The performance of steam power plants, utilizing recovered waste heat from air-fuel and oxy-fuel combustion, are compared. Temperature profiles in the heat recovery steam generator (HRSG), steam production rate, net-work output and energy efficiency are simulated for different conditions. Investigations are made into the effect of varying pinch point on HRSG performance, net-work and energy efficiency for power generation utilizing oxy-fuel combustion. It is found that with increased pinch point there is an associated decrease in HRSG and steam plant efficiencies. Exhaust gas composition influences the energy efficiency of the power plant. When air-fuel and oxy-fuel combustion are compared there is a reduced amount of nitrogen in the oxidant stream in the latter case. When comparing air-fuel and oxy-fuel combustion, a considerable deviation in HRSG and steam power plant performance is exhibited, with oxy-fuel combustion offering benefits in system efficiency and plant output. The exhaust gas composition at the HRSG inlet contributes significantly the performance characteristics of the system. Raising the HRSG inlet temperature also increases power generation and system efficiency. The results provide insights into the use of oxy-fuel combustion for systems utilizing HRSG for power generation while demonstrating the influence of gas composition, pinch point, and exhaust gas temperature on system performance, and suggest that oxy-fuel combustion can help enhance the contribution to sustainable development of some energy systems.

Mining is the typical method of extracting coal, but it can only recover 20%–25% of global coal resources. Mining has many challenges and requires much time, resources, and personnel. A new method of coal extraction, underground coal gasification (UCG), could address some of these problems while greatly expanding recoverable coal resources. Underground coal gasification is a gasification process applied to in situ coal seams. When combined with carbon capture and storage, UCG has significant potential for providing a relatively clean energy source. This chapter reviews key concepts and technologies of UCG, providing insights into this developing coal extraction method. A case study is also presented that illustrates the modeling and analysis of UCG and assesses the feasibility of using an auxiliary power plant and utilizing waste heat rejected syngas processing, to supply the required energy associated with amine-based carbon dioxide capture and compression processes.

One method of creating economic and environmentally advantageous heating systems is through the use of renewable and alternative heat sources. These are often intermittent and availability for immediate use is sometimes limited. This limitation can be reduced with seasonal thermal energy storage systems. An approach to analyze and compare performance, economic, and environmental aspects of various design options related to heating systems with seasonal thermal energy storage systems is presented. The approach permits the choice of subsystem models to be applied within the core model and offers added accuracy over rule of thumb estimates while providing a level of precision appropriate for general analysis.

Background and Objective: The use of intermittent thermal energy sources for heating, in combination with seasonal thermal energy storage, may be advantageous compared to conventional heating systems.The analysis of heating systems with seasonal thermal energy storage is complex, as there are many variables that potentially affect overall design and operation.The effects of subsystem characteristics on overall system economics and environmental impact are not fully understood at present.This study investigates how subsystem efficiencies, pipe losses and peak consumer load affect economics and carbon dioxide emissions.Materials and Methods: A method for analyzing the economic and environmental aspects of a heating system with seasonal thermal energy storage is developed and presented.The present study focuses on the influence of subsystem efficiency values and losses on system performance, rather than on detailed thermodynamic analyses.Values of subsystem efficiencies and thermal losses are varied within ranges reported in the literature.The system utilizes a solar thermal source, an underground thermal energy storage and a natural gas backup boiler, and is taken to serve a residential building in Ottawa, Canada.Results: The thermal supply piping and seasonal thermal energy storage are found to have the highest capital cost followed by the solar collectors and backup boiler.The consumer load has the greatest effect on economics and carbon dioxide emissions.The backup system efficiency has little effect on system economics due to the high solar fraction.Conclusions: The study provides insight into the importance of the characteristics of various subsystems of the system on its operation, cost and carbon dioxide emissions.The results and trends developed can aid design and feasibility studies.Future work is merited to analyze heating systems using alternative subsystem technologies.

