1. Introduction
Cartridge dust collectors have been widely used to collect the dust generated from the production process in many fields such as metallurgy, chemical industry, electric power, and machinery because of their significant advantages such as high fold ratio, large filtration area, and high space utilization efficiency [
1,
2,
3]. Generally, the circular filter cartridge is more widely used as its cleaning method and principle are consistent with the bag filter, which can better ensure the cleaning effect in the present stage [
4]. The rectangular flat pleated filter, which was proposed in recent years, has attracted more and more attention. The square structure enables the rectangular flat pleated filter to have a greater space utilization efficiency and better operation convenience, especially for the situation of limited space [
5,
6,
7]. However, despite the many advantages of the rectangular cartridge, it has not yet been used on a large scale, such as in China [
8,
9,
10]. This is because its dust removal control is essentially different from that of the circular filter cartridge or filter bag, and its poor dust removal performance is currently the main reason that restricts its wide-range application [
11,
12]. A reasonable cleaning method and revealing the relationship between various cleaning parameters and cleaning effects are effective means of improving its cleaning performance, which is of great significance to promote its wide-range application, solve the problem of dust cleaning inside the confined space, ensure the occupational health of workers, and protect the environment [
13,
14].
The rectangular flat pleated filter is currently in the primary application stage, and the research on its cleaning performance is relatively small. In fact, the parameters, such as the structure and size of the blowing hole, are important factors that have an impact on the deashing performance, especially on the uniformity of the deashing [
15,
16]. Chen comparatively studied the effect of dust discharge and system pressure drop of a flat square filter cartridge in the deashing performance by using slotted and round-holed nozzles, respectively; the experiment proved that the slotted nozzle had a better deashing performance [
17]. Zhang et al. studied the relationships between the solenoid valve, opening hole type, blowing distance, blowing pressure, and value distribution of the side wall pressure on the self-built pulse blowing test bench [
18]. Kang designed a new type of slotted nozzle for ash removing from the rectangular flat pleated filter and comparatively studied its ash removing performance with that of the round-holed nozzle; the results showed that the slotted nozzle had a better deashing performance, but there is still a problem of uneven distribution of air flow in each injection hole [
19]. Li proposed a new kind of deashing method named the colliding pulse jet technique for dust filter cleaning. The results showed that the performance of ash removal by the collision jet without time interval was improved, but there was a problem of high gas consumption [
20]. The study by Li et al., using the methods of theoretical calculation, numerical simulation, and industrial coating experiments, demonstrated that: (1) the size of the slot nozzle has an effect on the cleaning effect; (2) 40~60% of dust usually remained located in the upper part of the filter bag which is not directly facing the nozzle hole; and (3) gas-solid concentration and pulse interval have little effect on the cleaning effect. Many achievements have been made, but the systematic disclosure of the relationship between the parameters and the cleaning effect of dust is still lacking, especially for the study of multiple holes on the same spray pipe, which generally adopts the designer’s experience value in the actual industry [
21].
One important issue focused on in this work was to demonstrate the mechanism and improve the situation of ash heavily accumulating at the bottom. This problem arose because the upper and lower sections of the rectangular cylinder are fixed, where they are weakened by the shock effect of pulsed back-blowing air, resulting in serious powder trapping at both ends of the cylinder and dust accumulation at the bottom due to the action of gravity. In this work, non-coated and coated powder tests were both carried out. The parameters, including the nozzle number, pulse pressure, jet distance, filtration velocity, dust mass concentration, were investigated to observe the effects on the system resistance, and the residual amount of dust was used to recognize the dust cleaning performance. Then, a numerical simulation was conducted to demonstrate the mechanism of the dust removing process. Last, a continuous industrial test was conducted to confirm the effect of the optimal combined condition of dust cleaning obtained in this study and identify the continuous service life of the rectangular filter cartridge under this combined condition. The objective of this paper is to provide an efficient method for controlling the ash cleaning parameters to obtain a good performance of ash cleaning, promoting the application of the rectangular flat pleated filter.
4. Conclusions
In this work, the impact factor, regulation, and performance of dust cleaning from flat box cartridge filters were studied. Dust cleaning experiments without dust coating, observing dust cleaning mechanisms by simulation, and industrial coating tests were carried out. Four conclusions could be stated:
(1) The peak pressure of the pulse air flow formed by the two-slit blowhole (2 × 99 mm) and five-slit blowhole (5 × 40 mm) in the upper part of the filter cylinder that is not directly against the blowhole cannot reach the pressure requirement of ash removal. The performance of dust cleaning produced by the three-slit blowhole (3 × 66 mm) is better than that of the four-slit blowhole (4 × 50 mm) from the aspect of raising the peak pressure of the non-positive-to blow area, and its optimal blowing distance is 20 mm.
(2) Higher blowing pressure can result in higher average surface side wall peak pressure. However, the higher peak pressure also results in more energy consumption and more serious wear and tear of filter materials. The optimal blowing pressure was determined as 0.2 MPa.
(3) Under the optimal condition of a 0.2 MPa blowing pressure, 20 mm blowing distance, and three-slit blowhole, the results from the industrial coating tests show that the system runs stably, the running resistance is relatively low, and the dust removing performance is good. At the same time, the problem of serious ash accumulation at the lower part of the flat box filter cartridge is also avoided.
(4) By comparing the existing relevant studies, the structure and size of the three-slit blowhole proposed in this study can induce more compressed gas to participate in the deashing process, obtaining greater cleaning strength and further improving the cleaning efficiency. For example, the results of the study carried out by Cheng [
17] showed that under the conditions of a blowing distance of 20 mm and blowing pressure of 0.3 MPa, the average surface side wall peak pressures inside the flat box cartridge filter were 1102 and 1654 Pa, which were caused by one-slit blowholes with sizes of 1 × 39 and 3 × 13 mm, respectively; these values are far less than that of the 2921 Pa obtained in our study under the same conditions.
The findings of this work can provide foundational data and technical support for the improvement of ash cleaning in flat box cartridge filters to reduce environmental pollution and human health damage.