Naseem Irfan

Effect of oxygenated liquid additives on the urea based SNCR process

An experimental investigation was performed to study the effect of oxygenated liquid additives, H(2)O(2), C(2)H(5)OH, C(2)H(4)(OH)(2) and C(3)H(5)(OH)(3) on NO(x) removal from flue gases by the selective non-catalytic reduction (SNCR) process using urea as a reducing agent. Experiments were performed with a 150kW pilot scale reactor in which a simulated flue gas was generated by the combustion of methane operating with 6% excess oxygen in flue gases. The desired levels of initial NO(x) (500ppm) were achieved by doping the fuel gas with ammonia. Experiments were performed throughout the temperature range of interest, i.e. from 800 to 1200 degrees C for the investigation of the effects of the process additives on the performance of aqueous urea DeNO(x). With H(2)O(2) addition a downward shift of 150 degrees C in the peak reduction temperature from 1130 to 980 degrees C was observed during the experimentation, however, the peak reduction efficiency was reduced from 81 to 63% when no additive was used. The gradual addition of C(2)H(5)OH up to a molar ratio of 2.0 further impairs the peak NO(x) reduction efficiency by reducing it to 50% but this is accompanied by a downward shift of 180 degrees C in the peak reduction temperature. Further exploration using C(2)H(4)(OH)(2) suggested that a 50% reduction could be attained for all the temperatures higher than 940 degrees C. The use of C(3)H(5)(OH)(3) as a secondary additive has a significant effect on the peak reduction efficiency that decreased to 40% the reductions were achievable at a much lower temperature of 800 degrees C showing a downward shift of 330 degrees C.

Impacts on ambient air quality due to flaring activities in one of Oman's oilfields.

ABSTRACT This work was conducted to assess the impacts on workplace and ambient air quality due to release of sulfur dioxide (SO2) into the atmosphere at Al-Noor production station, located in southern desert of Sultanate of Oman. The SO2 is released because of oxidation of H2S to SO2 on flaring of H2S rich off gas at the Al-Noor. In the first phase of the study, CALPUFF modeling system was used to predict the ground level concentrations of SO2 emissions from the flare stacks. The evaluation of the modeling system was carried out by comparing the predicted results with that of the measured. In the second stage of the study, the estimated results were compared with the air quality standards/guidelines set by Omani regulatory authorities as well as by World Health Organization (WHO). It was concluded on the basis of current study that the sensitive individuals in the workplace of the Al-Noor could experience adverse health effects due to short-term exposure of SO2.

Simulation of atmospheric dispersion of radionuclides using an Eulerian–Lagrangian modelling system

In this paper we present an atmospheric dispersion scenario for a proposed nuclear power plant in Pakistan involving the hypothetical accidental release of radionuclides. For this, a concept involving a Lagrangian stochastic particle model (LSPM) coupled with an Eulerian regional atmospheric modelling system (RAMS) is used. The atmospheric turbulent dispersion of radionuclides (represented by non-buoyant particles/neutral traces) in the LSPM is modelled by applying non-homogeneous turbulence conditions. The mean wind velocities governed by the topography of the region and the surface fluxes of momentum and heat are calculated by the RAMS code. A moving least squares (MLS) technique is introduced to calculate the concentration of radionuclides at ground level. The numerically calculated vertical profiles of wind velocity and temperature are compared with observed data. The results obtained demonstrate that in regions of complex terrain it is not sufficient to model the atmospheric dispersion of particles using a straight-line Gaussian plume model, and that by utilising a Lagrangian stochastic particle model and regional atmospheric modelling system a much more realistic estimation of the dispersion in such a hypothetical scenario was ascertained. The particle dispersion results for a 12 h ground release show that a triangular area of about 400 km(2) situated in the north-west quadrant of release is under radiological threat. The particle distribution shows that the use of a Gaussian plume model (GPM) in such situations will yield quite misleading results.

Simulation of Monsoon Precipitation over South-Asia Using RegCM3

The objective of this study is to explore the capability of the Regional Climate Model (RegCM3), to predict the extreme weather events in south-Asian region with particular reference to precipitation during monsoon season (July, August and September) over northern mountainous and southern plain regions of Pakistan. Different cumulus parameterization schemes in RegCM3 for prediction of convective precipitation are tested for monsoon period during the years 1998 and 2001. The model results are compared with the Climate Research Unit (CRU) observational data and the surface synoptic data of the Pakistan Meteorological Department (PMD). The year 1998 was a dry year and proved to be the beginning of a severe drought lasted up to the year 2000. While in year 2001 the precipitation over some parts of the country exceeded the normal, especially the northern parts of the country observed exceptionally high rainfall rate. The results indicate that some convective parameterization schemes of RegCM3 well captured the summer monsoon precipitation over Pakistan. However, the schemes need to be selected carefully depending upon the region of interest. It was found that the Grell scheme with both closures: Arakawa-Schubert (AS) and Fritsch-Chappell (FC) satisfactorily captured the monsoon phenomenon in Pakistan specially for the northern mountainous regions.

