Giorgio Cau

Energy and economic assessment of IGCC power plants integrated with DME synthesis processes

Abstract The combined production of dimethylether (DME) and electrical energy in Integrated Gasification Combined Cycle (IGCC) power plants is a very attractive option for exploiting the worlds huge coal reserves achieving high efficiency and low pollutant emissions, as well as for enhancing the flexibility and economic performance of coal gasification plants. Besides being used for power generation in combined cycle plants, the clean synthesis gas produced by coal gasification processes can also be used as raw material for producing hydrogen, methanol, DME, and other chemicals. In particular, recent studies show the growing interest of DME as a new clean fuel for diesel engines, gas turbines, fuel cells, and household uses. This article concerns an energy and economic assessment of two different IGCC power plants integrated with a once-through DME synthesis process. In particular, the study has been carried out by examining two different solutions for the gasification process: one based on a dry-fed and the other on a slurry-fed entrained-flow gasifier. The energy assessment has shown that the DME production in IGCC power plants leads to a DME/coal energy conversion of ∼31—32 per cent and an electrical/coal energy conversion of ∼22—25 per cent. Overall, the solution based on the dry-fed gasifier exhibits the best exergy performance (50.8 versus 52.7 per cent). Finally, the economic analysis reveals DME production costs (6—6.5

Energy and economic analysis of concentrating solar power plants based on parabolic trough and linear Fresnel collectors

/GJ) comparable with other premium fuels such as natural gas, liquefied petroleum gases, and so on.

Thermodynamic and Environmental Assessment of Integrated Gasification and Methanol Synthesis (IGMS) Energy Systems with CO2 removal

This paper compares the performance of 1 MWe concentrating solar power (CSP) plants based on an organic Rankine cycle (ORC) power generation unit integrated with parabolic trough and linear Fresnel collectors. The CSP plants studied herein use thermal oil as heat transfer fluid and as storage medium in a two-tank direct thermal storage system. The performance of the CSP plants was evaluated on the basis of a 1 MWe ORC unit with a conversion efficiency of about 24%. The comparative performance analysis of the two CSP solutions was carried out by means of specifically developed simulation models and considering different values of solar multiple and thermal storage capacity. The results of the performance assessment demonstrate that CSP plants based on linear Fresnel collectors lead to higher values of electrical energy production per unit area of occupied land (about 50–60 kWh/y per m2 vs. 45–55 kWh/y m2 produced by solutions based on parabolic troughs). However, owing to their better optical efficiency, the use of parabolic troughs gives better values of energy production per unit area of solar collector (about 185–205 kWh/m2 vs. 125–140 kWh/m2) and, therefore, better conversion efficiencies (about 10.8–11.9% vs. 7.3–8.1%). The results of a preliminary economic analysis show that CSP plants based on linear Fresnel collectors are still not competitive with those based on parabolic trough owing to their higher energy production cost (about 380 €/MWh vs. 340 €/MWh).

Performance Assessment of Semi-Closed Chemically Recuperated Gas Turbine Systems

Environmental and technical concerns arise from the extensive utilization of the huge world coal reserves. They can nowadays be overcome only resorting to advanced energy conversion technologies. Integrated coal gasification and methanol synthesis power plants can perform a load-following service, by producing and storing liquid methanol, and reduce the carbon dioxide emissions, by removing CO2 and disposing it outside the atmosphere. In this paper, a comparative performance analysis among the different IGMS power plants has been carried out, by evaluating the influence of the coal gasification and methanol synthesis technologies on the main performance characteristics, such as the methanol production, the specific CO2 emissions and the overall efficiency.

Experimental investigation of a packed bed thermal energy storage system

The paper is concerned with thermochemical recuperation in semi-closed gas turbine systems. Semi-closed turbines use CO2 as the main working fluid and the combustion process takes place with pure oxygen, allowing the CO2 produced to be easily removed. On the other hand, the exhaust heat recovery through thermochemical recuperation offers interesting capabilities in terms of high conversion efficiency and low polluting emissions.System analysis and performance evaluation of the semi-closed, chemically recuperated gas turbine systems has been conducted and their performance assessed. A comparative analysis of semi-closed and open gas turbine cycles, with and without thermochemical recuperation, has been also carried out.The results of the analysis show that thermochemical recuperation in semi-closed gas turbine systems can allow to remove the CO2 with high cycle efficiency and specific power.Copyright

Performance and emissions of CRGT power generation systems with reformed methanol

In this work experimental investigations on a thermal energy storage system with a solid material as storage media and air as heat transfer fluid will be presented. The experimental test rig, installed at the DIMCM of the University of Cagliari, consists of a carbon steel tank filled with freely poured alumina beads that allows investigations of heat transfer phenomena in packed beds. The aim of this work is to show the influence of the operating conditions and physical parameters on thermocline formation and, in particular, the thermal behaviour of the thermal energy storage for repeated charging and discharging cycles. Better charging efficiency is obtained for lower values of mass flow rate and maximum air temperature and for increasing aspect ratio. A decreasing influence of the metal wall with continuous operation is also highlighted. In conclusion, the analysis focuses on the thermal hysteresis phenomenon, which causes degradation of the thermocline and the reduction of the energy that can be stored by the accumulator as the repeated number of cycles increases.