The use of intermittent thermal energy sources, in combination with seasonal thermal energy storage (STES), may offer competitive heating solutions compared to conventional heating systems. Currently, influence of subsystem characteristics on overall system economic and environment aspects is not fully understood. In this study, the effects of consumer load, subsystem efficiency and thermal supply losses are investigated through parametric studies using a simplified model. The system considered includes a single residential building located in Ottawa, Ontario, with a solar thermal source, underground thermal energy storage unit and natural gas backup boiler. Overall the thermal supply piping and STES have the highest capital cost followed by the solar collectors and backup boiler. The consumer load has the greatest effect on economics and CO2 emissions. Due to high solar fraction the varying backup efficiency has little effect on system economics. INTRODUCTION The use of renewable energy resources, like solar radiation and wind, for heating is limited as they typically have intermittent production rates, which may not coincide with heating loads of a building (Pinnau and Breitkopf, 2015). Through the use of thermal energy storage (TES) the effect of source intermittency and fluctuating heat demand can be reduced (Kapsalaki et al., 2012; Pavlov and Olesen, 2012). Combining renewable energy resources with TES allows for energy to be collected and stored until there is a demand, which could lead to more economic utilization of intermittent renewable and alternative energy sources (Dincer and Rosen, 2011; Haeseldonckx et al., 2007; Kapsalaki et al., 2012; Pavlov and Olesen, 2011; Pavlov and Olesen, 2012). TES can be categorized by storage duration: short-, mediumand long-term. Short-term TES is used to assist in peak thermal loads and has storage lengths of hours up to a day (Sharma et al., 2009). Medium-term has a storage capacity from a day to a week. Long-term storage involves storage requirements from a week up to multiple months (Dincer and Rosen, 2011). Longterm thermal storage can take advantage of seasonal climatic variations and is often referred to as seasonal thermal energy storage (STES) (Dincer and Rosen, 2011; Gaine and Duffy, 2010; Novo et al., 2010; Schmidt et al., 2004). In northern climates, where seasonally varying space heating loads dictate energy consumption, STES can contribute significantly to intermittent thermal source integration for heat production (Dincer and Dost, 1996; Pavlov and Olesen, 2011; Novo et al., 2010). A common use for STES is the storage of heat in the summer for space heating applications in the winter (Sweet and McLeskey, 2012). Heating systems incorporating renewable energy sources, with STES, consist of five main subsystems: consumer, STES, intermittent/alternative source, backup source and thermal supply piping. The characteristics of each subsystem’s affect the operation of the heating system. Effective integration of STES into heating systems requires detailed knowledge of subsystem operation and understanding of the interactions between subsystems. Currently, limited work has been reported on the effects of intermittent/alternative and backup source characteristics, associated with a wide range of sources, on performance, economic and environmental aspects. Typically STES are custom built for the specific application and require detailed knowledge to conduct accurate performance, economic and environmental feasibility analyses. More information on the overall system design of heating systems with STES including the significance of subsystem parameters and interaction between subsystems would assist with the optimal integration into building applications and communities. Through investigating significant design considerations it may be possible to develop accurate guidelines for use in basic and detailed system designs. To help address these needs, a simplified method to analyzing the economic and environmental aspects of a heating system with STES is developed and presented here. In an attempt to quantify the significance of different subsystem parameters and the interaction between subsystems on system performance, parametric studies are conducted. The effects of varying consumer load, STES efficiency, intermittent source and backup source efficiency, supply network pipe losses on cost and CO2 emissions are investigated. METHODOLOGY A detailed thermodynamic analysis of heating systems with STES is not a significant focus of the present study. Rather, the influence of subsystem efficiency values and losses is of primary interest. Since a detailed thermodynamic analysis was not the focus of this investigation, estimation of the subsystem efficiency and losses were assumed to be within the range of typical values found in literature. The model is developed in such a fashion to allow for flexibility in analysis through independent variation in subsystem characteristics. Ideally, the interdependency of subsystem characteristics should be considered as variation of some characteristics may affect the choice of applicable subsystem technologies and range of operating conditions. Information about consumer heating load and intermittent source availability are key characteristics in the analysis of heating systems with STES. RETScreen® (Natural Resources Canada, 2016) was used to determine the consumer load characteristics over the course of a year using the combined heat and power project template contained in the software. System location, building floor area, and peak heating load of the building per unit of floor area were provided to the software. Values for total amount of thermal energy consumed annually, average rate of thermal energy consumption for each month and the peak rate of thermal energy consumption for the entire building space were returned. Ideally consumer load characteristics would be determined using consumer load profiles developed through daily, hourly, or minute by minute values. This method provides a simplified approach to estimate consumer heating load characteristics using monthly averages. This limits the accuracy of the study since the heating load may vary considerable from the average values provided by the software. Solar energy was taken as the intermittent source of heat production through the use of solar thermal collectors. RETScreen was used to determine the amount of thermal energy available for heat production using the solar power project template. System location, collector slope and solar azimuth were specified in the software and values of monthly average daily solar radiation per unit area on horizontal and tilted orientations were returned. The values were used for the thermodynamic analysis of the system. SYSTEM DESCRIPTION The proposed system model includes the main subsystems required for a heating system with STES including: consumer, intermittent energy source, STES, backup energy source and thermal supply piping. As a simplification the model excludes auxiliary components typically found in heating systems such as heat pumps, pumps, heat exchangers, controls and monitoring devices. Exclusion of these auxiliary components may affect the accuracy of the results as the energy losses and consumption associated with their operation are excluded in the analysis. The system considered is shown in Figure 1. The energy is supplied to the consumer through an intermittent source supply chain and a backup source supply chain. In the intermittent source supply chain energy is introduced to the system through the intermittent subsystem. The energy introduced to the system represents the amount of energy presented from the original intermittent energy source (amount of available sun). Heat is generated and transferred to the system through the intermittent source heat production subsystem and then split into two paths through pipe sections one and two. Pipe section one leads to the consumer for immediate use of the thermal energy. Whether the energy can be used immediately is dependent on the intermittent source production and consumer loads coinciding. When the rate of heat introduced to the system, by the intermittent source, exceeds the consumer load, it is directed through pipe section two delivered to the STES subsystem. Heat is extracted from the STES and delivered to the consumer through pipe section three when the consumer load is higher than the supply through pipe section one. A backup thermal energy source is included in the system to respond to the peak heating demands of the consumer and is contained in the backup source supply chain. Fuel is consumed (e.g. fossil fuel and electricity) by the backup subsystem and the thermal energy produced is delivered to the consumer through pipe section four. ANALYSIS The following outlines the assumptions, equations and other relations and expressions used perform a thermodynamic, economic and environmental analysis of the system in Figure 1. The following assumptions are invoked to simplify the analysis and to assist in developing the governing relations:  At the end of every annual cycle the amount of energy stored in the STES system returns the equivalent amount stored at beginning of the cycle (no annual thermal accumulation).  Heat transfer between thermal supply pipes and other components is considered adiabatic.  Intermittent source, backup source and STES efficiency are independent of subsystem capacity.  Losses per unit length of thermal supply pipe is independent of pipe capacity.  Intermittent source, backup source and STES specific cost are independent of subsystem capacity.  Energy quality is not considered; working temperatures are assumed to be correct for the transfer and use of energy in all subsystems.  Cost of thermal supply pipe per meter length is independent of pipe capacity.  Costs associated with maintenance, personnel, and decommissioning or refurbis

