Service Consistency in Vehicle Routing

This thesis studies service consistency in the context of multi-period vehicle routing problems (VRP) in which customers require repeatable services over a planning horizon of multiple days. Two types of service consistency are considered, namely, driver consistency and time consistency. Driver consistency refers to using the fewest number of different drivers to perform all of the visits required by a customer over a planning horizon and time consistency refers to visiting a customer at roughly the same time on each day he/she needs service. First, the multi-objective consistent VRP is defined to explore the trade-offs between the objectives of travel cost minimization and service consistency maximization. An improved multi-objective optimization algorithm is proposed and the impact of improving service consistency on travel cost is evaluated on various benchmark instances taken from the literature to facilitate managerial decision making. Second, service consistency is introduced for the first time in the literature to the periodic vehicle routing problem (PVRP). In the PVRP, customers may require multiple visits over a planning horizon, and these visits must occur according to an allowable service pattern. A service pattern specifies the days on which the visits required by a customer are allowed to occur. A feasible service pattern must be determined for each customer before vehicle routes can be optimized on each day. Various multi-objective optimization approaches are implemented to evaluate their comparative competitiveness in solving this problem and to evaluate the impact of improving service consistency on the total travel cost. Third, a branch-and-price algorithm is developed to solve the consistent vehicle routing problem in which service consistency is enforced as a hard constraint. In this problem, the objective is to minimize the total travel cost. New constraints are devised to enhance the original mixed integer formulation of the problem. The improved formulation outperforms the original formulation regarding CPLEX solution times on all benchmark instances taken from the literature. The proposed branch-and-price algorithm is shown to be able to solve instances with more than fourteen customers more efficiently than either the existing mixed integer formulation or the one we propose in this paper

Fossil-Fuel-Fired Power Plant

A power plant includes a boiler, a stream turbine generator, a post combustion processing system, a feed water regeneration processing system and a heat exchanger. Heat from the heat exchanger is used to regenerate (a) a reagent that absorbs carbon dioxide from flue gas and (b) a water-lean desiccant used to increase plant operating efficiency

Flue Gas Desulfurization Apparatus

An apparatus is provided for removing sulfur oxides from a flue gas stream. That apparatus includes an absorber tower having an upper section and a lower section. A packed bed unit is provided in the upper section of the absorber tower. A first recycling circuit is provided for recycling lime water to the lower section of the absorber. Further the apparatus includes a second recycling circuit for recycling caustic solution to the packed bed unit

Thermal Degradation Pathways of Aqueous Diamine CO\u3csub\u3e2\u3c/sub\u3e Capture Solvents

Diamines have shown promise as CO2 capture solvents, yet very little is known about their pathway for thermal degradation. In this study, diamine thermal degradation was quantitatively monitored in lab-scale experiments on four aqueous diamine solvents; ethylenediamine (EDA) 1,2-propanediamine (1,2-DAP), 1,3-diaminopropane (1,3-DAP) and N-methyl-1,2-ethanediamine (NMEDA), to gain a more comprehensive understanding of their degradation pathway(s). The major degradation products were identified by high resolution time-of-flight mass spectrometry (TOF-MS). Degradation pathways were proposed showing that the primary thermal degradation route for this class of amine are through carbamate formation followed by intermolecular cyclization to form an imidazolidinone or nucleophilic attack by a free amine to form a diamine urea

Hybrid Process Using a Membrane to Enrich Flue Gas CO\u3csub\u3e2\u3c/sub\u3e with a Solvent-Based Post-Combustion CO\u3csub\u3e2\u3c/sub\u3e Capture System