A comparative kinetic study of SNCR process using ammonia

The paper presents comparative kinetic modelling of nitrogen oxides (NOx) removal from flue gases by selective non-catalytic reduction process using ammonia as reducing agent. The computer code SENKIN is used in this study with the three published chemical kinetic mechanisms; Zanoelo, Kilpinen and Skreiberg. Kinetic modeling was performed for an isothermal plug flow reactor at atmospheric pressure so as to compare it with the experimental results. A 500 ppm NOx background in the flue gas is considered and kept constant throughout the investigation. The ammonia performance was modeled in the range of 750 to 1250 oC using the molar ratios NH3/NOx from 0.25 to 3.0 and residence times up to 1.5 seconds. The modeling using all the mechanisms exhibits and confirms a temperature window of NOx reduction with ammonia. It was observed that 80% of NOx reduction efficiency could be achieved if the flue gas is given 300 msec to react with ammonia, while it is passing through a section within a temperature range of 910 to 1060 oC (Kilpinen mechanism) or within a temperature range of 925 to 1030 oC (Zanoelo mechanism) or within a temperature range of 890 to 1090 oC (Skreiberg mechanism).

Computational modelling of NOx removal by selective non-catalytic reduction

This paper presents the results of computational kinetic modelling of the removal of nitrogen oxides (NOx) from flue gases by selective non-catalytic reduction (SNCR) process using urea as a reducing agent. CHEMKIN and SENKIN computer codes were used with latest reaction mechanism parameters for simulated conditions in an isothermal plug flow reactor. Flue gas initial conditions were simulated as 70 litres/min propane containing 500 ppm background NOx. A range of molar ratios was studied at optimum temperature. Carbon monoxide and hydrogen were investigated as potential enhancers to lower the temperature window. The modelling results suggested that the optimum temperature for peak reduction was around 1075C with optimum molar ratios of 1.5. Hydrogen was found to be an efficient enhancer. The optimum residence time was found to be about 80 milliseconds.

Dispersion of radionuclides released into a stable planetary boundary layer using a Monte Carlo model

In this paper a Monte Carlo model for describing the atmospheric dispersion of radionuclides (represented by Lagrangian particles/neutral tracers) continuously released into a stable planetary boundary layer is presented. The effect of variation in release height and wind directional shear on plume dispersion is studied. The resultant plume concentration and dose rate at the ground is also calculated. The turbulent atmospheric parameters, like vertical profiles of fluctuating wind velocity components and eddy lifetime, were calculated using empirical relations for a stable atmosphere. The horizontal and vertical dispersion coefficients calculated by a numerical Lagrangian model are compared with the original and modified Pasquill-Gifford and Briggs empirical sigmas. The comparison shows that the Monte Carlo model can successfully predict dispersion in a stable atmosphere using the empirical turbulent parameters. The predicted ground concentration and dose rate contours indicate a significant increase in the affected area when wind shear is accounted for in the calculations.

Dust particle collection efficiency of venturi scrubber with varying number of orifices using CFX

In the present study, computational fluid dynamics (CFD) investigation of dust particle collection efficiency in a force feed venturi scrubber has been performed using ANSYS CFX. A Venturi scrubber provides an effective way to remove dust particles flowing in a contaminated gas which are captured in fine droplets formed due to disintegration of a liquid as a result of high kinetic energy of air. Eulerian-Lagrangian approach is used to analyze the dust particle collection in a venturi scrubber for gas (air) flow rate at 1 g/s and liquid flow rate of 6 g/s with 2, 4, 6 and 8 orifices placed at the start of throat, end of throat and on the converging section. Cascade atomization and breakup model (CAB) is used for the prediction of liquid breakup in the venturi scrubber. Dust particles (TiO2) having diameter of 1 μm are used in this research. Velocity of gas at the throat, droplet size, volume fractions and collection efficiency are studied to analyze the working of venturi scrubber.

Adsorption of indoor toxic gas by ionic liquid impregnated activated carbons

Butylpyridinium thiocyanate [BuPyr]SCN ionic liquid was synthesized by metathesis and characterized. NMR spectrum has shown the [BuPyr] cation while FTIR has shown the SCN anion peak which confirms the structure of the synthesized ionic liquid. The ionic liquid was impregnated on activated carbon in order to enhance performance of sulfur dioxide adsorption compared to the non-impregnated raw activated carbon. Two types of activated carbons were used; activated carbon cylindrical granules and cloth. Different percentages of ionic liquid loading (1%, 10% and 20%) were applied. The capacity of the adsorbent for treatment of 10 ppm and 50 ppm SO2 was determined by breakthrough curve analysis whereby optimum breakthrough time was obtained. [BuPyr]SCN impregnated on activated carbon cloth have shown higher adsorption performance.