization and Reactor Efficiency
Zhiquan Zhou, Lu Han, George M. Bollas*
Department of Chemical & Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, USA
ABSTRACT
A model-assisted comparison of two types of chemical-looping (CL) reactors (fixed bed and fluidized bed), with the same oxygen carrier loading and fuel capacity, is carried out to examine performance and efficiency of CL Reducers, operating with methane as the feedstock and nickel oxide as the oxygen carrier. The study focuses on the reduction step of chemical-looping combustion (CLC), for which the reactor efficiency and fuel utilization are crucial in terms of economics and carbon capture efficiency.
Process models (a three phase dynamic model for bubbling fluidized beds and a two dimensional homogeneous model for fixed beds) and reaction kinetics developed and validated in previous studies are used. A fluidized bed chemical-looping combustion Reducer is compared to a fixed bed equivalent reactor, scaled-up from a smaller experimental reactor, constrained to bed height to reactor diameter ratios that prohibit excessive temperature and pressure drops across the bed. Through a detailed comparison, CLC operated in the fluidized bed reactor is shown to deliver superior performance, i.e., uniform temperature and pressure distribution; high methane conversion (> 95%) and carbon dioxide selectivity (> 95%) sustained for longer reduction periods; negligible carbon formation (< 2 mol% C basis); and better efficiency in oxygen carrier utilization. 
fts: http://aaqr.org/VOL14_No2_March2014/10_AAQR-13-06-OA-0198_559-571.pdf

Nonlinear model predictive control for chemical looping process (Alstom Technology)

CATEGORY: CHEMICAL LOOPING
PATENT
Nonlinear model predictive control for chemical looping process (Alstom Technology)
Publication number US20140025210 A1
Application number US 13/946,115
Publication date Jan 23, 2014
Also published as CA2821463A1, CN103576551A, EP2690512A2, EP2690512A3
Inventors
Abhinaya Joshi, Hao Lei, Xinsheng Lou
Original Assignee
Alstom Technology Ltd
Abstract
A control system for optimizing a chemical looping (“CL”) plant includes a reduced order mathematical model (“ROM”) that is designed by eliminating mathematical terms that have minimal effect on the outcome. A non-linear optimizer provides various inputs to the ROM and monitors the outputs to determine the optimum inputs that are then provided to the CL plant. An estimator estimates the values of various internal state variables of the CL plant. The system has one structure adapted to control a CL plant that only provides pressure measurements in the CL loops A and B, a second structure adapted to a CL plant that provides pressure measurements and solid levels in both loops A, and B, and a third structure adapted to control a CL plant that provides full information on internal state variables. A final structure provides a neural network NMPC controller to control operation of loops A and B.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
The United States Government has certain rights in this invention pursuant to Department of Energy Contract No. DE-FC26-07 NT 43095.
TECHNICAL FIELD
The present invention relates to a control optimization system for a chemical looping process, and more specifically to a control optimization system for a chemical looping process employing a nonlinear model predictive controller.
BACKGROUND The Chemical Looping Process
A typical chemical looping (CL) system utilizes a high temperature process, whereby solids such as calcium- or metal-based compounds, for example, are “looped” between a first reactor, called an oxidizer, and a second reactor, called a reducer. In the oxidizer, oxygen from air injected into the oxidizer is captured by the solids in an oxidation reaction. The captured oxygen is then carried by the oxidized solids to the reducer to be used for combustion and/or gasification of a fuel such as coal, for example. After a reduction reaction in the reducer, the solids, no longer having the captured oxygen, are returned to the oxidizer to be oxidized again, and the cycle repeats.
Depending on a ratio of the fuel to the air, different gases are produced in the oxidation and reduction reactions. As a result, the ratio of fuel to air can be controlled such that the CL system may be utilized in different ways, such as: as a hybrid combustion-gasification process which produces hydrogen for gas turbines, fuel cells and/or other hydrogen-based applications; as a hybrid combustion-gasification process which produces a synthesis gas (syngas) containing varying amounts of hydrogen and carbon dioxide for gas turbines and/or fuel cells; or as a combustion process for a combustion-based steam power plant.
The CL process is more complicated than processes of traditional plants such as conventional circulating fluidized bed (CFB) plants, for example. As a result, traditional plant controls applied to the CL process necessarily result in separate control loops for each CL loop. However, using separate control loops for each CL loop is inefficient and does not optimize performance of the CL process, since accurate control depends on coordinated control of multiple parameters in each loop, and parameters which crossover between loops.
In addition, the CL process has multi-phase flows and chemical reactions which are characterized by process nonlinearities and time delays due to mass transport and chemical reaction rates. As a result, traditional power plant design without considering control optimization systems in early stages of process design are further inadequate for integrated optimization of process performance and system operability.
Further, many of the variables in the CL process have nonlinear relationships with other variables, e.g., inter-loop interaction of variables. As a result, process models need to be developed so as to effectively characterize these multi-interdependent variable relationships.
Chemical looping technology is a method of heat production that can produce a separate stream of CO2 that can be sequestered, reducing the exhaust of greenhouse gases. This concept is based on a process utilizing high temperature chemical and thermal looping technology. As studied in previous projects, the chemical looping plant was assessed very favorably in terms of capital cost and electricity cost with up to 95% CO2 capture. However, due to the inherent nonlinearity of the process and the multi-loop interactions of solid particles, it is a quite challenging problem to control the particle flows and stabilize the reactants (solids) transport in the loops such that the system can sustain desired chemical reactions and provide stable energy production.
Nonlinear Model Predictive Control
In order to achieve the goals of stability and maximum profitability for the chemical looping process, the design of advanced process control becomes one of the important components in the development of this technology. Model predictive control (“MPC”) is an advanced method of model based process control. It is a multivariable control algorithm that uses an internal dynamic model of the process and an optimization solver to calculate the optimum control moves. MPC schemes that are based on nonlinear models and consider linear or non-linear cost-functions and general nonlinear constraints on the state and input variables are considered nonlinear model predictive control (NMPC). Nonlinear model predictive control (NMPC) is presented schematically in FIG. 1.
Values are provided for input variables (or manipulated variables) to a plant 1, that is intended to be controlled. The plant 1 produces outputs that are fed to a NMPC 100 that includes an internal nonlinear model 120 that is defined by non-linear equations between at least one input and at least one output.
Nonlinear model 120 is a mathematical model of various processes of plant 1 that provide outputs similar to plant 1 when each are supplied with the same inputs.
NMPC 100 also includes a nonlinear optimizer 130. The nonlinear optimizer 130 receives input constraint ranges and at least one goal. Nonlinear optimizer 130 provides input values within the constraint range to the nonlinear model 120 which creates outputs. Nonlinear optimizer 130 monitors and stores the outputs of the nonlinear model 120. Nonlinear optimizer 130 repeats this process for a plurality of input variable values spanning the constraint range while monitoring and storing the outputs. It then analyzes the outputs and goals to determine an optimum output and the inputs associated with the optimum output.
An estimator 110 interacts with nonlinear model 120 to estimate the values of internal state variables for given input and output variables.
To develop an NMPC a mathematical model of the chemical looping system must be designed which accurately depicts the functioning of the chemical looping system and its control structures.
Usually these models solve non-linear problems, and are therefore are computationally demanding due to the large number of computations required for each output calculation. Therefore, to be practical, there must be a way to use the model to arrive at estimated output quickly.
It is important to consider costs of running a chemical looping plant. Therefore, one of the control goals should include optimization of operating costs instead of simply optimizing operation. Therefore, there is currently a need for a controller for a chemical looping process that can stabilize its operation and minimize its operating costs.
The above described and other features are exemplified by the following figures and detailed description.
Free Full Text Source: http://www.google.com/patents/US20140025210

