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|The Queensland Nickel Refinery, in Townsville, is a leading example of a company heading towards sustainable minerals processing in Australia. The company, as part of the BHP Billiton Stainless Steel Materials Customer Service Group, has been working since 2001 to implement the Yabulu Optimisation Initiative (or YOI). The YOI focuses on increasing the quantity of nickel and cobalt produced per tonne of fuel, water and ore input to the processing plant. Three projects specifically aimed at energy and water reuse with the additional benefit of increased cobalt recovery were commissioned in 2003, and are very successful, once again proving that projects that benefit the environment can have a sound economic benefit. These and other projects within the Yabulu Optimisation Initiative and refinery have contributed to record nickel production at the refinery in 2003.
QNI and BHP Billiton report on a number of Environmental Performance Indicators as part of their Annual HSEC Report. The projects described in this case study have reduced material and energy intensity at the refinery. In combination, the projects have reduced the quantity of new water used in the process from 206 kL per tonne of final product (2002 HSEC Report) by 20.3 kL per tonne of final product. The quantity of energy used per tonne of product has been reduced from 583 GJ/tonne (2002 HSEC Report) by 16 GJ/tonne. The greenhouse gas emissions from the plant have been reduced from 46.5 tonne CO2e per tonne of final product (2002 HSEC report) to 45.4 tonne CO2e per tonne of final product. The projects represent a saving of AUD 3.8 million per annum.
Queensland Nickel (QNI) operates a nickel refinery at Yabulu, 25 kilometres north of Townsville. QNI is owned by BHP-Billiton, the world's largest diversified resources company. The operation has an interesting history of surviving downturns in the nickel market and implementing significant process improvements developed by in-house technical expertise.
Using the Caron Process QNI refines a laterite ore into 30,000 tonnes per annum of nickel as nickel oxide granules and powder, Nickel Compacts (QNC) and HIGRADE (99 and 99.5 % nickel respectively); and 2,000 tonnes per annum QN ChemGrade Cobalt. The nickel and cobalt products are sold to customers to produce stainless and speciality steels, alloys and chemicals. The process flow diagram is shown in Figure 1.
Figure 1: Process Flow Diagram
The boiler feed water preheat project involves the use of hot off gases from the distillation columns (stills), to preheat the water used to generate steam in the coal fired boiler. Figure 2a and 2b shows the process before the project was implemented. Figure 3 shows the process after the project was implemented. Before implementation two separate heat exchange processes occur. The first is the use of cooling water in the Gas Cooler Condensers (GCC) to remove heat from the hot gases exiting the stills. The heat energy of the warm cooling water is then lost to atmosphere by evaporation in the cooling towers. This energy is wasted. The second heat exchange process occurs in a separate part of the plant. Boiler feed water has to be heated in the hot lime vessel to remove impurities and prepare the water to a required quality for use in the coal fired boiler. The hot lime vessel uses steam generated in the coal fired boiler to heat the boiler feed water. This steam could be used in other parts of the process which can be steam limited. Steam limited means the coal fired boiler can not produce enough steam to process all the liquors.
Figure 2a: Before project implementation - heat exchange at the GCCs
Figure 2b: Before project implementation - heat exchange at the hot lime vessels
The boiler feed water preheat project involved the installation of two plate heat exchangers on the gas which use cool boiler feed water to condense the still off gases (ammonia, carbon dioxide and water). Figure 3 shows hot gases exiting the top of the magma still and being cooled in a heat exchanger by the boiler feed water. The energy in the off gases preheats the boiler feed water prior to the hot lime vessel and therefore a significantly reduced amount of steam is used to heat the boiler feed water.
Figure 3: After project implementation - heat exchange at the gas main
The Basic Nickel Carbonate (BNC) slurry (water and BNC) from the magma stills goes into a thickener to reduce the amount of water in the slurry. This good quality water stream of 1.3 ML/day at approximately 85°C was being sent to the green water pond to allow the recovery of BNC from the water stream. When the thickener operated poorly the nickel content of this stream can represent a significant loss of nickel. Due to old and blocked pipe work, water from this pond was disposed of to the tailings dam. The old process resulted in a loss of nickel and a valuable hot water (energy) stream to the tailings dam. The green water re-use project has diverted the hot water from the thickener to preheat the nickel rich liquor going to the magma stills in a plate heat exchanger. A new pipeline now sends this water from the magma still plate heat exchanger to the pond for cooling and then the water is pumped back to the process water tank for re-use. The process flow of the implemented project is shown in Figure 1 in blue.
