baghouse dust collector

1. Working Principle

The XLMC offline ash-cleaning low-pressure pulse baghouse filter adopts an outer filtration type for gas purification. Dust-laden gas enters each unit filter chamber through the guide pipe and passes through the flue gas guiding device installed in the hopper. Since a sufficient and reasonable vertical clearance is reserved between the bag bottom and the upper opening of the air inlet in the design, the airflow is properly guided and naturally distributed to achieve uniform airflow distribution inside the entire filter chamber. After separation by natural sedimentation, the particulate dust in the dust-laden gas falls directly into the hopper. Guided by the flow guiding system, the remaining dust enters the filter area of the middle box along with the airflow and adheres to the outer surface of the filter bags. The clean gas after filtration penetrates the filter bags and is discharged through the upper box and exhaust duct.

The filter bags are cleaned by jetting compressed air. The ash cleaning mechanism consists of a main jet pipe, branch jet pipes, electromagnetic pulse control valves and other components. A jet pipe is installed at the top of the outlet of each row of filter bags inside the filter chamber. Jet nozzles are arranged on the lower side of each jet pipe, directly facing the center of the corresponding filter bag. Each jet pipe is equipped with a pulse valve connected to a compressed air reservoir. During ash cleaning, the solenoid valve opens the pulse valve, and compressed air is jetted toward the filter bag through the nozzle. Together with the entrained surrounding air, it rushes into the filter bag, causing the filter bag to vibrate thoroughly and generating an inside-out reverse airflow to remove dust adhering to the outer surface of the filter bag for ash cleaning.

As the filtration process proceeds, when the dust accumulated on the surface of the filter bags reaches a certain level, the ash cleaning control device (differential pressure, timing or manual control) opens the electromagnetic pulse valves for jetting according to the preset program. In an extremely short time, compressed gas sequentially passes through each pulse valve and, via the nozzles on the jet pipes, induces air several times the volume of the jetted gas into the filter bags to form an air wave. This triggers rapid expansion and shock vibration of the filter bags from the opening to the bottom, delivering powerful ash cleaning performance and shaking off the dust on the filter bags

Pre-coating is carried out before the dust collector is put into operation to protect the filter bags; the pre-coating device is activated for pipeline powder injection to protect the filter bags when the boiler burns oil under low load and at the initial stage of "four-tube" burst; the bypass protection system is started during boiler oil-firing startup, "four-tube" burst and abnormal flue gas temperature.

Dust falling into the ash hopper is discharged through the outlet and then conveyed centrally by ash conveying facilities.

The dust collector is equipped with on-line and off-line dust cleaning functions as well as an off-line maintenance function.

The dust collector is fitted with a filter bag leak detection device to check the condition of filter bags, along with on-line monitoring devices for differential pressure, temperature, material level and other parameters.

The control of the dust collector (including dust cleaning control, etc.) adopts PLC control. The whole dust removal system realizes automatic unattended control, and can feed back information to the main plant system and accept remote control from the main plant system.

All maintenance and overhaul work is performed in the clean gas chamber of the dust collector and outside the unit, with no need to enter the interior of the dust collector.

2. Technical Features

The development and application of the XLMC high-efficiency low-pressure pulse bag dust collector embodies the wisdom of numerous industry experts, and many technical staff of the company have devoted tremendous efforts to it. The integration of low-pressure pulse, off-line dust cleaning, non-stop maintenance and protection technologies, which adds functions to the dust collector in accordance with the flue gas characteristics of utility boilers and the operation requirements of power plants, has gradually demonstrated its advantages and gained increasing recognition and praise from design institutes and power plants. Its technical features different from pulse bag dust collectors used in other industries are as follows:

1) Low-pressure injection technology

Given the high concentration of flue gas and dust generated by the combustion of utility boilers, the equipment resistance will rise rapidly and the dust cleaning frequency will accordingly increase. The adoption of high-pressure injection will exert adverse impacts on the service life of filter bags. In addition, the dust layer attached to the filter bags will be completely blown away, which is not conducive to dust falling into the ash hopper by its own gravity and tends to cause secondary re-adhesion of dust.

