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Problems and solutions of dust removal system of vacuum degassing furnace

Views: 4     Author: Site Editor     Publish Time: 2022-09-23      Origin: Site

Problem and cause analysis of vacuum degassing furnace dust removal sysem

The mechanical vacuum degassing furnace system consists of 16 first-stage oil rotary pumps, 8 second-stage Roots pumps, and 20 third-stage Roots pumps. The system can basically meet the metallurgical requirements since its operation, but with the large-scale production Due to the frequent burning of the bag filter, a large amount of dust accumulates into the pump set, which causes the Roots pump rotor to accumulate dust and block, the current increases during the rotation process, the temperature rises, and the serious If the pump gets stuck, it will fail; the oil of the oil rotary pump will be polluted, which will cause the system to exhaust the system smoothly, the exhaust gas temperature will rise, and the burning damage will occur in serious cases. Since the system is a synchronous dynamic system, once the pollution is basically synchronized, it is extremely harmful. There have been 16 oil rotary pumps burning at the same time.

Cause analysis 

1. Filter design flaws

(1) The filtration area is small, resulting in a large pressure loss.

(2) The filtering effect is poor, and the dust accumulation on the air outlet side of the filter is serious, which affects the life of the mechanical pump.

(3) The design of the dust collector is defective, resulting in the ineffectiveness of the bag purging, and the bag is squeezed together when the air is broken, which is the main reason for the accumulation of dust.

(4) The setting of breaking air is unreasonable. In order to avoid dust burning in the bag filter of vacuum degassing furnace, the filter should be emptied with 100% nitrogen. The accumulated dust is in contact with the high-speed broken air, which can easily cause combustion, which is the main reason for the burning of the bag.

2. Incomplete equipment configuration

(1) The tank body-extraction pipeline-cyclone dust removal-filter-vacuum pump system does not achieve reasonable gas cooling.

(2) The front dust collector installed between the tank body and the cyclone dust collector does not solve the problem of burning cloth bags.

(3) The equipment layout is too compact and the vacuum pipeline is short, which makes it easy for hot dust to enter the filter bag.

3. Slag overflow during vacuuming

Slag overflow often occurs in the vacuuming stage of conventional vacuum degassing furnaces. If the vacuuming process is not well controlled and the vacuum degree is adjusted in time, it is easy to cause the waste residue to enter the rear system. The process operation should minimize the number of residue overflows.vacuum refining furnace factory -Chnzbtech

Transformation plan of vacuum furnace dust removal system

1. Add a filter system with a larger filter area to reduce the resistance loss of the cloth bag, improve the cleanliness of the flue gas when it leaves the filter, meet the requirements of the mechanical pump system, and reduce the maintenance requirements caused by excessive dust in the vacuum pump area. Adopt squirrel cage filter bag structure to reduce system pressure loss. The process gas enters from the outside of the bag, and the dust adheres to the outside of the bag. During nitrogen pulse purging, nitrogen is blown from the inside of the cloth bag to the outside, and the dust attached to the outside of the cloth bag can be blown to the bottom of the filter to ensure the cleaning effect.

2. Add an automatic pulse purging system to ensure timely cleaning of dust after each mechanical pump cycle. The filter bag can be cleaned under vacuum, and the filter only needs to be emptied when the equipment is shut down. The dust cleaned by the cloth bag is collected at the bottom of the filter and discharged to the dust box under the filter through the double vacuum valve system to avoid the accumulation of dust in the cloth bag.

3. Install a gas cooler with a tangential inlet. Install a gas cooler, the gas cooler is a plate cyclone structure, which can not only ensure that the flue gas temperature at the outlet of the gas cooler is less than 130 °C, reduce the risk of high temperature dust entering the filter, and at the same time reduce the process gas temperature and reduce the suction of the pump system. The volume of flue gas can be improved, the efficiency of the equipment can be improved, and the effect of coarse dust removal can be achieved, and the large particle dust can be captured and discharged into the ash box.

4. Upgrading the air-breaking system. 100% empty bag filter with nitrogen. Install a vacuum isolation valve between the filter and the tank. Using the cooperation of the existing vacuum valve and the vacuum valve at the front end of the new filter, the pulse purging and ash discharge under vacuum are realized, and the pre-vacuuming capacity is increased. At the same time, only when the vacuum degassing furnace equipment has been shut down for a long time, it is necessary to completely empty the bag filter, reduce the consumption of nitrogen, realize 100% of the filter nitrogen emptying, and avoid the burning of the bag.

5. Adopt industrial monitoring system to provide support for human intervention in foam slag control, control bottom blowing effect and improve degassing efficiency.

6. Renovated new equipment: vacuum pipeline, cyclone gas cooler (with vacuum ash collector), bag filter with patented technology (with pulse purging control), vacuum control valve group, various sensor instruments and other components, upgrade Electronic control system and program control.

Transformation effect 

1. Completely solve the problem of bag burning and oil pump pollution caused by bag burning.

2. Shorten the vacuum degassing treatment time of each furnace by 5min, and reduce the additional energy consumption of the mechanical pump group.

3. Reduce the temperature drop of molten steel by 10°C per furnace, reduce the consumption of more energy in the pre-stage process of vacuum degassing, and raise the molten steel to a higher temperature to make up for the additional temperature drop of molten steel.

4. Improve the degassing effect of molten steel.

Benefit analysis

The most direct benefit after transformation is the benefit to production. Reduce the degassing time, provide better and more stable protection for the mechanical pump set; improve the degassing quality of molten steel, and make the production rhythm smoother. From the perspective of shortening the vacuum degassing treatment time and reducing the additional energy consumption of the previous process due to the temperature drop of molten steel, we can see the intuitive benefits brought by the transformation.

1. The vacuum degassing treatment time is shortened by at least 5 minutes per furnace to reduce the additional power consumption of the pump set. There are 44 pump sets with a single pump power of 18.5kW and a total power consumption of 67kW•h.

2. Reduce the temperature drop of molten steel by 10°C for each heat, and increase the temperature of molten steel in each heat by 10°C to make up for this extra temperature drop and ensure the temperature requirements of the subsequent process. The 120t molten steel needs to consume at least 60kW·h of electricity for every 1°C increase in the LF furnace, and each molten steel needs to consume an additional 600kW·h of energy in the LF.

3. The maintenance amount of the new dust collector is much smaller than that of the original dust collector, the frequency of bag replacement is 1 time/a, and the operation and maintenance cost is much lower than that of the original dust collector. Only since 2016, the phenomenon of random burning of cloth bags has occurred frequently. In order to maintain the current operation, the cloth bags are replaced 3 times every 2 months on average, and the annual consumption of cloth bags is RMB 524,160; RMB 494,000 in cloth bag consumption can be saved every year.

4. Due to the improvement of the dust removal effect, the total amount of dust entering the pump system is reduced, and the replacement frequency of the oil film rotary vane pump lubricating oil is reduced accordingly (at least 4 times a year before the renovation, and at most 2 times a year after the renovation), saving the cost of oil change every year 800,000 RMB.

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