Ennio Antonio Carnevale

A review of technologies and performances of thermal treatment systems for energy recovery from waste

The aim of this work is to identify the current level of energy recovery through waste thermal treatment. The state of the art in energy recovery from waste was investigated, highlighting the differences for different types of thermal treatment, considering combustion/incineration, gasification and pyrolysis. Also different types of wastes - Municipal Solid Waste (MSW), Refuse Derived Fuel (RDF) or Solid Refuse Fuels (SRF) and some typologies of Industrial Waste (IW) (sludge, plastic scraps, etc.) - were included in the analysis. The investigation was carried out mainly reviewing papers, published in scientific journals and conferences, but also considering technical reports, to gather more information. In particular the goal of this review work was to synthesize studies in order to compare the values of energy conversion efficiencies measured or calculated for different types of thermal processes and different types of waste. It emerged that the dominant type of thermal treatment is incineration associated to energy recovery in a steam cycle. When waste gasification is applied, the produced syngas is generally combusted in a boiler to generate steam for energy recovery in a steam cycle. For both the possibilities--incineration or gasification--co-generation is the mean to improve energy recovery, especially for small scale plants. In the case of only electricity production, the achievable values are strongly dependent on the plant size: for large plant size, where advanced technical solutions can be applied and sustained from an economic point of view, net electric efficiency may reach values up to 30-31%. In small-medium plants, net electric efficiency is constrained by scale effect and remains at values around 20-24%. Other types of technical solutions--gasification with syngas use in internally fired devices, pyrolysis and plasma gasification--are less common or studied at pilot or demonstrative scale and, in any case, offer at present similar or lower levels of energy efficiency.

Analysis of energy recovery potential using innovative technologies of waste gasification

In this paper, two alternative thermo-chemical processes for waste treatment were analysed: high temperature gasification and gasification associated to plasma process. The two processes were analysed from the thermodynamic point of view, trying to reconstruct two simplified models, using appropriate simulation tools and some support data from existing/planned plants, able to predict the energy recovery performances by process application. In order to carry out a comparative analysis, the same waste stream input was considered as input to the two models and the generated results were compared. The performances were compared with those that can be obtained from conventional combustion with energy recovery process by means of steam turbine cycle. Results are reported in terms of energy recovery performance indicators as overall energy efficiency, specific energy production per unit of mass of entering waste, primary energy source savings, specific carbon dioxide production.

Performance and economic enhancement of cogeneration gas turbines through compressor inlet air cooling

Gas turbine air cooling systems serve to raise performance to peak power levels during the hot months when high atmospheric temperatures cause reductions in net power output. This work describes the technical and economic advantages of providing a compressor inlet air cooling system to increase the gas turbines power rating and reduce its heat rate. The pros and cons of state-of-the-art cooling technologies, i.e., absorption and compression refrigeration, with and without thermal energy storage, were examined in order to select the most suitable cooling solution. Heavy-duty gas turbine cogeneration systems with and without absorption units were modeled, as well as various industrial sectors, i.e., paper and pulp, pharmaceuticals, food processing, textiles, tanning, and building materials. The ambient temperature variations were modeled so the effects of climate could be accounted for the simulation. The results validated the advantages of gas turbine cogeneration with absorption air cooling as compared to other systems without air cooling.

Performance of a biogas upgrading process based on alkali absorption with regeneration using air pollution control residues

This work analyzes the performance of an innovative biogas upgrading method, Alkali absorption with Regeneration (AwR) that employs industrial residues and allows to permanently store the separated CO2. This process consists in a first stage in which CO2 is removed from the biogas by means of chemical absorption with KOH or NaOH solutions followed by a second stage in which the spent absorption solution is contacted with waste incineration Air Pollution Control (APC) residues. The latter reaction leads to the regeneration of the alkali reagent in the solution and to the precipitation of calcium carbonate and hence allows to reuse the regenerated solution in the absorption process and to permanently store the separated CO2 in solid form. In addition, the final solid product is characterized by an improved environmental behavior compared to the untreated residues. In this paper the results obtained by AwR tests carried out in purposely designed demonstrative units installed in a landfill site are presented and discussed with the aim of verifying the feasibility of this process at pilot-scale and of identifying the conditions that allow to achieve all of the goals targeted by the proposed treatment. Specifically, the CO2 removal efficiency achieved in the absorption stage, the yield of alkali regeneration and CO2 uptake resulting for the regeneration stage, as well as the leaching behavior of the solid product are analyzed as a function of the type and concentration of the alkali reagent employed for the absorption reaction.

Comparison of different biological treatment scenarios for the organic fraction of municipal solid waste

The possibility of applying anaerobic digestion (AD) process of the source-selected organic fraction (SS-OF) of municipal solid waste in the south of Tuscany (IT) territory was proposed and evaluated. With respect to a reference scenario, in which the overall amount of SS-OF and garden waste—expected in 2013—is addressed to aerobic composting process, three alternative scenarios were proposed, modeled, and compared by life cycle assessment (LCA). The first one is based on realizing six AD plants upstream of each already existing aerobic plant. The second one is based on realizing only three centralized anaerobic plants. The third alternative is based on co-digestion of a part of the SS-OF with sludge from waste water treatment plants in existing sludge AD plants; the remaining part of SS-OF is processed in devoted AD plants upstream of each already existing aerobic plant. LCA results show that AD application is always favorable with respect to the reference scenario in which organic wastes are aerobically processed. AD allows for net production of thermal and electric energy, generating negative impacts due to avoided emissions and avoided resource consumptions. Among the compared alternatives of AD application, the scenario based on decentralized plants (one anaerobic plant upstream of each existing aerobic plant) resulted to be most favorable, collecting the best value for almost all the considered environmental indicators.

