Baghouses systems

Lime kilns dust emissions are controlled by baghouse systems. Kiln fuels can be selected to reduce SO, emissions however, this is not normally a problem, since most of the sulfur dioxide that is formed is absorbed in the kiln. 

A baghouse system consists of the following pneumatic-conveyor system, filter media, a back-flush cleaning system, and a fan or blower to provide airflow. 

Since these units provide the motive power required to transport and collect the dust-laden air, their operating condition is critical to the baghouse system. The type and size of air-moving unit varies with the baghouse type and design. 

The primary measure of baghouse-system performance is its ability to consistently remove dust and other particulate matter from the dirty-air stream. Pressure drop and collection efficiency determine the effectiveness of these systems. 

Most baghouse systems are provided as complete assemblies by the vendor. While the unit may require some field assembly, the vendor generally provides the structural supports, which in most cases are adequate. The only controllable installation factors that may affect performance are the foundation and connections to pneumatic conveyors and other supply systems. 

Baghouse systems efficiently control particulate emissions from grinding and blending processes. Vents from feed hoppers, crushers, pulverizers, blenders, mills, and cyclones are typically routed to baghouses for product recovery. This method is preferable to using wet scrubbers. However, even scrubber effluent can be largely eliminated by recirculation. 

Because of the draft limitations on the baghouse, the melt furnace firing rate had to be maintained at a reduced rate, which limited metal output. Time constraints and economics precluded upgrading the baghouse system to accommodate the combined dust and fume loads from the melting furnace and dross reclamation systems. 

Dust accumulated on the outside of the bags, when blown off the bag surface, falls into the hopper at the base of the baghouse. A large proportion of baghouse systems use a pulse jet blow-back (Figure 3.44), in which each bag has a separate valve from a compressed air supply above it, so that any bag can be blown free of... 

Air cleaning systems are often used to remove dust or vapors from plant or process exhaust streams. Dust collecting systems such as filters or electrostatic precipitators that handle heavy loads of dust are usually designed to be self-cleaning, but it is stiU. necessary to enter the air cleaner periodically for inspection or repair. Dust deposits inside the equipment are likely to be stirred up and inhaled by unprotected workers. Baghouses are particularly likely to cause exposure because large amounts of dust may be retained in the cloth and released when the bags are handled. 

Gases from the furnace, metal tap, slag tap, and feed system are combined and fed to a sis-ceU pulse baghouse containing 864 high temperature Teflon bags. The dust from the electric furnace system is fed continuously back to the reverberatory furnace in a close screw conveyor. 

The high temperatures in the MHD combustion system mean that no complex organic compounds should be present in the combustion products. Gas chromatograph/mass spectrometer analysis of radiant furnace slag and ESP/baghouse composite, down to the part per biUion level, confirms this behef (53). With respect to inorganic priority pollutants, except for mercury, concentrations in MHD-derived fly-ash are expected to be lower than from conventional coal-fired plants. More complete discussion of this topic can be found in References 53 and 63. 

Dry-Throwaway Processes. Dry-throwaway systems were the precursor of processes that removed SO2 iu the ductwork, eg, the BCZ and IDS processes. Here, however, the device is a spray chamber similar to the wet scmbbers such as the three modules of the Colstrip iastallation (Fig. 12). Into the upper portion of the chamber a slurry or clear solution containing sorbent is sprayed. Water evaporates from the droplets, the sorbent reacts with SO2 both before and after drying, and the dry product is removed ia a downstream baghouse or ESP (72). Unfortunately, dry scmbbiag is much less efficient than wet scmbbiag and lime, iastead of the much less expensive limestone, is required to remove SO2 effectively. Consequentiy, a search has been conducted for more reactive sorbents (72—75). 

Dried product is collected in either cyclones or baghouses depending upon the product-particle size. When primary coUection is carried out in cyclones, secondary collection in a baghouse or scrubber is usually necessary in order to comply with environmental regulations. A rotary valve is used to provide an airlock at the discharge point. Screws are utihzed to combine product from multiple cyclones or large bag-houses. If required, a portion of the dried product is separated from the main stream and returned to the feed system for use as backmix. 

Aluminum reduction plants Materials handling Buckets and belt Conveyor or pneumatic conveyor Anode and cathode electrode preparation Cathode (haldng) Anode (grinding and blending) Particulates (dust) Hydrocarbon emissions from binder Particulates (dust) Exhaust systems and baghouse Exhaust systems and mechanical collectors... 

Asphalt plants Materials handling, storage and classifiers elevators, chutes, vibrating screens Particulates (dust) Wetting exhaust systems with a scrubber or baghouse... 

Drying rotary oil- or gas-fired Particulates, SO2, NO, VOC, CO, and smoke Proper combustion controls, fuel-oil preheating where required local exhaust system, cyclone and a scrubber or baghouse... 

Dry processes materials handling, air separator (hot-air furnace) Particulates (dust) Local exhaust system with mechanical collectors and baghouse... 

Granulation Particulates (dust)(product recovery) Exhaust system, scrubber, or baghouse... 

Pouring Zinc oxide fume, lead oxide fume cover high-zinc-content brass use of good combustion controls, local exhaust system, and baghouse or... 

---