Studies and Articles
Heating Iron Ore Slurry... Continued.
Written for the CIM Conference (May 2010), Vancouver, BC, Canada
Author: Robert E Wood
Submerged Combustion Technology
The slurry heating system highlighted in this paper is trademarked SubCom and was developed by Inproheat Industries in the early 1970’s in response to the global energy crisis. A SubCom liquid heating system consists of a fuel burner mounted at the top of a combustion chamber, which extends down from the top of a tank containing the liquid-to-be-heated, as shown in Figure 1. The burner is connected to a blower that provides air for combustion as well as heat transfer. The blower evacuates the liquid from the combustion chamber allowing the flame to burn in a dry atmosphere without impingement, for complete combustion. The heat transfer takes place between the exhaust gases and the liquid-to-be-heated. An inherent property of the technology is that the temperature of the exhaust gases are the same, or close to the same, temperature as the heated liquid, which means high heat transfer efficiencies.
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 Figure 1 – SubCom Cutaway
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The Plant
The project is located at an integrated steel production facility. The facility receives concentrate from a its mine via a 400 km pipeline. A diagram of the partial process is shown below in Figure 2. Part of the processing requires the dewatering of iron ore concentrate slurry (approx. SG = 2) in order to make iron pellets. Dewatering of the slurry is done by vacuum disc filters.
Figure 2 – Iron Ore Processing Flow Diagram
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The Beginning
AHMSA approached Inproheat wondering if submerged combustion could provide an economic and operational advantage versus upgrades to the pelletising operation. Over several months of investigation, including a pilot project, the customer determined that a SubCom system would provide the increased operating capacity at a lower cost than upgrading the vacuum disc filter system. The expected result was an efficiency gain of at least 30% at the vacuum disc filters (AHMSA).
Heating the slurry reduces the surface tension of the water, which improves the capacity of the vacuum filters. AHMSA
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indicated preliminary results showed an increase in filtering capacity of 33% and a reduction in water content of 0.5%. They stated heating the iron ore slurry also increased the temperature of the green pellet entering the furnace from 30°C to 50°C, reducing the moisture content by a further one percent. The reduced moisture content results in fuel savings at the furnace of 1.6m3 of natural gas per tonne of pellet product (3.1m3 of coke gas per tonne of pellet product). At an annual production rate of 3.55M tonnes per year this equates to a fuel savings of $900,000 at a price of $0.16/m3 ($4.25/GJ) for natural gas.
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