The performance of hydrogen production using various types of biomass in an iron oxide-based thermochemical energy conversion system is assessed and compared. Since biomass, although abundant in supply, contains carbon, a mechanism for carbon capture and sequester could be used if greenhouse gas emissions are to be avoided (going beyond the neutrality of biomass in this regard). This is facilitated in the iron oxide based system because it enables separate streams for hydrogen and carbon dioxide. Hydrogen production trends are compared for various biomass inputs. The effects on hydrogen production are investigated for fuel moisture content. Simulation techniques are used. It is observed that a 10% moisture content in the source fuel eliminates the possibility of hydrogen production from low-grade biomass within the available energy region.

Heating is a major requirement in many regions, and growing energy demands and pollutant emissions have allowed unconventional heating technologies to be considered, including geothermal. Geothermal heat pumps are reviewed, including heat pump technology, earth connections, current world status and recent developments. Geothermal heat pump technology and conventional heating systems are compared in terms of costs, CO2 emissions and other parameters. Geothermal heat pump use is economically advantageous when the price of electricity is low. Alternatively geothermal heat pump units have the lowest emissions depending when electricity is produced from a low emitting source.

Underground coal gasification is a method of converting in situ coal into synthesis gas through the same chemical reactions that occur in surface gasifiers. If underground coal gasification systems are combined with carbon capture and storage methods, CO2 emissions can be greatly reduced. Carbon capture and storage methods require considerable amount of energy to separate CO2 and prepare it for transport and storage, which is typically considered a parasitic loss. This study investigates utilizing waste heat rejected during processing of syngas from underground coal gasification using an auxiliary power plant, to supply the required energy associated with amine-based CO2 capture and compression processes necessary for transport and sequestration. The system investigated is the Newman Spinney underground coal gasification test plant coupled with a basic Rankine cycle. It is shown that the energy requirement for CO2 processing can be met through the use of an auxiliary plant. The basic model illustrates that the power produced by the auxiliary plant is 2.1 times greater than that required by CO2 compression, while supplying the required heat for amine-based CO2 capture. Parametric analyses are performed to investigate the impact of air injection rate, syngas cooling and CO2 capture and compression requirements on system performance.

Reductions in fossil fuel use and increases in system efficiency are required to make space heating more environmentally benign. Ground loop heat pumps offer a heating option that is more environmentally benign than conventional methods. Past studies of these heat pumps have usually focused on basic system arrangements, but new advanced systems are being developed. Here, energy analyses are reported for an advanced heat pump arrangement comprised of a vapor compression cycle with an economizer. A parametric analysis is performed to identify and quantify the influence of condenser pressure, evaporator pressure, intermediate pressure, degree of subcooling at the condenser outlet and degree of super heating at the evaporator outlet on system performance and ground loop requirements. The results show that, of the operating conditions investigated, condenser pressure has the greatest effect on the coefficient of performance (COP). The effect on COP of the other parameters, ranked from highest to lowest, are evaporator pressure, degree of subcooling, intermediate pressure and degree of superheating within this study.

It is thought that the world coal reserve is close to 150 years, which only includes recoverable reserves using conventional techniques. Mining is the typical method of extracting coal, but it has been estimated that only 15% to 20% of the total coal resources can be recovered in this manner. If unrecoverable coal is considered in the reserves, the lifetime of this resource would be greatly extended, by perhaps a couple hundred years. Mining involves a large amount of time, resources, and personnel and contains many challenges such as drastic changes in landscapes, high machinery costs, elevated risk to personnel, and post-extraction transport. A new type of coal extraction method, known as underground coal gasification (UCG), that addresses most of the problems of coal mining is being investigated and implemented globally. UCG is a gasification process applied to in situ coal seams. UCG is very similar to aboveground gasification where syngas is produced through the same chemical reactions that occur in surface gasifiers. UCG has a large potential for providing a clean energy source through carbon capture and storage techniques and offers a unique option for CO 2 storage. This paper reviews key concepts and technologies of underground coal gasification, providing insights into this developing coal conversion method.