Cleaning frequency

Determinants of baghouse performance include the fabric chosen, the cleaning frequency and methods, and the particulate characteristics. Fabrics can be chosen which will intercept a greater fraction of particulate and some fabrics are coated with a membrane with very fine openings for enhanced removal of submicron particulate. Such fabrics tend to be more expensive. 

As discussed in the preceding section, filter bags must be periodically cleaned to prevent excessive build-up of dust and to maintain an acceptable pressure drop across the filters. Two of the three designs discussed, reverse-flow and reverse-pulse, depend on an adequate supply of clean air or gas to provide this periodic cleaning. Two factors are critical in these systems the clean-gas supply and the proper cleaning frequency. 

Proper operation of a baghouse, regardless of design, depends on frequent cleaning of the filter media. The system is designed to operate within a specific range of pressure drops that defines clean and fully-loaded filter media. The cleaning frequency must assure that the maximum recommended pressure drop is not exceeded. 

This can be a real problem for baghouses that rely on automatic timers to control cleaning frequency. The use of a timing function to control cleaning frequency is not recommended unless the dust load is known to be consistent. A better approach is to use differential-pressure gages to physically measure the pressure drop across the filter media to trigger the cleaning process based on preset limits. 

As previously indicated, most bag-type filters require a pre-coat of particulates before they can effectively remove airborne contaminates. However, particles can completely block air flow if the filter material becomes overloaded. Therefore, the primary operating criterion is to maintain the efficiency of the filter media by controlling the cleaning frequency. 

Most systems use a time-sequence to control the cleaning frequency. If the particulate load entering the bag-house is constant, this approach would be valid. However, the incoming load generally changes constantly. As a result, the straight time-sequence methodology does not provide the most efficient mode of operation. 

The typical factors to consider when pondering B2C will include size and scale of operation, use of existing equipment, flexibility for multiproduct operation, start-up and shutdown, cleaning frequency, inventory, validation, traceability of product with respect to raw materials, equipment design, and availability as well as operational experience [50]. 

Frequent mould cleaning is essential in long-run production to ensure good product appearance. The cleaning frequency is dependent on the application of the components being manufactured, the type of compound being processed and the temperature of vulcanisation. 

Conserve water. Reuse rinse waters if possible. Reduce equipment-cleaning frequency where beneficial in reducing net waste generation. 

Membrane pretreatment can improve the feed water quality and reduce particulate matter to a greater degree than other pretreatment methods. This reduces the required cleaning frequency of the downstream membranes and the amount of cleaning chemicals that are required and subsequently disposed of (Pearce 2007). 

The determination of the quantity 4, the fractional increase in cleaning frequency due to particulate matter, is the difficult part of the problem. The data of chelson and Tourin (cited in Spence and Haynie ) suggest a value of v for paint of 1.5/yr. The value of Q is obtained as follows According to Noble, the annual production of paint in 1968 was 2.59 billion. Because the economic life of paint is considered to be 4 yr, 10.36 billion worth of paint is in place, of which only 70% is exposed to atmospheric pollutants. Thus, 7.25 billion is the manufacturers value of in-place paint exposed to air pollution. Using a labor factor of 3.3, the total in-place value of paint is 23.9 billion. Because i - 1.5 for particulate soiling, the cost of pollution damage (cleaning costs) is some 36 billion/yr. 

The following general guidelines for filter cleaning frequency and duration are recommended. 

Cartridge filters These offer continuous processing and require cleaning frequency of 10-30 seconds. 

The cleaning frequency and cleaning duration is now offered as an automated system where instead of having base the cleaning frequency on time, the trigger point for filter cleaning is the buildup of a pressure drop across the filters. This automates the process and eliminates operator input. 

Membrane cleaning frequency. RO systems that require more than four cleanings per year have a membrane fouling and/or scaling problem. 

If the membranes do foul or scale, they can often be cleaned. A typical cleaning frequency is once per year. Cleaners include... 

HERO—High-Efficiency RO Process Boosts Recovery Ratios, Cuts Cleaning Frequency," GE Water Process Technologies, www. gewater.com/products/equipment/spiral membrane/HERO.jsp... 

A primary objective of these waste-minimization efforts has been to reduce the quantity and/or the toxicity of the waste. For equipment-cleaning residues, this can be done, as outlined here, by determining Why is the deposit present and how was it formed How can cleaning frequency be reduced Which cleaning method and medium will generate the least amount of the least-toxic waste when cleaning is unavoidable ... 

Cleaning is needed because deposits form on the surfaces exposed to the process (Table I). Understanding how and why these deposits are formed, one can concentrate on reducing cleaning frequency, and reducing the quantity and toxicity of cleaning waste. 

The type of exchanger influences cleaning frequency. For example, spiral-plate units are often used in fermentation plants, owing to the ease of solid resuspension and the devices nonplugging characteristics. A rod-baffle design provides more-effective shellside turbulence at a lower pressure drop than a segmented-baffle unit, so the former is likely to have less fouling. 

Dedicating equipment to one function or formulation also reduces cleaning frequency. Dedication can be maximized by converting from a batch to a continuous process, or by using the unit intermittently for just one product. 

This is another way to decrease cleaning frequency. Equipment-utilization strategies and the resulting production schedules should meet the desired production goals, with due consideration of such constraints as available equipment, cost of turnaround, labor availability, and storage, and at the same time minimizing cleaning frequency. 

MF and UF used in pretreatment to RO are more frequently cleaned by physical cleaning and less frequently by chemical cleaning. Cleaning frequencies reported in ht-erahire varied widely. Physical cleaning frequency is approximately every 40 min with a chemical clean scheduled every 6 mo (98). An air backwash frequency of 15-20 min is sufficient for hollow-fiber MF membranes (77). In a UF evaluation study, backwashing was able to achieve an average flux recovery of 86.5% (99). It was observed in the same study that flux restoration could be achieved even when backwash was reduced from 10 to 1 min. 

The slits in the distribution header are designed to be essentially self-cleaning, and the accumulation of insolubles and precipitates does not constitute as serious a problem as it does in a downflow saturator. Cleaning frequency of the distribution header will depend on the usage and amount debris accumulated in the saturator. 

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