Zaliya Ilgamovna Akhmedyanova, Student, Magnitogorsk State Technical University named after. G.I. Nosova", Magnitogorsk [email protected]
Olga Borisovna Bobrova, senior lecturer of the Department of Industrial Ecology and Safety, Magnitogorsk State Technical University named after. G.I. Nosov", Magnitogorsk [email protected]
Tatyana Borisovna Ponamareva, department engineer Chemical technology non-metallic materials and physical chemistry Federal State Budgetary Educational Institution of Higher Professional Education “Magnitogorsk State Technical University named after. G.I. Nosova", Magnitogorsk [email protected]
Reducing hydrogen sulfide emissions during granulation of blast furnace slag
Abstract: Thermal crushing of blast furnace slag by granulating it in a stream of water is the most rational way to prepare this waste from ferrous metallurgy for reuse as a building material. The granulation process is accompanied by contamination atmospheric air as a result of the release of steam and gas emissions containing hydrogen sulfide, a substance of the second hazard class. Options for reducing the intensity of steam and gas emissions during hydrotrough granulation of blast furnace slag are considered. Key words: blast furnace slag, granulation, pollution environment, furnace granulation.
Blast furnace slag is formed as a result of reduction-oxidation processes at high (1200 °C at most) temperatures, by fusing waste rock and fluxes of iron ore material (sinter and pellets), to which ash from burnt coke is added in the furnace hearth. Granulated blast furnace slags are good material for road construction. Treated with viscous bitumen (a product of coke oven gas processing) mixed with gravel, they serve effective substitutes hot mix asphalt concrete; bitumen and slag road surfaces are 2.5 times cheaper than asphalt concrete ones. The granulation process can be carried out in three ways: wet, dry and semi-dry. The dry method is currently not used in the Russian Federation or in other countries. The reason is the low cooling rate of slag droplets in air, as a result of which the resulting granulate partially crystallizes and then undergoes silicate self-decomposition. Semi-dry and wet granulation plants are common. Water consumption for wet granulation is about 3 m3/t of granulate, for semi-dry granulation it is 2 m3/t. For wet granulation, basin and hydrotrough installations are used. The basin installation for slag granulation has disadvantages: during its operation, H2S and SO2 are released into the atmosphere. The water used in swimming pools is saturated with alkalis, so it is necessary to renew the water in the pool. There are known attempts to use water from granulation plants for medicinal purposes, since after purification and dilution, its mineral and chemical composition is close to the composition of the waters of the Matsesta spring in Sochi. The hydrotrough installation makes it possible to capture and neutralize acid vapors if an exhaust and gas purification path is installed behind the steam collector. However, in practice, these systems quickly fail due to the corrosive effects of sulfur dioxide emissions. In addition, emission removal and neutralization designs reduce the coverage area of grab bridge cranes, increase capital and current operating costs for granulation. Semi-dry granulation of blast furnace slag is carried out on drum and hydraulic shock units. Drum units have the following disadvantages: the melt has time to partially crystallize in flight through the air, which leads to a deterioration in the quality of the granulated slag. Crystals of threads and granules consist mainly of β-dicalcium silicate, which, when cooled, goes into the γ modification with an increase in volume and subsequent disintegration into dust. This worsens working conditions and equipment operation, reduces the quality of the granulate. Also, the drums wear out quickly; Pops and explosions occur when cast iron and slag crusts enter the granular unit. Therefore, drum granulation plants are not widely used. recent years at the State Research Center of the Russian Federation OJSC Ural Institute Metals" has developed technology and equipment for semi-dry granulation of melts of both blast furnace and steelmaking slag. The drum is inclined 50 degrees horizontally, its surface has slots (grid-iron). Formation of structure and size finished product-granular slag occurs in the cavity of the grate drum with the simultaneous supply of large quantity