The process of liquid iron production in the Blast Furnace (BF) generates gas at the top of the furnace which is an important by-product of the BF process. The gas exiting at the top of the Blast Furnace is at a high temperature and pressure and usually contaminated with dust and water particles. This top gas has a substantial calorific value and is known as raw Blast Furnace gas, or contaminated Blast Furnace gas. The composition and quantity of this top gas depends on the nature of the technological process in the Blast Furnace, and the type and the quality of the raw materials used, for the iron production in the Blast Furnace. To further use the raw Blast Furnace gas, it is necessary to clean it by using certain process systems – which reduces its content of solid particles from 18 to 20 mg/Nm3, to less than 5 mg/Nm3 and reduces pressure as per the requirement of the downstream process.
The top gas contains Carbon Mono Oxide (CO) and is known as Blast Furnace gas after its cleaning. It is used as fuel gas for heating blast air in the hot blast stoves, as well as a supplemental fuel in the steel plant. For the BF gas to be used as a fuel gas, it is necessary that the raw Blast Furnace gas is cleaned and cooled, to reduce the volume of the gas along with the moisture content. Moreover, pressure also must be reduced. Furthermore, cooling and reduction in gas volume, is also necessary since it results in substantial savings in delivery costs throughout the extensive distribution system of the steel plant.
The Gas cleaning plant is designed for following varying input conditions and should deliver dust emission at the outlet as less than 5 mg/Nm3 and reduction in top pressure to 800-1000 mm WC.
RIECO Gas Cleaning plant consists of 1 st stage Ventury, 2 nd stage Ventury followed by Separator.
The primary function of the blast furnace gas cleaning system is to remove particulate matter (18 to 20 gm/Nm3) from this gas to less than 5 mg/Nm3 emission and reducing it to the desired pressure, for the downstream process. In addition, the system also cools the gas to reduce its moisture content, thus increasing its calorific value. The recovered sludge/dust, contains relatively high quantities of iron and carbon which can thus be recycled, through the sinter plant.
Operation: The dust-laden blast furnace gases after dust catcher are cleaned in the Gas Cleaning Plant. The unit is of the latest design, consisting of a two-stage High Energy Venturi Scrubber system. The first stage venturi pre-cleans BF gases. The second stage venture executes the final cleaning of the BF gases. The system is highly efficient, and yields cleaned BF Gas. Coarse dust particles are removed in the scrubber, removing 90 – 95% of the dust from the gases. Water is supplied to the scrubber through recirculation, (clean) water pumps from the Clarifier plant. Dust laden water is discharged through a water sealing system, to the launder for treatment and recycling.
The precleaned gases leaving after the first stage venturi, passes into the second stage of the gas cleaning plant, which comprises of a high energy venturi scrubber of adjustable flaps. In the Venturi throat, the gas moves against the water spray for the separation of fine dust particles. The Venturi throat is equipped with a mechanism to adjust the throat area, which allows optimum adaption to the gas volume generated, in the Blast Furnace. Differential pressure across the GCP, controls second stage venturi throat opening automatically. The gas leaving the second stage Venturi, enters the Centrifugal separator where the finest water droplets are flung against the scrubber shell, and run down into the sump, and gas gets free from water particles, leaving the gas cleaning plant for distribution through a pipeline network, to various applications.
By achieving the desired outlet parameters at the outlet of Gas cleaning plants, this gas can be reused for the following: