Zheming Zhang

Transient Simulations of Spouted Fluidized Bed for Coal-Direct Chemical Looping Combustion

Chemical-looping combustion holds significant promise as one of the next generation combustion technology for high-efficiency low-cost carbon capture from fossil fuel power plants. For thorough understanding of the chemical-looping combustion process and its successful implementation in CLC based industrial scale power plants, the development of high-fidelity modeling and simulation tools becomes essential for analysis and evaluation of efficient and cost-effective designs. In this paper, multiphase flow simulations of coal-direct chemical-looping combustion process are performed using ANSYS Fluent CFD code. The details of solid–gas two-phase hydrodynamics in the CLC process are investigated by employing the Lagrangian particle-tracking approach called the discrete element method (DEM) for the movement and interaction of solid coal particles moving inside the gaseous medium created due to the combustion of coal particles with an oxidizer. The CFD/DEM simulations show excellent agreement with the experimen...

Numerical Simulation of CO2 Sequestration in Large Saline Aquifers

With heightened concerns over CO2 emissions from pulverized-coal power plants, there has been major emphasis in recent years on the development of safe and economical geological carbon sequestration (GCS) technology. Although it is one of the most promising technologies to address globalwarming due to anthropogenic CO2 emissions, the detailed mechanisms of GCS are not well understood. As a result, there remain many uncertainties in determining the sequestration capacity of the formation/reservoir and the safety of sequestered CO2 due to leakage. These uncertainties arise due to lack of information about the detailed interior geometry of the formation and the heterogeneity in its geological properties, such as perme‐ ability and porosity, which influence the sequestration capacity and plume migration. Furthermore, the sequestration efficiency is highly dependent on the injection strategy, which includes injection rate, injection pressure, type of injection well employed and its orientation etc. The goal of GCS is to maximize the sequestration capacity and minimize the plume migration by optimizing the GCS operation before proceeding with its large-scale deployment. In this chapter, numerical simulations of GCS are conducted using the US Department of Energy (DOE) multi-phase flow solver TOUGH2 (Transport of Unsaturated Groundwater and Heat). A multi-objective optimization code based on genetic algorithm is also developed to optimize the GCS operation for a given geological formation. It is described in Chapter titled,” Optimization of CO2 Sequestration Saline Aquifers”. Most of the studies are conducted for sequestration in a saline formation (aquifer). Large-scale GCS studies are conducted for the Mt.Simon, Frio and Utsira saline formations, for which some experimental data and compu‐ tations performed by other investigators are available. These simulation studies provide important insights as to the key sources of uncertainties that can influence the accuracy of simulations.

Numerical Simulation of Geological Carbon Sequestration in Saline Aquifers: Three Case Studies

Geological carbon sequestration (GCS) is one of the most promising technologies to address the issue of excessive anthropogenic CO2 emissions in the atmosphere due to fossil fuel combustion for electricity generation. For GCS, the saline aquifer geological carbon sequestration is considered very attractive compared to other options because of their huge sequestration capacity in U.S. and other parts of the world. However, in order to fully exploit their potential, the injection strategies need to be investigated that can address the issues of both the CO2 storage efficiency and safety along with their economic feasibility. Numerical simulations can be used to determine these strategies before the deployment of full scale sequestration in saline aquifers. This paper presents the numerical simulations of CO2 sequestration in three large identified saline aquifers (Mt. Simon, Frio, Utsira) where the sequestration is currently underway or has recently been completed (in case of Frio). The numerical simulations are in acceptable agreement with the seismic data available for plume migration. The results of large scale history-matching simulation in Mt. Simon, Frio, and Utsira formations provide important insights in the uncertainties associated with the numerical modeling of saline aquifer GCS.Copyright

