For the textile industry, heating is a process that is essential in production but produces pollution. After dyeing or printing, the textile must be dried to 300-400. In this temperature range, the oil and wax will volatilize and evaporate, and then be cooled to the dew point. The suspended dust particles of the sub-micron oil droplets are blue-grey. Smoke appears. Due to the high visibility and odor of the smoke, the pollution control agency has ordered a reduction in such pollution.
The visibility of emissions in most pollution control regulations is the most difficult to achieve, and most exhaust gases have an opacity of 40 to 60 before control. Today, environmental agencies generally require an invisible stream of smoke, that is, opacity below 5. In addition, any visible volatiles can cause odors, discomfort and disease to the surrounding community. A wide range of smoke removal systems can control this problem, including afterburners, wet gas scrubbers and fiber layer filters. After considering the use of energy, operating costs and maintenance factors, many textile companies are turning to electronic dust collectors.
The afterburner is a smoke incinerator that heats the exhaust gas to a combustion temperature of 1500 in half a second. The main disadvantage of the afterburner system is the high cost, not only the initial equipment is expensive, but also because of the need to generate high heat and high running costs. For example, processing 10,000 cubic feet per minute of exhaust gas requires 1.4 x 106 BUT/h.
Different principles of wet gas scrubbers have long been used for textile soot elimination and have achieved varying degrees of success. Since the smoke molecules are very small and require a lot of energy to be removed from the air stream, the oil agent is insoluble in Water, so low pressure drop or low energy scrubbers are generally not satisfactory in this application. First, the working principle of the aerosol trap type scrubber is that the smoke molecules are captured when they hit the water surface, but the large amount of submicron particles cannot be removed because these fine molecules move with the air and escape from the water surface. Second, the literary tube scrubber is generally a high-energy system. If there is enough pressure difference, it may have 40 inches of water to 70 inches of water to meet the current dust removal requirements. For a device with a processing capacity of 10,000 cubic feet per minute, the power required to achieve a sufficiently high differential pressure is 200 horsepower.
In addition to these problems, one major limitation of the wet gas scrubber is that it produces an opaque condensate column (or vapor stream) just like the visible blue-gray oil mist. Although these water columns are usually forbidden, they cause people to pay attention to the exhaust gas chimney, causing deeper complaints and dissatisfaction about the odor and discomfort.
The fiber bed filter is a 10 ft to 20 ft long cylindrical filter composed of very fine fibers, and the oil droplets are trapped by the filter as the exhaust gas passes through the filter. Fiber bed filters are best suited for handling relatively low oil mist levels and for the absence of solids.
Both high static pressure loss systems and low static pressure loss systems have their own high cost. High static pressure loss systems have high operating costs, low static pressure loss systems have high initial costs, and installation costs are often high due to the volume and weight of these systems.
The daily maintenance of fiber bed filters is more problematic than other systems, the cost of which depends on the amount of fiber layer adsorbed and the type of oil and other materials that are adhered. However, if the adherent has an oil agent, a waxy substance, or an oil agent is polymerized and oxidized, the cleaning or replacement cost is quite high. Another important maintenance factor is processing because the waste filtration must be disposed of at a hazardous waste plant.
Compared with the above systems, electrostatic precipitators have many characteristics and are attractive to textile companies in dealing with smoke and odor. An important advantage of electrostatic precipitators is that they can remove submicron smoke particles with very little energy, and the static pressure loss after passing through the precipitator is less than 1 inch of water column, and the cost of electricity is also low. Another important advantage of electrostatic precipitators is that the adsorption efficiency of submicron particles is quite high, in fact the efficiency can reach more than 90.
The electrostatic precipitators of the two types (dry and wet) work in the same way, ie an anion is produced and then attached to the smoke particles, causing the smoke particles to be negatively charged; in turn, the negatively charged smoke particles are positively charged. The trap is attracted. Dry film electrostatic precipitators have a long history and are recommended for use in continuous operation.
For wet-tube electrostatic precipitators, a measure to increase efficiency is that the exhaust stream is wetted by water before reaching the trap. This has several effects: first, cooling the airflow, turning more steam into Submicron particles of smoke to remove more contaminants from the exhaust and reduce condensation of contaminants before they reach the trap.
Secondly, the water helps keep the system clean. Just like cleaning, the water accumulates in the pipe, the water droplets become heavier and heavier, eventually falling, and the pipe is rinsed to a certain extent. Daily maintenance is always needed because only the built-in cleaning head simply flushes the trap, but it doesn't have to be as clean as other systems.
In addition, cooling the exhaust gas can eliminate some odors. Electrostatic precipitators must be condensed as odor-eliminating devices. Textile printing and finishing are usually carried out at temperatures below 20, which can eliminate smog and remove odors from lubricating oil or plasticizer fumes.
Please note that for some substances with low boiling points, there is still some odor even if the smoke is removed.
The advantage of the wet pipe electrostatic precipitator system is that the precipitator assembly can be connected to some exhaust gas exhaust stacks, and even to a plurality of drying ovens or tenters, so that the dust removal of multiple drying ovens or tenters can be simultaneously processed. And the production company also eliminates the trouble and cost of installing a smoke suppression system for each drying oven or tenter.
The final choice of smoke eliminator is still subject to the company's needs, processing parameters and local pollution prevention agency regulations. Moreover, if the analysis of all parameters is complicated, the cost of improper selection of the system will be expensive. It is recommended to accept the services of design engineering companies familiar with the textile smoke removal system, but it is worth mentioning that the fact that the unique properties of wet pipe electrostatic precipitators can bring significant benefits to textile manufacturers is obvious.
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