This paper compares the laboratory-based fireside corrosion tests on superheater/reheater materials in simulated air-firing combustion conditions with oxy-firing combustion conditions (with hot gas recycling before flue gas de-sulphurisation). The gaseous combustion environment was calculated based on a specific co-firing ratio of CCP with Daw Mill coal. The fireside corrosion tests were carried out using the deposit recoat'' test method to simulate the damage anticipated in specific environments. A synthetic deposit (Na-2 SO4:K2SO4:Fe2O3 = 1.5:1.5:1 mol.) which has commonly been used in fireside corrosion screening trials and is a mix that forms alkali-iron tri-sulphate (identified in many investigations as a cause of fireside corrosion) was used in these tests. The air-fired tests were carried out at temperatures of 600, 650 and 700 degrees C and oxy-fired tests were carried out at temperatures of 600, 650, 700 and 750 degrees C to represent the superheater/reheater metal temperatures anticipated in future power plants with and without synthetic deposits, with four candidate materials: T92, HR3C and 347HFG steels; nickel-based alloy 625 (alloy 625 was only tested with screening deposits). The progress of the samples during their exposures was measured using mass change methods. After the exposures, the samples were examined by SEM/EDX to characterise the damage. To quantify the metal damage, pre-exposure micrometre measurements were compared to the post-exposure image analyser measurements on sample cross-sections. The trends in corrosion damage in both air and oxy-firing conditions showed a bell-shaped'' curve, with the highest metal damage levels (peak) observed at 650 degrees C for air-firing and 700 degrees C for oxy-firing tests. However, at 600 and 650 degrees C similar damage levels were observed in both environments. The shift in peak corrosion damage in oxy-firing condition is believed to be the presence of higher levels of SOx, which stabilised the alkali-iron tri-sulphate compounds. Generally, in both air and oxy-firing conditions the mean metal damage was reduced with increasing the amount of Cr in the alloys. However, at the highest temperatures in both air-firing (700 degrees C) and oxy-firing conditions (750 degrees C) the metal damage of nickel based superalloy 625 was higher than HR3C. (C) 2013 The Authors. Published by Elsevier Ltd. All rights reserved.

Fuel reburning usually serves in mitigating NOx formation in stationary combustion sources. However, the use of biomass as reburning fuel could facilitate the production of relatively more nitrogen-containing aromatic products of incomplete combustion. This study investigates the heterogeneous reaction between biomass and mixtures of NO/O-2 gases, employing isothermal high-temperature experiments in a vertically-entrained reactor, and in situ diffuse reflective infrared Fourier transform spectroscopy (DRIFTS) under a non-isothermal heating condition ranging from ambient temperature to 700 degrees C. The method enables sensitive evaluation of the surface species ensuing during the thermal reaction. Results from this study elucidate the formation of nitrated structures as active intermediate species of the heterogeneous reaction. The nitrogenated signatures persist on the surface of the residual ash, suggesting the production of N-aromatics such as nitro-PAH. Considering the severe toxicity and bioaccumulative properties of these by-products, further research should focus on the relative contribution of various reburning fuels, while favouring sustainable fuels such as non-charring plastics.

The oxidation of di-n-propyl-ether (DPE), was studied in a jet-stirred reactor. Fuel-lean, stoichiometric and fuel-rich mixtures (phi = 0.5-4) were oxidized at a constant fuel mole fraction of 1000 ppm, at temperatures ranging from 470 to 1160 K, at 10 atm, and constant residence time of 700 ms. The mole fraction profiles were obtained through sonic probe sampling and gas chromatography and Fourier transform infrared spectrometry analyses. As was the case in our previous studies on ethers (diethyl ether and di-n-butyl ether), the carbon neighboring the ether group was found to be the most favorable site for H-abstraction reactions and the chemistry of the corresponding fuel radical drives the overall reactivity. The fuel concentration profiles indicated strong low-temperature chemistry. A kinetic sub-mechanism is developed based on rules similar to those for the two symmetric ethers previously investigated (DEE and DBE). The proposed mechanism shows good performances in representing the present experimental data, nevertheless, more data such as atmospheric pressure speciation will be needed in order to better interpret the kinetic behavior of DPE.

Pressurized fluidized bed hydroretorting of beneficiated eastern USA oil shale leaves sufficient carbon (15-27 wt%) in the retorted shale to warrant utilization of that calorific value by combustion. A sample of hydroretorted shale from a bench scale unit test (oil yield was 233% of Fischer Assay) was used as a feedstock for combustion tests using air. The tests were conducted at 815-1080-degrees-C, 0.1-7 MPa and residence times from 1 to 30 min in a thermobalance unit and a continuous (0.5 kg h-1) fluidized bed laboratory scale unit. Thermobalance tests indicate that combustion of the shale begins at 260-315-degrees-C depending on the oxygen partial pressure used. Carbon conversions up to 100%, with greater than 99.5% recovery, of the gross calorific value of the shale were achieved.

The transport of fluids in industrial units takes place usually inside cylindrical ducts. Multiphase systems flowing inside pipes are very common and many times there are also mass, energy and momentum transfer. Two-phase flow is found in many petrochemical processes, as is the case of preheating furnaces where normally the liquid vaporizes as it flows inside the heater. In the great majority of these heaters, there is a phase change from liquid to gas. The objective of this work is to simulate the two-phase gas-liquid flow of crude oil inside pipes of petrochemical fired heaters with the use of a Computational Fluid Dynamics (CFD) model to be later used in the prediction of coke formation through a thermal cracking model and a ternary solubility diagram for the petrol feed, according to Souza et al. [28]. The CFD free software OpenFOAM was used. There is a growing interest in the use of the OpenFoam project and many successful models have been implemented using this software. New routines were implemented to estimate temperature and concentration inside the tube, taking into consideration the interaction between the phases. To estimate the momentum it was used a phase intensive formulation for dispersed two-phase flow already implemented in OpenFOAM. The temperature profiles were predicted. The k-epsilon model was used to describe the turbulence and a vaporization model was implemented to estimate the phase change. A kinetic reaction net for crude oil with seven lumps was used in order to predict the thermal cracking of the crude oil. (C) 2012 Elsevier Ltd. All rights reserved.

Oxyfuel combustion is envisaged as one of the main options for near future CO2 reduction in conventional power production. There are many aspects of oxy-combustion still at the research stage. One of those is the issue of boiler materials resistance to corrosion due to solid deposits formed as a consequence of slagging in CO2 rich flue gases. The novel approach to the issue is the simulation of realistic slagging by pyrite (FeS2) projection through an oxyacetylene spray gun, flying along a controlled flame and impacting onto metallic surfaces of selected composition for fireside waterwall construction (F22, P91, 409, 347, 304H, and 800HT). Metallic surface temperatures were kept at 400, 500, 600 or 700 degrees C, and after deposition, metallic coupons were aged for long periods (150 and 1500 h) at the selected conditions (O-2/N-2, CO2/N-2). The characterisation of deposits was performed with XRD, SEM-EDX and carburisation tests. The first finding is that the oxidation progression is different when partially transformed pyrite covers metallic surfaces. In that case, no iron oxide (Fe2O3) scale is generated, only the chromium oxide (Cr3O4) grows between the steel and the deposit as a response to oxidation. There is a clear presence of chromium sulphides in competition with the chromium oxide. On the other hand, comparison of scales in CO2 vs. air indicates the same chemical composition but different morphology; in air combustion, corrosion layers are thicker and cracked. These results can improve the prediction of operational problems in coal oxy-fuel combustion. (C) 2011 Elsevier Ltd. All rights reserved.