Knowledge of light penetration in soils is of particular interest for photolytic degradation of pesticides, for laser-induced fluorescence spectroscopy and remote sensing, and for understanding better the germination of seeds. To date little information has been available in the literature on this topic. In this paper light penetration in soils is determined successfully using diffuse reflectance and transmittance spectroscopy and the relatively simple Kubelka-Munk model. Using the latter model of light propagation in turbid media, the optical properties of kaolinite, montmorillonite, barium sulphate, goethite and 19 different soils were determined in the wavelength range 275-700 nm. In particular, the light absorption coefficient, k, and light scattering coefficient, s, were determined. The depth at which the light intensity at the surface is reduced by 99% (light penetration depth) and the depth of the sample contributing to the measured reflected radiation (information depth) could also be calculated from k and s. For kaolinite, the light penetration depth ranged between 10 and 200 mm for wavelengths between 275 and 700 nm, respectively; the information depth was between 5 and 80 mm. For soils, the penetration depth was in the range 17-110 mm at 275 nm and 120-300 mm at 700 nm, and the information depth was in the range 8-60 mm at 275 nm and 60-175 mm at 700 nm. Hence, the information depth is about half the penetration depth for media with reflectance smaller than 0.7 (e.g. soils). For dry soils, an empirical relationship was established between the light absorption coefficient and the amount of particlesize fractions. The effect of water content was also investigated: addition of water to kaolinite reduced its scattering coefficients, whereas the absorption coefficient was hardly affected. For the soils, addition of water had a more complex mode of action affecting both absorption and scattering coefficients. With the measured optical properties of dry minerals and soils it is possible to calculate light intensity profiles with depth and to quantify photochemical processes occurring in these media.

Sorption to dissolved organic matter (DOM) may influence significantly the fate and the effects of organic pollutants in the aquatic environment. To date, most studies on DOMwater partitioning have focused on neutral hydrophobic compounds. Very little is known on the binding of hydrophobic organic cations to DOM. In this study, the association of triorganotin compounds (TOTs) with dissolved Aldrich and Suwannee River humic acids has been systematically investigated as a function of pH and sodium perchlorate concentration. The organotin compounds studied include the two widely used biocides tributyltin (TBT) and triphenyltin (TPT) as well as other trialkyltin compounds of various hydrophobicities. Between pH 3 and pH 9, for both TBT and TPT, the overall DOM-water distribution ratio (D DOM ) was strongly pH-dependent and exhibited a maximum close to the acidity constant (pK a ) of the compounds. The observed pH dependence of D DOM could be described successfully with a semiempirical discrete log K spectrum model. It was found that, over the whole pH range investigated, sorption was governed by complexation of the corresponding TOT cation (TOT + ) by negatively charged ligands (i.e., carboxylate and phenolate groups) of the humic acids. The determining factors of the TOT + binding are postulated to be (i) complex formation between the tin atom and the deprotonated ligands and (ii) hydrophobic interactions. Significant differences in D DOM of TBT were observed between Suwannee River and Aldrich humic acid. D DOM values of TOTs determined for Aldrich humic acid were in the same range as particulate organic matter-water distribution ratios reported in the literature for soils and sediments.

This paper introduces and presents validation of the Constant Pressure Sequential Combustion system (denoted CPSC), a second generation concept developed for and applied to the new Ansaldo GT36 H-class gas turbine combustors. It has evolved from the well-established sequential burner technology applied to all current GT26 and GT24 gas turbines, and contains all architectural improvements implemented since original inception of this engine frame in 1994, with beneficial effects on the operation turndown, fuel flexibility, on the overall system robustness, and featuring the required aspects to stay competitive in the present day energy market. The applied air and fuel management therefore facilitate emission and dynamics control at both the extremely high and low firing temperature ranges required for existing and future Ansaldo gas turbine engine classes.

The use of highly reactive fuels in the lean premixed combustion systems employed in stationary gas turbines can lead to many practical problems, such as unwanted autoignition in regions not designed for combustion. In the present study, autoignition characteristics for hydrogen, diluted with up to 30 vol. % nitrogen, were investigated at conditions relevant to reheat combustor operation (p = 15 bar, T >1000K, hot flue gas, relevant residence times). The experiments were performed in a generic, optically accessible reheat combustor, by applying high-speed imaging and particle image veiocimetry. Autoignition limits for different mixing section (temperature, velocity) and fuel jet (N2 dilution) parameters are described. The dominant factor influencing autoignition was the temperature, with an increase of around 2% ieading to a reduction of the higiiest possible H2 concentration without "flame-stabilizing autoignition kernels" of approximately 16 vol. %. Furtiierniore, the onset and propagation of the ignition kernels were elucidated using the high-speed measurements. It was found that the ability of individual autoignition kerneis to develop into stable flames depends on the initial position of tire kernel and tiie corresponding axial velocity at that position. Whiie unwanted autoignition occurred prior to reaching the desired operating point for most investigated conditions, for certain conditions the reheat combtistor could be operated stably with up to 80 vol. % H2 in the fuei.

Excess energy generation from renewables can be conveniently stored as hydrogen for later use as a gas turbine fuel. Also, the strategy to sequestrate CO2 from natural gas (NG) will require gas turbines to run with hydrogen-based fuels. In such scenarios, high temperature low emission combustion of hydrogen is a key requirement for the future gas turbine market. Ansaldo Energia's gas turbines featuring sequential combustion have an intrinsic advantage when it comes to fuel flexibility and in particular hydrogen-based fuels. The sequential combustion system is composed of two complementary combustion stages in series: one premix stage followed by an auto-ignited second stage overcoming the limits of traditional premix combustion systems through a highly effective extra tuning parameter, i.e., the temperature between the first and the second stage. The standard constant pressure sequential combustion (CPSC) system as applied in the GT36 engine is tested, at high pressure, demonstrating that a modified operation concept allows stable combustion with no changes in combustor hardware for the whole range of NG and hydrogen blends. It is shown that in the range from 0% to 70% (vol.) hydrogen, stable combustion is achieved at full nominal exit temperature, i.e., without any derating and thus clearly outperforming other available conventional premixed combustors. Operation between 70% and 100% is possible as well and only requires a mild reduction of the combustor exit temperature. By proving the transferability of the single-can high pressure results to the engine, this paper demonstrates the practicality of operating the Ansaldo Energia GT36 H-Class gas turbine on fuels containing unprecedented concentrations of hydrogen while maintaining excellent performance and low emissions both in terms of NOx and CO2.