water on the surface of moving metal bodies: balls or cylinders. This avoids the disadvantages listed above. The drum is placed in a casing and connected to a system for collecting and localizing steam and gas emissions. Unloading occurs through the lower end of the drum. Granular slag undergoes magnetic separation to extract metal. The State Scientific Center of the Russian Federation OJSC Ural Institute of Metals has developed technical documentation for installations with a capacity of 0.2 to 5 t/min of liquid slag. A drum-type plant is being designed to produce 750 thousand tons of crushed stone per year from liquid blast furnace slag at the Nizhny Tagil Iron and Steel Works. The technological process and technical documentation for the processing of converter slag in a drum-type unit with a capacity of 5 t/min was purchased by Baosteel (Shanghai, China). The common disadvantages of wet and semi-dry granulation methods are the imperfection of circulating water supply systems, environmental pollution, loss of sensible heat from the slag . These disadvantages can be eliminated by reducing water consumption for granulation (by improving water supply systems) and by improving recycling water supply systems. Another disadvantage of existing granulation plants is the use of overhead cranes, which is associated with significant capital costs for the construction of a colonnade. The operation of overhead cranes, their prevention and repair are associated with a complex of harmful production factors: vibration, noise, thermal loads, the release of gases during granulation containing sulfide compounds. Currently, overhead cranes can be replaced by mobile (crawler or wheeled) loading and unloading manipulator devices, with more comfortable working conditions for the operator. However, not all slag released from a blast furnace is granulated. A significant portion of the slag solidifies on the walls of the ditches, but most of it solidifies in steel slag buckets. The time from filling the ladle with liquid slag to emptying it during granulation ranges from 100 to 150 minutes. To service a large blast furnace shop, a large number of buckets are required. For example, at OJSC MMK (~10 million tons of cast iron per year) there are over 120 ladles with a volume of 16 m3. Every day, more than 400 ladles with slag are removed from the blast furnace shop. Such cargo flows require efficient operation of slag processing plants and significant material costs. The proportion of slag solidified in the ladle (ladle residue) can reach 25% or more of the original liquid volume. The total share of granulated slag is 6070%. Ladle residue contains scrap of settled and hardened cast iron. Therefore, ladle residue is processed for metal recovery in slag yards. Processing consists of knocking out slag-metal cakes from slag bowls and destroying the cakes using mobile pile drivers. Only crushed stone can be obtained from ladle residue slag. This is due to the fact that in its structure the amount of glassy phase is significantly less than in granulated slag, which has gone through the freezing stage. Consequently, the value of ladle residue slag as a raw material for the production of binders is low, but the quality of crushed stone from it is quite high and meets the requirements of GOST for crushed slag stone. One of the proposals for reducing emissions is the use of a semi-dry or dry method of slag granulation. The most described and used is the roller or drum method, which can be either purely dry or using a small amount of water - the so-called semi-dry. This method is positioned by the authors as a method of furnace processing of blast furnace and steel-smelting slag, which allows reducing the cost of granulated slag production by 2.53 times, reducing the cost of maintaining and operating a fleet of slag carriers, reducing production space, and simplifying the sorting and extraction of metal. At the same time, conditions are created to neutralize harmful emissions and utilize the heat of the molten slag. The second option for eliminating steam and gas emissions is to install shelters above the hydraulic chute to capture and purify gas emissions. For example, a shelter design with a common steam-gas outlet (Fig. 1), from which the steam-gas mixture is directed either to a tower with an adsorption purification system, or to a pipe for dispersion. Shelters must be equipped with electrically driven gate valves to alternately open a section of the gas duct.
