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Mount Isa Mines
Cleaner Production - Reduction in Energy Consumption

MIM Holdings Limited has implemented a program of innovations which has enabled the company to open a new mine and add new electricity-using activities while cutting total annual electricity use and carbon dioxide emissions.
MIM has committed to the Australian Government's Greenhouse Challenge. This Federal and State Government sponsored initiative requires companies to reduce emissions of carbon dioxide and other greenhouse gases by accepting specific targets. Greenhouse Challenge staff have been using MIM's outstanding record in energy management and carbon dioxide reduction at Mount Isa as a case study in promoting the Challenge.

Background

Until early 1997, MIM was the main generator of electrical power for north-west Queensland. Transmission of the power external to the MIM leases was carried out by the Northwest Queensland Electricity Board (NORQEB).

Local discoveries of many new ore bodies meant the inevitable increase in power demand for new mines. In addition, its own expansion at Mount Isa meant that MIM had either to invest in new generating capacity or utilise excisting generating plant more effectively. More effective use meant that MIM was required to undertake rigorous energy management within its own operations. Energy management relied on a personal computer based system and more energy efficient operation of plant.

Aerial view of Mount Isa

Aerial view of Mount Isa

The Process

MIM's Mount Isa operations are situated in north-west Queensland and form part of the Carpentaria Minerals Province. The Province is remote from the electrical grid systems of both the Northern Territory and Queensland. Most of the electrical power for the province is generated from Mica Creek Power Station (MCPS) and the Isa Mine Power Station (MPS). Until recently, the total generating capacity of MCPS was 198MW of which 165MW was coal fired and a further 33MW was from a distillate fired gas turbine set. In addition at MPS, a maximum of 29MW can be generated from a cogeneration plant using waste heat from the smelters and if necessary distillate.

The generation of electricity at MCPS and MPS is responsible on average for about 72 percent of total emissions from Isa operations. The remainder of the emissions are from explosives (less than 1 percent), transport (2 percent), copper smelter (14 percent) and lead smelter (11 percent). The emissions from the smelters are from fuels such as coal, coke, distillate, gas and the 1 percent carbon content of the ore, which in the smelters combines with oxygen to form CO².

Cleaner Production Initiative

If energy management was to be a viable option to the continued growth in energy use, large gains would quickly have to be made and seen to be made. Key areas of Isa operations where such gains could be made was in underground operations and to a much lesser extent, on the surface.

Surface plant

On the surface, energy efficiency was improving:

Underground plant

Most of the dramatic rise in overall load was caused by underground plant. It was therefore decided to concentrate on the underground operations. Major reductions in energy consumption, peak demands and greenhouse emissions were achieved by implementing initiatives in five specific areas.

Underground operations

Underground operations

  1. A 1,000kW impulse turbine (a turbine which uses high pressure water driven bucket wheel principles) and generating set was installed 1,000m underground. Chilled water at 1°C is discharged at around 100l/s down a vertical pipe from the surface to underground. Prior to the installation of the set, the water gained around 2.5°C between the surface inlet and the underground outlet, resulting in a temperature of 3.5°C. The installation of the set not only generated emission free electrical energy but, recooled the water by 2°C down to 1.5°C, reducing the chilled water requirement by around 11 percent. Required generating capacity could also be lowered by running the set during times of peak demand.
  2. After passing through the impulse turbine the chilled water is collected in a cold water dam on 20 level. This water was initially pumped through fan cooling units in all of the underground cribrooms. Pumping costs were very high. Many of the cribrooms were subsequently fitted with dedicated refrigerated air conditioners, reducing pumping costs and the need for chilled water.

  3. The twelve 1MW or 2MW axial ventilation fans on the surface are mounted over vertical shafts, which are typically 1,000m deep. Operation of the fans is to either extract or supply air to the underground workings. The pitches of the fan blades are automatically changed at regular intervals during the day by a process controller installed on the surface. Fan blades are driven to minimum pitch during times such as change of shifts, when ventilation of the whole mine is not required.