Assessment and optimization of an airplane's environmental impact

Purpose – The ratio of the energy liberated during a flight to the revenue work done (ETRW) of an airplane can be employed as a key indicator to assess its environmental impact. It remains constant during the life cycle of the aircraft and is fixed by its designers. The goal of an environmentally optimum airplane is to minimize the ETRW. This paper seeks to address these issues.Design/methodology/approach – For an existing airplane, there are two major parameters that can greatly affect the ETRW, which are the ratio of actual payload to maximum possible payload “c” and the flight range R. The goal of this paper is to study the effect of c and R on ETRW and minimize it by using a genetic algorithm (GA). The study is performed on a Boeing 737‐800 and a Boeing 747‐400 aircraft as well as recently proposed aircraft designs, namely the Boeing second generation Blended‐Wing‐Body (BWB) and MIT Double‐Bubble D8.2.Findings – It turns out that the maximum possible values of payload and range do not necessarily lead...

Process and Reactor Level Simulations of Coal-Direct Chemical-looping Combustion

Reducing carbon emissions from fossil-fueled power plants has been an active area of research in recent years. One technology that appears to be very promising for high-efficiency low-cost carbon capture is chemical-looping combustion (CLC) (Leion et al. 2009a). CLC involves combustion of fuels (either gas or solid) by heterogeneous chemical reactions with an oxygen carrier, usually a particulate metal oxide. Because of the absence of air in the fuel reactor, the combustion products are not diluted by other gases (e.g., N2), resulting in high purity of CO2 available at the fuel reactor outlet. Also, the net energy release from a CLC process is theoretically identical to that from conventional combustion of the fuel (Abad et al. 2012; Linderholm et al. 2013; Mattisson et al. 2009a). Research by Lyngfelt et al. (2001) has shown that the energy cost of solid circulation, which is the only energy cost of separation, is a very small percentage (approximately 0.3 %) of the total energy released by the combustion process compared to other pre-combustion technologies such as the oxy-fuel combustion in which the oxygen separation process consumes nearly 15 % of the electricity generation (Hong et al. 2009a, b). Therefore, CLC holds significant promise as a next-generation combustion technology due to its potential to allow zero CO2 emission with little effect on the efficiency of the power plant.

Assessment and optimization of an airplane

Purpose – The ratio of the energy transformed to the revenue work done (ETRW) during a flight of an airplane can be employed as a key indicator to assess its environmental impact. It remains constant during the life cycle of the aircraft and is fixed by its designers. The goal of an environmentally optimum airplane is to minimize the ETRW. Design/methodology/approach – For an existing airplane, there are two major parameters that can greatly affect the ETRW, which are the ratio of actual payload to maximum possible payload “c” and the flight range R. The goal of this paper is to study the effect of c and R on ETRW and minimize it by using a genetic algorithm (GA). The study is performed on a Boeing 737-800 and a Boeing 747-400 aircraft as well as recently proposed aircraft designs namely the Boeing second-generation Blended-Wing-Body (BWB) and MIT Double-Bubble D8.2. Findings – It turns out that the maximum possible values of payload and range do not necessarily lead to a flight with minimal environmental...

The Effect of First- and Second-Order Slip Condition on Oscillatory Flows: Several Exact Solutions

In last two decades, several studies have been conducted to understand the molecular mechanism of slip of fluids (both liquids and gases) at a solid wall. Most of these studies have dealt with steady flow. Recently, Thalakkottor and Mohseni have shown by molecular dynamics simulations that in unsteady flow there is an additional slip above the slip observed in the steady flow. They have developed an unsteady slip flow model by extending the Maxwell’s slip theory for steady flows to encapsulate unsteady flows. The model indicates that the slip velocity of a fluid in unsteady flow is also a function of the acceleration of the fluid in addition to its shear rate. Thus the slip velocity is both a function of firstand second-order derivatives normal to the wall multiplied by different coefficients dependent upon the nature of the fluid (liquid or gas). In this paper, we consider several unsteady flows – the Stokes flow, the Couette flow, and flow in a channel due to an oscillatory wall. In addition, we consider unsteady flow due to an impulsively started flat plate. Exact solutions are obtained by using the most general form of slip boundary condition that contains both first and second-order derivatives normal to the boundary. The coefficients that multiply these derivatives can be determined by knowledge of the nature of the fluid. It should be noted that these solutions can also be reduced to steady flows with slip with higher-order slip boundary condition that includes both firstand second-order derivatives normal to the wall.

