Simon Harvey

Analysis of a reheat gas turbine cycle with chemical recuperation using ASPEN

Gains in the power output and thermal efficiency of industrial gas turbines have occurred in the past, primarily from increased firing temperatures and operating pressures. More recently, there is growing interest in investigating advanced cycle concepts that make use of one or more of the following performance enhancement modifications: compression intercooling, reheat expansion and exhaust heat recovery. Recent attention has focused, in particular, on the chemical heat recovery concept. The “waste” heat in the turbine exhaust is used to convert a methane-steam mixture into a hydrogen-rich fuel in a methane-steam reformer. The potential benefits of such cycles include high conversion efficiency, ultra-low NOx emission levels (less than 1 ppm) and high power density per unit of land. However, such cycles require high turbine exhaust temperatures, which may be achieved effectively by staging the turbine expansion and including a reheat combustor. ABB recently unveiled its new GT26 series stationary gas turbines using staged expansion with reheat combustion, allowing high thermal efficiencies with relatively low turbine inlet temperatures. This type of turbine appears particularly well-suited for chemical heat recovery. In this paper, we present a CRGT cycle based on a reheat gas turbine with key design features similar to those of ABBs GT26 machine. The cycle analysis is performed using Aspen Technologys ASPEN+ process simulation software. The paper includes a detailed first and second law analysis of the cycle.

Thermodynamic analysis of chemically recuperated gas turbines

Significant research effort is currently centred on developing advanced aero-derivative gas turbine systems for electric power generation applications, in particular for intermediate duty operation. Compared to industrial gas turbines, aero-derivatives offer high simple cycle efficiency, a quick and frequent start capability without significant maintenance cost penalty. A key element for high system performance (efficiency and power output) is the development of improved heat recovery systems, leading to advanced cycles such as the STeam Injected Gas Turbine (STIG) cycle, Humid Air Turbine (HAT) cycle or the Chemically Recuperated Gas Turbine (CRGT) cycle. In this paper the chronology of development of this last technology and a detailed description of our research program “Thermodynamic analysis of chemically recuperated gas turbines” is presented. A comparative study of the performance potentials of CRGT cycles and the other advanced cycles for design and off-design mode is presented. The analysis method accounts for turbine blade cooling requirements, which have a decisive impact on cycle performance. Exergy calculations are included in the analysis method. Research perspectives for this technology are suggested.

Integration Study for Alternative Methanation Technologies for the Production of Synthetic Natural Gas from Gasified Biomass

This paper analyzes the integration of two different methanation technologies – fixed bed adiabatic and fluidised bed isothermal - in a SNG production process and the consequences for the overall process energy conversion performance. The different operating conditions of the two methanation technologies lead to a change in temperature levels and quantities of recoverable heat, respectively, but also to differences in the overall processes’ power consumption. Using pinch methodology for optimal internal heat recovery in combination with flowsheeting software (ASPEN Plus), the two methanation alternatives are fitted into the SNG production process. The potential power production from recovered process heat is analysed based on the Carnot efficiency and compared to the overall power consumption within the SNG process. Both methanation alternatives perform equally within the given boundary conditions, resulting in an output of SNG of 63.3 MWLHV per 100 MWLHV dry fuel input and a ratio of about 1.22 between theoretical power production and overall power consumption.

Modular approach to analysis of chemically recuperated gas turbine cycles

Current research programmes such as the CAGT programme investigate the opportunity for advanced power generation cycles based on state-of-the-art aeroderivative gas turbine technology. Such cycles would be primarily aimed at intermediate duty applications. Compared to industrial gas turbines, aeroderivatives offer high simple cycle efficiency, and the capability to start quickly and frequently without a significant maintenance cost penalty. A key element for high system performance is the development of improved heat recovery systems, leading to advanced cycles such as the humid air turbine (HAT) cycle, the chemically recuperated gas turbine (CRGT) cycle and the Kalina combined cycle. When used in combination with advanced technologies and components, screening studies conducted by research programmes such as the CAGT programme predict that such advanced cycles could theoretically lead to net cycle efficiencies exceeding 60%. In this paper, the authors present the application of the modular approach to cycle simulation and performance predictions of CRGT cycles. The paper first presents the modular simulation code concept and the main characteristics of CRGT cycles. The paper next discusses the development of the methane–steam reformer unit model used for the simulations. The modular code is then used to compute performance characteristics of a simple CRGT cycle and a reheat CRGT cycle, both based on the General Electric LM6000 aeroderivative gas turbine.