  4. Dispersed throughout the mine are around 1,000 smaller ventilation fans, each fan having an average connected load of 11kW. These fans increase general air movement underground and direct ventilation to priority areas. Many of the fans have been fitted with ripple frequency controllers. Two NORQEB owned and operated ripple frequency transmitters inject into the NORQEB electrical reticulation control pulses at 750Hz. Initially these transmitters were only used to control domestic hot water heaters in the city and surrounding properties, which used off peak electricity supplied at a lower tariff. The transmitters are now used to control both the hot water heaters and fans underground. Fans are turned off at the end of each shift.

  5. Desynchronising skip hoisting. The hoisting control systems of the R62 (lead mine) and U62 (copper mine) ore skips operated independently. Coincidently, during their hoisting cycles, full copper and full lead skips would be accelerated from rest at the same time. The mass of each skip and contained ore is 40 tonnes, the acceleration time for both is about 20 seconds. This meant that there were random occurrences of high current, short duration demands on the generators. To allow for these occasions, the maximum sustainable load of MCPS has been set at 5MW below the station's maximum steady state generating capacity. The two winders are now controlled by interconnected Programmable Logic Controllers (PLCs) such that only one skip can be accelerated from rest at a time.

Underground and surface plant

It was realised that even greater energy efficiency and reduced emissions would result if operators were made more accountable for energy use. In early 1997, MIM sold an 80 percent interest in MCPS to a specialist power generator, which assumed management of the plant requiring MIM to order its electricity 24 hours in advance. These two factors gave impetus to the development of a lease wide personal computer based energy and emission management system (PC: EMS).

PC: EMS was designed to allow easy data input together with meaningful displays. Plant operators are the key to PC: EMS. All plant operators were supplied with a PC. Each PC was connected to an area network which covered a surface area of about 28kms by 2kms and it also reaches deep underground.

Plant operators are set the task of entering daily operational forecasts at half hour increments via their terminals. These forecasts are entered into Forecast Advice Sheets such that there are always displayed, eight days of forecasts for each plant area. Forecast Advice Sheets for the current day cannot be changed by the plant operators as they form the basis of the order for electricity. Plant operators are not expected to directly forecast electrical loads and greenhouse gas emissions. Instead, operators forecast the fraction of their plant that is expected to be operational. In the central database, the forecast demand and energy requirements are calculated by multiplying the proportion of plant estimated to be operating by the full load rating (MW) of the plant. During the current day, a copy of each plant forecast is modified by the MPS Load Controller to reflect actual operation. This modified forecast is also saved. Therefore, two sets of daily forecasts are both available and saved each day.

Greenhouse gas emissions are calculated by applying a conversion factor to the plant forecasts, changing MW to tonnes of CO². Emissions of greenhouse gas can be fairly accurately calculated because both the type of fuel and station efficiencies are known. All operators can call up a display to see how much CO² their plant will emit during the day. The forecast displays are only used as a management tool for the operators.

Each plant operator, therefore, is able at any time to see the energy and environmental costs of running his or any other plant in dollars, energy consumed in MWh, peak demand in MW, and tonnes of carbon dioxide emitted to generate the necessary power. Previous to these displays, most operators rarely had any idea of the environmental and monetary costs of their operating practices. They had even less appreciation that they could significantly affect those costs.

Power meters with electronic outputs are being installed and new connections are continuously being made with plant control systems so that comparisons of forecasts with actual or measured loads, and energy costs can be displayed. At present the target is for forecasts to be within a band between 110 percent and 90 percent of actual. Because local operators may not be immediately aware of influences outside their control, their forecasts are subject to adjustment by the PC: EMS Administrator. These adjusted or final forecasts are then issued to MCPS. Final forecasts are usually within 105 percent and 95 percent of the actual and are typically 104 percent of the actual or measured value.

Advantages of the Process

Energy management has resulted in reduced energy consumption and the postponement of further capital outlay for generating plant. As a direct result, carbon dioxide emissions have been substantially reduced.

