Dry Cooling of Coke Apr25

Dry Cooling of Coke

Dry Cooling of Coke Dry cooling of coke is known as coke dry quenching (CDQ) and is an alternative to the traditional wet quenching.  During wet quenching of run of oven coke, sensible heat of the hot coke is dissipated into the atmosphere and is lost. In addition there are air borne emissions (0.5 ton of steam per ton of coke laden with phenol, cyanide, sulfide and dust) and a large quantity of water (around 0.6 Cu m per ton of coke) is needed for wet quenching. The contaminants in water are also discharged in the environment. In a Coke Dry Cooling Plant (CDCP) red hot coke is cooled by inert gases. The heat energy from the red hot coke is recovered in a waste heat boiler for use as steam, resulting in energy conservation as well as a reduction in coke particle emissions.  Around 80 % of sensible heat is recovered. The CDCP process flow is in Fig 1. Fig 1 Process flow in CDCP History After pilot and pilot/commercial trials the first full scale CDCP installation was commissioned in 1965 at the Cherepovets Iron and Steel Works in then USSR. By 1978 around 50 CDCP modules of 56 tons per hour were in operation in then USSR. Japan purchased license from USSR and three Japanese installations were commissioned in 1976 – 77. In India MECON purchased license for Giprokoks design CDCP from USSR and the first 12 chambers were installed at Visakhapatnam Steel Plant. The first CDCP plant was commissioned in September 1989. Presently 19 chambers of this design are in operation. Concept of Coke Dry Cooling Hot coke is brought from the battery to the CDCP in bottom opening bucket kept on the quenching car. This bucket is lifted at the...

Stainless steels

                         Stainless steels  Stainless steel is a family of alloys of iron that contains at least 10.5% Chromium and a maximum of 1.2 % carbon which is essential of ensuring formation of a self healing surface passive layer. This passive layer provides the corrosion resistance. These characteristics make stainless steels totally different from mild steels. The stainless steel was discovered between 1900 and 1915. In 1904, Leon Guillet discovered alloys with composition similar to steel grades 410, 420, 442, 446 and 440-C. In 1906 he also discovered an iron-nickel-chromium alloy which was similar to the 300 series of stainless steel. In 1909 Giesen researched on the chromium-nickel (austenitic 300 series) stainless steels. In Germany, in 1908, Monnartz & Borchers found that a relationship exists between a minimum level of chromium (10.5%) on corrosion resistance as well as the importance of low carbon content and the role of molybdenum in increasing corrosion resistance to chlorides.  Stainless steel production process Stainless steel is produced in an electric arc furnace where carbon electrodes contact recycled stainless scrap and various alloys of chromium, nickel and molybdenum etc. depending on the type of stainless steel. A current is passed through the electrode and the temperature increases to a point where the scrap and alloys melt. The liquid steel can also be produced in LD converter using hot metal as a major input material. The liquid steel from the electric arc furnace or LD converter is then transferred into an AOD (Argon Oxygen Decarbonization) converter, where the carbon levels are reduced and the final alloy additions are carried out to achieve the desired chemistry.  The liquid steel is either cast into ingots or continually cast into slabs or billets. The slabs or billets are either hot rolled or forged into...

Pickling of scale formed on hot rolled strip of carbon steel Apr23

Pickling of scale formed on hot rolled strip of carbon steel...