A process for recovery of CO2 from a post-combustion gas includes pre-concentrating a CO2 component of the post-combustion flue gas by passing the post-combustion gas through a CO2-selective membrane module to provide a CO2-enriched permeate stream and a CO2-lean reject stream. Next, in a CO2 absorber, both the CO2-enriched permeate stream and CO2 lean reject stream, fed to separate feed locations on the CO2 absorber, are contacted with a scrubbing solvent to absorb CO2 and provide a carbon-rich scrubbing solvent. Finally, absorbed CO2 is stripped from the carbon-rich scrubbing solvent by a two-stage CO2 stripping system. The CO2-selective membrane may be a high flux, low pressure drop, low CO2 selectivity membrane. The two stage stripping system includes a primary CO2 stripping column for stripping CO2 from the carbon-rich scrubbing solvent exiting the CO2 absorber, and a secondary CO2 stripping column for stripping CO2 from a carbon-lean scrubbing solvent exiting the primary CO2 stripping column. Apparatus for CO2 removal from post-combustion gases in a pulverized coal power plant incorporating the described processes are described

Solubility and Thermodynamic Modeling of Carcinogenic Nitrosamines in Aqueous Amine Solvents for CO\u3csub\u3e2\u3c/sub\u3e Capture

A better understanding of key fundamental properties of nitrosamines, including their solubility in aqueous amine solvents, is needed to understand and accurately model the vapor-phase emission levels from operating CO2 capture systems. In this work, the first experimental Henry\u27s volatility coefficient of a nitrosamine was obtained with a novel method using static headspace solid phase micro extraction (SPME) and gas chromatography mass spectrometry (GC/MS). The experimentally determined Henry\u27s volatility coefficient of nitrosopyrrolidine (NPY) was found to be around 0.02 (dimensionless) at 25 °C, and falls in the range of a semi-volatile compound. A linear temperature dependency of the Henry\u27s volatility coefficient can be observed, however additional data is need to verify this trend

Reduction of Amine Emissions from an Aqueous Amine Carbon Dioxide Capture System Using Charged Colloidal Gas Aphrons

The present invention includes a system and process to reduce amine mist emissions (or MEA) from carbon capture systems using colloidal gas aphrons (CGA), and includes a method for separating and recovering an amine solvent (e.g., in the form of entrained droplets/mist and/or fine aerosol particles) from a carbon dioxide scrubbed flue gas stream exiting a carbon capture system (e.g., oil-fired power plants, coal-fired power plants, and/or natural gas combined cycle plants)

Potential of Zero Charge-Based Capacitive Deionization

The invention is a capacitive, aka electrostatic, deionization apparatus and method that solves the problem of short lifetime of conventional capacitive deionization (CDI) and of membrane capacitive deionization (MCDI) devices and methods by shifting the Potential of Zero Charge of electrode surfaces through surface modifications. Such electrode surface modifications provide very long lifetime capacitive deionization devices and methods

CFD Modeling on Hydrodynamic Characteristics of Multiphase Counter-Current Flow in a Structured Packed Bed for Post-Combustion CO\u3csub\u3e2\u3c/sub\u3e Capture

Solvent-based post combustion CO2 capture is a promising technology for industrial application. Gas-liquid interfaces and interactions in the packed bed are considered one of the key factors affecting the overall CO2 absorption rate. Understanding the hydrodynamic characterizations within packed beds is essential to identify the appropriate enhanced mass transfer technique. However, multiphase counter-current flows in the structured packing typically used in these processes are complicated to visualize and optimize experimentally. In this paper, we aim to develop a comprehensive 3D multiphase, counter-current flow model to study the liquid/gas behavior on the surface of structured packing. The output from computational fluid dynamics (CFD) clearly visualized the hydrodynamic characterizations, such as the liquid distributions, wettability, and film thicknesses, in the confined packed bed. When the liquid We (Weber number) was greater than 2.21, the channel flow became insignificant and flow streams became more disorganized with more droplets at larger sizes. The portion of dead zones is decreased at higher liquid We, but it cannot be completely eliminated. Average film thickness was about 0.6–0.7 mm, however, its height varied significantly

Method of Inhibiting Nitrosation of an Aqueous Amine Solution Used in a Process of Removing Carbon Dioxide from a Flue Gas

A method is provided for inhibiting nitrosation of an aqueous amine solution used in a process of removing carbon dioxide from a flue gas. That method includes a step of adding an effective amount of an antioxidant to the aqueous amine solution being circulated between an absorber and a stripper of a carbon dioxide capture system