The capacity was increased to 525 tons/day by installing the “heat-train” from a larger used nitric acid plant.
This nitric acid plant is designed to produce 500 tons/day in the summer and 540 tons/day in the winter of 65% concentrated nitric acid with less than 0.2% sulfur, less than 0.1% non-volatile matter, and less than 0.1% NO2. This plant is a net steam exporter with 550, 175, and 60 psig steam being produced on various waste-heat boilers and 520 psig steam being consumed by the air compressor steam-turbine drive. The plant can run as low as 300 tons/day of nitric acid production.
A general plant material and energy balance is shown in the table below. However, we have a complete, detailed material and energy balance at various production rates available with the plant electronic process flow diagram package.
Ammonia: 0.3032 tonHydrogen: 919 SCFNatural Gas: 918 SCF500 psig Steam (Export): -2,337 lb25 psig Steam (Export): -307 lb5 psig Steam: 310 lbBoiler Feed Water: 3,697 lbCooling Water: 24.3 M galElectricity: 4.0 KWhrDemin Water: 380 lbNet PT Catalyst Loss: 0.005 Troy Oz.
Ammonia is vaporized, filtered, mixed with air, and fed to the converter. The air is compressed in a two-stage centrifugal Ingersoll-Rand air compressor that is driven by a 520 psig steam turbine and assisted by a tail gas expander. The converter assembly discharges directly to the “heat train”, which consists of the expander gas heater, high-pressure waste heat boiler, tail gas heater, filter, and low-pressure waste heat boiler. The product then goes through the cooler/condenser before entering the lower section of the absorber column.
The air compressor is an Ingersoll-Rand unit with a CVM-4F first body and a CVM-4FIC second body. It has a Terry model GF-4 steam-turbine drive rated for 13,000 hp with a tail gas expander assisting. The tail gas expander is a Dresser-Rand rated for 11,300 hp with 2,970 lb/min gas flow rate. The inlet conditions are 123.9 psia at 1,250°F with a 14.7 psia outlet pressure. We have detailed inspection reports for the compressors and turbines from the most recent 2010 inspection.
The converter is constructed of 304L stainless steel with an Inconel 617 basket. The catalyst composition is 90% platinum, 5% rhodium, and 5% palladium. The mesh size is 80 per linear inch with a 0.003” wire diameter and a 60" overall catalyst gauze diameter. Over 96% of the ammonia is converted under normal operating conditions.
The 304L stainless steel absorber column is 11 feet diameter by 126'-9" tall with 44 sieve trays in the absorber section and five sieve trays in the bleach section. It has 5,875 square feet of cooling area and is rated for 140 psig at 200°F. The column has been tested at 550 tons/day capacity.
The absorber feed water is fed to the top of the column. Weak acid pumps are used with a cooler to circulate weak acid from the bottom to the top of the column for reflux. The column bottoms, which is the 65% nitric acid product, is pumped through a platinum filter, cooled, and then sent to storage.
The absorber column operates at 98% efficiency with the inlet pressure at or below 133 psig. Cooling water flow to the absorber is 5,555 gpm with the flow per cooling coil varying from 12 to 27 gpm. The column overheads return through the tail gas heater and then the expander gas heater in the “heat train”. The heated tailgas is used to make steam in the tail gas high-pressure boiler.
The tail gas then proceeds through the catalytic combustor on its way to drive the tail gas expander. The combustor uses hydrogen and natural gas to react with oxygen and the 2,500 ppm of NOx in the tail gas to produce nitrogen, carbon dioxide, and water. This enables the plant to run less than 3 lbs of NOx emissions per ton of nitric acid product. The stainless steel combustor uses a Sud-Chemie ceramic honeycomb catalyst with platinum and palladium. The vessel is rated for 140 psig at 1,250°F. The catalytic combustor uses less than 1,200 SCF of hydrogen per ton of nitric acid produced. A small amount of natural gas is also used as fuel in the combustor. The natural gas may have some sulfur content, so it is first passed through carbon beds and a desulfurizer for purification.
The nitric acid plant vent stack analysis along with all ammonia fugitive emissions data are available in an environmental report, dated August, 2011. The overall stack emissions are less than 3 lbs of NOx per ton of nitric acid produced.
We have an abundance of electronic documentation available immediately on this Nitric Acid Plant including process flow diagrams with mass and energy balances. Some Aspen modeling of the plant is also available.
Construction and operating details for all of the major equipment are shown in the following table.
Documentation is excellent for this facility, with much being available electronically. Documents include process flow diagrams with mass and energy balances. Some Aspen modeling of the plant is also available.
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