Fuel Processing Technology (v.87, #8)

A study of thermal decomposition of alkanethiols in pressure reactor by Bo Yang; Songbai Tian; Shanlin Zhao (673-678).
The thermal decomposition of four alkanethiols was investigated in this paper. The test was processed in a pressure reactor at 200–400 °C. GC/MS and GC/SCD were used to detect the products of thermal decomposition. The result indicates that the alkane groups of alkanethiols have great influence on the thermal stability of alkanethiols. N-butylthiol, isobutylthiol and n-hexylthiol begin to pyrolyse at about 250 °C and more than 75% decomposes at 400 °C after being maintained for 4 h. However, tert-octylthiol can be broken down at lower temperature below 200 °C and almost 75% decomposes at 250 °C after 4 h. The main product of thermal decomposition is H2S and a free radical reaction is used to explain the decomposition mechanism.
Keywords: Alkanethiols; Thermal decomposition; Free radical reaction;

Stability of mercury on three activated carbon sorbents by Zhongyang Luo; Changxing Hu; Jinsong Zhou; Kefa Cen (679-685).
The stability of adsorbed mercury on activated carbon (AC) is very important for avoiding reemission. Based on research concerning the stability of mercury on the AC relative to leaching and thermal desorption, our conclusions are as follows. Leaching tests show that mercury appears to be very stable on the AC. The Hg concentration in the leachate is much lower than the TCLP safety limit of 0.025 mg/l. Leaching time and liquid to solid (L/S) have some influence on the leaching results, but the influence is far less than which leads the Hg concentrate to exceed the safety limit. Leaching tests for mercury at lower and higher pH are aggressive compared with the neutral pH test. There is much more mercury released from the AC at longer heating time for mercury. At the same time, it seems that the stability of adsorbed original Hg0 on the AC is stronger than that of adsorbed original Hg2+.
Keywords: Stability; Mercury; Activated carbon; Leaching; Reemission;

Investigation of wear pattern in a complex coal pulveriser using CFD modelling by R. Vuthaluru; O. Kruger; M. Abhishek; V.K. Pareek; H.B. Vuthaluru (687-694).
In this study, we have constructed a commercial-scale pulveriser and simulated motion of air and coal particles inside the pulveriser to investigate the effect of air passage on the wear pattern. Simulations were carried out using Eulerian–Lagrangian approach. The results indicated that the primary air entering into the pulveriser under the bowl via splitters, exited the pulveriser vanes to the left with the highest velocity. This validates the constructed model as the nozzle ring above the bowl has vanes that run clockwise making most of the primary air to exit the vanes to the left. Additional simulations with modified inlet duct geometry led to a possible solution for making the airflow distribution even at the base of the mill, which is expected to reduce the wear pattern. The results presented in the paper provides impetus for the modification of the airflow path using baffle splitters in the primary air duct, which could prove valuable to designers for the optimisation of airflow and the potential reduction of wear on the components within the coal pulveriser.
Keywords: Pulveriser; Turbulent flow; Multiphase flow; Grid generation; CFD; Particle trajectories;

Simulation of natural gas steam reforming furnace by Zunhong Yu; Enhong Cao; Yifei Wang; Zhijie Zhou; Zhenghua Dai (695-704).
A mathematical model for natural gas reformer is established to draw up homogeneous phase one-dimensional reaction kinetics equation in the reforming tubes, and compute the tube external radiant heat transfer with zone method. Simulation result is compared with the operating data carried on Selas reformer used in Brown and Root Braun 1000 t NH3/day production system in Urumqi Second Ammonia Plant, and they match well. This model has laid the foundation for the design variable optimization research, for example, the relations among specific heat transfer area of furnace tube, tube outlet temperature, tube pressure drop and maximum tube-wall temperature, as well as the effect of tube pitch, furnace chamber width, burner arrangement, furnace wall blackness, production load, water carbon ratio and fuel distribution on operation behaviors.
Keywords: Natural gas reformer; Hydrocarbon steam converter; Tubular reactor; Radiant heat transfer; Reformer structure optimization; Reformer operation optimization;

The impact of catalytic reforming and catalyst regeneration process parameters on cycle duration and product quality was investigated. Overall data were based on catalyst manufacturer data and process data of the Platforming plant at the Rijeka Oil Refinery (Croatia). Used catalyst was Pt–Re on high purity aluminia as carrier.For the reformate octane number of 99 the reduction of charge from the designed 90 m3/h to 75 m3/h results in the lowering of the Start of Run reactor temperature from 515.2 to 511.0 °C with a hydrogen/hydrocarbon ratio of 7.3:1 and 23 bar at the high pressure separator. Knowing the maximal inlet reactor temperatures at Platforming of around 528 °C for the existing catalyst type, it turns out that the temperature range of catalyst usability goes up from 12.8 to 17.1 °C. In this way, from a cycle duration of 116 days, we come to a more acceptable duration of 198 days. Such cycle duration enables two catalyst regenerations per year.Catalyst cycle duration, as well as the quality of catalytic reforming products, greatly depends on the way catalyst regeneration is carried out. This relates to the distribution of active metal sites on catalyst fines after the coke, deposited on the catalyst, had been burned out. Regeneration process itself must be adjusted to the maximum allowed operating pressure and the maximum volume flow of gas phase through the high pressure catalytic section.
Keywords: Catalytic reforming; Pt–Re catalyst; Catalyst regeneration;

