Ammonia Pyrolysis and Oxidation in the Claus Furnace

In Situ Spectroscopic Studies of NH3 Oxidation of Fe-Oxide/Al2O3

Simple temperature-regulated chemical vapor deposition was used to disperse iron oxide nanoparticles on porous Al₂O₃ to create an Fe-oxide/Al₂O₃ structure for catalytic NH₃ oxidation. The Fe-oxide/Al₂O₃ achieved nearly 100% removal of NH₃, with N₂ as a major reaction product at temperatures above 400 °C and negligible NO_x emissions at all experimental temperatures. The results of a combination of in situ diffuse reflectance infrared Fourier-transform spectroscopy and near-ambient pressure-near-edge X-ray absorption fine structure spectroscopy suggest a N₂H₄-mediated oxidation mechanism of NH₃ to N₂ via the Mars-van Krevelen pathway on the Fe-oxide/Al₂O₃ surface. As a catalytic adsorbent-an energy-efficient approach to reducing NH₃ levels in living environments via adsorption and thermal treatment of NH₃-no harmful NO_x emissions were produced during the thermal treatment of the NH₃-adsorbed Fe-oxide/Al₂O₃ surface, while NH₃ molecularly desorbed from the surface. A system with dual catalytic filters of Fe-oxide/Al₂O₃ was designed to fully oxidize this desorbed NH₃ to N₂ in a clean and energy-efficient manner.

Performance assessment and process optimization of a sulfur recovery unit: a real starting up plant

Sulfur recovery units (SRU) have an important role in the industrial production of elemental sulfur from hydrogen sulfide, whereas the generated acidic gas emissions must be controlled and treated based on local and international environmental regulations. Herein, Aspen HYSYS V.11 with Sulsim software is used to simulate the industrial and treatment processes in a refinery plant in the Middle East. In the simulation models, in temperature, pressure, flow, energy, and gas emissions were monitored to predict any expected change that could occur during the industrial processes. The simulation models were validated by comparing the obtained data with actual industrial data, and the results showed low deviation values. The simulation results showed that the current process temperature conditions can work efficiently for sulfur production without causing any environmental consequences. Interestingly, the simulation results revealed that sulfur can be produced under the optimized temperature conditions (20° less than design temperatures) with a total amount of steam reduction by 1040.12 kg/h and without any negative impact on the environment. The steam reduction could have a great economic return, where an average cost of 7.6 $ per ton could be saved with a total estimated cost savings by 69,247.03 $ per year. The simulation revealed an inaccurate production capacity calculated by real data in the plant during the performance test guarantee (PTG) where the real data achieved around 1 ton/h higher capacity than the simulation result, with an overall recovery efficiency of 99.96%. Based on this significant result, a solution was raised, and the level transmitters were calibrated, then the test was repeated. The simulation models could be very useful for engineers to investigate and optimize the reaction conditions during the industrial process in sulfur production facilities. Hence, the engineers can utilize these models to recognize any potential problem, thereby providing effective and fast solutions. Additionally, the simulation models could participate in assessing the performance test guarantee (PTG) calculations provided by the contractor.

Process Modeling, Optimization and Cost Analysis of a Sulfur Recovery Unit by Applying Pinch Analysis on the Claus Process in a Gas Processing Plant

The Claus process is one of the promising technologies for acid gas processing and sulfur recovery. Hydrogen sulfide primarily exists as a byproduct in the gas processing unit. It must be removed from natural gas. The Environmental Protection Agency (EPA) notices that increasing SO2 and CO2 in the air harms the environment. Sulfur generally has an elemental content of 0.1–6 wt % in crude oil, but the value could be higher than 14% for some crude oils and asphalts. It produces SO2 and CO2 gases, which damage the environment and atmosphere of the earth, called primary pollutants. When SO2 gas is reacted with water in the atmosphere, it causes sulphur and nitric acid, called a secondary pollutant. The world countries started desulphurization in 1962 to reduce the amount of sulfur in petroleum products. In this research, the Claus process was modeled in Aspen Plus software (AspenTech, Bedford, MA, USA) and industrial data validated it. The Peng–Robinson method is used for the simulation of hydrocarbon components. The influence of oxygen gas concentration, furnace temperature, the temperature of the first catalytic reactor, and temperature of the second catalytic reactor on the Claus process were studied. The first objective of the research is process modeling and simulation of a chemical process. The second objective is optimizing the process. The optimization tool in the Aspen Plus is used to obtain the best operating parameters. The optimization results show that sulfur recovery increased to 18%. Parametric analysis is studied regarding operating parameters and design parameters for increased production of sulfur. Due to pinch analysis on the Claus process, the operating cost of the heat exchangers is reduced to 40%. The third objective is the cost analysis of the process. Before optimization, it is shown that the production of sulfur recovery increased. In addition, the recovery of sulfur from hydrogen sulfide gas also increased. After optimizing the process, it is shown that the cost of heating and cooling utilities is reduced. In addition, the size of equipment is reduced. The optimization causes 2.5% of the profit on cost analysis.

