Cement Energy and Environment

PLEATED FILTERELEMENTS IMPROVE BAGHOUSE PERFORMANCE AT NORTHTEXAS CEMENT" C linker coolers am/ cement mills are traditional sources ofparticulate emission and major pollution ltazards from any operating cement plant. ESP's as well as bag filters am/ dust collectors are used extensively for suppression of dust emission. In recent years considerable improvement has taken place in the efficiency of bag filters fl/1{1 functioning of haglwuses, restricting tlte particulate emission wit/tin negligible levels. Tlte e.\]Jerience ofNorth Texas Cement in improved design of bnglwuse is a good example of very ltiglt efficiency j.· of dust collection from clinker coolers -Ed. Pulse-jet cleaning baghouses are a common form of dust collection onapplications in cement plantsthroughout the world. Clinker coolers, fin ish milis, raw mills, coal milis, silos, transfer points, truck load-outs, bagging stations and pneumatic conveyi.1g systems are only a few of the many areas where pulse-jet dust collectors are in operation. Even though this design ofbaghouse cleaning has many advantages, there are also common problems associated with these dust collection systems used in cement plant applications. Potential challenges include: + Inlet abrasion of filter bags; + Compressed air usage and avai lability; + Em issions caused by poor filtering efficiency of traditional felted media; and + Insu nicient airflow or pick-up draft. Many of these problems are caused by aggressive designs that may have been adequate for past operating conditions, but have since changed. Since the baghouse is already constructed, there are limits to how many filters can be installed, based on the physical size ofthe baghouse. Application background North Texas Cement Co., with its sole plant located in Midlothian, Texas, was having problems associated with one of the three pul se-jet baghouses that ventilate its clinker cooler system. These systems are designated * Courte.sy : Cement Americas, Oct. 1999 as numbers I,2 and 3. All three baghouses contain 864.5- in-diam x 3-ft- long Nomex felt filter bags. Each unit has nine compartments (each with 96 filter bags per cage) and is rated by design at 32,800 acfm with a designed air-to-media ratio of3.63-to 1. During an engineering eva luation visit by BHA in April 1998, North Texas Cement personne l discussed problems they were having with unit No. 3. The unit had extremely poor bag life due to in let, high-velocity abrasion, which would abrade the bottom of the 8-ft– long filter bags. It was reported that an average of 15 to 20 bags were changed out every seven to 14 days due to this condition. This resulted in freq uent and expensive labour, as well as reduc~d air volume during the recuJTi ng filter bag changeouts. After reviewing the system design specifications and operational performance of th is unit, it was noted that one distinct difference between the three co llectors was that unit No. 3 had pyramid design hoppers versus a trough design hopper under unit I and 2. This was a result of initial building design on unit No.3 that would not allow construction of trough design hoppers due to structural support configurations in the area where the bag-house was erected. The pyramid design hoppers are shallow (short) and the inlet duct work was causing the abrasive dust to enter the hopper, resulting in a high-velocity wear area on the wa ll opposite the inlet. A thorough insp~ction confirmed th at there were very apparent abras ion I "zones" within the compartment causing the shortened bag life. 7