Potential for greenhouse gas reduction in industry through increased heat recovery and/or integration of combined heat and power

The potential for greenhouse gas (GHG) reduction in industry through process integration measures depends to a great extent on prevailing technical and economic conditions. A step-wise methodology developed at the authors department based on pinch technology was used to analyse how various parameters influence the cost-optimal configuration for the plants energy system, and the opportunities for costeffective GHG emissions reduction compared to this solution. The potential for reduction of GHG emissions from a given plant depends primarily on the design of the industrial process and its energy system (internal factors) and on the electricity-to-fuel price ratio and the specific GHG emissions from the national power generation system (external factors).

Gas turbines in district heating combined heat and power systems: influence of performance on heating costs and emissions

Abstract Much work is currently focussed on identifying economically and environmentally optimal strategies for increasing gas turbine based combined heat and power (CHP). In many such studies, only a few fixed parameters are used to describe the CHP plant. These are typically total and electrical efficiencies, investment and running costs, minimum and maximum acceptable size, and minimum acceptable part-load. However, for gas turbine based systems these characteristics are clearly functions of the operating conditions, especially for part-load operation. This study examines the effects of varying performance of the gas turbine on the overall heat production costs and CO2 emissions of a medium sized community district heating plant. Both single and double-shaft engines are considered in the study. The results show that the assumption of constant efficiencies for all operating conditions leads to an overestimation of the optimal CHP plant size, thereby underestimating the heat production costs and overestimating the CO2 emissions of the plant. The results also show marked differences according to the type of gas turbine used and part-load operating strategy adopted. In particular, the paper discusses the part-load operating difficulties for CHP plants running gas turbines equipped with low emissions burners.

Integration opportunities for substitute natural gas (SNG) production in an industrial process plant

This paper investigates opportunities for integration of a Substitute Natural Gas (SNG) process based on thermal gasification of lignocellulosic biomass in an industrial process plant currently importing natural gas (NG) for further processing to speciality chemicals. The assumed SNG process configuration is similar to that selected for the ongoing Gothenburg Biomass Gasification demonstration project (GoBiGas) and is modelled in Aspen Plus. The heat and power integration potentials are investigated using Pinch Analysis tools. Three cases have been investigated: the steam production potential from the SNG process excess heat, the electricity production potential by maximizing the heat recovery in the SNG process without additional fuel firing, and the electricity production potential with increased steam cycle efficiency and additional fuel firing. The results show that 217 MWLHV of woody biomass are required to substitute the site’s natural gas demand with SNG (162 MWLHV). The results indicate that excess heat from the SNG process has the potential to completely cover the site’s net steam demand (19 MW) or to produce enough electricity to cover the demand of the SNG process (21 MWel). The study also shows that it is possible to fully exploit the heat pockets in the SNG process Grand Composite Curve (GCC) resulting in an increase of the steam cycle electricity output. In this case, there is a potential to cover the site’s net steam demand and to produce 30 MWel with an efficiency of 1 MWel/MWadded heat. However, this configuration requires combustion of 36 MWLHV of additional fuel, resulting in a marginal generation efficiency of 0.80 MWel/MWfuel (i.e. comparing the obtained electricity production potentials with and without additional fuel firing).

Optimization of process configuration and strain selection for microalgae-based biodiesel production.

A mathematical model was developed for the design of microalgae-based biodiesel production system by systematically integrating all the production stages and strain properties. Through the hypothetical case study, the model suggested the most economical system configuration for the selected microalgae strains from the available processes at each stage, thus resulting in the cheapest biodiesel production cost, S

Design issues and performance of a chemically recuperated aeroderivative gas turbine

2.66/kg, which is still higher than the current diesel price (S

Process industry energy retrofits: the importance of emission baselines for greenhouse gas reductions

1.05/kg). Interestingly, the microalgae strain properties, such as lipid content, effective diameter and productivity, were found to be one of the major factors that significantly affect the production cost as well as system configuration.