Fume Extraction and Dedusting Systems
Fume extraction and de-dusting systems are installed to capture the fugitive dust/fumes generated in furnaces or during handling of material before or after various processes. The system consists of suction hoods at various dust/fume generating points, elaborate ductwork, butterfly dampers (both manual and automatic) at appropriate locations, a modular, casing entry, offline, pulsejet bag filter, a centrifugal ID fan and a self-supported stack.
Thermax has over 25 years of expertise in design, engineering, supply, construction, erection and commissioning of fume extraction and de-dusting systems, including all electrical, instrumentation and civil work.
- No dust cake formation and hence no binding or clogging of bags
- No dust deposition in the ducts due to optimally designed air velocity
- Minimum power consumption
- Completely safe operation
- Assured smooth running of the rotary air lock valves and screw conveyors
- Minimum downtime which is crucial in case of process equipment
Coal Preparation Plants & Related Systems
Fine coal is injected in the blast furnace to improve the furnace productivity and to reduce the consumption of high priced coke. During coal injection, coal is ground to a fine size and to a desired moisture content level, which is stored in an inert atmosphere and conveyed by an inert gas to the blast furnace tuyeres.
Essentially, a coal injection system consists of the following sections:
- Coal handling plant with material handling equipments and a storage silo for handling and storing of raw coal.
- Coal preparation/pulverization: grinding & drying through a coal mill, pneumatic conveying and collection of coal through bag filter.
- Fine coal injection system comprising injection vessels, distributors, lances etc. (from coal silo to blast furnace).
In coal preparation plants Thermax has a technical association with M/s Claudius Peters Technologies, Germany (earlier BMH) which is a predominant and well known player in coal grinding and injection.
Thermax has jointly and independently executed many coal preparation plants in almost all steel majors in India.
Thermax has wide experience in coal preparation plants for more than 20 years and is capable of giving coal preparation plant up to 60 TPH (on a single stream).
Safety First - handling the pulverized coal is hazardous due to high inflammability of fine coal. The system designed by Thermax incorporates numerous safety features so as to minimize possibility of any explosion.
Experience and know-how of bag filter – Thermax has substantial experience in design of bag filters on coal applications and various special features are incorporated in bag filter.
Pushing Emission Control Systems
A process for controlling emissions resulting from hot coke being discharged from an oven of a battery of coke ovens from the beginning of discharge until the time when the coke arrives at a quenching station. The coke from the oven passes through a coke guide and a fume hood into an open-top, one-spot quenching car. The hood covers the car during discharge and is connected to an exhaust system, including a gas cleaning device, which draws air into the hood in an amount sufficient to control emissions and for combustion of the volatile matter.
Other combustibles emitted from the coke during the time coke is discharged into the quenching car and for a short period of time thereafter. During the movement of the open-top, one-spot quenching car from under the hood to the quenching station, the visible emissions given off by the hot coke are less than 40% opacity.
The process can also be practiced with one-spot quenching cars of a different design, including a covered one-spot car that receives coke through an opening in the car. Associated with the car is a gas exhaust-cleaning system which, as hot coke is discharged from an oven into the car, operates at a predetermined rate to draw air into the car in an amount sufficient to control emissions and for combustion of volatile matter and other combustibles emitted from the coke.
It is the aim of pushing emission control system to catch the gaseous and gas-carried solid emissions emitted during coke pushing, from the hot coke bucket car and to clean them such as:
- The dust extraction duct is conveyed to an air pollution control (APC) system. The system comprise of, cyclone (as a spark arrestor), bag filter and ID fan leading the clean gases through a stack. Dust handling facility with storage silo and pneumatic conveying can be provided.
- The suction at the battery limit is maintained by means of induced draft fan installed downstream the filter plant. The suction capacity is adjusted to meet the required flow demand by a VVVF-controlled fan motor.
- The dust content in the clean gas at the outlet of the filter plant do not exceed 25 mg/Nm3.
- Efficient yet optimized power consumption system. Stack emission can be less than 10 mg/Nm3.
- Execution of turnkey project of the system.
- Wide experience on dust extraction system – over 300 successful installations.
Flue Gas Desulphurisation
Sulfur dioxide (SO2) is produced during combustion of fuels containing Sulfur (S). SO2 formed during combustion, affects the environment in number of ways like acid rains, corrosion and severe damages to the health.
Flue Gas De-sulphurisation Systems
Dry systems - Dry systems for flue gas de-sulphurisation includes injection of lime/limestone/Sodium bi-carbonate in the gaseous stream followed by dry dust collection using equipment like bag filters or electrostatic precipitators.
Semi-dry systems - Semi-dry flue gas de-sulphurisation includes preparation of slurry of limestone/hydrated lime or solution of sodium bi-carbonate and atomising it in the gas stream and then collecting the dust by dry dust collection dystems like bag filters or electrostatic precipitators.
Wet Systems - Wet FGD systems are normally based upon the type of scrubbing fluid used. There are number of absorbents used for removal of SOX. Depending on the absorbent the wet FGD systems can be classified as:
Above mentioned systems are followed normally on the commercial scale.
- Lime based system
- Caustic based system
- Double alkali system
- Ammonia based system
- Sea water based system
85 % of systems installed for flue gas de-sulphurisation worldwide are of wet type. Normally limestone/ hydrated lime are used as absorbent as it is one of the most economical absorbent available.
Sinter Plant & Pellet Plant De-dusting
Sintering process is a pre-treatment step in the production of iron, where fine particles of iron ores, Coke, Flues viz., Lime stone & Dolomite and in some plants, also secondary iron oxide wastes (collected dusts, mill scale), are agglomerated by combustion. Agglomeration of the fines is necessary to enable the passage of hot gases during the subsequent blast furnace operation.
Sintering involves the heating of fine iron ore with flux and coke fines or coal to (1300 to 1480oC) produce a semi-molten mass that solidifies into porous pieces of sinter with the size and strength characteristics necessary for feeding into the blast furnace. Moistened feed is delivered as a layer onto a continuously moving grate or 'strand.' The surface is ignited with gas burners at the start of the strand, and air is drawn through the moving bed causing the fuel to burn. Strand velocity and gas flow are controlled to ensure that 'burn through' (i.e. the point at which the burning fuel layer reaches the base of the strand) occurs just prior to the sinter being discharged.
The solidified sinter is then broken into pieces in a crusher and is air-cooled. Product outside the required size range is screened out, oversize material is recrushed, and undersize material is recycled back to the process. Sinter plants that are located in a steel plant recycle iron ore fines from the raw material storage and handling operations and from waste iron oxides from steel plant operations .Waste Gasses coming outside the wind boxes are treated in an APC equipment Viz., ESP & dust so collected is again reprocessed to produce courser sinter. However, Sinter dust collected in final field is usally dumped in land fill due to high Alkali content.
Pelletizing turns very fine-grained iron ore into balls of a certain diameter, also known as pellets, which are suitable for blast furnace and direct reduction.
The Palletizing Plant can be broadly classified into the following sections:
ESP is well suited for this application for an emission of 50mg/Nm3. For emission less than 30 mg/Nm3 & up to 10mg/Nm3 Fabric Filters are recommended. Emission less than 10 mg/Nm3 can be achieved by High efficiency Scrubber for Particulate & Gaseous pollution control.
- Ore benification & grinding section
- Filtration section
- Weighing & mixing section
- Balling (green pelletizing) & screening section
- Indurating section
- Dedusting section
- More than 35 ESP installations across the world in sinter and pellet plants
- Expertise in both top as well as bottom rapping
- Successful installations in India with emissions meeting the desired norms