E. Kakaras

Pyrolysis characteristics and kinetics of biomass residuals mixtures with lignite

Abstract Biomass residues in the Mediterranean region come mainly from agricultural and agro-industrial activities and forest byproducts. The paper presents the results of kinetic parameters and main devolatilisation characteristics of three biomass materials, when these are used either alone or in conjunction with Greek lignite. Namely, olive kernel, forest and cotton residues were pyrolysed in a thermogravimetric analyser, under dynamic conditions. The effect of material particle size and heating rate was investigated both on the pyrolysis behavior and reaction kinetics, over the temperature range of 25–850 °C. Furthermore, experiments with blends of lignite and biomass were conducted under the same conditions at the lower heating rate. The biomass materials presented higher thermochemical reactivity than lignite. Their decomposition was successfully modeled by three first-order independent parallel reactions, describing the degradation of hemicellulose, cellulose and lignin. No significant influence of the particle size was detected, both on the devolatilisation characteristics and kinetics. The effect of the heating rate on the pyrolysis behavior was more pronounced for biomass materials rather than lignite. A comparison between slow and fast heating rate tests reveals a small displacement of the DTG profiles to higher temperatures. It was concluded that such ‘solid bio-fuels’ could support the combustion of poor coals, because of the faster and in much higher quantity release of volatile compounds.

Thermogravimetric studies of the behavior of lignite-biomass blends during devolatilization

The behaviour of Greek pre-dried lignite, four biomass materials and their blends in the devolatilization stage was investigated by thermogravimetry. Biomass was added in the percentages of 5, 10 and 20% wt. in the fuel blend. All the tests were carried out in nitrogen atmosphere under dynamic conditions at a heating rate of 10 °C/min. The kinetic parameters for the thermal conversion of the pure fuels were determined through the independent parallel, first-order, reaction model. No significant interaction was detected in the solid phase between the components of the coal–biomass blends, under the same experimental conditions.

Inlet Air Cooling Methods for Gas Turbine Based Power Plants

Background: Power generation from gas turbines is penalized by a substantial power output loss with increased ambient temperature. By cooling down the gas turbine intake air the power output penalty can be mitigated. Method of Approach: The purpose of this paper is to review the state of the art in applications for reducing the gas turbine intake air temperature and examine the merits from integration of the different air-cooling methods in gas-turbine-based power plants. Three different intake air-cooling, methods (evaporative cooling, refrigeration cooling, and evaporative cooling of precompressed air) have been applied in two combined cycle power plants and two gas turbine plants. The calculations were performed on a yearly basis of operation. taking into account the time-varying climatic conditions. The economics from integration of the different cooling systems were calculated and compared. Results: The results have demonstrated that the highest incremental electricity generation is realized by absorption intake air-cooling. In terms of the economic performance of the investment, the evaporative cooler has the lowest total cost of incremental electricity generation and the lowest payback period (PB). Concerning the cooling method of pre-compressed air the results show a significant gain in capacity, but the total cost of incremental electricity generation in this case is the highest. Conclusions: Because of the much higher capacity gain by an absorption chiller system. the evaporative cooler and the absorption chiller system may both be selected for boosting the performance of gas-turbine-based power plants, depending on the prevailing requirements of the plant operator.

Smart Recovery of Materials and Upgrade of Organic Compost and RDF in Existing Mechanical Biological Treatment Plants by Using NIR Technology

The study aims to present the objectives and the results of the project with title “Smart Recovery of materials and upgrade of organic compost and RDF in existing mechanical biological treatment plants by using NIR technology” which is funded by the Greek General Secretariat for Research and Technology. The main goals for the SmartWasteTech project are summarized to the smart recovery of the materials by using NIR technology in order to increase the quality of the produced compost and recovered materials (PET, PE/PP, LDPE film) and to optimize the process by using online monitoring software for the MBT plant operation. The paper presents the results of the recovery rate, the purity of the final products, the efficiency of the technology performance and the effective role of the NIR technology in existing MBT plants.

CO2 Mitigation Options for Retrofitting Greek Low-Quality Coal-Fired Power Plants

We consider possible application of the state-of-the-art in technological concepts of CO 2 capture and sequestration to retrofitting of low-quality coal-fired power plants. The most promising options, namely the oxy-fuel combustion and the flue gases treatment by amine scrubbing, were evaluated as retrofit options for a typ- ical modern lignite-fired power plant. Results from thermodynamic simulations of the examined cases were used to demonstrate the potential for emissions reduction and evaluate the associated power output and efficiency penalties. Furthermore, an economic assessment of electricity production cost was carried out, in relation to the application of different existing and near future technologies. The economical impact related to fuel prices and CO 2 emission risks was assessed.

Novel Solid Fuel Gasification Power Plant for In Situ CO2 Capture

The work presented in this paper aims to examine and analyse a novel concept dealing with the carbonation-calcination process of lime for CO2 capture from coal-fired power plants. The scheme is based on a novel steam gasification process of low rank coals with calcined limestone where in-situ CO2 capture and steam reforming are performed in a single reactor. CO2 is separated reacting exothermically with CaO based sorbents, providing also the necessary heat for the gasification reactions. The produced gas is a H2 -rich gas with low carbon or near zero carbon content, depending on the ratio of lime added to the process. The produced fuel gas can be used in state-of-the-art combined cycles where it is converted to electricity, generating almost no CO2 emissions. After being captured in the gasification process, CO2 is released in a separate reactor where extra energy is provided through the combustion of low rank coal. Regenerated CaO is produced in this reactor and is continuously recycled within the process. The key element of the concept is the high-pressure steam gasification process where CO2 is captured by CaO based sorbents and fuel gas with high hydrogen content is produced, without using additional shift reactors. Two optimised power plant configurations are presented in detail and examined. In the first case, pure oxygen is utilised for the low rank coal combustion in the limestone regeneration process, while in the second case fuel is combusted with air instead. Results from the equilibrium based mass balance of the two reactors as well as the power plant thermodynamic simulations, dealing with the most important features for CO2 reduction are presented concerning the two different options. The energy penalties are quantified and the power plant efficiencies are calculated. The calculated results demonstrate the capability of the power plant to deliver decarbonised electricity while achieving high overall electrical efficiencies, comparable to other technological alternatives for CO2 capture power plants. The Aspen Plus software is used for the equilibrium based mass balance of the gasifier and the regenerator while the combined cycle power plant cycle calculations are performed with the thermodynamic cycle calculation software ENBIPRO (ENergie-BIllanz-PROgram), a powerful tool for heat and mass balance solving of complex thermodynamic circuits, calculation of efficiency, exergetic and exergoeconomic analysis of power plants [1].Copyright