The Impact of Operating Parameters on the Gas-Phase Sulfur Concentration after High Temperature Sulfur Sorption on a Supported Mo-Mn Sorbent

The impact of operating parameters on H2S capture from a syngas mixture by a Mo-promoted Mn-based high-temperature sorbent was investigated. The parameters investigated included temperature, space velocity, H2S concentration in the feed gas, and steam content. The H2S and SO2 concentrations in the gas after passing over a bed of the sorbent were analyzed and compared with thermodynamic calculations. The results confirmed that low temperature, low space velocity, low H2S concentration, and a dry feed were favorable for achieving a low residual concentration of sulfur compounds in the effluent gas. The sorbent was able to reduce the residual H2S concentration to below 1 ppm under all tested conditions. However, the unavoidable steam content in the gas phase had a significant adverse effect on sulfur removal from the gas. An empirical model, containing the three variables, i.e., temperature, space velocity, and H2S concentration in the feed, was developed and can be used to predict the effluent H2S residual concentration after treatment by the 15Mn8Mo sorbent.

The Homogeneous Conversion Mechanism of Cellulose Pyrolysis Tar Under the Effect of Steam

Biomass accounts for the largest proportion of rural solid waste with high moisture content, which affects the thermal treatment process. This paper studied the effect of steam on the pyrolysis tar of microcrystalline cellulose (MCC) by a two-stage fixed bed. The experiments had been carried out under different steam/feedstock mass ratios (S/F= 0, 0.8, 1.2, 1.6) when the first stage was at 600℃, and the second stage was at 800 ℃. The tar content in the syngas was reduced effectively from 6.68% to 2.30% when the S/F was from 0 to 1.6. Under the four S/F conditions, aromatic compounds accounted for more than 80%, which was the largest proportion of tar products. Significantly, formic acid phenyl ester (FAPE) decreased obviously with the growth of S/F. Besides, when the steam content was excessive, the MAHs, such as phenols and indenes, could be further cyclized and aromatized to form PAHs. To further study the removal mechanism of tar, the FAPE was investigated by density functional theory (DFT). It was concluded that the O3-C4 bond of FAPE was most likely to be attacked by the H2O molecule to form phenol, CO2, and H2 directly, among the four possible paths.

Effect of Operating Conditions on the Performance of Rh/TiO2 Catalyst for the Reaction of LPG Steam Reforming

The catalytic performance of Rh/TiO2 catalyst was investigated for the reaction of Liquefied Petroleum Gas (LPG) steam reforming with respect to the operating conditions employed. The impacts of reaction temperature, steam/C ratio, Gas Hourly Space Velocity (GHSV), and time were examined and discussed both in the absence and presence of butane in the feed. It was found that the catalytic performance is improved by increasing the reaction temperature, steam content in the feed, and/or by decreasing GHSV. In the presence of butane in the feed, the effect of H2O/C ratio on catalytic performance is prominent, whereas the opposite was observed for the effect of GHSV. The propane conversion curve decreases by adding butane in the feed, indicating that the presence of butane retards propane steam reforming. The investigation of the dynamic response of Rh/TiO2 catalyst to variations of H2O/C ratio showed that neither catalytic activity nor product selectivity is varied with time following abrupt changes of the steam/C ratio between 2 and 7. The catalyst exhibited excellent stability with time-on-stream at 500 and 650 °C. However, a reversible catalyst deactivation seems to be operable when the reaction occurs at 600 °C, resulting in a progressive decrease of propane conversion, which, however, can be completely restored by increasing the temperature to 650 °C in He flow, respectively. The long-term stability of Rh/TiO2 catalyst in the form of pellets showed that this catalyst is not only active and selective but also stable, and therefore, it is a promising catalyst for the reaction of LPG steam reforming.

Design and Experimental Characterization of a Swirl-Stabilized Combustor for Low Calorific Value Gaseous Fuels

Low calorific value (LCV) gaseous fuels are generated as by-products in many commercial sectors. Their efficient exploitation can be a considerable source of primary energy. Typically, product gases from biomass are characterized by low lower heating values (LHV) due to their high concentration of inert gases and steam. At the same time, their composition varies strongly based on the initial feedstock and may contain unwanted components in the form of tars and ammonia. These properties make the design of appropriate combustion systems very challenging and issues such as ignition, flame stability, emission control, and combustion efficiency must be accounted for. By employing a proprietary gas turbine burner at the TU Berlin, the combustion of an artificial LCV gas mixture at stoichiometric conditions has been successfully demonstrated for a broad range of steam content in the fuel. The current work presents the stability maps and emissions measured with the swirl-stabilized burner at premixed conditions. It was shown that the flame location and shape primarily depend on the steam content of the LCV gas. The steam content in the fuel was increased until flame blow-out occurred at LHVs well below the target condition of 2.87MJ/kg (2.7MJ/Nm3). The exhaust gas is analyzed in terms of the pollutants NOx and CO for different fuel compositions, moisture contents, and thermal powers. Finally, OH* measurements have been carried out in the flame. A simple reactor network simulation was used to confirm the feasibility of the experimental results.

