Replacement waste heat boilers in plants for the production of nitric acid, formaldehyde and caprolactam
BORSIG Process Heat Exchanger GmbH offers replacement waste heat recovery systems and repairs of boilers that have been delivered by BORSIG or STEINMÜLLER to plants for the production of nitric acid, formaldehyde and caprolactam.
In general Process Gas Coolers / Waste Heat Boilers with integrated reactor are used for the production of nitric acid, caprolactam or formaldehyde.
The feed gas enters the reactor and reacts in the catalyst bed to an intermediate or end product.
The heat released during this reaction is transferred to a coolant (e.g. water) while the process gas is flowing over heating surfaces directly arranged below the catalyst bed.
Waste Heat Boiler Downstream of Ammonia Combustion in Nitric Acid and Caprolactam Plants
Nitric acid is produced by means of catalytic oxidation of ammonia to nitric oxides. The catalyst used is a finely woven platinum gauze with approximately 15 % rhodium. The oxidation is an exothermic process in which the gas is heated to approx. 900 °C. The process operates under a pressure of about 5 bar (500 kPa). The released thermal energy is recovered by cooling the gas to 300 °C, which in turn generates and superheats steam. Superheated steam temperatures of up to 500 °C are possible. The usual steam pressure levels are between 40 bar (4,000 kPa) and 80 bar (8,000 kPa).
The integrated waste heat boiler is of a forced circulation design to ensure the necessary compactness. The heating surfaces are either flat spiral elements or meander coil elements in a square section gas duct. Usually evaporator, superheater and economizer are arranged in one shell. In larger plants, however, the feed water preheating is sometimes outside the waste heat boiler. A different design comprises a spirally coiled superheater in front of an evaporator as a two-pass fire-tube boiler
Waste Heat Boiler Downstream of Dehydration of Methanol in Formaldehyde Plants
Among others, formaldehyde is produced by the „Silver Contact Process“. The feedstock for the reaction is a gas mixture of methanol, water and air. The reaction type is a catalytic oxy-dehydration, which heats the product gas to 600 to 700 °C.
The reactors used to produce the formaldehyde have an integrated waste heat boiler to recover the heat reaction from the gas. Saturated steam is produced when the gas cools down to 150 °C.
The waste heat boiler is designed as a fired-tube boiler. The produced steam will be delivered to the main process. The feedstock enters the reactor in the upper section with the catalyst, the product gas is cooled down in the subsequent tube bundle. Usual steam parameters for pressure and temperature are 20 bar (2,000 kPa) and 200 °C.