Pressure pulse cleaning

Each filter has demonstrated the capacity to filter the full brine flow of 195 m3 h 1. The pressure drop through the filter medium is measured and monitored continuously. Typically, it is nearly constant over a 2-h filtration at 195 m3 h 1. Back-pulse cleaning restores the initial pressure drop from cycle to cycle, with only a slow increase over time. After 12 months running time, the initial pressure drop at the beginning of the filter cycle had increased by 0.6 bar. The filter membranes were chemically cleaned with 5 % hydrochloric acid. After a cleaning time of 2 h the filter was started again and the pressure drop was less than 0.1 bar greater than that of new filter socks. 

Description The clean tubular reactor (CTR) process is characterized by a nonfouling reactor for all grades. This is realized without pressure pulsing hence, constant pressure and temperature profiles produce a more consistent and better quality product. Also, the absence of mechanical fatigue and decompositions are important features. 

For a low and stable conditioned pressure loss, successful pulse cleaning of the filter is clearly essential. There are two parts to this problem i) the geometry and reservoir pressure of the cleaning system must be selected to deliver the required conditions for dust cake removal at the filter surface, and ii) the magnitude of the cleaning action which is necessary to detach the cake must be known. 

When the filter cake has built up to a thickness whereby resistance over the filter has reached its desired maximum value. The fitter is cleaned by stopping circulation and transmitting a short pressure pulse, with duration of only a few milliseconds, into the filter element in the reverse direction to normal flow. The pressure wave fluidizes the sand and the sand moves slightly horizontally between the louvers. As a result, some of the sand together with the filter cake falls from the filter element, thereby cleaning the filter surface. The mixture of dust and sand is precipitated into a hopper for dust separation and sand recirculation. 

Three bulk (candle pieces) exposures at 850°C with and without water vapour were completed to cause microstructural changes in order to find out their possible role in changes in mechanical properties of materials. The coding and conditions of the bulk exposures are described in Table 1. The water vapour pressure in the exposures corresponded to the atmospheric pressure. Thermal cycling between 150 and 400 °C was done without water vapour in order to see the effect of thermal shock caused by back pulse cleaning and the phase transformation of silica. 

Cleaning by reverse-flow pulses of high pressure air is normally applied to fabric filters and to pleated cartridge collectors alike. The high pressure pulses may be created by a pressure blower or come directly from a compressed air supply. In the latter case the type is normally called a pulse-jet filter. 

Some manufacturers are using relatively low-pressure air (100 kPa, or 15 Ibfiin", instead of 690 kPa, or 100 Ibf/in") and are eliminating the venturi tubes for clean-gas induction. Others have eliminated the separate jet nozzles located at the individual bags and use a single jet to inject a pulse into the outlet-gas plenum. 

Air cleaning (dust collection) can be cost effective for LVHV systems handling valuable dusts. Care must be taken when handling potentially toxic dusts from air cleaners. Regular, routine reconditioning of fabric filters (e.g., by automatic shaking or pneumatic pulsing) is impottant. This can be accomplished on a set maintenance schedule or as a function of pressure drop across the fabric filter. It is not recommended to recirculate airflow back to the workplace because of the low air volume and potential hazards in the event of filter failures. 

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. 

In reverse-pulse applications, most plants rely on plant-air systems as the source for the high-velocity pulses required for cleaning. In many cases, however, the plant-air system is not sufficient for this purpose. Although the pulses required are short (i.e., 100 milliseconds or less), the number and frequency can deplete the supply. Therefore, care must be taken to ensure that both sufficient volume and pressure are available to achieve proper cleaning. 

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