Experimental Study of the Pyrolysis of NH3 under Flow Reactor Conditions

The possibility of using ammonia (NH₃), as a fuel and as an energy carrier with low pollutant emissions, can contribute to the transition to a low-carbon economy. To use ammonia as fuel, knowledge about the NH₃ conversion is desired. In particular, the conversion of ammonia under pyrolysis conditions could be determinant in the description of its combustion mechanism. In this work, pyrolysis experiments of ammonia have been performed in both a quartz tubular flow reactor (900-1500 K) and a non-porous alumina tubular flow reactor (900-1800 K) using Ar or N₂ as bath gas. An experimental study of the influence of the reactor material (quartz or alumina), the bulk gas (N₂ or Ar), the ammonia inlet concentration (1000 and 10 000 ppm), and the gas residence time [2060/T (K)-8239/T (K) s] on the pyrolysis process has been performed. After the reaction, the resulting compounds (NH₃, H₂, and N₂) are analyzed in a gas chromatograph/thermal conductivity detector chromatograph and an infrared continuous analyzer. Results show that H₂ and N₂ are the main products of the thermal decomposition of ammonia. Under the conditions of the present work, differences between working in a quartz or non-porous alumina reactor are not significant under pyrolysis conditions for temperatures lower than 1400 K. Neither the bath gas nor the ammonia inlet concentration influence the ammonia conversion values. For a given temperature and under all conditions studied, conversion of ammonia increases with an increasing gas residence time, which results into a narrower temperature window for NH₃ conversion.

Selective catalytic oxidation of ammonia over LaMAl11O19−δ (M = Fe, Cu, Co, and Mn) hexaaluminates catalysts at high temperatures in the Claus process

A method for selective catalytic oxidation of ammonia at high temperature was proposed to remove the ammonia impurity in the Claus process. Cu substituted hexaaluminate catalysts achieved the highest N₂ yield at around 520 °C and the reaction followed the i-SCR mechanism.

Modification of Claus Sulfur Recovery Unit by Isothermal Reactors to Decrease Sulfur Contaminant Emission: Process Modeling and Optimization

Due to environmental limitations and issues, the main goal of this research is modification of conventional Claus sulfur recovery process to decreases sulfur contaminant emission. In this regard, two environmentally friendly alternatives are proposed based on the isothermal concept in reactors. Since Claus reaction is exothermic and reversible, the adiabatic fixed bed reactors in the catalytic section of Claus process are substituted by the isothermal reactors. The furnace and catalytic reactors are modeled based on the mass and energy conservation laws at steady state condition. To prove accuracy of the developed model, the simulation results of conventional process are compared with the available plant data. Then, the optimal condition of modified processes are calculated considering sulfur recovery as the objective function using the Genetic algorithm as a useful method in global optimization. The attainable decision variables are inlet temperature of furnace and reactors, coolant temperature, feed split fraction and air flow rate in the furnace. The simulation results show that H2S conversion in the proposed cases increases about 1.87 % and 1.78 % compared to the conventional process. Generally, the main advantages of proposed structures are higher sulfur recovery and lower sulfur contaminant emission such as COS and CS2 emission.

Effect of ammonia on chemical vapour deposition and carbon nanotube nucleation mechanisms

Chemical vapour deposition (CVD) growth of carbon nanotubes is currently the most viable method for commercial-scale nanotube production. However, controlling the 'chirality', or helicity, of carbon nanotubes during CVD growth remains a challenge. Recent studies have shown that adding chemical 'etchants', such as ammonia and water, to the feedstock gas can alter the diameter and chirality of nanotubes produced with CVD. To date, this strategy for chirality control remains sub-optimal, since we have a poor understanding of how these etchants change the CVD and nucleation mechanisms. Here, we show how ammonia alters the mechanism of methane CVD and single-walled carbon nanotube nucleation on iron catalysts, using quantum chemical molecular dynamics simulations. Our simulations reveal that ammonia is selectively activated by the catalyst, and this enables ammonia to play a dual role during methane CVD. Following activation, ammonia nitrogen removes carbon from the catalyst surface exclusively via the production of hydrogen (iso)cyanide, thus impeding the growth of extended carbon chains. Simultaneously, ammonia hydrogen passivates carbon dangling bonds, which impedes nanotube nucleation and promotes defect healing. Combined, these effects lead to slower, more controllable nucleation and growth kinetics.

Advances in selective catalytic oxidation of ammonia to dinitrogen: a review

Selective catalytic oxidation of ammonia to dinitrogen.

Potential of electric discharge plasma methods in abatement of volatile organic compounds originating from the food industry

Increased volatile organic compounds emissions and commensurate tightening of applicable legislation mean that the development and application of effective, cost-efficient abatement methods are areas of growing concern. This paper reviews the last two decades' publications on organic vapour emissions from food processing, their sources, impacts and treatment methods. An overview of the latest developments in conventional air treatment methods is presented, followed by the main focus of the paper, non-thermal plasma technology. The results of the review suggest that non-thermal plasma technology, in its pulsed corona discharge configuration, is an emerging treatment method with potential for low-cost, effective abatement of a wide spectrum of organic air pollutants. It is found that the combination of plasma treatment with catalysis is a development trend that demonstrates considerable potential. The as yet relatively small number of plasma treatment applications is considered to be due to the novelty of pulsed electric discharge techniques and a lack of reliable pulse generators and reactors. Other issues acting as barriers to widespread adoption of the technique include the possible formation of stable oxidation by-products, residual ozone and nitrogen oxides, and sensitivity towards air humidity.