Читать книгу Encyclopedia of Renewable Energy - James Speight G., James G. Speight - Страница 93

Ammonia is a valuable chemical that is often produced from renewable sources (biomass) that contain nitrogen. It is recoverable from both the liquid and gas streams and can be readily separated from the liquid, by an ammonia still. The fixed salts must be treated with lime or caustic in a lime leg. The gaseous ammonia may be absorbed with sulfuric acid to produce ammonium sulfate, processed to anhydrous ammonia, or destroyed by combustion.

The standard procedure for the manufacture of ammonium sulfate from a gas stream involves several steps. The gas is first cooled to approximately 32°C (90°F) in an appropriate condensation system. Any tar, which is a very troublesome contaminant of ammonium sulfate (and vice versa), condenses and, in addition, much of the water containing approximately 25% of the ammonia (NH₃), primarily as ammonium (NH₄+) salts, also condenses. This water is rendered basic (lime treatment), thereby converting the ammonium ion to ammonia, which is recovered by being stripped off in a lime still and placed back in the coal gas stream. The coal gas stream is heated to above its dew point (approximately 65°C; 150°F), and the ammonia is adsorbed in 5 to 10% sulfuric acid solution contained in a lead-lined saturator at a temperature of 50 to 60°C (120 to 140°F); ammonium sulfate crystals precipitate from the sulfuric acid solution.

See also: Petrochemicals.