Summary of Costs and Benefits

 

Investment
$

Savings
$ pa

Deferred Expenditure
$m

Payback
Turbine/Generating Set
1,000,000
450,000
2.5
< 1 year
Air Conditioning
500,000
2,000,000
 
weeks
Mine Processor
500,000
400,000
10.0

< 1 year

Underground Ventilation
"Ripple control"
20,000
600,000
500,000
 
weeks
7 weeks
Hoisting
20,000
 
13.0
 
PC:EMS
300,000
(1)
   

(1) PC:EMS reduced energy costs by 5% in its initial year of operation (1997/98)

As a result of the initiatives, a number of general conclusions can be made:

Cleaner Production Incentive

During the late 1980s, MIM owned both MCPS and MPS. Electricity supply and allied problems came increasingly into focus.

MIM was subjected to increased market competition with lower prices from the sale of metals. In this situation a reduction in operating costs was essential. MIM was also looking to meet growing environmental concerns internationally by reducing the carbon dioxide emissions from its coal and oil fired generators.

On an annual basis, the electrical system load averaged on an annual basis, over 83 percent of availability. Because of the high load factor, there was the need to frequently run an expensive distillate fired gas turbine generating set. The Isa operations base load consisted of three underground mines and associated surface plant. Two of these mines were the copper and lead/zinc/silver mines at Mount Isa. The third, a lead/zinc/silver mine, was being developed some 20km north of Mount Isa at Hilton. The load of these three mines was increasing. Also, plans for a third mine at Mount Isa were well advanced, this new mine would increase the load still further. The base load of north-west Queensland was also growing.

There was the possibility that sometime in the future natural gas, (for electrical generating purposes), would be available from a long distance pipeline. However, there were no firm commitments.

Intensive exploration of the province was beginning to discover ore bodies with the potential to become mines if their development and operating costs made them viable. These extra mines would increase power demand, but would not all be owned or operated by MIM.

As the operator of both power stations, MIM had three options to meet the increasing demand:

It was decided, therefore, that energy management was the preferred option.

Barriers

The energy management team was very quickly made conscious of the fact that the installation and commissioning of a lease wide PC based energy and emission management system (PC: EMS) would be difficult.

One of the main difficulties was that off the shelf software suitable to the company's needs could not be found. Therefore the team had to write, install, debug, develop and commission software whilst training operators in its use. The operators were scattered over a large geographical area. During operator training and equipment commissioning, production had to continue. Throughout this time, both power stations were operating and accurate forecasts of energy consumption and power demand were needed. Many of the software 'bugs' encountered were not from PC: EMS, but were inherited from excisting PCs. Isa operations have over 2,000 personal computers and they have been purchased at different times from different suppliers. PC: EMS had to contend with a multitude of PC types with varied operating systems. Furthermore, some PC units were installed with different software, different sizes of random access memory and different versions of a given software. Operating failures were inevitable. Additionally, a great many load calculations, meter installations, calibrations and energy forecasts were still required.

Further Developments

Due to significant changes to MIM's operation at Mount Isa, some of the information contained in this document is now out of date. MIM will update this document in due course and will also include its latest energy savings initiatives.

Contacts

Arjuna Seneviratne
Principal Adviser Gas and Energy 
M.I.M. Holdings Limited
Mount Isa, QLD 4825
Ph: (07) 4744 3211
Fax: (07) 4744 3890
Email: aqsene@isa.mim.com.au

Mark Garrahay
Environmental Planning Superintendent
M.I.M. Holdings Limited
Mount Isa, QLD 4825
Ph: (07) 4744 2045
Fax: (07) 4744 3962
Email: mark.garrahy@isa.mim.com.au
Web site: www.mim.com.au

Implementation: 1995
Casestudy initially prepared: June 1998 by Environment Management Industry Association of Australia (EMIAA) based on material contained in a paper presented by Barry Budd to a seminar organised by International Business Communications on Emissions Trading: First International Briefing, Sydney, June 1998.

EMIAA logo

Last modified: May 2001