Rice. 1 Shelter over gutters
The third option is to build a new granulation site. An example of such a section is a granulation plant built in 1998 in Germany at the Salzgitter plant of the SalzgitterFlachstahl GmbH company, consisting of a granulation tower, a pipe 32 m high, into the lower part of which liquid slag is supplied (Fig. 2). A special feature of the installation is a ring (Fig. 3) spraying water around the slag chute, with the help of which most of the steam and gas emissions are injected into the tower, as well as supplying water for granulation along the slag chute (as usual) and spraying it inside the tower from above. As a result, gaseous products, mainly water vapor and gaseous compounds H2S and SO2, are deposited in the condenser part of the granulation tower due to water spray. As a result of oxidation and reaction with calcium, gaseous sulfur compounds are deposited on the surface of granulated slag particles in the form of gypsum. Thus, thanks to condensation, emission-free operation of the plant is achieved. The installation capacity is 1400 tons of slag per day or about 1 t/min; water consumption for granulation at a pressure of 2.12.5 atm is 14503300 m3/min. Dehydration of granulate up to 10% is carried out in special vertically installed cylindrical bunkers. Operating costs are 0.8 euros per 1 ton of granulated slag.
Rice. 2 Diagram of a tower for slag granulation
Rice. 3 Scheme of hydrotrough granulation of slag with trapping of released gases
The fourth option is to neutralize steam and gas emissions by adding a neutralizer (milk of lime) and oxidizing agents (Fe2O3, CaCO3, KMnO4) to the granulation water under unfavorable weather conditions. Along with milk of lime, organic waste from the chemical industry can be used to reduce the hydrogen sulfide content in steam and gas emissions. In this case, the complex set of units necessary for the preparation of lime milk is eliminated. The great advantage of organic hydrogen sulfide absorbers is that they significantly slow down the setting time of carbonate sediments in pipelines, pumps, settling tanks and tanks of the circulating water supply system, as well as in slag receiving bins and dehydrators. To reduce emissions into the water before granulation, various oxidizing agents can be added that prevent the formation of H2S, forming SO2 and SO3. Also, to reduce the hydrogen sulfide content in steam-gas emissions, surfactants, for example from cellulose production, can be used. Most a prominent representative Surfactant is soap: accessible, inexpensive. The cleaning efficiency in this case is 84%.
Links to sources 1. Panfilov M.I. Metallurgical plant without slag dumps. M.: Metallurgy, 1978. 248 pp. 2. Panfilov M.I., Shkolnik Ya.Sh., Orinsky N.V., Kolomiets V.A. and others. Slag processing and waste-free technology in metallurgy. M.: Metallurgy, 1987. 238 p. 3. Sorokin Yu.V., Demin B.L. Environmental and technological aspects of processing steelmaking slag // Chermetinformatsiya OJSC. Bulletin "Ferrous metallurgy". 2003. No. 3. P. 7579.4. Study of the characteristics of steam-gas emissions during blast furnace granulation / Kormyshev V.V., Pototsky V.P., Zubkov V.F., Markman L.G. on Sat. “Cleaning water and air basins at ferrous metallurgy enterprises”, No. 5 M.: Metallurgy, 1976. P. 3239.5. Proshkina O.B., Karbainova N.V. Sources of atmospheric air pollution during slag processing // Theory and technology of metallurgical production. 2010. No. 1. P. 177181.6. Senik A.I., Milyukov S.V., Proshkina O.B. Formation of hydrogen sulfide emissions during extra-furnace granulation of blast furnace slag // Bulletin of the Magnitogorsk State University technical university them. G.I. Nosova. 2008. No. 3. P. 7579.7.K.H. Grospic, V. Evers, G. Dabrowski New slag granulation plant // Ferrous metals. 2004. January. S. 3340.