Experimental and Numerical Investigation of Ultra-Wet Methane Combustion Technique for Power Generation

Using steam as heat carrier and working media has merits to increase electric efficiency up to 60% and decrease NOx emission to single-digit compared to dry gas turbine cycles. These attribute to the physical properties of steam as having high heat capacity to reduce local flame temperature, and hence reduce emissions by inhibiting thermal NOx forward reaction rate. In this work, ultra-high steam content with steam-to-air mass ratio up to 40% is premixed with methane air mixture before entering a swirl-stabilized HP-burner for combustion. Significant change of flame from V-shape (attached) to M shape (detached) is observed through a transparent combustion chamber. The measurement of chemiluminescence OH* is conducted with an intensified CCD-camera band-pass filtered at 320nm. Large eddy simulation is used to capture reacting flow features. Reasonably well agreements between experimental data and numerical results are obtained for both attached and detached flames in terms of OH* distribution. Distributed flame front is clearly identified with LES for wet methane combustion associated with 35% steam-to-air ratio corresponding to a high Karlovitz number flame. Slightly unstable combustion is observed when steam-to-air ratio exceeds 40% featuring an onset of flame blow-off. Interaction between precessing vortex core and the flame is presented at different level of steam dilution, and conclusions are drawn regarding flame stabilization. The in-depth understanding of ultra-wet combustion is an important step towards the use of sustainable, steam-diluted bio-syngas for electricity production.

Design and Experimental Characterization of a Swirl-Stabilized Combustor for Low Calorific Value Gaseous Fuels

Low calorific value (LCV) gaseous fuels are generated as by-products in many commercial sectors, e.g. as mine gas or bio-gas. Their efficient exploitation can be a considerable source of primary energy. Typically, product gases from biomass are characterized by low lower heating values (LHV) due to their high concentration of inert gases and steam. At the same time, their composition varies strongly based on the initial feedstock and may contain unwanted components in the form of tars and ammonia. These properties make the design of appropriate combustion systems very challenging and issues such as ignition, flame stability, emission control, and combustion efficiency must be accounted for. By employing a proprietary gas turbine burner at the TU Berlin, the combustion of an artificial LCV gas mixture at stoichiometric conditions has been successfully demonstrated for a broad range of steam content in the fuel. The current work presents the stability maps and emissions measured with the swirl-stabilized burner at premixed conditions. It was shown that the flame location and shape primarily depend on the steam content of the LCV gas. The steam content in the fuel was increased until flame blow-out occurred at LHVs well below the target condition of 2.87 MJ/kg (2.7 MJ/mN3). The exhaust gas is analyzed in terms of the pollutants NOx and CO for different fuel compositions, moisture contents, and thermal powers. Finally, OH* measurements have been carried out in the flame. A simple reactor network simulation was used to confirm the feasibility of the experimental results.

Experimental and Numerical Investigation of Ultra-Wet Methane Combustion Technique for Power Generation

Using steam as a heat carrier and working media has merits to increase electric efficiency up to 60% and decrease NOx emission to single-digit compared to dry gas turbine cycles. These attribute primarily to the physical properties of steam as having high heat capacity to reduce local flame temperature, and hence reduce emissions by inhibiting the thermal NOx forward reaction rate. In this work, ultra-high steam content with a steam-to-air mass ratio of up to 40% is premixed with methane-air mixture before entering into a swirl-stabilized HP-burner for combustion. A significant change of flame from V-shape (attached) to M shape (detached) is observed through a transparent combustion chamber whilst changing steam content. The measurement of chemiluminescence OH* is conducted with an intensified CCD-camera band-pass filtered at 320nm. Following these measurements, large eddy simulation is used to capture reacting flow features. Reasonably well agreements between experimental data and numerical results are obtained for both attached and detached flames in terms of the OH* distribution. Slight inconsistency of OH* intensity is mainly due to uncollected wall temperature which leads to either over- or under-prediction of chemical reaction rate depending on the experimental flame positions. Distributed flame front is clearly identified with LES for wet methane combustion associated with 35% steam-to-air ratio corresponding to a high Karlovitz number flame. Slightly unstable combustion is observed when the steam-to-air ratio exceeds 40% featuring an onset of flame blow-off. In addition, interaction between precessing vortex core and the flame is presented for different level of steam dilution, and conclusions are drawn regarding the flame stabilization. The in-depth understanding of the ultra-wet combustion is an important step towards the use of sustainable, steam-diluted biosyngas for electricity production.