Within the cobalt plant process, steam stripping is used to form the product cobalt oxide hydroxide in a kettle. The result is a cobalt solid and a clean good quality water stream. The old process was to dispose of this water with the tailings slurry to the tailings dam. This represented a waste of this hot water stream.
Now this hot water (an average 0.35 ML/day) has been used to replace new water used in another part of the process. At the start of the cobalt plant process, cobalt sulphide solids are washed in a counter current thickener circuit. New water was used to dilute the ammonia liquor thereby aiding the washing process. The hot water is now used in the counter current thickener circuit to wash ammonia liquor from the cobalt sulphide solids. The process flow of the implemented project is shown in Figure 1 in red.
QNI use approximately 206 kL of new water per tonne of final product. This water is sourced from the local bore field and from a dam in the Mt Spec National Park, located north of the plant. Townsville although in North Queensland has a dry climate most of the year and only in some years does it experience typical monsoonal rainfall. Any reduction in the amount of water used benefits the local environment.
Due to the technology of the nickel refining process and the availability and cost of energy sources in the past, QNI is dependent on fuels that produce greater quantities of greenhouse gas than other fuels. A large portion of the fuels used by QNI are fuel oil and coal. The process produces 46.5 tonnes of CO2 equivalents per tonne of final product (excluding purchased electricity). Carbon dioxide is the main greenhouse gas associated with coal combustion. The process is energy intensive and QNI uses approximately 583 GJ of energy per tonne of final product. QNI have now started a study to enable them to convert some of their process to coal seam gas.
The boiler feed water preheat project represented technical risk from the perspective of the hot gas main control. It was difficult to predict with any accuracy the effect of cooling the hot gases would be on the control of the gas main and the distillation columns and the ability of the GCCs to produce strip liquor. As a result, modelling within QNI and external to the company was used to predict the effect of the project. An extensive and thorough commissioning plan was developed. The project ended up being commissioned smoothly in about two days instead of the planned fourteen days.
The success of the three projects post implementation has included:
The benefits of these projects are best summarised in Table 1. The environmental performance indicators published in the BHP Billiton Annual HSEC Report for 2002 are as follows:
|Project||Capital Cost||Operating Benefit||Payback||Environmental Performance Indicators|
|Boiler Feed Water Preheat||AUD 5.6 million||AUD 3.3 million||2.3 years||Reduction in energy use per tonne of final product* = 16 GJ per tonne
Reduction in GHG emissions per tonne final product = 1.1 tonnes of CO2 equivalent per tonne
Reduction in raw water consumption per tonne of final product = 4.8 kL per tonne
|Green Water Re-use||AUD 0.9 million||AUD 0.44 million||2.8 years||Reduction in raw water consumption per tonne of final product = 12.1 kL per tonne|
|Cobalt Plant water re-use||AUD 0.2 million||AUD 0.06 million||4.7 years||Reduction in raw water consumption per tonne of final product = 3.4 kL per tonne|
|* This includes a 3 GJ/tonne reduction based on the increase in cobalt production - noting that cobalt production represents only 6 % of total final products.|
BHP Billiton, 2002, BHP Billiton Health Safety Environment and Community Report 2002 - Operations Performance Report Financial Year 2002 Health Safety Environment Quality and Community - QNI Yabulu Refinery, http://www.bhpbilliton.com/hsecReport/2002 site accessed January 2004.
Queensland Nickel Refinery, Reports on the YOI Projects, 2003
This case study was produced in April 2004 by the UNEP Working Group for Cleaner Production on behalf of the Queensland Nickel Refinery
For Further Details Contact:
UNEP Working Group for Cleaner Production
Environmental Management Centre
University of Queensland 4072
Ph: 3365 1594
Fax: 3365 6083
QNI YOI Projects Manager
Queensland Nickel Pty Ltd
Private Mail Bag 5, Mail Centre
Ph: 0419 743 396