Through on-site monitoring with camera probes, the fly ash in flue gas is relatively dry under operating temperature. Meanwhile, we have treated the filter bags for easy dust cleaning. Dust cleaning at a relatively low pressure can not only achieve ideal dust cleaning effect, but also shorten the time for dust to settle into the ash hopper. It can avoid secondary re-adhesion and the shortening of filter bag service life caused by frequent dust cleaning.

2) Flow guiding technology

Solenoid pulse valves and filter bags are the core components of the XLMC high-efficiency low-pressure pulse bag dust collector, and flow guiding serves as the core technology. Combined with our company’s design philosophy, a series of measures are adopted to make flue gas evenly distributed to each filter bag. This ensures uniform load on filter bags to extend their service life and greatly reduces equipment resistance.

3) Offline Dust Cleaning / Non-stop Maintenance Technology

To achieve more thorough and effective dust cleaning, pneumatic lift valves are installed at the air outlet of each unit bin, which can independently isolate the bin undergoing dust cleaning. This prevents the rising airflow from interfering with the cleaning process and speeds up dust settling.

The pneumatic lift valve adopts a pneumatic thin-plate quick-opening structure. Its entire opening and closing process is linear motion, supported by auxiliary guide slide rails for accurate positioning. This avoids the high failure rate common to rotating structures under high-temperature conditions.

By closing the pneumatic lift valve and the manual air regulating valve at the ash hopper air inlet, bag replacement and other maintenance work on the current bin can be carried out, while all other operations are performed outside the machine, enabling non-stop maintenance.

4) Fixed Pipe Jet Dust Cleaning Technology

Fixed pipe jet dust cleaning technology is widely used in the dust removal industry today. It eliminates high failure rates caused by easily damaged bearings and difficult lubrication in rotating jet systems, as well as persistently high equipment resistance resulting from incomplete reverse-air dust cleaning.

It uses treated compressed air to induce clean air from the upper box to jet instantly into the inner cylinder of filter bags, creating pulsed vibration. Dust adhering to the outer surface of filter bags detaches from the bags and falls into the ash hopper under this sudden strong vibration.

5) Fixed Jet Pipe

6) Bypass Protection Technology

The dust collector is equipped with a built-in bypass, which is aesthetic and practical. The system automatically opens the bypass under the following conditions:

① When the flue gas temperature at the boiler tail outlet exceeds the allowable operating temperature of the selected bag filter material;

② When tube bursts occur on the water wall, superheater, reheater or economizer during boiler operation;

③ During boiler start-up with full oil firing, mixed combustion of oil and coal, and low-load oil-support combustion;

④ When other conditions that affect the service life of filter bags occur.

While the bypass protection technology protects the filter bags, it cannot guarantee the flue gas emission concentration. The boiler shall be overhauled as soon as possible to restore the normal (automatic) operation of the dust collector.

7) Application Technology of High-temperature Resistant Filter Material

Based on the conditions of flue gas in power plants and the application experience of PPS filter material at the boiler tail in the domestic power industry, PPS filter material is an economical filter material suitable for dust removal at the boiler tail in the power industry. After anti-oxidation and acid & alkali resistance treatment, the service life of PPS filter material is further extended.

The maximum tolerable oxygen content in flue gas for filter bags is 8%. The dust collector will switch to bypass operation when this value is exceeded.

When the flue gas temperature is lower than 100°C, the filter bags are prone to acid corrosion, and the dust collector will switch to bypass operation.

8) Application of Detection and Monitoring Technology: In accordance with the operating characteristics of the dust collector, advanced online detection and monitoring devices are installed for flue gas temperature, dust collector operating pressure, material level and operating equipment fault detection.

9) Application of PLC Programmable Logic Controller realizes automatic control of the dust collector as a key operating equipment of the power plant.

10) Equipment Resistance Control: Through a series of distinctive considerations in equipment design, the safety and reliability of the overall equipment resistance are guaranteed from both the equipment structure and filter material aspects.

The adoption of a series of advanced technologies ensures that the dust collectors manufactured by our company feature first-class technology and excellent cost-performance ratio.