Search

Some hybrid methanol fuelled SOFC-GT power cycles including a few innovative features are analyzed, compared and discussed. The low reforming temperature of methanol allows high heat recovery from the exhaust of hybrid fuel cell gas turbine cycles, which produces high overall efficiency. Different layouts of hybrid SOFC-GT cycles are presented and discussed, including the possibility of coupling the GT to a bottoming steam plant to further improve the overall performance. A target 10 MW GT size is taken as a reference, coupled to different possible SOFC sizes. The modeling of power cycles, reactors and SOFC is done with author-developed codes. The results show that the most efficient solutions are those considering pressurized fuel cells, which partially replace the GT combustor. Cycles with atmospheric fuel cells placed downstream of the gas turbine are also investigated. In both cases, very interesting levels of efficiency are achieved, ranging from 55 to more than 73%.Copyright © 2008 by ASME

The Semi Closed Gas Turbine Cycle (SCGT) was introduced as a short to medium term solution for applying existing CO2 removal techniques to current production gas turbine powerplants. Thus, one of the main goals is the adaptability to existing turmomachinery, with only minor changes to the equipment. In this manuscript, the off–design analysis of two previously proposed and thermodynamically assessed configurations was carried out: the first one is the combined cycle (SCGT/CC), related to an heavy duty gas turbine, whereas the second one is the recuperative–evaporative cycle (SCGT/RE). Both of them may be equipped with intercooled or, either, aftercooled compression, which is done with spray water injection. The analysis was carried out with special reference to the off design conditions of the compressor and to its coupling with turbine when the partial exhausts recirculation is applied to originally open cycle GTs. In the SCGT/CC configurations, the steam pressure levels are increased due to the increased GT exhausts temperature with respect to the open cycle. When no water injection is applied, the working point of the compressor due to the different gas composition and temperature are largely within the operating margins, thus the semi closed configuration may be applied even to compressors with reduced stall bounds and no large decays in compressor efficiency were found compared to the design operation. On the contrary, when water injection is applied, heavy variations of the compressor working point were found, which make the effects of exhausts recirculation comparatively marginal and leads to unavoidable compressor efficiency drop. It suggests that the application of water injection may be suitable only for the short peakload times, whereas current technology allows the shifting to SCGT.Copyright © 2006 by ASME

The goal of the present manuscript is the investigation of two novel systems for partial CO2 capture from the exhausts of fossil fuelled powerplants. These systems should be relatively cheap and easily applicable to existing powerplants with minor modification, in order to make them accessible by a large range of users and favour a significant diffusion of partial CO2 sequestration. Two basic processes were proposed: 1. Absorption with a liquid solution of water and NH3; 2. Absorber/desorber system with a liquid solution of water and phosphates. In the first one, the exhausts react into an absorber column with a liquid sorbent, which is a solution of water and ammonia. The process sequestrates the CO2 in carbammate and bicarbonate and the final product are salt of ammonia, i.e. ammonium carboamate (NH4HCO3) and ammonium bicarbonate (NH4NH2COO). The outgoing streams of this process are the exhaust gas with a reduced content of CO2 and a secondary product formed by salts of ammonium, which have an interesting market potential as fertilizers. The obtained CO2 reduction level was more than 40%, while the amount of secondary products is high enough to get it marketable. In the second process, the exhausts passing through an absorber column react with a liquid sorbent, which is a solution of water and sodium (or potassium) phosphate. The process sequestrates the CO2 in bicarbonate ions by means of the ions phosphate and the outlet stream is a solution of water and phosphate and carbonate ions. This stream is collected in a desorbing column, where the phosphate ions are almost completely regenerated. The CO2 reduction level is always higher than 20% and it can also reach very high values, depending on the parameters of process.

