Environment industries archive
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Tiwest's Pigment Plant has been actively pursuing cleaner production initiatives in the areas of energy, materials and water efficiency. These include a new process to recover synthetic rutile, which has potential net savings of about $31,000 a day. In an example of 'industrial ecology' waste hydrochloric acid is converted by a neighbouring company into ammonium chloride for use at another Tiwest operation supplying the Pigment Plant.
Tiwest Joint Venture (Tiwest) is an equal joint venture between Ticor Resources Pty Ltd and KMCC Western Australia Pty Ltd, a wholly owned subsidiary of Kerr McGee Chemical Corporation (USA). Tiwest has developed a fully integrated titanium minerals project in Western Australia based on titanium minerals extracted from the Cooljarloo mine near Cataby, WA. The operations include: a titanium mine and wet processing plant at Cooljarloo producing titanium minerals concentrate; road transport to a dry separation plant at Chandala 60 km north of Perth, which produces ilmenite, rutile, zircon and leucoxene; a synthetic rutile plant at Chandala to upgrade ilmenite to synthetic rutile; a pigment plant at Kwinana, south of Perth, converting synthetic rutile to titanium dioxide pigment; warehouses at Henderson, south of Perth, for storing the pigment; and exporting and other facilities at the Kwinana port. The principal end-product, titanium dioxide pigment, has broad application in, for example, paint, plastics, paper, ink and pharmaceutical products.
The first stage of the integrated titanium minerals project was the commissioning of the Cooljarloo mine in 1989. The project became fully integrated with the commissioning of the Pigment Plant in May 1991. Production capacity of the Pigment Plant has been increased several times since 1995 through a range of process improvements. The Pigment plant produces more than 95,000 tons of titanium dioxide pigment using technology licensed by Kerr McGee Chemical. Production is expected to increase as market requirements dictate.
Tiwest operations have been subject from the start to environmental planning and other regulatory controls and Tiwest is committed to continual improvement in its environmental performance. All Tiwest operations have environmental management systems and the Pigment Plant was recommended for ISO 14001 in June 2001. Tiwest has implemented a range of cleaner production initiatives in all of its main operations to achieve improvements in process efficiency and environmental performance while reducing costs. This case describes progress at its Pigment Plant where there has been scope for improvement in materials and energy efficiency.
The process is based on chloride technology adopted by many companies during the 1980s and 1990s to improve pigment quality and reduce effluent rates.
Using feedstock from the Chandala complex, the operation reacts synthetic rutile with petroleum coke and chlorine in fluidised bed reactors or chlorinators. The reaction process produces titanium tetrachloride which is purified by condensation and fractional distillation. The remaining gases are systematically treated by scrubbing and incineration. Liquid effluent goes to the wastewater treatment plant and treated effluent goes to ponds where further settlement takes place. The treated water from the ponds is discharged to the Cockburn Sound under strict environmental controls.
The next stage of the process uses a special process for reacting titanium tetrachloride with superheated oxygen and support fuel to produce base titanium dioxide pigment.
The base pigment goes through a finishing process which involves milling, classification, surface treatment, filtering, drying, micronising and bagging. Various grades of pigment are produced to meet market requirements.
Residue from the operation is separated and returned to Cooljarloo where it is encased in specially constructed clay lined pits and used as part of the mine rehabilitation programme.
Various initiatives have been implemented under the broad headings of energy, materials and water efficiency
Some energy efficiency initiatives had been implemented earlier but a major programme of improvement began in 1997 to address rising energy consumption.
Initiatives undertaken since 1997 to reduce natural gas consumption were:
Electricity reduction initiatives in 1997 included:
Initiatives to reduce petroleum coke consumed by the chlorination reaction included tightening feed control and improving reaction efficiency.
Initiatives to reduce consumption of LPG as support fuel for the oxidation reactors included improving LPG flow metering, monitoring oxidation reaction stability and improving combustion efficiency in the oxidisers.
Further energy efficiency initiatives since 1997 have included:
A major initiative has been installing a cogeneration plant, commissioned in 1998 and owned by Western Power. A gas turbine generates electricity and the exhaust gases which would have been vented into the atmosphere in the past, are used to generate superheated steam for the microniser, the last part of the production process. The plant generates all of Tiwest’s power requirements plus surplus electricity for the South West interconnecting grid. It also reduces steam demand from the package boilers and reduces greenhouse gas emissions.
Production of hydrochloric acid: Dilute hydrochloric acid (HCl), generated from scrubbing the gas stream from chlorination, was previously neutralised in the waste treatment plant. Two initiatives was realised during 1997 to recover the HCl: first as acid for sale and secondly for use as ammonium chloride at the Chandala operation. For this purpose a second scrubber was installed to produce HCl at a higher concentration that enables reuse as a low quality acid.
In this conversion process to ammonium chloride, waste HCl is transferred to neighbouring Coogee Chemicals which converts it to ammonium chloride and tankers it to Chandala for use in the production of synthetic rutile. The cost of the ammonium chloride to Tiwest is significantly cheaper than that previously imported.
Rutile Recovery Plant: The aim of this initiative has been to recover synthetic rutile from process effluent. After chlorination, all metallic chlorides go to a sump and to the wastewater treatment plant. Overflow from the fluidised bed reactor is rich in unreacted synthetic rutile and petroleum coke but this went with the metal chlorides to effluent treatment.
A new plant was installed and commissioned in 2000 to recover synthetic rutile from the effluent using hydrocyclones separating on particle size. The titanium-rich fraction is filtered on a belt filter, washed, dried in a fluidised bed drier and returned to the chlorinator with the normal input material. The titanium-poor fraction continues to the wastewater treatment plant.
Use of supplementary fuel: In 2001 a switch was made to using an alternative fuel that produces less water to react with the chlorine and form HCl. This has improved overall chlorine efficiency significantly.
Synthetic Rutile Plant
Efficiency of water use has been improving at the Pigment Plant since commissioning. In 1995 Tiwest conducted an in-house water audit which identified opportunities for reducing scheme water consumption and a number of initiatives were implemented. Further investigation in 1996 identified other possible areas for savings and reuse, including:
Investigations included considering using deep groundwater and treated contaminated groundwater.
Successful projects have included the commissioning of counter-current washing in pigment filtration, the reuse of microniser condensate in pigment filtration, and the installation of a recovery tank for water reuse.
The use of groundwater and reprocessed water are currently being pursued as part of the Kwinana Waste Water Recycling Plant.
The various initiatives have resulted in significant financial and environmental benefits as follows:
Significant savings have been achieved plus reduced greenhouse gases.
Besides Tiwest's commitment to environmental improvement these initiatives have been driven by cost, productivity and environmental compliance considerations.
No significant barriers were encountered in implementing these initiatives other than the challenges of initiating new processes and ensuring that they are economical.