CFD Simulation of Melting and Solidification of PCM in Thermal Energy Storage Systems of Different Geometry

The performance of two different technological classes of chemically recuperated gas turbines (CRGT), with methanol used as primary fuel, has been evaluated. The analysis of the influence of the main CRGT parameters on the thermal matching between the flue gas and the reforming fuel in the reformer has been carried out. Emissions in lean premixed and nonpremixed combustors have been computed for various reformed methanol fuels of different compositions. This study shows that the CRGT could achieve thermodynamic performance superior to systems with conventional internal recovery and comparable with that of the more complex gas steam combined power plants. Furthermore, the levels of NO/sub x/ and N/sub 2/O, produced by the reformed fuels combustion, have been found to be considerably lower than for methane, while the CO emitted is roughly the same as in the case of conventional fuel.

Solar assisted Ultra Supercritical steam power plants with Carbon Capture and Storage

At the Department of Mechanical, Chemical and Materials Engineering of the University of Cagliari an experimental and numerical research project has begun with the aim of developing highly efficient thermal energy storage (TES) systems using phase change materials (PCM) of particular interest in concentrating small-medium scale solar power (CSP) applications. The present work aims to simulate the melting and solidification processes in containing boxes and heat transfer devices of different geometrical features which may constitute the elementary cell of a more complex TES system.Two-dimensional axisymmetric numerical models, developed with COMSOL Multiphysics are considered and used to simulate TES, heat conduction and natural convection. The models are used to determine the temperature profile inside the PCM to identify which configurations are capable of enhancing thermal response between a solid wall and a PCM. The results obtained will be used for comparison with experimental data acquired from a pilot plant under construction in the DIMCM laboratories. At the current stage the laboratory is being brought to completion.

Energy and Cost Analysis of Small Size CHP Coal Gasification Plants Integrated With Syngas Storage Systems

This chapter focuses on the evaluation of the potential benefits arising from the integration of concentrating solar systems into coal-based ultra-supercritical (USC) power plants with post-combustion CO2 capture (PCC). In order to offset the efficiency penalty introduced by CO2 removal, the USC-PCC plant was integrated with a concentrating solar field with direct steam generation based on parabolic trough and linear Fresnel collectors. The performance of the solar-assisted USC-PCC power plant was evaluated by means of specifically developed simulation models by using data sets for a typical meteorological year for the sites of Cagliari (Sardinia, Italy) and the North Western Australia Coast. A preliminary cost analysis was also carried out.

Integration of Combined Cycle Power Plants and Parabolic Solar Troughs Using CO2 as Heat Transfer Fluid

This study evaluates the load modulation capabilities of small and medium size CHP systems based on integrated coal gasification and syngas storage (ICGSS) power plants. ICGSS systems can perform a load-following service since a portion of the produced syngas is stored during periods of low energy demand and used to increase power output during periods of peaking demand. In particular, the main energy and economic performance of ICGSS power generation plants were evaluated with reference to three different prime movers (gas turbines, internal combustion engines and hybrid fuel cell systems) and as a function of the required electrical load curve. Moreover, a preliminary economic analysis was also carried out to evaluate the energy production cost in comparison with base-load energy production cost.The results of the study show that ICGSS power plants offer considerable scope for enhancing operating flexibility and load modulation capabilities of CHP systems based on coal gasification. In comparison to coal gasification power plants designed to produce only base-load energy, ICGSS systems require a more powerful prime mover and a larger coal gasification section. In the field of duty-cycles of more likely interest, the coal gasification section needs to be enlarged by 5–50% and a fraction from 2% to 16% of the produced syngas needs to be stored. ICGSS plants based on hybrid fuel cells performed better in terms of electrical efficiency. Moreover, with respect to the corresponding base-load systems, electrical efficiency decreases by about 2–3 percentage points for ICGSS-GT and ICGSS-ICE, while it increases by about 1–2 percentage points for ICGSS-HFC. Finally, syngas storage can reduce energy costs in CHP systems, especially in the case high peaking electricity requirements, large useful heat productions and by using ICGSS based on ICE as prime movers.Copyright