Feasibility and cost of converting oil- and coal-fired utility boilers to intermittent use of natural gas

The continuous or intermittent use of natural gas in place of oil or coal in existing utility boilers would reduce emissions of sulfur and thereby the concentration of sulfate ions in precipitation. This report examines the technological feasibility and capital cost of retrofitting oil and coal fired utility boilers to burn intermittently natural gas and the parent fuel. Using extensive studies of the retrofitting of such boilers to burn synthetic gas of low to moderate heating value (LBG), it is found that natural gas closely simulates the combustion properties of LBG of medium heating value. Based upon this comparison, it is concluded that little or no modifications to the boiler are required to achieve the same boiler rating as when burning the original fuel, and that only a small efficiency penalty must be paid. Examination of the history of four eastern utility boiler conversions from oil to natural gas confirms these performance estimates, and shows that conversion costs for in-plant equipment are very small, less than 19 $(1985)/KW in all instances, while conversion times are less than one year (with little down time beyond that required for annual maintenance). Pipelining costs will vary with the local conditions.American Gas Associatio

Development of Electric Field Stress Control Devices for a 132 kV Insulating Cross-arm using Finite Element Analysis

Insulating cross-arms (ICAs) allow compaction or upgrading of transmission lines. The process of designing and verifying the performance of electric-field grading devices is reported for rigid cross-arms on a 132 kV lattice tower. For the grounded end, traditional grading devices resembling rings which follow the general shape of the insulators were designed. For the high-voltage end, an iterative process yielded a novel grading device which is a unibody piece of cast aluminium that manages the field on all four ICA members. Finite-element analysis simulations show that the electric-field magnitude at the triple junctions of the insulating members meet the design criteria of 3.5 kV/cm. Also, the field magnitude on the metallic end-fittings and electric-field grading devices is maintained below 18 kV/cm. The corona extinction test was performed on ICA assemblies showing that the grading devices can effectively control the electric field at voltages up to 132 kV since the average corona extinction voltage was 173.7 kV, well above the required value. The complete ICA assemblies were installed on an existing line in Scotland in August 2013. This paper provides a set of recommendations for use of FEA in the design of complex insulation geometries

Including Limited Partners in the Diversity Jurisdiction Analysis

This paper presents the results of the Dynamic Pricing Challenge, held on the occasion of the 17th INFORMS Revenue Management and Pricing Section Conference on June 29–30, 2017 in Amsterdam, The Netherlands. For this challenge, participants submitted algorithms for pricing and demand learning of which the numerical performance was analyzed in simulated market environments. This allows consideration of market dynamics that are not analytically tractable or can not be empirically analyzed due to practical complications. Our findings implicate that the relative performance of algorithms varies substantially across different market dynamics, which confirms the intrinsic complexity of pricing and learning in the presence of competition

Student perspectives on the relationship between a curve and its tangent in the transition from Euclidean Geometry to Analysis

The tangent line is a central concept in many mathematics and science courses. In this paper we describe a model of students’ thinking – concept images as well as ability in symbolic manipulation – about the tangent line of a curve as it has developed through students’ experiences in Euclidean Geometry and Analysis courses. Data was collected through a questionnaire administered to 196 Year 12 students. Through Latent Class Analysis, the participants were classified in three hierarchical groups representing the transition from a Geometrical Global perspective on the tangent line to an Analytical Local perspective. In the light of this classification, and through qualitative explanations of the students’ responses, we describe students’ thinking about tangents in terms of seven factors. We confirm the model constituted by these seven factors through Confirmatory Factor Analysis

A Novel Electrical Sensor for Combined Online Measurement of Partial Discharge (OLPD) and Power Quality (PQ)

A novel inductive sensor has been developed that can be used for both for online partial discharge (OLPD) monitoring and power quality (PQ) monitoring. The sensor has been designed for attachment onto power cables with 50/60 Hz currents up to 800 A. The sensor comprises a high frequency (HF) winding to detect partial discharge (PD) pulses between 200 kHz and 30 MHz with a flat frequency response within this range. A low frequency (LF) winding is aimed at monitoring the power frequency (50/60 Hz) and its harmonics up to the 63rd order; it can also be used for current signature analysis (CSA) in rotating machines. A passive low-pass filter is integrated inside the sensor casing to suppress the higher frequencies not relevant to power quality monitoring. The sensor has a split-core design, making it easy to install and allows for retrofit installations. The combined sensor is well suited to places where space is limited such as compact cable boxes where it would be difficult to install two separate sensors. The sensor is primarily used for high voltage (HV) rotating machines (direct or VSD fed) and can be used in a variety of other applications such as monitoring of onshore and offshore wind farms. The paper begins by reviewing the main types of sensors used for partial discharge monitoring followed by the development of the novel sensor. Finally, two case studies where the sensor has been successfully installed are presented

A Trial Installation of High Voltage Composite Cross-arms

Four high voltage composite cross-arms have been installed as part of a non-energised trial taking place in the Scottish Highlands. The non-cylindrical geometry of their two main structural members offers improved mechanical strength-to-weight ratio compared to cylindrically-shaped insulators of similar cross-sectional area. The instrumentation system aims to monitor mechanical performance through the use of embedded strain gauges and a combination of a load cell, accelerometer and inclinometer at the cross-arm nose. An industrial data capture and control platform is used to capture sensor outputs and store them until retrieval. Networked cameras with local storage capabilities are used to capture video recordings of the cross-arms. The trial has helped establish handling, transportation and installation procedures. The first results from the instrumentation system indicate the resilience of the cross-arms to winds reaching up to 151 mph (243 km/h) while no irregularities regarding snow and ice accretion have been observed