Mathematical models for kinetics of batchwise hydrogenation of shale oil by I. Johannes; H. Luik; K. Kruusement (711-716).
Hydrogenation of shale oil in a batch autoclave is described by a second order kinetic equation depending on the hydrogen current concentration (H) and on the current value of a total characteristic of the oil (x i ), both approaching to their equilibrium levels (H , x i). Algorithms are proposed to estimate the values of hydrogenation rate coefficient (k) and H from the plot of decrease in hydrogen concentration in time versus H at isothermal conditions. A new concept “specific change of the characteristic” (β i  = dx i  / dH) is introduced to handle various x i (oil yield, viscosity, density, iodine number, and yield of the fraction 200–275 °C).The equilibrium constants (K i ) and β i for the characteristics are estimated on the basis of experimental results. The temperature-dependencies for k, K i and β i are determined. A scheme is proposed to predict current values of H and x i for different H 0, T max and oil mass under isothermal and non-isothermal conditions.The model deduced and the coefficients and constants found can be applied for quantitative evaluation of catalysts and initial oils for hydrogenation.
Keywords: Kinetic model; Shale oil; Hydrogenation;

Use of energy crops for domestic heating with a mural boiler by Juan F. González; Carmen M. González-García; Antonio Ramiro; José Gañán; Antonio Ayuso; Joao Turegano (717-726).
The combustion process of two residues from energy crops in a 12 kW mural boiler for domestic heating was studied. The fuels used were common reed (Arundo donax L.), sorghum (Sorghum bicolor L.) and forest pellet recommended by the boiler manufacturer. A comparison with the combustion process of two industrial residues (tomato residue and almond pruning) and other energy crop (Cynara cardunculus L.) has been established. The experimental tests carried out in “La Orden” farm on common reed and sorghum cultivation revealed a production of dry biomass of 35 and 30 t/ha, respectively. Previously, the fuels were characterised by means of the higher heating value, proximate and ultimate analyses. The influence of the residue type, fuel mass flow, draught and residues mixture on the combustion parameters has been studied. A TESTO 300 M-I analyzer was employed to determinate the principal parameters of the combustion process (CO2, CO, and O2 contents, fumes temperature, not-burnt gaseous and sensitive heat losses in the fumes, air excess coefficient, flow rate and velocity of the fumes, and efficiency). The behaviour shown by the two studied residues was similar to that of the forest pellet. The boiler efficiencies obtained with the maximum fuel mass flow (100%) and minimum draught (0%) were 84% and 85.3% for reed and sorghum pellets, respectively. The obtained efficiency with the forest pellet was 90.5%. The optimum residue mixture assayed was almond pruning (75%) and sorghum (25%), with a boiler efficiency of 87.2% for a mass flow and draught of 100% and 0%, respectively.
Keywords: Biomass combustion; Pellets; Energy crops; Efficiency;

A techno-economic analysis of the application of continuous staged-combustion and flameless oxidation to the combustor design in gas turbines by Y.D. Wang; Y. Huang; D. McIlveen-Wright; J. McMullan; N. Hewitt; P. Eames; S. Rezvani (727-736).
The impact of NO x reduction technologies upon a gas turbine power station has been investigated using the ECLIPSE process simulator. Technical, environmental and economic assessments were performed, based upon a model of the simple cycle gas turbine, fuelled by natural gas.The technologies assessed were: a) selective catalytic reduction (SCR); b) continuous staged air combustion (COSTAIR); and c) flameless oxidation method (FLOX).The SCR method produced a 90% reduction of NO x emissions, at an additional penalty to the electricity cost of 0.19–0.20 p/kWh, over the base case of simple cycle with standard combustor.The COSTAIR method reduced 80.4% of NO x emissions, at an additional electricity cost of 0.03–0.04 p/kWh, over the base case; but 0.16–0.17 p/kWh less than the SCR method at a slightly higher level of NO x emissions.The FLOX method generated 92.3% less of NO x emissions, at an additional electricity cost of 0.08–0.11 p/kWh, over the base case; but 0.09–0.11 p/kWh less than the SCR method at a lower level of NO x emissions.A sensitivity analysis of the Break-Even Selling Price (BESP) of electricity and the Specific Investment (SI) versus the cost of different burner systems shows that the SCR system had the highest values for BESP and SI; and the COSTAIR system had the lowest.The results show that the use of these non-standard burners could offer an effective method of reducing NO x emissions considerably for simple cycle gas turbine power plants with minimal effect on system capital cost and electricity selling price, and were also cheaper than using SCR.
Keywords: Combustion; NO x emissions; Combustor design; Techno-economic analysis;

An entrained flow reactor has been used to characterize the slagging behaviour of twelve coals/blends, under different experimental conditions. Besides measuring the weight of the deposits, a detailed characterization of the coals, fly ashes and deposits has been performed using ASTM procedures and Computer-Controlled SEM. Two different indices are used to represent the deposition behaviour: capture efficiency (CE) is a measure of the intrinsic tendency of the particles to form a deposit, while the energy-based growth rate (GRE) also considers the ash and energy contents of the different fuels. The coals tested ranged from lignites to anthracites and showed widely different values for those slagging indices. The experimental results are interpreted making use of a detailed analysis of the physico-chemical properties of the coals and fly ashes. In particular, a consistent relationship is found between deposit growth rates and the aerodynamic diameter of the fly ash particles. Coal blending showed in all cases non-linear behaviours with respect to the parent coals. The experimental programme was also extended to evaluate the influence of variations in some experimental parameters, including exposure time, gas temperature, surface temperature and distance from injection. The results obtained are useful both to characterize the experimental method and to determine the influence of some parameters relevant to deposition phenomena.
Keywords: Slagging; Coal ash deposition; Entrained flow reactors; Coal blends;

Response to the comment on “The application of thermal processes to valorise waste tyre” by J.C. Jones by R. Murillo; E. Aylón; M.V. Navarro; M.S. Callén; A. Aranda; A.M. Mastral (755).

Calendar (757).