Jacques De Ruyck

Dioxin levels in wood combustion—a review

Dioxins, formed in any combustion process where carbon, oxygen and chlorine are present, are a subject of major interest due to their carcinogenicity. Much research has been carried out to study emissions from hazardous and municipal waste incinerators. Dioxin emissions from wood combustion plants are also of interest, especially those due to the combustion of treated, varnished or PVC-coated wood, which can produce high PCDD/F emissions. This work reviews the available data about the levels of dioxins in gases and ashes produced in wood combustion.

A POSSIBLE NEW ROUTE FOR NO FORMATION VIAN2H3

A possible new route for NO formation in hydrogen combustion is explored. The reaction sequence that converts molecular nitrogen into nitrogen oxides involves sequential recombination of N2 with H atoms: N2→NNH→N2H2→N2H3. N-N bond cleavage occurs in the reaction of N2H3 with H2 forming NH3 and NH2; These last species are oxidized mainly in the sequence NH3→NH2→NH→N→NO. Key reactions of the N2H3 formation and consumption as well as other important reactions revealed by sensitivity analysis and reaction path analysis are examined and discussed. Kinetic modeling of hydrogen combustion in stirred reactors demonstrates that this mechanism can be of importance in rich mixtures at relatively low temperatures (below about 1500 K) when other routes of NO formation are suppressed. Available measurements of NO formation in hydrogen combustion in stirred reactors have been modeled and analyzed. They neither confirm nor contradict the proposed route forming NO via N2H3, because these experiments have been conducted outside the range of conditions where this route is manifested.

Measurement of adiabatic burning velocity in ethane-oxygen-nitrogen and in ethane-oxygen-argon mixtures

Abstract Experimental measurements of the adiabatic burning velocity in ethane–oxygen–nitrogen and in ethane–oxygen–argon mixtures are presented. Non-stretched flames were stabilized on a perforated plate burner at 1 atm. Dilution ratio O 2 /(O 2 +N 2 ) was varied from 15% to 21%; dilution ratios O 2 /(O 2 +Ar) were 15% and 16%. A heat flux method was used to determine burning velocities under conditions when the net heat loss from the flame to the burner is zero. An overall accuracy of the burning velocities was estimated to be better than ±0.8 cm/s. Experimental results are in a good agreement with recent literature data for ethane–air mixtures. New measurements of the adiabatic burning velocity in diluted ethane–oxygen–nitrogen and in ethane–oxygen–argon mixtures extend the basis for validation of detailed reaction schemes. Predictions of the detailed chemical mechanism developed in this laboratory agree well with the measurements. The influence of the inert diluent on the flame burning velocity is discussed.

Exergy analysis tools for Aspen applied to evaporative cycle design

Abstract A general two-step approach for cycle development and finding optimal cycle layouts is discussed. Tools for applying this approach with ASPEN+ are presented. The technique is applied to evaporative gas-turbine cycles with one intercooler stage, no reheat and no steam-turbine. In a first step, several evaporative cycle layouts are optimized by considering one single black box evaporative heat recovery system. The feasibility of each cycle is quantified by the exergy destruction and exergetic efficiency of the black box heat recovery system. In a second step, after cycle optimization, insights provided by a composite curve analysis of the black box are used to guide the design for a feasible evaporative heat exchanger network. All cycle simulations are performed with ASPEN+. Two recently home-made ASPEN+ subroutines are presented. One introduces the exergy concept in ASPEN+, the other generates composite curve, hence avoiding the use of ADVENT™. The analysis shows that optimal evaporative gas-turbine cycles yield performances similar to that of combined cycles. A new heat recovery system is disclosed (REVAP®), where the intercooler heat, the aftercooler heat and the turbine exhaust heat are recovered simultaneously.

Nitric oxide formation in premixed flames of H2+CO+CO2 and air

Burning velocity and probe sampling measurements of the concentrations of O 2 , CO 2 , CO, and NO in the postflame zone of the flames of H 2 +CO+CO 2 and air are reported. The heat flux method was used for stabilization of laminar, premixed, non-stretched flames on a perforated plate burner at 1 atm. Axial profiles of the concentrations of major species were used to evaluate the influence of the ambient air entrainment and downstream heat losses. The influence of the downstream heat losses to the environment has been included in the modeling. The numerical predictions of the concentrations of O 2 , CO 2 , and CO in the postflame zone are in a good agreement with the experiment. The amount of the NO formed in the adiabatic flame front is significantly higher than that formed downstream. It is shown that in rich mixtures, where the NNH route forming NO is dominant, the heat losses do not affect significantly the calculated [NO]. The comparison of the experimental data with the detailed flame structure modeling strongly suggests a reduced value of the rate constant k 1 for the reaction NNH+O=NH+NO. The calculations with k 1 =(1±0.5)×10 14 exp(−16.75±4.2 kJ/mol/ RT ) cm 3 /mol s bring the modeling close to the measurements not only in rich but also in stoichiometric and lean flames. The rate constant proposed in the present study is consistent with earlier evaluations within uncertainty limits.

