Large Volume Inorganic Chemicals - Ammonia ... - ammk-rks.net

Chapter77.4.6 Recycling warm airDescriptionThe traditional practice for handling exhaust air from the product cooler (and equipment vents)was to send it through a scrubber system. However, it is not necessary or efficient to use a wetrecovery system. The preferred option is to first take this warm air (about 60 – 65 ºC, and about40000 m 3 /hour) and use a fabric filter or high efficiency cyclones to recover the dust. After dustremoval, the warm air is then recycled as dilution air to the dryer combustion system, replacingambient air. Good experience has been reported in a number of plants that have switched to thistype of system. This system has proven feasible in both dry (Western US) and humid (US GulfCoast) climates, however, the moisture content of the recycled air is a sensitive factor that mustbe carefully evaluated.Figure 7.4 gives an overview of the change over from the conventional setup to the optimisedsetup. Primary components of this revised configuration are as follows:• removal of old equipment and ductwork• new fabric filter (or high efficiency cyclones)• new “recycle air” fan (if the existing unit is not available or not sufficient)• revised ductwork.H 2 OEmissionto airConventionalScrubbingsystemScrubber effluent toreaction systemExhaust gasfrom coolerOptimisedFabricfilterWarm air to dryercombustionCycloneExhaust gasfrom equipmentventDustRecycle toprocessFigure 7.4: Overview of the recycling of warm air[54, Snyder, 2003]Achieved environmental benefitsIn general, a dry recovery system is expected to be a simplified, more efficient operation withreduced pluggage, corrosion, and resultant maintenance. Specific benefits from a warm airrecycle system are as follows:Large Volume Inorganic Chemicals – Ammonia, Acids and Fertilisers 307