A Model to Account for the Virtual Camber Effect in the Performance Prediction of an H-Darrieus VAWT Using the Momentum Models

This study reports an investigation on the influence of the virtual camber effect on the performance prediction of an H-Darrieus VAWT using a theoretical approach based on the Momentum Models. In detail, a simplified model is proposed which highlights a limit point below which the virtual camber effect must be neglected to correctly evaluate the performance of the airfoils. This correction provides a more accurate description of the unstable region of the power curve, for which very few in-depth studies are available. An accurate description of the left side of the power curve is, however, of particular importance for a correct prediction of the self-starting capabilities of the rotor, which are presently considered as a decisive requirement for small-power machines. On this basis, the effects of the new virtual camber estimation on the transient study of an H-Darrieus rotor are also presented here. This has been carried out by means of a specifically developed numerical code. All the theoretical conjectures and the numerical models have been validated with the experimental data of two wind-tunnel campaigns on two different models of H-Darrieus turbine.

Performance Improvements of a Natural Gas Injection Station Using Gas Turbine Inlet Air Cooling

Gas Turbine (GT) performance seriously deteriorates at increased ambient temperature. This study analyses the possibility of improving GT power output and efficiency by installing a gas turbine inlet air cooling system.Different cooling systems were analyzed and preliminary cost evaluations for each system were carried out.The following three cooling systems were considered in detail:a) Traditional compression cooling system;b) Absorption single-acting cooling system using a solution of lithium bromide;c) Absorption double-acting cooling system using a solution of lithium bromide.Results clearly indicate that there is a great potential for GT performance enhancement by application of an Inlet Air Cooling (IAC). Technical and economical analyses lead to selection of a particular type of IAC for significant savings in capital outlay, operational and maintenance costs and other additional advantages.© 1997 ASME

Biochemical methane potential tests of different autoclaved and microwaved lignocellulosic organic fractions of municipal solid waste.

The aim of this research was to enhance the anaerobic biodegradability and methane production of two synthetic Organic Fractions of Municipal Solid Waste with different lignocellulosic contents by assessing microwave and autoclave pre-treatments. Biochemical Methane Potential assays were performed for 21days. Changes in the soluble fractions of the organic matter (measured by soluble chemical oxygen demand, carbohydrates and proteins), the first order hydrolysis constant kh and the cumulated methane production at 21days were used to evaluate the efficiency of microwaving and autoclaving pretreatments on substrates solubilization and anaerobic digestion. Microwave treatment led to a methane production increase of 8.5% for both the tested organic fractions while autoclave treatment had an increase ranging from 1.0% to 4.4%. Results showed an increase of the soluble fraction after pre-treatments for both the synthetic organic fractions. Soluble chemical oxygen demand observed significant increases for pretreated substrates (up to 219.8%). In this regard, the mediocre results of methanes production led to the conclusion that autoclaving and microwaving resulted in the hydrolysis of a significant fraction of non-biodegradable organic substances recalcitrant to anaerobic digestion.

Evaluation and Comparison of Different Blade Cooling Solutions to Improve Cooling Efficiency and Gas Turbine Performances

The performance increase for Heavy Duty (HD) gas turbines requires very high R&D efforts to improve life and reliability of the hot components. In fact the maximum temperature increase is the most important factor for the HD gas turbines development. Blade cooling of hottest and most loaded turbine stages becomes a fundamental key for R&D process in gas turbine design. Several innovations have been realised in last years about blade cooling and many industrial manufacturers have recently proposed new coolants, like steam or water. In this paper a detailed comparison among different cooling systems and coolants is proposed. Therefore performances of the most important HD gas turbine models are predicted and applications of the various cooling solutions are evaluated. An advanced cooling scheme based on air cooling closed loop is also studied. The simulations have been made from the point of view of blade cooling design and of global plant performances prediction. Interesting results have been obtained to confirm the present trend of R&D of HD gas turbines. Finally a wide comparison between different cooling solutions for several gas turbine models is presented.Copyright

Environmental impact from wet plumes in combined-cycle power plants

In the present study, we have carried out an investigation into some of the environmental effects of high energy efficiency power generation plants that produce electrical and thermal energy. The use of natural gas fuels may represent a success for the replacement of liquid or solid fuels, because of drastic reductions of sulphur oxides, carbon dioxide and particulates. An additional problem involves the study of the effects of vapour emissions from the combustion of fuels and from the cooling towers of the condenser device. Particulary, the problem of the analysis of vapour and drift diffusion, because of emissions from the wet cooling devices, is faced in terms of modelling the plume rise and mass loss of drift in the atmosphere, because of evaporation, in order to predict the increment of rain and the humidity effect. The results obtained show that the amount of water emitted in the forms of vapour and drift, in terms of local scale diffusion, do not create problems of high increments of relative humidity or dangerous rainfall phenomena: while the effects of vapour emission are shown as insignificant problems because of the deposition of a sensible amount of drift, correlated with the type of separator devices chosen can appear, but only on very limited areas.