AMMONIUM NITRATE
Flow Conditioner Improves Nitric Acid (NHO3) Production & Savings By Eliminating Hot Spots, Improving Gauze Life & Increasing Conversion Efficiency
Nitric acid is produced in a two-stage process. Ammonia is oxidized with air typically over a rhodium-platinum catalyst to produce nitric oxide. This is followed by the oxidation and absorption of nitric oxide in water to form nitric acid.
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The ammonia oxidation process can be optimized only if a uniform mixture of air and ammonia is presented to the catalyst surface at a uniform velocity over the whole surface. Most converter heads (conical section) have sight-glasses to allow the operator to view the catalyst gauze during production. The presence of hot spots or “flicker” indicates poor performance and excessive catalyst burn-off rates. In-line flow conditioners will provide a sufficiently homogenous mixture and are widely used through the industry. However, the quality of the velocity profile at the catalyst surface has been neglected by most of the producers. Our Flow Conditioners are custom designed to produce the greatest achievable flat velocity profile following an elbow and/or a conical expansion.
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â–º APPLICATION
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The installation of an in-line Flow Conditioner will assure both a uniform linear gas velocity to the catalyst gauze and a uniform temperature profile over the gauze.
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A Flow Conditioner creates a uniform exit flow profile and eliminates back mixing of the fluids. Fluids will obey trajectories and will be distributed uniformly in the expansion eliminating back-mixing and pressure-losses.
â–º SOLUTION
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The Flow Conditioner will be designed for the specific geometry of the application and should be installed before the elbow at the entrance to the reactor, to improve flow around the elbow.
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â–º DESIGN CONSIDERATIONS
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The Flow Conditioners are designed and fabricated such that active dust collection is minimized, which limits pre-gauze oxidation.
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Installing the Flow Conditioners results in no net increase in pressure drop for the system.
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Many different plant designs are employed in the nitric acid industry. Among the plant designs that we have reviewed, the commercial and industrial plant will see the largest benefit from the Flow Conditioners, as they use fewer gauzes in their catalyst packs and they are more sensitive to initial gas distribution.
“Due to the uniform velocity over the entire catalyst surface. These plants are seeing extended on time operation. Usually they come down 4 times year, now were seeing 3 times. One plant said 91% to 97% usage.” –Plant Operator
Ammonium, ammonia plant, NHO3, Nitric Acid, platinum gauze, fertilizer plant, nitrate, chemical plant, platinum catalyst, ammonia reaction
Ammonium, ammonia plant, NHO3, Nitric Acid, platinum gauze, fertilizer plant, nitrate, chemical plant, platinum catalyst, ammonia reaction
Ammonium, ammonia plant, NHO3, Nitric Acid, platinum gauze, fertilizer plant, nitrate, chemical plant, platinum catalyst, ammonia reaction
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A reduction in the linear velocity of the gas will increase the probability of gas impingement onto the catalyst surface. The conversion efficiency of ammonia to nitric oxide is therefore improved.
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As the catalyst burn off rate is reduced, the rate of formation of rhodium oxide is also reduced. Rhodium oxide masks the catalyst surface and slows the conversion of ammonia to nitric oxide.
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Lowering the gas velocity will also reduce the loss of precious metal from the gauze due to erosion.
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The reduction in temperature will slow the evaporation of the platinum.
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The uniform temperature profile will provide more accurate thermocouple readings which will allow better control of the ammonia feed rate.
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Different velocity regions in the air/ammonia feed create higher combustion temperatures. Some producers see melting in the support grid structure which indicates temperatures over 2,000 degrees F and possibly as high as 2,700 degrees F. This implies a need for reduced operating temperature and creating uniform flow profile in order to avoid overfeeding ammonia beyond available oxygen in the air stream.
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Reduced operating temperature implies further extension of gauze life. Lower temperatures reduce the rate of rhodium oxide formation. Rhodium oxide shells mask the catalytic surface and reduce activity by preventing reagents from reaching the surface.
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Lower pressure drop for the system due to the elimination of flow separation in the elbow and in the conical expansion. If the plant is air limited, production can be increased or energy savings on compressor will be realized.
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Some nitric acid is used as an intermediate in the polymer industry, notably in the manufacture of polyamides and polyurethanes.