Numerical Simulation and Optimization of CO2 Sequestration in Saline Aquifers

With recent concerns on CO2 emissions from coal fired electricity generation plants; there has been major emphasis on the development of safe and economical Carbon Dioxide Capture and Sequestration (CCS) technology worldwide. Saline reservoirs are attractive geological sites for CO2 sequestration because of their huge capacity for sequestration. Over the last decade, numerical simulation codes have been developed in U.S, Europe and Japan to determine a priori the CO2 storage capacity of a saline aquifer and provide risk assessment with reasonable confidence before the actual deployment of CO2 sequestration can proceed with enormous investment. In U.S, TOUGH2 numerical simulator has been widely used for this purpose. However at present it does not have the capability to determine optimal parameters such as injection rate, injection pressure, injection depth for vertical and horizontal wells etc. for optimization of the CO2 storage capacity and for minimizing the leakage potential by confining the plume migration. This paper describes the development of a “Genetic Algorithm (GA)” based optimizer for TOUGH2 that can be used by the industry with good confidence to optimize the CO2 storage capacity in a saline aquifer of interest. This new code including the TOUGH2 and the GA optimizer is designated as “GATOUGH2”. It has been validated by conducting simulations of three widely used benchmark problems by the CCS researchers worldwide: (a) Study of CO2 plume evolution and leakage through an abandoned well, (b) Study of enhanced CH4 recovery in combination with CO2 storage in depleted gas reservoirs, and (c) Study of CO2 injection into a heterogeneous geological formation. Our results of these simulations are in excellent agreement with those of other researchers obtained with different codes. The validated code has been employed to optimize the proposed water-alternating-gas (WAG) injection scheme for (a) a vertical CO2 injection well and (b) a horizontal CO2 injection well, for optimizing the CO2 sequestration capacity of an aquifer. These optimized calculations are compared with the brute force nearly optimized results obtained by performing a large number of calculations. These comparisons demonstrate the significant efficiency and accuracy of GATOUGH2 as an optimizer for TOUGH2. This capability holds a great promise in studying a host of other problems in CO2 sequestration such as how to optimally accelerate the capillary trapping, accelerate the dissolution of CO2 in water or brine, and immobilize the CO2 plume.Copyright

A simple integrated model of global warming and policymaking

This paper describes a simple integrated model of global warming due to anthropogenic CO2 emissions, which can be used by policy makers for quick screening of various mitigation scenarios to achieve desired carbon reduction targets. First, the constant airborne fraction model was generalised to establish a relationship between CO2 emissions and CO2 concentration in the atmosphere, which was then used to determine the global average surface temperature using Oglesby and Saltzman’s general circulation model. Using these simple relationships, the forecast for CO2 emission, CO2 concentration and average global surface temperature was made for the years 2030 and 2050 under the Business As Usual (BAU) scenario. To achieve an acceptable target increase in global average surface temperature, several CO2 mitigation strategy models, as proposed by Socolow and Lam, were considered. The comparison of the predictions of the proposed model with those of other researchers suggests that, although simple, the proposed model is credible for the purpose of quick assessment of various CO2 mitigation scenarios.

An Integrated Model of Global Warming and Policy Making

This paper describes a simple integrated model of global warming due to anthropogenic CO2 emissions, which can help the policy makers in considering various CO2 mitigation strategies. First, the constant airborne fraction model is generalized to establish relationship between CO2 emissions and CO2 concentration in the atmosphere which is then used to determine the global average surface temperature using the Oglesby and Saltzman’s general circulation model. Using these simple relationships, the forecast for CO2 emissions, CO2 concentration and average global surface temperature is made for years 2030 and 2050 under Business as Usual (BAU) scenario. In order to achieve an acceptable target increase in global average surface temperature, several simple CO2 mitigation approaches, proposed by Socolow and Lam, are included in the integrated model.Copyright