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Jul 5, 2017

Improvements carried out at Huelva smelter in the 2013 general shutdown: a review

The license agreement of the Flash Smelter Furnace was signed in January 1973 and the new furnace started up in September 1975. A 1000 tpd Outokumpu Flash Furnace was commissioned, to replace two Momoda Blast Furnaces.
Design of new cooling elements

Lots of improvements and modifications, directed to a more efficient, environmental friendly and economical operation, were carried out during four decades of smelter`s operation with five campaigns as part of the general shut down.

The objective of this article is to describe a paper that was voted as one of the three most important contributions presented in the 14th International Flash Smelting Congress (IFSC), dealing with modifications and improvements of the operational process carried out in the Huelva smelter during general shutdown in 2013. The shutdown lasted for 68 days, from the 4thof September until the 11th of November 2013 (see Fig. 1). Additionally, more than eight million tonnes of copper concentrate were smelted in the flash furnace during the last campaign (2004-2013).

Plan schedule for recent shutdown of FSF at Huelva
Figure 1: Plan schedule for recent shutdown of FSF at Huelva

Modifications and Improvements

The most important modifications and improvements, including process control, maintenance practices, as well as the environmental issues, are given below:

  • Increase of preheating enriched air capacity up to 230ºC.
  • 100% refractory relining (hearth included) and new FSF cooling elements.
  • Waste Heat Boiler (WHB) modifications.

Regarding energy consumption, a new preheater for process air was installed in order to increase the temperature of process air from 135ºC to 230ºC. The preheater is heated by high pressure steam (40bar). In addition to energy consumption, the higher temperature of process air will be also used to increase or decrease the amount of enriched air in the concentrate burner.

Despite energy savings, another important factor in smelter operation is the efficiency of the process. Thus, in order to improve the efficiency of the process, the hearth of flash furnace was relined, after being in use for 38 years.

Two main improvements were included. The first was the introduction of a third 150 mm magnesia-chrome brick refractory layer to reinforce the hearth. The second improvement was the replacement of the isolating concrete by additional clay bricks, in order to avoid any risk arising from insufficient curing of concrete during the FSF warm up. In addition, the uptake shaft arched roof was changed to a flat roof design (see Fig. 3).

New flat roof of the uptake shaft
Figure 3: New flat roof of the uptake shaft

As the critical point in the operation of the FSF is the water cooling system, several modifications and improvements have been made to extend the furnace brick life. Thus, first,with Outotec recommendation, the thickness of the cooling elements in the settler under the reaction shaft has been increased from 70mm to 115mm, in order to avoid some detected problems like bending and leakage during the last campaign. Second, in order to reinforce the cooling capacity, in the areas where high wear was measured during the last campaign, 70 new cooling elements have been installed (Figure 4). Consequently, the whole cooling water system including a new cooling tower, new pumps, and emergency systems was needed to review in order to ensure proper cooling capacity.

Design of new cooling elements
Figure 4: Design of new cooling elements

Furthermore, as the waste heat boiler has proven to be the most critical piece of process equipment in the smelter, several areas were identified to be replaced in order to guarantee normal operation and to achieve the expected performance.

In accordance with inspections carried out during the short shutdowns in 2007, 2009 and 2011, the following modifications and replacements have been accomplished:

  • Installation of a superheater using the existing radiation bank.
  • Modification of the compound tubes at the inlet of the radiation section.
  • Hammering system renewal and installation of some pneumatic hammers.
  • New opening to access the accretions in the joint FSF-WHB.
  • Modification of the supporting points of the WHB.
  • New drag conveyor at the convection section.

In conclusion, increasing sulfur content in copper concentrates and new environmental requirements imply new challenges for smelters in terms of production and operation costs. A policy based on continuous improvement, implemented in the Huelva Smelter, gave an opportunity for improving the efficiency of the process and designing carefully the whole production chain.

Mining Metals refining