Numerical Simulation of Three-dimensional Heat and Mass Transfer in Spray Cooling of Converter Gas in a Venturi Scrubber

In order to predict the pressure drop, collection efficiency, velocity, temperature and mole fraction of vapor in an industrial venturi scrubber with water spraying for converter gas cooling, a three-dimensional model of heat and mass transfer with phase change is established. The gas flow and liquid droplets are treated as a continuous phase with a Eulerian approach and as a discrete phase with a Lagrangian approach, respectively. The coupled problem of heat, force, and mass transfers between gas flow and liquid droplets is solved by a commercial computational fluid dynamics（CFD） package, FLUENT. The numerical results show that the water injections have an important influence on the distributions of pressure, velocity, temperature, and mole fraction of vapor, especially for the spraying region in the throat. In the spraying region, the pressure drop is higher and the velocity is lower than in other regions due to the gas-droplet drag, while the temperature is lower because the droplet absorbs large amounts of heat from the high temperature gas and the mole fraction of vapor is higher due to the phase change of the liquid droplet. A number of cases with different Water-to-gas volume flow ratios and baffle openings were simulated. The dependence of pressure drop, velocity, temperature, mole fraction of vapor, and collection efficiency on both the water-to-gas volume flow ratio and baffle opening are analyzed. The good agreements between simulation results and experiment data of pressure drop, temperature, and collection efficiency validate the model. The model should facilitate optimization of the venturi scrubber design in order to give better performance with lower pressure drops and higher collection efficiency.

Self-developed Pneumatic Spraying Scrubber for Recovering NO_x from Metallurgical Exhaust

NOx is generally composed of NO,NO2,N2O,N2O4,and N2O5,which may form photochemical smoke and may lead to acid rain,greenhouse effect and destruction of the ozone layer in the atmosphere.In this paper,a new pneumatic spraying scrubber was developed for recovering NOx from metallurgical exhaust.In this device,NOx was converted into nitric acid,which was then recycled in the oxidization reactor.Compared with conventional pneumatic spraying scrubbers,the self-developed pneumatic spraying scrubber had significant advantages,such as the simple structure without liquid circulation pump,easy operation,energy conservation,and the high recovery rate.The influences of various parameters,such as the spray tube height,the spray nozzle diameter,the concentration and temperature of the absorbent,and the operating pressure,on the recovery of NOx were also investigated.The best NOx removal efficiency was 76.08%.When the spray tube height was 0.74 m,the nozzle diameter was 0.5 mm,the absorbent content was 5%at 30℃,and the operating pressure was 0.15-0.17 MPa.The invented pneumatic spraying scrubber successfully solves the problems of high-concentration NOx absorption and regeneration of nitric acid.In addition,the device can also absorb other harmful gases and provide a possible new treatment process for air pollution control.

Removing ammonia from air with a constant pH, slightly acidic water spray wet scrubber using recycled scrubbing solution

Previous research on wet scrubbers has only studied highly acidic scrubbing solutions because of their high ammonia capture efficiencies; however, the high acidity created practical problems. Lower acidity solutions would reduce corrosion, maintenance, and cost; however, designers may need to use strategies for increasing scrubber effectiveness, such as using lower air velocities. The objective of this studywas to determine if a spray scrubber with slightly acidic and higher p H scrubbing solution （pH from 2 to 8） could effectively remove NH3 from NH3 laden air （such as animal building exhaust air）, and also collect this valuable resource for rater use as a fertilizer. A bench-scale spray wet scrubber treated 20 ppmv NH3/air mixture in a countercurrent contact chamber. First, the solution pH was varied from 2 to 8while maintaining constant air velocity at 1.3 m. s-1. Next, air velocity was increased （2and 3 m.s-1） while solution pH remained constant at pH6. At 1.3 m.s -1, NH3 removal efficiencies ranged between 49.0% （pH8） and 84.3% （pH2）. This study has shown that slightly acidic scrubbing solutions are a practical means of removing ammonia from air especially if the scrubber is designed to increase collisions between solution droplets and NH3 molecules. The NH3 removed from the air was held in solution as NH4＋ and accumulates over time so the solution should be an excellent fertilizer.