The issue was approved by Resolution of the State Committee for Labor of the USSR, the Secretariat of the All-Union Central Council of Trade Unions dated December 27, 1984 N 381/23-157
(as amended by the Resolution of the State Committee for Labor of the USSR, the Secretariat of the All-Union Central Council of Trade Unions dated June 12, 1990 N 233/9-49,
Order of the Ministry of Health and Social Development of the Russian Federation dated October 20, 2008 N 578)
Blast furnace slag granulator
§ 22. Blast furnace slag granulator, 2nd category
Characteristics of work. Granulation of fire-liquid slag in wet, semi-dry and dry granulation plants with a capacity of up to 1 million tons of slag per year. Controlling the installation mechanisms, turning on the water supply to the pool, granulation chute, trench and maintaining the required level. Regulating the ratio of slag and water during drainage in a granulation plant. Turning of slag ladles. Cleaning slag chutes, drainage ditches and breaking up slag frozen in buckets using pneumatic breakers and other tools. Control of a scraper winch or other mechanisms when loading granulated slag into railway cars. Slag removal on the territory of the granulation plant and access roads. Participation in the repair of serviced equipment.
Must know: the operating principle of the granulation plant equipment, bucket tilting mechanisms, pneumatic jackhammers and loading mechanisms used; properties of liquid and granular slag; plumbing.
§ 23. Blast furnace slag granulator, 3rd category
Characteristics of work. Granulation of fire-liquid slag in wet, semi-dry and dry granulation plants with a capacity of over 1 million tons of slag per year. Maintenance of a plant for the production of slag pumice, thermosite, cast crushed stone, slag wool, etc. Supply of compressed air. Control of hydroscreen installation. Identification and elimination of malfunctions in the operation of serviced equipment.
Must know: design and rules of technical operation of serviced installations; chemical properties pumice, thermosite and other slag processing products.
When servicing a bucketless blast furnace slag granulation plant with a capacity of up to 1 million tons of slag per year - 4th category;
when servicing a bucketless blast furnace slag granulation plant with a capacity of over 1 million tons of slag per year - 5th category.
Annotation
A Russian company in the Sverdlovsk region, specializing in the optimization of metallurgical production, has developed a technology for furnace slag granulation, applicable in blast furnace production. The use of this technology provides advantages in the form of high energy efficiency and quality of the resulting products. The authors are looking for partners to establish cooperation within the framework of concluding a license agreement and a service agreement.
Description of the offer
Since 2010, the Russian research engineering company of the Sverdlovsk region has been developing effective metallurgical technologies in the field of ferrous metallurgy. The company carries out the following work on a turnkey basis: Development of a feasibility study for the construction of a new or modernization of the existing technology for furnace slag granulation. Development of technological specifications, project, working and design documentation for the technology of furnace slag granulation. Manufacturing and installation of equipment for furnace slag granulation technology. Installation of equipment. Commissioning and testing of technological operating modes of blast furnace slag granulation technology, development of operational documents. The company has developed an innovative technology for furnace granulation of blast furnace slag. This technology provides a high quality final product. The technology in terms of the composition of the equipment adapts to the volume of the blast furnace and can be effectively used both in small blast furnaces of 1000-2000 m 3 and large ones of 3000-6000 m 3. The resulting product, depending on the initial characteristics of the liquid slag, can be used as a hydraulic active additive to cement or in road construction. The basic principle of the technology: Liquid slag from the blast furnace flows through a chute to the granulation unit, where, due to the mechanical action of water jets, it is crushed and in the form of a three-phase mixture enters a receiving hopper filled with water. The granulation unit is represented by a hydraulic monitor mounted under the slag chute. The receiving hopper is equipped metal grille , delaying oversized objects. When immersed in water, the slag particles cool and harden. The steam generated during the granulation process is released into the atmosphere through an exhaust pipe. Granulated slag along with water enters the airlift compartment through an opening in the vertical wall. Rising through the airlift well, the water is clarified and poured into the clarified water chamber, from where it is taken by the granulation pump and supplied to the hydromonitor for the next granulation cycle. If the opening is blocked with granulated slag, water enters the airlift well through an upper overflow device equipped with a downpipe. Transportation of granulated slag is carried out by slag airlift 6, which is a vertical pipe lined with stone casting. The use of airlift for pumping slag is due to the fact that airlift