Packed towers maintenance

Rendering plants Feedstock storage and housekeeping Cookers and percolators Grinding Odors SO2, mercaptans, ammonia, odors Particulates (dust) Quick processing, washdown of all concrete surfaces, paving of dirt roads, proper sewer maintenance, enclosure, packed towers Exhaust system, condenser, scrubber, or incinerator Exhaust system and scrubber... 

Case Study 1. Pump-and-Treat System with a Packed-Tower Air Stripper, McClellan Air Force Base Superfund Site, California, Operable Units B/C, 1987. The costs associated with pump-and-treat system used at the site were estimated in 1994. Costs were approximately 80 per pound of removed volatile organic compounds (VOCs) based on operating costs alone and approximately 150 per pound when capital costs were included (D141286, p. 135). It should be noted that the operation and maintenance costs for the an air stripper could not be separated from the total cost of the project. Capital cost and operating cost information for this project are summarized in Case Study 1. 

The main factors favoring packed columns are (1) very corrosive applications, where plastic or ceramic packings are favored over trays, which are almost always constructed of metal (2) low pressure drop requirement, which is easier to achieve with packings than with trays (3) small-diameter columns, because trays require access for inspection and maintenance and (4) foaming systems, which are easier to handle in packed towers. 

The use of ozone os on oxidant for industrial wastes containing cyanides and other reducible toxic substances appears worthy of careful investigation. The oxidation of simple cyanides by ozone is rapid and complete. Mass transfer controls the absorption. The use of packed towers or sieve plate towers is indicated, and the maintenance of a pH of at least 9.0 is recommended. The destruction of cyanates and cyanide complexes is slower than the cyanide oxidation. These substances are destroyed if sufficient contact time and proper pH control are maintained so that these slower reactions can take place. The use of redox potential to control the degree of oxidation appears promising. Proper interpretation of the redox potential of the treated waste will give an excellent indication of the effectiveness of the treatment and the degree of removal of cyanide and cyanate. 

The packed-bed scrubber (PBS), a major type of wet scrubber applied as the APC in waste combustion systems, is not considered a PM control device, especially for submicrometer particulates. The major problems in using packed-bed scrubbers for particulate removal are plugging of the packing and the maintenance problems subsequently incurred. A general rule of thumb is to allow a maximum of 0.2 g/ft of dust to enter a packed tower. 

Tower maintenance is usually limited to removal of exterior items (e.g., relief or control vi ves) and interior components (e.g., trays or packing rings). Han-... 

For example, heat-transfer surfaces foul, packed towers develop channels, catalysts lose activity, and bearings on pumps and compressors become worn. Plants are shut down periodically for maintenance to restore equipment performance. 

Maintenance and production records, along with the used lean and rich glycol analyses, can be very helpful to the troubleshooter. A history of filter element, carbon, tower packing, and firetube changeouts can sometimes be very revealing. The frequency of pump repairs and chemical cleaning jobs is also beneficial. With this type of knowledge, the troubleshooter can quickly eliminate and prevent costly problems. 

A 2-ft tower would be expected to perform satisfactorily with properly designed trays. However, a 2.5-ft tower is the minimum diameter suitable for internal inspection and maintenance. The cost of a tray tower of 2.5-ft has been found to be no more, and from some bids 5 percent less, than the smaller 2-ft. tower. A 2-ft. tower would either be used with packing or with trays inserted from the top on rods with spacers. This would allow removal of the trays for inspection and maintenance. 

Some other representative cost relationships can also be found in this reference (12), but these cannot be used as a substitute for data from the supplier. In general, the equipment costs include the following components fans, water pumps to dehver the water to the top of the tower, tower structure and packing, exterior covering, and electrical installation. The principal operating and maintenance costs are electrical power for pumping water and air, operating and maintenance labor, and chemicals to raise the pH. 

Packed-bed towers can achieve removal efficiencies of over 99% and have relatively lower water consumption requirements. They also offer design and retrofit flexibility. Disadvantages include high system pressure drops, relatively high clogging and fouling potential, potentially high maintenance costs, and waste water disposal requirements. Packed-bed scrubbers are also more expensive to install and operate than spray towers. 

The space required for installation of the unit and for maintenance activities later on should be clearly indicated in the offer. This may include cleaning and replacement of internal tubes, tower packing, impellers of blower, replacement of belt drive pulleys, etc. 

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