Kinetic Modeling of Nitrogen Oxides Decomposition at Flame Temperatures

Abstract A detailed N/O kinetic mechanism has been developed and tested in comparison with experimental data for N2O ignition, NO and NO2 decomposition at high temperatures. It consists of 27 reactions among 11 species. A sensitivity analysis reveals which reactions are critical for the quality of the modeling in particular experimental conditions. The choice of the rate constants for these reactions is discussed. Good agreement has been obtained for the ignition delays in the pure N2O and its mixtures with Ar, decomposition rates of the NO and NO2 in static reactors and behind shock waves. The modeling using recently suggested controversial rate constants for the key reactions N2O + O = N2 + O2 N20 + O = NO + NO has been performed as well. It is demonstrated that the use of too-low or too-high values of the reactions (8,9) rate constants is incompatible with available experimental data

Entropy generation reduction through chemical pinch analysis

The pinch analysis (PA) concept emerged, late ‘80s, as one of the methods to address the energy management in the new era of sustainable development. It was derived from combined first and second law analysis, as a technique ensuring a better thermal integration, aiming the minimization of entropy production or, equivalently, exergy destruction by heat exchanger networks (HEN). Although its ascendance from the second law analysis is questionable, the PA reveals as a widespread tool, nowadays, helping in energy savings mostly through a more rational use of utilities. Unfortunately, as principal downside, one should be aware that the global minimum entropy production is seldom attained, since the PA does not tackle the whole plant letting aside the chemical reactors or separation trains. The chemical reactor network (CRN) is responsible for large amounts of entropy generation (exergy losses), mainly due to the combined composition and temperature change. The chemical pinch analysis (CPA) concept focuses on, simultaneously, the entropy generation reduction of both CRN and HEN, while keeping the state and working parameters of the plant in the range of industrial interest. The fundamental idea of CPA is to include the CRN (through the chemical reaction heat developed in reactors) into the HEN and to submit this extended system to the PA. This is accomplished by replacing the chemical reactor with a virtual heat exchanger system producing the same amount of entropy. For an endothermic non-adiabatic chemical reactor, the (stepwise infinitesimal) supply heat δq flows from a source (an external/internal heater) to the stream undergoing the chemical transformation through the reactor, which in turn releases the heat of reaction ΔHR to a virtual cold stream flowing through a virtual cooler. For an exothermic non-adiabatic chemical reactor, the replacement is likewise, but the heat flows oppositely. Thus, in the practice of designing or retrofitting a flowsheet, in order to minimize the entropy production, the chemical reactor should be viewed as a group of two or three virtual heaters/coolers destroying the same amount of exergy. As a result of PA, new operating conditions could be revealed for some or all of the chemical reactors, ensuring a further reduction of the global entropy production of the plant. In this paper, the simple case of the methanol synthesis heat integrated reactor will be analyzed, proving the benefits of the CPA.

A comparison between the combustion of natural gas and partially reformed natural gas in an atmospheric lean premixed turbine-type combustor

A small-scale combustor was set up to analyze the combustion of natural gas and two mixtures of partially reformed natural gas. The partially reformed mixtures can be formed using biomass to feed the endothermic reforming reactions. Before combusting these mixtures in a gas turbine, experimental work was done on a primary zone combustion chamber to examine the combustor behavior when switching from natural gas to the wet and dry hydrogen-rich mixtures. Temperature profiles, flame location and ignition limits have been investigated for a variety of stoichiometries and several air temperatures. Possible problems concerning blow-off, flashback, increased pollutant products and excessive liner wall temperatures were analyzed. It was concluded that the switch in operation from natural gas to these wet and/or dry partially reformed natural gas mixtures lowers the blow-off limits while maintaining similar liner wall temperature profiles. Furthermore, no significant changes in pollutant production were observed. Flame area, shape and position display considerable differences in combustion regime for the three tested fuel types.

FT-IR Spectroscopy for the in-Flame Study of a 15 MW Dual Fuel Gas/Oil Burner

An FT-IR (Fourier transform infrared) analyzer has been configured for combustion research and allows the simultaneous quantification of CO, CO2, CH4, C2H6, C2H2, C2H4, NO, and N2O concentrations in the flame of natural gas burners. The calibration has been carried out by the multivariate PLS1 algorithm, with calculated standard spectra. For the multivariate CO/CO2 model, special attention has been given to nonlinear effects caused by interference in the 2210–2250 cm−1 region. For this model, two methods of calculating mixture spectra and their influence on prediction parameters are evaluated. Furthermore, the sensitivity of the CO/CO2 model for N2O interference has been tested. The presented results show that conclusions drawn from statistical prediction parameters should be treated cautiously in models that have to deal with spectral interference.

A Study on the Performance of Steam Injection in a Typical Micro Gas Turbine

Microturbines are very promising for small-scale Combined Heat and Power (CHP) production. Due to the simultaneous production of heat and power, the Turbec T100 microturbine CHP System has the potential of realizing considerable energy savings, compared to classic separate production. The power production however is strictly bound to the heat production. A reduction in heat demand will mostly lead to a shutdown of the unit, since electric efficiency is too low and not competitive with electricity from the net. The reduced amount of running hours has a severe negative impact on the lifetime profitability of the unit. A solution is proposed by injecting auto-generated steam in the T100 micro Gas Turbine (mGT), in order to increase electric efficiency during periods with low heat demand. By doing so, a forced shut down of the unit can be avoided.The goal of this study was to investigate and quantify the beneficial effect of steam injection on the performance of a typical recuperated mGT. This paper reports on an extended series of steam injection experiments performed on a Turbec T100 microturbine. Previous experiments revealed the necessity for a more accurate determination of the mass flow rate and more precise compressor characteristics. Therefore the test rig was equipped with an additional oxygen analyzer in the exhaust and a pressure gauge to allow for the accurate determination of the pressure ratio. Experiments with steam injection in the compressor outlet of the T100 were performed to demonstrate and validate the benefits of introducing steam in the cycle and to verify its ability to handle the injected steam. It is expected that the mGT will produce a constant power at reduced shaft speed and increased electric efficiency.Steam injection experiments validated the increase in electric efficiency during stable operation of the mGT. At nominal 100 kWe power production, the replacement of 3.5% of the air mass flow with steam (adiabatic steam injection limit) resulted in an absolute electric efficiency increase of 1.7%. The experiments successfully demonstrated the potential for steam/water injection in the T100 mGT.Copyright