has greater reliability, less wear and tear and greater efficiency compared to pumps when pumping hot pulp with a slag to water ratio of about 1:2. To agitate granulated slag, a water supply is provided at the airlift suction from a separate pump that draws water from the clarified water chamber. Under the influence of compressed air introduced into the airlift nozzle, a mixture of water and granulated slag rises into the separator, from where it flows by gravity through a slurry line into a carousel-type dehydrator. The carousel-type dehydrator is a rotating welded structure (body) of a toroidal shape, divided into segments and equipped with a stationary lid and tray. Through the cover, slag pulp is supplied from the airlift separator, as well as the steam-air mixture is evacuated into the exhaust pipe. The pan ensures the collection of filtered water and its return to the receiving hopper, as well as the unloading of dewatered slag into the hopper. Dewatered granulated slag from the bunker is unloaded onto a belt conveyor and transferred to the warehouse. The recommended method for storing granulated slag is an open stack-type warehouse. The moisture content of the slag in the stack increases towards the base of the stack. Rational organization of work on transshipment and shipment of slag will further reduce the moisture content of the slag. Currently, slag trucks are used to transport molten slag to a centralized granulation plant. In this case, the liquid slag loses temperature during transportation and does not provide high quality granulated slag; it is necessary to maintain the ladle facility, losses due to build-up on the walls of the ladle, etc. The proposed technology is free from these disadvantages. This technology makes it possible to solve the following problems associated with the disposal of blast furnace slag: 1 Obtaining a given structure and fractional composition of granulated slag to ensure the most effective use of slag, primarily as a hydraulically active additive to cement. Required characteristics can be achieved only with water heating technology of granulation of the initial melt with the highest possible initial temperature of the melt before granulation. 2 Ensuring explosion safety of granulation. Achieved by organizing the dispersion of the melt over the pool, and not in hydrotroughs. 3 Achieving the maximum possible reduction in the moisture content of granulated slag. This is achieved by pumping granulated slag using an airlift from the pool into a specially designed dehydrator that ensures effective dewatering of granulated slag. 4 Providing environmentally comfortable conditions in the area of the blast furnace casting yard due to the maximum localization of steam and gas emissions and their removal through the pipe due to gravity, ensuring the dispersion of emissions. 5. Partial heat recovery of the original slag melt can be achieved through condensation of steam generated during granulation, for example, during evaporation using vacuum evaporators of contaminated wastewater present in any metallurgical production. 6. The introduction of furnace granulation plants in the cramped conditions of existing blast furnace shops is achieved due to the relative compactness and monoblock nature of the technology. The proposed technology for furnace granulation of blast furnace slag has been implemented at metallurgical plants in Russia (3 enterprises), Ukraine (1 enterprise), India (1 enterprise) and China (2 enterprises). The resulting product, depending on the initial characteristics of the liquid slag, can be used as a hydraulically active additive to cement or in road construction. The result of concluding a service agreement will be the performance of engineering services (for example, development of basic engineering) under a contract with a partner (metallurgical plants) or a company providing engineering services to the partner for adaptation (linking) of technology to the features of existing production, supervision of the implementation of development and commissioning works. The result of the licensing agreement will be the sale of furnace granulation technology to partners, that is, metallurgical plants.
Innovative aspects and advantages
The innovative aspect of the technology is to ensure that liquid slag is supplied directly to the granulator, bypassing intermediate transportation by slag buckets, which leads to a higher cooling rate of the slag and high quality granulated slag, which can be used as a hydraulically active additive to cement in the construction industry. Advantages of the technology: high quality of the resulting granular product; high energy efficiency of the technology due to heat recovery during slag granulation; explosion safety technology; ensuring environmentally comfortable conditions in the area of the foundry yard; long term operation of the installation; adaptation of technology to the volume of the furnace and the possibility of implementation in cramped conditions of existing blast furnace shops; low capital costs due to an optimal set of equipment and a reduction in the fleet of slag carriers and vehicles; low operating costs associated with the absence of the need to maintain a fleet of slag ladles and the low number of personnel servicing the installation; no loss of slag in the form of crusts on the surface and deposits on the walls of the ladles.
