Measures to Improve the Efficiency of Vacuum Drum Filter

Rotray Drum Screen September 24, 2022 Vacuum Drum Filter

Background:

Refineries require vacuum drum filters for lube solvent dewaxing and wax solvent deoiling processes. However, due to the long operating years, there are often problems of poor wax scraping and decreased filtering capacity. To this end, this article introduces some measures to deal with the problem of filter efficiency decline.

The working process of the vacuum drum filter includes five steps: filtration, washing, drying, wax removal and cold backwashing. When the drum rotates, the lower part of the drum is immersed in the filtrate liquid after cooling treatment. At this time, several compartments are transferred into the filtrate liquid. These compartments are connected to the vacuum suction area of the dispensing head. In the case of suction, the dewaxed oil and solvent are concentrated into the vacuum filter tank through the filter cloth, grille, collecting pipe and distribution head, and the crystallized wax is adsorbed on the outer surface of the filter cloth and forms a wax cake. The drum rotates to leave the filtration area, is washed with mineral spirits to remove most of the oil in the wax, and
in the drying area, the washing liquid and the oil in the wax are further pumped out by vacuum to dry and solidify the wax, and then blow back with inert gas to make the wax cake separate from the filter cloth, and then fall into the spiral wax conveyer through the scraper to send the wax paste out of the vacuum drum filter outside.

1. Problems and solutions of filter cloth:
The filter cloth is the main component of the filter. If a lot of colloid and wax paste are attached to the filter cloth, the air permeability of the filter cloth will decrease, which will directly affect the efficiency of the filter. For this reason, the filter cloth is required to be cleaned at least once per shift, and the damaged filter cloth should be repaired or replaced in time, so that the filter cloth is always in good working condition to ensure the stable efficiency of the filter.

2. Problems and solutions of scraper gap:
Since the out-of-roundness of the drum cannot be adjusted on site, the gap between the scraper and the drum cannot be adjusted to the best state. If the gap between the scraper and the drum is too small, the scraper will contact the filter cloth, causing the filter cloth to be damaged prematurely, so the gap between the drum and the scraper can only be increased. At this time, the filter cake on the drum can only be blown by the blowback pressure. From the drum, if the pressure of the backflush is low, part of the filter cake is returned to the filtrate liquid, which reduces the efficiency of the filter. In response to this problem, it is necessary to adopt a method of adjusting the gap between each scraper and the drum in a single group, so that the optimal gap between each group of scrapers and the drum is maintained, so as to improve the
filter efficiency.

3. Problems and solutions of sprinkler system:
The spraying system includes a spraying part arranged in the washing area and the drip portion of the highest point of spraying part arranged in the upper casing. According to the process requirements, when the drum is transferred to the washing area, the spray nozzle on the shower pipe should spray the mist-like washing liquid and spray it evenly on the wax cake. According to our experience: the filtering spray and dripping liquid in the ketone and benzene workshop and the wax deoiling workshop are non-uniform mist spraying and dripping. In some locations, the flow of washing liquid is large, and a large amount of washing liquid washes the wax cake from the filter cloth down the outer circle of the drum and return to the filtrate liquid; there are also some positions, washing can rarely wash out the oil in the wax cake, resulting in an increase in the oil content in the wax cake and a decrease in the filter efficiency. In response to this situation, both the washing nozzle and the drip tube need to be adjusted.