S.G. Vygran, at present deputy head of the capital repair department, spoke to a journalist about the realization of the PCI project. When the problem regarding the economical practicability of the usage of natural gas in the blast furnace production occurred, he was the deputy head of the project and design department for advanced engineering. As a member of the working group of plant specialists, which studied foreign experience in the usage of pulverized coal instead of natural gas, he visited Germany and Poland, where he saw with his own eyes the operation of PCI units.
– Sergey Georgiyevich, can it be considered that the PCI unit of firm “Kuettner” is the most modern one and what are its advantages?
– Before the decision was taken concerning the construction of this unit our specialists and managers thoroughly and in detail studied this subject. Delegations headed by the main specialist for metallurgical production A.P. Fomenko visited iron and steel works in Belgium, Sweden, Germany and other countries, where such units of different manufacturers are in operation. The design and technology of the unit manufactured by firm ‘Kuettner” is the newest and most modern unit which can be found today in the world market. This firm has a wide experience in designing, construction and mastering of systems for using coal dust in blast furnace smelting. All the processes are automated. The technological specialists control the processes with the help of computer programs. We saw for ourselves after visiting, for example, Krakov steel plant. Such a unit is also being built at our Works, though with some structural alterations, which the firm introduced according to the requirements of our specialists. They concern the delivery of pulverized coal to blast furnaces via “nonstatic distributor” and injection of pulverized coal directly to the tuyere area where coal is burnt (technology “oxy-coal”). According to this technology together with the supply of dust oxygen will also be delivered to the tuyere device as an intensifier of coal burning.
It has been decided to build the unit where the dismantled blast furnace No.1 was located, i.e. quite close to the blast furnaces and bin trestle. Coal prepared for grinding is charged into these bins. Coal will be delivered from the storehouses in hoppers, i.e. in special wagons where discharging is mechanized. The discharging process is controlled by the loco engine driver who opens the hopper hatches. A special rotary feeder, which moves under the bunkers, will unload the coal on the conveyor. Further the coal will be transported to the dust preparation department by conveyors.
– Was it easy to breathe when you were in the area of such bins in Krakov?
– There were no problems with breathing. A spraying system is used for dust suppression. A similar installation is also foreseen in our project. In the premises where the dust preparation equipment is installed the air is also clean because grinding and drying is done in air tight closed containers. The most advanced measures to protect environment are used in the new technology.
– What does this new technology represent?
– The main component of this unit is the mill which turns coal into coal dust. It represents a plate on a vertical axle (it looks like a grinding mill). The drive rotates the plate and three taper rollers with a diameter of 600-700 mm move on it. The initial coal falls on this plate and is grinded by these rollers. Hot circulated gas is delivered under the plate. It catches and transports the dust through the separator where large and small fractions are sorted out. Large fractions return to the mill plate again for additional grinding. Small fractions, ready for blowing into the furnace, are delivered to the filter by pipelines and get dried on the way. All this takes place in a flow of the air heaters hot waste gas with content of oxygen less than 10%. This condition is necessary for the fire-safety process. The by-product of the blast furnace process, i.e. hot blast stove gas, is useful to be applied to dry coal dust.
– What happens after that? How does the dust enter the furnaces?
– The gas cleaned of dust returns to the contour line of the mill. The dust is transported to a special container, a silo. From there, through pipe lines under nitrogen pressure, it is transported to the blast furnace tuyeres. In the nozzle of the tuyere device apart from a tube with dust, there is also a tube through which oxygen is delivered. Both coal and oxygen are delivered to the tuyere. Already at the tuyere section this coal is burnt. Oxygen speeds up the burning reaction. The smart point of this technology is the following: the proper operating condition has to be chosen during which the coal particle has to have time to get burnt while it is still in the tuyere zone.
– How many tuyeres does each furnace have?
– Furnace No.2 has 20 tuyeres, No.5 — 18, No.3 and 4 — 16 each. During capital repair of blast furnace No.4 the number of tuyeres will be increased to 20.
– In brief, the PCI unit is quite a complicated one. And it’s even more difficult to tell about the automation system.
– Yes, it is difficult to tell about the work of measuring and control systems. It should be simply noted that they are foreseen and they provide control of all the technological processes. They control the processes automatically. Reserve containers are foreseen, starting from the coal store house, bunkers, coal dust silos, and finishing with nonstatic distributors at each furnace, where there also will be containers with storages of dust for several hours of work in case of preventive repairs and off-normal situations. There is no manual work at the PCI unit but the production engineers, mechanics, electricians, instrumentation and automation specialists require special knowledge to provide stable work of the unit. But our young blast furnace operators have proved more than once that they can master new complicated technologies.