Evaluation of the Effect of Sulfur on Iron-Ore Oxygen Carrier in Chemical-Looping Combustion

CATEGORY: CHEMICAL LOOPING
Ind. Eng. Chem. Res., 2013, 52 (5), pp 1795–1805, DOI: 10.1021/ie303023w
Evaluation of the Effect of Sulfur on Iron-Ore Oxygen Carrier in Chemical-Looping Combustion
Haiming Gu , Laihong Shen *, Jun Xiao , Siwen Zhang , Tao Song , and Dingqian Chen
Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, Southeast University, 2 Sipailou, Nanjing 210096, China
lhshen@seu.edu.cn  
Abstract
The presence of sulfur contaminants in fossil fuels means that the gaseous products of sulfur species and the interactions between these sulfur contaminants and the oxygen carrier are significant concerns in chemical-looping combustion.
Researchers studied chemical-looping combustion of a sulfur-containing gaseous fuel with iron ore as the oxygen carrier using thermogravimetric analysis and Fourier transform infrared (TGA–FTIR) spectroscopy. They examined the effects of reaction atmosphere (N₂ and CO₂), H₂S concentration, and pressure on the reactivity of iron ore in the presence of H₂S. They also explored the evolution of gaseous sulfur species in both N₂ and CO₂ atmospheres. With a higher concentration of H₂S in the gaseous fuel, the weight loss was slower. They noted sulfidation of iron ore in both N₂ and CO₂ atmospheres, while elevated pressure contributed to a higher sulfidation rate. Compared with N₂ atmosphere, CO₂ atmosphere gave higher concentrations of COS and an initial SO₂ peak but a lower concentration of CS₂. The effect of sulfidation on the structure of the iron ore was studied in a fluidized bed. The sulfidation of iron ore caused a decrease in both surface area and pore volume, and the porous surface of the oxygen carrier became smoother and almost imperforate. FeS was the only iron sulfide noted during the sulfidation process. The vulcanized iron ore could be regenerated with air calcination treatment, and the addition of H₂O in the gaseous fuel was able to prevent the sulfidation of iron ore. The addition of CaO in the oxygen carrier was effective in mitigating the sulfidation and reducing the emission of gaseous sulfur species.
Full Text Source (Subscription or Fee): http://pubs.acs.org/doi/abs/10.1021/ie303023w