Pickling of scale formed on hot rolled strip of carbon steel During the hot rolling or heat treatment of steel, oxygen from the atmosphere reacts with the surface iron to form a crust that is made up of oxides of iron. This crust is known as scale and need to be removed before steel is further processed in cold rolling mill. Non removal of scale will have the following detrimental effects. Scale not only give bad appearance to the product but also accelerate corrosion During cold rolling of the strip scale patches affects the reduction with the possibility of the skidding of rolls. Effective scale removal is essential for the success of not only for cold rolling but also of subsequent annealing and coating operations. During cold rolling and annealing the scale will produce a dirty surface and cause the rusting of the strip During coating of the strip, presence of scale causes poor to total adhesion failure. Fig 1 shows hot rolled strip surface as well as pickled surface.   Fig 1 hot rolled surface and pickled surface Scale and its origin The normal scale found on hot rolled strip is blue/grey in colour and covers the entire strip surface. This scale is generated during rolling in the last stands of the finishing mill, across the run out table (ROT) and during cooling of the coil. It is composed of three well defined layers of iron oxides. Adjacent to the steel is the thickest layer consisting of wustite having an approximate composition of FeO. The intermediate layer consists of magnetite (Fe3O4) while the outermost layer is hematite (Fe2O3). The thickness of these layers will depend on the temperature of the strip at the exit of the finishing mill, temperature of the coiling and...

Fly ash

                       Fly ash Fly ash is a product of combustion of coal. It is normally produced while burning coal in a boiler of a power plant and is generally captured before the flue gas goes to the chimney. The other ash from the boiler is bottom ash which is removed from the bottom of coal fired boiler. Depending upon the type of the coal used, the composition of the fly ash vary widely  but all the types of fly ash include silicon dioxide (SiO2) (both amorphous and crystalline) and calcium oxide (CaO). Fly ash is a fine glass like powder. The particle size of the ash is in microns. The composition of fly ash in case of bituminous coals is as follows: SiO2 – 20%- 60% Al2O3 – 7% – 35% Fe2O3 – 12% – 40% CaO – 2% – 12% LOI – 0%- 12% Fly ash contains environmental toxins in significant amounts. These toxins include arsenic (45 ppm); barium (805 ppm); beryllium (5 ppm); boron (310 ppm); cadmium (3 ppm); chromium (135 ppm); chromium VI (90 ppm); cobalt (35 ppm); copper (110 ppm); fluorine (30 ppm); lead (55 ppm); manganese (250 ppm); nickel (75 ppm); selenium (8 ppm); strontium (775 ppm); thallium (10 ppm); vanadium (250 ppm) and zinc (180 ppm). The use of fly ash as an engineering material is due to its pozzolanic nature, spherical shape, and relative uniformity. The following are the various uses of fly ash: Portland cement and and in materials for grout Embankments and structural fill Waste stabilization and solidification Raw feed for cement clinkers Mine reclamation Stabilization of soft soils Sub base for road Aggregates Flowable fill Mineral filler in asphaltic concrete Roofing tiles Filler in wood and plastic products Fly ash is used as a...

Thin Slab Casting and Rolling Apr21

Thin Slab Casting and Rolling...

Thin Slab Casting and Rolling For the production of flat products, liquid steel is generally cast in form of slabs in continuous slab casting machines. These slabs are inspected, scarfed and then reheated in slab reheating furnace to the rolling temperatures before being rolled to hot rolled coils in a semi continuous or continuous hot strip mill.  Development of thin slab casting and rolling (TSCR) is a step forward to reduce the number of process steps in the production of hot rolled coils (HRC). Originally TSCR technology was developed with the primary goal of reducing the production and investment costs but today it has become one of the most promising production routes to maintain steel as a leading material in technological application and it is being considered as the technology which has reached a high degree of maturity. Casting speed of 6.0 m/min for slab thickness of 50/55 mm is quite common. Initially, only commercial quality plain carbon steels were being cast through thin slab caster route. But presently most of the steel grades including low, medium & high carbon, HSLA line pipe grades and steel grades for automotive application including IF grades can be cast through thin slab caster route. In fact this technology has brought paradigm shift in steel technology of casting and rolling. The thin slab casting and rolling technology was made possible because of the following improvements in casting and rolling processes. Design of mould Hydraulic mold oscillations Use of electromagnetic brakes (EMBR) Use of high pressure descaler and roller side guide (edger) in the mill Dynamic liquid core reduction (LCR) Mold powder quality and redesigned SEN Water spray cooling History The implementation of TSCR concept did not achieve any success till mid eighties due to numerous technological challenges associated...