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Dry cleaning of blast furnace gas

Recently, on the newly built and reconstructed blast furnaces, particularly in the People's Republic of China, dry cleaning of blast furnace gas by bag filters has found the wide application. Dry gas cleaning has the following advantages over the wet gas cleaning using scrubbers and Venturi tubes:
  • absence of water in the cleaning process that eliminates or reduces the construction scope of a number of blast furnace waterworks facilities: sludge pumping station of gas cleaning system, sludge settling tanks and floculators, pump station for slurry transfer, circulating pump station of turnaround cycle of gas cleaning, etc.;
  • the temperature of gas after cleaning is 100-120ºC, which is 50-70ºC higher than in the wet gas cleaning; the humidity of gas is reduced by 50-60 g/m³, which together is equal to an increase in caloric content of blast furnace gas by 50-60 kkal/m³. This allows to increase the temperature of heating blast air in the hot stoves;
  • reduction in the dust content in blast furnace gas to 2-3 mg/m3 that improves the service life of hot blast stoves and also enhances the performance of gas recovery compressor less turbines by 30% and the service of the turbine vanes up to 1 year;
  • environmental improvement in the plant due to a better gas cleaning from dust and elimination of sludge handling facilities.
According to the market needs, industrial production of equipment for dry gas cleaning systems is well established at the machine-building plants in China.
KALUGIN JSC has set up a fruitful and successful cooperation for development and introduction of novel technologies in blast furnace iron making (such as designing and construction of Kalugin shaftless hot blast stoves in China, participation in tender bidding for designing and construction of pulverized coal injection units into blast furnaces in Russian steel plants etc.) and we would like to acquaint you with dry cleaning unit for blast furnace gas based on bag filters.
 
KALUGIN JSC guarantees timely project performance on a high technical level, its adaptation to the standards, norms and safety regulations operating in the territory of the Russian Federation according to Customer’s requirements and the norms of Russian legislation, and also contract supporting at all stages (designing, equipment delivery, construction, supervision, starting-up and adjustment works) till the achievement of guarantee parameters of the project.
Photo 1 – Systems of blast furnace gas dry cleaning Photo 2 – Systems of blast furnace gas dry cleaning
The proposed system of blast furnace gas dry cleaning consists of:
  • The bag filter itself with several sections, in each of them there are installed some tens of filtering bags;
  • System of pulse bags cleaning from dust by nitrogen;
  • Supporting and protecting metal structures;
  • Systems of gas ducts with valves and thermal effect compensators;
  • System of cleaning and recycling of captured dust (pneumatic or with scraper conveyors);
  • System of nitrogen supply for the filter purging and for pneumatic dust transport;
  • System of pressure relief from the bag filter;
  • Unit of captured dust gathering;
  • Systems of automatics, inspection, and electrical control.
The bag filter normally having 8 to 16 sections, which are arranged in two rows (see Photo 1), where one or two sections are stand-by, one more section is in cyclic purge nitrogen cleaning mode and other sections are in gas cleaning mode. As a filtering material, a fabric with high refractory, wear & tear resistance etc. is selected. Besides, after chemical treatment the fabric is easy to clean from dust during purge cleaning, since it has improved water- and oil-repellent properties. The fabric also prevents occurrence of electrostatic current. Maximum filtering rate is 1,0-1,5 m³/min. gas temperature – 50 to 280ºC (the system can also operate stably (reliably) for 2 hrs at gas temperature of 300ºC).
 
The guaranteed dust content of blast furnace gas after cleaning is not more than 3 mg/m³. Service life of fabric bags is up to 24 months.
To collect entrapped dust from the system’s conical section, a system of dust collection into one of two modular sections is arranged (one section is in operation, the other one is in stand-by mode). Entrapped dust (as it gets accumulated) is discharged from the modular section into trucks or railway cars (as specified by the Customer).
 
For the dust discharging, a gate feeder, a screw auger and dust suppression system using water spraying while dust unloading are installed. Upon the Customer’s request we can design and supply a system of dust loading to cement trucks or to other special transportation means, and also can execute dust supply directly from sections by pneumatic transport up to 500m distance to the related production units (sinter plant, briquetting plant, etc.).
In order to avoid condensate formation at the dust cooling and its coagulation, that leads to the dust adhesion to the wall of the bag filter cone section, and can lead to clogging the cone’s bottom part, the latter is isolated and heated by steam.
 
Bag filter sections in the bottom are connected through pipelines to dirty blast furnace gas header, while the upper part is connected to clean gas header. The inlet and outlet of each section are equipped with slide-valves and butterfly valves with electric drives to isolate it from the system. In the top part of chamber, pressure relief valves are provided for normal operating and emergency modes.
 
Training of Customer’s experts on operation and adjustment of dry gas cleaning systems is carried out in the People’s Republic of China (a group of 6 persons during two weeks).