The relatively innovative gas turbine based power cycles R-ATR and R-REF (Recuperative – Auto Thermal Reforming GT cycle and Recuperative – Reforming GT cycle) here proposed, are mainly aimed to allow the upstream CO2 removal by the natural gas fuel reforming. The 2nd part of the paper is dedicated to the R-REF cycle: the power unit is a Gas Turbine (GT), fuelled with reformed and CO2 cleaned gas, obtained by the addition of several sections to the simple GT cycle, mainly: • Reformer section (REF), where the reforming reactions of methane fuel with steam are accomplished: the necessary heat is supplied partially by the exhausts cooling and, partially, with a post–combustion. • Water Gas Shift Reactor (WGSR), where the reformed fuel is, shifted into CO2 and H2 with the addition of water. • CO2 removal unit for the CO2 capture from the reformed and shifted fuel. No water condensing section is adopted for the R-REF configuration. Between the main components, several heat recovery units are applied, together with GT Cycle recuperator, compressor intercooler and steam injection into the combustion chamber. The CO2 removal potential is close to 90% with chemical absorption by an accurate choice of amine solution blend: the heat demand for amine regeneration is completely self-sustained by the power cycle. The possibility of applying steam blade cooling (the steam is externally added) has been investigated: in these conditions, the RREF has shown efficiency levels close to 43–44%. High values of specific work have been observed as well (around 450–500 kJ/kg). The efficiency is slightly lower than that found for the R–ATR solution, and 2–3% lower than CRGTs with CO2 removal and steam bottoming cycle, not internally recuperated. If compared with these, the R-REF offers higher simplicity due to absence of the steam cycle, and can be regarded as an improvement to the simple GT. In this way, at least 5–6 points efficiency can be gained, together with high levels of CO2 removal. The effects of the reformed fuel gas composition, temperature and pressure on the amine absorption system for the CO2 removal have been investigated, showing the beneficial effects of increasing pressure (i.e. pressure ratio) on the specific heat demand.

The relatively innovative gas turbine based power cycles R–ATR and R–REF (Recuperative – Auto Thermal Reforming GT cycle and Recuperative–Reforming GT cycle) here proposed are mainly aimed to allow the upstream CO2 removal by the way of natural gas fuel reforming. The power unit is a Gas Turbine (GT), fuelled with reformed and CO2 cleaned syngas produced by adding some basic sections to the simple GT cycle: • Auto Thermal Reforming (ATR) for the R-ATR solution, where the natural gas is reformed into CO, H2 , CO2 , H2 O and CH4 ; this endothermic process is completely sustained by the heat released from the reactions between the primary fuel (CH4 ), exhausts and steam. • Water Gas Shift Reactor (WGSR), where the reformed fuel is, as far as possible, shifted into CO2 and H2 by the addition of water. • Water Condensation, in order to remove a great part of the fuel gas humidity content (this water is totally reintegrated into the WGSR). • CO2 removal unit for the CO2 capture from the reformed fuel. Among these main components, several heat recovery units are inserted, together with GT Cycle recuperator, compressor intercooler and steam injection in combustion chamber. The CO2 removal potential is close to 90% with chemical scrubbing using an accurate choice of amine solution blend: the heat demand is completely provided by the power cycle itself. The possibility of applying steam blade cooling by partially using the water released from the dehumidifier downstream the WGSR has been investigated: in these conditions, the R-ATR has shown an efficiency range of 44–46%. High specific work levels have also been observed (around 450–550 kJ/kg). These efficiency values are satisfactory, especially if compared with ATR combined cycles with CO2 removal, more complex due to the steam power section. If regarded as an improvement to the simple GT cycle, R-ATR shows an interesting potential if directly applied to a current GT model; however partial redesign with respect to the commercially available version is required. Finally, the effects of the reformed fuel gas composition and conditions on the amine CO2 absorption system have been investigated, showing the beneficial effects of increasing pressure (i.e. pressure ratio) on the thermal load per kg of removed CO2 .Copyright © 2002 by ASME

A model of the vaned intake of a centrifugal compressor was instrumented and tested for the investigation of aero-acoustic excitation modes for specific flow conditions, in order to check the possibility of damage to the Inlet Guide Vanes (IGV). The tests demonstrate that several acoustic modes occur for such complex geometries, and that their frequencies and amplitudes should be verified in order to avoid the excitation of forced vibration of the blades.Copyright © 2002 by ASME