Technology keywords
02007008 Cast iron and steel, metal structures
02007010 Metals and alloys
Market Application Codes
09003001 Engineering and technical services
Blast furnace slag is a good raw material for the production of various insulating and building materials, including cement. In this regard, they undergo granulation, the methods of which are divided into dry, air, semi-dry and wet. Based on the place of production, it is divided into non-furnace and furnace. Pre-furnace slag granulation was developed in domestic production during the construction of powerful blast furnaces and is currently considered the most rational type of slag processing. It eliminates the use of a fleet of slag ladles, which greatly simplifies the organization and reduces the cost of production.
Currently, out-of-furnace granulation is preserved only for furnaces built in the 30-60s. Most often, water-jet granulation is used by loosening the slag with jets of water in gutters through special nozzles with a pressure of 7-8 atm and a water flow rate of up to 3 m 3 /t of slag. Gutters are made up to 10 m long and approximately 0.8 m wide with a slope of 3°. Bandwidth up to 3.5 t/min.
Modern blast furnaces with round foundry yards are equipped with two granulating units, one for every two cast iron tapholes. The units are served by a common blower station, a conveyor system and storage facilities. Each installation has two technological lines, of which one is reserve. The installation diagram is shown in Fig. 1. Slag from the blast furnace, flowing down chute 4 onto the water flow of granulator 3, is crushed and, entering the settling hopper 2, is cooled. The resulting steam is discharged through pipe 7.
The water level in bunker 2 is constant, since the excess is discharged into the chamber recycled water 1, from where the airlift 5, consisting of an air duct, an air nozzle, a riser pipe, a separator, a pressure tank and a pipe for discharging exhaust air and excess water, is supplied again to granulation. Under the influence of air supplied by pipe 12, slag from well 14 is pumped by airlift 13 (at a solid to liquid ratio of 1: 2) into the separator and then by gravity flows into a carousel-type dehydrator 8, consisting of 16 sections with mesh bottoms. The dehydrator rotates and each section is sequentially filled with pulp, the water from which is filtered through a mesh bottom, after which the slag is unloaded into drying hopper 9. The filtered water is poured into the annular water collector 10, from where it enters settling tank 2. The slag in hopper 9 has a temperature of about 90 ° C . An additional reduction in humidity and temperature is carried out by blowing air into the bunker, after which the dehydrated and cooled slag is unloaded onto conveyor 11 and delivered to the warehouse or loaded into cars. The air exhausted in the airlift and drying bunker is removed through a pipe into the atmosphere.
Small-sized blast furnace slag granulation "Tulachermet". In 1994, the first small-sized blast furnace granulation plant in Russia (MGUPGSH), built according to the design of OJSC Gipromez for blast furnace No. 3 of AK Tulachermet, was put into operation.
MGUPGSH, consisting of two independent technological lines (one working, the other - reserve), occupies a plan area of 24 x 16.5 m. It is approximately 3 times smaller than the installations currently built and operated at blast furnaces HJ1MK, Severstal, Krivorozhstal, as well as at factories in Dungapur (India) and Bokoro (China). The new installation does not require a deep water pool, which reaches 15 m in typical installations. Due to high pressure water and other new structural elements, MGUPGSh makes it possible to switch to 100% near-furnace processing of slag of almost any composition. This completely eliminates the removal of slag to dumps and eliminates the need for a fleet of slag buckets.
In 1998, a complex with three MGUPGSH was put into operation at blast furnace No. 3 with a volume of 2560 m 3 at the Tangshan Iron and Steel Works (China). Currently, all the slag from this furnace is completely granulated at MGUPGSh without the use of slag ladles.
The blast furnace slag installation allows reducing fugitive emissions of H 2 S and S0 2 into the atmosphere.